Rapid 3-D imaging of contrast flow: application in a perfused kidney phantom

Soft Phantom for the Training of Renal Calculi Diagnostics and Lithotripsy

Organ models are important for medical training and surgical planning. With the fast development of additive fabrication technologies, including 3D printing, the fabrication of 3D organ phantoms with precise anatomical features becomes possible. Here, we develop the first high-resolution kidney phantom based on soft material assembly, by combining 3D printing and polymer molding techniques. The phantom exhibits both the detailed anatomy of a human kidney and the elasticity of soft tissues. The phantom assembly can be separated into two parts on the coronal plane, thus large renal calculi are readily placed at any desired location of the calyx. With our sealing method, the assembled phantom withstands a hydraulic pressure that is four times the normal intrarenal pressure, thus it allows the simulation of medical procedures under realistic pressure conditions. The medical diagnostics of the renal calculi is performed by multiple imaging modalities, including X-ray, ultrasound imaging and endoscopy. The endoscopic lithotripsy is also successfully performed on the phantom. The use of a multifunctional soft phantom assembly thus shows great promise for the simulation of minimally invasive medical procedures under realistic conditions.

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.

High Resolution Ultrasound Superharmonic Perfusion Imaging: In Vivo Feasibility and Quantification of Dynamic Contrast-Enhanced Acoustic Angiography

Mapping blood perfusion quantitatively allows localization of abnormal physiology and can improve understanding of disease progression. Dynamic contrast-enhanced ultrasound is a low-cost, real-time technique for imaging perfusion dynamics with microbubble contrast agents. Previously, we have demonstrated another contrast agent-specific ultrasound imaging technique, acoustic angiography, which forms static anatomical images of the superharmonic signal produced by microbubbles. In this work, we seek to determine whether acoustic angiography can be utilized for high resolution perfusion imaging in vivo by examining the effect of acquisition rate on superharmonic imaging at low flow rates and demonstrating the feasibility of dynamic contrast-enhanced superharmonic perfusion imaging for the first time. Results in the chorioallantoic membrane model indicate that frame rate and frame averaging do not affect the measured diameter of individual vessels observed, but that frame rate does influence the detection of vessels near and below the resolution limit. The highest number of resolvable vessels was observed at an intermediate frame rate of 3 Hz using a mechanically-steered prototype transducer. We also demonstrate the feasibility of quantitatively mapping perfusion rate in 2D in a mouse model with spatial resolution of ~100 μm. This type of imaging could provide non-invasive, high resolution quantification of microvascular function at penetration depths of several centimeters.

Fulminant musculoskeletal and neurologic sarcoidosis: case report and literature update

We report a case of fulminant sarcoidosis in a 28-year-old man presenting with skin nodules, multifocal small and large joint arthralgias, and blurred vision. Characteristic bone, soft tissue, articular, and CNS findings were evident on multimodality imaging. Bony abnormalities included near-complete destruction of a distal phalanx, "lace-like" lucent lesions, erosive arthritis, lytic lesions with and without sclerotic margins, and bone marrow replacement visible only on MRI. The extent of bony disease at time of presentation was unusual. We review the widely varying reported prevalence of imaging findings of bony sarcoidosis in the literature, and discuss reasons for this variability. We found that musculoskeletal findings at US and MRI were less specific than radiographic and CT findings, but were useful in quantifying extent of disease.

Extrapulmonary manifestations of sarcoidosis

Sarcoidosis is a systemic disease characterized by the development of epithelioid granulomas in various organs. Although the lungs are involved in most patients with sarcoidosis, virtually any organ can be affected. Recognition of extrapulmonary sarcoidosis requires awareness of the organs most commonly affected, such as the skin and the eyes, and vigilance for the most dangerous manifestations, such as cardiac and neurologic involvement. In this article, the common extrapulmonary manifestations of sarcoidosis are reviewed and organ-specific therapeutic considerations are discussed.

