Vendor-Specific Correction Software for Apparent Diffusion Coefficient Bias Due to Gradient Nonlinearity in Breast Diffusion-Weighted Imaging Using Ice-Water Phantom.

OBJECTIVE: This study aimed to evaluate a vendor-specific correction software for apparent diffusion coefficient (ADC) bias due to gradient nonlinearity in breast diffusion-weighted magnetic resonance imaging using an ice-water phantom. METHODS: The phantom consists of 5 plastic tubes with a length of 100 mm and a diameter of 15 mm, filled with distilled water and immersed in an ice-water bath. Diffusion-weighted images were acquired by echo-planar imaging sequence on a 3.0-T scanner. ADC maps with and without correction were calculated using 4 b-values (0, 100, 600, and 800 s/mm2). The mean ADCs were measured using a rectangular profile with 5 × 40 pixels in the anterior-posterior (AP) and a square region of interest with 5 × 5 pixels in the right-left (RL) and superior-inferior (SI) directions on the ADC map. ADC was compared with and without correction using a paired t test. Additionally, ADC of the ice-water phantom was measured at the magnet isocenter. RESULTS: ADC increased in the AP and RL directions and decreased in the SI direction with increasing distance from the isocenter before correction. After the correction, ADC at the off-center positions in the AP, RL, and SI directions was reduced to within 5% of the expected value. There were significant differences in the ADC at the off-center positions without and with correction (P < 0.001); however, ADC at the magnet isocenter did not vary after correction (1.08 ± 0.02 × 10-3 mm2/s). CONCLUSIONS: The vendor-specific software corrected the ADC bias due to gradient nonlinearity at the off-center positions in the AP, RL, and SI directions. Therefore, the software will contribute to the accurate ADC assessment in breast DWI.

Patient Positioning Assistive Technology Applicable to the Existing Computed Tomography System: Estimation by Pixel Value of Scout Image.

ABSTRACT: This study aimed to propose a patient positioning assistive technique using computed tomography (CT) scout images. A total of 210 patients who underwent CT scans in a single center, including on the upper abdomen, were divided into a study set of 127 patients for regression and 83 patients for verification. Linear regression analysis was performed to determine the R2 coefficient and the linear equation related to the mean pixel value of the scout image and ideal table height (TH ideal ). The average pixel values of the scout image were substituted into the regression equation to estimate the TH ideal . To verify the accuracy of this method, the distance between the estimated table height (TH est ) and TH ideal was measured. The medians of age (in years), gender (male/female), height (in centimeters), and body weight (in kilograms) for the regression and verification groups were 68 versus 70, 85/42 versus 55/28, 163.8 versus 163.0, and 59.9 versus 61.9, respectively. Linear regression analysis indicated a high coefficient of determination ( R2 = 0.91) between the mean pixel value of the scout image and TH ideal . The correlation coefficient between TH ideal and TH est was 0.95 (95% confidence interval, 0.92-0.97; P < 0.0001), systematic bias was 0.2 mm, and the limits of agreement were -5.4 to 5.9 ( P = 0.78). The offset of the table height with TH est was 2.8 ± 2.1 mm. The proposed estimation method using scout images could improve the automatic optimization of table height in CT, and it can be used as a general-purpose automatic positioning technique.

Pacemaker Malfunction During Passive Proton Beam Therapy for Localized Prostate Cancer: Case Reports and a Literature Review.

We report two cases of pacemaker malfunction occurring during proton beam therapy (PBT) for localized prostate cancer treatment. The first case involved mode changes in the pacemaker, while the second exhibited prolongation of the RR interval. Remarkably, both cases did not manifest significant clinical changes. Our findings indicate that careful consideration should be given to passive PBT in patients with localized prostate cancer who have pacemakers, like the considerations in patients with thoracic and abdominal cancers. Moreover, our report highlights the importance of recognizing potential cardiac implantable electronic devices malfunction in various PBT scenarios.

