Yoshimasa Hamazawa

Osaka City University, Ōsaka-shi, Osaka-fu, Japan

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Publications (3)2.82 Total impact

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    ABSTRACT: A patient who had been on long-term hemodialysis (HD) was diagnosed as having renal cell carcinoma (RCC) and pheochromocytoma. Abdominal computed tomography scanning demonstrated a right renal mass and a right adrenal mass, whereas positron emission tomography (PET) using F-18 fluorodeoxyglucose (FDG) revealed increased accumulation in both the renal and adrenal masses. FDG-PET is useful for detecting RCC in HD patients because FDG is not excreted in the urine, but it is difficult to distinguish pheochromocytoma from an adrenal metastasis by this imaging method.
    Annals of Nuclear Medicine 07/2007; 21(4):239-43. · 1.41 Impact Factor
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    ABSTRACT: We investigated the optimum time for the differentiation tumor from inflammation using dynamic FDG-microPET scans obtained by a MicroPET P4 scanner in animal models. Forty-six rabbits with 92 inflammatory lesions that were induced 2, 5, 7, 14, 30 and 60 days after 0.2 ml (Group 1) or 1.0 ml (Group 2) of turpentine oil injection were used as inflammatory models. Five rabbits with 10 VX2 tumors were used as the tumor model. Helical CT scans were performed before the PET studies. In the PET study, after 4 hours fasting, and following transmission scans and dynamic emission data acquisitions were performed until 2 hours after intravenous FDG injection. Images were reconstructed every 10 minutes using a filtered-back projection method. PET images were analyzed visually referring to CT images. For quantitative analysis, the inflammation-to-muscle (I/M) ratio and tumor-to-muscle (T/M) ratio were calculated after regions of interest were set in tumors and muscles referring to CT images and the time-I/M ratio and time-T/M ratio curves (TRCs) were prepared to show the change over time in these ratios. The histological appearance of both inflammatory lesions and tumor lesions were examined and compared with the CT and FDG-microPET images. In visual and quantitative analysis, All the I/M ratios and the T/M ratios increased over time except that Day 60 of Group 1 showed an almost flat curve. The TRC of the T/M ratio showed a linear increasing curve over time, while that of the I/M ratios showed a parabolic increasing over time at the most. FDG uptake in the inflammatory lesions reflected the histological findings. For differentiating tumors from inflammatory lesions with the early image acquired at 40 min for dual-time imaging, the delayed image must be acquired 30 min after the early image, while imaging at 90 min or later after intravenous FDG injection was necessary in single-time-point imaging. Our results suggest the possibility of shortening the overall testing time in clinical practice by adopting dual-time-point imaging rather than single-time-point imaging.
    Annals of Nuclear Medicine 02/2007; 21(1):47-55. · 1.41 Impact Factor
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    ABSTRACT: MicroPET P4 is a Positron Emission Tomography (PET) scanner designed for small animal study with a 22-cm animal port and a 7.8-cm axial field of view (FOV). The scanner consists of 168 detector modules, each with an 8×8 array of 2.2×2.2×10 mm3 lutetium oxyorthosilicate (LSO) crystals, arranged as 32 crystal rings with an inner diameter of 26 cm. The system operates in 3D mode and data acquisition is done in list mode. The object animals and target regions for ongoing microPET studies in this site were rat and monkey brains and rabbit lungs. The purpose of this study is to determine the attenuation effects of these objects. Three cylindrical phantoms with outer diameters of 3, 7 and 9 cm and simulated rat and monkey heads and rabbit thorax, respectively, were used for investigating the attenuation effects. The attenuation effects can be divided into “factor changing” (FC) and “increasing nonuniformity” (NU). The NU values were 10.2%, 31.8% and 42.5% in 3-, 7- and 9-cm phantoms, respectively. The FC values were −26.6%, −49.2% and −59.3% in 3-, 7- and 9-cm phantoms, respectively.
    International Congress Series 01/2004; 1265:69-73.