ULTRASOUND PERFUSION IMAGING AS A TOOL TO DIRECT PATIENT MANAGEMENT: HUMAN CASE EXAMPLES

摘要

The availability of contrast agents has allowed x-ray computed tomography (CT) and magnetic resonance imaging (MRI) to expand the role imaging from defining and depicting structure of normal and diseased tissues to assessing function. Using intravenous contrast, which is common practice with these two techniques, provides information on the relative vascularity and perfusion of a region within a solid organ or a suspected lesion. With repeated observations the wash-in and washout patterns of the contrast agent allows for gross assessment of the temporal patterns of tissue perfusion and with kinetic modeling the extraction of blood flow, fractional blood volume and the capillary-surface product that describes the rate of equilibration between the vascular and interstitial fluid. The major challenge of CT and MRI is the extremely rapid equilibration between these two compartments. In fact, the intravascular contrast concentration on the venule side of the capillary becomes nearly equal to the interstitial concentration during each pass particularly when capillary flow is slow as may be the case in rumors. This extremely rapid equilibration makes it difficult to model the kinetics because of the limited temporal resolution. Attempts at quantifying tumor response to anti-angiogenesis therapy have had mixed results [1].