Diffusion Kurtosis Imaging of Acute Infarction: Comparison with Routine Diffusion and Follow-up MR Imaging

High b-Value and Ultra-High b-Value Diffusion Weighted MRI in Stroke

PURPOSE

To explore the application value of high-b-value and ultra-high b-value DWI in noninvasive evaluation of ischemic infarctions.

STUDY TYPE

Prospective.

SUBJECTS

Sixty-four patients with clinically diagnosed ischemic lesions based on symptoms and DWI.

FIELD STRENGTH/SEQUENCE

3.0 T/T2-weighted fast spin-echo, fluid-attenuated inversion recovery, pre-contrast T1-weighted magnetization prepared rapid gradient echo sequence, multi-b-value trace DWI and q-space sampling sequences.

ASSESSMENT

Lesions were segmented on standard b-value DWI (SB-DWI, 1000 s/mm2), high b-value DWI (HB-DWI, 4000 s/mm2) and ultra-high b-value DWI (UB-DWI, 10,000 s/mm2), and cumulative segmented areas were the final abnormality volumes. Normal white matter (WM) areas were obtained after binarization of segmented brain. In 47 patients, fractional anisotropy (FA) and apparent diffusion coefficients (ADCs) at b values of 1000, 4000, and 10,000 s/mm2 were extracted from symmetrical WM masks and lesion masks of contralateral WM (CWM) and lesion-side WM (LWM).

STATISTICAL TESTS

Wilcoxon matched-pairs signed-rank test and Pearson correlation analysis. Two-tailed P-values <0.05 were considered statistically significant.

RESULTS

Various signals of HB-/UB-DWI (hypo-, iso- or hyper-intensity) were observed in strokes compared with SB-DWI, and some areas with iso-intensity of SB-DWI manifested with hyper-intensity on HB-/UB-DWI. Abnormality volumes from SB-DWI were significantly smaller than those from HB-DWI and UB-DWI (10.32 ± 16.45 cm3, vs. 12.25 ± 19.71 cm3 and 11.83 ± 19.41 cm3), while no significant difference exist in volume between HB-DWI and UB-DWI (P = 0.32). In CWM, FA significantly correlated with ADC4000 and ADC10,000 (maximum r = -0.51 and -0.64), but did not significantly correlate with ADC1000 (maximum r = -0.20, P = 0.17). ADC1000 or ADC4000 of LWM not significant correlated with FA of CWM (maximum r = -0.28, P = 0.06), while ADC10,000 of LWM significantly correlated with FA of CWM (maximum r = -0.46).

DATA CONCLUSION

HB- and UB-DWI have potential to be supplementary tools for the noninvasive evaluation of stroke lesions in clinics.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Application of Diffusional Kurtosis Imaging on Normal-Appearing White Matter in Cerebral Small Vessel Disease

BACKGROUND

This study aimed to investigate the diagnostic potential of diffusional kurtosis imaging (DKI) parameters in detecting pathological alterations in the normal-appearing white matter (NAWM) associated with cerebral small vessel disease (CSVD).

METHODS

A total of 56 patients diagnosed with CSVD were enrolled, all exhibiting confirmed lacunar infarction in the corticospinal tract (CST) as verified by conventional magnetic resonance imaging. A control group of 24 healthy individuals who exhibited no discernible abnormalities on conventional magnetic resonance imaging (MRI) scans was also included. The following DKI parameters were recorded, including mean kurtosis (MK), axial kurtosis (Ka), and radial kurtosis (Kr). Regions of interest were placed at representative levels of the CST on the affected side, encompassing the pons, anterior part of the posterior limb of the internal capsule (PLIC), corona radiata, and subcortex.

RESULTS

Variations in MK, Ka, and Kr values in the pons, anterior part of the PLIC, corona radiata, and subcortex of the control group were observed. Notably, the MK and Kr values of the normal-appearing pons in CSVD patients were significantly elevated compared with the control group. The MK, Ka value of the normal-appearing anterior part of the PLIC was significantly higher in the CSVD group than in the control group. The Kr value of the normal-appearing corona radiata exhibited a significant elevation in CSVD patients compared with the control group. Lastly, patients with CSVD displayed lower Ka values and higher Kr values in the normal-appearing subcortex compared with the control group.

CONCLUSIONS

DKI is an effective tool for assessing NAWM in patients with CSVD. These findings potentially offer novel insights into the prognosis of CSVD and serve as a foundational platform for future DKI studies on NAWM in other diffuse brain lesions.

Diffusional kurtosis imaging in differentiating nonarteritic anterior ischemic optic neuropathy from acute optic neuritis

PURPOSE

We aimed to determine the feasibility of using DKI to characterize pathological changes in nonarteritic anterior ischemic optic neuropathy (NAION) and to differentiate it from acute optic neuritis (ON).

METHODS

Orbital DKI was performed with a 3.0 T scanner on 75 patients (51 with NAION and 24 with acute ON) and 15 healthy controls. NAION patients were further divided into early and late groups. The mean kurtosis (MK), axial kurtosis (AK), radial kurtosis (RK), mean diffusivity (MD), fractional anisotropy (FA), radial diffusivity (RD), and axial diffusivity (AD) were calculated to perform quantitative analyses among groups; and receiver operating characteristic curve analyses were also performed to determine their effectiveness of differential diagnosis. In addition, correlation coefficients were calculated to explore the correlations of the DKI-derived data with duration of disease.

RESULTS

The MK, RK, and AK in the affected nerves with NAION were significantly higher than those in the controls, while the trend of FA, RD, and AD was a decline; in acute ON patients, except for RD, which increased, all DKI-derived kurtosis and diffusion parameters were significantly lower than controls (all P < 0.008). Only AK and MD had statistical differences between the early and late groups. Except for MD (early group) and FA, all other DKI-derived parameters were higher in NAION than in acute ON; and parameters in the early group showed better diagnostic efficacy in differentiating NAION from acute ON. Correlation analysis showed that time was negatively correlated with MK, RK, AK, and FA and positively correlated with MD, RD, and AD (all P < 0.05).

CONCLUSION

DKI is helpful for assessing the specific pathologic abnormalities resulting from ischemia in NAION by comparison with acute ON. Early DKI should be performed to aid in the diagnosis and evaluation of NAION.

MR imaging and outcome in neonatal HIBD models are correlated with sex: the value of diffusion tensor MR imaging and diffusion kurtosis MR imaging

Objective

Hypoxic-ischemic encephalopathy can lead to lifelong morbidity and premature death in full-term newborns. Here, we aimed to determine the efficacy of diffusion kurtosis (DK) [mean kurtosis (MK)] and diffusion tensor (DT) [fractional anisotropy (FA), mean diffusion (MD), axial diffusion (AD), and radial diffusion (RD)] parameters for the early diagnosis of early brain histopathological changes and the prediction of neurodegenerative events in a full-term neonatal hypoxic-ischemic brain injury (HIBD) rat model.

Methods

The HIBD model was generated in postnatal day 7 Sprague-Dawley rats to assess the changes in DK and DT parameters in 10 specific brain structural regions involving the gray matter, white matter, and limbic system during acute (12 h) and subacute (3 d and 5 d) phases after hypoxic ischemia (HI), which were validated against histology. Sensory and cognitive parameters were assessed by the open field, novel object recognition, elevated plus maze, and CatWalk tests.

Results

Repeated-measures ANOVA revealed that specific brain structures showed similar trends to the lesion, and the temporal pattern of MK was substantially more varied than DT parameters, particularly in the deep gray matter. The change rate of MK in the acute phase (12 h) was significantly higher than that of DT parameters. We noted a delayed pseudo-normalization for MK. Additionally, MD, AD, and RD showed more pronounced differences between males and females after HI compared to MK, which was confirmed in behavioral tests. HI females exhibited anxiolytic hyperactivity-like baseline behavior, while the memory ability of HI males was affected in the novel object recognition test. CatWalk assessments revealed chronic deficits in limb gait parameters, particularly the left front paw and right hind paw, as well as poorer performance in HI males than HI females.

Conclusions

Our results suggested that DK and DT parameters were complementary in the immature brain and provided great value in assessing early tissue microstructural changes and predicting long-term neurobehavioral deficits, highlighting their ability to detect both acute and long-term changes. Thus, the various diffusion coefficient parameters estimated by the DKI model are powerful tools for early HIBD diagnosis and prognosis assessment, thus providing an experimental and theoretical basis for clinical treatment.

Diffusion kurtosis imaging and diffusion weighted imaging comparison in diagnosis of early hypoxic-ischemic brain edema

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) refers to cerebral hypoxic-ischemic injury caused by asphyxia during perinatal period, which is one of the important causes of neonatal death and sequelae. Early and accurate diagnosis of HIE is of great significance for the prognostic evaluation of patients. The purpose of this study is to explore the efficacy of diffusion-kurtosis imaging (DKI) and diffusion-weighted imaging (DWI) in the diagnosis of early HIE.

