Quantitative contrast-enhanced ultrasound imaging: a review of sources of variability

3-D Velocity and Volume Flow Measurement In Vivo Using Speckle Decorrelation and 2-D High-Frame-Rate Contrast-Enhanced Ultrasound

Being able to measure 3-D flow velocity and volumetric flow rate effectively in the cardiovascular system is valuable but remains a significant challenge in both clinical practice and research. Currently, there has not been an effective and practical solution to the measurement of volume flow using ultrasound imaging systems due to challenges in existing 3-D imaging techniques and high system cost. In this study, a new technique for quantifying volumetric flow rate from the cross-sectional imaging plane of the blood vessel was developed by using speckle decorrelation (SDC), 2-D high-frame-rate imaging with a standard 1-D array transducer, microbubble contrast agents, and ultrasound imaging velocimetry (UIV). Through SDC analysis of microbubble signals acquired with a very high frame rate and by using UIV to estimate the two in-plane flow velocity components, the third and out-of-plane velocity component can be obtained over time and integrated to estimate volume flow. The proposed technique was evaluated on a wall-less flow phantom in both steady and pulsatile flow. UIV in the longitudinal direction was conducted as a reference. The influences of frame rate, mechanical index (MI), orientation of imaging plane, and compounding on velocity estimation were also studied. In addition, an in vivo trial on the abdominal aorta of a rabbit was conducted. The results show that the new system can estimate volume flow with an averaged error of 3.65% ± 2.37% at a flow rate of 360 mL/min and a peak velocity of 0.45 m/s, and an error of 5.03% ± 2.73% at a flow rate of 723 mL/min and a peak velocity of 0.8 m/s. The accuracy of the flow velocity and volumetric flow rate estimation directly depend on the imaging frame rate. With a frame rate of 6000 Hz, a velocity up to 0.8 m/s can be correctly estimated. A higher mechanical index (MI = 0.42) is shown to produce greater errors (up to 21.78±0.49%, compared to 3.65±2.37% at MI = 0.19). An in vivo trial, where velocities up to 1 m/s were correctly measured, demonstrated the potential of the technique in clinical applications.

High-Frame-Rate Contrast Echocardiography Using Diverging Waves: Initial In Vitro and In Vivo Evaluation

Contrast echocardiography (CE) ultrasound with microbubble contrast agents has significantly advanced our capability for assessment of cardiac function, including myocardium perfusion quantification. However, in standard CE techniques obtained with line by line scanning, the frame rate and image quality are limited. Recent research has shown significant frame-rate improvement in noncontrast cardiac imaging. In this work, we present and initially evaluate, both in vitro and in vivo, a high-frame-rate (HFR) CE imaging system using diverging waves and pulse inversion sequence. An imaging frame rate of 5500 frames/s before and 250 frames/s after compounding is achieved. A destruction-replenishment sequence has also been developed. The developed HFR CE is compared with standard CE in vitro on a phantom and then in vivo on a sheep heart. The image signal-to-noise ratio and contrast between the myocardium and the chamber are evaluated. The results show up to 13.4-dB improvement in contrast for HFR CE over standard CE when compared at the same display frame rate even when the average spatial acoustic pressure in HFR CE is 36% lower than the standard CE. It is also found that when coherent compounding is used, the HFR CE image intensity can be significantly modulated by the flow motion in the chamber.

Renal perfusion parameters measured by contrast-enhanced ultrasound in healthy dogs demonstrate a wide range of variability in the long-term

Contrast-enhanced ultrasound may be helpful for detecting early renal microvascular damage and dysfunction in dogs. However, before this noninvasive imaging method can be tested as an early-stage screening tool in clinical patients, an improved understanding of long-term variation in healthy animals is needed. In this prospective, secondary, longitudinal, serial measurements study, variability of contrast-enhanced ultrasound renal perfusion parameters was described for eight healthy dogs, using seven time points and a period of 83 weeks. Dogs were sedated with butorphanol (0.4 mg/kg), and contrast-enhanced ultrasound of each kidney was performed after an intravenous bolus injection of a microbubble contrast agent (0.04 mL/kg). Time-intensity curves were created from regions-of-interest drawn in the renal cortex and medulla. Intensity-related parameters representing blood volume and time-related parameters representing blood velocity were determined. A random-effects model using restricted maximum likelihood was used to estimate variance components. Within-dog coefficient of variation was defined as the ratio of the standard deviation over the mean. Time-related parameters such as time-to-peak, rise and fall time had lowest within-dog variability. Intensity-related parameters such as peak enhancement, wash-in and wash-out area under the curve, total area under the curve, and wash-in and washout rates had high within-dog variability (coefficient of variation > 45%). Authors therefore recommend the use of time-related parameters for future studies of renal perfusion. Within-dog variability for bilateral kidney measurements was extremely low, therefore contrast-enhanced ultrasound may be particularly useful for detecting unilateral changes in renal perfusion. Future studies are needed to compare contrast-enhanced ultrasound findings in healthy dogs versus dogs with renal disease.

Contrast-Enhanced Ultrasound Determines Supraspinatus Muscle Atrophy After Cuff Repair and Correlates to Functional Shoulder Outcome

BACKGROUND

Muscle degeneration as a consequence of rotator cuff tears is mainly assessed by magnetic resonance imaging. Contrast-enhanced ultrasound (CEUS) is a new functional imaging method to assess microvascular perfusion as a fundamental parameter of muscle tissue vitality. In this cross-sectional study, the authors evaluated supraspinatus muscle perfusion after cuff repair and analyzed its association with functional shoulder outcome and the grade of echogenicity in B-mode ultrasound indicating fatty infiltration.

HYPOTHESIS

The authors expected reduced microperfusion of the operated versus the contralateral supraspinatus muscle and a correlation of the muscular microperfusion with functional shoulder outcome.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Patients who received unilateral repair of the supraspinatus tendon between 2009 and 2014 were invited for a single follow-up examination. Functional scores were assessed, including the Constant-Murley score and American Shoulder and Elbow Surgeons score. CEUS examination was performed bilaterally in an oblique sagittal plane of the supraspinatus fossa. Perfusion was quantified by the parameters wash-in perfusion index (WiPI) and peak enhancement via VueBox quantification software. The results of the Constant-Murley score, American Shoulder and Elbow Surgeons score, and perfusion parameters were referenced to the contralateral shoulder. Echogenicity of the supraspinatus muscle was classified with a 3-point scale as compared with the trapezius muscle.

RESULTS

Sixty-seven patients were available, with a mean follow-up of 38.0 ± 18.5 months. Functional assessment showed impaired shoulder function on the operated shoulder as compared with the contralateral side (relative Constant Score [CS], 80% ± 19%). CEUS revealed diminished perfusion on the operated shoulder (WiPI, 55.1% ± 40.2%, P < .001). A strong correlation could be demonstrated between the perfusion deficit and functional impairment (relative WiPI and CS: r_s = .644, P < .001). Higher grade of echogenicity in B-mode ultrasound was associated with reduced perfusion.

CONCLUSION

CEUS could visualize impaired supraspinatus muscle perfusion after rotator cuff repair as compared with the contralateral, healthy shoulder. With its ability to quantify microvascular perfusion as a surrogate parameter for muscle vitality and function, CEUS may serve as a quantitative method to evaluate rotator cuff muscles.

A Pilot Study on Diagnostic Performance of Contrast-Enhanced Ultrasonography for Detection of Early Cervical Cancer

In this cohort study of 49 women with all stages of cervical cancer and 21 healthy controls, we compared contrast-enhanced ultrasonography (CEUS) filling pattern and semi-quantitative parameters in the two groups. Participants were examined with conventional grayscale and power Doppler ultrasound (US) followed by CEUS, using a 2.5 mL bolus of intravenous contrast agent. CEUS video clips were analyzed with regard to contrast distribution (focal or global) and semi-quantitative parameters. Focal contrast distribution was found in 3% (1/32) of the women with no tumor versus 89% (34/38) of women with histologically detectable tumor. A semi-quantitative analysis showed that the amount of contrast over a period of the whole tumor (area under the curve [AUC[ 0.92, 95% confidence interval [CI] 0.87-1.0), and the maximal intensity area (AUC 0.94, 95% CI 0.84-1.0) could accurately distinguish tumors from healthy tissue. In conclusion, the CEUS parameters differ significantly between tumors and healthy cervical tissue.

