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

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).

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.

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 = 4.245x-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 = 0.990x + 0.552, r = 0.990, n = 231, s.e.e. = 1.340 ml/100 g/min).

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.