[Application of N-isopropyl-p-[123I] iodoamphetamine quantification of regional cerebral blood flow using iterative reconstruction methods: selection of the optimal reconstruction method and optimization of the cutoff frequency of the preprocessing filter].

In cerebral blood flow tests using N-Isopropyl-p-[123I] Iodoamphetamine "I-IMP, quantitative results of greater accuracy than possible using the autoradiography (ARG) method can be obtained with attenuation and scatter correction and image reconstruction by filtered back projection (FBP). However, the cutoff frequency of the preprocessing Butterworth filter affects the quantitative value; hence, we sought an optimal cutoff frequency, derived from the correlation between the FBP method and Xenon-enhanced computed tomography (XeCT)/cerebral blood flow (CBF). In this study, we reconstructed images using ordered subsets expectation maximization (OSEM), a method of successive approximation which has recently come into wide use, and also three-dimensional (3D)-OSEM, a method by which the resolution can be corrected with the addition of collimator broad correction, to examine the effects on the regional cerebral blood flow (rCBF) quantitative value of changing the cutoff frequency, and to determine whether successive approximation is applicable to cerebral blood flow quantification. Our results showed that quantification of greater accuracy was obtained with reconstruction employing the 3D-OSEM method and using a cutoff frequency set near 0.75-0.85 cycles/cm, which is higher than the frequency used in image reconstruction by the ordinary FBP method.

[Application of collimator broad correction three dimensional ordered subsets expectation maximization for regional cerebral blood flow measurement].

Autoradiography (ARG) has been used for quantitative analysis of the cerebral blood flow using 123I-IMP, and the regional cerebral blood flow (rCBF) can be assessed more accurately with scatter and attenuation correction. Currently, the filtered back projection (FBP) method is generally used for image reconstruction. However, we anticipate obtaining more accurate rCBF by the ordered subsets expectation maximization method with collimator broad correction three dimensional ordered subsets expectation maximization (3D-OSEM). In the present study, we optimized the processing conditions to quantify rCBF using the 3D-OSEM method and compared them with the FBP method. Regarding the method, we determined the subsets and iteration, compared rCBF values using a profile curve, and compared them with the rCBF values obtained by the XeCT (Xenon-enhanced computed tomography)/CBF method. We found that in the 3D-OSEM method using 90 direction collection and 1.72 mm/pixel, the most accurate image was obtained around subset 9 and iteration 10. In addition, as compared to the profile curve and the XeCT/CBF method, the thalamus rCBF was high in the 3D-OSEM method with a good correlation with that of the XeCT/CBF. Accordingly, we concluded that the 3D-OSEM method can improve the decrease in rCBF due to blurring of the distance between the source (i.e., a structure located in the central part of the brain such as the thalamus and the collimator).