Imaging lung perfusion

Pulmonary MRI in Newborns and Children

Lung MRI is an important tool in the assessment and monitoring of pediatric and neonatal lung disorders. MRI can provide both similar and complementary image contrast to computed tomography for imaging the lung macrostructure, and beyond this, a number of techniques have been developed for imaging the key functions of the lungs, namely ventilation, perfusion, and gas exchange, through the use of free-breathing proton and hyperpolarized gas MRI. Here, we review the state-of-the-art in MRI methods that have found utility in pediatric and neonatal lung imaging, the structural and physiological information that can be gleaned from such images, and strategies that have been developed to deal with respiratory (and cardiac) motion, and other technological challenges. The application of lung MRI in neonatal and pediatric lung conditions, in particular bronchopulmonary dysplasia, cystic fibrosis, and asthma, is reviewed, highlighting our collective experiences in the clinical translation of these methods and technology, and the key current and future potential avenues for clinical utility of this methodology. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 2.

Quantitative MRI detects delayed perfusion and impact of bronchial artery dilatation on pulmonary circulation in patients with cystic fibrosis

OBJECTIVES

MRI detects abnormal lung perfusion in patients with cystic fibrosis (CF). However, little is known about the contribution of bronchial arteries to lung perfusion in CF. We hypothesized that delayed perfusion can be detected by dynamic contrast-enhanced (DCE-)MRI and that bronchial artery dilatation (BAD) is associated with changes in lung perfusion.

MATERIALS AND METHODS

Morpho-functional MRI was prospectively acquired in 75 patients with CF (18.7 ± 7.6 years, range 6-39 years). Lungs and perfusion defects were segmented automatically to quantify perfusion defects in percent (QDP). Pulmonary blood flow (PBF), mean transit time (MTT), and perfusion delay were calculated for the whole lung, inside normally perfused and perfusion defect areas. Chest MRI score and BAD were assessed visually.

RESULTS

QDP and PBF correlated with MRI global score (r = 0.58 and -0.53, p < 0.001). In normally perfused lung, PBF was higher (161.2 ± 77.9 mL/100 mL/min vs. 57.5 ± 26.4 mL/100 mL/min, p < 0.001), and MTT (5.4 ± 1.7 s vs. 6.9 ± 2.3 s, p < 0.001) and perfusion delay were shorter than in perfusion defect areas (4.6 ± 5.3 s vs. 13.4 ± 16.2 s, p < 0.001). 48 (64.0%) patients showed BAD, had higher QDP (44.6 ± 20.8% vs. 17.3 ± 11.0%, p < 0.001) and lower PBF (91.9 ± 54.8 mL/100 mL/min vs. 178.3 ± 77.4 mL/100 mL/min, p < 0.001) than patients without BAD. MTT was shorter (6.3 ± 1.9 s vs. 8.0 ± 2.6 s, p < 0.001), and perfusion delay was longer (13.8 ± 10.1 s vs. 12.8 ± 23.7 s, p < 0.02) inside perfusion defects of patients with BAD compared to without BAD.

CONCLUSION

Perfusion parameters correlate with lung disease severity, and perfusion defects showed delayed perfusion in patients with CF. BAD was associated with more extensive perfusion defects and reduced PBF.

KEY POINTS

Question Dilated bronchial arteries are a common comorbidity in cystic fibrosis (CF), which can cause hemoptysis, but their quantitative contribution to lung perfusion is little researched. Findings Perfusion defects in percent (QDP) enabled objective assessment of perfusion abnormalities in CF patients, while perfusion delay and arterial correlation showed bronchial artery perfusion contribution. Clinical relevance The usage of quantitative perfusion metrics in CF may help tracking disease progression. By also including the proposed metrics perfusion delay and arterial correlation, bronchial artery inflow could be assessed and used to detect early onset of bronchial artery dilation.

Compartment-specific 129Xe HyperCEST z spectroscopy and chemical shift imaging of cucurbit[6]uril in spontaneously breathing rats

129Xe hyperpolarized gas chemical exchange saturation transfer (HyperCEST) MRI has been suggested as molecular imaging modality but translation to in vivo imaging has been slow, likely due to difficulties of synthesizing suitable molecules. Cucurbit[6]uril-either in readily available non-functionalized or potentially in functionalized form-may, combined with 129Xe HyperCEST MRI, prove useful as a switchable 129Xe MR contrast agent but the likely differential properties of contrast generation in individual chemical compartments as well as the influence of 129Xe signal drifts encountered in vivo on HyperCEST MRI are unknown. Here, HyperCEST z spectroscopy and chemical shift imaging with compartment-specific analysis are performed in a total of 10 rats using cucurbit[6]uril injected i.v. and under a protocol employing spontaneous respiration. Differences in intensity of the HyperCEST effect between chemical compartments and anatomical regions are investigated. Strategies to mitigate influence of signal instabilities associated with drifts in physiological parameters are developed. It is shown that presence of cucurbit[6]uril can be readily detected under spontaneous 129Xe inhalation mostly in aqueous tissues further away from the lung. Differences of effect intensity in individual regions and compartments must be considered in HyperCEST data interpretation. In particular, there seems to be almost no effect in lipids. 129Xe HyperCEST MR measurements utilizing spontaneous respiration protocols and extended measurement times are feasible. HyperCEST MRI of non-functionalized cucurbit[6]uril may create contrast between anatomical structures in vivo.

GOLD grade-specific characterization of COPD in the COSYCONET multi-center trial: comparison of semiquantitative MRI and quantitative CT

OBJECTIVES

We hypothesized that semiquantitative visual scoring of lung MRI is suitable for GOLD-grade specific characterization of parenchymal and airway disease in COPD and that MRI scores correlate with quantitative CT (QCT) and pulmonary function test (PFT) parameters.

METHODS

Five hundred ninety-eight subjects from the COSYCONET study (median age = 67 (60-72)) at risk for COPD or with GOLD1-4 underwent PFT, same-day paired inspiratory/expiratory CT, and structural and contrast-enhanced MRI. QCT assessed total lung volume (TLV), emphysema, and air trapping by parametric response mapping (PRMEmph, PRMfSAD) and airway disease by wall percentage (WP). MRI was analyzed using a semiquantitative visual scoring system for parenchymal defects, perfusion defects, and airway abnormalities. Descriptive statistics, Spearman correlations, and ANOVA analyses were performed.

RESULTS

TLV, PRMEmph, and MRI scores for parenchymal and perfusion defects were all higher with each GOLD grade, reflecting the extension of emphysema (all p < 0.001). Airway analysis showed the same trends with higher WP and higher MRI large airway disease scores in GOLD3 and lower WP and MRI scores in GOLD4 (p = 0.236 and p < 0.001). Regional heterogeneity was less evident on MRI, while PRMEmph and MRI perfusion defect scores were higher in the upper lobes, and WP and MRI large airway disease scores were higher in the lower lobes. MRI parenchymal and perfusion scores correlated moderately with PRMEmph (r = 0.61 and r = 0.60) and moderately with FEV1/FVC (r = -0.56).

CONCLUSION

Multi-center semiquantitative MRI assessments of parenchymal and airway disease in COPD matched GOLD grade-specific imaging features on QCT and detected regional disease heterogeneity. MRI parenchymal disease scores were correlated with QCT and lung function parameters.

KEY POINTS

Question Do MRI-based scores correlate with QCT and PFT parameters for GOLD-grade specific disease characterization of COPD? Findings MRI can visualize the parenchymal and airway disease features of COPD. Clinical relevance Lung MRI is suitable for GOLD-grade specific disease characterization of COPD and may serve as a radiation-free imaging modality in scientific and clinical settings, given careful consideration of its potential and limitations.

Mechanical power is associated with cardiac output and pulmonary blood flow in an experimental acute respiratory distress syndrome in pigs

Background

Despite being essential in patients with acute respiratory distress syndrome (ARDS), mechanical ventilation (MV) may cause lung injury and hemodynamic instability. Mechanical power (MP) may describe the net injurious effects of MV, but whether it reflects the hemodynamic effects of MV is currently unclear. We hypothesized that MP is also associated with cardiac output (CO) and pulmonary blood flow (PBF).

Methods

24 anesthetized pigs with experimental acute lung injury were ventilated for 18 h according to one of three strategies: 1) Open lung approach (OLA), 2) ARDS Network high-PEEP/FIO2 strategy (HighPEEP), or 3) low-PEEP/FIO2 strategy (LowPEEP). Total MP was assessed as the sum of energy dissipated to overcome airway resistance and energy temporarily stored in the elastic lung tissue per minute. The distribution of pulmonary perfusion was determined by positron emission tomography. Regional PBF and MP, assessed in three iso-gravitational regions of interest (ROI) with equal lung mass (ventral, middle, and dorsal ROI), were compared between groups.

Results

MP was higher in the LowPEEP than in the OLA group, while CO did not differ between groups. After 18 h, regional PBF did not differ between groups. During LowPEEP, regional MP was higher in the ventral ROI compared to OLA and HighPEEP groups (2.5 ± 0.3 vs. 1.4 ± 0.4 and 1.6 ± 0.3 J/min, respectively, P < 0.001 each), and higher in the middle ROI compared to the OLA group (2.5 ± 0.4 vs. 1.6 ± 0.5 J/min, P = 0.04). MP in the dorsal ROI did not differ between groups (1.4 ± 0.9 vs. 1.4 ± 0.5 vs. 1.3 ± 0.8 J/min, P = 0.916). Total MP was independently associated with CO [0.34 (0.09, 0.59), P = 0.020]. Regional MP was positively associated with PBF irrespective of the regions [0.52 (0.14, 0.76), P = 0.01; 0.49 (0.10, 0.74), P = 0.016; 0.64 (0.32, 0.83), P = 0.001 for ventral, middle, and dorsal ROI, respectively]. Subgroup analysis revealed a significant association of MP and CO only in the OLA group as well as a significant association between MP with regional PBF only in the HighPEEP group.

Conclusion

In this model of acute lung injury in pigs ventilated with either open lung approach, high, or low PEEP tables recommended by the ARDS network, MP correlated positively with CO and regional PBF, whereby these clinically relevant lung-protective ventilation strategies influenced the associations.

