Hideo Onishi

Prefectural University of Hiroshima, Hirosima, Hiroshima, Japan

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Publications (22)3.01 Total impact

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    ABSTRACT: The aim of this study was to investigate an appropriate analysis method and multicenter reproducibility of heart-to-mediastinum ratio (H/M) and washout rate (WR) in iodine-123-labeled metaiodobenzylguanidine ((123)I-MIBG) myocardial scintigraphy with a phantom. We evaluated the optimal region of interest (ROI) setting method about the mediastinum and heart by varying the position and shape of the ROI. The mathematical method was changed to a combination of decay time correction (DTC) and background correction (BC). We evaluated the reproducibility of the H/M and WR between institutions. H/M decreased to 23.49% and WR increased to 20.68% by changing the mediastinum ROI position from upper to lower. H/M increased to 26.03% by changing the heart ROI position from base to apex. H/M decreased to 38.36% with BC, and WR was reduced up to 48.51% with DTC. Reproducibility of the H/M and WR between institutions was improved by performing optimization of the ROI setting and unification of the mathematical method. The position of the mediastinum ROI should be set on the upper mediastinum. The position of the heart ROI should be set on the apex of the heart. WR should be calculated with DTC and BC. Our results suggest that the reproducibility of the H/M and WR between institutions was improved by performing optimization of the ROI setting and unification of the mathematical method.
    Nippon Hoshasen Gijutsu Gakkai zasshi 12/2014; 70(12):1420-8. DOI:10.6009/jjrt.2014_JSRT_70.12.1420
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    ABSTRACT: Unlabelled: The purpose of this study was to evaluate the relationship of body habitus, blood glucose level and injected dose, respectively, with BGO (Bi₄Ge₃O₁₂) positron emission tomography (PET) image quality using commercially available 2-deoxy-2-[¹⁸F] fluoro-D-glucose (FDG). We also evaluated the relationship between PET image quality and acquisition time for each weight group. Method: One hundred twenty-five patients (66 male, 59 female) were enrolled in the study. We adopted liver signal-to-noise ratio (liver SNR) as an image quality index, derived from the region of interest (ROI) placed on the axial image of the liver. Results: The correlation coefficient between liver SNR and dose per weight was 0.502. The liver SNR indicated a negative relationship with body weight, body mass index (BMI) and cross sectional area of the patient's body, with the correlation coefficients of -0.594, -0.479 and -0.522, respectively. For all weight groups, an extended acquisition time of at least 60 s/bed was necessary to improve liver SNR. Conclusion: The findings of this study are potentially of use for designing imaging protocols for the BGO-PET/CT system when using commercially available FDG. It is easy to obtain good image quality for patients of low to average body size with the standard injection dose. However, large patients should be injected, wherever possible, with an FDG dose of up to 5 MBq/kg. The acquisition time in overweight and obese patients should be as longer as possible than in standard weight patients.
    Nippon Hoshasen Gijutsu Gakkai zasshi 08/2014; 70(8):784-92. DOI:10.6009/jjrt.2014_JSRT_70.8.784
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    ABSTRACT: Purpose: Massive calcification complicates the diagnosis of the blood vessel lumen in computed tomography angiography (CTA) of the arteries of the lower extremities. The purpose of this study was to evaluate subtraction CTA with the use of orbital synchronized helical scanning (OS-SCTA). Method: Phantom study: We performed OS-SCTA and non-OSCTA of a calcified vessel phantom (ψ2.5 mm), and compared them with a non-calcified vessel phantom as the reference by full width at half maximum (FWHM) and full width at tenth maximum (FWTM) of maximum intensity projection (MIP) images. Clinical study: 58 patients with peripheral artery disease who were referred for angiography also underwent OS-SCTA. OS-SCTA was produced using MIP images. Findings were graded according to three categories: (1) stenosis greater than 50% or occluded; (2) stenosis less than 50%; (3) not detected due to insufficient image quality. OS-SCTA findings were compared with the angiographic findings for each arterial segment. Results: In the phantom study, FWHM showed no significant difference between OS-SCTA and the reference (P=0.135), whereas FWTM showed a significant difference (P<0.001). FWHM and FWTM showed a significant difference between non-OS-SCTA and the reference (P<0.001), due to misregistration with helical artifacts. In a clinical study comparing OS-SCTA with angiography, the sensitivity and specificity were 93.3% and 95.1% in calcified segments, 91.8% and 93.9% in non-calcified segments, and 92.2% and 94.6% in all segments. There was no significant difference between calcified segments and non-calcified segments (sensitivity: P=0.568, specificity: P=0.549). Conclusion: OS-SCTA is beneficial for the diagnosis of lower extremity arteries with vessel wall calcification, since it shows detection accuracy comparable to that of angiography.
