Biomedical subjects

Masaaki Hirata

Publications and source records attributed to Masaaki Hirata.

5 recordsLinked to original sources

PubMed2005

Effect of x-ray tube current on the accuracy of cerebral perfusion parameters obtained by CT perfusion studies.

The purpose of this study was to investigate the effect of x-ray tube current on the accuracy of cerebral perfusion parameters obtained by CT perfusion studies using multi-detector row CT (MDCT). Following the standard CT perfusion study protocol, continuous (cine) scans (1 s/rotation x 60 s) consisting of four 5 mm thick contiguous slices were performed using an MDCT scanner with a tube voltage of 80 kVp and a tube current of 200 mA. We generated the simulated images with tube currents of 50 mA, 100 mA and 150 mA by adding the corresponding noise to the raw scan data of the original image acquired above using a noise simulation tool. From the original and simulated images, we generated the functional images of cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) in seven patients with cerebrovascular disease, and compared the correlation coefficients (CCs) between the perfusion parameter values obtained from the original and simulated images. The coefficients of variation (CVs) in the white matter were also compared. The CC values deteriorated with decreasing tube current. There was a significant difference between 50 mA and 100 mA for all perfusion parameters. The CV values increased with decreasing tube current. There were significant differences between 50 mA and 100 mA and between 100 mA and 150 mA for CBF. For CBV and MTT, there was also a significant difference between 150 mA and 200 mA. This study will be useful for understanding the effect of x-ray tube current on the accuracy of cerebral perfusion parameters obtained by CT perfusion studies using MDCT, and for selecting the tube current.

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PubMed2005

Measurement of radiation dose in cerebral CT perfusion study.

PURPOSE: To evaluate radiation dose in cerebral perfusion studies with a multi-detector row CT (MDCT) scanner on various voltage and current settings by using a human head phantom. MATERIALS AND METHODS: Following the CT perfusion study protocol, continuous cine scans (1 sec/rotation x60 sec) consisting of four 5-mm-thick contiguous slices were performed three times at variable tube voltages of 80 kV, 100 kV, 120 kV, and 140 kV with the same tube current setting of 200 mA and on variable current settings of 50 mA, 100 mA, 150 mA, and 200 mA with the same tube voltage of 80 kV. Radiation doses were measured using a total of 41 theroluminescent dosimeters (TLDs) placed in the human head phantom. Thirty-six TLDs were inside and three were on the surface of the slice of the X-ray beam center, and two were placed on the surface 3 cm caudal assuming the lens position. RESULTS: Average radiation doses of surface, inside, and lens increased in proportion to the increases of tube voltage and tube current. The lowest inside dose was 87.6+/-15.3 mGy, and the lowest surface dose was 162.5+/-6.7 mGy at settings of 80 kV and 50 mA. The highest inside dose was 1,591.5+/-179.7 mGy, and the highest surface dose was 2,264.6+/-123.7 mGy at 140 kV-200 mA. At 80 kV-50 mA, the average radiation dose of lens was the lowest at 5.5+/-0.0 mGy. At 140 kV-200 mA the radiation dose of lens was the highest at 127.2+/-0.6 mGy. CONCLUSION: In cerebral CT perfusion study, radiation dose can vary considerably. Awareness of the patient's radiation dose is recommended.

Basal Ganglia↗

PubMed2005

Extraskeletal osteosarcoma in the thigh: a case report.

Extraskeletal osteosarcoma is a rare malignant soft-tissue tumor. There are few reports describing the radiological findings of this tumor, especially concerning its MRI and scintigraphic appearance. We report a 58-year-old man with extraskeletal osteosarcoma in the thigh. Radiographs showed small foci of mineralization in the mass. The tumor showed low intensity on T1-weighted images and predominantly high intensity on T2-weighted images, and the tumor was heterogeneously well enhanced on Gd-DTPA-enhanced T1-weighted images. Bone scintigraphy showed extraskeletal uptake in the tumor, and thallium-201 scintigraphy revealed marked inhomogeneous accumulation.

Contrast Media↗

PubMed2005

A method for reducing radiation dose in cerebral CT perfusion study with variable scan schedule.

PURPOSE: To propose a method for reducing the radiation dose in cerebral CT perfusion studies by using a variable scan schedule. MATERIALS AND METHODS: Original images were obtained with a multi detector-row CT (MDCT) scanner using the following CT perfusion protocol: continuous scans of 1 sec/rotation x 60 sec, four 5-mm-thick contiguous slices. The original images were thinned-out using combinations of various numbers of former continuous images (10, 15, 20, 25, and 30), and the later skipped images with various scan intervals (2, 5, 10, 15 and 20 sec). The thinned-out images were interpolated by linear interpolation. In five patients with cerebrovascular disease, we generated functional images of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) from both original and interpolated data. The correlation coefficients (CC) for these parameters between the original and interpolated images were evaluated. RESULTS: The CC decreased with dose reduction. To keep the correlation coefficients greater than 0.9, the estimated dose was reduced to 33.3% on CBF with a set of 10 continuous images and scan interval of 5 sec, to 20.0% on CBV with a set of 10 continuous images and scan interval of 20 sec, and to 58.3% on MTT with a set of 10 continuous images and scan interval of 2 sec. CONCLUSION: The variable scan schedule method would be useful to reduce radiation dose while maintaining the accuracy of CT perfusion (CTP) parameters.

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PubMed2005

Evaluation of optimal scan duration and end time in cerebral CT perfusion study.

PURPOSE: The purpose of this study was to evaluate the optimal end time of scanning and the influence of varying the number of source images adopted for calculation of the parameter values in computerized tomography (CT) perfusion. MATERIALS AND METHODS: Nineteen CT perfusion studies in 14 patients with cerebrovascular disease were retrospectively analyzed. CT perfusion scanning was performed using continuous scans of 1 sec/rotation x60 sec with 5-mm-thick sections. To determine the appropriate end time of scanning, the time-density curves (TDCs) of the anterior cerebral artery (ACA), superior sagittal sinus (SSS), and basal ganglia were analyzed. The functional maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) were retrospectively generated from various numbers (30, 35, 40, 45, 50, 55, and 60) of source images. Defining the values calculated from the number of source images equal to the end time of the first pass as standard values, the percentage difference between the standard values and the values generated from various numbers of sources were evaluated. RESULTS: The TDCs of SSS showed the latest end time of the first pass (mean, 38.6+/-5.2 sec; range, 32 to 48 sec). Therefore, the values calculated from the number of source images equal to the end time of the first pass of SSS were defined as standard values. Increase and decrease of the number of source images for calculation resulted in increase of the percentage difference in every parameter value. The percentage differences ranged up to 49.6% for CBF, 48.0% for CBV, and 20.0% for MTT. CONCLUSIONS: Scanning until the end time of the first pass of SSS is necessary and sufficient for reliable measurement. Variable scan time based on the TDC of the SSS may be of better utility than use of fixed scan time. Further, the radiation dose could be minimized in many cases by reducing the scan time.

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