Impact of airway closure and lung collapse on inhaled nitric oxide effect in acute lung injury: an experimental study

BACKGROUND

Efficacy of inhaled therapy such as Nitric Oxide (iNO) during mechanical ventilation may depend on airway patency. We hypothesized that airway closure and lung collapse, countered by positive end-expiratory pressure (PEEP), influence iNO efficacy. This could support the role of an adequate PEEP titration for inhalation therapy. The main aim of this study was to assess the effect of iNO with PEEP set above or below the airway opening pressure (AOP) generated by airway closure, on hemodynamics and gas exchange in swine models of acute respiratory distress syndrome. Fourteen pigs randomly underwent either bilateral or asymmetrical two-hit model of lung injury. Airway closure and lung collapse were measured with electrical impedance tomography as well as ventilation/perfusion ratio (V/Q). After AOP detection, the effect of iNO (10ppm) was studied with PEEP set randomly above or below regional AOP. Respiratory mechanics, hemodynamics, and gas-exchange were recorded.

RESULTS

All pigs presented airway closure (AOP > 0.5cmH2O) after injury. In bilateral injury, iNO was associated with an improved mean pulmonary pressure from 49 ± 8 to 42 ± 7mmHg; (p = 0.003), and ventilation/perfusion matching, caused by a reduction in pixels with low V/Q and shunt from 16%[IQR:13-19] to 9%[IQR:4-12] (p = 0.03) only at PEEP set above AOP. iNO had no effect on hemodynamics or gas exchange for PEEP below AOP (low V/Q 25%[IQR:16-30] to 23%[IQR:14-27]; p = 0.68). In asymmetrical injury, iNO improved pulmonary hemodynamics and ventilation/perfusion matching independently from the PEEP set. iNO was associated with improved oxygenation in all cases.

CONCLUSIONS

In an animal model of bilateral lung injury, PEEP level relative to AOP markedly influences iNO efficacy on pulmonary hemodynamics and ventilation/perfusion match, independently of oxygenation.

Quantitative Total-Body Imaging of Blood Flow with High Temporal Resolution Early Dynamic 18F-Fluorodeoxyglucose PET Kinetic Modeling

Quantitative total-body PET imaging of blood flow can be performed with freely diffusible flow radiotracers such as 15O-water and 11C-butanol, but their short half-lives necessitate close access to a cyclotron. Past efforts to measure blood flow with the widely available radiotracer 18F-fluorodeoxyglucose (FDG) were limited to tissues with high 18F-FDG extraction fraction. In this study, we developed an early-dynamic 18F-FDG PET method with high temporal resolution kinetic modeling to assess total-body blood flow based on deriving the vascular transit time of 18F-FDG and conducted a pilot comparison study against a 11C-butanol reference.

Methods

The first two minutes of dynamic PET scans were reconstructed at high temporal resolution (60×1 s, 30×2 s) to resolve the rapid passage of the radiotracer through blood vessels. In contrast to existing methods that use blood-to-tissue transport rate (K 1 ) as a surrogate of blood flow, our method directly estimates blood flow using a distributed kinetic model (adiabatic approximation to the tissue homogeneity model; AATH). To validate our 18F-FDG measurements of blood flow against a flow radiotracer, we analyzed total-body dynamic PET images of six human participants scanned with both 18F-FDG and 11C-butanol. An additional thirty-four total-body dynamic 18F-FDG PET scans of healthy participants were analyzed for comparison against literature blood flow ranges. Regional blood flow was estimated across the body and total-body parametric imaging of blood flow was conducted for visual assessment. AATH and standard compartment model fitting was compared by the Akaike Information Criterion at different temporal resolutions.

Results

18F-FDG blood flow was in quantitative agreement with flow measured from 11C-butanol across same-subject regional measurements (Pearson R=0.955, p<0.001; linear regression y=0.973x-0.012), which was visually corroborated by total-body blood flow parametric imaging. Our method resolved a wide range of blood flow values across the body in broad agreement with literature ranges (e.g., healthy cohort average: 0.51±0.12 ml/min/cm3 in the cerebral cortex and 2.03±0.64 ml/min/cm3 in the lungs, respectively). High temporal resolution (1 to 2 s) was critical to enabling AATH modeling over standard compartment modeling.

Conclusions

Total-body blood flow imaging was feasible using early-dynamic 18F-FDG PET with high-temporal resolution kinetic modeling. Combined with standard 18F-FDG PET methods, this method may enable efficient single-tracer flow-metabolism imaging, with numerous research and clinical applications in oncology, cardiovascular disease, pain medicine, and neuroscience.

Magnetic Resonance Imaging of Lung Perfusion

"Lung perfusion" in the context of imaging conventionally refers to the delivery of blood to the pulmonary capillary bed through the pulmonary arteries originating from the right ventricle required for oxygenation. The most important physiological mechanism in the context of imaging is the so-called hypoxic pulmonary vasoconstriction (HPV, also known as "Euler-Liljestrand-Reflex"), which couples lung perfusion to lung ventilation. In obstructive airway diseases such as asthma, chronic-obstructive pulmonary disease (COPD), cystic fibrosis (CF), and asthma, HPV downregulates pulmonary perfusion in order to redistribute blood flow to functional lung areas in order to conserve optimal oxygenation. Imaging of lung perfusion can be seen as a reflection of lung ventilation in obstructive airway diseases. Other conditions that primarily affect lung perfusion are pulmonary vascular diseases, pulmonary hypertension, or (chronic) pulmonary embolism, which also lead to inhomogeneity in pulmonary capillary blood distribution. Several magnetic resonance imaging (MRI) techniques either dependent on exogenous contrast materials, exploiting periodical lung signal variations with cardiac action, or relying on intrinsic lung voxel attributes have been demonstrated to visualize lung perfusion. Additional post-processing may add temporal information and provide quantitative information related to blood flow. The most widely used and robust technique, dynamic-contrast enhanced MRI, is available in clinical routine assessment of COPD, CF, and pulmonary vascular disease. Non-contrast techniques are important research tools currently requiring clinical validation and cross-correlation in the absence of a viable standard of reference. First data on many of these techniques in the context of observational studies assessing therapy effects have just become available. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 5.

MR Perfusion Imaging of the Lung

Lung perfusion assessment is critical for diagnosing and monitoring a variety of respiratory conditions. MRI perfusion provides a radiation-free technique, making it an ideal choice for longitudinal imaging in younger populations. This review focuses on the techniques and applications of MRI perfusion, including contrast-enhanced (CE) MRI and non-CE methods such as arterial spin labeling (ASL), fourier decomposition (FD), and hyperpolarized 129-Xenon (129-Xe) MRI. ASL leverages endogenous water protons as tracers for a non-invasive measure of lung perfusion, while FD offers simultaneous measurements of lung perfusion and ventilation, enabling the generation of ventilation/perfusion mapsHyperpolarized 129-Xe MRI emerges as a novel tool for assessing regional gas exchange in the lungs. Despite the promise of MRI perfusion techniques, challenges persist, including competition with other imaging techniques and the need for additional validation and standardization. In conditions such as cystic fibrosis and lung cancer, MRI has displayed encouraging results, whereas in diseases like chronic obstructive pulmonary disease, further validation remains necessary. In conclusion, while MRI perfusion techniques hold immense potential for a comprehensive, non-invasive assessment of lung function and perfusion, their broader clinical adoption hinges on technological advancements, collaborative research, and rigorous validation.

Role of pulmonary perfusion magnetic resonance imaging for the diagnosis of pulmonary hypertension: A review

Among five types of pulmonary hypertension, chronic thromboembolic pulmonary hypertension (CTEPH) is the only curable form, but prompt and accurate diagnosis can be challenging. Computed tomography and nuclear medicine-based techniques are standard imaging modalities to non-invasively diagnose CTEPH, however these are limited by radiation exposure, subjective qualitative bias, and lack of cardiac functional assessment. This review aims to assess the methodology, diagnostic accuracy of pulmonary perfusion imaging in the current literature and discuss its advantages, limitations and future research scope.

Comparison of phase contrast magnetic resonance imaging and scintigraphy for determination of split pulmonary blood flow in children and young adults with congenital heart disease

BACKGROUND

Measurement of differential blood flow to the lungs is important to understanding flow dynamics in the setting of congenital heart disease. Split blood flow via the pulmonary arteries guides and demonstrates the effect of interventions. Minimally invasive imaging of pulmonary blood flow can be achieved with scintigraphy or magnetic resonance imaging (MRI).

OBJECTIVE

To assess agreement of pulmonary blood flow measurements obtained by scintigraphy and MRI in children and young adults.

MATERIALS AND METHODS

We performed a retrospective review of patients < 21 years of age who had undergone both nuclear medicine pulmonary perfusion scans (Tc-99 m MAA) and cardiac MRI examinations from January 2012 to August 2021 at our tertiary pediatric hospital. Patient demographics, medical/surgical information, and estimates of split blood flow by both modalities were recorded. Pearson's correlation coefficient was used to determine the relationship between split blood flow measured by the two examinations. Agreement was calculated using interclass correlation coefficient (ICC) for absolute agreement and Bland-Altman difference analysis.

RESULTS

Correlation between split blood flow measured by scintigraphy and MRI using net flow was 0.90 (95% CI: 0.83-0.94, P < 0.001) and the ICC for agreement on split blood flow was 0.90 (95% CI: 0.84-0.94). Mean difference in split blood flow by Bland-Altman analysis was 0.79% with 95% limits of agreement (-11.2 to 12.8%).

CONCLUSION

There is excellent agreement between Tc-99 m scintigraphy and phase contrast MRI for quantification of split pulmonary blood flow in children and young adults with congenital heart disease.

Validation of CT-based ventilation and perfusion biomarkers with histopathology confirms radiation-induced pulmonary changes in a porcine model

Imaging biomarkers can assess disease progression or prognoses and are valuable tools to help guide interventions. Particularly in lung imaging, biomarkers present an opportunity to extract regional information that is more robust to the patient's condition prior to intervention than current gold standard pulmonary function tests (PFTs). This regional aspect has particular use in functional avoidance radiation therapy (RT) in which treatment planning is optimized to avoid regions of high function with the goal of sparing functional lung and improving patient quality of life post-RT. To execute functional avoidance, detailed dose-response models need to be developed to identify regions which should be protected. Previous studies have begun to do this, but for these models to be clinically translated, they need to be validated. This work validates two metrics that encompass the main components of lung function (ventilation and perfusion) through post-mortem histopathology performed in a novel porcine model. With these methods validated, we can use them to study the nuanced radiation-induced changes in lung function and develop more advanced models.

