[Development of simple processing for deleting undershooting artifact using the FBP method ─evaluation of simulation data─].

The undershooting artifact occurs using the filtered back projection (FBP) method. This artifact is influenced by a ramp filter. Thereby, the fall of the target accumulation and a deficit arise and it becomes a clinical problem. We developed a new image reconstruction method based on the FBP method to delete the undershooting artifact of FBP. The image quality of the FBP method is equivalent to that obtained by an evaluation using a digital phantom. The two segmentation and ordinary FBP methods were evaluated in terms of hot contrast, cold contrast, coefficient of variation (%CV), and root mean square uncertainty (%RSMU). The two segmentation FBP method showed equivalent values of hot contrast, % CV, and% RSMU compared with those of the ordinary FBP method. With a threshold level value, cold contrast sharply changed. However, when the threshold level of the two segmentation FBP method was set as the proper value, 90% contrast was obtained. It is necessary to set a threshold level as a proper value using the two segmentation FBP methods. I thought that it can delete an artifact in a simple way, without impairing the image quality. However, it is an examination of only a digital phantom this time. Before using it clinically, one has to use and verify a real phantom.

[Usefulness of top-hat transform processing in whole body bone scintigraphy].

To assess the usefulness of top-hat transform processing in whole body bone scintigraphy, five radiological technicians interpreted both original and top-hat processed images to determine the improvement of lesion detectability and interpretation time. For the evaluation of detectability, receiver operating characteristic (ROC) analysis was performed. The area under the curve (AUC) calculated from the ROC curve was improved in all observers (from 0.786 to 0.864 in average), although no significant difference was observed. However, the interpretation time was improved significantly (from 24.5 to 16.2 s in average). Top-hat transform processing in whole body bone scintigraphy is thought to be useful for the improvement of lesion detectability and interpretation time.

[A comparison of absorbed doses to water in photon beams in Japan Society of Medical Physics 01 and 12].

A comparison of absorbed doses to water at a calibration depth determined by Japan Society of Medical Physics (JSMP) 12 and 01 was conducted, using a farmer type ionization chamber. The absorbed dose to water calibration factor (ND,W,Q0) and beam quality conversion factor (kQ,Q0) for JSMP 12 were smaller than the absorbed dose to water calibration factor and beam quality conversion factor for JSMP 01. Differences in absorbed doses at a calibration depth were -0.78% for 6 MV photon beam and -0.94% for 10 MV photon beam. In the present experiment, absorbed doses at a calibration depth were measured, using a farmer type ionization chamber. Further experiments at a larger number of facilities should be conducted to reveal the status of measurement of absorbed doses at a calibration depth using JSMP 12.

[Comparison of the absorbed dose at calibration depth of photon beams using the Japan Society of Medical Physics 12 beam quality conversion factor in the presence or absence of a waterproofing sleeve].

In standard external beam radiotherapy dosimetry, which is based on absorbed dose by water, the absorbed dose at any calibration depth is calculated using the same beam quality conversion factor, regardless of the presence or absence of a waterproofing sleeve. In this study, we evaluated whether there were differences between absorbed doses at calibration depths calculated using a beam quality conversion factor including a wall correction factor that corresponds to a waterproofing sleeve thickness of 0.3 mm, and without a waterproofing sleeve. The Japan Society of Medical Physics (JSMP) has reported that the uncertainty of the results using a beam quality conversion factor that included a wall correction factor corresponding to a waterproofing sleeve thickness of 0.3 mm, regardless of the presence or absence of the sleeve, was 0.2%. This uncertainty proved to be in agreement with the reported range.

[A simple method for generating temporal subtraction image in bone SPECT-initial evaluation in pelvic region-].

We proposed and optimized a simple method of temporal subtraction image between successive bone single photon emission computed tomography (SPECT) images for supporting interpretation of temporal changes, and we evaluated its clinical utility. This method consisted of image registration, count normalization, and image subtraction. For image registration, we used a BEAT-Tl software. For count normalization, a pixel value of the normal accumulation part in a SPECT image was used as a reference region. We evaluated accuracy of image registration and optimized the normalization procedure. The accuracy of image registration ranged within 1 pixel in all directions (x, y, x-axis, and rotation). As the reference region, the second lumbar vertebra showed the best results in terms of the normalization procedure. Our method simply allowed the production of a temporal subtraction image. Because the software used in this method can be used free, this method would be available in every institution.