Physical characteristics of deep learning-based image processing software in computed tomography: a phantom study.

PURPOSE: This study aimed to assess the image characteristics of deep-learning-based image processing software (DLIP; FCT PixelShine, FUJIFILM, Tokyo, Japan) and compare it with filtered back projection (FBP), model-based iterative reconstruction (MBIR), and deep-learning-based reconstruction (DLR). METHODS: This phantom study assessed the object-specific spatial resolution (task-based transfer function [TTF]), noise characteristics (noise power spectrum [NPS]), and low-contrast detectability (low-contrast object-specific contrast-to-noise ratio [CNRLO]) at three different output doses (standard: 10 mGy; low: 3.9 mGy; ultralow: 2.0 mGy). The processing strength of DLIPFBP with A1, A4, and A9 was compared with those of FBP, MBIR, and DLR. RESULT: The standard dose with high-contrast TTFs of DLIPFBP exceeded that of FBP. Low-contrast TTFs were comparable to or lower than that of FBP. The NPS peak frequency (fP) of DLIPFBP shifts to low spatial frequencies of up to 8.6% at ultralow doses compared to the standard FBP dose. MBIR shifted the most fP compared to FBP-a marked shift of up to 49%. DLIPFBP showed a CNRLO equal to or greater than that of DLR in standard or low doses. In contrast, the CNRLO of the DLIPFBP was equal to or lower than that of the DLR in ultralow doses. CONCLUSION: DLIPFBP reduced image noise while maintaining a resolution similar to commercially available MBIR and DLR. The slight spatial frequency shift of fP in DLIPFBP contributed to the noise texture degradation suppression. The NPS suppression in the low spatial frequency range effectively improved the low-contrast detectability.

Improvement of diagnostic performance of hyperacute ischemic stroke in head CT using an image-based noise reduction technique with non-black-boxed process.

PURPOSE: This study aims to investigate whether an image-based noise reduction (INR) technique with a conventional rule-based algorithm involving no black-boxed processes can outperform an existing hybrid-type iterative reconstruction (HIR) technique, when applied to brain CT images for diagnosis of early CT signs, which generally exhibit low-contrast lesions that are difficult to detect. METHODS: The subjects comprised 27 patients having infarctions within 4.5 h of onset and 27 patients with no change in brain parenchyma. Images with thicknesses of 5 mm and 0.625 mm were reconstructed by HIR. Images with a thickness of 0.625 mm reconstructed by filter back projection (FBP) were processed by INR. The contrast-to-noise ratios (CNRs) were calculated between gray and white matters; lentiform nucleus and internal capsule; infarcted and non-infarcted areas. Two radiologists subjectively evaluated the presence of hyperdense artery signs (HASs) and infarctions and visually scored three properties regarding image quality (0.625-mm HIR images were excluded because of their notably worse noise appearances). RESULTS: The CNRs of INR were significantly better than those of HIR with P < 0.001 for all the indicators. INR yielded significantly higher areas under the curve for both infarction and HAS detections than HIR (P < 0.001). Also, INR significantly improved the visual scores of all the three indicators. CONCLUSION: The INR incorporating a simple and reproducible algorithm was more effective than HIR in detecting early CT signs and can be potentially applied to CT images from a large variety of CT systems.

Number of computed tomography scanners and regional disparities based on population and medical resources in Japan.

