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[en] We developed a quantification analysis software program for measuring regional cerebral blood flow (rCBF) at rest and under acetazolamide (ACZ) stress by the modified split-dose (MSD) method with iodine-123 N-isopropyl-p-iodoamphetamine (IMP) and compared the rCBF values measured by the MSD method and by the split dose ¹²³I-IMP SPECT (SD) method requiring one continuous withdrawal of arterial blood. Since the MSD method allows the input of two arterial blood sampling parameter values, the background subtraction procedure for obtaining ACZ-induced images in the MSD method is not identical to the procedure in the SD method. With our software program for rCBF quantification, the resting rCBF values determined by the MSD method were closely correlated with the values measured by the SD method (r=0.94), and there was also a good correlation between the ACZ-induced rCBF values obtained by the MSD method and by the SD method (r=0.81). The increase in rCBF under ACZ stress was estimated to be approximately 26% by the SD method and 38% by the MSD method, suggesting that the MSD method tends to overestimate the increase in rCBF under ACZ stress in comparison with the SD method, but the variability of the rCBF values at rest and during ACZ stress analyzed by the MSD method was smaller than the variability with the SD method. Further clinical studies are required to validate our rCBF quantification analysis program for the MSD method. (author)

[en] The group for the methods in the title herein reported the summary of their investigations on literatures concerning the brain, heart, liver and kidney evaluation. The report consisted of the history, kinetics of the agents, methods for quantitative evaluation and summary for each organ. As for the brain, the quantitative evaluation of cerebral blood flow scintigraphy with ¹²³I-IMP and ^99mTc-HMPAO or -ECD were reviewed to conclude that the present convenient methods are of problems in precision, for which a novel method and/or tracer should be developed. For cardiac functions, there is a method based either on the behavior of tracer in the blood which is excellent in reproducibility, or on the morphology of cardiac wall of which images can be analyzed alternatively by CT and MRI. For these, ¹³¹I-albumin, ^99mTc-albumin, -red blood cells, -MIBI and -tetrofosmin have been used. For myocardium, ²⁰¹Tl has been used to evaluate the ischemic region and, with simultaneous use of ^99mTc-MIBI or -tetrofosmin, the viability. ¹²³I-BMIPP and -MIBG have been developed for myocardial fatty acid metabolism and for cardiac sympathetic nerve functions. Liver functions have been evaluated by the blood elimination rate, hepatic uptake, hepatic elimination and hepatic blood flow with use of ^99mTc-labeled colloids, -PMT and -GSA. Quantitative evaluation of renal functions is now well established with high precision since the kinetic behavior of the tracers, like ^99mTc-DTPA, -MAG3, -DMSA and ¹³¹I-OIH, is simple. (K.H.)

[en] An attenuation correction is necessary to improve quantitative single photon emission computed tomography (SPECT) evaluation. The aim of this study was to evaluate the performance of several different types of commercial attenuation correction algorithms. We investigated the performance of four attenuation correction algorithms using a simulation phantom with and without scatter. The attenuation correction was performed on clinical SPECT workstations: GMS5500/PI (Toshiba), GMS7700/A (Toshiba), e.soft (Siemens), and Xeleris (GE). Then, the effect of the attenuation correction was evaluated using the count profile curve and attenuation coefficient that maintained uniformity of the radioisotope distribution in the uniform region of the images. In the without-scatter condition, the count profile curve showed a similar shape on all workstations. The attenuation coefficients that maintained uniformity were 0.134, 0.133, 0.133, and 0.135 cm^-1 using GMS5500/PI, GMS7700/A, e.soft, and Xeleris, respectively. There was no significant difference among these workstations. With scatter, the attenuation coefficients differed by 0.109-0.121 cm^-1 with the types of attenuation correction algorithms. Without scatter, the effects of the attenuation corrections were equivalent. However, with scatter, a few differences were observed in the effects of correction with several types of algorithms. Therefore, our results suggest that careful evaluation should be considered when different types of clinical SPECT workstations are used. (author)

