Usefulness of pituitary high-resolution 3D MRI with deep-learning-based reconstruction for perioperative evaluation of pituitary adenomas.

PURPOSE: To evaluate the diagnostic value of T1-weighted 3D fast spin-echo sequence (CUBE) with deep learning-based reconstruction (DLR) for depiction of pituitary adenoma and parasellar regions on contrast-enhanced MRI. METHODS: We evaluated 24 patients with pituitary adenoma or residual tumor using CUBE with and without DLR, 1-mm slice thickness 2D T1WI (1-mm 2D T1WI) with DLR, and 3D spoiled gradient echo sequence (SPGR) as contrast-enhanced MRI. Depiction scores of pituitary adenoma and parasellar regions were assigned by two neuroradiologists, and contrast-to-noise ratio (CNR) was calculated. RESULTS: CUBE with DLR showed significantly higher scores for depicting pituitary adenoma or residual tumor compared to CUBE without DLR, 1-mm 2D T1WI with DLR, and SPGR (p < 0.01). The depiction score for delineation of the boundary between adenoma and the cavernous sinus was higher for CUBE with DLR than for 1-mm 2D T1WI with DLR (p = 0.01), but the difference was not significant when compared to SPGR (p = 0.20). CUBE with DLR had better interobserver agreement for evaluating adenomas than 1-mm 2D T1WI with DLR (Kappa values, 0.75 vs. 0.41). The CNR of the adenoma to the brain parenchyma increased to a ratio of 3.6 (obtained by dividing 13.7, CNR of CUBE with DLR, by 3.8, that without DLR, p < 0.01). CUBE with DLR had a significantly higher CNR than SPGR, but not 1-mm 2D T1WI with DLR. CONCLUSION: On the contrast-enhanced MRI, compared to CUBE without DLR, 1-mm 2D T1WI with DLR and SPGR, CUBE with DLR improves the depiction of pituitary adenoma and parasellar regions.

A Triphasic Split-bolus Contrast Injection Protocol for Artery-vein Separation During Pulmonary Computed Tomographic Angiography.

PURPOSE: Accurate artery-vein separation on pulmonary computed tomographic (CT) angiography is desirable for preoperative 3-dimensional image simulation, while using a minimal amount of contrast medium. This study aimed to verify whether a split-bolus contrast enhancement protocol with test-bolus tracking would provide contrast differentiation between the pulmonary arteries (PA) and pulmonary veins (PV) during high-pitch single-pass CT angiography. MATERIALS AND METHODS: Fifty patients underwent pulmonary CT angiography with a triphasic split-bolus injection protocol with the main bolus of contrast medium for 6 seconds, followed by a subsequent bolus of 20% diluted contrast medium/80% saline for another 6 seconds and a 5-second saline chaser. The single-scan timing was individually tailored to the peak enhancement at the left atrium, that is, the pulmonary-venous dominant phase, by monitoring a time-enhancement curve with test bolus. RESULTS: Time-enhancement curves of the test bolus demonstrated that the interval times between the peak enhancements at the PA and PV were ~6 seconds. For contrast enhancement image analyses with our protocol, the attenuation measurements at the main PA and left atrium were performed. The mean (SD) CT numbers were 246.4 (50.0) HU at the main PA, and 410.8 (59.0) HU at the left atrium. The mean difference in the CT numbers was 164.4 HU (95% confidence interval: 149.2-179.6, P <0.001) between the main PA and left atrium. CONCLUSIONS: Our contrast enhancement protocol for high-pitch single-pass pulmonary CT angiography could provide the desired artery-vein separation while maintaining adequate attenuations of the pulmonary vasculature.

A novel algorithm for comprehensive quality assessment of clinical magnetic resonance images based on natural scene statistics in spatial domain.

BACKGROUND: A magnetic resonance imaging (MRI)-specific objective image quality assessment (IQA) algorithm, the quality evaluation using multidirectional filters for MRI (QEMDIM), was previously reported. QEMDIM requires a set of reference images to calculate the quality score (SQ) for an assessed image. SQ may be affected by the quality of the reference set owing to the calculation procedure. PURPOSE: To propose a modified version of the IQA algorithm and compare the IQA performance of the original and modified algorithms. ASSESSMENT: Brain axial T1- and T2-weighted spin-echo images of varying quality levels (noise and blurring) were acquired from seven healthy men. Subjective IQA (paired comparisons) was conducted on the images, and subjective quality scores were obtained. With reference sets of various quality levels, QEMDIM and modified IQA were applied to the same images that underwent the subjective IQA. The correlation of each SQ and modified score (Smod) with the subjective scores was evaluated for content-related subsets of assessed images and for each reference set. The effect of the reference-set quality on the distribution of the correlation coefficients (CCs) was statistically evaluated for SQ and Smod using a one-way analysis of variance test with a significance level of 0.05. We also evaluated the variation in Smod for images with almost the same qualities using the standard deviation (SD). RESULTS: The CCs of SQ varied significantly with the quality of the reference set, whereas that of Smod did not. The SD of Smod for almost-same-quality images was less than that corresponding to the confidence interval of the subjective scores. CONCLUSION: Our modified algorithm was superior to QEMDIM in terms of IQA performance in clinical practice, especially in terms of accuracy, robustness, and reproducibility.