Improving pulmonary perfusion assessment by dynamic contrast-enhanced computed tomography in an experimental lung injury model

Pulmonary perfusion has been poorly characterized in acute respiratory distress syndrome (ARDS). Optimizing protocols to measure pulmonary blood flow (PBF) via dynamic contrast-enhanced (DCE) computed tomography (CT) could improve understanding of how ARDS alters pulmonary perfusion. In this study, comparative evaluations of injection protocols and tracer-kinetic analysis models were performed based on DCE-CT data measured in ventilated pigs with and without lung injury. Ten Yorkshire pigs (five with lung injury, five healthy) were anesthetized, intubated, and mechanically ventilated; lung injury was induced by bronchial hydrochloric acid instillation. Each DCE-CT scan was obtained during a 30-s end-expiratory breath-hold. Reproducibility of PBF measurements was evaluated in three pigs. In eight pigs, undiluted and diluted Isovue-370 were separately injected to evaluate the effect of contrast viscosity on estimated PBF values. PBF was estimated with the peak-enhancement and the steepest-slope approach. Total-lung PBF was estimated in two healthy pigs to compare with cardiac output measured invasively by thermodilution in the pulmonary artery. Repeated measurements in the same animals yielded a good reproducibility of computed PBF maps. Injecting diluted isovue-370 resulted in smaller contrast-time curves in the pulmonary artery (P < 0.01) and vein (P < 0.01) without substantially diminishing peak signal intensity (P = 0.46 in the pulmonary artery) compared with the pure contrast agent since its viscosity is closer to that of blood. As compared with the peak-enhancement model, PBF values estimated by the steepest-slope model with diluted contrast were much closer to the cardiac output (R2 = 0.82) as compared with the peak-enhancement model. DCE-CT using the steepest-slope model and diluted contrast agent provided reliable quantitative estimates of PBF.NEW & NOTEWORTHY Dynamic contrast-enhanced CT using a lower-viscosity contrast agent in combination with tracer-kinetic analysis by the steepest-slope model improves pulmonary blood flow measurements and assessment of regional distributions of lung perfusion.

Modulation of pulmonary blood flow in patients with acute respiratory failure

BACKGROUND

Impairment of ventilation and perfusion (V/Q) matching is a common mechanism leading to hypoxemia in patients with acute respiratory failure requiring intensive care unit (ICU) admission. While ventilation has been thoroughly investigated, little progress has been made to monitor pulmonary perfusion at the bedside and treat impaired blood distribution. The study aimed to assess real-time changes in regional pulmonary perfusion in response to a therapeutic intervention.

METHODS

Single-center prospective study that enrolled adult patients with ARDS caused by SARS-Cov-2 who were sedated, paralyzed, and mechanically ventilated. The distribution of pulmonary perfusion was assessed through electrical impedance tomography (EIT) after the injection of a 10-ml bolus of hypertonic saline. The therapeutic intervention consisted in the administration of inhaled nitric oxide (iNO), as rescue therapy for refractory hypoxemia. Each patient underwent two 15-minute steps at 0 and 20 ppm iNO, respectively. At each step, respiratory, gas exchange, and hemodynamic parameters were recorded, and V/Q distribution was measured, with unchanged ventilatory settings.

RESULTS

Ten 65 [56-75] years old patients with moderate (40%) and severe (60%) ARDS were studied 10 [4-20] days after intubation. Gas exchange improved at 20 ppm iNO (PaO₂/FiO₂ from 86 ± 16 to 110 ± 30 mmHg, p = 0.001; venous admixture from 51 ± 8 to 45 ± 7%, p = 0.0045; dead space from 29 ± 8 to 25 ± 6%, p = 0.008). The respiratory system's elastic properties and ventilation distribution were unaltered by iNO. Hemodynamics did not change after gas initiation (cardiac output 7.6 ± 1.9 vs. 7.7 ± 1.9 L/min, p = 0.66). The EIT pixel perfusion maps showed a variety of patterns of changes in pulmonary blood flow, whose increase positively correlated with PaO₂/FiO₂ increase (R² = 0.50, p = 0.049).

CONCLUSIONS

The assessment of lung perfusion is feasible at the bedside and blood distribution can be modulated with effects that are visualized in vivo. These findings might lay the foundations for testing new therapies aimed at optimizing the regional perfusion in the lungs.

Imaging human lung perfusion with contrast media: A meta-analysis

PURPOSE

To pool and summarise published data of pulmonary blood flow (PBF), pulmonary blood volume (PBV) and mean transit time (MTT) of the human lung, obtained with perfusion MRI or CT to provide reliable reference values of healthy lung tissue. In addition, the available data regarding diseased lung was investigated.

METHODS

PubMed was systematically searched to identify studies that quantified PBF/PBV/MTT in the human lung by injection of contrast agent, imaged by MRI or CT. Only data analysed by 'indicator dilution theory' were considered numerically. Weighted mean (wM), weighted standard deviation (wSD) and weighted coefficient of variance (wCoV) were obtained for healthy volunteers (HV), weighted according to the size of the datasets. Signal to concentration conversion method, breath holding method and presence of 'pre-bolus' were noted.

RESULTS

PBV was obtained from 313 measurements from 14 publications (wM: 13.97 ml/100 ml, wSD: 4.21 ml/100 ml, wCoV 0.30). MTT was obtained from 188 measurements from 10 publications (wM: 5.91 s, wSD: 1.84 s wCoV 0.31). PBF was obtained from 349 measurements from 14 publications (wM: 246.26 ml/100 ml ml/min, wSD: 93.13 ml/100 ml ml/min, wCoV 0.38). PBV and PBF were higher when the signal was normalised than when it was not. No significant differences were found for PBV and PBF between breathing states or between pre-bolus and no pre-bolus. Data for diseased lung were insufficient for meta-analysis.

CONCLUSION

Reference values for PBF, MTT and PBV were obtained in HV. The literature data are insufficient to draw strong conclusions regarding disease reference values.

Comparison of dual-energy CT with positron emission tomography for lung perfusion imaging in patients with non-small cell lung cancer

Objective.Functional lung avoidance (FLA) radiotherapy treatment aims to spare lung regions identified as functional from imaging. Perfusion contributes to lung function and can be measured from the determination of pulmonary blood volume (PBV). An advantageous alternative to the current determination of PBV from positron emission tomography (PET) may be from dual energy CT (DECT), due to shorter examination time and widespread availability. This study aims to determine the correlation between PBV determined from DECT and PET in the context of FLA radiotherapy.Approach.DECT and PET acquisitions at baseline of patients enrolled in the HI-FIVE clinical trial (ID: NCT03569072) were reviewed. Determination of PBV from PET imaging (PBVPET), from DECT imaging generated from a commercial software (Syngo.via, Siemens Healthineers, Forchheim, Germany) with its lowest (PBVsyngoR=1) and highest (PBVsyngoR=10) smoothing level parameter value (R), and from a two-material decomposition (TMD) method (PBVTMDL) with variable median filter kernel size (L) were compared. Deformable image registration between DECT images and the CT component of the PET/CT was applied to PBV maps before resampling to the PET resolution. The Spearman correlation coefficient (r_s) between PBV determinations was calculated voxel-wise in lung subvolumes.Main results.Of this cohort of 19 patients, 17 had a DECT acquisition at baseline. PBV maps determined from the commercial software and the TMD method were very strongly correlated [r_s(PBVsyngoR=1,PBVTMDL=1) = 0.94 ± 0.01 andr_s(PBVsyngoR=10,PBVTMDL=9) = 0.94 ± 0.02].PBVPETwas strongly correlated withPBVTMDL[r_s(PBVPET,PBVTMDL=28) = 0.67 ± 0.11]. Perfusion patterns differed along the posterior-anterior direction [r_s(PBVPET,PBVTMDL=28) = 0.77 ± 0.13/0.57 ± 0.16 in the anterior/posterior region].Significance. A strong correlation between DECT and PET determination of PBV was observed. Streak and smoothing effects in DECT and gravitational artefacts and misregistration in PET reduced the correlation posteriorly.

Quantitative analysis of pulmonary perfusion with dual-energy CT angiography: comparison of two quantification methods in patients with pulmonary embolism

The study aimed to evaluate a quantification method of pulmonary perfusion with Dual-Energy CT Angiography (DE-CTA) normalized by lung density in the prediction of outcome in acute pulmonary embolism (PE). In this prospective study with CTA scans acquired with different breathing protocols, two perfusion parameters were calculated: %PBV (relative value of PBV, expressed per unit volume) and PBVm (PBV normalized by lung density, expressed per unit mass). DE-CTA parameters were correlated with simplified pulmonary embolism severity index (sPESI) and with outcome groups, alone and in combinationwith tomographic right-to-left ventricular ratios (RV/LV). PBVm showed significant correlation with sPESI. PBVm presented higher accuracy than %PBV In the prediction of ICU admission or death in patients with PE, with the best performance when combined with RV/LV volumetric ratio.

Utility of dual-energy computed tomography in the association of COVID-19 pneumonia severity

Aim

Coronavirus disease 2019 pneumonia differs from ordinary pneumonia in that it is associated with lesions that reduce pulmonary perfusion. Dual-energy computed tomography is well suited to elucidate the etiology of coronavirus disease 2019 pneumonia, because it highlights changes in organ blood flow. In this study, we investigated whether dual-energy computed tomography could be used to determine the severity of coronavirus disease 2019 pneumonia.

Methods

Patients who were diagnosed with coronavirus disease 2019 pneumonia, admitted to our hospital, and underwent dual-energy computed tomography were included in this study. Dual-energy computed tomography findings, plane computed tomography findings, disease severity, laboratory data, and clinical features were compared between two groups: a critical group (18 patients) and a non-critical group (30 patients).

Results

The dual-energy computed tomography results indicated that the percentage of flow loss was significantly higher in the critical group compared with the non-critical group (P < 0.001). Additionally, our data demonstrated that thrombotic risk was associated with differences in clinical characteristics (P = 0.018). Receiver operating characteristic analysis revealed that the percentage of flow loss, evaluated using dual-energy computed tomography, could predict severity in the critical group with 100% sensitivity and 77% specificity. However, there were no significant differences in the receiver operating characteristic values for dual-energy computed tomography and plane computed tomography.

Conclusion

Dual-energy computed tomography can be used to associate the severity of coronavirus disease 2019 pneumonia with high accuracy. Further studies are needed to draw definitive conclusions.

