A CLINICALLY PRACTICAL METHOD TO ACQUIRE PARAMETRIC IMAGES OF UNIDIRECTIONAL METABOLIC RATES AND BLOOD SPACES

As SPECT imaging has become more quantitative with the advent of the a ttenuation correction, SPECT parametric imaging can become a reality i f the data acquisition and the numeric reduction procedures can be sim plified. Methods: A method that is clinically practical for acquiring quantitative parametric images of unidirectional metabolic rate consta nts and apparent blood space is proposed. Its application to PET imagi ng with FDG was investigated. This procedure requires a short postinje ction waiting period, three sequential imaging scans and one blood sam ple (1 ml) during each scan, obviating the requirements of continuous blood sampling, ''assumed'' rate constants (autoradiographic method) a nd difficult nonlinear regression computations. The effect of the earl y-phase blood input function is computed directly from the image. The clinical procedure is completed 1 hr after FDG injection. The computat ion time for generating 21 metabolic rate image slices and blood space slices is negligible (30 sec after image reconstruction). Preliminary human studies on brain, heart, liver and tumor were performed. Result s: The method was tested on seven normal subjects. The results showed that the rapidly changing early-phase blood input can be derived from the raw image and that the metabolic rate images of this method agreed with the results from the graphical analysis method, using continuous sampling, and with published data from three-compartment models. Conc lusion: This study is clinically more practical and computationally si mpler as a method to acquire parametric images of the metabolic rate c onstant, K-i, and the apparent blood space V-d for unidirectional trac ers. Applying this simple quantitative parametric imaging method to ro utine clinical studies may improve the accuracy of routine clinical ev aluations.