The 10 most-cited articles in Japanese Journal of Radiological Technology, 2021

Purpose: Knowledge-based planning (KBP) has disadvantages of high monitor unit (MU) and complex multi-leaf collimator (MLC) motion. We investigated the optimal aperture shape controller (ASC) level for the KBP to reduce these factors in volumetric modulated arc therapy (VMAT) for prostate cancer. Methods: The KBP model was created based on 51 clinical plans (CPs) of patients who underwent the VMAT for prostate cancer. Another 10 CPs were selected randomly, and the KBPs with/without ASC, changed stepwise from very low (KBP-VL) to very high (KBP-VH), were performed with a single auto-optimization. The parameters of dose-volume histograms (DVHs) and MLC performance metrics were evaluated. We obtained the modulation complexity score for VMAT (MCSv), closed leaf score (CLS), small aperture score (SAS), leaf travel (LT), and total MU. Results: The ASC did not affect the DVH parameters negatively. The following comparisons of MLC performance were obtained (KBP vs. KBP-VL vs. KBP-VH, respectively): 0.25 vs. 0.27 vs. 0.30 (MCSv), 0.19 vs. 0.18 vs. 0.16 (CLS), 0.50 vs. 0.45 vs. 0.40 (SAS10…

PURPOSE: We focused on deep learning for a reduction of motion artifacts in MRI. It is difficult to collect a large number of images with and without motion artifacts from clinical images. The purpose of this study was to create motion artifact images in MRI by simulation. METHODS: We created motion artifact images by computer simulation. First, 20 different types of vertical pixel-shifted images were created with different shifts, and the amount of pixel shift was set from -10 to 10 pixels. The same method was used to create pixel-shifted images for horizontal shift, diagonal shift, and rotational shift, and a total of 80 types of pixel-shifted images were prepared. These images were Fourier transformed to create 80 types of k-space data. Then, phase encodings in these k-space data were randomly sampled and Fourier transformed to create artifact images. The reproducibility of the simulation images was verified using the deep learning network model of U-net. In this study, the evaluation indices used were the structural similarity index measure (SSIM) and peak signal-to-noise ratio…

Validation study of simulation codes was performed based on the measurement of a sphere phantom and the National Electrical Manufacturers Association (NEMA) body phantoms. SIMIND and Prominence Processor were used for the simulation. Both source and density maps were generated using the characteristics of 99mTc energy. A full width at half maximum (FWHM) of the sphere phantom was measured and simulated. Simulated recovery coefficient and the background count coefficient of variation were also compared with the measured values in the body phantom study. When the two simulation codes were compared with actual measurements, maximum relative errors of FWHM values were 3.6% for Prominence Processor and -10.0% for SIMIND. The maximum relative errors of relative recovery coefficients exhibited 11.8% for Prominence Processor and -2.0% for SIMIND in the body phantom study. The coefficients of variation of the SPECT count in the background were significantly different among the measurement and two simulation codes. The simulated FWHM values and recovery coefficients paralleled measured…

PURPOSE: Because of the promotion of cancer screening, the number of patients with lung cancer detected at the early stage has increased. However, it was reported that 30-40% of the lung cancer patients at stage I relapsed. If the recurrence risk can be accurately predicted, it is possible to give medical care for improving the prognosis of lung cancer patients. The purpose of this study was to develop a method for the prediction of recurrence risk of patients with lung cancer by using survival analysis of radiomics approach. METHOD: A public database was used in this study. Fifty patients (25 recurrences and 25 censored cases) classified as stage I or II were selected and their pretreatment computed tomography (CT) images were obtained. First, we selected one slice containing the largest tumor area and manually segmented the tumor regions. We subsequently calculated 367 radiomic features such as tumor size, shape, CT values, and texture. Radiomic features were selected by using least absolute shrinkage and selection (Lasso). Cox regression model and random survival forest (RSF)…

PURPOSE: To evaluate image quality for chest radiography at different radiation qualities, using phantoms with scatter fractions similar to those of lungs. METHODS: Two base phantoms with 10 and 4 cm thicknesses, respectively, made of a soft tissue-equivalent material, were used to mimic the X-ray attenuation of the human lung. Two plates with soft tissue- and bone-equivalent materials, respectively, were placed on the base phantom as contrast objects. The image data were obtained with the same entrance surface dose in each radiation quality. Six radiation qualities generated using 120 and 90 kV, and additional copper filters with thicknesses 0, 0.1, and 0.2 mm were selected. The signal-difference-to-noise ratio (SdNR) and a contrast ratio of the soft tissue to the bone were measured for the six radiation qualities. RESULTS: The thicker the additional filter, the better the SdNR at both tube voltages. The SdNR values were not significantly different between 120 and 90 kV for the same filter thickness. The contrast ratio was higher at 120 than at 90 kV by approximately 8%.…

