Estimation of 123I-IMP arterial blood activity from dynamic planar imaging of the chest using a graph plot method for...

I-123-labeled N-isopropyl-p-iodoamphetamine ((123)I-IMP) is used for the measurement of regional cerebral blood flow (rCBF). A continuous or single arterial blood sampling (ABS) is necessary to estimate an integral of arterial input function (AIF) for the measurement of rCBF by using a microsphere model analysis. Therefore, a method of measuring rCBF without any blood sampling is desired. The aim of this study was to establish a method to estimate the AIF from the time-activity curve of the lungs after an injection of (123)I-IMP, using a regression analysis for the measurement of rCBF without any blood sampling.

Thirty-seven prospective studies in 10 consecutive patients were enrolled. A chest planar dynamic imaging for 3 min and continuous ABS for 5 min after a bolus injection of 167MBq (123)I-IMP were performed in all studies. Data from the chest imaging were analyzed in comparison with ABS data (AIF(5)) in the first 10 studies, and an equation for estimation yielding accurate AIF(5) from the total counts cleared from the lungs, during 5 min after injection of (123)I-IMP (TCL(5)), was derived. The validity of the proposed method was evaluated in the subsequent 27 studies.

A good correlation was obtained between the AIF and TCL by regression analysis in the first 10 studies (r = 0.94, P < 0.001). An equation for the estimation of AIF by the regression analysis in the first 10 studies was defined as follows: estimated AIF = 2147 + 4.174 x TCL(5). In the subsequent 27 studies, a good linear correlation was obtained between the measured and the estimated AIF(5) by using the equation (r = 0.79, P < 0.001).

AIF(5) can be accurately estimated from TCL(5). Therefore, estimated AIF(5) can be used for the measurement of rCBF instead of ABS data.