We showed scanner dependence of brain 18F-FDG and 11C-PiB images by using phantom examination with nine kinds of positron emission tomography (PET) scanners. We used two types of phantoms, cylindrical phantom with 15 cm inside diameter and three-dimensional (3D) brain phantom, and we set the body phantom on the bed to examine the effect of scatter and random coefficients from outside of the axial field of view (AFOV). Radioactivity and distance of the two phantoms were determined by a pilot study to obtain a condition similar to the clinical study. Axial uniformity was evaluated by circular region of interest (ROI) of 12 cm diameter, set in the center of the reconstruction image of the cylindrical phantom. As a result, the standardized uptake value (SUV) was lower than the true value in some scanners, and there was a scanner in which the axial uniformity was deteriorated by high radioactivity outside the AFOV. In the cylindrical phantom, the axial uniformity of the scanner was improved using the new dead-time correction method; however, it was not improved in the 3D brain phantom. Quality-controlled PET scanners are important to maintain constant levels for multicenter studies.
In order to produce a cheap and stable X-ray generator system for calibration of dosimeters used in mammographic field, a dummy source of mammographic X-ray was developed using a tungsten (W) target X-ray tube and a molybdenum (Mo) filter. The photon fluence spectra of mammographic equipment were calculated using Birch’s formula and aluminum (Al) attenuation curves were derived. The Al attenuation curves of X-rays from W target with Mo filter of various thicknesses were similarly obtained. Comparing the similarities of attenuation curves, the best fit Mo filter thickness was chosen. Consequently, a 0.04 mm thick Mo plus a 4 mm thick poly-methylmethacrylate filter were chosen to be added to W target industrial X-ray tube. The similarity of Al attenuation curves were verified by ionization chamber measurements.
Purpose: This study aims to evaluate the fundamental performance of four leading advanced resolution recovery methods. Method: To evaluate the performance of the resolution recovery algorithm, we carried out the computer simulation with the cone/sphere digital phantoms. These phantoms were used to investigate the basic properties of those algorithms. The software of four packages (advance) were also tested, specifically AstonishTM (AST), EvolutionTM (EVL), Flash-3DTM (FL3), and 3D-OSEM (3DOS). The performance was evaluated in the collimator systems (LEHR) reconstruction conditions using the full width at half maxi am (FWHM), aspect ratio (ASR), and artifacts of conical part. Result: In the “without BG,” FWHM of the advance method indicated a true-FWHM with SI (subset×iteration)=20, 40. As SI increased, FWHM was composed with over estimate. Each advances of FWHM indicated only 5% of improvement as compared with reference FWHM in the “with BG.” The ASR increased 20% to AST, FL3, and ASR of 3DOS remained in 10% in the outside. As for the reproducibility of the conical part, an artifact was caused by the FL3, EVL, and AST methods. This artifact did not occur in 3DOS. Discussions: An SI needs more than 150 to obtain an accurate compensation effect. As for the advance method, the major compensation effect was not demonstrated very much as compared with the OS-EM. The EVL, FL3, and AST overestimated values due to a Gibb’s oscillation in the artifacts of the conical part.
During examinations using radionuclide methods, technicians sometimes need to interact directly with patients. The initial point of contact is when they assist patients onto the examination table, the second is when the patients are positioned for radionuclide examination, and the third occurs if the patients experience a sudden change in condition and assistance is deemed necessary. The dose of radiation increases proportionately to the size of the area being treated. Therefore, we verified that the lateral area received a lower dose of radiation than the anterior areas because of their smaller surface area. The doses in the anterior and lateral areas of the patients were measured following administration of 99mTc-hydroxymethyl enebisphosphonic acid (HMDP), 131I, 18F-fluoro-2-deoxy-d-glucose (18F-FDG), and 99mTc-galactosyl-human serum albumin-diethylenetriamine-pentaacetic acid (GSA). The lateral/anterior (L/A) ratio was defined as an approximation of the ratio of measured values of the lateral and anterior areas; it was calculated as follows: L/A (%)=[(lateral dose–BG)/(anterior dose–BG)]×100. In all patients, the radiation dose rate from the lateral areas was lower than from the anterior areas. L/A was 52% with 99mTc-HMDP, 51% with 131I, 58% with 18F-FDG, and 33% with 99mTc-GSA, and radiation doses were found to be reduced by approximately 50% when interaction with patients was from the lateral side rather than the anterior side. Therefore, we confirmed that when interacting closely with patients undergoing radionuclide examinations, it is best to approach the patients from the lateral side in order to reduce radioactive exposure of the technicians.
Purpose: The aim of this study was to derive optimal coronary angiography (CAG) angle for the form information on the left main trunk (LMT) by use of multi detector computed tomography (MDCT). Methods: To verify the accuracy of angle measurement with MDCT, the angle of phantom with known angle was compared with MDCT (CT method) and angiography (AG method). The take-off angle of LMT was derived using CT method from 200 cases who underwent cardiac CT in this institution. Results: In the phantom, both CT and AG methods were indicated to have high accuracy and the errors were very small (0.3%, 0.3%). The take-off mean angle of LMT was 130.7±19.0 degrees in male, and 139.1±19.3 degrees in female. The optimal CAG angle was indicated at left anterior oblique (LAO) 41 degrees (male) and LAO 49 degrees (female). Conclusion: The optimal CAG angle of LMT was derived from the CT method.
The purpose of administering a saline solution flush after contrast medium injection is to more effectively utilize the contrast medium remaining in the vessels from the subclavian vein to the superior vena cava. In order to investigate the effects of administering a saline solution flush after a contrast medium injection, we evaluated the effects of various contrast medium injection durations and injection methods on the time-density curve (TDC) using a custom-made TDC measurement phantom. The TDC was found to have a biphasic appearance, showing a rapid increase after the arrival of contrast medium in the target region followed by a slower increase from an inflection point at 25 s after the start of contrast medium injection, reflecting the differences in circulatory dynamics for each duration. The results showed that the effect of saline solution flush was allowed the differences by contrast medium duration at the inflection point. Specifically, when the saline solution flush was administered before the inflection point, the CT number was increased, and when it was administered after the inflection point, contrast enhancement was prolonged. With regard to the method in which the saline solution flush is administered before the inflection point, it was found that injecting a mixture of contrast medium and saline solution before the saline solution flush reduced the degree of inflection of the TDC, resulting in a more stable TDC.
The exposure of the eye lens caused by multi-detector row computed tomography (MDCT) of the temporal bone is a serious problem. Our aim was to evaluate the radiation dose to the eye lens by different scan baselines (orbitomeatal line; OML, acanthiomeatal line; AML) and examine the difference of the depiction of the temporal bone structures. Measurement of the exposure to the eye lens was performed by means of MDCT of the temporal bone with a radio-photoluminescence glass dosimeter using a rand phantom. Moreover, we studied only one volunteer (58-year-old male) who had no symptom and was not suspected of having any ear abnormalities with a two scan baseline. Visualization of the major anatomical structures of the temporal bone (the tympanic portion of the facial nerve canal, the body of the incus, stapes superstructures, vestibule etc.) was performed on the volunteer. The average absorbed dose was 6.42 mGy by the OML and 1.59 mGy by the AML, respectively. With regard to visualization of the temporal bone structures, all structures were of equal quality with the two scan baseline. With the AML line, the radiation dose to the eye lens was reduced to 75%. Therefore, the authors recommended an AML for use for MDCT of the temporal bone. In clinical practice, the optimization of scanning factor (kVp, mAs etc.) and the use of the radio-protection should be implemented for radiation dose reduction of the eye lens by MDCT of the temporal bone.