Influence of monitor display resolution and displayed image size on the spatial resolution of ultra-high-resolution CT images: a phantom study.

To determine the optimal display conditions for ultra-high-resolution computed tomography (UHRCT) images in clinical practice, this study investigated the effects of liquid-crystal display (LCD) resolution and displayed image size on the spatial resolution of phantom images acquired using a UHRCT system. A phantom designed to evaluate the high-contrast resolution was scanned. The scan data were reconstructed into four types of UHRCT image series consisting of the following possible combinations: two types of reconstruction kernels on the filtered back-projection method (for the lung and mediastinum) and two types of matrix sizes (10242 and 20482). These images were displayed under eight types of display conditions: three image sizes displayed on a 2-megapixel (MP) and 3-MP color LCD and two image sizes on an 8-MP color LCD. A total of 32 samples (four image series × eight display conditions) were evaluated by eight observers for high-contrast resolution. The high-contrast resolution of the displayed UHRCT images was significantly affected by the displayed image size, although the largest (full-screen) displayed image size did not necessarily show the maximum high-contrast resolution. When the images were displayed in the full-screen size, LCD resolution affected the high-contrast resolution of only the 20482-matrix-size images reconstructed using the lung kernel. In conclusion, the spatial resolution of UHRCT images may be affected by LCD resolution and displayed image size. To optimize the clinical display conditions for UHRCT images, it is necessary to adopt an LCD with an adequate resolution for each viewing situation.

Medical display application for degraded image sharpness restoration based on the modulation transfer function: initial assessment for a five-megapixel mammography display monitor.

An image-display application for medical liquid-crystal display (LCD) monitors called the sharpness recovery (SR) function has been developed to compensate for image sharpness as a function of deficiencies in the modulation transfer function (MTF) of a monitor. We investigated the effects of the SR function for a five-megapixel (MP) mammography LCD monitor on the resolution and noise properties of the displayed images by measuring the MTF and overall noise power spectrum (NPS), respectively. Furthermore, the effectiveness of the SR function for the 5-MP monitor in displaying subtle microcalcifications on digital mammograms was verified using a two-alternative-forced-choice sensitivity measurement as an initial application for medical image interpretation. Four radiologists compared the visibility of 45 regions of interest with a malignant microcalcification cluster shown on SR-processed and unprocessed mammograms. SR processing improved the MTF of the displayed images by approximately 40% at the Nyquist frequency of the 5-MP monitor, whereas it slightly increased the overall NPS values. All observers indicated that the fraction of cases considered to have better visibility of microcalcifications with the SR processing was significantly greater than that without the processing (averaging 82%, with the 95% confidence interval ranging from 70 to 93%). The SR processing for the 5-MP monitor yielded a significant improvement in the resolution properties of the displayed images, with a certain increase in the image noise. The SR function has the potential to improve the observer performance of radiologists, particularly when reading subtle microcalcifications reproduced on 5-MP monitors.

[Assessment Tool of Image Quality for Medical Liquid-crystal Displays Using Commercially Available Digital Cameras].

We developed a simplified tool for measuring image quality of medical liquid-crystal displays (LCDs) using a commercially available color digital camera. This tool implemented as a plug-in software for ImageJ (open-source image processing program) was designed to compute modulation transfer functions (MTFs) and Wiener spectra (WS) of monochrome and color LCDs from LCD photographed images captured by a camera. The intensities of the red (R), green (G), and blue (B) signals of the unprocessed image data depend on the spectral sensitivity of the image sensor used in the camera. In order to evaluate image quality based on LCD luminance, the plug-in software calibrates the RGB signals from the camera using measured luminance of the LCD and converts them into grayscale signals that correspond to the luminance of the LCD. The MTFs and WS are determined based on the line response from a one-pixel line image and the one-dimensional noise profiles acquired by scanning the uniform image using numerically synthesized slit, respectively. With this plug-in software for ImageJ, we are able to readily compute MTFs and WS of both monochrome and color LCDs from unprocessed image data of cameras. Our simplified tool is helpful to evaluate and understand the physical performance of LCDs for a large number of display users in hospitals and medical centers.