METHODS

Twenty Yorkshire newborn piglets (3-5 days) were randomly divided into control group and experimental group. DWI and DKI scanning were performed at timepoints of 3, 6, 9, 12, 16, and 24 h after hypoxic-ischemic exposure. At each timepoint, the parameter values obtained by each group scan were measured, and the lesion area of the apparent diffusion coefficient (ADC) map and mean diffusion coefficient (MDC) map were measured. (For better interpretation of this study, we replaced the description of MD with MDC). Then, we completely removed the brain for pathological examination, and observed the state of cells and mitochondria in the ADC/MDC matching area (the actual area of the lesion), and the mismatch area (the area around the lesion).

RESULTS

In the experimental group, the ADC and MDC values decreased with time, but the MDC decreased more significantly and the change rate was higher. Both MDC and ADC values changed rapidly from 3 to 12 h and slowly from 12 to 24 h. The MDC and ADC images showed obvious lesions at 3 h for the first time. At this time, the area of ADC lesions was larger than that of MDC. As the lesions developed, the area of ADC maps was always larger than that of the MDC maps within 24 h. By observing the microstructure of the tissues by light microscopy, we found that the ADC and MDC matching area in the experimental group showed swelling of neurons, infiltration of inflammatory cells, and local necrotic lesions. Consistent with the observation under light microscope, pathological changes were observed in the matching ADC and MDC regions under electron microscopy as well, including collapse of mitochondrial membrane, fracture of partial mitochondrial ridge, and emergence of autophagosomes. In the mismatching region, the above pathological changes were not observed in the corresponding region of the ADC map.

CONCLUSIONS

DKI's characteristic parameter MDC is better than ADC (parameter of DWI) to reflect the real area of the lesion. Therefore, DKI is superior to DWI in diagnosing early HIE.

Tissue perfusion of the kurtosis/diffusion mismatch differs from the central core and peripheral regions in acute cerebral infarction patients

BACKGROUND

Despite its wide adoption in stroke imaging, the diffusion-weighted imaging (DWI) lesion is heterogeneous. The emerging diffusion kurtosis imaging (DKI) has been postulated to resolve the graded DWI lesion.

PURPOSE

To determine the perfusion characteristics of the central infarction core, kurtosis/diffusion mismatch, and peripheral regions.

MATERIAL AND METHODS

Patients with acute ischemic stroke underwent DWI, DKI, and perfusion-weighted imaging (PWI) scans. The patients were divided into mean kurtosis (MK)/mean diffusivity (MD) match and mismatch groups. Perfusion parameters were measured in the MK/MD lesion and peripheral areas in the MK/MD match group. We also analyzed perfusion status in the MK/MD lesion mismatch area for the mismatch group.

RESULTS

A total of 40 eligible patients (24 MK/MD match and 16 MK/MD mismatch) were enrolled in the final data analysis. The MTT and TTP progressively decreased, while the cerebral blood flow (CBF) and cerebral blood volume (CBV) increased from the central to peripheral areas. In addition, CBF in the MK/MD mismatch region was significantly higher than that in the central region (P < 0.05), but similar to the peripheral region. Furthermore, CBV in the MK/MD mismatch region did not differ significantly from that of the central region, but both were significantly lower than that of the peripheral area (P < 0.05).

CONCLUSION

The MK/MD mismatch region had blood flow similar to the peripheral region but with a reduced blood volume, indicating that it was less ischemic from the infarction core, albeit insufficient collateral circulation.

Preliminary research of the classification of the brain acute stroke lesions by the Diffusion Kurtosis Imaging (DKI) and Diffusion Weighted Imaging (DWI) parameters

BACKGROUND

Diffusion-weighted magnetic resonance imaging (DWI) is a mature scanning technique. With high sensitivity in detecting cerebral infractions, it has become an essential part of the clinical evaluation of acute stroke. However, with the update in medical ideals and treatment, clinicians are now focusing on distinguishing between reversible and irreversible brain tissue damage rather than detecting ischaemic lesions alone.

OBJECTIVE

We supposed that Diffusion Kurtosis Imaging (DKI) could classify heterogeneous DWI lesions, deepening the understanding of tissue injury. We systematically studied the different parameters of DKI in acute stroke patients in the literature.

METHODS

We collected 41 patients (26 male, 15 female), including different infarctions with acute cerebral infarction in different brain regions. Of all patients, 20 were single-infarction, while others were multi-infarctions. In this paper, we categorized acute cerebral infarction lesions into two types according to the parametric characteristics of both DKI and DWI. Type I means the DKI and DWI were matched, and Type II means the DKI and DWI were mismatched. Based on each parametric map, the region of interest (ROI) is outlined in each most severe lesion area (as large as possible in the center of the lesion). In the control group, ROIs of the same size are located in the corresponding regions of the contralateral hemisphere.

RESULTS

In both Type I and Type II, all parameters conform to a normal distribution. An independent sample T-test was used to compare the differences between each group. In Type I, we found the FA, MD, Da, Dr, MK and Ka values were statistically different (P< 0.05), while in Type II, only the MK and Ka values were statistically different (P< 0.05).

CONCLUSION

DKI, compared to DWI, can provide more imaging information about intracranial ischemic infarction, which can deepen the understanding of the mechanism of ischemic tissue damage. Our classification of the brain acute stroke lesions by DKI parameters and DWI may help us rediscover the real core of infraction.

Neuroimaging in Pediatric Stroke

Pediatric stroke is unfortunately not a rare condition. It is associated with severe disability and mortality because of the complexity of potential clinical manifestations, and the resulting delay in seeking care and in diagnosis. Neuroimaging plays an important role in the multidisciplinary response for pediatric stroke patients. The rapid development of adult endovascular thrombectomy has created a new momentum in health professionals caring for pediatric stroke patients. Neuroimaging is critical to make decisions of identifying appropriate candidates for thrombectomy. This review article will review current neuroimaging techniques, imaging work-up strategies and special considerations in pediatric stroke. For resources limited areas, recommendation of substitute imaging approaches will be provided. Finally, promising new techniques and hypothesis-driven research protocols will be discussed.

Altered brain functional activity and connectivity in bone metastasis pain of lung cancer patients: A preliminary resting-state fMRI study

Bone metastasis pain (BMP) is one of the most prevalent symptoms among cancer survivors. The present study aims to explore the brain functional activity and connectivity patterns in BMP of lung cancer patients preliminarily. Thirty BMP patients and 33 healthy controls (HCs) matched for age and sex were recruited from inpatients and communities, respectively. All participants underwent fMRI data acquisition and pain assessment. Low-frequency fluctuations (ALFF) and regional homogeneity (ReHo) were applied to evaluate brain functional activity. Then, functional connectivity (FC) was calculated for the ALFF- and ReHo-identified seed brain regions. A two-sample t-test or Manny–Whitney U-test was applied to compare demographic and neuropsychological data as well as the neuroimaging indices according to the data distribution. A correlation analysis was conducted to explore the potential relationships between neuroimaging indices and pain intensity. Receiver operating characteristic curve analysis was applied to assess the classification performance of neuroimaging indices in discriminating individual subjects between the BMP patients and HCs. No significant intergroup differences in demographic and neuropsychological data were noted. BMP patients showed reduced ALFF and ReHo largely in the prefrontal cortex and increased ReHo in the bilateral thalamus and left fusiform gyrus. The lower FC was found within the prefrontal cortex. No significant correlation between the neuroimaging indices and pain intensity was observed. The neuroimaging indices showed satisfactory classification performance between the BMP patients and HCs, and the combined ALFF and ReHo showed a better accuracy rate (93.7%) than individual indices. In conclusion, altered brain functional activity and connectivity in the prefrontal cortex, fusiform gyrus, and thalamus may be associated with the neuropathology of BMP and may represent a potential biomarker for classifying BMP patients and healthy controls.

Oxygen Challenge Imaging Reveals Differences in Metabolic Activity Between Kurtosis Lesion and Diffusion/Kurtosis Lesion Mismatch in a Rodent Model of Acute Stroke

OBJECTIVE

Accurate identification of potentially salvageable tissues is critical for improving acute stroke treatment. A previous study showed that the kurtosis lesion exhibited insignificant response after prompt reperfusion treatment, while the diffusion/kurtosis lesion mismatch could recover after reperfusion. We hypothesized that these 2 regions are in different metabolic states.

MATERIALS AND METHODS

Transient oxygen challenge (OC) is a procedure that uses oxygen as a metabolic bio-tracer and has been performed to explore metabolic activity in tissues. We combined OC with multiparameter magnetic resonance imaging (including diffusion kurtosis imaging and T2* mapping sequences) to study metabolic activity in the ischemic brain of Sprague Dawley rats.

