Faculty Bibliography

PURPOSE: To use speckle decorrelation in the presence of ultrasonographic (US) contrast agent as an alternative flow measurement technique to Doppler US. MATERIALS AND METHODS: In vivo and in vitro studies were performed. A tube with flowing saline solution containing contrast agent was positioned horizontally across a US image. The amount of decorrelation between a series of images was recorded. The flow profile across the tube was generated by averaging the decorrelation values and was compared with a Doppler frequency shift image. In addition, B-mode images of six rabbit kidneys were obtained during and after intravenous injection of contrast agent. Images were analyzed to compute the correlation between successive points in time. RESULTS: The velocity profiles across the tube were parabolic, with the fastest flow rates measured in the center of the tube. In the rabbit kidneys, measurements indicated the largest decorrelation rates occurred in the larger vessels. The cortical decorrelation rates were significantly slower than those for the hilar vessels (P < .05) and were relatively angle independent. CONCLUSIONS: Decorrelation flow measurements can be used to estimate flow in vitro and in vivo similar to measurements obtained with Doppler US but with less angle dependence. These measurements could lead to a US perfusion technique.

Improvements in high-resolution gray-scale imaging and clinical expertise performing musculoskeletal ultrasound will undoubtedly continue. Development of digital beam formers, two-dimensional arrays along with exploitation of nonlinear techniques to achieve higher resolution and use of ultrasound contrast to improve flow sensitivity will all contribute to the utility of ultrasound in the musculoskeletal system. It behooves the radiologic community to become familiar with these techniques, not only for economic reasons, but also because of the rich complement of future applications of this modality. The few potential applications mentioned here may only scratch the surface of what is possible. In addition to improved images of tissue morphology, ultrasound may play a role in functional and quantitative assessment of soft tissues. It may likewise play a role in the evaluation of prosthetic implants, bone mineralization, and cartilage integrity. Thus, the role of this modality in future musculoskeletal applications may significantly impact clinical diagnosis and therapy.

OBJECTIVE: We report our initial experience with segmented color Doppler velocity-based estimates of tumor vascularity for various histogically proven soft-tissue masses. SUBJECTS AND METHODS: Color Doppler sonography of 23 histologically proven masses in 22 patients was performed. Digital color Doppler images were acquired directly off the scanner output or from video recordings and stored on a personal computer as 24-bit gray-scale and color composite images. A color Doppler velocity segmentation and analysis algorithm was applied to the digital images, from which we calculated the normalized percentage of color Doppler area. Normalization was determined by expressing color Doppler area as a percentage of the area enclosed by a preselected region of interest. We also calculated mean percentage, SD, and cumulative distribution of color Doppler area, relative to a fixed threshold, for the acquired image data sets. RESULTS: Estimates of mean percentage of color Doppler area showed a dynamic range of at least two or three orders of magnitude between lowest and highest values obtained. A scatterplot of mean percentage of color Doppler area versus SD of percentage of color Doppler area showed a linear monotonic relationship (r2 = .92), illustrating increasing vascular heterogeneity with mean vascularity. Preliminary data also suggest the presence of at least two distinct groups of masses (p < .0001) based on these vascularity estimates. One group corresponds to high-grade lesions in which tumor angiogenesis is expected to be important in predicting biologic behavior. The second group appeared to have little or no relationship to tumor vascularity or was of an intermediate (or lower) histologic grade. CONCLUSION: Quantitative color Doppler estimates of tumor vascularity can be obtained over a wide dynamic range. Such estimates provide a mechanism to assess vascular heterogeneity of soft-tissue tumors. Preliminary data suggest that two biologically distinct groups of masses may be separable on the basis of quantitative velocity-based estimates of tumor vascularity as obtained from color Doppler sonography.