    Nippon Hoshasen Gijutsu Gakkai zasshi 10/2013; 69(10):1119-29. DOI:10.6009/jjrt.2013_JSRT_69.10.1119
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    ABSTRACT: Purpose: The aim of this study was evaluate to impact of standardized uptake value (SUV) on the body trunk with truncation error of μ-map for CT attenuation correction (CTAC) in whole-body 2-deoxy-2-[(18)F] fluoro-D-glucose ((18)F-FDG)-positron emission tomography (PET)/CT with use of anthropomorphic phantom. Methods: We used body phantom (2.5 MBq/l) including simulated tumor targets (11.25 MBq/l) and arm phantom. The CT scan was used with a field of view (FOV) of 50 cm. The μ-maps were created by assuming a state of the arm protruding from the FOV (Pmap). A 3D-PET scan with an emission time of 20 min was performed. The PET images were then reconstructed with CTAC, and with and without scatter correction. We evaluated the relationship to Pmap size and the count of simulated tumors and background (B.G.) in PET images which reconstructed the use of each Pmap, respectively. Results: The count of simulated tumor (large) with scatter correction was decreased to 1.3% (Pmap: 15 mm) and 8.8% (Pmap: 35 mm). Then, the count severe reduction was 86.9% in Pmap of 65 mm. The same trend was shown by simulated tumor (middle, small) and B.G. The count of the simulated tumor (large) without scatter correction decreased to 1.3% (Pmap: 15 mm), 6.4% (Pmap: 35 mm) and 13.1% (Pmap: 65 mm). Conclusion: Truncation error by μ-map for CTAC in whole-body (18)F-PET/CT caused a decrease of the SUV on the body trunk used for attenuation and scatter correction in the PET images.
    Nippon Hoshasen Gijutsu Gakkai zasshi 03/2013; 69(2):178-83. DOI:10.6009/jjrt.2013_JSRT_69.2.178
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    ABSTRACT: Purpose: The wavelet transform is a newly developed signal-processing tool that decomposes a signal into various levels of resolution. The wavelet transform based noise reduction has the characteristics of optimally separating signal from noise, preserving the rapid rises and falls of a signal, and reconstructing a smooth signal from noise-imposed observations. The aim of this study was to evaluate the effects of applying a new noise reduction technique, the wavelet transform based noise reduction, to single photon emission computed tomography (SPECT) images. Methods: Three experiments were performed using cylindrical phantom, line source, and hot-rod phantom, respectively. We acquired SPECT image datasets of each phantom, and reconstructed SPECT images using the wavelet transform based noise reduction with filter back projection (FBP). Images were de-noised by 3 parameters of wavelet transform based noise reduction: 1st wavelet weight (WW), 2nd WW, and 3rd WW, respectively. We evaluated the variances of full width at half maximum (FWHM), coefficients of variation (%CV), and frequency domains (radius direction distribution function in the power spectrum), respectively. Results: In the cylindrical phantom test, %CV was reduced from 27.92% to 15.38% using the wavelet approach. On the other hand, FWHM values showed no significant change. However, the increases of wavelet weights caused artifacts on the reconstructed images in some cases. Conclusions: The wavelet based noise reduction had the significant potential to improve SPECT image. Therefore, the wavelet method should prove to be a robust approach to improve image quantification and fidelity.
    Nippon Hoshasen Gijutsu Gakkai zasshi 01/2013; 69(1):49-57. DOI:10.6009/jjrt.2013_JSRT_69.1.49
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    ABSTRACT: This study aims to evaluate the fundamental performance of four leading advanced resolution recovery methods. To evaluate the performance of the resolution recovery algorithm, we carried out the computer simulation with the cone/sphere digital phantoms. These phantoms were used to investigate the basic properties of those algorithms. The software of four packages (advance) were also tested, specifically Astonish(TM) (AST), Evolution(TM) (EVL), Flash-3D(TM) (FL3), and 3D-OSEM (3DOS). The performance was evaluated in the collimator systems (LEHR) reconstruction conditions using the full width at half maxi am (FWHM), aspect ratio (ASR), and artifacts of conical part. In the "without BG," FWHM of the advance method indicated a true-FWHM with SI (subset×iteration)=20, 40. As SI increased, FWHM was composed with over estimate. Each advances of FWHM indicated only 5% of improvement as compared with reference FWHM in the "with BG." The ASR increased 20% to AST, FL3, and ASR of 3DOS remained in 10% in the outside. As for the reproducibility of the conical part, an artifact was caused by the FL3, EVL, and AST methods. This artifact did not occur in 3DOS. An SI needs more than 150 to obtain an accurate compensation effect. As for the advance method, the major compensation effect was not demonstrated very much as compared with the OS-EM. The EVL, FL3, and AST overestimated values due to a Gibb's oscillation in the artifacts of the conical part.