Feasibility of flow-related enhancement brain perfusion MRI

Purpose

Brain perfusion imaging is of enormous importance for various neurological diseases. Fast gradient-echo sequences offering flow-related enhancement (FREE) could present a basis to generate perfusion-weighted maps. In this study, we obtained perfusion-weighted maps without contrast media by a previously described postprocessing algorithm from the field of functional lung MRI. At first, the perfusion signal was analyzed in fast low-angle shot (FLASH) and balanced steady-state free precession (bSSFP) sequences. Secondly, perfusion maps were compared to pseudo-continuous arterial spin labeling (pCASL) MRI in a healthy cohort. Thirdly, the feasibility of the new technique was demonstrated in a small selected group of patients with metastases and acute stroke.

Methods

One participant was examined with bSSFP and FLASH sequences at 1.5T and 3T, different flip angles and slice thicknesses. Twenty-five volunteers had bSSFP imaging and pCASL MRI. Three patients with cerebral metastases and one with acute ischemic stroke had bSSFP imaging and were compared to T1 post-contrast images and CT perfusion. Frequency analyses, SNR and perfusion contrast were compared at different flip angles and slice thicknesses. Regional correlations and Sorensen-Dice overlap were calculated in the healthy cohort. Dice overlap of the pathologies in the patient cohort were calculated.

Results

The bSSFP sequence presented detectable perfusion signal within brain vessel and parenchyma together with superior SNR compared to FLASH. Perfusion contrast and its corticomedullary differentiation increased with flip angle. Mean regional correlation was 0.36 and highly significant between FREE maps and pCASL and grey and white matter Dice match were 72% and 60% in the healthy cohort. Pathologies presented good overlap between FREE perfusion-weighted and T1 post-contrast images.

Conclusion

The feasibility of FREE brain perfusion imaging has been shown in a healthy cohort and selected patient cases with brain metastases and acute stroke. The study demonstrates a new approach for non-contrast brain perfusion imaging.

[Update on cystic fibrosis : From neonatal screening to causal treatment]

Cystic fibrosis (CF) is a multiorgan disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Approximately 90% of the morbidity and mortality are caused by pulmonary involvement. The mean life expectancy of patients with CF in 2020 was more than 52 years in Germany. The introduction of neonatal screening for CF and the development of a causally acting CFTR modulator treatment have clearly improved the prognosis of these patients. As an introduction, this article describes important aspects of CF in this context in order to go into details of the CF neonatal screening which was introduced in Germany in 2016.

CT-derived vessel segmentation for analysis of post-radiation therapy changes in vasculature and perfusion

Vessel segmentation in the lung is an ongoing challenge. While many methods have been able to successfully identify vessels in normal, healthy, lungs, these methods struggle in the presence of abnormalities. Following radiotherapy, these methods tend to identify regions of radiographic change due to post-radiation therapytoxicities as vasculature falsely. By combining texture analysis and existing vasculature and masking techniques, we have developed a novel vasculature segmentation workflow that improves specificity in irradiated lung while preserving the sensitivity of detection in the rest of the lung. Furthermore, radiation dose has been shown to cause vascular injury as well as reduce pulmonary function post-RT. This work shows the improvements our novel vascular segmentation method provides relative to existing methods. Additionally, we use this workflow to show a dose dependent radiation-induced change in vasculature which is correlated with previously measured perfusion changes (R² = 0.72) in both directly irradiated and indirectly damaged regions of perfusion. These results present an opportunity to extend non-contrast CT-derived models of functional change following radiation therapy.

Pulmonary Blood Volume Among Older Adults in the Community: The MESA Lung Study

BACKGROUND

The pulmonary vasculature is essential for gas exchange and impacts both pulmonary and cardiac function. However, it is difficult to assess and its characteristics in the general population are unknown. We measured pulmonary blood volume (PBV) noninvasively using contrast enhanced, dual-energy computed tomography to evaluate its relationship to age and symptoms among older adults in the community.

METHODS

The MESA (Multi-Ethnic Study of Atherosclerosis) is an ongoing community-based, multicenter cohort. All participants attending the most recent MESA exam were selected for contrast enhanced dual-energy computed tomography except those with estimated glomerular filtration rate <60 mL/min per 1.73 m2. PBV was calculated by material decomposition of dual-energy computed tomography images. Multivariable models included age, sex, race/ethnicity, education, height, weight, smoking status, pack-years, and scanner model.

RESULTS

The mean age of the 727 participants was 71 (range 59-94) years, and 55% were male. The race/ethnicity distribution was 41% White, 29% Black, 17% Hispanic, and 13% Asian. The mean±SD PBV in the youngest age quintile was 547±180 versus 433±194 mL in the oldest quintile (P<0.001), with an approximately linear decrement of 50 mL per 10 years of age ([95% CI, 32-67]; P<0.001). Findings were similar with multivariable adjustment. Lower PBV was associated independently with a greater dyspnea after a 6-minute walk (P=0.04) and greater composite dyspnea symptom scores (P=0.02). Greater PBV was also associated with greater height, weight, lung volume, Hispanic race/ethnicity, and nonsmoking history.

CONCLUSIONS

Pulmonary blood volume was substantially lower with advanced age and was associated independently with greater symptoms scores in the elderly.

Measuring Indirect Radiation-Induced Perfusion Change in Fed Vasculature Using Dynamic Contrast CT

Recent functional lung imaging studies have presented evidence of an “indirect effect” on perfusion damage, where regions that are unirradiated or lowly irradiated but that are supplied by highly irradiated regions observe perfusion damage post-radiation therapy (RT). The purpose of this work was to investigate this effect using a contrast-enhanced dynamic CT protocol to measure perfusion change in five novel swine subjects. A cohort of five Wisconsin Miniature Swine (WMS) were given a research course of 60 Gy in five fractions delivered locally to a vessel in the lung using an Accuray Radixact tomotherapy system with Synchrony motion tracking to increase delivery accuracy. Imaging was performed prior to delivering RT and 3 months post-RT to yield a 28−36 frame image series showing contrast flowing in and out of the vasculature. Using MIM software, contours were placed in six vessels on each animal to yield a contrast flow curve for each vessel. The contours were placed as follows: one at the point of max dose, one low-irradiated (5−20 Gy) branching from the max dose vessel, one low-irradiated (5−20 Gy) not branching from the max dose vessel, one unirradiated (<5 Gy) branching from the max dose vessel, one unirradiated (<5 Gy) not branching from the max dose vessel, and one in the contralateral lung. Seven measurements (baseline-to-baseline time and difference, slope up and down, max rise and value, and area under the curve) were acquired for each vessel’s contrast flow curve in each subject. Paired Student t-tests showed statistically significant (p < 0.05) reductions in the area under the curve in the max dose, and both fed contours indicating an overall reduction in contrast in these regions. Additionally, there were statistically significant reductions observed when comparing pre- and post-RT in slope up and down in the max dose, low-dose fed, and no-dose fed contours but not the low-dose not-fed, no-dose not-fed, or contralateral contours. These findings suggest an indirect damage effect where irradiation of the vasculature causes a reduction in perfusion in irradiated regions as well as regions fed by the irradiated vasculature.

Lobar pulmonary perfusion quantification with dual-energy CT angiography: Interlobar variability and relationship with regional clot burden in pulmonary embolism

Purpose

Semi-automated lobar segmentation tools enable an anatomical assessment of regional pulmonary perfusion with Dual-Energy CTA (DE-CTA). We aimed to quantify lobar pulmonary perfusion with DE-CTA, analyze the perfusion distribution among the pulmonary lobes in subjects without cardiopulmonary diseases and assess the correlation between lobar perfusion and regional endoluminal clots in patients with acute pulmonary embolism (PE).

Methods

We evaluated 151 consecutive subjects with suspected PE and without cardiopulmonary comorbidities. DE-CTA derived perfused blood volume (PBV) of each pulmonary lobe was measured applying a semi-automated lobar segmentation technique. In patients with PE, blood clot location was assessed, and CT-based vascular obstruction index of each lobe (CTOI_lobe) was calculated and classified into three groups: CTOI_lobe= 0, low CTOI_lobe (1–50%) and high CTOI_lobe (>50%).

Results

Among patients without PE (103/151, 68.2%), median lobar PBV was 13.7% (IQR 10.2–18.0%); the right middle lobe presented lower PBV when compared to all the other lobes (p < .001). In patients with PE (48/151, 31.8%), lobar PBV was 12.6% (IQR 9.6–15.7%), 13.7% (IQR 10.1–16.7%) and 6.5% (IQR 5.1–10.2%) in the lobes with CTOI_lobe= 0, low CTOI_lobe and high CTOI_lobe scores, respectively, with a significantly decreased PBV in the lobes with high CTOI_lobe score (p < .001). ROC analysis of lobar PBV for prediction of high CTOI_lobe score revealed AUC of 0.847 (95%CI 0.785–0.908).

Conclusion

Pulmonary perfusion was heterogeneously distributed along the pulmonary lobes in patients without cardiopulmonary diseases. In patients with PE, the lobes with high vascular obstruction score (CTOI_lobe> 50%) presented a decreased lobar perfusion.

•

Semi-automated tools enable assessment of lobar perfusion with Dual-Energy CTA.

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The pulmonary perfusion is heterogeneously distributed along the pulmonary lobes.

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Lobar perfusion was decreased only in the lobes with high vascular obstruction index.

A dual center and dual vendor comparison study of automated perfusion-weighted phase-resolved functional lung magnetic resonance imaging with dynamic contrast-enhanced magnetic resonance imaging in patients with cystic fibrosis

For sensitive diagnosis and monitoring of pulmonary disease, ionizing radiation-free imaging methods are of great importance. A noncontrast and free-breathing proton magnetic resonance imaging (MRI) technique for assessment of pulmonary perfusion is phase-resolved functional lung (PREFUL) MRI. Since there is no validation of PREFUL MRI across different centers and scanners, the purpose of this study was to compare perfusion-weighted PREFUL MRI with the well-established dynamic contrast-enhanced (DCE) MRI across two centers on scanners from two different vendors. Sixteen patients with cystic fibrosis (CF) (Center 1: 10 patients; Center 2: 6 patients) underwent PREFUL and DCE MRI at 1.5T in the same imaging session. Normalized perfusion-weighted values and perfusion defect percentage (QDP) values were calculated for the whole lung and three central slices (dorsal, central, ventral of the carina). Obtained parameters were compared using Pearson correlation, Spearman correlation, Bland-Altman analysis, Wilcoxon signed-rank test, and Wilcoxon rank-sum test. Moderate-to-strong correlations between normalized perfusion-weighted PREFUL and DCE values were found (posterior slice: r = 0.69, p < 0.01). Spatial overlap of PREFUL and DCE QDP maps showed an agreement of 79.4% for the whole lung. Further, spatial overlap values of Center 1 were not significantly different to those of Center 2 for the three central slices (p > 0.07). The feasibility of PREFUL MRI across two different centers and two different vendors was shown in patients with CF and obtained results were in agreement with DCE MRI.