OBJECTIVE: The objective of this study was to evaluate how well high-frequency linear array sonography reveals xanthomas in the Achilles' tendons of individuals with heterozygous familial hypercholesterolemia before the xanthomas enlarge the tendons enough to become palpable. SUBJECTS AND METHODS: Both Achilles' tendons of 23 individuals (18 female and five male; age range, 16-69 years old) who had heterozygous familial hypercholesterolemia but no clinically apparent Achilles' tendon xanthomas were studied with high-frequency linear array sonography. Hypoechoic areas, consistent with xanthomas, were noted. RESULTS: Xanthomas were revealed in 36 (78%) of 46 tendons and 19 (83%) of 23 individuals. CONCLUSION: Sonography reveals Achilles' tendon xanthomas in many individuals with heterozygous familial hypercholesterolemia before the xanthomas are clinically apparent. Because tendon xanthomas in a hypercholesterolemic individual are essentially pathognomonic of heterozygous familial hypercholesterolemia and are a mainstay in its diagnosis, our study suggests that sonography is useful in the early diagnosis of heterozygous familial hypercholesterolemia.

PURPOSE: To determine if power Doppler sonography allows differentiation of infectious from noninfectious hip effusions and thereby obviates joint aspiration. MATERIALS AND METHODS: Twenty-nine consecutive children (30 hips) with sonographically identified hip effusion were prospectively evaluated with power Doppler sonography. Both hips were evaluated in each patient by using identical imaging parameters and were then compared. Medical charts were reviewed to determine the eventual diagnosis. RESULTS: At power Doppler sonography, none of 16 patients with transient synovitis had increased flow in the affected hip compared with the contralateral normal hip. Of 11 patients with septic arthritis, one had asymmetric increased flow, and two others, in whom contralateral comparison images were limited, had probable increased flow. Three patients with miscellaneous diagnoses had symmetric normal flow. CONCLUSION: Because power Doppler sonograms did not depict increased flow in most patients with septic arthritis, normal flow on power Doppler sonograms does not allow exclusion of septic arthritis and should not preclude aspiration when clinically warranted.

The aim of this study was to evaluate the ability of power Doppler sonography to distinguish between hypoechoic fluid and synovium in patients with suspected tenosynovitis. Gray scale sonography and power Doppler sonography were performed on 26 tendons in 24 patients with tenosynovitis and 30 tendons in five asymptomatic volunteers. Peritendinous blood flow was graded on a scale of 0 to 3 and the percentage of the hypoechoic rim that contained blood flow was also noted. In the symptomatic group, flow was demonstrated in more than 50% of the peritendinous hypoechoic rim in 17 of 26 tendons. A positive correlation was found between the power Doppler sonographic grade and the percentage of the rim that had flow. These results suggest that a significant proportion of the hypoechoic rim probably represents vascularized synovium rather than complex fluid.

Power Doppler sonography (PDS) is a recently developed technique that depicts moving blood volume within tissues. The enhanced sensitivity of PDS makes it possible to depict soft tissue vascularity, facilitating its role in the evaluation of musculoskeletal inflammatory diseases. A broad range of new and potential applications of PDS in the musculoskeletal system will be described including its use in the setting of bursal, tendon, articular, and muscle diseases, and in the evaluation of fluid collections and soft tissue masses.

PURPOSE: To normalize the power Doppler ultrasound (US) signal to the expected signal from 100% blood in the calculation of a fractional moving blood volume estimate. MATERIALS AND METHODS: To locate the signal from flowing blood with a consistent backscatter coefficient, the authors estimated the knee of the cumulative Doppler power distribution function. They used a flow-tube phantom to test the use of this knee to locate a radial position that would fall into a region of high shear stress and minimal rouleaux formation. They also studied how well the method normalized fractional moving blood volume estimates of the right renal cortex in a volunteer when simulating different body habitus and in a group of six healthy volunteers to estimate variability. RESULTS: Over five flow velocities and over undersaturated to severely oversaturated receiver gains, the calculated flow-tube area was a mean 89% +/- 7 (+/- standard deviation) of a standard. In humans, the technique normalized the fractional moving blood volume estimates over an 8-dB receiver gain variation; the mean +/- standard deviation of fractional moving blood volume estimates for the six volunteers was 37.6% +/- 3.6. CONCLUSION: Vascularity estimates with power Doppler US are feasible with a normalization scheme based on the cumulative Doppler power distribution function.