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Biomedical subjects

Hidemichi Kawata

Publications and source records attributed to Hidemichi Kawata.

5 recordsLinked to original sources
PubMed2006

[Development of automatic analyses for star-shot images using computed radiography (CR)].

Recent progress in radiation therapy has been greatly enhanced in many facilities by the development of new machines for treatment, improved computer technology for radiotherapy treatment planning systems (RTPs), increased accuracy of radiation therapy such as stereotactic irradiation, and intensity-modulated radiation therapy (IMRT). Quality control (QC) of the isocenter, which has consisted of gantry rotation and limiting the radiation field, is important for greater accuracy of these radiation therapy technologies. Star-shot analyses using computed radiography (CR) for evaluation of the isocenter were employed in this study. Devices to support CR were created, and a method of automatically analyzing images obtained by the star-shot technique, which calculated the error (distance) from the isocenter and the incident beam angle, were developed. In terms of the accuracy of our method, the average maximum error was 0.33 mm (less than 2 pixels: 0.35 mm), the average absolute error and incident beam angle errors were 0.3 mm and 0.4 degrees at maximum and at one standard deviation (SD), respectively. In this study, the processing times were 16 sec at minimum, 152 sec at maximum, 18 sec at most frequencies, and 23.6 sec on average. In conclusion, it was considered that our newly developed method for analyzing star-shot images using CR enabled immediate, quantitative evaluation of the isocenter.

Algorithms↗
PubMed2005

[Research on time-course differential imaging by bone scintigraphy].

The temporal image subtraction technique was applied to bone scintigraphy, using Photoshop (commercially available image processing software) and Morpher (public domain warping software). For the temporal subtraction images, 81 subtraction images (19 cases) were prepared by a method used to subtract the previous images from the current ones. Registration of the current and previous images was performed by manual operation using Photoshop, and warping was done using the warping function of Morpher. In addition, difference images prepared after correcting the distributions of radioactive isotopes of the current and previous images using the count of the pelvic region were also examined. Compared with manual operation, alignment of images by warping improved registration and reduced the generation of pseudo-images of subtraction images. The rate of identification of abnormal accumulation-enhanced regions and subjective evaluation by doctors was improved for warping more than for manual operation. Furthermore, abnormal hot regions, which are difficult to find in film images, could be found in three subtraction images. In addition, it was confirmed that abnormal hot regions become more visible in many cases by preparing subtraction images after correcting the count between images using the count of the pelvic region. Thus, it is suggested that the temporal image subtraction technique in bone scintigraphy enables more accurate observation of enhancement of or changes in abnormal hot regions, which will support diagnostic reading. It is considered that enhancement of or changes in abnormal hot regions will be more accurately understood through further detailed discussion in the future.

Bone and Bones↗
PubMed2004

[Fundamental study of magnetization transfer contrast (MTC) effect: optimization of MT pulse condition using experimental phantom].

Magnetization transfer contrast (MTC) was evaluated by changing the off-set frequency and pulse intensity of MTC with the spoiled gradient echo (SPGR) sequence (T2*-weighted image) using an experimental phantom that included olive oil, protein, fiber, collagen, and pure water. The intensity of pure water reached a constant level just above the off-set frequency (1200 Hz) regardless of MT pulse power. The contrast-to-noise ratio (CNR) in each of the phantom materials was maximal at the MT pulse power of 2500 degrees (equivalent flip angle). The CNR and image noise obtained by body coil were inferior to those obtained with an extremity coil. In clinical application, the MTC effect on chondrosarcoma was higher (MT ratio, ROI-1:0.448, ROI-2:0.382) than those of other cases in this study. Since the image contrast was improved between the malignant fibrous histiocytoma (MFH, MT ratio, ROI-1:0.282, ROI-2:0.289) and peripheral tissues, extraskeletal extension could be observed more easily than without MTC imaging. In conclusion, the effects of MTC might be in providing useful information, in presuming composed tissues, differential diagnoses, and extent to the surrounding structures because of changing the image contrast to surrounding tissues corresponding to the rate of included bound water.

Bone Neoplasms↗
PubMed2003

[Investigation of beam quality for digital chest radiography with RbBr:Tl(+) photostimulable storage phosphors].

Beam quality for digital chest radiography in digital radiography systems (DR systems) with RbBr:Tl(+) photostimulable storage phosphors was investigated. Measurements of overall Wiener spectrum (overall WS) and observer performance experiments by means of Scheffé's method of paired comparisons were performed under the same exposure (5.16x10(-7)C/kg) at the X-ray detector of DR systems (sampling distance: 175 micro m, 2,048x2,048 pixels, 12 bits, look-up table: THX2) with a phantom lung and metacryl plates. Overall WS values were indicated to be inferior at higher tube voltages. All of the overall WS values were greater than those of screen film systems (HGM/UR1:S/F) at radiographic density 0.50, which was considered the density of the mediastinum and the area below the diaphragm (low density area), and at radiographic densities 1.00 and 1.50, considered as lung, WS values of S/F were located between the overall WS values of 80 kV and 100 kV, and 120 kV and 140 kV, respectively. Evaluation of visibility including mediastinum, lung, and total were indicated to be superior at the lower tube voltages. In evaluation of the mediastinum, the base image, which was obtained by 100 kV tube voltage (effective energy: 46.0 kV) in this study, was not significant from 90 kV to 110 kV tube voltages (range, +/-10 kV), and in-lung and total evaluations were not significant from 90 kV to 120 kV (range, -10 kV to +20 kV), and from 80 kV to 120 kV (range, +/-20 kV) tube voltages by 99% confidence interval. In conclusion, optimal beam quality for digital chest radiography with RbBr:Tl(+) photostimulable storage phosphors was considered to be less than 110 kV tube voltage (effective energy, 47.9 keV) in 0.1 mm copper and 3.8 mm aluminum total filtration. In this case, the granularity in low-density areas were inferior to those of S/F systems but nearly equal to the middle and high-density areas of chest images, and exposure dose was 14.3% lower than that of the base image obtained by 100 kV (effective energy, 46.0 keV) tube voltage in this study.

Bromides↗