RESULTS

Oxygen challenge image analysis revealed changes in T2* values, most significantly in the mean diffusivity (MD)/mean kurtosis (MK) lesion mismatch (22.3 ± 1.6%) and least significantly in the MK lesions (6.6 ± 0.6%). The MD images acquired within 138 ± 9 minutes after ischemia showed a larger ischemic lesion (45.5 ± 3.0% of the total area) than the MK images (33.2 ± 4.2% of the total area). The change rate of the MK value (53.0 ± 4.4%) was higher than that of the MD value (37.5 ± 3.2%).

CONCLUSIONS

The present study shows that MK lesion and MD/MK lesion mismatch exhibited different metabolic activity states. The MK lesion presented metabolic-related values close to the ischemic core, while at least part of the MD/MK mismatch area was comparable with ischemic penumbra metabolic activity. These findings are important to support image-guided individualized stroke therapies.

Brain Micro-Structural and Functional Alterations for Cognitive Function Prediction in the End-Stage Renal Disease Patients Undergoing Maintenance Hemodialysis

RATIONALE AND OBJECTIVES

The goal of this study was to investigate the relationship between altered brain micro-structure and function, and cognitive function in patients with end-stage renal disease (ESRD) undergoing maintenance hemodialysis. Specially, diffusion kurtosis imaging (DKI), the resting-state functional connectivity (FC) algorithm, and the least squares support vector regression machine (LSSVRM) were utilized to conduct our study.

MATERIALS AND METHODS

A total of 50 patients and 36 matched healthy controls were prospectively enrolled in our study. All subjects completed the Montreal cognitive assessment scale (MoCA) test. DKI and resting-state functional magnetic resonance imaging were measured. Relationship between DKI parameters, FC, and MoCA scores was evaluated. LSSVRM combined with the whale optimization algorithm (WOA) was used to predict cognitive function scores.

RESULTS

In ESRD patients, altered DKI metrics were identified in 12 brain regions. Furthermore, we observed changes in FC values based on regions of interest (ROIs) in nine brain regions, involved in default mode network (DMN), frontoparietal network (FPN), and the limbic system. Significant correlations among DKI values, FC values, and MoCA scores were found. To some extent, altered FC showed significant correlations with changed DKI parameters. Furthermore, optimized prediction models were applied to more accurately predict the cognitive function associated with ESRD patients.

CONCLUSION

Micro-structural and functional brain changes were found in ESRD patients, which may account for the onset of cognitive impairment in affected patients. These quantitative parameters combined with our optimized prediction model may be helpful to establish more reliable imaging markers to detect and monitor cognitive impairment associated with ESRD.

Fast diffusion kurtosis imaging in acute ischemic stroke shows mean kurtosis-diffusivity mismatch

BACKGROUND AND PURPOSE

Diffusion kurtosis imaging (DKI) is an advanced technique more specific to irreversible ischemic injury than conventional diffusion-weighted imaging (DWI). However, its clinical translation has been limited by a long acquisition time and complex postprocessing.

METHODS

A fast DKI sequence (3 minutes) was implemented on a 3T MRI (Siemens Trio) and piloted as part of an inpatient brain MRI protocol. Mean kurtosis (MK) and mean diffusivity (MD) maps were postprocessed automatically at the scanner console and sent to the Picture Archiving and Communications System. We retrospectively reviewed consecutive patients in a 5-month period with acute ischemic stroke due to large vessel occlusion. MK and MD of the ischemic infarcts and contralateral normal brain were measured, and lesion volumes were measured in large infarcts using semiautomated segmentation.

RESULTS

Twenty-two patients were included in the study (median age 66). The median time from last known well to MRI was 37 hours. MD and MK maps were successfully processed and demonstrated acute infarction in concordance with DWI in all cases. Infarcted regions had higher MK and lower MD compared to contralateral normal-appearing regions. MK lesion volume was significantly smaller than MD volume.

CONCLUSION

In this pilot study, we demonstrated the feasibility of incorporating a fast DKI sequence into a clinical MRI protocol. Acute infarcts were depicted on kurtosis maps, and MK lesion volumes were smaller than MD, in accordance with prior works. Future studies are needed to determine the role of DKI in acute stroke treatment selection and prognostication.

Reduced Severity of Tissue Injury Within the Infarct May Partially Mediate the Benefit of Reperfusion in Ischemic Stroke

BACKGROUND

Emerging data suggest tissue within the infarct lesion is not homogenously damaged following ischemic stroke but has a gradient of injury. Using blood-brain-barrier (BBB) disruption as a marker of tissue injury, we tested whether therapeutic reperfusion improves clinical outcome by reducing the severity of tissue injury within the infarct in patients with ischemic stroke.

METHODS

In a pooled analysis of patients treated for anterior circulation large vessel occlusion in the EXTEND-IA TNK (Tenecteplase Versus Alteplase Before Endovascular Therapy for Ischemic Stroke) and EXTEND-IA part-2 (Determining the Optimal Dose of Tenecteplase Before Endovascular Therapy for Ischaemic Stroke) trials, post-treatment BBB permeability at 24 hours was calculated based on the extent of T1-brightening by extravascular gadolinium on T2* perfusion-weighted imaging and measured within the diffusion-weighted-imaging lesion. First, to determine the clinical significance of BBB disruption as a marker of severity of tissue injury, we examined the association between post-treatment BBB permeability and functional outcome. Second, we performed an exploratory (reperfusion, BBB permeability, functional outcome) mediation analysis to estimate the proportion of the reperfusion-outcome relationship that is mediated by change in BBB permeability.

RESULTS

In the 238 patients analyzed, an increased BBB permeability measured within the infarct at 24 hours was associated with a reduced likelihood of favorable outcome (90-day modified Rankin Scale score of ≤2) after adjusting for age, baseline National Institutes of Health Stroke Scale, premorbid modified Rankin Scale, infarct topography, laterality, thrombolytic agent, sex, parenchymal hematoma, and follow-up infarct volume (adjusted odds ratio, 0.86 [95% CI, 0.75-0.98], P=0.023). Mediation analysis suggested reducing the severity of tissue injury (as estimated by BBB permeability) accounts for 18.2% of the association between reperfusion and favorable outcome, as indicated by a reduction in the regression coefficient of reperfusion after addition of BBB permeability as a covariate.

CONCLUSIONS

In patients with ischemic stroke, reduced severity of tissue injury within the infarct, as determined by assessing the integrity of the BBB, is independently associated with improved functional outcome. In addition to reducing diffusion-weighted imaging-defined infarct volume, reperfusion may also improve clinical outcome by reducing tissue injury severity within the infarct.

Consistent depiction of the acidic ischemic lesion with APT MRI-Dual RF power evaluation of pH-sensitive image in acute stroke

PURPOSE

Amide proton transfer-weighted (APTw) MRI provides a non-invasive pH-sensitive image, complementing perfusion and diffusion imaging for refined stratification of ischemic tissue. Although the commonly used magnetization transfer (MT) asymmetry (MTR_asym ) calculation reasonably corrects the direct RF saturation effect, it is susceptible to the concomitant semisolid macromolecular MT contribution. Therefore, this study aimed to compare the performance of MTR_asym and magnetization transfer and relaxation-normalized APT (MRAPT) analyses under 2 representative experimental conditions.

METHODS

Multiparametric MRI scans were performed in a rodent model of acute stroke, including relaxation, diffusion, and Z spectral images under 2 representative RF levels of 0.75 and 1.5 µT. Both MTR_asym and MRAPT values in the ischemic diffusion lesion and the contralateral normal areas were compared using correlation and Bland-Altman tests. In addition, the acidic lesion volumes were compared.

RESULTS

MRAPT measurements from the diffusion lesion under the 2 conditions were highly correlated (R² = 0.97) versus MTR_asym measures (R² = 0.58). The pH lesion sizes determined from MRAPT analysis were in good agreement (178 ± 43 mm³ vs. 186 ± 55 mm³ for B₁ of 0.75 and 1.5 µT, respectively).

CONCLUSIONS

The study demonstrated that MRAPT analysis could be generalized to moderately different RF amplitudes, providing a more consistent depiction of acidic lesions than the MTR_asym analysis.

Accelerating joint relaxation-diffusion MRI by integrating time division multiplexing and simultaneous multi-slice (TDM-SMS) strategies

PURPOSE

To accelerate the acquisition of relaxation-diffusion imaging by integrating time-division multiplexing (TDM) with simultaneous multi-slice (SMS) for EPI and evaluate imaging quality and diffusion measures.