    Nippon Hoshasen Gijutsu Gakkai zasshi 07/2012; 68(6):686-96. DOI:10.6009/jjrt.2012_JSRT_68.6.686
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    ABSTRACT: Several resolution recovery (RR) methods have been developed. This study was aimed to validate the following performance of the advanced RR methods: Evolution™, Astonish™, Flash3D™, and 3D-OSEM. We compared the advanced RR method with filtered back projection (FBP) and standard order-subset expectation maximization (OSEM) using resolution (RES), cylinder/sphere (CYS), and myocardial (MYD) digital phantoms. The RES phantom was placed in three spheres. Sixteen spheres (hot and cold) were then placed in a concentric configuration (diameter: 96-9.6 mm) inside the CYS phantom. The MYD phantom was created by computer simulation with the use of an electron γ-shower 4 (EGS4) and it included two left ventricular defects in the myocardium. The performance was evaluated at source-to-detector distances (R-distance) of 166, 200, and 250 mm with reconstruction parameters (product of subset and iteration: SI) with use of the resolution recovery factor, count recovery, normalized mean square error (NMSE), and %CV. According to increased SI updates, the value of the FWHM decreased, and the effect was more obvious as the R-distance increased. The spatial resolution of the advanced RR method was 20 % better than that of FBP and OSEM. The resolution recovery ratio was 80 %, and the count recovery was maintained only in objects with a diameter of >30 mm in the advanced RR method. The NMSE and %CV was 50 and 30 % improved over FBP and OSEM, respectively. The advanced RR method caused overestimation due to Gibbs's phenomenon in the marginal region when the diameter of the sphere was 16-28.8 mm.
    Radiological Physics and Technology 07/2012; 6(1). DOI:10.1007/s12194-012-0168-z
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    ABSTRACT: A normal perfusion database (NDB) is imperative for the statistical imaging of brain function. This study validates a novel NDB created under the same injection dose and acquisition conditions for three gamma camera systems and evaluates optimal pre-filter parameters for three-dimensional stereotactic surface projections (3D-SSPs). We compared a novel NDB that matched the databases in each of three vendor gamma camera systems with a conventionally constructed NDB (conventional NDB) and a NDB constructed in-house for 3D-SSP. We generated hypoperfused regions where pre-specified volumes were simulated for various areas in SPECT images. The properties of each NDB were evaluated based on the distribution of the standard deviation (SD). Abnormal accumulation regions were validated using Z, extent, and artifactual scores. Detection error was used to evaluate the optimal Butterworth pre-filter cutoff frequency with the perfusion defect rate (PDR) in 3D-SSP. The SD distribution was the same in the novel NDB and in the NDB constructed in-house, and the SD of the peak distribution was 0.08-0.07. The Z and extent scores of the novel DB and the NDB constructed in-house were similar, but increased along with the artifactual scores when using the conventional NDB. Many artifacts appeared in the Z score map when using the conventional NDB. The detection error deviated from the actual value by -1.3% at a cutoff frequency of 0.58 cycles/cm and a PDR of 30%, which was the lowest. The cutoff frequency became lower or higher, and the low-perfusion defect rate increased according to the increasing detection error. The optimal cutoff frequency was between 0.52 and 0.58 cycles/cm. We generated a novel NDB according to the individual devices and compared it with a conventional and a NDB constructed in-house. The Z and extent scores were essentially equal when using the novel DB and the NDB constructed in-house, but considerably differed when using the conventional NDB. The optimal cutoff frequency of the Butterworth filter evaluated from the detection error was in the range of 0.52-0.58 cycles/cm. The detection error increased the perfusion defect rate by <15% and this was undetectable in 3D-SSP. The next step will be to improve the accuracy of the extent of abnormal regions and the sensitivity of the Z score using a novel NDB constructed according to the individual devices.
