Intensity modulated radiation therapy (IMRT) requires a precise set-up for which 3D matching using cone beam computed tomography (CBCT) is useful. Because images are acquired before every irradiation, investigating the exposure dose is essential. Such studies have been reported, but fewer reports have attempted to compare the dose with those in other modalities, as we did in this study. The exposure doses for imaging using 3 devices, including on board imager(OBI) CBCT, were measured using a tough water phantom, a self-made phantom, and a radiophotoluminescence glass dosimeter. The highest measured value was observed on OBI CBCT: the exposure dose was 4.3 times higher at some measurement sites than that from CT. Because this phenomenon is derived from the projection angle, a localized increase in the exposure dose may be prevented by changing the projection angle on each acquisition. Because the exposure dose for OBI CBCT was the highest and acquisition is performed before every irradiation, procedural modification is necessary, such as minimizing acquisition and the use of ultrasonography to confirm urine retention.
A presumption calculating formula of the X-ray spectrum generated from a molybdenum target X-ray tube is presented. The calculation procedure is to add an amount of characteristic X-ray photons that corresponds to the ratio of characteristic photons and bremsstrahlung photons to the bremsstrahlung spectrum obtained using semiempirical calculation. The bremsstrahlung spectrum was calculated by using a corrected Tucker's formula. The corrected content was a formula for calculating the self-absorption length in the target that originated in the difference of the incident angle to the target of the electron and the mass stopping power data. The measured spectrum was separated into the bremsstrahlung component and the characteristic photon component, and the ratio of the characteristic photons and bremsstrahlung photons was obtained. The regression was derived from the function of the tube voltage. Based on this calculation procedure, computer software was constructed that can calculate an X-ray spectrum in arbitrary exposure conditions. The X-ray spectrum obtained from this presumption calculating formula and the measured X-ray spectrum corresponded well. This formula is very useful for analyzing various problems related to mammography by means of Monte Carlo simulations.
Multi-detector computed tomography (MDCT) has rapidly evolved and is increasingly used for treatment simulation of thoracic and abdominal radiotherapy. A 320-detector row CT scanner has recently become available that allows axial volumetric scanning of a 16-cm-long range in a patient without table movement. Current radiotherapy techniques require a generous margin around the presumed gross tumor volume (GTV) to account for uncertainties such as tumor motion and set up error. Motion analysis is useful to evaluate the internal margin of a moving target due to respiration and to improve therapeutic precision. The purpose of this study is to propose a method using phase-only correlation to automatically detect the target and to assess the motion of the target in numerical phantoms and patients. Free-breathing scans using 320-detector row CT were acquired for 4 patients with lung tumor(s). The proposed method was feasible for motion analysis of all numerical phantoms and patients. The results reproduced the facts that the motion of tumors in the patients varied in orbits during the respiratory cycle and exhibited hysteresis. The maximum distance between peak exhalation and inhalation increased as the tumors approached the diaphragm. The proposed method detected the three-dimensional position of the targets automatically and analyzed the trajectories. The tumor motion due to respiration differed by region and was greatest for the lower lobe.
Super paramagnetic iron oxide (SPIO) is taken up in the bone marrow and lymph nodes, as well as by the liver. Focusing on the intervertebral disks, which are unaffected by contrast effects, we examined the relationship between magnetic resonance image (MRI) signal intensity after SPIO uptake in the vertebral body and intervertebral disks and investigated MRI signal intensity in bone marrow metastases and osteomyelitic (inflammatory) lesions after SPIO uptake by bone marrow. The lumbar spine was imaged in 5 healthy volunteers (age range, 26–48 years). A specified amount of SPIO was administered intravenously, and signal intensities before and after administration were measured. The signal intensity ratio with respect to the value before administration was calculated, and quantitative signal analysis was conducted. A similar investigation was performed in patients with bone metastasis and osteomyelitis. As a result of the metastasis, the signal intensity ratio showed a low value in comparison with normal marrow, and the osteomyelitis showed a high value in comparison with normal marrow. We report the usefulness of evaluations of changes in marrow signal intensity using SPIO in MRI.
In the data sampling in single photon emission computed tomography (SPECT), the continuous rotating acquisition method has high clinical utility. There have been various reports about the optimum sampling step angle for continuous rotating acquisition. Objective evaluation was performed visually and by measuring spatial resolution with a column phantom to find the optimum sampling step angle for continuous rotating acquisition. In locations far from the rotation center, a large sampling step angle produced artificial images with tangential elongation. The spatial resolution was 11.58 ± 0.19 mm full width half maximum (FWHM) as measured at a sampling step angle of 3 degrees and at 10 cm away from the rotation center. Increasing the sampling step angle to more than 3 degrees resulted in an increase of FWHM in the tangential direction. The optimum sampling step angle for continuous rotating acquisition in SPECT needs to be below that calculated from the sampling theorem.
Chest radiography is a widely used X-ray inspection. The numbers of patients who use wheelchairs in everyday life has increased in Japan, and their need for radiography has also increased. A unique supporting pad that enables chest radiography for patients in wheelchairs has been developed. This supporting pad applies the force of the patient’s weight and the frictional force to hold a cassette on. Performing chest radiography in the wheelchair using the supporting pad reduces the corporal burden of the patient in the wheelchair and the radiological technologist.
Quality assurance (QA) guidelines for medical display systems in Japan, JESRA X-0093, were published in August 2005 and have been used in many medical fields to maintain image quality on medical displays. This report offers detailed explanations of terms and testing methodologies in the guidelines, taking into account users with little knowledge of display technology. The management grade classifications, luminance meters, test patterns, and evaluation methods for executing the QA are supplementally described based on the technical background of related things. In addition, the validity of the evaluation methods and judgment criteria for uniformity and contrast response tests were examined in some experiments. The experimental results of the contrast response indicated that some cases presented inadequate display contrast even if the contrast responses were set within ±15% of the standard acceptable range for grade 1. The luminance responses of displays used in two computed tomography systems (CTs) and one magnetic resonance imaging system (MRI) were also measured, and the results indicated that their responses with conventional gamma responses were problematic for comparing images with those of medical displays.