Measurement of blood radioactivity for quantification of cerebral blood flow using a gamma camera

Objective: This study was designed to determine whether gamma cameras can be substituted for well-type scintillation counters in measuring blood radioactivity counts to be used as an input function for the quantitative measurement of cerebral blood flow (CBF). Methods: Twelve different aqueous ¹²³I solutions were prepared by serial dilution of the original concentration of 281.9 kBq/ml, and the radioactivity count of each dilution was measured with a gamma camera with the collimator removed, and with a well-type scintillation counter. When measuring the radioactivity counts with a gamma camera, static images were acquired using a 128 x 128 matrix for 5 min, and the regions of interest with 14 x 14 pixels (21 mm x 21 mm) were defined. Results: There was a good correlation between the results obtained by these two procedures in the range of concentration between 0.008 kBq/ml and 281.9 kBq/ml (y = 4.245χ - 2.549, r = 1.0, n = 12, s.e.e. = 7.217 kcpm). There was good agreement between the CBF values (ml/100 g/min) obtained using the cross-calibration factor (CCF) and blood radioactivity counts measured with the two procedures (y = 0.990χ + 0.552, r = 0.990, n = 231, s.e.e. = 1.340 ml/100 g/min). Conclusion: The results suggest that gamma cameras can be substituted for well-type scintillation counters in the quantitative measurement of CBF, and make it unnecessary to measure CCF after routine calibration of a SPECT apparatus.