Effects of Imaging Parameters on the Quality of Contrast-Enhanced MR Angiography of Cerebral Aneurysms Treated Using Stent-Assisted Coiling: A Phantom Study.

PURPOSE: To quantitatively investigate in vitro the effects of flip angle (FA), receiver bandwidth (BW), echo time (TE), and magnetic field strength (FS) on image noise and artifacts induced by stent-assisted coiling on contrast-enhanced MR angiography (CE-MRA) images, as a first step towards optimization of imaging parameters. METHODS: A phantom simulating a cerebral aneurysm treated using stent-assisted coiling was filled with diluted gadolinium contrast medium, and MR angiography were obtained using varied parameters: FA (10°-60°), BW (164-780 Hz/pixel), and FS (1.5 and 3.0T). The TE varied automatically with BW because the TE was set to the smallest value. Three kinds of indices were semi-automatically calculated to quantify the severity of stent- and coil-induced artifacts: artificial lumen narrowing (ALN) representing a decrease in the in-stent luminal area, and relative in-stent signal (RISS) and relative in-coil signal (RISC) representing an increase in the in-stent and in-coil signal intensities, respectively. We also measured the ratio of in-stent signal to noise (IS/N) for each parameter. The variation in these indices with variations in FA, BW (TE), and FS was analyzed. RESULTS: An increase in FA led to an increase of up to 65% in the RISS, while the IS/N increased by up to three times. The 1.5T scanner indicated fewer artifacts (71% lower ALN, two times higher RISS, and 40% higher RISC) than the 3.0T scanner. On the other hand, the 1.5T scanner worsened the IS/N compared with the 3.0T scanner, although the difference was relatively small. Variation in BW (and hence, TE) led to a trade-off between artifact severity and IS/N. CONCLUSION: A high FA and low FS should be used for improved artifact severity and IS/N on CE-MRA images of a stent-assisted coil. A wide BW (short TE) could improve artifact severity at the expense of the image noise.

Visual assessment method of angular performance in medical liquid-crystal displays by use of the ANG test pattern: effect of ambient illuminance and effectiveness of modified scoring.

A visual assessment method of the angular performance in medical liquid-crystal displays (LCDs) by use of the "ANG test pattern" was proposed by Badano and the International Electrotechnical Commission. Our goals were to examine the effect of ambient illuminance on the visual assessment, and to investigate whether our modified visual assessment (with the ANG test pattern) can be used instead of the conventional assessment based on luminance measurements. As the ambient illuminance increased, the original scores obtained with the visual assessment decreased. The modified score of the visual assessment was in reasonable agreement with the results of the luminance-based assessment. We conclude that the visual assessment with the ANG test pattern should be performed in a room with constant ambient illuminance, and the modified visual assessment could have the potential to be used instead of the luminance-based assessment for quality assurance of medical LCDs.

Analysis of dominant factors affecting fatigue caused by soft-copy reading.

RATIONALE AND OBJECTIVES: The aim of this study was to analyze the dominant factors affecting fatigue caused by soft-copy reading to identify a method for decreasing fatigue in clinical practice. MATERIALS AND METHODS: Two types of fatigue-fatigue in the central nervous system and subjective visual fatigue-were evaluated using a critical fusion frequency test and a questionnaire administered to 17 male radiologists before and after soft-copy reading. Reading-induced fatigue was assumed to be affected by 20 hypothetical factors associated with personal characteristics, time required for reading, content or amount of reading, and the reading environment. We used multiple linear regression analysis with a variable selection method to detect the best combination of factors capable of expressing variations in each of the measured fatigue values. The effects of the detected (dominant) factors on fatigue were also examined based on coefficients of the dominant factors in multiple regression models. RESULTS: Fatigue in the central nervous system decreased with a higher corrected visual acuity and a higher ambient illuminance in the reading room and was also affected by the type of monitor used. Visual fatigue was relieved when there was a larger difference in the brightness of the monitor and the surfaces surrounding the monitor and tended to be more severe when glasses rather than contact lenses were worn. CONCLUSIONS: Increasing the ambient illuminance, using an appropriate type of monitor, improving the corrected visual acuity, and using contact lenses rather than eyeglasses could help decrease reading-induced fatigue in male radiologists.