[Object] To provide a method for accurately determining cerebral blood flows both in rest state and under medication with less invasive operations.[Solution] Cerebral blood flow is determined based on a formula represented by the following formulas (1) or (2) for a time under medication that continuously follows a resting time. Bt=k1e-k2t3mCf∫t0t3Sτek2τⅆτe-k2dt-t3+k1dmCf∫t3tSτ+Sτ-t3⋅e-k2d⋅t-τⅆτt≥t3∫t5t6Btⅆt=k1k2de-k2t3mCf∫t0t3Sτek2τⅆτ⋅e-k2dt5-t3-e-k2dt6-t3+∫t5t6k1dmCf∫t3tSτ+Sτ-t3⋅e-k2d⋅t-τⅆτdtt≥t3 (B(t): the radiation count at the time of t, t3: the time when a radioisotope medicine is administered, t5: the time when acquisition of the imaging data started for the state under medication, t6: the time when acquisition of the imaging data finished for the state under medication, mCf: a scaling factor, k1: cerebral blood flow rest state, k2: the blood-outflow-rate-constant of brain tissues rest state, k1d: a cerebral blood flow under medication, and k2d: the blood-outflow-rate-constant of brain tissues under medication)