PURPOSE: The method using a numerical slit (slit method) is used commonly to obtain the one-dimensional (1D) noise power spectrum (NPS) in computed tomography. However, the relationship between the 1D-NPS obtained by the slit method and the original two-dimensional (2D) NPS derived by the 2D Fourier transformation has not been elucidated clearly. The purpose of this study was to clarify their relationship based on the well-known central slice theorem (projection slice theorem) and validate it using computer simulation analysis. METHODS: With the application of the central slice theorem, we described that the 1D-NPS obtained by the slit method was equal to the central slice (profile) in the 2D-NPS when we set the slit length to the maximum (i.e. the matrix size of the noise image). To verify this, we generated computer-simulated noise images with the known 2D-NPS (true 2D-NPS). From those images, we obtained the 1D-NPS that was obtained by the slit method and compared it with the central slice in the true 2D-NPS. RESULTS: When we set the slit length to the maximum, the 1D-NPS…

PURPOSE: To investigate the actual condition of the crystalline lens equivalent dose and effective dose according to the type of job and the type of duties in a medical institution. We also sought to clarify effective exposure reduction strategies. METHODS: Equivalent crystalline lens doses, effective doses, job type, and duties for 8656 persons · year were obtained from 17 medical facilities. We analyzed the relationship between the effective dose and the crystalline lens equivalent dose in uniform exposure control and non-uniform exposure control conditions. Exposure data were obtained for 13 unique job types and duties. RESULTS: The ratio of the lens equivalent dose to the effective dose of non-uniform exposure managers was 2 to 6 times and varied depending on the occupation. The percentage of persons whose annual lens equivalent dose exceeded 20 mSv was 4.75% for medical doctors, 1.17% for nurses, and 0.24% for radiological technologists. Highly exposed tasks included doctors in cardiology and gastroenterology performing angiography and endoscopy, nurses in endoscopy, and…

We conducted a nationwide multicenter survey of various interventional radiology (IVR) procedures. Data were collected from 385 X-ray systems in 126 institutions, including 432 cine programs and 380 digital subtraction angiography (DSA) programs for diagnostic catheterization, percutaneous coronary intervention (PCI), ablation, transcatheter aortic valve implantation (TAVI), neurologic IVR, thorax IVR, abdominal IVR, and endovascular therapy (EVT). Fluoroscopic and cine dose rates were 10.1 mGy/min and 110.7 mGy/min, respectively, whereas for DSA programs, the median fluoroscopic and DSA dose rates were 8.0 mGy/min and 224.8 mGy/min, respectively. The DSA dose rate was more than twice the cine dose rate. The largest difference between dose rates was for diagnostic catheterization, which had a cine dose rate of 142.6 mGy/min and a fluoroscopic dose rate of 12.6 mGy/min (by a factor of 12.5), followed by EVT, which had a DSA dose rate of 216.0 mGy/min and a fluoroscopic dose rate of 7.7 mGy/min (by a factor of 29.6). The smallest difference between dose rates was for TAVI, which had a…

PURPOSE: Quantitative analysis using a standardized uptake value (SUV) has become possible for single-photon emission computed tomography-computed tomography (SPECT-CT) of bone. However, previous research was targeted to the trunk area, and there are few studies for the head and neck region. Therefore, the purpose of this study was to determine the optimal image reconstruction conditions for bone SPECT of the head and neck using a phantom study. METHOD: Tc solution enclosed in the cylindrical phantom was set to the same count rate as in clinical cases, and six hot spheres (10, 13, 17, 22, 28, 37 mm) with four times the concentration were placed within it. The image reconstruction was 3D-OSEM, and the reconstruction conditions were varied by the number of iterative updates and the width of the Gaussian filter. Quantitative evaluations of the image quality were performed using the % contrast, background variability, and SUV for the hot spheres and background. A visual evaluation was performed by four observers to determine the optimal image reconstruction conditions for bone SPECT of…