    Annals of Nuclear Medicine 09/2011; 26(1):16-25. DOI:10.1007/s12149-011-0534-7 · 1.68 Impact Factor
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    ABSTRACT: The present study aimed to quantify which image reconstruction conditions for normal databases and patients affect statistical brain function image analysis using an easy z score imaging system (eZIS) and 3-dimensional stereotactic surface projections (3D-SSP). We constructed normal databases based on cerebral perfusion SPECT images obtained from 15 healthy individuals. Each normal database was created with the following unique conditions: a variable Butterworth filter cutoff frequency (fc) with and without scatter and attenuation corrections. To simulate patient data, we selected 1 dataset from among those created from the 15 healthy individuals. The simulated patient data were designed to include hypoperfused regions with prespecified volumes. Using 3D-SSP and eZIS, we compared how the above processing conditions affect the distribution of SD in normal database images and the accuracy of detecting specific regions. The SD for the SPECT images increased with the fc of the Butterworth filter. The z score decreased by 30% for 3D-SSP and by 14% for eZIS, indicating that the prefilter significantly affected z scores. The accuracy of detecting the hypoperfused regions was significantly influenced by the fc; 3D-SSP decreased by 7.51%, and eZIS decreased by 55.34%. The detection accuracy with eZIS, which involves a smoothing process, was significantly decreased. The error of the area of hypoperfused regions was minimized when normal database and patient data were both corrected for scatter and attenuation. When the reconstruction conditions (fc, scatter correction, and attenuation correction) at normal database creation differed from those at patient data processing, the z scores widely underestimated the analytic results because the SD varied according to the reconstruction conditions. The accuracy of brain function image analysis can be improved by considering the reconstruction conditions and correcting for scatter and attenuation on both normal databases and patient data.
    Journal of Nuclear Medicine Technology 07/2011; 39(3):231-6. DOI:10.2967/jnmt.110.079871
  • Norikazu Matsutomo · Hideo Onishi · Akio Nagaki
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    ABSTRACT: An attenuation correction is necessary to improve quantitative 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.
    Nippon Hoshasen Gijutsu Gakkai zasshi 01/2011; 67(5):534-40. DOI:10.6009/jjrt.67.534
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    ABSTRACT: In single photon emission computed tomography (SPECT) cerebral blood flow studies, two major algorithms are widely used statistical parametric mapping (SPM) and three-dimensional stereotactic surface projections (3D-SSP). The aim of this study is to compare an SPM algorithm-based easy Z score imaging system (eZIS) and a 3D-SSP system in the errors of anatomical standardization using 3D-digital brain phantom images. We developed a 3D-brain digital phantom based on MR images to simulate the effects of head tilt, perfusion defective region size, and count value reduction rate on the SPECT images. This digital phantom was used to compare the errors of anatomical standardization by the eZIS and the 3D-SSP algorithms. While the eZIS allowed accurate standardization of the images of the phantom simulating a head in rotation, lateroflexion, anteflexion, or retroflexion without angle dependency, the standardization by 3D-SSP was not accurate enough at approximately 25° or more head tilt. When the simulated head contained perfusion defective regions, one of the 3D-SSP images showed an error of 6.9% from the true value. Meanwhile, one of the eZIS images showed an error as large as 63.4%, revealing a significant underestimation. When required to evaluate regions with decreased perfusion due to such causes as hemodynamic cerebral ischemia, the 3D-SSP is desirable. In a statistical image analysis, we must reconfirm the image after anatomical standardization by all means.
    Annals of Nuclear Medicine 01/2011; 25(1):59-67. DOI:10.1007/s12149-010-0448-9 · 1.68 Impact Factor
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    ABSTRACT: 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.
    Nippon Hoshasen Gijutsu Gakkai zasshi 01/2011; 67(3):221-8. DOI:10.6009/jjrt.67.221
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    ABSTRACT: The influence of the numbers of projection of SPECT exerting on a re-constructed image cannot be strictly evaluated by phantom studies. Therefore, we compared re-constructed images of the FBP method and the ML-EM method by using simulation data. Simulation data was entered in the image processing software, and the projection data that changed the numbers of projection was made. Afterwards, reconstructed images of the FBP and the ML-EM methods were compared with respect to contrast, %COV, and the NMSE value. When the numbers of projection of the FBP and the ML-EM method were decreased, all of the contrast, %COV, and the NMSE value were more deteriorated than that of the ideal image. Therefore, the image quality of SPECT improves with both FBP and ML-EM methods when there are many numbers of projection. Moreover, the FBP method was excellent in a cold contrast, and the ML-EM method was uniformly excellent. Therefore, an understanding of features and their inspection are effective for the selection of each image reconstruction method.
