COMPARISON OF POWER DOPPLER AND B-SCAN SONOGRAPHY FOR RENAL IMAGING USING A SONOGRAPHIC CONTRAST AGENT

The goal of this study was to evaluate the relative performance of pow er Doppler and B-scan imaging modes in detecting vascular perfusion ch anges resulting from injection of a contrast agent. To allow this comp arison the imaging plane and the contrast agent injection must be the same for both modes. We achieved this by using a rigid transducer hold er and simultaneously recording power Doppler and B-scan images on sep arate videotapes. The kidneys of five adult beagles were scanned to al low a comparison of how power Doppler and B-scan imaging methods monit or changes during the injection of 0.1 ml/kg of a contrast agent, Echo Gen emulsion (Sonus Pharmaceuticals, Bothelll WA). The changes in the images were assessed qualitatively by three radiologists and quantitat ively using a custom-designed image analysis software. All of the radi ologists agreed that no visually detectable changes occurred in B-scan images but that significant changes could be observed in power Dopple r images. Image analysis also indicated a difference between power Dop pler and B-scan images. The change in mean color level of power Dopple r images could be displayed as an indicator dilution curve with a peak enhancement of 46 +/- 16 above the preinjection value. The time at wh ich mean color level peaked was 18 +/- 13 s. The mean color level retu rned to half of the peak value by 69 +/- 42 s and returned to the prei njection baseline value by 148 +/- 73 s. Conversely, B-scan images sho wed statistically insignificant changes, and time measurements could n ot be made. By all measures used to evaluate images, power Doppler ima ging had a greater sensitivity in detecting changes resulting from con trast agent injection than B-scan imaging. This finding indicates that power Doppler imaging of contrast agent injections can be used to map regional differences in flow as well as quantitative measurements of a contrast agent's transit time and has the potential to assess kidney abnormalities associated with renal blood flow.