High-resolution functional imaging with ultrasound contrast agents based on RF processing in an in vivo kidney experiment

Knowledge of the relative tissue perfusion distribution is valuable in the diagnosis of numerous diseases. Techniques for the assessment of the relati ve perfusion distribution, based on ultrasound (US) contrast agents, have s everal advantages compared to established nuclear techniques. These are, am ong others, a better spatial and temporal resolution, the lack of exposure of the patient to ionizing radiation and the relatively low cost. In the pr esent study, US radiofrequency (RF) image sequences are acquired, containin g the signal intensity changes associated with the transit of a bolus contr ast agent through the microvasculature of a dog kidney. The primary objecti ve is to explore the feasibility of calculating functional images with high spatial resolution, The functional images characterize the transit of the contrast agent bolus and represent distributions of peak time, peak value, transit time, peak area, wash-in rate and wash-out decay constant, For the evaluation of the method, dog experiments were performed under optimized co nditions where motion artefacts were minimized and an IA injection of the c ontrast agent Levovist (R) was employed. It was demonstrated that processin g of RF signals obtained with a 3.5-MHz echo system can provide functional images with a high spatial resolution of 2 mm in axial resolution, 2 to 5 m m in lateral resolution and a slice thickness of 2 mm, The functional image s expose several known aspects of kidney perfusion, like perfusion heteroge neity of the kidney cortex and a different peripheral cortical perfusion co mpared to the inner cortex, Based on the findings of the present study, and given the results of complimentary studies, it is likely that the function al images reflect the relative perfusion distribution of the kidney. (C) 20 01 World Federation for Ultrasound in Medicine & Biology.