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Noninvasive Quantification of Cerebral Blood Flow Using ^99mTc-ECD and SPECT

Department of Radiology, Niigata University School of Medicine, Niigata
Department of Research for Nuclear Medicine, Medical System Division, Shimadzu Corporation, Kyoto, Japan

Correspondence: For correspondence or reprints contact: Ikuo Odano, MD, Department of Radiology, Niigata University School of Medicine, Asahimachi 1-757, Niigata 951-8510, Japan.

ABSTRACT

The aim of this study was to develop a simple, noninvasive method for quantifying regional cerebral blood flow (rCBF) using ^99mTc-ethyl cysteinate dimer (ECD) by a single SPECT scan and single venous sampling. Methods: Using a three-compartment model, we introduced the regional brain fractionation index (BFI) ; Cb(T_s)/₀^Ts Ca()d[Ca(t), arterial input; Cb(t), brain activity]. Regional BFI obtained at the optimum time T_s (min) was converted to rCBF using an exponential function, which was obtained by analyzing the relationship between regional BFI and rCBF (= F) obtained by the standard ¹³³Xe inhalation SPECT method. The integral of the concentration of ^99mTc-ECD in arterial blood corrected for physical decay [Ca(t)] in BFI was estimated from a single venous blood sample obtained at the optimum time T_v using the regression line obtained by analyzing the relationship between the integral of Ca(t) and venous sample data. The data come from three groups of patients. The first group of patients (n = 16) underwent a complete ^99mTc-ECD BFI study with measurementof Ca(t) and dynamic SPECT scanning, as well as a ¹³³Xe inhalation study to measure rCBF. The results were used to analyze the relationship between regional BFI and rCBF (obtained with ¹³³Xe) and to determine the optimum time T_s for obtaining BFI. Data from the second group of patients (n = 15) were used to analyze the relationship between the integral of Ca(t) and venous sample data and to determine the optimum time T_v for one-point venous blood sampling. Finally, the third group of patients (8 patients, 10 studies) was used to validate the current method by comparing the results with ¹³³Xe inhalation SPECT. Results: Regional BFI obtained at time T_s = 20 min showed good agreement (r = 0.907; a = 0.552, b = 0.962) with rCBF. The venous sample data obtained at time T_v = 6 min showed a good correlation (r = 0.988) with BFI. In comparing rCBF values thus obtained and those obtained by the ¹³³Xe method, we found a good correlation (r = 0.917, slope = 1.01). Conclusion: The proposed method has three advantages: (a) accurate quantification of rCBF without underestimation in the high flow range, (b) simplicity and noninvasiveness and (c) the ability to use any type of SPECT camera for the study.

Key Words: ^99mTc-ethyl cysteinate dimer • regional cerebral blood flow measurement • SPECT • three-compartment model