A new preclinical ultrasound platform for widefield 3D imaging of rodents

Noninvasive in vivo imaging technologies enable researchers and clinicians to detect the presence of disease and longitudinally study its progression. By revealing anatomical, functional, or molecular changes, imaging tools can provide a near real-time assessment of important biological events. At the preclinical research level, imaging plays an important role by allowing disease mechanisms and potential therapies to be evaluated noninvasively. Because functional and molecular changes often precede gross anatomical changes, there has been a significant amount of research exploring the ability of different imaging modalities to track these aspects of various diseases. Herein, we present a novel robotic preclinical contrast-enhanced ultrasound system and demonstrate its use in evaluating tumors in a rodent model. By leveraging recent advances in ultrasound, this system favorably compares with other modalities, as it can perform anatomical, functional, and molecular imaging and is cost-effective, portable, and high throughput, without using ionizing radiation. Furthermore, this system circumvents many of the limitations of conventional preclinical ultrasound systems, including a limited field-of-view, low throughput, and large user variability.

Evaluation of integrated color-coded perfusion analysis for contrast-enhanced ultrasound (CEUS) after percutaneous interventions for malignant liver lesions: First results

BACKGROUND

 With the rising number of percutaneous ablation therapies in malignant liver lesions there is a need of reliable diagnostics after the intervention to differentiate between reactive changes and tumor.

PURPOSE

To assess the success of percutaneous ablation therapies for malignant liver lesions using CEUS with perfusion analysis.

MATERIAL AND METHODS

Retrospective analysis of perfusion analysis for 67 patients with 94 malignant liver lesions, treated with ablation therapies. The lesions were 70 hepatocellular carcinomas (HCC), 18 metastases, 4 cholangiocellular carcinomas (CCC), 2 lesions remained unclear. CEUS was performed after bolus injection of 1.6-2.4 ml of sulfur-hexafluoride microbubbles. The perfusion analysis was calculated using Peak, TTP, mTT and AUC with integrated software during the late arterial to early portal-venous phase for approximately 9 sec (5-15 sec). For the evaluation of the success after percutaneous treatment the perfusion results were compared to the follow-up control after 6 months with CT and MRI and CEUS.

RESULTS

Perfusion analyses after percutaneous treatment of malignant liver lesions showed highly significant perfusion differences when comparing the center to the surrounding tissue and the margins (p<0.0001) for Peak and also for AUC. 62 lesions were successfully treated, meaning there was no local recurrence after 6 months. In cases of residual tumor CEUS showed a nodular marginal enhancement, the corresponding perfusion analyses showed nodular red and yellow pseudo-color shades.

CONCLUSIONS

Using CEUS and perfusion analysis, a critical analysis of post-ablation defects in malignant liver lesions is possible. With the help of pseudo-colors, remaining tumor-vascularization can be detected.

Fully Automatic Myocardial Segmentation of Contrast Echocardiography Sequence Using Random Forests Guided by Shape Model

Myocardial contrast echocardiography (MCE) is an imaging technique that assesses left ventricle function and myocardial perfusion for the detection of coronary artery diseases. Automatic MCE perfusion quantification is challenging and requires accurate segmentation of the myocardium from noisy and time-varying images. Random forests (RF) have been successfully applied to many medical image segmentation tasks. However, the pixel-wise RF classifier ignores contextual relationships between label outputs of individual pixels. RF which only utilizes local appearance features is also susceptible to data suffering from large intensity variations. In this paper, we demonstrate how to overcome the above limitations of classic RF by presenting a fully automatic segmentation pipeline for myocardial segmentation in full-cycle 2-D MCE data. Specifically, a statistical shape model is used to provide shape prior information that guide the RF segmentation in two ways. First, a novel shape model (SM) feature is incorporated into the RF framework to generate a more accurate RF probability map. Second, the shape model is fitted to the RF probability map to refine and constrain the final segmentation to plausible myocardial shapes. We further improve the performance by introducing a bounding box detection algorithm as a preprocessing step in the segmentation pipeline. Our approach on 2-D image is further extended to 2-D+t sequences which ensures temporal consistency in the final sequence segmentations. When evaluated on clinical MCE data sets, our proposed method achieves notable improvement in segmentation accuracy and outperforms other state-of-the-art methods, including the classic RF and its variants, active shape model and image registration.

In-vitro evaluation of accuracy of dynamic contrast-enhanced ultrasound (DCEUS)-based parametric perfusion imaging with respiratory motion-compensation

PURPOSE

The accuracy of multi-parametric perfusion imaging (PPI) based on dynamic contrast-enhanced ultrasound is disturbed by the respiratory motion in some cases, especially during characterizing hemodynamic features of abdominal tumor angiogenesis. This study aimed to effectively remove those disturbances on PPI and evaluate its accuracy.

METHOD

The respiratory motion-compensation (rMoCo) strategy in PPI was modified by employing non-negative matrix factorization combined with phase-by-phase compensation. According to the known and controllable ground truths in in-vitro perfusion experiments, the accuracy of the modified rMoCo strategy was further evaluated from multiple perspectives in a simulated dual-vessel flow phantom.

RESULTS

Compared with that of PPIs without rMoCo, the mean correlation coefficient between six PPIs with rMoCo and the corresponding static PPIs was up to 0.98 ± 0.01 and improved by 0.17 ± 0.04 (P < 0.05). The estimated error of vascular diameter decreased from 87.85% (P < 0.05) to 7.25% (P < 0.05) after rMoCo. PPIs with rMoCo were significantly consistent with static PPIs without respiratory motion disturbances.

CONCLUSIONS

These quantitative results illustrated the disturbances induced by respiratory motion were effectively removed and the accuracy of PPIs was significantly improved. The partial parabolic and bimodal hemodynamic characteristics and the anatomical structures and sizes were accurately quantified and depicted by PPIs with rMoCo. The modified method can benefit physicians in providing accurate diagnoses and in developing appropriate therapeutic strategies for abdominal diseases.

Quantitative evaluation of canine urinary bladder transitional cell carcinoma using contrast-enhanced ultrasonography

Background

In veterinary medicine, contrast-enhanced ultrasonography allowed the accurate quantification of liver, splenic and kidney vascularization in healthy dogs and the differentiation between malignant and benign hepatic, renal, and splenic nodules in dogs and cats based on perfusion patterns. The utility of contrast-enhanced ultrasonography in other applications is still under study.

The aim of this study was to develop diagnostic criteria by contrast-enhanced ultrasonography in 8 client-owned adult dogs affected by urinary bladder transitional cell carcinoma with definitive diagnosis made by cytopathologic evaluation after suction biopsy. The contrast enhancement pattern and the quantification of blood flow parameters of this tumor were reported.

Results

Examinations with B-mode, Doppler ultrasonography and contrast-enhanced ultrasonography were performed in all not sedated dogs. Assessments of bladder masses and bladder wall infiltration were performed. Each dog received 2 bolus injections of sulfur hexafluoride during the contrast-enhanced ultrasonography. Quantitative analysis of the contrast-enhanced ultrasonography images were performed. For each dog, one region of interest was manually drawn around the entire tumor. Software analysis of contrast-enhanced time-intensity curves was used to identify peak enhancement, time to peak enhancement, regional blood volume, regional blood flow, and mean transit time.

Contrast-enhanced ultrasonography showed an avid enhancement of the tumour tissue, with a heterogeneous or homogeneous pattern. The exam also showed the loss of planes between the lesion and the muscular layer. The presence of vascularized tissue through the bladder wall confirms the infiltrative feature of the tumour. Post-processing quantitative analysis showed a time-intensity curve with a rapid wash-in, a low level of signal intensity and a slow wash-out.

Conclusions

Contrast-enhanced ultrasonography provided useful clinical information and defined a vascular enhancement patterns and calculated parameters associated with TCC. It may be a useful, noninvasive and reproducible tool for detecting these tumors in dogs.

DCEUS-based focal parametric perfusion imaging of microvessel with single-pixel resolution and high contrast

This study aimed to develop a focal microvascular contrast-enhanced ultrasonic parametric perfusion imaging (PPI) scheme to overcome the tradeoff between the resolution, contrast, and accuracy of focal PPI in the tumor. Its resolution was limited by the low signal-to-clutter ratio (SCR) of time-intensity-curves (TICs) induced by multiple limitations, which deteriorated the accuracy and contrast of focal PPI. The scheme was verified by the in-vivo perfusion experiments. Single-pixel TICs were first extracted to ensure PPI with the highest resolution. The SCR of focal TICs in the tumor was improved using respiratory motion compensation combined with detrended fluctuation analysis. The entire and focal PPIs of six perfusion parameters were then accurately created after filtrating the valid TICs and targeted perfusion parameters. Compared with those of the conventional PPIs, the axial and lateral resolutions of focal PPIs were improved by 30.29% (p < .05) and 32.77% (p < .05), respectively; the average contrast and accuracy evaluated by SCR improved by 7.24 ± 4.90 dB (p < .05) and 5.18 ± 1.28 dB (p < .05), respectively. The edge, morphostructure, inhomogeneous hyper-enhanced distribution, and ring-like perfusion features in intratumoral microvessel were accurately distinguished and highlighted by the focal PPIs. The developed focal PPI can assist clinicians in making confirmed diagnoses and in providing appropriate therapeutic strategies for liver tumor.