Quantitative volumetric perfusion mapping of the microvasculature using contrast ultrasound

OBJECTIVES

Contrast-enhanced ultrasound imaging has demonstrated significant potential as a noninvasive technology for monitoring blood flow in the microvasculature. With the application of nondestructive contrast imaging pulse sequences combined with a clearance-refill approach, it is possible to create quantitative time-to-refill maps of tissue correlating to blood perfusion rate. One limitation to standard two-dimensional (2D) perfusion imaging is that the narrow elevational beamwidth of 1- or 1.5-D ultrasound transducers provides information in only a single slice of tissue, and thus it is difficult to image exactly the same plane from study to study. We hypothesize that inhomogeneity in vascularization, such as that common in many types of tumors, makes serial perfusion estimates inconsistent unless the same region can be imaged repeatedly. Our objective was to evaluate error in 2D quantitative perfusion estimation in an in vivo sample volume because of differences in transducer positioning. To mitigate observed errors due to imaging plane misalignment, we propose and demonstrate the application of quantitative 3-dimensional (3D) perfusion imaging. We also evaluate the effect of contrast agent concentration and infusion rate on perfusion estimates.

MATERIALS AND METHODS

Contrast-enhanced destruction-reperfusion imaging was performed using parametric mapping of refill times and custom software for image alignment to compensate for tissue motion. Imaging was performed in rats using a Siemens Sequoia 512 imaging system with a 15L8 transducer. A custom 3D perfusion mapping system was designed by incorporating a computer-controlled positioning system to move the transducer in the elevational direction, and the Sequoia was interfaced to the motion system for timing of the destruction-reperfusion sequence and data acquisition. Perfusion estimates were acquired from rat kidneys as a function of imaging plane and in response to the vasoactive drug dopamine.

RESULTS

Our results indicate that perfusion estimates generated by 2D imaging in the rat kidney have mean standard deviations on the order of 10%, and as high as 22%, because of differences in initial transducer position. This difference was larger than changes in kidney perfusion induced by dopamine. With application of 3D perfusion mapping, repeatability in perfusion estimated in the kidney is reduced to a standard deviation of less than 3%, despite random initial transducer positioning. Varying contrast agent administration rate was also observed to bias measured perfusion time, especially at low concentrations; however, we observed that contrast administration rates between 2.7 × 10(8) and 3.9 × 10(8) bubbles/min provided results that were consistent within 3% for the contrast agent type evaluated.

CONCLUSIONS

Three-dimensional perfusion imaging allows a significant reduction in the error caused by transducer positioning, and significantly improves the reliability of quantitative perfusion time estimates in a rat kidney model. When performing perfusion imaging, it is important to use appropriate and consistent contrast agent infusion rates to avoid bias.

Validation of dynamic contrast-enhanced ultrasound in rodent kidneys as an absolute quantitative method for measuring blood perfusion

Contrast-enhanced ultrasound (CEUS) has demonstrated utility in the monitoring of blood flow in tissues, organs and tumors. However, current CEUS methods typically provide only relative image-derived measurements, rather than quantitative values of blood flow in milliliters/minute per gram of tissue. In this study, CEUS derived parameters of blood flow are compared with absolute measurements of blood flow in rodent kidneys. Additionally, the effects of contrast agent infusion rate and transducer orientation on image-derived perfusion measurements are assessed. Both wash-in curve and time-to-refill algorithms are examined. Data illustrate that for all conditions, image-derived flow measurements were well-correlated with transit-time flow probe measurements (R > 0.9). However, we report differences in the sensitivity to flow across different transducer orientations as well as the contrast analysis algorithm utilized. Results also indicate that there exists a range of contrast agent flow rates for which image-derived estimates are consistent.

Subcutaneous sarcoidosis: report of two cases and review of the literature

Sarcoidosis is a multisystemic disease with cutaneous lesions present in about one fourth of patients. Cutaneous lesions may be specific or nonspecific based on the presence or the absence of sarcoidal granulomas. Subcutaneos sarcoidosis is the less frequent of the specific cutaneous lesions of sarcoidosis. We report here 2 new cases and review 83 cases reported in literature of subcutaneous sarcoidosis. Subcutaneous sarcoidosis present usually with asymptomatic firm nodules covered by normal-appearing skin, mostly on the forearms and legs. Diagnosis may require a high index of suspicion. In the vast majority of patients, subcutaneous nodules were the manifestation that allowed the diagnosis of systemic sarcoidosis. There is a strong association between subcutaneous sarcoidosis and bilateral hilar lymphadenopathy (72.7%). About 15% of patients have in order of frequency uveitis, parotitis, arthritis, mucositis, dactylitis, neurological and renal involvement, hepatosplenomegaly.