METHODS

The time-division multiplexing (TDM) technique and SMS method were integrated to achieve a high slice-acceleration (e.g., 6×) factor for acquiring relaxation-diffusion MRI. Two variants of the sequence, referred to as TDM3e-SMS and TDM2s-SMS, were developed to simultaneously acquire slice groups with three distinct TEs and two slice groups with the same TE, respectively. Both sequences were evaluated on a 3T scanner with in vivo human brains and compared with standard single-band (SB) -EPI and SMS-EPI using diffusion measures and tractography results.

RESULTS

Experimental results showed that the TDM3e-SMS sequence with total slice acceleration of 6 (multiplexing factor (MP) = 3 × multi-band factor (MB) = 2) provided similar image intensity and microstructure measures compared to standard SMS-EPI with MB = 2, and yielded less bias in intensity compared to standard SMS-EPI with MB = 4. The three sequences showed a similar positive correlation between TE and mean kurtosis (MK) and a negative correlation between TE and mean diffusivity (MD) in white matter. Multi-fiber tractography also shows consistency of results in TE-dependent measures between different sequences. The TDM2s-SMS sequence (MP = 2, MB = 2) also provided imaging measures similar to standard SMS-EPI sequences (MB = 2) for single-TE diffusion imaging.

CONCLUSIONS

The TDM-SMS sequence can provide additional 2× to 3× acceleration to SMS without degrading imaging quality. With the significant reduction in scan time, TDM-SMS makes joint relaxation-diffusion MRI a feasible technique in neuroimaging research to investigate new markers of brain disorders.

Jointly estimating parametric maps of multiple diffusion models from undersampled q-space data: A comparison of three deep learning approaches

PURPOSE

While advanced diffusion techniques have been found valuable in many studies, their clinical availability has been hampered partly due to their long scan times. Moreover, each diffusion technique can only extract a few relevant microstructural features. Using multiple diffusion methods may help to better understand the brain microstructure, which requires multiple expensive model fittings. In this work, we compare deep learning (DL) approaches to jointly estimate parametric maps of multiple diffusion representations/models from highly undersampled q-space data.

METHODS

We implement three DL approaches to jointly estimate parametric maps of diffusion tensor imaging (DTI), diffusion kurtosis imaging (DKI), neurite orientation dispersion and density imaging (NODDI), and multi-compartment spherical mean technique (SMT). A per-voxel q-space deep learning (1D-qDL), a per-slice convolutional neural network (2D-CNN), and a 3D-patch-based microstructure estimation with sparse coding using a separable dictionary (MESC-SD) network are considered.

RESULTS

The accuracy of estimated diffusion maps depends on the q-space undersampling, the selected network architecture, and the region and the parameter of interest. The smallest errors are observed for the MESC-SD network architecture (less than 10 % normalized RMSE in most brain regions).

CONCLUSION

Our experiments show that DL methods are very efficient tools to simultaneously estimate several diffusion maps from undersampled q-space data. These methods can significantly reduce both the scan ( ∼ 6-fold) and processing times ( ∼ 25-fold) for estimating advanced parametric diffusion maps while achieving a reasonable accuracy.

The value of diffusion weighted imaging in predicting the clinical progression of perforator artery cerebral infarction

•

Diffusion weighted imaging helps the diagnosticist assess the status of the patient with cerebral infarction;

•

Apparent diffusion coefficient is sensitive to cellular edema of early cerebral infarction;

•

Treatment of cerebral infarction is more individualized;

Objectives

To investigate the value of diffusion weighted imaging (DWI) in predicting the clinical progression of perforator artery cerebral infarction.

Methods

The magnetic resonance imaging (MRI) data of patients with perforator artery cerebral infarction hospitalized in our hospital from October 2015 to February 2022 were analyzed retrospectively. Then we compared the differences of apparent diffusion coefficient (ADC) value, maximal size, location of cerebral infarction, clinical data and treatment plan between the two groups.

Results

A total of 81 patients with perforating artery cerebral infarction were included, with 33 patients in the progressive cerebral infarction (PCI) group and 48 patients in the non-progressive cerebral infarction (NPCI) group. The ADC value in the progressive group was lower than that in the non-progressive group (P < 0.001), and ADC value was an independent factor influencing the clinical progression (OR = 0.974, 95 %CI = 0.960–0.989, P = 0.001); The average area of cerebral infarction in the progressive group was larger than that in the non-progressive group (P = 0.004). There was no difference between the two groups (P > 0.05) in terms of clinical data and treatment plan.

Conclusions

The ADC value and maximal size of infarction were correlated with the clinical Progression. ADC value was an independent factor influencing the clinical progression of perforating artery cerebral infarction, which could be used for the prediction of clinical progress and provide guidance for the development of individualized treatment.

Ultra-high b value DWI in distinguishing fresh gray matter ischemic lesions from white matter ones: a comparative study with routine and high b value DWI

Background

Fresh ischemic lesions (FILs) can occur in both the brain's gray matter (GM) and white matter (WM), with each location signifying a different prognosis for patients. This study aims to investigate the application of ultra-high b value diffusion-weighted imaging (DWI) in distinguishing FILs in these two areas via a comparative study with routine and high b value DWI.

Methods

Multiple b value DWI (b=0, 500, 1,000, 2,000, 4,000, 6,000, 8,000, 10,000 s/mm²) was performed on 47 patients with suspected acute ischemic stroke (AIS). Apparent diffusion coefficient (ADC) maps, including ADC₅₀₀, ADC_1,000, ADC_2,000, ADC_4,000, ADC_6,000, ADC_8,000, and ADC_10,000, were calculated, and the mean ADC value of the FILs in the GM and WM on each map was obtained by referring to the structural magnetic resonance imaging (MRI). ADC value differences of the FILs in the GM and WM were compared using Mann-Whitney U tests, and receiver operating characteristic (ROC) curves evaluated the diagnostic efficiency of each ADC value in distinguishing FILs in the two areas.

Results

In the enrolled 34 patients, 145 FILs were identified, of which 42 involved the GM, 87 the WM, and 16 both the GM and WM. A total of 161 regions were delineated, 58 in the GM and 103 in the WM. The values of FILs in the WM on ADC_2,000, ADC_4,000, ADC_6,000, ADC_8,000, and ADC_10,000 maps were significantly lower than those in the GM (P=0.007, P<0.001, P<0.001, P<0.001 and P<0.001, respectively), while no significant differences were found on ADC₅₀₀ and ADC_1,000 maps (P=0.427 and P=0.225, respectively). ROC curves demonstrated that the area under the curve (AUC) paralleled the increasing b value, ascending from ADC₅₀₀ to ADC_10,000 (0.538, 0.558, 0.629, 0.766, 0.827, 0.859, 0.872, in that order).

Conclusions

Ultra-high b value DWI is extremely sensitive to the slight diffusion difference between FILs in the GM and the WM. Its sensitivity parallels the increasing b value, indicating its clinical advantage in identifying the microstructure of FILs.

Advanced Diffusion of the Pediatric Brain and Spine

This article discusses new diffusion-weighted imaging (DWI) sequences, diffusion tensor imaging (DTI), and fiber tractography (FT), as well as more advanced diffusion imaging in pediatric brain and spine. Underlying disorder and pathophysiology causing diffusion abnormalities are discussed. Multishot echo planar imaging (EPI) DWI and non-EPI DWI provide higher spatial resolution with less susceptibility artifact and distortion, which are replacing conventional single-shot EPI DWI. DTI and FT have established clinical significance in pediatric brain and spine. This article discusses advanced diffusion imaging, including diffusion kurtosis imaging, neurite orientation dispersion and density imaging, diffusion spectrum imaging, intravoxel incoherent motion, and oscillating-gradient spin-echo.

Refined Ischemic Penumbra Imaging with Tissue pH and Diffusion Kurtosis Magnetic Resonance Imaging

Imaging has played a vital role in our mechanistic understanding of acute ischemia and the management of acute stroke patients. The most recent DAWN and DEFUSE-3 trials showed that endovascular therapy could be extended to a selected group of late-presenting stroke patients with the aid of imaging. Although perfusion and diffusion MRI have been commonly used in stroke imaging, the approximation of their mismatch as the penumbra is oversimplified, particularly in the era of endovascular therapy. Briefly, the hypoperfusion lesion includes the benign oligemia that does not proceed to infarction. Also, with prompt and effective reperfusion therapy, a portion of the diffusion lesion is potentially reversible. Therefore, advanced imaging that provides improved ischemic tissue characterization may enable new experimental stroke therapeutics and eventually further individualize stroke treatment upon translation to the clinical setting. Specifically, pH imaging captures tissue of altered metabolic state that demarcates the hypoperfused lesion into ischemic penumbra and benign oligemia, which remains promising to define the ischemic penumbra's outer boundary. On the other hand, diffusion kurtosis imaging (DKI) differentiates the most severely damaged and irreversibly injured diffusion lesion from the portion of diffusion lesion that is potentially reversible, refining the inner boundary of the penumbra. Altogether, the development of advanced imaging has the potential to not only transform the experimental stroke research but also aid clinical translation and patient management.

