Objective: The present study aimed to clarify gross tumor volume (GTV) contouring accuracy at the diaphragm boundary using respiratory-gated PET/CT. Methods: The lung/diaphragm boundary was simulated using a phantom containing 18F solution (10.6 kBq/mL). Tumors were simulated using spheres (diameter, 11–38 mm) containing 18F and located at the positions of the lungs and liver. The tumor background ratios (TBR) were 2, 4, and 8. The phantom was moved from the superior to inferior direction with a 20-mm motion displacement at 3.6 s intervals. The recovery coefficient (RC), volume RC (VRC), and standardized uptake value (SUV) threshold were calculated using stationary, non-gated (3D), and gated (4D) PET/CT. Results: In lung cancer simulation, RC and VRC in 3D PET images were, respectively, underestimated and overestimated in smaller tumors, whereas both improved in 4D PET images regardless of tumor size and TBR. The optimal SUV threshold was about 30% in 4D PET images. In liver cancer simulation, RC and VRC were, respectively, underestimated and overestimated in smaller tumors, and when the TBR was lower, but both improved in 4D PET images when tumors were >17 mm and the TBR was >4. The optimal SUV threshold tended to depend on the TBR. Conclusions: The contouring accuracy of GTV was improved by considering TBR and using an optimal SUV threshold acquired from 4D PET images.
The purpose of this study is to assess working environment preferences of radiological technologists using conjoint analysis. We carried a questionnaire survey on working environment preferences for 200 radiological technologists working in medical facilities in Japan. We defined eight characteristics for virtual medical facilities as follows: presence of colleagues who can be consulted, employment status, number of overtime work per month, academic meeting participation, number of hospital beds, presence of nuclear medicine imaging systems and radiation therapy systems, location of medical facilities, and change rate in annual income. A total of 18 virtual medical facilities were selected by an orthogonal array table using above-mentioned characteristics. The acquired data by the pairwise comparison method were analyzed by conjoint analysis. Marginal rates of substitution between income and non-pecuniary characteristics, which represent radiological technologists’ preferences, were also calculated. The factors influenced on their preferences were the following: employment status is not part-time, medical facility is smaller in scale, nuclear medicine imaging systems and radiation therapy systems are set up, and the number of overtime work is less. It was suggested that radiological technologists have a tendency to avoid increase of workloads and select his/her working place with emphasis on own experiences.
Purpose: The purpose of this study was to evaluate the effect of the virtual monochromatic spectral images (VMSI) and the model-based iterative reconstruction (MBIR) images, to evaluate the influence of the aperture size (40- and 20-mm beam) on renal pseudoenhancement (PE) compared with the filtered back projection (FBP) images. Methods: The renal compartment-CT phantom was filled with iodinated contrast material diluted to the attenuation of 180 Hounsfield units (HU) at 120 kV. The water-filled spherical structures, which simulate cyst, were inserted into the renal compartment. Those diameters were 7, 15 and 25 mm. These were scanned by conventional mode (helical scan, 120 kV-FBP) and dual energy mode. 70 keV-VMSI were reconstructed from the dual energy mode, and MBIR images were reconstructed from conventional mode at 40- and 20-mm aperture. Additionally, the phantom was scanned using non-helical mode with 20-mm aperture, and FBP images were reconstructed. The CT value of the PE for cyst areas was measured for these images. Results: The CT values of the cysts were 20.0–14.3 HU on the FBP images, 12.8–12.7 HU on the 70 keV-VMSI (PE-inhibition ratio was 36.0–11.2%) and 16.2–14.0 HU on the MBIR images (19.0–2.1%), respectively, at 40-mm aperture. The PE-inhibition ratio scanned by 20-mm aperture was improved by 28.0% with FBP, 32.8% with 70 keV-VMSI and 29.6% with MBIR compared with 40-mm aperture. One of the FBP images with non-helical mode was 11.6 HU. Conclusions: The best CT technique to minimize PE was the combination of 70 keV-VMSI and 20-mm aperture.
Half scan can acquire images at the 200° rotation in image-guided radiation treatment using cone-beam CT and is useful to evaluate the influence of the half-scan-imaging start angle and imaging direction on image registration accuracy. The half-scan-imaging start angle is changed from 180° to 340° in the clockwise direction and from 180° to 20° in the counter clockwise direction to calculate the registration error. As a result, registration errors between −0.37 mm and 0.27 mm in the left and right directions occur because of the difference in the imaging start angle and approximately 0.3° in the gantry rotation direction because of the difference in the imaging direction. Because half scan does not have data for 360° rotation, depending on the subject structure, inconsistency of opposing data can lower reconstruction accuracy and cause a verification error. In addition, in image acquisition during rotation, the slower the shutter speed is, the more the actual gantry angle and angle information of the image are apart, which is considered the cause of rotation errors. Although these errors are very minute, it is thought that there is no influence on the treatment effect, but these errors are considered an evaluation item indispensable for ensuring the accuracy of high-precision radiation treatment. In addition, these errors need to be considered for ensuring the quality of high-precision radiation treatment.
