A deep learning model based on fusion images of chest radiography and X-ray sponge images supports human visual characteristics of retained surgical items detection.

PURPOSE: Although a novel deep learning software was proposed using post-processed images obtained by the fusion between X-ray images of normal post-operative radiography and surgical sponge, the association of the retained surgical item detectability with human visual evaluation has not been sufficiently examined. In this study, we investigated the association of retained surgical item detectability between deep learning and human subjective evaluation. METHODS: A deep learning model was constructed from 2987 training images and 1298 validation images, which were obtained from post-processing of the image fusion between X-ray images of normal post-operative radiography and surgical sponge. Then, another 800 images were used, i.e., 400 with and 400 without surgical sponge. The detection characteristics of retained sponges between the model and a general observer with 10-year clinical experience were analyzed using the receiver operator characteristics. RESULTS: The following values from the deep learning model and observer were, respectively, derived: Cutoff values of probability were 0.37 and 0.45; areas under the curves were 0.87 and 0.76; sensitivity values were 85% and 61%; and specificity values were 73% and 92%. CONCLUSION: For the detection of surgical sponges, we concluded that the deep learning model has higher sensitivity, while the human observer has higher specificity. These characteristics indicate that the deep learning system that is complementary to humans could support the clinical workflow in operation rooms for prevention of retained surgical items.

Improvement of Image Quality Using Hybrid Iterative Reconstruction with Noise Power Spectrum Model in Computed Tomography During Hepatic Arteriography.

OBJECTIVES: In CT during hepatic arteriography (CTHA), the addition of a noise power spectrum (NPS) model to conventional hybrid iterative reconstruction (HIR) may improve spatial resolution and reduce image noise. This study aims at assessing the image quality provided by HIR with a NPS model at CTHA. METHODS: This institutional review board-approved retrospective analysis included 26 patients with hepatocellular carcinomas (HCCs) who underwent CTHA. In all acquisitions, images were reconstructed with filtered back projection (FBP), adaptive iterative dose reduction 3D (AIDR), and AIDR enhanced (eAIDR) with the NPS model. Four radiologists analyzed the signal-to-noise ratio (SNR) of HCC nodules and its associated feeding arteries. The radiologists used a semiquantitative scale (-3 to +3) to rate the subjective image quality comparing both the FBP and eAIDR images with the AIDR images. RESULTS: The feeding arteries' attenuation was significantly higher in eAIDR compared to AIDR [514.3 ± 121.4 and 448.3 ± 107.3 Hounsfield units (HU), p < 0.05]. The image noise of eAIDR was significantly lower than that of FBP (15.2 ± 2.2 and 28.5 ± 4.8 HU, p < 0.05) and comparable to that of AIDR. The SNR of feeding arteries on eAIDR was significantly higher than on AIDR (34.1 ± 7.9 and 27.4 ± 6.3, p < 0.05). Subjective assessment scores showed that eAIDR provided better visibility of feeding arteries and overall image quality compared to AIDR (p < 0.05). The HCC nodule visibility was not significantly different among the three reconstructions. CONCLUSION: In CTHA, eAIDR improved the visibility of feeding arteries associated with HCC nodules without compromising nodule detection.

X-ray dose reduction using additional copper filtration for dental cone beam CT.

This study aims to quantitatively evaluate the effect of additional copper-filters (Cu-filters) on the radiation dose and contrast-to-noise ratio (CNR) in a dental cone beam computed tomography (CBCT). The Cu-filter thickness and tube voltage of the CBCT unit were varied in the range of 0.00-0.20 mm and 70-90 kV, respectively. The CBCT images of a phantom with homogeneous materials of aluminum, air, and bone equivalent material (BEM) were acquired. The CNRs were calculated from the voxel values of each homogeneous material. The CTDIvol was measured using standard polymethyl methacrylate CTDI test objects. We evaluated and analyzed the effects of tube current and various radiation qualities on the CNRs and CTDIvol. We observed a tendency for higher CNR at increasing tube voltage and tube current in all the homogeneous materials. On the other hand, the CNR reduced at increasing Cu-filter thickness. The tube voltage of 90 kV showed a clear advantage in the tube current-CNR curves in all the homogeneous materials. The CTDIvol increased as the tube voltage and tube current increased and decreased with the increase in the Cu-filter thickness. When the CNR was fixed at 9.23 of BEM at an exposure setting of 90 kV/5 mA without a Cu-filter, the CTDIvol at 90 kV with Cu-filters was 8.7% lower compared with that at 90 kV without a Cu-filter. The results from this study demonstrate the potential of adding a Cu-filter for patient dose reduction while ensuring the image quality.