Multifunctional nanoparticles for real-time evaluation of toxicity during fetal development

Increasing production of nanomaterials in industrial quantities has led to public health concerns regarding exposure, particularly among pregnant women and developing fetuses. Information regarding the barrier capacity of the placenta for various nanomaterials is limited due to challenges working with ex vivo human placentas or in vivo animal models. To facilitate real-time in vivo imaging of placental transport, we have developed a novel, multifunctional nanoparticle, based on a core of mesoporous silica nanoparticles (MSN), and functionalized for magnetic resonance imaging (MRI), ultrasound, and fluorescent microscopy. Our MSN particles were tested as a tracking method for harmful and toxic nanomaterials. In gravid mice, intravenous injections of MSN were administered in the maternal circulation in early gestation (day 9) and late gestation (day 14). MRI and ultrasound were used to track the MSN following the injections. Changes in contrast relative to control mice indicated that MSN were observed in the embryos of mice following early gestation injections, while MSN were excluded from the embryo by the placenta following late gestation injections. The timing of transplacental barrier porosity is consistent with the notion that in mice there is a progressive increasing segregation by the placenta in later gestation. In addition, built-in physico-chemical properties of our MSN may present options for the therapeutic treatment of embryonic exposure. For example, if preventive measures such as detoxification of harmful compounds are implemented, the particle size and exposure timing can be tailored to selectively distribute to the maternal side of the trophoblast or delivered to the fetus.

The effect of sedation with a combination of butorphanol and midazolam on quantitative contrast-enhanced ultrasonography of duodenum in healthy dogs

Quantitative contrast-enhanced ultrasonography (CEUS) enables non-invasive and objective evaluation of intestinal perfusion by quantifying the intensity of enhancement on the intestine after microbubble contrast administration. During CEUS scanning, sedation is sometimes necessary to maintain animal cooperation. Nevertheless, the effect of sedative administration on the canine intestinal CEUS is unknown. This study aimed to investigate the effect of sedation with a combination of butorphanol and midazolam on the duodenal CEUS-derived perfusion parameters of healthy dogs. For this purpose, duodenum was imaged following contrast administration (Sonazoid^®, 0.01 ml/kg) in six healthy beagles before and after intravenous injection of a combination of butorphanol (0.2 mg/kg) and midazolam (0.1 mg/kg). Furthermore, hemodynamic parameters including blood pressure and heart rate were recorded during the procedure. Five CEUS derived perfusion parameters including time-to-peak (TTP), peak intensity (PI), area under the curve (AUC), wash-in and wash-out rates (WiR and WoR, respectively) before and after sedation were statistically compared. The result showed that no significant change was detected in any of perfusion parameters. Systolic and mean arterial pressures significantly reduced after sedative administration, but diastolic arterial pressure and heart rate did not significantly change. Moreover, no significant partial correlation was observed between perfusion parameters and hemodynamic parameters. Thus, we concluded that the combination did not cause significant influence in duodenal CEUS perfusion parameters and could be a good option for sedation prior to duodenal CEUS in debilitated dogs.

Development of a Fluid Dynamic Model for Quantitative Contrast-Enhanced Ultrasound Imaging

Contrast-enhanced ultrasound (CEUS) is a non-invasive imaging technique extensively used for blood perfusion imaging of various organs. This modality is based on the acoustic detection of gas-filled microbubble contrast agents used as intravascular flow tracers. Recent efforts aim at quantifying parameters related to the enhancement in the vascular compartment using time-intensity curve (TIC), and at using these latter as indicators for several pathological conditions. However, this quantification is mainly hampered by two reasons: first, the quantification intrinsically solely relies on temporal intensity variation, the explicit spatial transport of the contrast agent being left out. Second, the exact relationship between the acquired US-signal and the local microbubble concentration is hardly accessible. This paper introduces the use of a fluid dynamic model for the analysis of dynamic CEUS (DCEUS), in order to circumvent the two above-mentioned limitations. A new kinetic analysis is proposed in order to quantify the velocity amplitude of the bolus arrival. The efficiency of proposed methodology is evaluated both in-vitro, for the quantitative estimation of microbubble flow rates, and in-vivo, for the classification of placental insufficiency (control versus ligature) of pregnant rats from DCEUS. Besides, for the in-vivo experimental setup, we demonstrated that the proposed approach outperforms the performance of existing TIC-based methods.

Repeatability of Contrast-Enhanced Ultrasonography of the Kidneys in Healthy Cats

Contrast-enhanced ultrasound can be used to image and quantify tissue perfusion. It holds great potential for the use in the diagnosis of various diffuse renal diseases in both human and veterinary medicine. Nevertheless, the technique is known to have an inherent relatively high variability, related to various factors associated with the patient, the contrast agent and machine settings. Therefore, the aim of this study was to assess week-to-week intra- and inter-cat variation of several perfusion parameters obtained with CEUS of both kidneys of 12 healthy cats. Repeatability was determined by calculating the coefficient of variation (CV). The contrast-enhanced ultrasound parameters with the lowest variation for the renal cortex were time-to-peak (CV 6.0%), rise time (CV 13%), fall time (CV 19%) and mean transit time (24%). Intensity-related parameters and parameters related to the slope of the time-intensity curve had a CV of >35%. Lower repeatability was present for perfusion parameters derived from the renal medulla compared with the renal cortex. Normalization to the inter-lobar artery does not cause a reduction in variation. In conclusion, time-related parameters for the cortex show a reasonable repeatability; whereas poor repeatability is present for intensity-related parameters and parameters related to in- and outflow of contrast agent. Poor repeatability is also present for all perfusion parameters for the renal medulla, except for time to peak, which has a good repeatability.

Solid Renal Tumors Isoenhancing to Kidneys on Contrast-Enhanced Sonography: Differentiation From Pseudomasses

OBJECTIVES

To estimate the prevalence of solid renal tumors isoenhancing to kidneys in all vascular phases on contrast-enhanced sonography and to investigate whether they can be differentiated from pseudomasses.

METHODS

A computer search of the databases of 3 institutions identified 31 patients with pseudomasses and 380 patients with solid tumors investigated with contrast-enhanced sonography. Nineteen of 380 (5%) patients had tumors isoenhancing in all phases. Images and clips of these 19 tumors and the 31 pseudomasses were blindly assessed by 2 radiologists. They were asked to differentiate tumors from pseudomasses based on echogenicity, vascular architecture, and the presence of the medulla.

RESULTS

Isoenhancing tumors were clear cell carcinomas (n = 7), angiomyolipomas (n = 3), papillary tumors (n = 3), metastasis (n = 1), and oncocytoma (n = 1). In the 4 nonoperated tumors, the diagnosis was confirmed by progression during the follow-up. There were 3 markedly hyperechoic, 11 mildly hypo/hyperechoic, and 5 isoechoic masses. Most pseudomasses were isoechoic to kidneys (23 of 31), with the medulla identified in 22 of 31 and 15 of 31 by radiologists 1 and 2, respectively. One and 2 pseudomasses were considered tumors by radiologists 1 and 2, respectively. One isoechoic isoenhancing tumor was not identified on contrast-enhanced sonography. Isoenhancing tumors in all phases were differentiated from pseudomasses by combining grayscale and contrast-enhanced sonography (areas under the receiver operating characteristic curve, 0.997 for reader 1; 0.969 for reader 2), with very good inter-reader agreement (weighted κ = 0.81).

CONCLUSIONS

In our retrospective study, 5% of solid renal lesions were isoenhancing to kidneys in all phases. Differentiation from pseudomasses was possible by looking at baseline sonographic features and vascular characteristics.

Quantification of Macrocirculation and Microcirculation in Brain Using Ultrasound Perfusion Imaging

OBJECTIVE

The aim of this study was to investigate the feasibility of simultaneous visualization of the cerebral macrocirculation and microcirculation, using ultrasound perfusion imaging (UPI). In addition, we studied the sensitivity of this technique for detecting changes in cerebral blood flow (CBF).

