日本放射線技術学会雑誌
Online ISSN : 1881-4883
Print ISSN : 0369-4305
ISSN-L : 0369-4305
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62 巻, 6 号
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巻頭言
Editorial
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教育講座―技師が書く技師のための読影講座―
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論文
原著
  • Emission/Transmission同時収集においてTransmission収集カウントが画質に与える影響
    井上 一雅, 織田 圭一, 福士 政広
    2006 年 62 巻 6 号 p. 815-821
    発行日: 2006年
    公開日: 2007/02/23
    DOIhttps://doi.org/10.6009/jjrt.62.815
    ジャーナル フリー
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    We compared the pre-injection transmission scan with the simultaneous emission/transmission scan (SET) using a body phantom in positron emission tomography (PET) to study the factors affecting emission (EMIS) images with different transmission (TRAN) data. The results showed that total count, region, scan method, and EMIS component influenced the bias and noise statistics. This influence was further passed on to the EMIS data and affected the reconstructed image. However, the result of fixing EMIS scan time at 10 minutes was that the noise statistics of EMIS had a greater effect on image quality than TRAN. The optimal scan counts of SET in this study were 20 Mcounts, with a scan time of about 10 minutes (85.5 MBq, 68Ge-68Ga radioactivity). In clinical use, optimal collection count differs, as radiation TRAN quantity depends on the size of the subject, even with fixed radioactivity of 68Ge-68Ga.
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  • 全身PET/MRI融合画像に関する検討―Partial Body Fusionの有用性―
    中野 喜正, 藤淵 俊王, 磯辺 智子, 内田 佳孝, 風間 俊基, 浜田 一男, 木川 隆司, 伊東 久夫
    2006 年 62 巻 6 号 p. 822-831
    発行日: 2006年
    公開日: 2007/02/23
    DOIhttps://doi.org/10.6009/jjrt.62.822
    ジャーナル フリー
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    Purpose: In this study, we created a whole body fusion image of PET and MRI using automated software for fusion imaging, and assessed the accuracy of the software. Materials and methods: Twenty patients with abnormal FDG-PET findings underwent whole body MRI. Images from both modalities were automatically fused in two ways using software (Fusion Viewer, Nihon Medi-Physics Co., Ltd., Nishinomiya, Japan) with a registration algorithm based on maximum mutual information. One was to create a whole body fusion image at once, named whole body fusion (WBF). The other was to create fusion images of the head and body separately, named partial body fusion (PBF). Two radiologists measured the misregistration between PET and MRI in the fusion images at nine landmarks (brain, cervical spine, chest, heart, liver, right kidney, left kidney, vertebra, base of bladder). Results: When fusion images were created using WBF at once, misregistration was observed in the head and neck area in approximately half of the cases, whereas almost no misregistration was observed in the body. When fusion images were created using PBF, the misregistration in the head and neck areas was significantly smaller than in those using WBF, and misregistration in the body was very small. Conclusion: The PBF technique that creates highly accurate whole body PET/MRI fusion images is easy to use and may provide clinically useful information.
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  • CTによる吸収補正と68Ge-68Ga外部線源による吸収補正の比較
    ―Emissionに与える影響―
    林 絵美, 岩瀬 幹生, 小島 滋, 西尾 正美
    2006 年 62 巻 6 号 p. 832-839
    発行日: 2006年
    公開日: 2007/02/23
    DOIhttps://doi.org/10.6009/jjrt.62.832
    ジャーナル フリー
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    Objectives: CT data can be used for both anatomical image and attenuation correction (CTAC) of PET data in PET-CT scanners. The CTAC method is useful for attenuation correction, because the CT scan time is much shorter than the external radionuclide (e.g., 68Ge) transmission scan time. However, the energy of the X-rays from CT is not monoenergetic and is much lower than that of the external radionuclide source. In this study, we evaluated the differences between emission PET images reconstructed with CT-based and 68Ge-based attenuation correction. Methods: CT scans and 68Ge-Transmission scans were acquired and used for attenuation correction (CTAC, MAC, and SAC). The PET emission scan time was 4 min. CT scans were acquired at 10, 20, 40, 80, and 160 mA. 68Ge-Transmission scans were acquired at 1, 3, 5, 10, 20, 40, 60, and 300 min. The attenuation-corrected emission image using MAC on a 300 min transmission scan was defined as the reference image. Seven cylinders (30 mm diameter) were filled with 18F-FDG placed in a heart-liver phantom with simulated pulmonary mass lesions. The PET value [counts/cc] was measured in circular regions of interest (ROI) over the cylindrical mass lesion. Averages [counts/cc], coefficients of variation [C. V. (%)], and ratios of difference [%Diff] from the reference value were calculated for all conditions. Results: In the CT-Transmission, analysis of variance revealed no significant effect of CT current on the average and the C. V. In the 68Ge-Transmission, the average and the C. V. changed in dependence on the acquisition time. All %Diff using CT-Transmission were small. It was shown that CT-Transmission is more appropriate than 68Ge-Transmission.