Novel -75°C SEM cooling stage: application for martensitic transformation in steel.

Microstructural changes during the martensitic transformation from face-centred cubic (FCC) to body-centred cubic (BCC) in an Fe-31Ni alloy were observed by scanning electron microscopy (SEM) with a newly developed Peltier stage available at temperatures to -75°C. Electron channelling contrast imaging (ECCI) was utilized for the in situ observation during cooling. Electron backscatter diffraction analysis at ambient temperature (20°C) after the transformation was performed for the crystallographic characterization. A uniform dislocation slip in the FCC matrix associated with the transformation was detected at -57°C. Gradual growth of a BCC martensite was recognized upon cooling from -57°C to -63°C.

Effect of differences in pixel size on image characteristics of digital intraoral radiographic systems: a physical and visual evaluation.

OBJECTIVES: To quantify and validate the effect of pixel size on a digital intraoral radiographic system according to International Electrotechnical Commission standards through physical and visual evaluations. METHODS: The digital intraoral radiographic system used was the photostimulable phosphor imaging plate and scanner system. The system had three image capture modes: high-speed (HS), high-resolution (HR), and super high-resolution (SHR) with different pixels. The physical characteristics of the system were evaluated using presampled modulation transfer function (MTF) and the normalized noise power spectrum (NNPS). An aluminum (Al) step phantom with different depths of holes was used to acquire images under various exposure conditions. The average number of perceptible holes from all steps was plotted against each exposure dose. The results were compared to analyze the effects of pixel size on image quality of intraoral radiographs. RESULTS: The MTF was slightly higher with SHR than with HR and HS. The NNPS with SHR showed about a 40% decrease in magnitude compared to HS. The total number of perceptible holes in the Al step phantom was higher with SHR than with HS and HR in all exposure conditions. CONCLUSIONS: The MTF and NNPS obtained with different pixel size could be quantified by physical evaluation, and the differences were visually validated with Al step phantom. The SHR mode has the potential to decrease the radiation dose without compromising the image quality.

Reduction Method of Operator and Medical Staff Radiation Exposure in Balloon Pulmonary Angioplasty for Chronic Thromboembolic Pulmonary Hypertension.

The purpose of this study is to investigate a reduction method of radiation exposure for operator and medical staff in balloon pulmonary angioplasty (BPA) for chronic thromboembolic pulmonary hypertension (CTEPH). We devised a new radiation protection, which is U-shaped acrylic supporting table with 0.35 mmPb unleaded radiation protection sheet. A human phantom was put on the bed of cardiac angiography system [C-arm angulation: posteroanterior (PA), L-arm angulation: left anterior oblique (LAO) 60°]. The ambient equivalent dose rate was measured under fluoroscopy with and without three radiation protections: U-shaped acrylic supporting table with 0.35 mmPb unleaded radiation protection sheet, radiation protection for the lower body, and radiation protection for the upper body. With the three radiation protections, the ambient equivalent dose rate was decreased more than 99% at the height of 100 cm above the floor at the operator position (PA: from 186.2 µSv/h to 0.5 µSv/h, LAO 60°: from 350.4 µSv/h to 1.6 µSv/h). Ambient equivalent dose rate at the other points are also decreased effectively. The devised dose reduction method can reduce operator and medical staff radiation exposure effectively and be set up without interference for BPA procedure.

