Purpose: Three-dimensional (3D) quantification using an interleaved Look-Locker acquisition sequence with a T₂ preparation pulse (QALAS) is a quantitative sequence used to measure relaxation times. The accuracy of the relaxation time measurement of 3D-QALAS at 3.0 T and the bias of 3D-QALAS have not yet been assessed. The purpose of this study was to clarify the accuracy of the relaxation time measurements using 3D-QALAS at 3.0 T MRI. Methods: The accuracy of the T₁ and T₂ values for 3D-QALAS was evaluated using a phantom. Subsequently, the T₁ and T₂ values and proton density of the brain parenchyma in healthy subjects were measured using 3D-QALAS and compared with those of 2D multi-dynamic multi-echo (MDME). Results: In the phantom study, the average T₁ value of 3D-QALAS was 8.3% prolonged than that for conventional inversion recovery spin-echo; the average T₂ value for 3D-QALAS was 18.4% shorter than that for multi-echo spin-echo. The in vivo assessment showed that the mean T₁ and T₂ values and PD for 3D-QALAS were prolonged by 5.3%, shortened by 9.6%, and increased by 7.0%, respectively, compared with those for 2D-MDME. Conclusion: Although 3D-QALAS at 3.0 T has high accuracy T₁ value, which is less than 1000 ms, the T₁ value could be overestimated for tissues with it longer than that T₁ value. The T₂ value for 3D-QALAS could be underestimated for tissues with T₂ values, and this tendency increases with longer T₂ values.

Purpose: Late arterial phase images of SD 8, SD 10, and SD 12 were acquired in the 3-phase dynamic study of the liver in combination with hybrid iterative reconstruction. We evaluated the low-contrast detectability by adding a simulated tumor to these images and aimed to formulate a standard image quality. Methods: We prepared images with and without signal for 60 series of 20 samples, each with 3 image quality types (total: 120 series). The continuous confidence method by 10 observers detected 60 simulated tumors. Results: The detection sensitivities were 0.765, 0.785, and 0.260 for SD 8, SD 10, and SD 12, respectively (p<0.001) with no significantly different specificities, and the areas under the curve were 0.901, 0.892, and 0.616 (p<0.001), respectively. The simulated mass detection rates were 74.5%, 75.0%, and 21.5% for SD 8, SD 10, and SD 12, respectively (p<0.001), and the intraclass correlation coefficients, which indicate interobserver reliability, were 0.697 at SD 10 without signal, and SD 12 without a signal significantly dropped to 0.185. Conclusion: Therefore, SD 12 images increase the possibility of overlooking lesions. Hence, image quality in the late arterial phase should be SD 10 or less.

Purpose: To validate the point-A dose and dose distribution of metal and resin applicators in comparison with those of TG-43U1. Methods: The metal and resin applicators consisting of tandem and ovoid were modeled by the egs_brachy. The doses to point A and dose distributions considering each applicator were calculated and compared to those of TG-43U1. Results: The dose to point A considering the metal applicator was 3.2% lower than that of TG-43U1, but there was no difference in the dose to point A considering the resin applicator. The dose distribution considering the metal applicator was lower than that of TG-43U1 at all calculation points, but there was no difference in the dose distribution considering the resin applicator at almost all calculation points. Conclusion: In this study, the dose distribution considering the metal applicator was lower than that of TG-43U1 at all calculation points, but there was no difference in the dose distribution considering the resin applicator at almost all calculation points. Therefore, TG-43U1 can accurately calculate the dose distribution when changing from the metal applicator to the resin applicator.

Purpose: This study aims to optimize the selection of the magnetic resonance imaging (MRI) scanners and metal artifact reduction magnetic resonance sequence (MARS) in patients with metallic implants by comparing the image quality of MARS at different static magnetic fields. Method: A titanium alloy hip prostheses stem was covered with the pork phantom. Nifedipine 10 mg was placed as a simulated lesion near the hip joint of the phantom. T₁-weighted imaging (T₁WI) and short tau inversion recovery (STIR) were acquired at both 1.5T and 3T. Several techniques of high-bandwidth (High BW), view angle tilting (VAT), and compressed sensing and slice encoding for metal artifacts correction (CS-SEMAC) were compared. Artifacts, sharpness, and visibility of lesions were evaluated visually by five radiological technologists using the normalized-rank approach. Result: CS-SEMAC reduced metal artifacts but showed bad sharpness. CS-SEMAC at 3T was the best visibility of lesions. Conclusion: If lesion visibility is a priority, CS-SEMAC with 3T is recommended as the first choice.

Purpose: The purpose of this study was to investigate the contrast effect of arteries and the distribution of contrast medium along the z-axis in three-dimensional computed tomography angiography from neck to lower extremity (neck-lower-extremity 3D-CTA) using the F variable-speed injection method. Method: The subjects were 112 patients who underwent neck-lower-extremity 3D-CTA. In the fixed-speed injection method, contrast medium was injected at the same rate for 35 s. In the variable-speed injection method, contrast medium was injected for 35 s at varying rates. CT values were measured in the common carotid artery (CCA), ascending aorta (AAo), abdominal aorta (AA), superficial femoral artery (SFA), popliteal artery (PA), anterior tibial artery (ATA), and dorsalis pedis artery (DPA). We normalized the CT values of each artery for each patient, defined the contrast uniformity, and compared them. We also performed a four-level visual evaluation. Result: A significant difference was found in the PA, ATA, and DPA, with the variable-speed injection method showing a higher CT value than the fixed-speed injection method (p<0.01). There were no significant differences in the CCA, AAo, AA, and SFA. Similarly, the variable-speed injection method scored significantly higher in the visual evaluation. Conclusion: The variable-speed injection method is useful in neck-lower-extremity 3D-CTA.

Magnetic resonance cholangiopancreatography (MRCP) is a valuable non-invasive technique that depicts bile or pancreatic juice as hyperintense in heavily T₂-weighted images. Data acquisition in the three-dimensional multi-slice MRCP method is acquired with respiratory triggered. Echo train duration (ETD) is the data acquisition time every breath is in inverse proportion to total acquisition time, and has influence of image contrast and spatial resolution in turbo spin echo (TSE) imaging. Therefore, the effects of image contrast and spatial resolution of three-dimensional heavily T₂-weighted variable refocusing flip angle TSE images on ETD in fundamental and clinical settings were measured using a phantom. No significant difference was detected with regard to image contrasts. Increasing ETD reduced spatial resolution, but no significant difference was detected regarding visual evaluation in the fundamental setting. On the other hand, in some of the clinical settings, increasing ETD with phase partial Fourier (PPF) reduced spatial resolution. The study result indicates that changing ETD fitting respiratory state of individual examinee without PPF is useful for optimized acquisition time without sacrificing image contrast and spatial resolution.