[en] The CT portion of positron emission tomography (PET)/CT provides attenuation correction of the PET emission scan. This study was performed to evaluate how much the CT tube current can be lowered while still providing attenuation maps on PET images. Two body phantoms (outside diameters of 300 and 500 mm) were used to investigate, and PET/CT acquisitions were performed with an Aquiduo PCA-7000B (Toshiba Medical Systems, Otawara, Japan). The CT scan was performed with the following parameters (120 kVp; 0.5-s rotation; 10, 20, 40, 80, 160, 200, 320, 460 mA). After the CT scan, PET images for ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) (5.3 kBq/mL) were obtained for 4 min/bed position. The linear attenuation coefficients for ¹⁸F-FDG in 300- and 500-mm phantoms, pixel values and SD of CT images, radioactivity concentration values and hot- and cold-sphere contrast on PET images in the 500-mm phantom were evaluated. In the 300-mm phantom, all eight tube currents gave average linear attenuation coefficients of approximately 0.095 cm^-1. In contrast, the average linear attenuation coefficients of the 500-mm phantom at 10, 20, and 40 mA were significantly decreased (0.081, 0.087, and 0.092 cm^-1, respectively; p<0.05) as compared to 0.096 cm^-1 of the other tube currents. Further, CT pixel values decreased 10 and 20 mA. Thus, the background radioactivity concentration values at 10 and 20 mA were substantially underestimated to be 57 and 80%, respectively (p<0.05); the hot-sphere contrast values at 10 and 20 mA were 0.26 and 0.29; the cold-sphere contrast values at 10, 20, and 40 mA were -0.33, -0.16, and 0.08. Although the linear attenuation coefficients in the 300-mm phantom remained the same with varying CT tube currents, the 500-mm phantom yielded significant differences in the range 10-40 mA. Therefore, the CT tube currents for attenuation correction should be adjusted over 40 mA in obese patients. (author)

[en] There are problems with dose management in X-ray computed tomography (CT) because the protocol used for any examination is not always in the same scan range. The purpose of this study was to investigate the usefulness of setting the CT protocol based on the scan range. We evaluated the examination data of patients who underwent plain CT based on a scan range of chest to pelvis and abdomen to pelvis. The previous protocol [Chest-Abdomen Routine] was changed to the current protocols [Chest_-Abdomen] and [Chest_-Pelvis], and the previous protocol of [Abdomen Routine] was changed to the current protocols [Abdomen] and [Abdomen_-Pelvis]. Examination data of height, scan length, volume CT dose index (CTDI_vol), and dose length product (DLP) were obtained from digital imaging and communications in medicine, and radiation dose structured report using Radimetrics. The relationship between patient height and scan range, and CTDI_vol and DLP was indicated in a scatter plot. Standard deviation (SD) of scan length and DLP were compared between current and previous protocols. Outliers were defined as the data exceeding average ±2SD. The SD of scan length decreased by 77.1% on abdomen to pelvis, and the SD of DLP decreased by 65.2% on abdomen to pelvis. The causes of the outliers were CT scan range, scan parameter, arm position, metal implants, and body thickness of patients. Setting CT protocols based on the scan range reduced SD of scan length and DLP. It was helpful for reducing the number of scan range outliers and analyzing the cause of outliers. (author)

[en] The subset number in the ordered subsets expectation maximization (OSEM) method is an important factor because an excellent contrast can be maintained by setting it to high values even if the numbers of iteration are set few, and it contributes to shortening the time required for reconstruction. However, in the setting of subset number neither definite guideline nor the influence on artifact generation has been shown except it is confined to the divisors of projection number. In this study, a basic examination using phantom was performed on the relations of set values of subset number with the artifact generation and the number of collecting projections. The artifact generation and the decrease in uniformity were prominent when the number of projections distributed in one subset ranged 2 to 5. On the other hand, no remarkable influence was observed on the linearity and the contrast of image. These results suggest that the optimum number of projections distributed in one subset are from 6 to 10 and setting to these numbers will contribute to suppress the generation of artifact and to maintain the uniformity, contrast, and linearity in single photon emission computed tomography (SPECT) images. (author)