This study aimed to discover the associations between the number of computed tomography (CT) scanners and the population, as well as number of medical resources to identify regional disparities in Japan. The number of CT scanners was tabulated for each detector row of CT scanners for hospitals and clinics in each prefecture. The number of CT scanners, patients, medical doctors, radiological technologists, facilities, and beds per 100,000 population was compared. Additionally, the number of hospitals with ≥ 200 beds and multidetector-row CT scanners with ≥ 64 rows were tabulated, and their ratios were calculated. Medical institutions in Japan have installed 14,595 scanners. CT scanners per 100,000 population were the highest in Kochi Prefecture, although the number of CT scanners in hospitals was the highest in Tokyo Prefecture. Multivariate analysis revealed the number of radiological technologists (ß coefficient: 0.49; P = 0.03), facilities (ß coefficient: 0.12; P < 0.01) and beds (ß coefficient: 0.46; P < 0.01) as independent factors for the number of CT scanners. Prefectures with a high proportion of hospitals with ≥ 200 beds also had a relatively high proportion of CT scanners with ≥ 64 rows (P < 0.01). Our survey revealed an association between regional disparities in the number of CT scanners in Japan, the population, and number of medical resources. A positive correlation was found between hospital size and number of CT scanners with ≥ 64 rows.

Patient dose increase caused by posteroanterior CT localizer radiographs.

INTRODUCTION: The aim of this study was to compare the output dose (volume CT dose index [ CTDIvol], and dose length product [DLP]) of automatic tube current modulation (ATCM) determined by localizer radiographs obtained in the anteroposterior (AP) and posteroanterior (PA) directions. METHODS: One hundred and twenty-four patients who underwent upper abdomen and/or chest-to-pelvis computed tomography (CT) were included. Patients underwent two series of CT examinations, and localizer radiographs were obtained in the AP and PA directions. The horizontal diameter of the localizer radiograph, scan length, CTDIvol, and DLP were measured. RESULTS: There was no significant difference in the scan length; however, all the other values were significantly higher in the PA direction. The mean horizontal diameter was 33.1 ± 2.6 cm and 35.4 ± 2.9 cm in the AP and PA directions of the localizer radiographs, respectively. The CTDIvol and DLP in the PA direction increased by approximately 7-8%. Bland-Altman plots between AP and PA localizer directions in upper abdominal CT showed a positive bias of 1.1 mGy and 30.0 mGy cm for CTDIvol and DLP, respectively. Correspondingly, chest-to-pelvic CT showed a positive bias of 0.93 mGy and 69.3 mGy cm for CTDIvol and DLP, respectively. CONCLUSION: The output dose of ATCM determined by localizer radiographs obtained in the PA direction was increased compared to the AP direction. Localizer radiographs obtained in the AP direction should be preferred for optimizing the output dose using ATCM. IMPLICATIONS FOR PRACTICE: Based on the evidence of this study, localizer radiographs obtained in the AP direction should be preferred for optimizing the output dose in CT examinations.

Computed tomographic pulmonary angiography: Three cases of low-tube-voltage acquisition with a slow injection of contrast medium.

Acute pulmonary thromboembolism occurring during cancer treatment has been increasing with the number of cancer patients and chemotherapy cases. Computed tomographic pulmonary angiography (CTPA) for evaluating the pulmonary artery is generally performed using rapid injection of contrast medium. However, intravenous catheters for contrast medium injection might cause extravasation due to rapid injection. This case series describes three patients who underwent contrast-enhanced computed tomography combined with low-tube-voltage imaging and slow injection. Low-tube-voltage slow-injection CTPA can be an effective technique for obtaining high contrast enhancement while accommodating fragile veins and low injection rates.

Inaccurate table height setting affects the organ-specific radiation dose in computed tomography.