MATERIALS AND METHODS

We performed an observational study in ten healthy volunteers. Ultrasound contrast was used for UPI measurements during normoventilation and hyperventilation. For the data analysis of the UPI measurements, an in-house algorithm was used to visualize the DICOM files, calculate parameter images and select regions of interest (ROIs). Next, time intensity curves (TIC) were extracted and perfusion parameters calculated.

RESULTS

Both volume- and velocity-related perfusion parameters were significantly different between the macrocirculation and the parenchymal areas. Hyperventilation-induced decreases in CBF were detectable by UPI in both the macrocirculation and microcirculation, most consistently by the volume-related parameters. The method was safe, with no adverse effects in our population.

CONCLUSIONS

Bedside quantification of CBF seems feasible and the technique has a favourable safety profile. Adjustment of current method is required to improve its diagnostic accuracy. Validation studies using a 'gold standard' are needed to determine the added value of UPI in neurocritical care monitoring.

Contrast-Enhanced Ultrasound for Assessing Renal Perfusion Impairment and Predicting Acute Kidney Injury to Chronic Kidney Disease Progression

AIMS

Acute kidney injury (AKI) is increasingly recognized as a major risk factor leading to progression to chronic kidney disease (CKD). However, the diagnostic tools for predicting AKI to CKD progression are particularly lacking. Here, we tested the utility of contrast-enhanced ultrasound (CEUS) for predicting progression to CKD after AKI by using both mild (20-min) and severe (45-min) bilateral renal ischemia-reperfusion injury mice.

RESULTS

Renal perfusion measured by CEUS reduced to 25% ± 7% and 14% ± 6% of the pre-ischemic levels in mild and severe AKI 1 h after ischemia (p < 0.05). Renal perfusion returned to pre-ischemic levels 1 day after mild AKI followed by restoration of kidney function. However, severe AKI caused persistent renal perfusion impairment (60% ± 9% of baseline levels) accompanied by progressive renal fibrosis and sustained decrease in renal function. Renal perfusion at days 1-21 significantly correlated with tubulointerstitial fibrosis 42 days after AKI. For predicting renal fibrosis at day 42, the area under the receiver operating characteristics curve of renal perfusion impairment at day 1 was 0.84. Similar changes in the renal image of CEUS were observed in patients with AKI-CKD progression.

INNOVATION

This study demonstrates that CEUS enables dynamic and noninvasive detection of renal perfusion impairment after ischemic AKI and the perfusion abnormalities shown by CEUS can early predict the progression to CKD after AKI.

CONCLUSIONS

These results indicate that CEUS enables the evaluation of renal perfusion impairment associated with CKD after ischemic AKI and may serve as a noninvasive technique for assessing AKI-CKD progression. Antioxid. Redox Signal. 27, 1397-1411.

Contrast-Enhanced Ultrasound of the Liver: Optimizing Technique and Clinical Applications

OBJECTIVE

The purpose of this article is to review the general principles, technique, and clinical applications of contrast-enhanced ultrasound of the liver.

CONCLUSION

Proper technique and optimization of contrast-enhanced ultrasound require a balance between maintaining the integrity of the microbubble contrast agent and preserving the ultrasound signal. Established and emerging applications in the liver include diagnosis of focal lesions, aiding ultrasound-guided intervention, monitoring of therapy, and aiding surgical management.

Repeatability of Bolus Kinetics Ultrasound Perfusion Imaging for the Quantification of Cerebral Blood Flow

Ultrasound perfusion imaging (UPI) can be used for the quantification of cerebral perfusion. In a neuro-intensive care setting, repeated measurements are required to evaluate changes in cerebral perfusion and monitor therapy. The aim of this study was to determine the repeatability of UPI in quantification of cerebral perfusion. UPI measurement of cerebral perfusion was performed three times in healthy patients. The coefficients of variation of the three bolus injections were calculated for both time- and volume-derived perfusion parameters in the macro- and microcirculation. The UPI time-dependent parameters had overall the lowest CVs in both the macro- and microcirculation. The volume-related parameters had poorer repeatability, especially in the microcirculation. Both intra-observer variability and inter-observer variability were low. Although UPI is a promising tool for the bedside measurement of cerebral perfusion, improvement of the technique is required before implementation in routine clinical practice.

Contrast-Enhanced Ultrasound Examination for the Assessment of Renal Perfusion in Cats with Chronic Kidney Disease

Background

Contrast‐enhanced ultrasound examination (CEUS) is a functional imaging technique allowing noninvasive assessment of tissue perfusion. Studies in humans show that the technique holds great potential to be used in the diagnosis of chronic kidney disease (CKD). However, data in veterinary medicine are currently lacking.

Objectives

To evaluate renal perfusion using CEUS in cats with CKD.

Animals

Fourteen client‐owned cats with CKD and 43 healthy control cats.

Methods

Prospective case‐controlled clinical trial using CEUS to evaluate renal perfusion in cats with CKD compared to healthy control cats. Time‐intensity curves were created, and perfusion parameters were calculated using off‐line software. A linear mixed model was used to examine differences between perfusion parameters of cats with CKD and healthy cats.

Results

In cats with CKD, longer time to peak and shorter mean transit times were observed for the renal cortex. In contrast, a shorter time to peak and rise time were seen for the renal medulla. The findings for the renal cortex indicate decreased blood velocity and shorter total duration of enhancement, likely caused by increased vascular resistance in CKD. Increased blood velocity in the renal medulla has not been described before and may be because of a different response to regulatory factors in cortex and medulla.

Conclusions and Clinical Importance

Contrast‐enhanced ultrasound examination was capable of detecting perfusion changes in cats with CKD. Further research is warranted to assess the diagnostic capabilities of CEUS in early stage of the disease process.

Myocardial contrast echocardiography in mice: technical and physiological aspects

Myocardial contrast echocardiography (MCE) offers the opportunity to study myocardial perfusion defects in mice in detail. The value of MCE compared with single-photon emission computed tomography, positron emission tomography, and computed tomography consists of high spatial resolution, the possibility of quantification of blood volume, and relatively low costs. Nevertheless, a number of technical and physiological aspects should be considered to ensure reproducibility among research groups. The aim of this overview is to describe technical aspects of MCE and the physiological parameters that influence myocardial perfusion data obtained with this technique. First, technical aspects of MCE discussed in this technical review are logarithmic compression of ultrasound data by ultrasound systems, saturation of the contrast signal, and acquisition of images during different phases of the cardiac cycle. Second, physiological aspects of myocardial perfusion that are affected by the experimental design are discussed, including the anesthesia regimen, systemic cardiovascular effects of vasoactive agents used, and fluctuations in body temperature that alter myocardial perfusion. When these technical and physiological aspects of MCE are taken into account and adequately standardized, MCE is an easily accessible technique for mice that can be used to study the control of myocardial perfusion by a wide range of factors.

Evaluation of Renal Perfusion in Hyperthyroid Cats before and after Radioiodine Treatment

Background

Hyperthyroidism and chronic kidney disease (CKD) are common in elderly cats. Consequently, both diseases often occur concurrently. Furthermore, renal function is affected by thyroid status. Because changes in renal perfusion play an important role in functional renal changes in hyperthyroid cats, investigation of renal perfusion may provide novel insights.

Objectives

To evaluate renal perfusion in hyperthyroid cats with contrast‐enhanced ultrasound (CEUS).

Animals

A total of 42 hyperthyroid cats was included and evaluated before and 1 month after radioiodine treatment.

Methods

Prospective intrasubject clinical trial of contrast‐enhanced ultrasound using a commercial contrast agent (SonoVue) to evaluate renal perfusion. Time‐intensity curves were created, and perfusion parameters were calculated by off‐line software. A linear mixed model was used to examine differences between pre‐ and post‐treatment perfusion parameters.

Results

An increase in several time‐related perfusion parameters was observed after radioiodine treatment, indicating a decreased blood velocity upon resolution of the hyperthyroid state. Furthermore, a small post‐treatment decrease in peak enhancement was present in the renal medulla, suggesting a lower medullary blood volume.

Conclusions and Clinical Importance

Contrast‐enhanced ultrasound indicated a higher cortical and medullary blood velocity and higher medullary blood volume in hyperthyroid cats before radioactive treatment in comparison with 1‐month post‐treatment control.