In this study, we propose an evaluation method for Bayesian estimation of Gumbel distribution parameters by the Hamiltonian Monte Carlo method (HMC method), with changing the pixel size of the CT image to investigate streak artifacts, without using a significant difference test. Placed a titanium endcap in the center of the CT dose index (CTDI) measurement phantom and got the CT image by changing the display-field of view (D-FOV) to S, M, L, LL. We compared Gumbel distribution parameters with conventional estimation method and Bayesian estimation method using HMC method. In addition, we evaluated streak artifacts by Bayesian statistical analysis. The difference in streak artifact between D-FOV was more than 90% except between D-FOV M and L. The effect of streak artifacts is small as the pixel size was small. By using the HMC method, we can estimate the Gumbel distribution parameters accurately and objectively, and quantitatively evaluated that the streak artifacts differ in pixel size using Bayesian statistical analysis.
Although fat suppression technique is used in breast MRI, artifacts often appear owing to susceptibility and defective fat suppression effect after breast surgery. This is due to the abundance of adipose tissue in the breast as well as the region of air around the circumference of the excision site. Therefore, we have evaluated the optimal pad material for achieving fat suppression in breast MRI to reduce image artifacts and patient discomfort while maintaining breast shape. Oil of the solidity was used as the breast phantom material after segmental resection surgery. Five pad materials, including rice, ball bullets, glass beads, acrylic beads, and bath salts were used to fill the defects. Fat-suppressed, T1-weighted, three-dimensional imaging was performed using a breast array coil. Images with and without the five pad materials, were evaluated physically, visually, and by contact. Physical evaluation consisted of measuring the maximum signal and standard deviation in the regions of interest (ROIs). Discomfort and the amount of perceived resistance were evaluated during contact evaluation by inserting a finger into each pad material. In results, glass beads and bath salts produced a significantly larger fat suppression effect in the ROIs. Visual and contact evaluation also highlighted the benefits of glass beads, the latter demonstrating a significant decrease in discomfort and perceived resistance. In conclusion, we consider glass beads as the optimal pad material for fat suppression in breast MRI after surgery.
Purpose: The aim of our study is to evaluate whether an 18F-FDG PET/CT image quality is influenced by the obesity type visceral fat or subcutaneous fat. Methods: We chose continuously 68 patients with obesity (35 subcutaneous fats and 33 visceral fats) who underwent an 18F-FDG PET/CT scan at our clinic from January 3, 2015 to June 30, 2015. And then, we calculated the noise equivalent count (NECdensity), the signal to noise ratio of the liver (SNRliver), and the ratio of random coincidence counts to total prompt (random/prompt countrate) on each PET/CT image. Results: We observed that NECdensity was decreased as the body mass index (BMI) and the abdominal circumference increased regardless of the obesity type. When the BMI was on the same degree between two types, however, NECdensity of a visceral fat was 21.6% that is inferior to that of subcutaneous fat on the average. A similar relation was satisfied also in abdominal circumference. Conversely, random/prompt countrate of a visceral fat was more than that of subcutaneous fat when the abdominal circumference and BMI were on the same degree, respectively. Overall, random/prompt countrate tended to increase as BMI and the abdominal circumference increased. With respect to SNRliver, the value of a visceral fat was inferior to that of subcutaneous fat unconditionally. Conclusion: When the BMI and abdominal circumference are on the same degree, respectively, the 18F-FDG PET/CT image quality of visceral fat is inferior to that of subcutaneous fat. The measure is to extend the collection time by about 20% in the pelvic area from the abdomen of visceral fat type obesity.
The purpose of this study was to investigate the effect of scattered radiation reduction to medical staff by attaching the leaded sheet on the collimator cover of the angiography equipment. Ambient dose equivalent was measured to compare the rate of scattered radiation reduction between with and without the leaded sheet. Shielding effect was confirmed for scattered radiation in all directions, especially 27% of shielding ratio in the head and neck area when angiography equipment installed with small detector, and more than 40% of shielding ratio when adjusting a cut portion of leaded sheet to the field size. However, it decreased when the dose area product meter was not attached. Therefore, our proposed leaded sheet can reduce radiation dose to medical staff during angiographic and interventional procedures.
Recently, dopamine transporter (DaT) scintigraphy, which contributes to the early diagnosis of Parkinsonʼs disease and Lewy body dementia, has been widely spread. It has been revealed that analytical results can be affected by the image-reformatting angle, and a horizontal section is recommended for the anterior commissure-posterior commissure (AC-PC) line according to the clinical guidelines for ioflupane. However, it is difficult to identify AC-PC line visually, as there is no remarkable accumulation in the cerebral parenchyma in DaT scintigraphy with poor contrast resolution. The objective of this study was to establish and optimize an adjustment method for the image-reformatting angle by using orbitomeatal base line (OM line). Evaluations were made on items such as comparison of image reformatting angles by an analyst, comparison of measurement angles of OM line, the angle formed by the intersection of OM line and AC-PC line, and the change in specific biding ratio (SBR) according to the difference in the image-reformatting angle. Consequently, the difference in analytical results among technicians became smaller, and consistent results were obtained by adjusting the image-reformatting angle.