Metabolic Magnetic Resonance Imaging in Neuroimaging: Magnetic Resonance Spectroscopy, Sodium Magnetic Resonance Imaging and Chemical Exchange Saturation Transfer

Magnetic resonance (MR) is a powerful and versatile technique that offers much more beyond conventional anatomic imaging and has the potential of probing in vivo metabolism. Although MR spectroscopy (MRS) predates clinical MR imaging (MRI), its clinical application has been limited by technical and practical challenges. Other MR techniques actively being developed for in vivo metabolic imaging include sodium concentration imaging and chemical exchange saturation transfer. This article will review some of the practical aspects of MRS in neuroimaging, introduce sodium MRI and chemical exchange saturation transfer MRI, and highlight some of their emerging clinical applications.

Accelerated diffusion and relaxation-diffusion MRI using time-division multiplexing EPI

PURPOSE

To develop a time-division multiplexing echo-planar imaging (TDM-EPI) sequence for approximately two- to threefold acceleration when acquiring joint relaxation-diffusion MRI data with multiple TEs.

METHODS

The proposed TDM-EPI sequence interleaves excitation and data collection for up to 3 separate slices at different TEs and uses echo-shifting gradients to disentangle the overlapping echo signals during the readout period. By properly arranging the sequence event blocks for each slice and adjusting the echo-shifting gradients, diffusion-weighted images from separate slices can be acquired. Therefore, we present 2 variants of the sequence. A single-TE TDM-EPI is presented to demonstrate the concept. Next, a multi-TE TDM-EPI is presented to highlight the advantages of the TDM approach for relaxation-diffusion imaging. These sequences were evaluated on a 3 Tesla scanner with a water phantom and in vivo human brain data.

RESULTS

The single-TE TDM-EPI sequence can simultaneously acquire 2 slices with a maximum b value of 3000 s/mm² and 2.5 mm isotropic resolution using interleaved readout windows with TE ≈ 78 ms. With the same b value and resolution, the multi-TE TDM-EPI sequence can simultaneously acquire 2 or 3 separate slices using interleaved readout sections with shortest TE ≈ 70 ms and ΔTE ≈ 30 ms. Phantom and in vivo experiments have shown that the proposed TDM-EPI sequences can provide similar image quality and diffusion measures as conventional EPI readouts with multiple echoes but can reduce the overall relaxation-diffusion protocol scan time by approximately two- to threefold.

CONCLUSION

TDM-EPI is a novel approach to acquire diffusion imaging data at multiple TEs. This enables a significant reduction in acquisition time for relaxation-diffusion MRI experiments but without compromising image quality and diffusion measurements, thus removing a significant barrier to the adoption of relaxation-diffusion MRI in clinical research studies of neurological and mental disorders.

Amide Proton Transfer-Weighted Imaging and Multiple Models Diffusion-Weighted Imaging Facilitates Preoperative Risk Stratification of Early-Stage Endometrial Carcinoma

BACKGROUND

Endometrial carcinoma (EC) risk stratification is generally based on histological assessment. It would be beneficial to perform risk stratification noninvasively by MRI.

PURPOSE

To investigate the application of amide proton transfer-weighted imaging (APTWI), monoexponential, biexponential, and stretched exponential intravoxel incoherent motion (IVIM), and diffusion kurtosis imaging (DKI) for the evaluation of risk stratification in early-stage EC.

STUDY TYPE

Prospective.

POPULATION

Eighty patients with early-stage EC (47 classified as low risk, 20 as medium risk, and 13 as high risk by histological grade and International Federation of Gynecology and Obstetrics stage).

FIELD STRENGTH/SEQUENCE

T1-weighted imaging, T2-weighted imaging, IVIM, APTWI, and DKI MRI at 3 T.

ASSESSMENT

The magnetization transfer ratio asymmetry (MTRasym [3.5 ppm]), apparent diffusion coefficient (ADC), diffusion coefficient (D), pseudo diffusion coefficient (D*), perfusion fraction (f), distributed diffusion coefficient (DDC), water molecular diffusion heterogeneity index (α), mean kurtosis (MK), and mean diffusivity (MD) were calculated and compared between low-risk and non-low-risk groups.

STATISTICAL TESTS

Individual sample t test, analysis of variance, and logistic regression. A P-value <0.05 was considered statistically significant.

RESULTS

The α, ADC, D, DDC, and MD were significantly higher and the f, MK, and MTRasym (3.5 ppm) were significantly lower in the low-risk group than in the non-low-risk group. The difference in D* between the two groups was not significant (P = 0.289). MTRasym (3.5 ppm), D, and MK were independent predictors of risk stratification. The combination of these three parameters was better able to identify low- and non-low-risk groups than each individual parameter.

DATA CONCLUSION

The IVIM, DKI, and APTWI parameters have potential as imaging markers for risk stratification in early-stage EC.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 3.

Evaluation of amide proton transfer-weighted imaging for endometrial carcinoma histological features: a comparative study with diffusion kurtosis imaging

OBJECTIVES

To investigate whether amide proton transfer-weighted imaging (APTWI) and diffusion kurtosis imaging (DKI) can be used to evaluate endometrial carcinoma (EC) in terms of clinical type, histological grade, subtype, and Ki-67 index.

METHODS

Eighty-eight patients with EC underwent pelvic DKI and APTWI. The non-Gaussian diffusion coefficient (D_app), apparent kurtosis coefficient (K_app), and magnetization transfer ratio asymmetry (MTRasym (3.5 ppm)) were calculated and compared based on the clinical type (type I, II), histological grade (high- and low-grade), and subtype (endometrioid adenocarcinoma (EA) and non-EA). Correlation coefficients were calculated for each parameter with histological grades and the Ki-67 index.

RESULTS

The MTRasym (3.5 ppm) and K_app values were higher in the type II group and high-grade group than in the type I and low-grade groups, respectively, while the D_app values were lower in the type I and low-grade groups, respectively (all p < 0.05). The K_app value was higher in the EA group than in the non-EA group (p = 0.022). The K_app value was the only independent predictor for the histological grade of EA and the clinical type of EC. The AUC (DKI) was higher than the AUC (APTWI) in the identification of type I and II EC and high- and low-grade EA (Z = 2.042, 2.013, p = 0.041, 0.044), while in the identification of EA and non-EA, only the difference in K_app was statistically significant. Moreover, the K_app and MTRasym (3.5 ppm) values and D_app values correlated positively and negatively, respectively, with histological grade (r = 0.759, 0.555, 0.624, and 0.462, all p < 0.05) and Ki-67 index (r = -0.704, -0.507, all p < 0.05).

CONCLUSION

Both DKI- and APTWI-related parameters have potential as imaging markers in estimating the histological features of EC, while DKI shows better performance than APTWI in this study.

KEY POINTS

• DKI and APTWI can be used to preliminarily evaluate the histological characteristics of endometrial carcinoma (EC). • The K_app was the only independent predictor for the histological grade of EA and the clinical type of EC. • The K_app, MTRasym (3.5 ppm), and D_app correlated positively and negatively, respectively, with histological grade and Ki-67 index.

Diffusion weighted imaging in acute ischemic stroke: A review of its interpretation pitfalls and advanced diffusion imaging application

Diffusion weighted imaging (DWI) is a widely used imaging technique to evaluate patients with stroke. It can detect brain ischemia within minutes of stroke onset. However, DWI has few potential pitfalls that should be recognized during interpretation. DWI lesion could be reversible in the early hours of stroke and the entire lesion may not represent ischemic core. False negative DWI could lead to diagnosis of DWI negative stroke or to a missed stroke diagnosis. Ischemic stroke mimics can occur on DWI with non-cerebrovascular neurological conditions. In this article, the history of DWI, its clinical applications, and potential pitfalls for use in acute ischemic stroke are reviewed. Advanced diffusion imaging techniques with reference to Diffusion Kurtosis Imaging and Diffusion Tensor Imaging that has been studied to evaluate ischemic core are discussed.

Time dependence in diffusion MRI predicts tissue outcome in ischemic stroke patients

Purpose:

Reperfusion therapy enables effective treatment of ischemic stroke presenting within 4–6 hours. However, tissue progression from ischemia to infarction is variable, and some patients benefit from treatment up until 24 hours. Improved imaging techniques are needed to identify these patients. Here, it was hypothesized that time dependence in diffusion MRI may predict tissue outcome in ischemic stroke.