Three-dimensional phase contrast magnetic resonance imaging validated to assess pulmonary artery flow in patients with chronic thromboembolic pulmonary hypertension.

In this study, three-dimensional phase contrast magnetic resonance imaging (3D-PC MRI), a novel technique, was validated to assess pulmonary artery (PA) flow in patients with chronic thromboembolic pulmonary hypertension (CTEPH). The MR data of PAs from 3D-PC and two-dimensional PC (2D-PC) from before and after treatment for 3 patients with CTEPH were retrospectively analyzed. Additionally, 3D- and 2D-PC MR scans of PA were performed in 5 healthy volunteers. Correlation of stroke volumes (SVs) obtained by 3D-PC and 2D-PC was analyzed using Pearson's correlation coefficients. There was an excellent correlation in the SV of main PA, left PA and right PA between 3D-PC and 2D-PC (main PA: r = 0.91, p < 0.01, left PA: r = 0.72, p < 0.01 and right PA: r = 0.77, p < 0.01). In conclusion, 3D-PC MRI was able to accurately quantify the PA flow in patients with CTEPH.

Imaging of surface spin textures on bulk crystals by scanning electron microscopy.

Direct observation of magnetic microstructures is vital for advancing spintronics and other technologies. Here we report a method for imaging surface domain structures on bulk samples by scanning electron microscopy (SEM). Complex magnetic domains, referred to as the maze state in CoPt/FePt alloys, were observed at a spatial resolution of less than 100 nm by using an in-lens annular detector. The method allows for imaging almost all the domain walls in the mazy structure, whereas the visualisation of the domain walls with the classical SEM method was limited. Our method provides a simple way to analyse surface domain structures in the bulk state that can be used in combination with SEM functions such as orientation or composition analysis. Thus, the method extends applications of SEM-based magnetic imaging, and is promising for resolving various problems at the forefront of fields including physics, magnetics, materials science, engineering, and chemistry.

Effect of fluorescent lighting on the color of liquid-crystal displays.

Liquid-crystal displays (LCDs) are used for displaying medical images under various illuminance conditions and with ambient-lighting colors. Our purpose in this study was to understand the variations of the chromaticity in LCDs under different fluorescent lighting conditions. The variation of chromaticity of LCDs at a white point consisting of equivalent pixel value in Red, Green, and Blue was examined under different types of fluorescent lighting. The direction of changes in the chromaticity diagram shifted to the color of each fluorescent lighting. When the differences in chromaticity (∆u'v') increased, the observers' confidence levels in distinguishing color differences also increased. When the luminance of the LCD increased, observers' sensitivities for recognizing differences in chromaticity also increased as compared to observers' sensitivities at lower luminances. Our results indicate that observers recognized slightly yellowish colors even if ∆u'v' was less than 0.01; thus, observers could perceive differences in chromaticity. These results could provide important and relevant information with regard to better ambient lighting conditions in an image-reading room.

A preliminary study for exploring the luminance ratio of liquid-crystal displays required for display of radiographs.

Medical-grade liquid-crystal displays (LCDs) with high contrast ratio (CR) values have recently been developed and become available for soft-copy reading. When the LCD is used under ambient light conditions, the luminance ratio (LR) is a more appropriate indicator than the CR. Our aim was to explore the LR required for LCDs for soft-copy reading by comparing the effective LR values with the LR of the LCD. We defined "the luminance ratio in an image (LRimg)", the ratio of the maximum to minimum luminance in a radiograph displayed on the LCD, as the effective LR values required for the LCD. The maximum LRimg values in chest radiographs and those in mammograms ranged from 109 to 143 and 372 to 431, respectively. The LR of the LCD was higher than the LRimg values of the radiographs. Our results indicate that currently available medical-grade LCDs have enough LR for display of radiographs.

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.

Effect of angular performance on the chromaticity of grayscale images displayed on medical liquid-crystal displays.

