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The purpose of this study was to shorten scan time for three-dimensional fat-suppressed T2-weighted imaging (3D FS-T2WI) using DIXON and compressed sensing (HyperSense: HS), while maintaining adequate visualization of the brachial plexus. 3D FS-T2WI of a phantom and the neck of healthy volunteers were acquired while varying the echo time (TE), echo train length (ETL) and HS factor (HSf). Image quality was evaluated based on the visual assessment of the brachial plexus in volunteers and the contrast ratios between nerve-mimicking, muscle-mimicking, blood-mimicking, and fat-mimicking materials in the phantom. The highest nerve-to-muscle and nerve-to-blood contrast ratios, as well as the best visual evaluation scores, were observed with longer TE values. As ETL increased, both tissue contrast ratios and visual evaluation scores decreased; however, scan time became shorter. Increasing the HSf did not significantly affect contrast ratios or visual evaluation scores, but it also contributed to a shorter scan time. Using the parameters TE=110 ms, ETL=120, and HSf=2.5, it was possible to shorten scan time while maintaining visualization of the brachial plexus.
The combination of vessel wall imaging (VWI) and MR angiography (MRA) is useful for differentiating between intracranial atherosclerotic disease and arterial dissection. However, additional VWI scans increase total scan time. The purpose of this study was to develop and evaluate a simultaneous acquisition method for VWI and MRA using phase-sensitive inversion recovery (PSIR) in brain MRI. Imaging parameters were optimized using a phantom simulating cerebral blood flow, brain parenchyma, and plaque. The proposed method was validated in an in vivo study by comparing it with the conventional method (T1-turbo spin echo+time of flight-MRA). The proposed method achieved a higher contrast ratio than the conventional method. Additionally, the acquisition time was reduced to less than one-half (2 min 18 s vs 7 min 15 s). This simultaneous acquisition method using PSIR is useful for brain MRI.
This study aimed to verify the contouring accuracy of the artificial intelligence (AI)-based auto-segmentation software Contour+ (MVision AI Oy, Helsinki, Finland) both quantitatively and visually, and to evaluate its clinical validity for the thoracic region in Japanese patients. Ten thoracic radiotherapy cases with lung lesions were analyzed. Contour+ was used to automatically delineate both lungs, trachea, bronchus, esophagus, spinal cord, and heart. Three observers visually evaluated the auto-contours using a five-point scoring system, and the final manually corrected contours were used as the reference to calculate the dice similarity coefficient (DSC), Hausdorff distance (HD), and volume differences. In all cases, the AI auto-contours were evaluated as "clinically acceptable with minor modifications (score ≥3)," with an average score of 4.4. The mean DSC values were 1.00 for the lungs, 0.99 for the trachea, 0.91 for the bronchi, 0.86 for the esophagus, 0.99 for the spinal cord, and 0.99 for the heart, indicating high agreement. The mean HD values were 5.68 mm, 8.72 mm, and 3.30 mm for the bronchi, esophagus, and heart, respectively. The mean volume changes after manual correction were 4.02 cc for the bronchi, 2.55 cc for the esophagus, and 2.58 cc for the heart. AI-based auto-segmentation software Contour+ demonstrated high geometric agreement and clinical validity for major thoracic organs in Japanese patients, suggesting its potential to reduce the contouring workload and promote standardization in radiotherapy treatment planning.
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The purpose of this study was to evaluate the impact of contrast enhancement and arterial diameter on the attenuation values of virtual non-contrast (VNC) images (HUVNC) obtained from abdominal dynamic computed tomography (CT) examinations using a rapid kilovolt-switching dual-energy CT system. Seventy-keV virtual monoenergetic (VME) and VNC images were reconstructed from scanned raw data of the unenhanced, arterial, portal, and delayed phases. Circular regions of interest (ROIs) were placed on four arteries of different diameters (abdominal aorta: 20 mmϕ, common iliac artery: 10 mmϕ, superior mesenteric artery: 5 mmϕ, and inferior mesenteric artery: 2.5 mmϕ) at the same anatomical level between each contrast enhancement level. The attenuation values and standard deviations of the VME images (HUVME) and HUVNC in each ROI were measured. VNCError, the differences between HUVME in the unenhanced phase and HUVNC in each contrast enhancement level, was calculated. HUVME decreased as the contrast enhancement level declined, regardless of the arterial diameter. Similarly, the HUVME in the same contrast enhancement level decreased as the arterial diameter decreased. This tendency was particularly evident at high contrast enhancement levels. As arterial diameter decreased or the contrast enhancement level increased, HUVNC and VNCError increased. At HUVME of 400 Hounsfield unit (HU), the maximum VNCError was 78.47 HU at 2.5 mmϕ and 6.68 HU at 20 mmϕ. At HUVME of 130 HU, the influence on HUVNC was smaller than at other contrast enhancement levels, with VNCError of no more than 13.67 HU at 2.5 mmϕ. This study suggests that HUVNC increases are significantly affected by both the contrast enhancement and arterial diameter, especially at high contrast enhancement levels and in narrow arteries.