Pulmonary functional imaging (PFI): A historical review and perspective

PFI Pulmonary Functional Imaging (PFI) refers to visualization and measurement of ventilation, perfusion, gas flow and exchange as well as biomechanics. In this review, we will highlight the historical development of PFI, describing recent advances and listing the various techniques for PFI offered per modality. Challenges PFI is facing and requirements for PFI from a clinical point of view will be pointed out. Hereby the review is meant as an introduction to PFI.

An efficient and fast multi-band focused bioimpedance solution with EIT-based reconstruction for pulmonary embolism assessment: a simulation study from massive to segmental blockage

OBJECTIVE

Pulmonary embolism (PE) is an acute condition that blocks the perfusion to the lungs and is a common complication of Covid-19. However, PE is often not diagnosed in time, especially in the pandemic time due to complicated diagnosis protocol. In this study, a non-invasive, fast and efficient bioimpedance method with the EIT-based reconstruction approach is proposed to assess the lung perfusion reliably.

APPROACH

Some proposals are presented to improve the sensitivity and accuracy for the bioimpedance method: (1) a new electrode configuration and focused pattern to help study deep changes caused by PE within each lung field separately, (2) a measurement strategy to compensate the effect of different boundary shapes and varied respiratory conditions on the perfusion signals and (3) an estimator to predict the lung perfusion capacity, from which the severity of PE can be assessed. The proposals were tested on the first-time simulation of PE events at different locations and degrees from segmental blockages to massive blockages. Different object boundary shapes and varied respiratory conditions were included in the simulation to represent for different populations in real measurements.

RESULTS

The correlation between the estimator and the perfusion was very promising (R = 0.91, errors < 6%). The measurement strategy with the proposed configuration and pattern has helped stabilize the estimator to non-perfusion factors such as the boundary shapes and varied respiration conditions (3-5% errors).

SIGNIFICANCE

This promising preliminary result has demonstrated the proposed bioimpedance method's capability and feasibility, and might start a new direction for this application.

Lung Perfusion Assessment by Bedside Electrical Impedance Tomography in Critically Ill Patients

As a portable, radiation-free imaging modality, electrical impedance tomography (EIT) technology has shown promise in the bedside visual assessment of lung perfusion distribution in critically ill patients. The two main methods of EIT for assessing lung perfusion are the pulsatility and conductivity contrast (saline) bolus method. Increasing attention is being paid to the saline bolus EIT method in the evaluation of regional pulmonary perfusion in clinical practice. This study seeks to provide an overview of experimental and clinical studies with the aim of clarifying the progress made in the use of the saline bolus EIT method. Animal studies revealed that the saline bolus EIT method presented good consistency with single-photon emission CT (SPECT) in the evaluation of lung regional perfusion changes in various pathological conditions. Moreover, the saline bolus EIT method has been applied to assess the lung perfusion in a pulmonary embolism and the effect of positive end-expiratory pressure (PEEP) on regional ventilation/perfusion ratio (V/Q) and acute respiratory distress syndrome (ARDS) in several clinical studies. The implementation of saline boluses, data analyses, precision, and cutoff values varied among different studies, and a consensus must be reached regarding the clinical application of the saline bolus EIT method. Further study is required to validate the impact of the described saline bolus EIT method on decision-making, therapeutic management, and outcomes in critically ill patients.

Radiation-induced Hounsfield unit change correlates with dynamic CT perfusion better than 4DCT-based ventilation measures in a novel-swine model

To analyze radiation induced changes in Hounsfield units and determine their correlation with changes in perfusion and ventilation. Additionally, to compare the post-RT changes in human subjects to those measured in a swine model used to quantify perfusion changes and validate their use as a preclinical model. A cohort of 5 Wisconsin Miniature Swine (WMS) were studied. Additionally, 19 human subjects were recruited as part of an IRB approved clinical trial studying functional avoidance radiation therapy for lung cancer and were treated with SBRT. Imaging (a contrast enhanced dynamic perfusion CT in the swine and 4DCT in the humans) was performed prior to and post-RT. Jacobian elasticity maps were calculated on all 4DCT images. Contours were created from the isodose lines to discretize analysis into 10 Gy dose bins. B-spline deformable image registration allowed for voxel-by-voxel comparative analysis in these contours between timepoints. The WMS underwent a research course of 60 Gy in 5 fractions delivered locally to a target in the lung using an MRI-LINAC system. In the WMS subjects, the dose-bin contours were copied onto the contralateral lung, which received < 5 Gy for comparison. Changes in HU and changes in Jacobian were analyzed in these contours. Statistically significant (p < 0.05) changes in the mean HU value post-RT compared to pre-RT were observed in both the human and WMS groups at all timepoints analyzed. The HU increased linearly with dose for both groups. Strong linear correlation was observed between the changes seen in the swine and humans (Pearson coefficient > 0.97, p < 0.05) at all timepoints. Changes seen in the swine closely modeled the changes seen in the humans at 12 months post RT (slope = 0.95). Jacobian analysis showed between 30 and 60% of voxels were damaged post-RT. Perfusion analysis in the swine showed a statistically significant (p < 0.05) reduction in contrast inside the vasculature 3 months post-RT compared to pre-RT. The increases in contrast outside the vasculature was strongly correlated (Pearson Correlation 0.88) with the reduction in HU inside the vasculature but were not correlated with the changes in Jacobians. Radiation induces changes in pulmonary anatomy at 3 months post-RT, with a strong linear correlation with dose. The change in HU seen in the non-vessel lung parenchyma suggests this metric is a potential biomarker for change in perfusion. Finally, this work suggests that the WMS swine model is a promising pre-clinical model for analyzing radiation-induced changes in humans and poses several benefits over conventional swine models.

Echo Time-Dependent Observed Lung T1 in Patients With Chronic Obstructive Pulmonary Disease in Correlation With Quantitative Imaging and Clinical Indices

BACKGROUND

There is a clinical need for imaging-derived biomarkers for the management of chronic obstructive pulmonary disease (COPD). Observed pulmonary T₁ (T₁ (TE)) depends on the echo-time (TE) and reflects regional pulmonary function.

PURPOSE

To investigate the potential diagnostic value of T₁ (TE) for the assessment of lung disease in COPD patients by determining correlations with clinical parameters and quantitative CT.

STUDY TYPE

Prospective non-randomized diagnostic study.

POPULATION

Thirty COPD patients (67.7 ± 6.6 years). Data from a previous study (15 healthy volunteers [26.2 ± 3.9 years) were used as reference.

FIELD STRENGTH/SEQUENCE

Study participants were examined at 1.5 T using dynamic contrast-enhanced three-dimensional gradient echo keyhole perfusion sequence and a multi-echo inversion recovery two-dimensional UTE (ultra-short TE) sequence for T₁ (TE) mapping at TE_1-5  = 70 μsec, 500 μsec, 1200 μsec, 1650 μsec, and 2300 μsec.

ASSESSMENT

Perfusion images were scored by three radiologists. T₁ (TE) was automatically quantified. Computed tomography (CT) images were quantified in software (qCT). Clinical parameters including pulmonary function testing were also acquired.

STATISTICAL TESTS

Spearman rank correlation coefficients (ρ) were calculated between T₁ (TE) and perfusion scores, clinical parameters and qCT. A P-value <0.05 was considered statistically significant.

RESULTS

Median values were T₁ (TE_1-5 ) = 644 ± 78 msec, 835 ± 92 msec, 835 ± 87 msec, 831 ± 131 msec, 893 ± 220 msec, all significantly shorter than previously reported in healthy subjects. A significant increase of T₁ was observed from TE₁ to TE₂ , with no changes from TE₂ to TE₃ (P = 0.48), TE₃ to TE₄ (P = 0.94) or TE₄ to TE₅ (P = 0.02) which demonstrates an increase at shorter TEs than in healthy subjects. Moderate to strong Spearman's correlations between T₁ and parameters including the predicted diffusing capacity for carbon monoxide (DLCO, ρ < 0.70), mean lung density (MLD, ρ < 0.72) and the perfusion score (ρ > -0.69) were found. Overall, correlations were strongest at TE₂ , weaker at TE₁ and rarely significant at TE₄ -TE₅ .

DATA CONCLUSION

In COPD patients, the increase of T₁ (TE) with TE occurred at shorter TEs than previously found in healthy subjects. Together with the lack of correlation between T₁ and clinical parameters of disease at longer TEs, this suggests that T₁ (TE) quantification in COPD patients requires shorter TEs. The TE-dependence of correlations implies that T₁ (TE) mapping might be developed further to provide diagnostic information beyond T₁ at a single TE.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 1.

Perfusion quantification using voxel-wise proton density and median signal decay in PREFUL MRI

PURPOSE

Contrast-free lung MRI based on Fourier decomposition is an attractive method to monitor various lung diseases. However, the accuracy of the current perfusion quantification is limited. In this study, a new approach for perfusion quantification based on voxel-wise proton density and median signal decay toward the steady state for Fourier decomposition-based techniques is proposed called Q_Quantified (Q_Quant ).

METHODS

Twenty patients with chronic obstructive pulmonary disease and 18 patients with chronic thromboembolic pulmonary hypertension received phase-resolved functional lung-MRI (PREFUL) and dynamic contrast-enhanced (DCE)-MRI. Nine healthy participants received phase-resolved functional lung-MRI only. Median values of Q_Quant were compared to a Fourier decomposition perfusion quantification presented by Kjørstad et al (Q_Kjørstad ) and validated toward pulmonary blood flow derived by DCE-MRI (PBF_DCE ). Blood fraction maps determined by the new approach were calculated. Regional and global correlation coefficients were calculated, and Bland-Altman plots were created. Histogram analyses of all cohorts were created.