PURPOSE: We aimed to prove that the locally absorbed doses in tissues and organs are affected by inaccurate table height in computed tomography. MATERIALS AND METHODS: We compared the volume CT dose index (CTDIvol) and the absorbed doses using an anthropomorphic phantom combined with a breast phantom. The phantom was set at the gantry center, from which the table height was changed every 20 mm between-40 mm and 40 mm. Data acquisition was performed using auto table height correction (AHC) for each table height. The CTDIvol was obtained from the CT console and the tube current value for each image slice (DICOM tag: 0018, 1151). The absorbed dose was measured by a glass dosimeter that was implanted at various positions in the phantom. RESULTS: The tube current values in the lung were lower at a table height of + 40 mm than those at other heights. The CTDIvol was slightly lower at + 40 mm than at the center (12.78 mGy vs. 13.42 mGy, p < 0.05). The CTDIvol values were almost the same at the other table heights (13.30-13.40 mGy). The absorbed doses at the lens and mammary gland were significantly different from those at the gantry center (-27.27%-17.77% and -24.31%-12.83%, respectively). Compared with the center, both the lens and mammary gland had higher absorbed doses at a table height of -40 mm. CONCLUSION: The absorbed dose was affected by the table height, but the CTDIvol was maintained by AHC. The operator should appropriately position patients even when using AHC.

Ultrahigh-Resolution Computed Tomography Improves Preoperative Computed Tomography Angiography for Deep Inferior Epigastric Artery Perforator Flap Reconstruction.

OBJECTIVE: The aim of the study was to compare computed tomography (CT) angiography (CTA) imaging of deep inferior epigastric artery perforator (DIEP) using the ultrahigh-resolution CT (UHRCT) and conventional multidetector CT (MDCT). METHODS: This retrospective study enrolled 20 patients who underwent CTA of DIEP flap with UHRCT and MDCT. Computed tomography values were measured at 4 large vessels (thoracic aorta, abdominal aorta, common iliac artery, and external iliac artery) and 5 peripheral vessels (proximal and distal internal thoracic artery, proximal and distal deep inferior epigastric artery, and DIEP). RESULTS: There were no significant differences in mean CT values of the major vessel between UHRCT and MDCT. Ultrahigh-resolution CT shows higher CT values of the peripheral vessels than MDCT (P < 0.05 for all). The median CT values of the DIEP in UHRCT were approximately 3 times higher than those in MDCT (P < 0.001). CONCLUSIONS: Ultrahigh-resolution CT provides higher-quality CTA of DIEP compared with MDCT.

Apparent diffusion coefficient measurement using thin-slice diffusion-weighted magnetic resonance imaging: assessment of measurement errors and repeatability.

We investigated the measurement error and repeatability of the apparent diffusion coefficient (ADC) obtained using thin-slice imaging. Diffusion-weighted images of an ice-water phantom were acquired using 1.5-T and 3.0-T scanners with 1-, 3-, and 5-mm thickness. ADC maps were generated at b = 0 and 1000 mm2/s using five consecutive scans. Measurement errors were assessed with accuracy and precision. Repeatability was assessed using the within-subject coefficient of variation. The ADC accuracy of both scanners agreed with the ADC of water at 0 °C. At 1-mm, precisions were 2.9% and 8.4% for the 3.0-T and 1.5-T scanners, respectively. The repeatabilities of 1-mm thickness were 1.3% and 3.4% in the 3.0-T and 1.5-T scanners, respectively. The 3.0-T scanner showed acceptable measurement errors and moderate repeatability compared with Quantitative Imaging Biomarkers Alliance recommendation. A 3.0-T scanner can be used for reliable ADC measurement, even with a 1-mm thickness at a reasonable scan time.

Comparison of five-phase computed tomography images of type 1 autoimmune pancreatitis and pancreatic cancer: Emphasis on cases with atypical images.