Reproducible Computer-Assisted Quantification of Myocardial Perfusion with Contrast-Enhanced Ultrasound

Myocardial perfusion can be quantified by myocardial contrast echocardiography (MCE) and is used for the diagnosis of coronary artery disease (CAD). However, existing MCE quantification software is highly operator dependent and has poor reproducibility and ease of usage. The aim of this study was to develop robust and easy-to-use software that can perform MCE quantification accurately, reproducibly and rapidly. The developed software has the following features: (i) semi-automatic segmentation of the myocardium; (ii) automatic rejection of MCE data with poor image quality; (iii) automatic computation of perfusion parameters such as myocardial blood flow (MBF). MCE sequences of 18 individuals (9 normal, 9 with CAD) undergoing vasodilator stress with dipyridamole were analysed quantitatively using the software. When evaluated against coronary angiography, the software achieved a sensitivity of 71% and a specificity of 91% for hyperemic MBF. With the automatic rejection algorithm, the sensitivity and specificity further improved to 77% and 94%, respectively. For MBF reproducibility, the percentage agreement is 85% (κ = 0.65) for inter-observer variability and 88% (κ = 0.72) for intra-observer variability. The intra-class correlation coefficients are 0.94 (inter-observer) and 0.96 (intra-observer). The time taken to analyse one MCE sequence using the software is about 3 min on a PC. The software has exhibited good diagnostic performance and reproducibility for CAD detection and is rapid and user-friendly.

Correlation analysis between the parameters of contrast-enhanced ultrasonography in evaluating cervical cancer metastasis and expression of E-cadherin

The study aims to investigate the correlation between the parameters of contrast-enhanced ultrasonography in evaluating cervical cancer metastasis and expression of E-cadherin. All 120 patients with cervical cancer underwent contrast-enhanced ultrasonography. According to the results of postoperative pathological examination, patients were divided into distant metastasis group (group A), lymph node metastasis without distant metastasis group (group B) and no metastasis group (group C). Expression of E-cadherin in cervical cancer tissues was detected by enzyme-linked immunosorbent assay (ELISA). Correlations between the parameters of contrast-enhanced ultrasonography in evaluating cervical cancer metastasis and expression of E-cadherin were analyzed by Pearsons correlation analysis. Comparison of parameters of contrast-enhanced ultrasonography showed that, the baseline intensity of group A was 11.9±2.2 dB, which was significantly lower than that of group B and C. Baseline intensity of group B was significantly lower than that of group C (13.0±2.4 vs. 15.3±3.6 dB), significant differences were found among three groups (P<0.05). The sensitivity and specificity of the use of enhanced intensity ~83.7 dB in evaluating tumor metastasis of patients with cervical cancer were 82.42 and 79.32%, respectively. Expression level of E-cadherin protein in group A was 0.030±0.003 ng/ml, which was significantly lower than that in group B and C (P<0.05), expression level of E-cadherin protein in group A was significantly lower than that in group C (0.037±0.007 vs. 0.045±0.012 ng/ml), significant differences in the expression level of E-cadherin protein were found among the three groups of cervical cancer patients (P<0.05). Pearsons correlation analysis showed that there was a positive correlation between the baseline intensity of contrast-enhanced ultrasonography and the expression level of E-cadherin (P<0.05), while there was a negative correlation between the enhanced intensity of contrast-enhanced ultrasonography and the expression level of E-cadherin (P<0.05). Contrast-enhanced ultrasonography can be used to determine the tumor metastasis of cervical cancer patients, in addition, the combined use of contrast-enhanced ultrasonography and E-cadherin protein expression can significantly improve the diagnosis and treatment of cervical cancer.

A Temporal and Spatial Analysis Approach to Automated Segmentation of Microbubble Signals in Contrast-Enhanced Ultrasound Images: Application to Quantification of Active Vascular Density in Human Lower Limbs

Contrast-enhanced ultrasound (CEUS) using microbubble contrast agents has shown great promise in visualising and quantifying active vascular density. Most existing approaches for vascular density quantification using CEUS are calculated based on image intensity and are susceptible to confounding factors and imaging artefact. Poor reproducibility is a key challenge to clinical translation. In this study, a new automated temporal and spatial signal analysis approach is developed for reproducible microbubble segmentation and quantification of contrast enhancement in human lower limbs. The approach is evaluated in vitro on phantoms and in vivo in lower limbs of healthy volunteers before and after physical exercise. In this approach, vascular density is quantified based on the relative areas microbubbles occupy instead of their image intensity. Temporal features of the CEUS image sequences are used to identify pixels that contain microbubble signals. A microbubble track density (MTD) measure, the ratio of the segmented microbubble area to the whole tissue area, is calculated as a surrogate for active capillary density. In vitro results reveal a good correlation (r² = 0.89) between the calculated MTD measure and the known bubble concentration. For in vivo results, a significant increase (129% in average) in the MTD measure is found in lower limbs of healthy volunteers after exercise, with excellent repeatability over a series of days (intra-class correlation coefficient = 0.96). This compares to the existing state-of-the-art approach of destruction and replenishment analysis on the same patients (intra-class correlation coefficient ≤0.78). The proposed new approach shows great potential as an accurate and highly reproducible clinical tool for quantification of active vascular density.

Image Monitoring of the Impaired Phagocytic Activity of Kupffer Cells and Liver Oxygen Saturation in a Mouse Cholangitis Model Using Contrast-Enhanced Ultrasound Imaging and Photoacoustic Imaging

Bile duct ligation (BDL) can cause cholangitis, which is known to induce impaired Kupffer cell (KC) function and increased oxygen consumption in a mouse model. It is important to monitor changes in KC function and tissue oxygen saturation, both of which are critical factors in the progression of cholangitis. The purpose of this study is to investigate the impaired phagocytic activity of KC and liver oxygen saturation (sO₂) in a mouse cholangitis model using contrast-enhanced ultrasound imaging (CEUS) and photoacoustic imaging (PAI). A mouse cholangitis model was created by ligation of the common bile duct (CBDL, n = 20), and the left intrahepatic bile duct (BDL-L, n = 19), both of which were compared with the non-ligation groups-right lobe measurement group after left intrahepatic bile duct ligation (BDL-R, n = 19) and the control group (n = 14). The echogenicity and sO₂ were measured by CEUS and PAI and the KC fraction was assessed at 1, 2 and 4 wk after ligation. We found a significantly lower echogenicity of the Kupffer phase in the CBDL and BDL-L groups compared with that in the control and BDL-R groups at 2 wk (p < .01). The CBDL and BDL-L groups showed a lower echogenicity than that of the BDL-R group at 4 wk (p < .01). We found a significantly lower sO₂ of the CBDL and BDL-L groups compared with that of the control and BDL-R groups at 4 wk (p < .01). The CBDL and BDL-L groups showed a higher KC fraction than that of the BDL-R and control groups at each time point (p < .01). In conclusion, our study suggests that the Sonazoid CEUS and PAI could be a useful tool for monitoring impaired KC phagocytic activity and the liver hypoxic state.

Interobserver Variation of the Bolus-and-Burst Method for Pancreatic Perfusion with Dynamic - Contrast-Enhanced Ultrasound

PURPOSE

Dynamic contrast-enhanced ultrasound (DCE-US) can be used for calculating organ perfusion. By combining bolus injection with burst replenishment, the actual mean transit time (MTT) can be estimated. Blood volume (BV) can be obtained by scaling the data to a vessel on the imaging plane. The study aim was to test interobserver agreement for repeated recordings using the same ultrasound scanner and agreement between results on two different scanner systems.

MATERIALS AND METHODS

Ten patients under evaluation for exocrine pancreatic failure were included. Each patient was scanned two times on a GE Logiq E9 scanner, by two different observers, and once on a Philips IU22 scanner, after a bolus of 1.5 ml Sonovue. A 60-second recording of contrast enhancement was performed before the burst and the scan continued for another 30 s for reperfusion. We performed data analysis using MATLAB-based DCE-US software. An artery in the same depth as the region of interest (ROI) was used for scaling. The measurements were compared using the intraclass correlation coefficient (ICC) and Bland Altman plots.

RESULTS

The interobserver agreement on the Logiq E9 for MTT (ICC=0.83, confidence interval (CI) 0.46-0.96) was excellent. There was poor agreement for MTT between the Logiq E9 and the IU22 (ICC=-0.084, CI -0.68-0.58). The interobserver agreement for blood volume measurements was excellent on the Logiq E9 (ICC=0.9286, CI 0.7250-0.98) and between scanners (ICC=0.86, CI=0.50-0.97).

CONCLUSION

Interobserver agreement was excellent using the same scanner for both parameters and between scanners for BV, but the comparison between two scanners did not yield acceptable agreement for MTT. This was probably due to incomplete bursting of bubbles in some of the recordings on the IU22.