RESULTS

The introduced parameter Q_Quant showed only 2 mL/min/100 mL mean deviation to PBF_DCE in the patient cohort and showed less bias than Q_Kjørstad . Significant increases of regional correlation with PBF_DCE were achieved (r = 0.3 vs. r = 0.2, P < .01*). The trend of global correlation toward PBF_DCE is not uniform, showing higher values for Q_Kjørstad in the chronic obstructive pulmonary disease cohort than for Q_Quant and vice versa in the chronic thromboembolic pulmonary hypertension cohort. In contrast to Q_Kjørstad , Q_Quant perfusion maps indicate a physiologic dorsoventral gradient in supine position similar to PBF_DCE with similar value distribution in the histograms.

CONCLUSION

We proposed a new approach for perfusion quantification of phase-resolved functional lung measurements. The developed parameter Q_Quant reveals a higher accuracy compared to Q_Kjørstad .

Automated assessment of functional lung imaging with 68Ga-ventilation/perfusion PET/CT using iterative histogram analysis

PURPOSE

Functional lung mapping from Ga⁶⁸-ventilation/perfusion (V/Q) PET/CT, which has been shown to correlate with pulmonary function tests (PFTs), may be beneficial in a number of clinical applications where sparing regions of high lung function is of interest. Regions of clumping in the proximal airways in patients with airways disease can result in areas of focal intense activity and artefact in ventilation imaging. These artefacts may even shine through to subsequent perfusion images and create a challenge for quantitative analysis of PET imaging. We aimed to develop an automated algorithm that interprets the uptake histogram of PET images to calculate a peak uptake value more representative of the global lung volume.

METHODS

Sixty-six patients recruited from a prospective clinical trial underwent both V/Q PET/CT imaging and PFT analysis before treatment. PET images were normalised using an iterative histogram analysis technique to account for tracer hotspots prior to the threshold-based delineation of varying values. Pearson's correlation between fractional lung function and PFT score was calculated for ventilation, perfusion, and matched imaging volumes at varying threshold values.

RESULTS

For all functional imaging thresholds, only FEV1/FVC PFT yielded reasonable correlations to image-based functional volume. For ventilation, a range of 10-30% of adapted peak uptake value provided a reasonable threshold to define a volume that correlated with FEV1/FVC (r = 0.54-0.61). For perfusion imaging, a similar correlation was observed (r = 0.51-0.56) in the range of 20-60% adapted peak threshold. Matched volumes were closely linked to ventilation with a threshold range of 15-35% yielding a similar correlation (r = 0.55-0.58).

CONCLUSIONS

Histogram normalisation may be implemented to determine the presence of tracer clumping hotspots in Ga-68 V/Q PET imaging allowing for automated delineation of functional lung and standardisation of functional volume reporting.

Overview of MRI for pulmonary functional imaging

Morphological evaluation of the lung is important in the clinical evaluation of pulmonary diseases. However, the disease process, especially in its early phases, may primarily result in changes in pulmonary function without changing the pulmonary structure. In such cases, the traditional imaging approaches to pulmonary morphology may not provide sufficient insight into the underlying pathophysiology. Pulmonary imaging community has therefore tried to assess pulmonary diseases and functions utilizing not only nuclear medicine, but also CT and MR imaging with various technical approaches. In this review, we overview state-of-the art MR methods and the future direction of: (1) ventilation imaging, (2) perfusion imaging and (3) biomechanical evaluation for pulmonary functional imaging.

Regional Lung Perfusion Analysis in Experimental ARDS by Electrical Impedance and Computed Tomography

Electrical impedance tomography is clinically used to trace ventilation related changes in electrical conductivity of lung tissue. Estimating regional pulmonary perfusion using electrical impedance tomography is still a matter of research. To support clinical decision making, reliable bedside information of pulmonary perfusion is needed. We introduce a method to robustly detect pulmonary perfusion based on indicator-enhanced electrical impedance tomography and validate it by dynamic multidetector computed tomography in two experimental models of acute respiratory distress syndrome. The acute injury was induced in a sublobar segment of the right lung by saline lavage or endotoxin instillation in eight anesthetized mechanically ventilated pigs. For electrical impedance tomography measurements, a conductive bolus (10% saline solution) was injected into the right ventricle during breath hold. Electrical impedance tomography perfusion images were reconstructed by linear and normalized Gauss-Newton reconstruction on a finite element mesh with subsequent element-wise signal and feature analysis. An iodinated contrast agent was used to compute pulmonary blood flow via dynamic multidetector computed tomography. Spatial perfusion was estimated based on first-pass indicator dilution for both electrical impedance and multidetector computed tomography and compared by Pearson correlation and Bland-Altman analysis. Strong correlation was found in dorsoventral (r = 0.92) and in right-to-left directions (r = 0.85) with good limits of agreement of 8.74% in eight lung segments. With a robust electrical impedance tomography perfusion estimation method, we found strong agreement between multidetector computed and electrical impedance tomography perfusion in healthy and regionally injured lungs and demonstrated feasibility of electrical impedance tomography perfusion imaging.

Comparison of phase-resolved functional lung (PREFUL) MRI derived perfusion and ventilation parameters at 1.5T and 3T in healthy volunteers

Purpose

The purpose of this study is to evaluate the influence of different field strengths on perfusion and ventilation parameters, SNR and CNR derived by PREFUL MRI using predefined sequence parameters.

Methods

Data sets of free breathing 2d FLASH lung MRI were acquired from 15 healthy subjects at 1.5T and 3T (Magnetom Avanto and Skyra, Siemens Healthcare, Erlangen, Germany) with a maximum period of 3 days in between. The processed functional parameters regional ventilation (RVent), perfusion (Q), quantified perfusion (Q_Quant), perfusion defect percentage (QDP), ventilation defect percentage (VDP) and ventilation-perfusion match (VQM) were compared for systematic differences. Signal- and contrast-to-noise ratio (SNR and CNR) of both acquisitions were analyzed.

Results

RVent, Q, VDP, SNR and CNR presented no significant differences between 1.5T and 3T. Q_Quant (1.5T vs. 3T, P = 0.04), and QDP (1.5T vs. 3T, P≤0.01) decreased significantly at 3T. Consequently, VQM increased significantly (1.5T vs. 3T, P≤0.01). Skewness and kurtosis of the Q-values increased significantly at 3T (P≤0.01). The mean Sørensen-Dice coefficients between both series were 0.91 for QDP and 0.94 for VDP. The Bland-Altman analysis of both series showed mean differences of 4.29% for QDP, 1.23% for VDP and -5.15% for VQM. Using the above-mentioned parameters for three-day repeatability at two different scanners and field strengths, the retrospective power calculation showed, that a sample size of 15 can detect differences of 3.7% for QDP, of 2.9% for VDP and differences of 2.6% for VQM.

Conclusion

Significant differences in QDP may be related to field inhomogeneities, which is expressed by increasing skewness and kurtosis at 3T. Q_Quant reveals only poor reproducibility between 1.5T and 3T. RVent, Q, VDP, SNR and CNR were not altered significantly at the used sequence parameters. Healthy participants with minimal defects present high spatial agreement of QDP and VDP.

From Early Morphometrics to Machine Learning-What Future for Cardiovascular Imaging of the Pulmonary Circulation?

Imaging plays a cardinal role in the diagnosis and management of diseases of the pulmonary circulation. Behind the picture itself, every digital image contains a wealth of quantitative data, which are hardly analysed in current routine clinical practice and this is now being transformed by radiomics. Mathematical analyses of these data using novel techniques, such as vascular morphometry (including vascular tortuosity and vascular volumes), blood flow imaging (including quantitative lung perfusion and computational flow dynamics), and artificial intelligence, are opening a window on the complex pathophysiology and structure-function relationships of pulmonary vascular diseases. They have the potential to make dramatic alterations to how clinicians investigate the pulmonary circulation, with the consequences of more rapid diagnosis and a reduction in the need for invasive procedures in the future. Applied to multimodality imaging, they can provide new information to improve disease characterization and increase diagnostic accuracy. These new technologies may be used as sophisticated biomarkers for risk prediction modelling of prognosis and for optimising the long-term management of pulmonary circulatory diseases. These innovative techniques will require evaluation in clinical trials and may in themselves serve as successful surrogate end points in trials in the years to come.

Current state of the art MRI for the longitudinal assessment of cystic fibrosis

Pulmonary MRI can now provide high-resolution images that are sensitive to early disease and specific to inflammation in cystic fibrosis (CF) lung disease. With specificity and function limited via computed tomography (CT), there are significant advantages to MRI. Many of the modern MRI techniques can be performed throughout life, and can be employed to understand changes over time, in addition to quantification of treatment response. Proton density and T1 /T2 contrast images can be obtained within a single breath-hold, providing depiction of structural abnormalities and active inflammation. Modern radial and/or spiral ultrashort echo-time (UTE) techniques rival CT in resolution for depiction and quantification of structure, for both airway and parenchymal abnormalities. Contrast perfusion MRI techniques are now utilized routinely to visualize changes in pulmonary and bronchial circulation that routinely occur in CF lung disease, and noncontrast techniques are moving closer to clinical translation. Functional information can be obtained from noncontrast proton images alone, using techniques such as Fourier decomposition. Hyperpolarized-gas MRI, increasingly using 129 Xe, is now becoming more widespread and has been demonstrated to have high sensitivity to early airway obstruction in CF via ventilation MRI. The sensitivity of 129 Xe MRI promises future use in personalized medicine, management of early CF lung disease, and in future clinical trials. By combining structural and functional techniques, with or without hyperpolarized gases, regional structure-function relationships can be obtained, giving insight into the pathophysiology of disease and improved clinical management. This article reviews the modern MRI techniques that can routinely be employed for CF lung disease in nearly any large medical center. Level of Evidence: 4 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2019.

Detection of invasive pulmonary aspergillosis in mice using lung perfusion single-photon emission computed tomography with [99mTc]MAA

There is an urgent need for development of better diagnostic strategies to improve outcomes in patients with invasive pulmonary aspergillosis (IPA). We hypothesized that lung perfusion single-photon emission computed tomography (SPECT) may be more sensitive and specific than computed tomography (CT) of the chest for detection of IPA because it is an angioinvasive pulmonary infection with characteristics that are different from those of bacterial pneumonia. We used SPECT with injection of technetium-99m-labeled macroaggregated albumin ([99mTc]MAA) to measure pulmonary perfusion in noninfected mice, mice with IPA, and mice with bacterial pneumonia. Histopathologic analysis was performed to evaluate the correlation between the perfusion defect and mould invasion. We also attempted to quantitatively evaluate the SPECT images to identify differences in decreased perfusion levels in affected areas in the mouse lung. Histopathologic analysis in the IPA mouse model showed a clear match between areas with a perfusion defect and the presence of mold, indicating that the location of the perfusion defect on a SPECT image reflects angioinvasion of the mould in the lungs. Some of these perfusion defects could be seen before appearance of the infiltrate of CT images. Quantitative analysis confirmed that perfusion in the affected areas was significantly decreased in the IPA model but not in the bacterial pneumonia model (P < .0001). This imaging method may be preferable to the alternative methods presently used to identify the presence of mold in a patient's lungs.