Methods:

Diffusion MRI data were acquired with multiple diffusion times in five non-reperfused patients at 2, 9, and 100 days after stroke onset. Maps of “rate of kurtosis change” (k), mean kurtosis, ADC, and fractional anisotropy were derived. The ADC maps defined lesions, normal-appearing tissue, and the lesion tissue that would either be infarcted or remain viable by day 100. Diffusion parameters were compared (1) between lesions and normal-appearing tissue, and (2) between lesion tissue that would be infarcted or remain viable.

Results:

Positive values of k were observed within stroke lesions on day 2 (P = .001) and on day 9 (P = .023), indicating diffusional exchange. On day 100, high ADC values indicated infarction of 50 ± 20% of the lesion volumes. Tissue infarction was predicted by high k values both on day 2 (P = .026) and on day 9 (P = .046), by low mean kurtosis values on day 2 (P = .043), and by low fractional anisotropy values on day 9 (P = .029), but not by low ADC values.

Conclusions:

Diffusion time dependence predicted tissue outcome in ischemic stroke more accurately than the ADC, and may be useful for predicting reperfusion benefit.

The value of bi-exponential and non-Gaussian distribution diffusion-weighted imaging in the differentiation of recurrent soft tissue neoplasms and post-surgical changes

Background

Many researches focused on the quantitative mono-exponential diffusion-weighted imaging (DWI) in the assessment of soft tissue neoplasms (STN), but few focused on the value of bi-exponential and non-Gaussian DWI in the application of Recurrent Soft Tissue Neoplasms (RSTN). This study aimed to explore the feasibility of bi-exponential decay and non-Gaussian distribution DWI in the differentiation of RSTN and Post-Surgery Changes (PSC), and compared with mono-exponential DWI.

Methods

The clinical, mono-exponential, bi-exponential [intravoxel incoherent motion (IVIM)] and non-Gaussian [diffusion kurtosis imaging (DKI)] DWI imaging of a cohort of 27 patients [15 RSTN (22 masses), and 12 PSC (12 lesions)] with 34 masses, from Nov 01 2017 to Sep 30 2018, were reviewed. The differences of apparent diffusion coefficient (ADC), true diffusion coefficient (D), pseudodiffusion coefficient (D*), perfusion fraction (f), mean diffusivity (MD), and mean kurtosis (MK) values were compared between RSTN and PSC groups. The mono-, bi-exponential, and non-Gaussian distribution based predictive models for RSTN and PSC were built and compared. ROC curves were generated and compared by the DeLong test.

Results

Intra-class correlation coefficient (ICC) of all IVIM/DKI parameters was high (≥0.841). There were significant differences in ADC, D, f, MD, and MK values between RSTN and PSC, but no difference in D* value. The ADC_IVIM, D, f and MD values of RSTN were lower than those of PSC, but with higher MK value. The ADC_IVIM and D values did better than f value in differentiating these two groups (P<0.05). While there was no significant difference in AUCs among ADC_DKI, MD, and MK values. Also, no significant difference was detected in AUCs between bi-exponential and mono-exponential (P=0.38), or between mono-exponential and non-Gaussian distribution based prediction models (P=0.09).

Conclusions

ADC, D, f, MD, and MK values can be used in the differentiation of RSTN and PSC.

Investigating the origin of pH-sensitive magnetization transfer ratio asymmetry MRI contrast during the acute stroke: Correction of T1 change reveals the dominant amide proton transfer MRI signal

PURPOSE

Amide proton transfer (APT) MRI is promising to serve as a surrogate metabolic imaging biomarker of acute stroke. Although the magnetization transfer ratio asymmetry (MTRasym ) has been used commonly, the origin of pH-weighted MRI effect remains an area of investigation, including contributions from APT, semisolid MT contrast asymmetry, and nuclear Overhauser enhancement effects. Our study aimed to determine the origin of pH-weighted MTRasym contrast following acute stroke.

METHODS

Multiparametric MRI, including T1 , T2 , diffusion and Z-spectrum, were performed in rats after middle cerebral artery occlusion. We analyzed the conventional Z-spectrum I Δ ω I 0 and the apparent exchange spectrum R ex Δ ω , being the difference between the relaxation-scaled inverse Z-spectrum and the intrinsic spinlock relaxation rate R 1 · cos 2 θ · I 0 I Δ ω - R 1 ρ Δ ω . The ischemia-induced change was calculated as the spectral difference between the diffusion lesion and the contralateral normal area.

RESULTS

The conventional Z-spectrum signal change at -3.5 ppm dominates that at +3.5 ppm (-1.16 ± 0.39% vs. 0.76 ± 0.26%, P < .01) following acute stroke. In comparison, the magnitude of ΔRex change at 3.5 ppm becomes significantly larger than that at -3.5 ppm (-2.80 ± 0.40% vs. -0.94 ± 0.80%, P < .001), with their SNR being 7.0 and 1.2, respectively. We extended the magnetization transfer and relaxation normalized APT concept to the apparent exchange-dependent relaxation image, documenting an enhanced pH contrast between the ischemic lesion and the intact tissue, over that of MTRasym .

CONCLUSION

Our study shows that after the relaxation-effect correction, the APT effect is the dominant contributing factor to pH-weighted MTRasym following acute stroke.

Diffusion kurtosis imaging and pathological comparison of early hypoxic-ischemic brain damage in newborn piglets

To investigate the application value of magnetic resonance diffusion kurtosis imaging (DKI) in hypoxic–ischemic brain damage (HIBD) in newborn piglets and to compare imaging and pathological results. Of 36 piglets investigated, 18 were in the experimental group and 18 in the control group. The HIBD model was established in newborn piglets by ligating the bilateral common carotid arteries and placing them into hypoxic chamber. All piglets underwent conventional MRI and DKI scans at 3, 6, 9, 12, 16, and 24 h postoperatively. Mean kurtosis (MK) and mean diffusivity (MD) maps were constructed. Then, the lesions were examined using light and electron microscopy and compared with DKI images. The MD value of the lesion area gradually decreased and the MK value gradually increased in the experimental group with time. The lesion areas gradually expanded with time; MK lesions were smaller than MD lesions. Light microscopy revealed neuronal swelling in the MK- and MD-matched and mismatched regions. Electron microscopy demonstrated obvious mitochondrial swelling and autophagosomes in the MK- and MD-matched region but normal mitochondrial morphology or mild swelling in the mismatched region. DKI can accurately evaluate early ischemic–hypoxic brain injury in newborn piglets.

Assessment of MRI-based anomalous diffusion changes in brain ischemic stroke with a fractional motion model

The actual diffusion process in human brain has been shown to be anomalous comparing to that predicted with traditional diffusion MRI (dMRI) theory. Recently, dMRI based on fractional motion (FM) model has demonstrated the potential to accurately describe anomalous diffusion in vivo. In this work, we explored the potential value of FM model-based dMRI in quantificational identification of ischemic stroke and compared that with the traditional apparent diffusion coefficient (ADC). We included 23 acute stroke patients, 8 of whom finished a follow-up scan, and 22 matched healthy controls. The dMRI images were acquired by using a Stejskal-Tanner single-shot spin-echo echo-planar-imaging sequence (diffusion gradients were applied in three orthogonal directions with 25 non-zero b values ranging from 248 to 4474 s/mm²) at 3.0 T MRI. We calculated the coefficient of variation (CV) for FM-related parameters in stroke lesions, and compared the mean values for FM-related parameters and ADC by using two-sample t-tests. Correlation analysis was achieved using Pearson correlation coefficient test. In acute stroke lesions, CV for FM-related parameters showed significant increase compared with normal tissues (P < 0.01), while those of ADC didn't appear statistical difference. Mean values for FM-related parameters showed significant decrease in acute lesion (P < 0.01) and their changing pattern during follow-up was positively correlated with ADC (P < 0.005). Our results initially verified the utility of the FM-model in detecting ischemic stroke compared with traditional dMRI.

Diffusion Kurtosis Imaging of Leptin Intervention in Early Hypoxic-Ischemic Brain Edema

The role of leptin in neuroprotection has recently been recognized. However, there are few reports on the use of imaging methods to dynamically evaluate the neuroprotection role of leptin. Diffusion kurtosis imaging (DKI), which is a method used to measure non-Gaussian water diffusion, can reflect the real water diffusion in brain tissues. In this study, a newborn piglet model was used to dynamically evaluate the leptin intervention in early hypoxic-ischemic brain edema via DKI. Thirty-two Yorkshire newborn piglets were divided into three groups: the hypoxic-ischemic encephalopathy (HIE) group, the leptin group, and the control group. DKI scanning was performed at time points of 3, 6, 9, 12, 16, and 24 h after hypoxic-ischemic exposure. After scanning, arterial blood was extracted from all piglets to measure NSE and S100β levels. Then, the brain was completely extracted for pathological examination. In the lesion areas, the MK, Ka, and Kr values in the leptin group were significantly lower than those in the HIE group, the MD, Da, and Dr values showed an opposite trend. The lesion areas in the leptin group were smaller than those of in the HIE group. In addition, the pathological results showed that less cell and organelle injury occurred in the leptin group. Our findings indicate that leptin can effectively reduce hypoxic-ischemic brain edema, and DKI can be more sensitive than conventional diffusivity metrics for visualizing the microstructural changes of HIE. This provides a new clue for the treatment and evaluation of HIE.

