Development of a simple non-invasive microsphere quantification method for cerebral blood flow using I-123-IMP

In clinical practice, measurement of the rCBF has mainly been conducted by I-123-N-isopropyl-p-iodoamphetamine (I-123-IMP) SPECT using the microsphere (MS) method, with continuous arterial blood sampling. While several non-invasive I-123-IMP quantification methods have been developed, their accuracy has been shown to be lower than that of the MS method. Therefore, a non-invasive quantification method for use in routine clinical practice is being sought. The purpose of this study was to develop a simple non-invasive I-123-IMP quantification method (SIMS method) with a simple input function-determining protocol based on the MS method. The input function for the SIMS method was determined using the administered dose and the integrated lung washout ratio obtained by analyzing the count-time activity curve of the pulmonary artery and lung on dynamic chest images. The mean CBF (mCBF) and input function measured in 80 patients by the SIMS method was compared with those determined using the MS method. A good correlation was observed between the counts measured by continuous arterial blood sampling in the MS method and the estimated counts by image analysis in the new method (r = 0.94, p < 0.01). Similarly, a good correlation was observed between the mCBF values determined by the MS method and the SIMS method (r = 0.83, p < 0.01). The mCBF values determined by the SIMS method were closely consistent with the values obtained by the MS method. This finding indicates the possibility of use of the SIMS method for routine clinical study.