[Magnetic resonance imaging of the lungs in cystic fibrosis]

CLINICAL ISSUE

Disease severity and mortality in patients with cystic fibrosis (CF) is mainly determined by (progressive) pulmonary lung disease. Early diagnosis and therapy are important and of prognostic value to conserve lung function.

STANDARD RADIOLOGICAL METHODS

Primary imaging techniques for lung imaging are x‑ray and computed tomography (CT) to monitor disease severity and regional distribution.

METHODICAL INNOVATIONS

Radiation-free imaging techniques such as magnetic resonance imaging (MRI) have gained interest over the last decade in order to prevent radiation damage.

PERFORMANCE

The main findings of CF lung disease are airway wall thickening, bronchiectasis, and mucus plugging, which are found in up to 60% of preschool age children. Pleural abnormalities and consolidations are often associated with pulmonary exacerbation. Young CF patients often show a mosaic pattern as functional changes and also perfusion defects can be seen from birth in 50% of CF patients by contrast-enhanced perfusion imaging, and in up to 90% of adult patients, with varying degrees of severity. Dilated bronchial arteries indicate an increased risk for hemoptysis.

ACHIEVEMENTS

Proton MRI is the sole imaging technique that can show structural and functional lung changes in one examination. Structured assessment using a scoring system helps to systematically grade the extent and severity of all CF-associated changes.

CONCLUSIONS

Lung MRI for cystic fibrosis has been recently established as a clinical standard examination and is routinely performed at experienced centers. More recently, it has also been used as an endpoint within the framework of clinical studies.

Expanding Applications of Pulmonary MRI in the Clinical Evaluation of Lung Disorders: Fleischner Society Position Paper

Pulmonary MRI provides structural and quantitative functional images of the lungs without ionizing radiation, but it has had limited clinical use due to low signal intensity from the lung parenchyma. The lack of radiation makes pulmonary MRI an ideal modality for pediatric examinations, pregnant women, and patients requiring serial and longitudinal follow-up. Fortunately, recent MRI techniques, including ultrashort echo time and zero echo time, are expanding clinical opportunities for pulmonary MRI. With the use of multicoil parallel acquisitions and acceleration methods, these techniques make pulmonary MRI practical for evaluating lung parenchymal and pulmonary vascular diseases. The purpose of this Fleischner Society position paper is to familiarize radiologists and other interested clinicians with these advances in pulmonary MRI and to stratify the Society recommendations for the clinical use of pulmonary MRI into three categories: (a) suggested for current clinical use, (b) promising but requiring further validation or regulatory approval, and (c) appropriate for research investigations. This position paper also provides recommendations for vendors and infrastructure, identifies methods for hypothesis-driven research, and suggests opportunities for prospective, randomized multicenter trials to investigate and validate lung MRI methods.

The role of imaging in malignant pleural mesothelioma: an update after the 2018 BTS guidelines

Malignant pleural mesothelioma (MPM) is a primary malignancy of the pleura and is associated with a poor outcome. The symptoms and signs of malignant mesothelioma present late in the natural history of the disease and are non-specific, making the diagnosis challenging and imaging key. In 2018, the British Thoracic Society (BTS) updated the guideline on diagnosis, staging, and follow-up of patients with MPM. These recommendations are discussed in this review of the current literature on imaging of MPM. It is estimated MPM will continue to cause serious morbidity and mortality in the UK late into the 21st century, and internationally, people continue to be exposed to asbestos. We aim to update the reader on current and future imaging strategies, which could aid early diagnosis of pleural malignancy and provide an update on staging and assessment of tumour response.

Dynamic pulmonary CT perfusion using first-pass analysis technique with only two volume scans: Validation in a swine model

PURPOSE

To evaluate the accuracy of a low-dose first-pass analysis (FPA) CT pulmonary perfusion technique in comparison to fluorescent microsphere measurement as the reference standard.

METHOD

The first-pass analysis CT perfusion technique was validated in six swine (41.7 ± 10.2 kg) for a total of 39 successful perfusion measurements. Different perfusion conditions were generated in each animal using serial balloon occlusions in the pulmonary artery. For each occlusion, over 20 contrast-enhanced CT images were acquired within one breath (320 x 0.5mm collimation, 100kVp, 200mA or 400mA, 350ms gantry rotation time). All volume scans were used for maximum slope model (MSM) perfusion measurement, but only two volume scans were used for the FPA measurement. Both MSM and FPA perfusion measurements were then compared to the reference fluorescent microsphere measurements.

RESULTS

The mean lung perfusion of MSM, FPA, and microsphere measurements were 6.21 ± 3.08 (p = 0.008), 6.59 ± 3.41 (p = 0.44) and 6.68 ± 3.89 ml/min/g, respectively. The MSM (PMSM) and FPA (PFPA) perfusion measurements were related to the corresponding reference microsphere measurement (PMIC) by PMSM = 0.51PMIC + 2.78 (r = 0.64) and PFPA = 0.79PMIC + 1.32 (r = 0.90). The root-mean-square-error for the MSM and FPA techniques were 3.09 and 1.72 ml/min/g, respectively. The root-mean-square-deviation for the MSM and FPA techniques were 2.38 and 1.50 ml/min/g, respectively. The CT dose index for MSM and FPA techniques were 138.7 and 8.4mGy, respectively.

CONCLUSIONS

The first-pass analysis technique can accurately measure regional pulmonary perfusion and has the potential to reduce the radiation dose associated with dynamic CT perfusion for assessment of pulmonary disease.

Ten years of chest MRI for patients with cystic fibrosis : Translation from the bench to clinical routine

BACKGROUND

Despite recent advances in our knowledge about the pathophysiology and treatment of cystic fibrosis (CF), pulmonary involvement remains the most important determinant of morbidity and mortality in patients with CF. Since lung function testing may not be sensitive enough for subclinical disease progression, and because young children may have normal spirometry results over a longer period of time, imaging today plays an increasingly important role in clinical routine and research for the monitoring of CF lung disease. In this regard, chest magnetic resonance imaging (MRI) could serve as a radiation-free modality for structural and functional lung imaging.

METHODS

Our research agenda encompassed the entire process of development, implementation, and validation of appropriate chest MRI protocols for use with infant and adult CF patients alike.

RESULTS

After establishing a general MRI protocol for state-of-the-art clinical 1.5-T scanners based on the available sequence technology, a semiquantitative scoring system was developed followed by cross-validation of the method against the established modalities of computed tomography, radiography, and lung function testing. Cross-sectional studies were then set up to determine the sensitivity of the method for the interindividual variation of the disease and for changes in disease severity after treatment. Finally, the MRI protocol was implemented at multiple sites to be validated in a multicenter setting.

CONCLUSION

After more than a decade, lung MRI has become a valuable tool for monitoring CF in clinical routine application and as an endpoint for clinical studies.

Design of Gadoteridol-Loaded Cationic Liposomal Adjuvant CAF01 for MRI of Lung Deposition of Intrapulmonary Administered Particles

Designing effective and safe tuberculosis (TB) subunit vaccines for inhalation requires identification of appropriate antigens and adjuvants and definition of the specific areas to target in the lungs. Magnetic resonance imaging (MRI) enables high spatial resolution, but real-time anatomical and functional MRI of lungs is challenging. Here, we describe the design of a novel gadoteridol-loaded cationic adjuvant formulation 01 (CAF01) for MRI-guided vaccine delivery of the clinically tested TB subunit vaccine candidate H56/CAF01. Gadoteridol-loaded CAF01 liposomes were engineered by using a quality-by-design approach to (i) increase the mechanistic understanding of formulation factors governing the loading of gadoteridol and (ii) maximize the loading of gadoteridol in CAF01, which was confirmed by cryotransmission electron microscopy. The encapsulation efficiency and loading of gadoteridol were highly dependent on the buffer pH due to strong attractive electrostatic interactions between gadoteridol and the cationic lipid component. Optimal gadoteridol loading of CAF01 liposomes showed good in vivo stability and safety upon intrapulmonary administration into mice while generating 1.5-fold MRI signal enhancement associated with approximately 30% T₁ relaxation change. This formulation principle and imaging approach can potentially be used for other mucosal nanoparticle-based formulations, species, and lung pathologies, which can readily be translated for clinical use.

Spect perfusion imaging versus CT for predicting radiation injury to normal lung in lung cancer patients

OBJECTIVES

In non-small cell lung cancer (NSCLC) patients, to establish whether the fractional volumes of irradiated anatomic or perfused lung differed between those with and without deteriorating lung function or radiation associated lung injury (RALI).

METHODS

48 patients undergoing radical radiotherapy for NSCLC had a radiotherapy-planning CT scan and single photon emission CT lung perfusion imaging (99mTc-labelled macroaggregate albumin). CT defined the anatomic and the single photon emission CT scan (co-registered with CT) identified the perfused (threshold 20 % of maximum) lung volumes. Fractional volumes of anatomic and perfused lung receiving more than 5, 10, 13, 20, 30, 40, 50 Gy were compared between patients with deteriorating (>median decline) vs stable (

RESULTS

Fractional volumes of anatomic and perfused lung receiving more than 10, 13 and 20 Gy were significantly higher in patients with deteriorating vs stable FEV1 ( p = 0.005, 0.005 and 0.025 respectively) but did not differ for higher doses of radiation (>30, 40, 50 Gy). Fractional volumes of anatomic and perfused lung receiving > 10 Gy best predicted decline in FEV1 (Area under receiver operating characteristic curve (Az = 0.77 and 0.76 respectively); sensitivity/specificity 75%/81 and 80%/71%) for a 32.7% anatomic and 33.5% perfused volume cut-off. Irradiating an anatomic fractional volume of 4.7% to > 50 Gy had a sensitivity/specificity of 83%/89 % for indicating RALI (Az = 0.83).