[en] One-point venous blood sampling method (Mimura, et al.) can evaluate the regional cerebral blood flow (rCBF) value with a high degree of accuracy. However, the method is accompanied by complexity of technique because it requires a venous blood Octanol value, and its accuracy is affected by factors of input function. Therefore, we evaluated the factors that are used for input function to determine the accuracy input function and simplify the technique. The input function which uses the time-dependent brain count of 5 minutes, 15 minutes, and 25 minutes from administration, and the input function in which an objective variable is used as the artery octanol value to exclude the venous blood octanol value are created. Therefore, a correlation between these functions and rCBF value by the microsphere (MS) method is evaluated. Creation of a high-accuracy input function and simplification of technique are possible. The rCBF value obtained by the input function, the factor of which is a time-dependent brain count of 5 minutes from administration, and the objective variable is artery octanol value, had a high correlation with the MS method (y=0.899x+4.653, r=0.842). (author)

[en] In the data sampling in single photon emission computed tomography (SPECT), the continuous rotating acquisition method has high clinical utility. There have been various reports about the optimum sampling step angle for continuous rotating acquisition. Objective evaluation was performed visually and by measuring spatial resolution with a column phantom to find the optimum sampling step angle for continuous rotating acquisition. In locations far from the rotation center, a large sampling step angle produced artificial images with tangential elongation. The spatial resolution was 11.58±0.19 mm full width half maximum (FWHM) as measured at a sampling step angle of 3 degrees and at 10 cm away from the rotation center. Increasing the sampling step angle to more than 3 degrees resulted in an increase of FWHM in the tangential direction. The optimum sampling step angle for continuous rotating acquisition in SPECT needs to be below that calculated from the sampling theorem. (author)

[en] IQ-SPECT is an advanced high-speed SPECT modality for myocardial perfusion imaging (MPI), which uses a multi-focus fan beam collimator with resolution recovery reconstruction. The aim of this study was to compare IQ-SPECT with conventional SPECT in terms of performance, based on standard clinical protocols. In addition, we examined the concordance between conventional and IQ-SPECT in patients with coronary artery disease (CAD). Fifty-three patients, undergoing rest-gated MPI for the evaluation of known or suspected CAD, were enrolled in this study. In each patient, conventional SPECT ("9"9"mTc-tetrofosmin, 9.6 min and "2"0"1Tl, 12.9 min) was performed, immediately followed by IQ-SPECT, using a short acquisition time (4.3 min for "9"9"mTc-tetrofosmin and 6.2 min for "2"0"1Tl). A quantitative analysis was performed on an MPI polar map, using a 20-segment model of the left ventricle. An automated analysis by gated SPECT was carried out to determine the left ventricular volume and function including end-diastolic volume (EDV), end-systolic volume (ESV), and left ventricular ejection fraction (LVEF). The degree of concordance between conventional SPECT and IQ-SPECT images was evaluated according to linear regression and Bland-Altman analyses. The segmental percent uptake exhibited a significant correlation between IQ-SPECT and conventional SPECT (P<0.05). The mean differences in "9"9"mTc-tetrofosmin studies were 1.1±6.6% (apex), 2.8±5.7% (anterior wall), 2.9±6.2% (septal wall), 4.9±6.7% (lateral wall), and 1.8±5.6% (inferior wall). Meanwhile, regarding the "2"0"1Tl-SPECT studies, these values were 1.6±6.9%, 2.0±6.6%, 2.1±5.9%, 3.3±7.2%, and 2.4±5.8%, respectively. Although the mean LVEF in IQ-SPECT tended to be higher than that observed in conventional SPECT (conventional SPECT=64.8±11.8% and IQ-SPECT=68.3±12.1% for "9"9"mTc-tetrofosmin; conventional SPECT= 56.0±11.7% and IQ-SPECT=61.5±12.2% for "2"0"1Tl), quantitative parameters were not significantly different between IQ-SPECT and conventional SPECT. According to the "9"9"mTc-tetrofosmin and "2"0"1Tl protocols, IQ-SPECT images were comparable to and in agreement with conventional SPECT images. Our results suggest that IQ-SPECT is a useful technology for MPI SPECT, and can lead to an increase in scan efficiency and patient comfort