Ultrasound propagation through dilute polydisperse microbubble suspensions

In a fully nonlinear model of wave propagation through bubbly media, computational complexity arises when the medium contains a polydisperse bubble population. This is because a nonlinear ordinary differential equation governing the bubble response must be solved for the current radius of each bubble size present at every spatial location and at every time step. In biomedical ultrasound imaging, commercial contrast agents typically possess a wide range of bubble sizes that exhibit a variety of differing behaviours at ultrasound frequencies of clinical interest. Despite the advent of supercomputing resources, the simulation of ultrasound propagation through microbubble populations still represents a formidable numerical task. Consequently, efficient computational algorithms that have the potential to be implemented in real time on clinical scanners remain highly desirable. In this work, a numerical approach is investigated that computes only a single ordinary differential equation at each spatial location which can potentially reduce significantly the computational effort. It is demonstrated that, under certain parameter regimes, the approach replicates the fully nonlinear model of an incident ultrasound pulse propagating through a polydisperse population of bubbles with a high degree of accuracy.

Quantitative Three-Dimensional Dynamic Contrast-Enhanced Ultrasound Imaging: First-In-Human Pilot Study in Patients with Liver Metastases

Purpose: To perform a clinical assessment of quantitative three-dimensional (3D) dynamic contrast-enhanced ultrasound (DCE-US) feasibility and repeatability in patients with liver metastasis, and to evaluate the extent of quantitative perfusion parameter sampling errors in 2D compared to 3D DCE-US imaging.

Materials and Methods: Twenty consecutive 3D DCE-US scans of liver metastases were performed in 11 patients (45% women; mean age, 54.5 years; range, 48-60 years; 55% men; mean age, 57.6 years; range, 47-68 years). Pairs of repeated disruption-replenishment and bolus DCE-US images were acquired to determine repeatability of parameters. Disruption-replenishment was carried out by infusing 0.9 mL of microbubbles (Definity; Latheus Medical Imaging) diluted in 35.1 mL of saline over 8 min. Bolus consisted of intravenous injection of 0.2 mL microbubbles. Volumes-of-interest (VOI) and regions-or-interest (ROI) were segmented by two different readers in images to extract 3D and 2D perfusion parameters, respectively. Disruption-replenishment parameters were: relative blood volume (rBV), relative blood flow (rBF). Bolus parameters included: time-to-peak (TP), peak enhancement (PE), area-under-the-curve (AUC), and mean-transit-time (MTT).

Results: Clinical feasibility and repeatability of 3D DCE-US using both the destruction-replenishment and bolus technique was demonstrated. The repeatability of 3D measurements between pairs of repeated acquisitions was assessed with the concordance correlation coefficient (CCC), and found to be excellent for all parameters (CCC > 0.80), except for the TP (0.74) and MTT (0.30) parameters. The CCC between readers was found to be excellent (CCC > 0.80) for all parameters except for TP (0.71) and MTT (0.52). There was a large Coefficient of Variation (COV) in intra-tumor measurements for 2D parameters (0.18-0.52). Same-tumor measurements made in 3D were significantly different (P = 0.001) than measurements made in 2D; a percent difference of up to 86% was observed between measurements made in 2D compared to 3D in the same tumor.

Conclusions: 3D DCE-US imaging of liver metastases with a matrix array transducer is feasible and repeatable in the clinic. Results support 3D instead of 2D DCE US imaging to minimize sampling errors due to tumor heterogeneity.

Contrast Microsphere Destruction by a Continuous Flow Ventricular Assist Device: An In Vitro Evaluation Using a Mock Circulation Loop

OBJECTIVES

Transthoracic echocardiography (TTE) is fundamental in managing patients supported with ventricular assist devices (VAD). However imaging can be difficult in these patients. Contrast improves image quality but they are hydrodynamically fragile agents. The aim was to assess contrast concentration following passage through a VAD utilising a mock circulation loop (MCL).

METHODS

Heartware continuous flow (CF) VAD was incorporated into a MCL. Definity® contrast was infused into the MCL with imaging before and after CF-VAD. 5 mm2 regions of interest were used to obtain signal intensity (decibels), as a surrogate of contrast concentration.

RESULTS

Four pump speeds revealed significant reduction in contrast signal intensity after CF-VAD compared to before CF-VAD (all p < 0.0001). Combined pre- and postpump data at all speeds showed a 22.2% absolute reduction in contrast signal intensity across the CF-VAD (14.8 ± 0.8 dB prepump versus 11.6 ± 1.4 dB postpump; p < 0.0001). Mean signal intensity reduction at each speed showed an inverse relationship between speed and relative reduction in signal intensity.

CONCLUSION

Contrast microsphere transit through a CF-VAD within a MCL resulted in significant reduction in signal intensity, consistent with destruction within the pump. This was evident at all CF-VAD pump speeds but relative signal drop was inversely proportional to pump speed.

Repeatability and reproducibility of quantitative contrast-enhanced ultrasonography for assessing duodenal perfusion in healthy dogs

Contrast-enhanced ultrasonography (CEUS) with microbubbles as a contrast agent allows the visualization and quantification of tissue perfusion. The assessment of canine intestinal perfusion by quantitative CEUS may provide valuable information for diagnosing and monitoring chronic intestinal disorders. This study aimed to assess the repeatability (intraday variability) and reproducibility (interday variability) of quantitative duodenal CEUS in healthy dogs. Six healthy beagles underwent CEUS three times within one day (4-hr intervals) and on two different days (1-week interval). All dogs were sedated with a combination of butorphanol (0.2 mg/kg) and midazolam (0.1 mg/kg) prior to CEUS. The contrast agent (Sonazoid^®) was administered using the intravenous bolus method (0.01 ml/kg) for imaging of the duodenum. Time-intensity curves (TIC) were created by drawing multiple regions of interest (ROIs) in the duodenal mucosa, and perfusion parameters, including the time-to-peak (TTP), peak intensity (PI), area under the curve (AUC), and wash-in and wash-out rates (WiR and WoR, respectively), were generated. Intraday and interday coefficients of variation (CVs) for TTP, PI, AUC, WiR and WoR were <25% (range, 2.27–23.41%), which indicated that CEUS was feasible for assessing duodenal perfusion in healthy sedated dogs. A further study of CEUS in dogs with chronic intestinal disorders is necessary to evaluate its clinical applicability.

Measuring Absolute Blood Perfusion in Mice Using Dynamic Contrast-Enhanced Ultrasound

We investigated the feasibility of estimating absolute tissue blood perfusion using dynamic contrast-enhanced ultrasound (CEUS) imaging in mice. We developed a novel method of microbubble administration and a model-free approach to estimate absolute kidney perfusion, and explored the kidney as a reference organ to estimate absolute perfusion of a neuroblastoma tumor. We performed CEUS on the kidneys of CD1 nude mice using the VisualSonics VEVO 2100 imaging system. We estimated individual kidney blood perfusion using the burst-replenishment (BR) technique. We repeated the kidney imaging on the mice after a week. We performed CEUS imaging of a neuroblastoma mouse xenograft tumor along with its right kidney using two sets of microbubble administration parameters to estimate absolute tumor blood perfusion. We performed statistical tests at a significance level of 0.05. Our estimated absolute kidney perfusion (425 ± 123 mL/min/100 g) was within the range of previously reported values. There was no statistical difference between the estimated absolute kidney blood perfusions from the 2 wk of imaging (paired t-test, p = 0.09). We estimated the absolute blood perfusion in the neuroblastoma tumor to be 16.49 and 16.9 mL/min/100 g for the two sets of microbubble administration parameters (Wilcoxon rank-sum test, p = 0.6). We have established the kidney as a reliable reference organ in which to estimate absolute perfusion of other tissues. Using a neuroblastoma tumor, we have determined the feasibility of estimating absolute blood perfusion in tissues using contrast-enhanced ultrasound imaging.

Dual-Frequency Piezoelectric Endoscopic Transducer for Imaging Vascular Invasion in Pancreatic Cancer

Cancers of the pancreas have the poorest prognosis among all cancers, as many tumors are not detected until surgery is no longer a viable option. Surgical viability is typically determined via endoscopic ultrasound imaging. However, many patients who may be eligible for resection are not offered surgery due to diagnostic challenges in determining vascular or lymphatic invasion. In this paper, we describe the development of a dual-frequency piezoelectric transducer for rotational endoscopic imaging designed to transmit at 4 MHz and receive at 20 MHz in order to image microbubble-specific superharmonic signals. Imaging performance is assessed in a tissue-mimicking phantom at depths from 1 cm [contrast-to-tissue ratio (CTR) = 21.6 dB] to 2.5 cm (CTR = 11.4 dB), in ex vivo porcine vessels, and in vivo in a rodent. The prototyped 1.1-mm aperture transducer demonstrates contrast-specific imaging of microbubbles in a 200- [Formula: see text]-diameter tube through the wall of a 1-cm-diameter porcine artery, suggesting such a device may enable direct visualization of small vessels from within the lumen of larger vessels such as the portal vein or superior mesenteric vein.