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  • 低線量CTを利用したSPECT減弱補正に関する検討
    井口 治巳, 木田 哲生, 野間 和夫, 吉村 雅寛, 濱津 尚就, 増田 一孝
    2006 年 62 巻 6 号 p. 840-847
    発行日: 2006年
    公開日: 2007/02/23
    DOIhttps://doi.org/10.6009/jjrt.62.840
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    Attenuation correction is necessary for the reconstruction of SPECT images. One report has mentioned that attenuation correction by X-ray computed tomography (CT) is effective for a non-uniform attenuation body. We examined the effect of attenuation correction on SPECT images by changing the scanning conditions of CT, and evaluated the possibility of attenuation correction by low-dose CT. The phantom was scanned under several X-ray tube conditions varying from 80 kV to 135 kV and from 7.5 mAs to 200 mAs. We obtained equations of attenuation correction based on the Hounsfield Unit (HU) units of each pixel and compared the effects of attenuation correction. The results showed that the equation for attenuation correction under each condition did not vary significantly, and the effects of attenuation correction by the equations did not vary significantly between CT of low dose and that of clinical dose. This result suggest that the attenuation correction obtained by low-dose CT was equal to that obtained by the clinical dose. In conclusion, it seemed that the equation and map of attenuation correction matched with each radionuclide yielded more adequate attenuation correction than conventional methods.
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ノート
  • 体幹部における3検出器型高速回転SPECT撮像法の開発
    ―肺血流シンチ・ファントムスタディ―
    岩永 秀幸, 大石 誉奈, 菅 一能
    2006 年 62 巻 6 号 p. 848-854
    発行日: 2006年
    公開日: 2007/02/23
    DOIhttps://doi.org/10.6009/jjrt.62.848
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    Purpose: A chest phantom study was conducted to evaluate the image quality of newly developed high-speed rotation multiplied projection-single photon emission computed tomography (HSRMP-SPECT) images. Materials and Methods: HSRMP-SPECT images of a chest phantom consisting of a simulated lung structure filled with 5000 ml of water containing 185 MBq Tc-99m-pertechnetate, and several small 11 mm simulated lung nodules of glass balls and one large 35 mm simulated lung nodule of a plastic sphere filled with water were obtained using a triple-headed SPECT system. During image acquisition, this phantom was regularly moving in the head-to-caudal direction with a range of 12 mm at a frequency of 15 cycles/min to simulate respiratory motion, and 360° projection data of this moving phantom was acquired with an image acquisition time of 20 sec, which was repeated 10 times. To eliminate the setting time between projection and acquisition of multiple temporal samples of data, each detector was continuously rotated in the clock-wise direction for 20 sec around a 120-degree arc. On the perspective SPECT images reconstructed from various numbers of the 20-sec projection data, the perfusion heterogeneity of the simulated lungs and perfusion defect clarity of the simulated nodules were assessed by the coefficient of variation (CV) of pixel counts and the defect-to-lung radioactivity ratios, respectively. The results were compared with those on conventional SPECT images of the moving phantom obtained with a data acquisition time of 8 min, and SPECT images of the standing phantom obtained with the same data acquisition time. Results: The average CV value of 0.28±0.01 on the SPECT image reconstructed from 5 projection data sets was not significantly different from that of 0.27±0.01 on the SPECT image reconstructed from 10 projection data sets (p<0.05). The perfusion defect contrast of the simulated nodules obtained from 5 projection data was significantly higher than that on conventional SPECT images (0.50 vs. 0.73). Conclusions: The present phantom study indicated that HSRMP-SPECT could be a useful technique for quickly obtaining high-quality SPECT images of a moving subject, thereby improving perfusion defect clarity in comparison with the conventional technique. This technique may have potential utility for obtaining high-quality breath-hold SPECT images of the chest in clinical practice.
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資料
  • 三次元18F-FDG PET/CT収集におけるオーバーラップ数の検討
    宍戸 博紀, 大塚 信昭, 富永 孝宏
    2006 年 62 巻 6 号 p. 855-862
    発行日: 2006年
    公開日: 2007/02/23
    DOIhttps://doi.org/10.6009/jjrt.62.855
    ジャーナル フリー
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    The purpose of this study was to determine the best bed overlaps in PET/CT 3D acquisition to reconstruct a transverse image with uniform quality not depending on axial slice position. First, the value of the image contrast ratio, non-uniformity (NU) value, and coefficient of variation (COV) were examined in the image of a cylindrical phantom at each slice position. The image-contrast ratio was almost constant in all slice images, and the NU value and COV were also constant in the slice images up to 13 and 19 slices from the center, respectively, but these values increased with closeness to the edge of the detector. Secondly, COV and image contrast ratios at different sizes of 18F-FDG concentration (φ19 mm, φ16 mm, φ13 mm, φ10 mm) were examined in the case of overlapping the bed frame with 11, 15, and 21 slices in acquiring data in 3D mode. In 21 and 15 slices overlapping in acquisition, the image contrast ratios for all concentrations were greater than 0.13, which was the threshold image contrast ratio needed to identify FDG concentration from the background image with naked eye scanning under our conditions. However, in 11 slices with overlapping acquisition, the image-contrast ratio for a φ10 mm concentration were close to or less than 0.13 in the all slice images. As a result, 15 overlapping slices was a reasonable minimum number of slices to identify a φ10 mm 18F-FDG concentration while maintaining the image quality in PET/CT 3D acquisition in our institution.
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