Nihon Hoshasen Gijutsu Gakkai zasshi最新文献

Purpose: This study aims to devise and identify the errors of the beam width measurements in a wide beam CT system using three tungsten rings (TR) in comparison with a flat-panel detector (FPD), and develop a new method to correct the errors.

Methods: A pencil-type ionization chamber was placed at the isocenter. The Kerma-length product ( KLP) was measured at 80 and 120 kV, 400 mA, and a rotation time of 0.5s with nominal beam widths ranging from 20 to 160 mm in 20 mm increments. Subsequently, each TR was attached to the chamber to measure the KLP_mask at the isocenter, and the beam width was calculated as KLP×ring length/( KLP-KLP_mask). To compare the measurement accuracy, the beam widths were measured using the FPD with a double-exposure technique. The X-ray exposures were performed at 80 kV, rotation time of 0.5 s, and 10 and 20 mA were used for the measurements. Finally, the heel effect correction, replacing the KLP at the anode side, was also compared.

Results: The measured beam widths using 5-, 10-, and 15-mm TRs at 80/120 kV, and the FPD were 182.5 /182.1, 167.5/165.7, 168.2/163.0, and 172.9 mm in the nominal beam width of 160 mm, respectively. The heel effect correction with 10- and 15-mm TRs at 80 kV improved the measurement accuracy, and the corrected beam widths were 172.4 and 173.2 mm, respectively.

Conclusion: In conclusion, 10- and 15-mm TRs in conjunction with the heel effect correction are appropriate for the beam width measurements in a wide beam CT system.

Purpose: Japanese normal databases (NDB) for quantitative evaluation of ^99mTc myocardial perfusion SPECT have traditionally been created by the filtered back projection (FBP) method but are also applied to the iterative reconstruction (IR) method in some institutions. Although creating the NDB specifically for the IR method is desirable, it has not been done partly due to the ethical aspects of creating an institution-specific database. This study investigated the impact of using NDBs created by the FBP method on quantitative evaluations performed with the IR method.

Methods: We analyzed single-photon emission computed tomography (SPECT) images from patients undergoing myocardial perfusion study in two hospitals with three SPECT vendors. Images were processed with and without various corrections, and a polar map was created by QPS software using a 17-segment model to obtain %uptake and scores. The effects of the reconstruction and correction methods were evaluated to determine the difference in the number of local segmental analyses by coronary artery territories.

Results: In most segments, quantitative values showed no significant difference across device types, with or without corrections. However, both choices of the SPECT device and correction methods influenced the scores in specific coronary artery regions. Application of attenuation correction resulted in lower defect scores in the right coronary artery region.

Conclusion: Applying FBP-derived NDB to the IR method generally yielded a consistent patient diagnosis in terms of defect score analysis. However, since the quantitative evaluation was partly affected by various correction methods and devices, recognizing these characteristics is crucial for enhancing diagnostic accuracy.

Purpose: This research aims to optimize the block sequential regularized expectation maximization (BSREM) reconstruction in bone single photon emission computed tomography (SPECT) images using a ring-type SPECT/computed tomography (CT) system in terms of image quality and accuracy of quantitative evaluation.

Methods: SPECT images were acquired using a ring-type SPECT/CT and from a SIM² bone phantom containing a 99m-Tc solution. BSREM parameters were assessed with coefficient of variation (CV), recovery coefficient (RC), contrast noise ratio (CNR), standardized uptake value max (SUVmax), and its root mean square error (RMSE_SUVmax). Clinical images were reconstructed, and the reconstructions were evaluated as superior based on phantom results.

Results: Increasing γ led to higher RC and CV, while increasing β lowered these values. CNR showed no consistent trend. In terms of quantitative evaluation, γ value 5.0, β values 0.3-0.9, and γ value 10, βvalues 0.3-0.9 resulted in lower RMSE_SUVmax compared to Anger type. Based on the phantom experiment, γ value 5.0, β values 0.5-0.9, and γ value 10, β values 0.7-0.9 were evaluated as superior. Clinical images under these reconstructions, determined from the phantom experiments, with γ value 5.0, β value 0.9, showed the smoothest of normal bone and the clearest separation of neighboring tumors.

Conclusion: As reconstruction parameters for BSREM reconstruction in bone SPECT on a ring-type semiconductor SPECT/CT system, a γ value of 5.0 and a β value of 0.9 were considered suitable for image quality and quantitative evaluation.

Purpose: Image-guided radiation therapy using cone-beam computed tomography (CBCT) for prostate cancer is problematic due to the increasing exposure dose at each treatment session. This study aimed to evaluate the effect of exposure dose reduction using bismuth sheets for pelvic CBCT.

Methods: Using a radiophotoluminescence dosimeter (GD-352M) and CBCT imaging conditions with three X-ray tube rotation angles (292°-88°, 92°-248°, and 92°-88°), absorbed doses were measured in the rectum, anterior and posterior bladder walls, right and left pelvic subcutaneous at 5 cm superior the prostate center of the pelvic phantom and in a testis. Next, the same measurements were performed when these measurement points were covered with a bismuth sheet.

Results: The absorbed doses at 92°-248° with the bismuth sheets were reduced by 31.3% from 16.3±0.2 mGy to 11.2±0.2 mGy for the rectum and by 57.1% from 45.0±2.7 mGy to 19.3±1.0 mGy for the testis, which were the lowest among the imaging conditions. Although the anterior and posterior bladder walls were the highest dose at 48.7±11.5 and 20.2±0.4 mGy, the high reduction rates of 42.0% and 36.9%, respectively.

Conclusion: From the viewpoint of the exposure risk to the bladder, rectum, and testis, using bismuth sheets and the X-ray tube rotation angle of 92°-248° effectively reduced the exposure dose.