BACKGROUND/OBJECTIVES: International consensus diagnostic criteria (ICDC) include characteristic images of autoimmune pancreatitis (AIP); however, reports on atypical cases are increasing. The aims of this study were to compare CT findings between AIP and pancreatic cancer (PC), and to analyze type 1 AIPs showing atypical images. METHODS: Five-phase CT images were compared between 80 type 1-AIP lesions and 80 size- and location-matched PCs in the case-control study. Atypical AIPs were diagnosed based on the four ICDC items. RESULTS: ICDC items were recognized in most AIP lesions; pancreatic enlargement (87.7%), narrowing of the main pancreatic duct (98.8%), delayed enhancement (100%), and no marked upstream-duct dilation (97.5%). CT values of AIPs increased rapidly until the pancreatic phase and decreased afterward, while those of PCs gradually increased until the delayed phase (P < 0.0001). Atypical images were recognized in 14.8% of AIPs, commonly without pancreatic enlargement (18.5 mm) and sometimes mimicking intraductal neoplasms. The CT values and their ratios were different between atypical AIPs and size-matched PCs most significantly in the pancreatic phase, but similar in the delayed phase. CONCLUSIONS: Ordinary type 1 AIPs can be diagnosed with the ICDC, but atypical AIPs represented a small fraction. "Delayed enhancement" is characteristic to ordinary AIPs, however, "pancreatic-phase enhancement" is more diagnostic for atypical AIPs.

Deep learning-based reconstruction in ultra-high-resolution computed tomography: Can image noise caused by high definition detector and the miniaturization of matrix element size be improved?

PURPOSE: This study aimed to assess the noise characteristics of ultra-high-resolution computed tomography (UHRCT) with deep learning-based reconstruction (DLR). METHODS: Two different diameters of water phantom were scanned with three different resolution acquisition modes. Images were reconstructed by filtered back projection (FBP), hybrid iterative reconstruction (hybrid-IR), and DLR. Image noise analysis was performed with noise magnitude, peak frequency (fp) of the noise power spectrum (NPS), and the square root of the area under the curve (√AUCNPS) for the NPS curve. RESULTS: The noise magnitude was up to 3.30 times higher for the FBP acquired in SHR mode than that for the NR mode. The fp values of the FBP were 0.20-0.21, 0.34-0.36, and 0.34-0.37 cycles/mm for normal resolution (NR), high resolution (HR), and super high resolution (SHR) mode, respectively. The fp of hybrid-IR was 0.16-0.19, 0.21-0.26, and 0.23-0.26 cycles/mm for NR, HR, and SHR mode, respectively. The fp of DLR was 0.21-0.32 and 0.22-0.33 cycles/mm for HR and SHR mode, respectively. √AUCNPS showed that the highest value in FBP images of the SHR mode was up to 1.89 times that of the NR mode. DLR in the HR and SHR modes showed high noise reduction while suppressing fp shift with respect to FBP. CONCLUSIONS: The new DLR algorithm could be a solution to the noise increase due to the high-definition detector elements and the small reconstruction matrix element size.

Radiation dose and image quality of CT fluoroscopy with partial exposure mode.

PURPOSE: The present study aimed to evaluate the scan technique of computed tomography (CT)-guided puncture procedures using partial exposure mode (PEM) on the radiation dose of the operator's hand and image quality. METHODS: Radiation dose was evaluated using three types of scanning methods: one-shot scan (OS), OS with a bismuth shield added (OSBismuth), and a half-scan (i.e., PEM) capable of an adjustable exposure angle. Dose evaluation was performed using a torso phantom, while a circular phantom simulating the liver parenchyma and lesions was used for image quality evaluation. For each scanning method, four measurements were made to determine the radiation dose to the operator's hand and the dose distribution on the surface of the patient's torso; the output-dose profile was determined from five measurements. Image quality was evaluated in terms of contrast and contrast-to-noise ratio (CNR). Analysis of variance (ANOVA) or Friedman test were used for comparison between groups as appropriate. The post hoc tests were Tukey's honestly difference (HSD) test for parametric data or Wilcoxon signed rank test with Bonferroni correction for nonparametric data. RESULTS: The PEM yielded a radiation dose to the operator's hand that was 84% (0.35 vs. 2.33 mGy) lower than that of the OS. The dose to the patient's torso was reduced by 35% and 68% for the OSBismuth and PEM, respectively, relative to that of the OS. Compared with the CNR of the other two scanning methods (OS, 2.9±0.1; OSBismuth, 2.9±0.1), the PEM increased the standard deviation and decreased the CNR (2.1±0.04, Tukey's HSD, P < 0.001 for all). Images acquired with PEM showed visibility equivalent to that of other scanning methods when window conditions were adjusted. CONCLUSION: This study demonstrated that CT-guided puncture procedure using PEM effectively reduces the operator's exposure to radiation while minimizing image quality deterioration.