    Nippon Hoshasen Gijutsu Gakkai zasshi 12/2010; 66(12):1587-97. DOI:10.6009/jjrt.66.1587
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    ABSTRACT: Degradation of SPECT images results from various physical factors. The primary aim of this study was the development of a digital phantom for use in the characterization of factors that contribute to image degradation in clinical SPECT studies. A 3-dimensional mathematic cylinder (3D-MAC) phantom was devised and developed. The phantom (200 mm in diameter and 200 mm long) comprised 3 imbedded stacks of five 30-mm-long cylinders (diameters, 4, 10, 20, 40, and 60 mm). In simulations, the 3 stacks and the background were assigned radioisotope concentrations and attenuation coefficients. SPECT projection datasets that included Compton scattering effects, photoelectric effects, and gamma-camera models were generated using the electron gamma-shower Monte Carlo simulation program. Collimator parameters, detector resolution, total photons acquired, number of projections acquired, and radius of rotation were varied in simulations. The projection data were formatted in Digital Imaging and Communications in Medicine (DICOM) and imported to and reconstructed using commercial reconstruction software on clinical SPECT workstations. Using the 3D-MAC phantom, we validated that contrast depended on size of region of interest (ROI) and was overestimated when the ROI was small. The low-energy general-purpose collimator caused a greater partial-volume effect than did the low-energy high-resolution collimator, and contrast in the cold region was higher using the filtered backprojection algorithm than using the ordered-subset expectation maximization algorithm in the SPECT images. We used imported DICOM projection data and reconstructed these data using vendor software; in addition, we validated reconstructed images. The devised and developed 3D-MAC SPECT phantom is useful for the characterization of various physical factors, contrasts, partial-volume effects, reconstruction algorithms, and such, that contribute to image degradation in clinical SPECT studies.
    Journal of Nuclear Medicine Technology 02/2010; 38(1):42-8. DOI:10.2967/jnmt.108.061192
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    ABSTRACT: One-point venous blood sampling method (Mimura, et al.) can evaluate the 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 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).
    Nippon Hoshasen Gijutsu Gakkai zasshi 10/2009; 65(10):1378-84. DOI:10.6009/jjrt.65.1378
  • Kaku igaku. The Japanese journal of nuclear medicine 06/2008; 45(2):126-7.
  • Yuki Matsutake · Hideo Onishi
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    ABSTRACT: Spatial smoothing performed after spatial normalization on the easy Z-score Imaging System (eZIS) is considered to affect signal size. The purpose of this study was to analyze quantitatively the influence of the smoothing process on eZIS using the voxel of interest (VOI) method. A normal database (NDB) was established using (99m)Tc-Hexamethylpropyleneamine oxime (HMPAO) brain perfusion SPECT images of thirty healthy volunteers. Then the NDB was smoothed with various Gaussian kernels (2, 4, 8, 12, 16 mm). Artificial lesions with known volumes and reduction of tracer uptake were made on one of the healthy volunteer images, and eZIS analysis was performed on the NDB of the same Gaussian kernel, respectively. The signal size of small-sized lesions was expanded 5.1 times to the true signal size of a 12 mm Gaussian kernel. On the other hand, the medium lesion size, which was approximately the same size as the posterior cingulate gyrus, was expanded 2.9 times to true signal size. Estimation of the false positive area using the extraction estimation method at lesion size medium indicated the lowest value at 8, 12 mm Gaussian kernel smoothing. The smoothing procedure at 8-12 mm Gaussian kernel is effective to detect a focal abnormality in the brain SPECT of Alzheimer's disease.