CONCLUSION

A 10-20 Gy radiation dose to anatomic or perfused lung results in decline in FEV1. A fractional anatomic volume of >5% receiving >50 Gy influences development of RALI.

ADVANCES IN KNOWLEDGE

Extent of low-dose radiation to normal lung influences functional respiratory decline.

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Key Words Collapse

MESH Headings

• Aged
• Aged, 80 and over
• Carcinoma, Non-Small-Cell Lung/diagnostic imaging
• Carcinoma, Non-Small-Cell Lung/radiotherapy
• Female
• Humans
• Lung/diagnostic imaging
• Lung/radiation effects
• Lung Neoplasms/diagnostic imaging
• Lung Neoplasms/radiotherapy
• Male
• Middle Aged
• Predictive Value of Tests
• Radiation Injuries/diagnostic imaging
• Radiotherapy Dosage
• Radiotherapy Planning, Computer-Assisted/methods
• Tomography, Emission-Computed, Single-Photon/methods
• Tomography, X-Ray Computed/methods

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Grants

• 16464 Cancer Research UK
• 19727 Cancer Research UK

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Affiliation(s)

Alex Weller
Alex Dunlop The Joint Department of Physics, The Royal Marsden Hospital NHS Foundation Trust and The Institute of Cancer Research, Sutton, Surrey
Adam Oxer The Royal Marsden Hospital NHS Foundation Trust, Sutton, Surrey
Ranga Gunapala The Royal Marsden Hospital NHS Foundation Trust, Sutton, Surrey
Iain Murray The Joint Department of Physics, The Royal Marsden Hospital NHS Foundation Trust and The Institute of Cancer Research, Sutton, Surrey
Matthew J Gray The Joint Department of Physics, The Royal Marsden Hospital NHS Foundation Trust and The Institute of Cancer Research, Sutton, Surrey
Glenn D Flux The Joint Department of Physics, The Royal Marsden Hospital NHS Foundation Trust and The Institute of Cancer Research, Sutton, Surrey
Nandita M deSouza The CRUK Cancer Imaging Centre, The Institute of Cancer Research and The Royal Marsden Hospital NHS Foundation Trust, Sutton, Surrey
Merina Ahmed The Royal Marsden Hospital NHS Foundation Trust, Sutton, Surrey

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Translation of Quantitative Imaging Biomarkers into Clinical Chest CT

Quantitative imaging has been proposed as the next frontier in radiology as part of an effort to improve patient care through precision medicine. In 2007, the Radiological Society of North America launched the Quantitative Imaging Biomarkers Alliance (QIBA), an initiative aimed at improving the value and practicality of quantitative imaging biomarkers by reducing variability across devices, sites, patients, and time. Chest CT occupies a strategic position in this initiative because it is one of the most frequently used imaging modalities, anatomically encompassing the leading causes of mortality worldwide. To date, QIBA has worked on profiles focused on the accurate, reproducible, and meaningful use of volumetric measurements of lung lesions in chest CT. However, other quantitative methods are on the verge of translation from research grounds into clinical practice, including (a) assessment of parenchymal and airway changes in patients with chronic obstructive pulmonary disease, (b) analysis of perfusion with dual-energy CT biomarkers, and (c) opportunistic screening for coronary atherosclerosis and low bone mass by using chest CT examinations performed for other indications. The rationale for and the key facts related to the application of these quantitative imaging biomarkers in cardiothoracic chest CT are presented. ^©RSNA, 2019 See discussion on this article by Buckler (pp 977-980).

Measurement of relative lung perfusion with electrical impedance and positron emission tomography: an experimental comparative study in pigs

BACKGROUND

Electrical impedance tomography (EIT) with indicator dilution may be clinically useful to measure relative lung perfusion, but there is limited information on the performance of this technique.

METHODS

Thirteen pigs (50-66 kg) were anaesthetised and mechanically ventilated. Sequential changes in ventilation were made: (i) right-lung ventilation with left-lung collapse, (ii) two-lung ventilation with optimised PEEP, (iii) two-lung ventilation with zero PEEP after saline lung lavage, (iv) two-lung ventilation with maximum PEEP (20/25 cm H₂O to achieve peak airway pressure 45 cm H₂O), and (v) two-lung ventilation under unilateral pulmonary artery occlusion. Relative lung perfusion was assessed with EIT and central venous injection of saline 3%, 5%, and 10% (10 ml) during breath holds. Relative perfusion was determined by positron emission tomography (PET) using ⁶⁸Gallium-labelled microspheres. EIT and PET were compared in eight regions of equal ventro-dorsal height (right, left, ventral, mid-ventral, mid-dorsal, and dorsal), and directional changes in regional perfusion were determined.

RESULTS

Differences between methods were relatively small (95% of values differed by less than 8.7%, 8.9%, and 9.5% for saline 10%, 5%, and 3%, respectively). Compared with PET, EIT underestimated relative perfusion in dependent, and overestimated it in non-dependent, regions. EIT and PET detected the same direction of change in relative lung perfusion in 68.9-95.9% of measurements.

CONCLUSIONS

The agreement between EIT and PET for measuring and tracking changes of relative lung perfusion was satisfactory for clinical purposes. Indicator-based EIT may prove useful for measuring pulmonary perfusion at bedside.

"Structure-Function Imaging of Lung Disease Using Ultrashort Echo Time MRI"

RATIONALE AND OBJECTIVES

The purpose of this review is to acquaint the reader with recent advances in ultrashort echo time (UTE) magnetic resonance imaging (MRI) of the lung and its implications for pulmonary MRI when used in conjunction with functional MRI technique.

MATERIALS AND METHODS

We provide an overview of recent technical advances of UTE and explore the advantages of combined structure-function pulmonary imaging in the context of restrictive and obstructive pulmonary diseases such as idiopathic pulmonary fibrosis (IPF) and cystic fibrosis (CF).

RESULTS

UTE MRI clearly shows the lung parenchymal changes due to IPF and CF. The use of UTE MRI, in conjunction with established functional lung MRI in chronic lung diseases, will serve to mitigate the need for computed tomography in children.

CONCLUSION

Current limitations of UTE MRI include long scan times, poor delineation of thin-walled structures (e.g. cysts and reticulation) due to limited spatial resolution, low signal to noise ratio, and imperfect motion compensation. Despite these limitations, UTE MRI can now be considered as an alternative to multidetector computed tomography for the longitudinal follow-up of the morphological changes from lung diseases in neonates, children, and young adults, particularly as a complement to the unique functional capabilities of MRI.

Towards quantitative perfusion MRI of the lung in COPD: The problem of short-term repeatability

Purpose

4D perfusion magnetic resonance imaging (MRI) with intravenous injection of contrast agent allows for a radiation-free assessment of regional lung function. It is therefore a valuable method to monitor response to treatment in patients with chronic obstructive pulmonary disease (COPD). This study was designed to evaluate its potential for monitoring short-term response to hyperoxia in COPD patients.

Materials and methods

19 prospectively enrolled COPD patients (median age 66y) underwent paired dynamic contrast-enhanced 4D perfusion MRI within 35min, first breathing 100% oxygen (injection 1, O₂) and then room air (injection 2, RA), which was repeated on two consecutive days (day 1 and 2). Post-processing software was employed to calculate mean transit time (MTT), pulmonary blood volume (PBV) and pulmonary blood flow (PBF), based on the indicator dilution theory, for the automatically segmented whole lung and 12 regions of equal volume.

Results

Comparing O₂ with RA conditions, PBF and PBV were found to be significantly lower at O₂, consistently on both days (p<10–8). Comparing day 2 to day 1, MTT was shorter by 0.59±0.63 s (p<10–8), PBF was higher by 22±80 ml/min/100ml (p<3·10–4), and PBV tended to be lower by 0.2±7.2 ml/100ml (p = 0.159) at both, RA and O_2, conditions.

Conclusion

The second injection (RA) yielded higher PBF and PBV, which apparently contradicts the established hypothesis that hyperoxia increases lung perfusion. Quantification of 4D perfusion MRI by current software approaches may thus be limited by residual circulating contrast agent in the short-term and even the next day.

Quantitative Dual-Energy Computed Tomography Predicts Regional Perfusion Heterogeneity in a Model of Acute Lung Injury

Objective

The aims of this study were to investigate the ability of contrast-enhanced dual-energy computed tomography (DECT) for assessing regional perfusion in a model of acute lung injury, using dynamic first-pass perfusion CT (DynCT) as the criterion standard and to evaluate if changes in lung perfusion caused by prone ventilation are similarly demonstrated by DECT and DynCT.

Methods

This was an institutional review board–approved study, compliant with guidelines for humane care of laboratory animals. A ventilator-induced lung injury protocol was applied to 6 landrace pigs. Perfused blood volume (PBV) and pulmonary blood flow (PBF) were respectively quantified by DECT and DynCT, in supine and prone positions. The lungs were segmented in equally sized regions of interest, namely, dorsal, middle, and ventral. Perfused blood volume and PBF values were normalized by lung density. Regional air fraction (AF) was assessed by triple-material decomposition DECT. Per-animal correlation between PBV and PBF was assessed with Pearson R. Regional differences in PBV, PBF, and AF were evaluated with 1-way analysis of variance and post hoc linear trend analysis (α = 5%).

Results

Mean correlation coefficient between PBV and PBF was 0.70 (range, 0.55–0.98). Higher PBV and PBF values were observed in dorsal versus ventral regions. Dorsal-to-ventral linear trend slopes were −10.24 mL/100 g per zone for PBV (P < 0.001) and −223.0 mL/100 g per minute per zone for PBF (P < 0.001). Prone ventilation also revealed higher PBV and PBF in dorsal versus ventral regions. Dorsal-to-ventral linear trend slopes were −16.16 mL/100 g per zone for PBV (P < 0.001) and −108.2 mL/100 g per minute per zone for PBF (P < 0.001). By contrast, AF was lower in dorsal versus ventral regions in supine position, with dorsal-to-ventral linear trend slope of +5.77%/zone (P < 0.05). Prone ventilation was associated with homogenization of AF distribution among different regions (P = 0.74).

Conclusions

Dual-energy computed tomography PBV is correlated with DynCT-PBF in a model of acute lung injury, and able to demonstrate regional differences in pulmonary perfusion. Perfusion was higher in the dorsal regions, irrespectively to decubitus, with more homogeneous lung aeration in prone position.