Spatial resolution compensation by adjusting the reconstruction kernels for iterative reconstruction images of computed tomography.

PURPOSE: Hybrid iterative reconstruction (IR) is useful to reduce noise in computed tomography (CT) images. However, it often decreases the spatial resolution. The ability of high spatial resolution kernels (harder kernels) to compensate for the decrease in the spatial resolution of hybrid IRs was investigated. METHODS: An elliptic cylindrical phantom simulating an adult abdomen was used. Two types of rod-shaped objects with ~330 and ~130 HU were inserted to simulate contrasts of arteries in CT angiography. Two multi-slice CT systems were used to scan the phantoms with 120 kVp and scan doses of 20 and 10 mGy. The task transfer functions (TTFs) were measured from the circular edges of the rod images. The noise power spectrum (NPS) was measured from the images of the water-only section. The CT images were reconstructed using a filtered back projection (FBP) with baseline kernels and two levels of hybrid IRs with harder kernels. The profiles of the clinical images across the aortic dissection flaps were measured to evaluate actual spatial resolutions. RESULTS: The TTF degradation of each hybrid IR was recovered by the harder kernels, whereas the noise reduction effect was retained, for both the 20 and 10 mGy. The profiles of the dissection flaps for the FBP were maintained by using the harder kernels. Even with the best combination of hybrid IR and harder kernel, the noise level at 10 mGy was not reduced to the level of FBP at 20 mGy, suggesting no capability of a 50% dose reduction while maintaining noise.

Wedged field using the half-field method with a flattening filter-free photon beam.

In this study, we propose a novel wedged field using a half-field flattening filter-free beam without a metallic filter or a moving jaw, and investigate the characteristics of the proposed technique. Dose distributions of the proposed method were first determined in virtual-water or anthropomorphic phantom using a radiotherapy planning system. We evaluated the wedge angle as a function of the field size, collimator rotation, and depth. The wedge angle at 10 MV was observed to be greater than that at 6 MV. The minimum angles at 6 and 10 MV were 17.7° and 40.4°, respectively, while the maximum angles were 33.9° and 48.4°, respectively. We determined that the wedge angle depended on the nominal beam energy and field size, and we verified that the proposed method is capable of delivering a gradient dose distribution and reducing treatment time.

[Improvement of Beam Hardening Effects of Virtual Monochromatic Image in Dual-energy CT: A Electron Density Phantom Study].

PURPOSE: A virtual monochromatic image (VMI) is acquired from two different types of polychromatic energy X-rays, not a monochromatic X-ray. The effective energy of monochromatic X-ray does not vary in passing through the patient's body. On the other hand, beam hardening effects are seen in images because of the change of polychromatic X-ray energy. The purpose of the present study was to evaluate the beam hardening improvement effect of VMI using a phantom with a bone mimicking ring. METHOD: We used a water equivalent electron density phantom with a hole in the center for inserting various measurement materials (i.e. fat, two types of bone with differing densities, contrast medium, blood, and water). Then, the CT numbers of each measurement materials were obtained from single energy CT (SECT) images and VMIs, respectively. Also, an additional bone-mimetic ring was used to obtain the CT numbers for evaluation of beam hardening effect. The CT number change rates were calculated from the obtained CT numbers with and without beam hardening effect. RESULT: The rate of CT number, change of VMI was significantly lower than that of SECT for all measured materials. CONCLUSION: In this study, VMI minimized changes in CT numbers due to the beam hardening effect and showed a higher beam hardening reduction effect.