Error Analysis of a Quantitative Cerebral Blood Flow Measurement Using H215O Autoradiography and Positron Emission Tomography, with Respect to the Dispersion of the Input Function
Journal of Cerebral Blood Flow and Metabolism
The effect of the inaccuracy of the input func tion on CBF measured by the H2150 autoradiographic method was investigated. In H2150 autoradiography the measured input function usually includes a larger disper sion than the true input function, as well as the absolute time axis having been already lost. The time constant of the external dispersion that occurred in our continuous sampling system was evaluated as 10-12 s when the dis persion function was approximated by a monoexponen tial
... ponen tial function. The internal dispersion occurring in arterial lines in a human body was evaluated as 4-6 s. Such dis persion, indispensable in a patient study, was found to produce large errors in calculating CBF, e.g., 5(10) s of the dispersion caused + 15(33) and + 10(20)% systematic With the recent development of positron emis sion tomography (PET), radioactivity in small re gions of tissue can be measured quantitatively. Using mathematical models to describe the physio logical behavior of the specific radioactive tracers, regional CBF and metabolism can be obtained from the radioactivity of blood and regional tissue. The C1502 steady-state method (Frackowiak et aI., 1980) may be one of the most stable and generalized methods to measure CBF. On the other hand, an increasing demand for a quick technique to mea sure CBF prompted H2150 autoradiography (Her scovitch et aI., 1983; Raichle et aI., 1983) as a method overcoming the Cl502 steady-state method.