RELATIVE RENAL UPTAKE AND TRANSIT-TIME MEASUREMENTS USING FUNCTIONAL FACTOR IMAGES AND FUZZY REGIONS OF INTEREST

The aim of the study was a quantitative comparison of relative renal u ptake and both the whole-kidney and the parenchymal transit time deriv ed from factor analysis of image sequences and provided by standard cl inical procedures. In order to extract the stable, well-interpretable factors, factor analysis was performed locally in the problem-specific time and spatial windows and the resulting factor images either evalu ated directly as functional images or used as fuzzy regions of interes t (ROIs) for the subsequent extraction of time-activity curves from th e analysed data. The values of relative renal uptake of the left kidne y measured in the functional factor images, which demonstrate the init ial accumulation of activity in renal parenchyma (mean 51.0%), did not differ significantly from the values obtained by a standard method (m ean 51.5%, r = 0.98, P<0.001). Whole-kidney transit time calculated us ing fuzzy ROI curves correlated well with the reference values (r = 0. 84, P<0.001); however, both its mean value (336.5 s) and the standard deviation (151.5 s) were substantially greater than those of the value s provided by a standard procedure (262.8+/-86.9 s). Parenchymal trans it time calculated using ROI curves correlated better with the transit time through a wider corticomedullary region rather than through a na rrow cortical region, which is decisive in a differential diagnosis of renal disorders. In general, values of transit times provided by fact or analysis correlated well with those provided by reference methods b ut with a shift towards the higher numerical values. This may have bee n a consequence of a greater extent of the automatically extracted fuz zy ROIs, or of occasionally delayed accumulation in the upper calyces. Results of the study provide quantitative evidence that the factor an alysis of dynamic data, even without the introduction of prior physiol ogical information, may yield clinically relevant information. However , some basic requirements, such as sufficiently high sampling frequenc y and count rate, adaption of the method to a specific clinical task, and proper selection of time and spatial windows for locally performed analysis, have to be fullfilled if the method is to be successfully a pplied clinically.