Role of Contrast-Enhanced Ultrasound in Diagnosis of Thyroid Nodules in Acoustic Radiation Force Impulse "Gray Zone"

The aim of this study was to evaluate the clinical value of contrast-enhanced ultrasound (CEUS) in the diagnosis of thyroid nodules in the acoustic radiation force impulse (ARFI) "gray zone" (the shear wave velocity is in the range 2.5-3 m/s). ARFI was performed before thyroidectomy in 70 patients with 200 thyroid nodules, and then CEUS was performed in 40 thyroid nodules in the "gray zone." The accuracy of ARFI for the 200 thyroid nodules was 82% (164/200). The accuracy of ARFI for the 40 "gray zone" thyroid nodules was 70% (28/40), whereas the accuracy of CEUS for the "gray zone" thyroid nodules was 90% (36/40). There was a significant difference in accuracy (p < 0.05). CEUS has better accuracy for thyroid nodules in the ARFI "gray zone." CEUS supplemented ARFI in differential diagnosis of benign and malignant thyroid nodules.

Optically and acoustically triggerable sub-micron phase-change contrast agents for enhanced photoacoustic and ultrasound imaging

We demonstrate a versatile phase-change sub-micron contrast agent providing three modes of contrast enhancement: 1) photoacoustic imaging contrast, 2) ultrasound contrast with optical activation, and 3) ultrasound contrast with acoustic activation. This agent, which we name 'Cy-droplet', has the following novel features. It comprises a highly volatile perfluorocarbon for easy versatile activation, and a near-infrared optically absorbing dye chosen to absorb light at a wavelength with good tissue penetration. It is manufactured via a 'microbubble condensation' method. The phase-transition of Cy-droplets can be optically triggered by pulsed-laser illumination, inducing photoacoustic signal and forming stable gas bubbles that are visible with echo-ultrasound in situ. Alternatively, Cy-droplets can be converted to microbubble contrast agents upon acoustic activation with clinical ultrasound. Potentially all modes offer extravascular contrast enhancement because of the sub-micron initial size. Such versatility of acoustic and optical 'triggerability' can potentially improve multi-modality imaging, molecularly targeted imaging and controlled drug release.

Bayesian Quantification of Contrast-Enhanced Ultrasound Images With Adaptive Inclusion of an Irreversible Component

Contrast Enhanced Ultrasound (CEUS) is a sensitive imaging technique to assess tissue vascularity and it can be particularly useful in early detection and grading of arthritis. In a recent study we have shown that a Gamma-variate can accurately quantify synovial perfusion and it is flexible enough to describe many heterogeneous patterns. However, in some cases the heterogeneity of the kinetics can be such that even the Gamma model does not properly describe the curve, with a high number of outliers. In this work we apply to CEUS data the single compartment recirculation model (SCR) which takes explicitly into account the trapping of the microbubbles contrast agent by adding to the single Gamma-variate model its integral. The SCR model, originally proposed for dynamic-susceptibility magnetic resonance imaging, is solved here at pixel level within a Bayesian framework using Variational Bayes (VB). We also include the automatic relevant determination (ARD) algorithm to automatically infer the model complexity (SCR vs. Gamma model) from the data. We demonstrate that the inclusion of trapping best describes the CEUS patterns in 50% of the pixels, with the other 50% best fitted by a single Gamma. Such results highlight the necessity of the use ARD, to automatically exclude the irreversible component where not supported by the data. VB with ARD returns precise estimates in the majority of the kinetics (88% of total percentage of pixels) in a limited computational time (on average, 3.6 min per subject). Moreover, the impact of the additional trapping component has been evaluated for the differentiation of rheumatoid and non-rheumatoid patients, by means of a support vector machine classifier with backward feature selection. The results show that the trapping parameter is always present in the selected feature set, and improves the classification.

A Novel Approach to Detecting Postpartum Hemorrhage Using Contrast-Enhanced Ultrasound

The aim of this study was to estimate the efficacy of contrast-enhanced ultrasound (CEUS) in detecting postpartum hemorrhage (PPH) after cesarean section. This is the first study of CEUS in obstetric hemorrhage. A total of 37 patients, operated at Nagoya University Hospital, underwent CEUS. We evaluated the findings of CEUS, which were qualitatively defined as positive when pooling or leakage of contrast agent was observed in the uterine cavity, by measuring the amount of bleeding during the first 4 h after cesarean section. The time-intensity curve patterns of leaked contrast agents were also analyzed for quantitative prediction of the amount of blood loss. Significant differences between the excessive hemorrhage (N = 7) and non-excessive hemorrhage groups (N = 30) were noted in the occurrence of positive CEUS (p = 0.011). Additionally, mean postpartum blood loss markedly increased in patients with a positive CEUS (p = 0.002). From a quantitative perspective, the time until leakage of contrast agents was detected correlated with the amount of bleeding, but the other characteristics of the time-intensity curve pattern did not provide valuable information. In conclusion, CEUS, which enables bedside assessment and rapid diagnosis, is a promising strategy for the detection of PPH.

A Pilot Clinical Study in Characterization of Malignant Renal-cell Carcinoma Subtype with Contrast-enhanced Ultrasound

Malignant renal cell carcinoma (RCC) is a diverse set of diseases, which are independently difficult to characterize using conventional MRI and CT protocols due to low temporal resolution to study perfusion characteristics. Because different disease subtypes have different prognoses and involve varying treatment regimens, the ability to determine RCC subtype non-invasively is a clinical need. Contrast-enhanced ultrasound (CEUS) has been assessed as a tool to characterize kidney lesions based on qualitative and quantitative assessment of perfusion patterns, and we hypothesize that this technique might help differentiate disease subtypes. Twelve patients with RCC confirmed pathologically were imaged using contrast-enhanced ultrasound. Time intensity curves were generated and analyzed quantitatively using 10 characteristic metrics. Results showed that peak intensity ( p = 0.001) and time-to-80% on wash-out ( p = 0.004) provided significant differences between clear cell, papillary, and chromophobe RCC subtypes. These results suggest that CEUS may be a feasible test for characterizing RCC subtypes.

Entropy of Ultrasound-Contrast-Agent Velocity Fields for Angiogenesis Imaging in Prostate Cancer

Prostate cancer care can benefit from accurate and cost-efficient imaging modalities that are able to reveal prognostic indicators for cancer. Angiogenesis is known to play a central role in the growth of tumors towards a metastatic or a lethal phenotype. With the aim of localizing angiogenic activity in a non-invasive manner, Dynamic Contrast Enhanced Ultrasound (DCE-US) has been widely used. Usually, the passage of ultrasound contrast agents thought the organ of interest is analyzed for the assessment of tissue perfusion. However, the heterogeneous nature of blood flow in angiogenic vasculature hampers the diagnostic effectiveness of perfusion parameters. In this regard, quantification of the heterogeneity of flow may provide a relevant additional feature for localizing angiogenesis. Statistics based on flow magnitude as well as its orientation can be exploited for this purpose. In this paper, we estimate the microbubble velocity fields from a standard bolus injection and provide a first statistical characterization by performing a spatial entropy analysis. By testing the method on 24 patients with biopsy-proven prostate cancer, we show that the proposed method can be applied effectively to clinically acquired DCE-US data. The method permits estimation of the in-plane flow vector fields and their local intricacy, and yields promising results (receiver-operating-characteristic curve area of 0.85) for the detection of prostate cancer.

Oesophageal Doppler guided optimization of cardiac output does not increase visceral microvascular blood flow in healthy volunteers

BACKGROUND

Oesophageal Doppler monitoring (ODM) is used clinically to optimize cardiac output (CO) and guide fluid therapy. Despite limited experimental evidence, it is assumed that increasing CO increases visceral microvascular blood flow (MBF). We used contrast-enhanced ultrasound (CEUS) to assess whether ODM-guided optimization of CO altered MBF.

METHODS

Sixteen healthy male volunteers (62 ± 3·4 years) were studied. Baseline measurements of CO were recorded via ODM. Hepatic and renal MBF was assessed via CEUS. Saline 0·9% was administered to optimize CO according to a standard protocol and repeat CEUS performed. Time-intensity curves were constructed, allowing organ perfusion calculation via time to 5% perfusion (TT5). MBF was assessed via organ perfusion rise time (RT) (5-95%).

