IMPROVING MR QUANTIFICATION OF REGIONAL BLOOD-VOLUME WITH INTRAVASCULAR T-1 CONTRAST AGENTS - ACCURACY, PRECISION, AND WATER EXCHANGE

The goal of this work was to develop a comprehensive understanding of the relationship between vascular proton exchange rates and the accura cy and precision of tissue blood volume estimates using intravascular T-1 contrast agents. Using computer simulations, the effects of vascul ar proton exchange and experimental pulse sequence parameters on measu rement accuracy were quantified. T-1 and signal measurements made in a rat model implanted with R3230 mammary adenocarcinoma tumors demonstr ated that the theoretical findings are biologically relevant; data dem onstrated that over-simplified exchange models may result in measures of tumor, muscle, and liver blood volume fractions that depend on expe rimental parameters such as the vascular contrast concentration. As a solution to the measurement of blood volume in tissues with exchange t hat is unknown, methods that minimize exchange rate dependence were ex amined. Simulations that estimated both the accuracy and precision of such methods indicated that both the inversion recovery and the transv erse-spoiled gradient echo methods using a ''noexchange'' model provid e the best trade-off between accuracy and precision.