In radiation therapy, the absorbed dose is corrected for changes in the nominal treatment distance using the inverse square law. However, in the case of electron beams, the inverse square law using the nominal treatment distance is invalid. Therefore, an effective source-to-surface distance (SSD) should be determined. The effective SSD must be measured for all electron beam energies and applicator sizes. Here, we calculated the effective SSD using a radiotherapy planning system with an electron Monte Carlo (eMC) calculation algorithm and evaluated its usefulness. The effective SSD was calculated from the absorbed dose ratio at dmax at extended SSDs under 5 gap conditions, using both eMC calculations and LINAC measurements. The consistency between calculated and measured values was evaluated based on the absorbed dose ratio at dmax, effective SSD, and distance correction factor. The difference in the absorbed dose ratio at dmax between eMC calculations and measurements at extended SSDs was within 1.38%, and the effective SSD values agreed within 5.40 cm. Larger discrepancies in effective SSD were observed under conditions of high energy with large field sizes and low energy with small field sizes. The good agreement in absorbed dose ratio at dmax, effective SSD, and distance correction factor between eMC calculations and measurements indicates that effective SSD calculation using eMC is feasible and can be employed for comparative verification against measured values.
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In mammography, it is desirable for the patient's mean glandular dose (MGD) to be minimal while the signal difference to noise ratio (SDNR) of lesions remains high. However, these two factors are inversely related, and the optimal automatic exposure control (AEC) settings have not been clearly defined. Even the quality assurance programme for digital mammography by the International Atomic Energy Agency (IAEA) specifies only acceptable and achievable SDNR and MGD values for AEC settings, based on the mammography machine model and polymethyl methacrylate (PMMA) phantom thickness. In this report, we propose a method to simultaneously optimize both SDNR and MGD at AEC settings.
The usefulness of dual-source dual-energy computed tomography (DECT) in distinguishing contrast staining (CS) from intracranial hemorrhage (ICH) has been reported. In this study, we evaluated ICH after mechanical thrombectomy (MT) using sequential acquisition DECT (SADE) and examined its diagnostic accuracy. Of the 76 patients who underwent MT for acute ischemic stroke between August 2022 and August 2023, 56 were ultimately included in the study. Using virtual non-contrast images (VNC) and iodine map images obtained from DECT, high-attenuation (HA) areas on mixed images were classified into ICH and CS, and the accuracy of DECT was evaluated using follow-up images of CT or magnetic resonance imaging within 48 hours after DECT. A total of 129 foci of HA areas were identified on the mixed image. There were 20 HA regions that were judged to have both ICH and CS, 109 that were judged to have CS only, and no HA regions that were judged to have ICH only. The sensitivity, specificity, and accuracy for identifying hemorrhage were 20.9%, 91.9%, and 65.8%, respectively. Misregistration artifacts occurred in VNC (n=2, 3.6%). In the evaluation of ICH after MT, although the sensitivity of SADE for bleeding is low due to the influence of delayed hemorrhagic changes, it has high specificity and is highly reliable for distinguishing CS. In addition, SADE may cause misregistration artifacts due to slight body movement.
We investigated flip angle (FA) and cerebrovascular imaging performance in three-dimensional time-of-flight magnetic resonance angiography (3D TOF-MRA) without using a venous signal saturation pulse in the diagnosis of acute cerebral infarction. 3D TOF-MRA was performed in healthy volunteers at FAs of 9°-21° without using a venous signal saturation pulse. The contrast of cerebral arteries, veins, and parenchyma was measured, and the visualization of blood vessels was compared by visual evaluation. Cerebral artery contrast was highest at a 19° FA, and the visual evaluation also showed the highest rated results at a 19° FA. The cerebral venous contrast did not depend on the FA, and it was almost constant. A repetition time of 10 ms and a 19° FA are the optimal settings for 3D TOF-MRA without using a venous signal saturation pulse, which reduces the imaging time by approximately 60% compared to the conventional method.