RESULTS

CO increased (4535 ± 241 ml/min versus 5442 ± 329 ml/min, P<0·0001) following fluid administration, whilst time to renal (22·48 ± 1·19 s versus 20·79 ± 1·31 s; P = 0·03), but not hepatic (28·13 ± 4·48 s versus 26·83 ± 1·53 s; P = 0·15) perfusion decreased. Time to renal perfusion was related to CO (renal: r = -0·43, P = 0·01). Hepatic nor renal RT altered following fluid administration (renal: 9·03 ± 0·86 versus 8·93 ± 0·85 s P = 0·86; hepatic: 27·86 ± 1·60 s versus 30·71 ± 2·19 s, P = 0·13). No relationship was observed between changes in CO and MBF in either organ (renal: r = -0·17, P = 0·54; hepatic: r = -0·07, P = 0·80).

CONCLUSIONS

ODM-optimized CO reduces time to renal perfusion but does not alter renal or hepatic MBF. A lack of relationship between microvascular visceral perfusion and CO following ODM-guided optimization may explain the absence of improved clinical outcome with ODM monitoring.

Contrast Enhanced Superharmonic Imaging for Acoustic Angiography Using Reduced Form-Factor Lateral Mode Transmitters for Intravascular and Intracavity Applications

Techniques to image the microvasculature may play an important role in imaging tumor-related angiogenesis and vasa vasorum associated with vulnerable atherosclerotic plaques. However, the microvasculature associated with these pathologies is difficult to detect using traditional B-mode ultrasound or even harmonic imaging due to small vessel size and poor differentiation from surrounding tissue. Acoustic angiography, a microvascular imaging technique that utilizes superharmonic imaging (detection of higher order harmonics of microbubble response), can yield a much higher contrast-to-tissue ratio than second harmonic imaging methods. In this paper, two dual-frequency transducers using lateral mode transmitters were developed for superharmonic detection and acoustic angiography imaging in intracavity applications. A single element dual-frequency intravascular ultrasound transducer was developed for concept validation, which achieved larger signal amplitude, better contrast-to-noise ratio (CNR), and pulselength compared to the previous work. A dual-frequency [Pb(Mg_1/3Nb_2/3)O₃]-x[PbTiO₃] array transducer was then developed for superharmonic imaging with dynamic focusing. The axial and lateral sizes of the microbubbles in a 200- [Formula: see text] tube were measured to be 269 and [Formula: see text], respectively. The maximum CNR was calculated to be 22 dB. These results show that superharmonic imaging with a low frequency lateral mode transmitter is a feasible alternative to thickness mode transmitters when the final transducer size requirements dictate design choices.

Quantitative Differences Between the First and Second Injection of Contrast Agent in Contrast-Enhanced Ultrasonography of Feline Kidneys and Spleen

Contrast-enhanced ultrasound is a valuable and safe technique for the evaluation of organ perfusion. Repeated injections of ultrasound contrast agent are often administered during the same imaging session. However, it remains unclear if quantitative differences are present between the consecutive microbubble injections. Therefore, the first and second injection of contrast agent for the left renal cortex, renal medulla and the splenic parenchyma in healthy cats were compared. A lower peak intensity and area under the curve were observed for the first injection of contrast agent in the feline kidney, both for the renal cortex and medulla, and spleen. Moreover, for the renal cortex, the time-intensity curve was steeper after the second injection. Findings from the present study demonstrate that a second injection of contrast agent provides stronger enhancement. The exact mechanism behind our findings remains unclear; however, saturation of the lung macrophages is believed to play an important role.

Effects of size and location of regions of interest examined by use of contrast-enhanced ultrasonography on renal perfusion variables of dogs

OBJECTIVE To determine effects of the size and location of regions of interest (ROIs) in the renal cortex of unsedated dogs on renal perfusion variables determined by use of contrast-enhanced ultrasonography (CEUS). ANIMALS 12 client-owned adult (1.5 to 2 years old) Labrador Retrievers (8 males and 4 females; mean ± SD body weight, 27 ± 1.6 kg). PROCEDURES Each dog received 2 bolus injections of sulfur hexafluoride during CEUS. Three small oval ROIs (area of each ROI, 0.11 cm(2)) located in a row with a distance of 1 mm between adjacent ROIs and 1 large oval ROI (area, 1 cm(2)) that encompassed the 3 smaller ROIs were manually drawn in the renal cortex. The ROIs were located at a depth of 1.5 to 2.0 cm in the near field of the renal cortex. Software analysis of time-intensity curves within each ROI was used to identify peak enhancement, time to peak enhancement, regional blood flow, and mean transit time. RESULTS The location and size of the ROIs of unsedated dogs did not cause significant differences in the mean values of the renal perfusion variables. CONCLUSIONS AND CLINICAL RELEVANCE The development of CEUS has provided a unique means for visually examining and quantifying tissue perfusion. Results of this study indicated that it was possible to use small or large ROIs during renal CEUS to evaluate renal perfusion in dogs.

Quantification of tumor perfusion using dynamic contrast-enhanced ultrasound: impact of mathematical modeling

Dynamic contrast-enhanced ultrasound has been proposed to monitor tumor therapy, as a complement to volume measurements. To assess the variability of perfusion parameters in ideal conditions, four consecutive test-retest studies were acquired in a mouse tumor model, using controlled injections. The impact of mathematical modeling on parameter variability was then investigated. Coefficients of variation (CV) of tissue blood volume (BV) and tissue blood flow (BF) based-parameters were estimated inside 32 sub-regions of the tumors, comparing the log-normal (LN) model with a one-compartment model fed by an arterial input function (AIF) and improved by the introduction of a time delay parameter. Relative perfusion parameters were also estimated by normalization of the LN parameters and normalization of the one-compartment parameters estimated with the AIF, using a reference tissue (RT) region. A direct estimation (rRTd) of relative parameters, based on the one-compartment model without using the AIF, was also obtained by using the kinetics inside the RT region. Results of test-retest studies show that absolute regional parameters have high CV, whatever the approach, with median values of about 30% for BV, and 40% for BF. The positive impact of normalization was established, showing a coherent estimation of relative parameters, with reduced CV (about 20% for BV and 30% for BF using the rRTd approach). These values were significantly lower (p  <  0.05) than the CV of absolute parameters. The rRTd approach provided the smallest CV and should be preferred for estimating relative perfusion parameters.

Targeted Contrast-Enhanced Ultrasound for Inflammation Detection

Molecular imaging is a form of nanotechnology that enables the noninvasive examination of biological processes in vivo. Radiopharmaceutical agents are used to target biochemical markers, permitting their detection and evaluation. Early visualization of molecular variations indicative of pathophysiological processes can aid in patient diagnoses and management decisions. Molecular imaging is performed by introducing into the body molecular probes, which are often contrast agents that have been nanoengineered to target and tether to molecules, thus enabling their radiologic identification. Through a nanoengineering process, ultrasound contrast agents can be targeted to specific molecules, extending ultrasound’s capabilities from the tissue to molecular level. Molecular ultrasound, or targeted contrast-enhanced ultrasound (TCEUS), has recently emerged as a popular molecular imaging technique due to its ability to provide real-time anatomic and functional information without ionizing radiation. However, molecular ultrasound represents a novel form of molecular imaging and consequently remains largely preclinical. This review explores the commonalities of TCEUS across several molecular targets and points to the need for standardization of kinetic behavior analysis. The literature underscores evidence gaps and the need for additional research. The application of TCEUS is unlimited but needs further standardization to ensure that future research studies are comparable.

Premature Destruction of Microbubbles during Voiding Urosonography in Children and Possible Underlying Mechanisms: Post Hoc Analysis from the Prospective Study

The aim of this study is to describe premature microbubbles destruction with contrast-enhanced voiding urosonography (ce-VUS) in children using 2nd-generation ultrasound contrast agents (UCA) and to hypothesize about the reason. 141 children (61 females and 80 males) were included in the study, with mean age of 3.3 years (range 4 weeks–16.0 years), who underwent ce-VUS examination between 2011 and 2014. Premature destruction of the microbubbles in the urinary bladder during ce-VUS was observed in 11 children (7.8%). In all these cases the voiding phase of ce-VUS examination could not be performed because of destroyed UCA microbubbles. This was noted in anxious, crying infants and children with restricted voiding. The premature destruction of ultrasound contrast agent during ce-VUS is an underreported, important limitation of ce-VUS, which prevents evaluation of the voiding phase and the establishment of vesicoureteric reflux (VUR). This was particularly noted in crying infants and children.