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Objective: The purpose of this study was to determine if enhanced power Doppler sonography can detect early ischemia of the capital femoral epiphysis induced by hip hyperabduction in piglets and to correlate these findings with angiography., Materials and Methods: Proximal femoral perfusion was evaluated in 18 studies of 10 piglet hips with unenhanced power Doppler sonography, enhanced power Doppler sonography with IV contrast agent, and digital angiography, in neutral position, hyperabduction, and after release to neutral position. Enhancement ratios between pixel intensities of power Doppler sonography and enhanced power Doppler images in each position were calculated. Angiograms were analyzed for differences in flow with changes in hip position., Results: With the piglet in neutral position, power Doppler sonography revealed few vessels in the femoral head. Contrast administration resulted in a temporary marked increase in the visualization of vessels in the femoral head. Quantitative enhanced power Doppler sonography revealed a marked decrease in pixel intensity with abduction (p < 0.001) that was not apparent on unenhanced studies (p = 0.28). The enhancement ratio decreased from 0.45 (mean +/- SD, +/- 0.26) in neutral position to 0.10 (+/- 0.21) after abduction; it returned to 0.41 (+/- 0.14) after release of abduction (p < 0.001 for each comparison). Angiographic studies in hyperabduction revealed a variable level of ischemia., Conclusion: Enhanced power Doppler sonography can be used to visualize the vascular supply to the cartilaginous femoral head in piglets and can detect reversible ischemia induced by hip hyperabduction. These differences correlate with digital angiographic evidence of ischemia.

Objective: Our purpose was to test the feasibility and optimization of contrast-enhanced gray-scale harmonic sonography for the evaluation of focal renal perfusion defects in an animal model., Subjects and Methods: We performed arteriography and contrast-enhanced harmonic sonography on six anesthetized piglets after embolization of each kidney with an autologous clot through the main renal artery. Harmonic images were obtained with continuous (30 Hz) and ECG-triggered acquisition. The two harmonic sonography strategies were compared with respect to the number and conspicuity of devascularized areas, and correlation was made with arteriographic findings., Results: Contrast-enhanced harmonic sonography showed focal areas of absent or diminished vascularity that corresponded closely with perfusion defects seen on angiography. Enhancement ratios to perfused cortex were significantly higher than to devascularized cortex in both continuous (mean +/- SD, 469 +/- 5% versus 102 +/- 8%, p < .0005 by t test) and triggered (673 +/- 7% versus 198 +/- 7%, p < .0001) modes. Triggered acquisition increased the conspicuity of perfusion defects over that obtained with continuous imaging (p < .002 by t test)., Conclusion: Contrast-enhanced harmonic sonography is an effective method of depicting focal renal perfusion defects. Triggered acquisition further improves lesion conspicuity.

Objective: Our goals were to describe and quantify redistribution of renal cortical blood flow during systemic hypotension in rabbits using contrast-enhanced power Doppler sonography and to explore the feasibility of creating real-time regional blood flow maps of the kidney., Materials and Methods: Mild, moderate, and severe systemic hypotension (70%, 50%, and 40% of baseline measurements, respectively) were induced by controlled exsanguination in nine anesthetized rabbits. Sagittal power Doppler sonograms of the kidney were obtained during and after i.v. injection of 0.2 ml per kilogram of body weight of an experimental microbubble-based contrast agent. Doppler sonograms were analyzed for anatomic distribution of contrast agent and changes in mean pixel intensity over time. Cortical time-intensity curves were drawn and the area under the curve was compared with regional renal blood flow as measured by radiolabeled microspheres using linear regression in eight of the nine rabbits during graded hypotension., Results: Graded hypotension resulted in increasing thickness of the nonperfused peripheral cortex (p < .001 by analysis of variance) with preservation of deeper cortical flow on enhanced Doppler sonograms. Other changes included decreased peak enhancement ratios and area under the curve values (p < .0001) and increased time to peak enhancement for cortex (p < .01). We found a strong correlation between cortical area under the curve and regional renal blood flow (r = .86, p < .0001). These changes were not shown without contrast enhancement., Conclusion: Peripheral cortical perfusion is disproportionately affected during systemic hypotension. Contrast-enhanced power Doppler sonography shows potential for depicting changes in regional renal blood flow in real time and without radiation.

Objective: We have used gadolinium-enhanced MR imaging to define the expected normal appearance of the developing cartilaginous epiphyses and physes in neonates, infants, and children and to define the changes with maturity in epiphyseal vascular pattern., Materials and Methods: We analyzed gadolinium-enhanced MR images of 80 normal epiphyses in 48 neonates, infants, and children who were 1 month to 15.5 years old. We studied the differences in enhancement ratios for the epiphyses and physes and the epiphyseal vascular pattern at various development stages. We correlated the MR imaging findings with histologic and injection studies of immature epiphyses., Results: Gadolinium enhancement allowed differentiation between physeal and epiphyseal cartilage and revealed epiphyseal vascular canals. Enhancement proved to be greater in the physeal than in the epiphyseal cartilage (p < .001). In the unossified epiphysis, the vascular canals were mainly parallel. After the development of the secondary ossification center, these canals came to have a radial pattern (p < .0001). Comparison with cadaveric specimens confirmed how, with age, the arrangement of these canals changed. Also, physeal enhancement decreased with physeal closure., Conclusion: Gadolinium-enhanced MR imaging reveals differential enhancement of the physis, epiphyseal vascular canals, and epiphyseal cartilage. The pattern of epiphyseal vessels and degree of enhancement of the physis change with maturity.

Objective: We have studied how gadolinium enhancement of T1-weighted MR images affects the expected normal differences in signal intensity between metaphyseal hematopoietic and epiphyseal fatty marrow. We have also analyzed how enhancement affects the expected normal changes in the MR images of the marrow due to fatty conversion., Materials and Methods: We analyzed gadolinium-enhanced MR images of normal distal femurs in 18 immature rabbits that were 5-11 weeks old and of normal proximal femurs in 18 infants, children, and young adults who were 2 months to 21 years old. In all subjects, we studied the change with age in signal intensity and enhancement ratio of the epiphyseal and metaphyseal marrow. In the rabbits, marrow composition and transformation were histologically verified., Results: On unenhanced T1-weighted MR images of the rabbits and of the infants, children, and young adults, epiphyseal signal intensity always exceeded metaphyseal signal intensity; however, the enhancement ratio was always greater in the metaphysis. The signal intensity in metaphyseal and epiphyseal marrow on unenhanced MR images increased with age. However, enhancement ratios decreased with age in both areas. In the rabbits, histologic studies showed more fatty marrow in the epiphysis than in the corresponding metaphysis and an age-related increase in marrow fat at both sites., Conclusion: In the marrow of the extremities, gadolinium enhancement is greater in the (hematopoietic) metaphysis than in the (fatty) epiphysis. In both areas, enhancement decreases as the marrow becomes more fatty. On T1-weighted images, administration of a gadolinium-containing contrast agent reduces the normal contrast between hematopoietic and fatty marrow and obscures the changes in marrow signal intensity due to fatty conversion.