Noninvasive estimation of the aorta input function for measurement of tumor blood flow with [O-15]water

Quantitative measurement of tumor blood flow with [O-15]water can be used t o evaluate the effects of tumor treatment over time, Since quantitative flo w measurements require an input function, we developed the profile fitting method (PFM) to measure the input function from positron emission tomograph y images of the aorta. First, a [C-11]CO scan was acquired and the aorta re gion was analyzed, The aorta diameter was determined by fitting the image d ata with a model that includes scanner resolution, the measured venous bloo d radioactivity concentration, and the spillover of counts from the backgro und, The diameter was used in subsequent fitting of [O-15]water dynamic ima ges to estimate the aorta and background radioactivity concentrations. Phan tom experiments were performed to test the model. Image quantification bias es (up to 15%) were found for small objects, particularly for those in a la rge elliptical phantom, However, the bias in the PFM concentration estimate s was much smaller (2%-6%), A simulation study showed that PFM had less bia s and/or variability in flow parameter estimates than an ROI method, PFM wa s applied to human [C-11]CO and [O-15]water dynamic studies with left ventr icle input functions used as the gold standard. PFM parameter estimates had higher variability than found in the simulation but with minimal bias, The se studies suggest that PFM is a promising technique for the noninvasive me asurement of the aorta [O-15]water input function.