Demonstration of magnetization transfer and relaxation normalized pH-specific pulse-amide proton transfer imaging in an animal model of acute stroke

PURPOSE

pH-weighted amide proton transfer (APT) MRI is promising to serve as a new surrogate metabolic imaging biomarker for refined ischemic tissue demarcation. APT MRI with pulse-RF irradiation (pulse-APT) is an alternative to the routine continuous wave (CW-) APT MRI that overcomes the RF duty cycle limit. Our study aimed to generalize the recently developed pH-specific magnetization transfer and relaxation-normalized APT (MRAPT) analysis to pulse-APT MRI in acute stroke imaging.

METHODS

Multiparametric MRI, including CW- and pulse-APT MRI scans, were performed following middle cerebral artery occlusion in rats. We calculated pH-sensitive MTR_asym and pH-specific MRAPT contrast between the ipsilateral diffusion lesion and contralateral normal area.

RESULTS

An inversion pulse of 10 to 15 ms maximizes the pH-sensitive MRI contrast for pulse-APT MRI. The contrast-to-noise ratio of pH-specific MRAPT effect between the contralateral normal area and ischemic lesion from both methods are comparable (3.25 ± 0.65 vs. 3.59 ± 0.40, P > .05). pH determined from both methods were in good agreement, with their difference within 0.1.

CONCLUSIONS

Pulse-APT MRI provides highly pH-specific mapping for acute stroke imaging.

Diffusion kurtosis imaging differs between primary central nervous system lymphoma and high-grade glioma and is correlated with the diverse nuclear-to-cytoplasmic ratio: a histopathologic, biopsy-based study

OBJECTIVES

To determine whether water kurtosis and diffusional metrics derived from diffusional kurtosis imaging (DKI) within primary central nervous system lymphomas (PCNSLs) and high-grade gliomas (HGGs) correlate with cellularity and/or nuclear-to-cytoplasmic (N/C) ratio.

METHODS

Forty-four and 43 pathologically confirmed high-grade glioma and primary central nervous system lymphoma specimens between May 2013 and November 2016 were retrospectively reviewed. Diffusional metrics, kurtosis metrics, cellularity, and N/C ratios in PCNSLs and HGGs were compared using the Mann-Whitney U test (significant level, p < 0.007 [0.05/7]); Bonferroni correction).

RESULTS

Mean kurtosis (MK), axial kurtosis (K_//), and radial kurtosis (K_⊥) in PCNSLs were 0.857 (0.693-0.924), 0.837 (0.660-0.941), and 0.834 (0.685-0.937), respectively; and 0.629 (0.524-0.716), 0.575 (0.511-0.689), and 0.675 (0.532-0.766), respectively, in HGGs (all p < 0.001). No significant differences in fractional anisotropy (FA), mean diffusion (MD), axial diffusion (λ_//), and radial diffusion (λ_⊥) were found between HGGs and PCNSLs. Cellularity was higher in PCNSLs than in HGGs (p = 0.125); whereas, the N/C ratio in PCNSLs was significantly higher than that in HGGs (p < 0.001). All DKI metrics (FA, MD, λ_//, λ_⊥, MK, K_//, and K_⊥) were significantly correlated with N/C ratio in PCNSLs with correlation coefficients being rho = 0.418, - 0.722, - 0.525, - 0.768, 0.704, 0.579, and 0.686, respectively. Cellularity in PCNSLs and HGGs did not correlate with any kurtosis or diffusional metrics.

CONCLUSIONS

Difference of kurtosis parameters between PCNSLs and HGGs is correlated with their diverse N/C ratio.

KEY POINTS

• DKI has considerable value in differentiating between PCNSLs and HGGs. • DKI can provide important information on nuclear-to-cytoplasmic ratio. • Difference of kurtosis parameters between PCNSLs and HGGs correlated well with their diverse N/C ratios.

Acute Subcortical Infarcts Cause Secondary Degeneration in the Remote Non-involved Cortex and Connecting Fiber Tracts

Background and Purpose: Remote white matter and cortex reorganization may contribute to functional reorganization and clinical outcome after acute infarcts. To determine the microstructural changes in the remote intact corticospinal tract (CST) and precentral gyrus cortex connected to the acute infarct after subcortical stroke involving the CST over 6 months. Methods: Twenty-two patients with subcortical stroke involving the CST underwent magnetic resonance imaging (MRI) and clinical assessment in the acute phase (baseline) and 6 months (follow-up) after the stroke. The MRI sequences included T1-weighted imaging, T2-weighted imaging, fluid-attenuated inversion recovery, diffusion tensor imaging (DTI), and diffusion kurtosis imaging. Fractional anisotropy (FA) and track-density imaging (TDI) values were generated using DTI data for the centrum semiovale, corona radiata, posterior limb of internal capsule, and cerebral peduncle. The mean kurtosis (MK) value of the precentral gyrus cortex was calculated. Changes in the FA, TDI, and MK values between the baseline and follow-up and the relationship between these changes were analyzed. Results: The TDI and FA values of all parts of the ipsilesional (IL) CST, including the noninvolved upper and lower parts, decreased at the 6-month follow-up (P < 0.001). The MK values of the stroke lesion (P < 0.001) and IL precentral gyrus cortex (P = 0.002) were lower at follow-up than at the baseline. The ΔTDI (r = 0.689, P < 0.001) and Δ FA values (r = 0.463, P = 0.03) of the noninvolved upper part of the IL CST were positively correlated with the ΔMK value of the IL precentral gyrus cortex. Conclusion: Secondary degeneration occurred in the remote part of the CST and the remote IL precentral gyrus cortex after subcortical stroke involving the CST. The secondary degeneration in the upper part of the CST was correlated with that in the IL precentral gyrus cortex.

Noninvasive assessment of renal fibrosis by magnetic resonance imaging and ultrasound techniques

Renal fibrosis is a useful biomarker for diagnosis and guidance of therapeutic interventions of chronic kidney disease (CKD), a worldwide disease that affects more than 10% of the population and is one of the major causes of death. Currently, tissue biopsy is the gold standard for assessment of renal fibrosis. However, it is invasive, and prone to sampling error and observer variability, and may also result in complications. Recent advances in diagnostic imaging techniques, including magnetic resonance imaging (MRI) and ultrasonography, have shown promise for noninvasive assessment of renal fibrosis. These imaging techniques measure renal fibrosis by evaluating its impacts on the functional, mechanical, and molecular properties of the kidney, such as water mobility by diffusion MRI, tissue hypoxia by blood oxygenation level dependent MRI, renal stiffness by MR and ultrasound elastography, and macromolecule content by magnetization transfer imaging. Other MR techniques, such as T1/T2 mapping and susceptibility-weighted imaging have also been explored for measuring renal fibrosis. Promising findings have been reported in both preclinical and clinical studies using these techniques. Nevertheless, limited specificity, sensitivity, and practicality in these techniques may hinder their immediate application in clinical routine. In this review, we will introduce methodologies of these techniques, outline their applications in fibrosis imaging, and discuss their limitations and pitfalls.

A comparative study of diffusion kurtosis imaging and T2* mapping in quantitative detection of lumbar intervertebral disk degeneration

PURPOSE

To assess the feasibility of diffusion kurtosis imaging (DKI) for diagnosing lumbar intervertebral disk degeneration (IDD) and to compare the potential of DKI and T2* mapping in the diagnosis of early IDD.

METHODS

Sagittal T2WI, DKI, and T2* mapping were performed in 75 subjects with 375 lumbar intervertebral disks at a 3.0-T MRI. DKI-related parameters including mean kurtosis (MK), mean diffusivity (MD), fractional anisotropy (FA), and T2* values were calculated for each disk which was segmented into three regions: nucleus pulposus (NP), anterior annulus fibrosus (AAF), and posterior annulus fibrosus (PAF).

RESULTS

MK and FA were positively correlated with Pfirrmann grade (all P < 0.001). MD and T2* were negatively correlated with Pfirrmann grade (all P < 0.001) except for T2* value of AAF (r = 0.087, P > 0.05). MK and FA values increased, while MD and T2* values decreased with age. No statistical significance was found between men and women (P > 0.05). Cephalic lumbar disks (L1/L2 and L2/L3) got lower MK and FA values than caudal lumbar disks (L4/L5 and L5/S1) (all P < 0.05), while cephalic lumbar disks got higher MD value than caudal lumbar disks (all P < 0.05). ROC analysis demonstrated that MK, MD, and FA showed significantly higher diagnostic accuracies than T2*, especially in NP and PAF.