    Nippon Hoshasen Gijutsu Gakkai zasshi 05/2008; 64(4):426-33. DOI:10.6009/jjrt.64.426
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    ABSTRACT: We have developed digital phantoms to be used for a basic education on an image quality and a quantification of SPECT data. Differing from the digital phantoms developed by Castiglioni and et al, several SPECT projection data sets were generated by Monte Carlo simulations (EGS4 code) with different acquisition parameters. A physical, brain and cardiac phantoms were generated. An external shape of the physical phantom is a 200 mm diameter and 200 mm long cylinder. Three objects, each of which consists of 4 mm, 10 mm, 20 mm, 40 mm and 60 mm diameter rods (each rod is 30 mm long) , are set in. Shapes of the brain phantom were created using a MRI data set. Shapes of the cardiac phantom were created using a CT image set. Tc-99m was used for the simulations. The Monte Carlo simulations were performed, taking account of Compton scattering, photoelectric effect and degradation of a spatial resolution due to collimator aperture. SPECT acquisition parameters were collimator type, pixel length, acquired photon count, projection number and radius of detector rotation. Ideal SPECT projection data and transaxial image were generated as reference (standard) data. Several attenuation maps with different attenuation coefficients can be used for an evaluation of an attenuation correction. The triple energy window setting was used for an evaluation of a scatter correction such as the TEW method. Overall, primary and scattered photons were saved in different files. By using the proposed phantoms, spatial resolution, contrast, signal to noise ratio and quantification with SPECT data acquisition and processing parameters were evaluated. The phantoms are considered to be useful for understanding the fundamental performance on SPECT.
    Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE; 01/2007
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    ABSTRACT: 原著 Original Article 国立情報学研究所で電子化 我々は,International Atomic Energy Agency (IAEA)肝ファントムを用いて^<67>Gaプレイナ画像における種々のphotopeak収集が画像に及ぼす影響について,画像コントラスト及び画像周波数解析を応用して定量的評価を行った。ファントムはIAEA肝ファントムを使用し,ファントム内に^<67>Gaを封入して実験を行った。評価した^<67>Gaのphotopeakは,93keV,185keV,300keVの組み合わせで画像収集を行った。画像コントラストは,散乱体の有無により大きく変化し,散乱体無しで93peak収集画像のコントラストが高くなったが,高いエネルギーが加わるとコントラスト低下が生じた。一方,散乱体が加わるとその厚さが増すにつれてコントラストが低下し,特に93peakでのコントラストが他のphotopeakに比較して著しく低下した。画像周波数解析では散乱体がない場合,動径強度分布関数(Pr(n))は93peak>93+185peak>3peak≒93+300peak>185peak>185+300peak>300peakの順となり93peakのphotopeakが良い結果となった。しかし,散乱体厚を増加するにつれて信号強度は弱くなり3peak>185peak>93+185peak≒93+300peak≒300peak≒185+300peak>93peakの順で3peakが良い結果となった。また,93peakのPr(n)は,0.1~0.3cyles/cmの低周渉領域の信号強度の劣化が激しく散乱体がない場合のそれに比較して約20%も低下した。散乱体厚が10cm以上の場合には,93peakは深部の情報を検出できなく,従来の3peak収集が良い結果となった。臨床におけるクエン酸ガリウム(^<67>Ga)プレイナ画像での収集photo peakは,単検出器型シンチレーションカメラでは高いphotopeakを含む3peak収集が良く,2検出器型シンチレーションカメラでは93+185peak収集が最も良い収集方法であった。 The purpose of this study was to analyze quantitatively the influence of acquisition of various combinations of photo-peaks on gallium-67 planar images using frequency analysis. A liver phantom provided by the International Atomic Energy Agency was imaged using a GCA-901WB (Toshiba, Tokyo) ; 37MBq of gallium-67 was injected into the phantom, and its planar images were acquired with each of three photo-peaks and the following combinations ; one each of 93, 185 and 300keV peaks, two of the three peaks, i.e. 93 and 185, 93 and 300, and 185 and 300 keV peaks, and all of the three peaks. Image contrast was varied with and without scatter material. Without scatter material, the 93keV-peak image had the highest contrast, and the contrast degraded when adding a higher energy photo-peak or photo-peaks. With scatter material, the image contrast decreased when the scatter material thickness increased, and the contrast degradation of the 93keV-peak image was particularly remarkable. Radius distribution function (Pr(n)) was used for quantitative frequency analysis. Images were collected up to 500 kcounts, and tough water phantoms (thicknesses: 5, 10, 20cm) were used as scatter material. The highest Pr(n) was obtained with the 93keV-peak without scatter material ; however, with a 20cm-thick tough water phantom, the image with three peaks had the highest Pr(n). According to the increase in tough water phantom thickness, the intensity of Pr(n) for the 93keV-peak in the range from 0.1 to 0.3 [cycles/cm] decreased by 20% of that without the tough water plate. When the thickness of the scatter material was over 10cm, 93keV-photons from the deep portion of the phantom were not detected properly. The optimal energy photo-peaks were three peaks for a single-head camera and the combination of 93 and 185keV peaks for a dual-head camera.
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    ABSTRACT: 報告 Reports