Although variation of chromaticity in medical liquid-crystal displays (LCDs) has created interest in the quality assurance and quality control of display devices for medical use, it is unknown how chromaticity varies with the viewing angle. Our aims in this study were to investigate the variations of chromaticity in grayscale images displayed on medical LCDs depending on viewing angles, and to examine color discrimination at different viewing angles. Variations in chromaticity, Δu'v', between 0° and each viewing angle (-60° to +60°) were investigated. The chromaticity of each LCD varied as the viewing angle changed. We examined confidence levels of color discrimination at different viewing angles by rotating the LCD for ten observers. When the viewing angle and variation in chromaticity increased, the confidence levels of color discrimination increased. Our results indicated that observers, such as radiologists and radiological technologists, could recognize variation in chromaticity at different viewing angles.

Effect of ambient lighting on liquid-crystal displays with different types of surface treatment.

Liquid-crystal displays (LCDs) with different types of surface treatment have been developed for decreasing the effect of ambient lighting on a displayed image. The effect of ambient lighting on LCDs with different surface treatments, namely, glare (G)-type, anti-glare (AG)-type, and anti-reflection (AR)-coating LCDs, was evaluated quantitatively in this study for appropriate selection. The effect of ambient lighting on diffuse reflection and specular reflection was investigated. The coefficient of diffuse reflection of the AR-coating LCD was smaller than the others. The effect of diffuse reflection on the display function of each LCD was evaluated in terms of the deviation of the contrast response at the lowest luminance level when the illuminance changed from the condition that was used for calibration of the grayscale standard display function. The display function of the AR-coating LCD was affected less by diffuse reflection compared to the others. On the other hand, the coefficient of specular reflection of the AG-type LCD was the smallest until the angle of aperture of the light source was 4.6°. The specular-reflected image on the AG-type LCD had a remarkably broad distribution compared to the others. Our results are merely examples for a limited number of LCDs; however, we clarified quantitatively that the AR-coating and the AG-type LCDs were affected less by diffuse and specular reflection than the G-type LCD.

Chromaticity and correlated color temperature of the white point in medical liquid-crystal display.

PURPOSE: The color characteristics of medical liquid-crystal displays (LCDs) have become one of the main interests in quality assurance and quality control of medical display devices. It is necessary to evaluate variations of the color characteristics in medical LCDs in order to provide consistent color characteristics for image reading. In this study, we characterize the color characteristics in grayscale images displayed on medical LCDs. METHODS: Eight medical color LCDs and eight medical monochrome LCDs were used in this study with operating times ranging from 800 to 25 000 h. Default settings of correlated color temperature (CCT) of white points for all color LCDs were set at 7500 K. We measured chromaticity in the Commission Internationale de l'Éclairage (CIE) u'v' color space and CCT of the white point at 18 luminance levels. A colorimeter and grayscale test patterns with various luminance levels were used for the measurements. First, we examined differences in chromaticity and CCT at 18 luminance levels for each LCD. Second, we compared chromaticities of the different LCDs. Then, chromaticity and CCT of LCDs were measured at different ambient light conditions (30 and 560 lux) and compared to those measured in a dark room. Finally, the relationship between operating times and CCT was evaluated. RESULTS: The chromaticities of monochrome LCDs changed toward the blue and CCT increased as luminance decreased. In color LCDs, the chromaticity and CCT of the white point except at the minimum luminance were nearly constant to those measured at the maximum luminance. We observed differences in chromaticity between color and monochrome LCDs because of the nonadjustable white point of monochrome LCDs. When the ambient light increased, chromaticity varied, and CCT decreased on every LCD. Ambient light had a much greater impact on chromaticity and CCT at lower luminance levels. The CCT of LCDs decreased in longer operating times. The grayscale of LCDs with longer operating times was measured to be more yellowish due to the degradation of cold cathode fluorescent lamps. CONCLUSIONS: Our results clearly indicate that the white point in grayscale images displayed on medical LCDs changes depending on luminance levels, color or monochrome LCDs, ambient light conditions, and operating times. These data provide useful information to understand color characteristics of LCD for image reading, especially for quality assurance and quality control of LCDs.