CONCLUSIONS

DKI can be used to assess human lumbar IDD. And DKI was more sensitive to the quantitative detection of early lumbar IDD than T2* mapping. These slides can be retrieved under Electronic Supplementary Material.

Collateral blood flow measurement with intravoxel incoherent motion perfusion imaging in hyperacute brain stroke

Objective

To determine if intravoxel incoherent motion (IVIM) magnetic resonance perfusion can measure the quality of the collateral blood flow in the penumbra in hyperacute stroke.

Methods

A 6 b values IVIM MRI sequence was acquired in stroke patients with large vessel occlusion imaged <16 hours of last seen well. IVIM perfusion measures were evaluated in regions of interest drawn in the infarct core (D < 600 mm2/s), in the corresponding region in the contralateral hemisphere, and in the dynamic susceptibility contrast penumbra. In patients with a penumbra >15 mL, images were reviewed for the presence of a penumbra perfusion lesion on the IVIM f map, which was correlated with infarct size metrics. Statistical significance was tested using Student t test, Mann-Whitney U test, and Fisher exact test.

Results

A total of 34 patients were included. In the stroke core, IVIM f was significantly lower (4.6 ± 3.3%) compared to the healthy contralateral region (6.3 ± 2.2%, p < 0.001). In the 25 patients with a penumbra >15 mL, 9 patients had an IVIM penumbra perfusion lesion (56 ± 76 mL), and 16 did not. Patients with an IVIM penumbra perfusion lesion had a larger infarct core (82 ± 84 mL) at baseline, a larger infarct growth (68 ± 40 mL), and a larger final infarct size (126 ± 81 mL) on follow-up images compared to the patients without (resp. 20 ± 17 mL, p < 0.05; 13 ± 19 mL, p < 0.01; 29 ± 24 mL, p < 0.05). All IVIM penumbra perfusion lesions progressed to infarction despite thrombectomy treatment.

Conclusions

IVIM is a promising tool to assess the quality of the collateral blood flow in hyperacute stroke. IVIM penumbra perfusion lesion may be a marker of nonsalvageable tissue despite treatment with thrombectomy, suggesting that the IVIM penumbra perfusion lesion might be counted to the stroke core, together with the DWI lesion.

Comparative analysis of the value of diffusion kurtosis imaging and diffusion-weighted imaging in evaluating the histological features of endometrial cancer

Purpose

This study evaluated and compared the performances of diffusion kurtosis imaging (DKI) and diffusion-weighted imaging (DWI) for diagnosing and histologically grading endometrial cancer.

Materials and methods

In this retrospective study, DKI and DWI data for 61 patients with endometrial cancer and 30 patients with a normal endometrium were analyzed, and the mean kurtosis (MK), mean diffusion coefficient (MD) and apparent diffusion coefficient (ADC) values for the endometrial cancer tissue and normal endometrial tissue were acquired. The parameters for the normal endometrium group (G0) and the endometrial cancer groups (G1, G2 and G3) were compared and analyzed. The receiver operating characteristic (ROC) curve was used to evaluate each parameter’s diagnostic accuracy and threshold. Spearman correlation analysis was used to analyze the correlations between all parameters and histological grades.

Results

The MK values for the G0, G1, G2 and G3 groups increased gradually, while the MD and ADC values decreased gradually. Except for the differences in the ADC values between G0 and G1, the differences among the groups were statistically significant (P < 0.05). The MK values had the highest diagnostic accuracy in differentiating G0 and (G1 + G2 + G3), G0 and G1, G1 and G2, and G2 and G3 (AUC = 0.93, 0.76, 0.91, 0.91, P < 0.05). MK was maximally correlated with histological grade, followed by MD and ADC (MK > MD > ADC; r = − 0.85, + 0.82, + 0.76, P < 0.01).

Conclusion

Both DKI and DWI can be used to evaluate the diagnosis and histological grading of endometrial cancer. Compared with DWI, the DKI model is a more complete mathematical model with more sensitive parameters, which can more effectively evaluate the pathological and physiological characteristics of endometrial cancer.

Mapping tissue pH in an experimental model of acute stroke - Determination of graded regional tissue pH changes with non-invasive quantitative amide proton transfer MRI

pH-weighted amide proton transfer (APT) MRI is sensitive to tissue pH change during acute ischemia, complementing conventional perfusion and diffusion stroke imaging. However, the currently used pH-weighted magnetization transfer (MT) ratio asymmetry (MTR_asym) analysis is of limited pH specificity. To overcome this, MT and relaxation normalized APT (MRAPT) analysis has been developed that to homogenize the background signal, thus providing highly pH conspicuous measurement. Our study aimed to calibrate MRAPT MRI toward absolute tissue pH mapping and determine regional pH changes during acute stroke. Using middle cerebral artery occlusion (MCAO) rats, we performed lactate MR spectroscopy and multi-parametric MRI. MRAPT MRI was calibrated against a region of interest (ROI)-based pH spectroscopy measurement (R² = 0.70, P < 0.001), showing noticeably higher correlation coefficient than the simplistic MTR_asym index. Capitalizing on this, we mapped brain tissue pH and semi-automatically segmented pH lesion, in addition to routine perfusion and diffusion lesions. Tissue pH from regions of the contralateral normal, perfusion/diffusion lesion mismatch and diffusion lesion was found to be 7.03 ± 0.04, 6.84 ± 0.10, 6.52 ± 0.19, respectively. Most importantly, we delineated the heterogeneous perfusion/diffusion lesion mismatch into perfusion/pH and pH/diffusion lesion mismatches, with their pH being 7.01 ± 0.04 and 6.71 ± 0.12, respectively (P < 0.05). To summarize, our study calibrated pH-sensitive MRAPT MRI toward absolute tissue pH mapping, semi-automatically segmented and determined graded tissue pH changes in ischemic tissue and demonstrated its feasibility for refined demarcation of heterogeneous metabolic disruption following acute stroke.

In vivo microscopic diffusional kurtosis imaging with symmetrized double diffusion encoding EPI

PURPOSE

Diffusional kurtosis imaging (DKI) measures the deviation of the displacement probability from a normal distribution, complementing the data commonly acquired by diffusion MRI. It is important to elucidate the sources of kurtosis contrast, particularly in biological tissues where microscopic kurtosis (intrinsic kurtosis) and diffusional heterogeneity may co-exist.

METHODS

We have developed a technique for microscopic kurtosis MRI, dubbed microscopic diffusional kurtosis imaging (µDKI), using a symmetrized double diffusion encoding (s-DDE) EPI sequence. We compared this newly developed µDKI to conventional DKI methods in both a triple compartment phantom and in vivo.

RESULTS

Our results showed that whereas conventional DKI and µDKI provided similar measurements in a compartment of monosphere beads, kurtosis measured by µDKI was significantly less than that measured by conventional DKI in a compartment of mixed Gaussian pools. For in vivo brain imaging, µDKI showed small yet significantly lower kurtosis measurement in regions of the cortex, CSF, and internal capsule compared to the conventional DKI approach.

CONCLUSIONS

Our study showed that µDKI is less susceptible than conventional DKI to sub-voxel diffusional heterogeneity. Our study also provided important preliminary demonstration of our technique in vivo, warranting future studies to investigate its diagnostic use in examining neurological disorders.

Preliminary evaluation of accelerated microscopic diffusional kurtosis imaging (μDKI) in a rodent model of epilepsy

PURPOSE

Our study aimed to develop accelerated microscopic diffusional kurtosis imaging (μDKI) and preliminarily evaluated it in a rodent model of chronic epilepsy.

METHODS

We investigated two μDKI acceleration schemes of reduced sampling density and angular range in a phantom and wild-type rats, and further tested μDKI method in pilocarpine-induced epilepsy rats using a 4.7 Tesla MRI. Single slice average μD_app and μK_app maps were derived, and Nissl staining was obtained.

RESULTS

The kurtosis maps from two accelerated μDKI sampling schemes (sampling density and range) are very similar to that using fully sampled data (SSIM > 0.95). For the epileptic models, μDKI showed noticeably different contrast from those obtained with conventional DKI. Specifically, the average μK_app was significantly less than that of the average of K_app (0.15 ± 0.01 vs. 0.47 ± 0.02) in the ventricle.

CONCLUSIONS

Our study demonstrated the feasibility of accelerated in vivo μDKI. Our work revealed that μDKI provides complementary information to conventional DKI method, suggesting that advanced DKI sequences are promising to elucidate tissue microstructure in neurological diseases.