Display Field Of View Research Articles

Tracing the disc: The novel qualitative morphometric MRI based disc degeneration classification system.

This study aimed to develop a classification system for lumbar disc degeneration using routine magnetic resonance images (MRIs) that is easily applicable and unaffected by existing classifications' limitations, and to compare its reliability, reproducibility, and discriminative power to the widely used Pfirrmann classification. Five features were graded. This new classification system has eight grades, with at least one of these five features altering each grade. The T2-weighted sagittal images were acquired using a rapid spin-echo sequence with a repetition time of 2680 to 4900 milliseconds, an echo time of 100 to 109 milliseconds, and an echo train length of 17. Slice thick was 4 mm and the display field of view was 32 × 32 cm. The new classification system used five features: signal intensity, disc height, disc boundary regularity, and nucleus annulus separation. Increased signal intensity, decreased height, decreased regularity, and decreased nucleus-annulus separation indicated degeneration. Four raters classified 400 discs from 80 patients using the Pfirrmann and Novel systems. Statistical analyses were conducted to investigate reliability and correlation. The overall ICC and kappa values were found to be higher in the novel classification. (0.988 indicating excellent agreement for ICC and 0.76/0.94 indicating good-very good agreement for kappa). The Kendall tau c value, which shows the correlation between the two classifications and indicates the validity of the new classification, was 0.872, which is very strong. Through the use of cross-tabulations, the discriminatory power of the two newly added classification criteria was determined. This study demonstrates the intra-rater and inter-rater reliability of an easy-to-use, discriminative novel morphometric MRI based classification system for lumbar disc degeneration. The differentiation of grades based on five distinct criteria may generate novel hypotheses regarding treatment selection and response monitoring, as well as new insights into the study of disc degeneration.

Spatially dependent veiling glare degrades image quality in medical extended reality

Spatially dependent veiling glare in medical extended reality (MXR) degrades image quality and needs to be characterized across technologies. Measurement methods of veiling glare on virtual and augmented reality (VR and AR) head-mounted displays (HMDs) have not been established in regulatory evaluation of MXR devices or display measurement standards. We describe an experimental bench setup enabling highly flexible translations and rotations of the light measuring device in five degrees of freedom within the eye box. Glare point spread functions (PSFs) of multiple VR and AR headsets are extracted and compared across the display field of view (FOV) in dark environment. At the center, the evaluated VR headsets (HTC VIVE Pro and VIVE Pro 2) demonstrate reduced long-range glare compared to the tested AR HMDs (Microsoft HoloLens 2 and Epson Moverio BT-300). The measured PSFs at multiple locations are spatially invariant for the HoloLens 2. However, veiling glare on the evaluated VR HMDs substantially increases toward the periphery of the FOV primarily due to optical aberration. For VR devices in medical use, increased peripheral glare can lead to image quality degradation and poor visualization of anatomical details.

Radially variant contrast measurement in virtual reality headsets using circular concentric ring patterns

AbstractImage quality on virtual reality (VR) head‐mounted displays (HMDs) is radially variant on each eyepiece from the visual center (optical axis of the HMD) towards the periphery. The virtual image is blurred at the periphery of display field of view (FOV) resulting in contrast and resolution degradation. Conventional measurement methods adopted from flat‐panel display evaluation do not consider the spatially dependent image artifacts by additional optical components such as HMD lenses and thus may not be adequate to assess the VR image quality. We develop a new method using circular concentric ring patterns to measure the radially variant Michelson contrast on multiple VR HMDs. The results show that measured image contrast reduces towards the periphery of display FOV especially at high‐spatial frequencies. In addition, image quality on VR HMDs can be affected by the 3D position of the eye (or the camera) within the eyebox. Specifically, contrast is further degraded if the interpupillary distance (IPD) setting of the HMD does not match that of the user. It also varies with the entrance pupil location of the light‐measuring device. We propose an efficient method for image quality evaluation that can facilitate the regulatory evaluation of VR headsets.

Accuracy of Virtual Non-contrast Image Reconstruction Using Material Decomposition for Fast kV-switching Dual-energy CT

Dual-energy computed tomography (DECT) system can generate virtual non-contrast (VNC) images. Although several reconstruction algorithms are defined, there are not many researches using deep learning image reconstruction (DLIR) algorithm. In this study, we evaluated the accuracy of the VNC image reconstruction under various conditions using DLIR algorithm. At first, each iodine insert with variable concentrations (2.0, 5.0, 10.0, 15.0 mg/ml) or diameters (2.0, 5.0, 10.0, 28.5 mm), or mixed insert including blood-mimicking material with iodine (iodine concentrations: 2.0, 4.0 mg/ml) was put in the center of the multi-energy CT phantom (Gammex, USA). This phantom was placed in the isocenter of DECT, and it scanned and reconstructed the VNC images. In addition, the VNC images were reconstructed with various display field of view (DFOV) sizes (240, 350 mm) or reconstruction algorithms (filtered back projection, advanced statistical iterative reconstruction, deep learning image reconstruction) for each iodine diameter. Attenuation values of these images (CTVNC) were measured and assessed by placing a circular region of interest (ROI) on each insert. CTVNC form iodine inserts increased with iodine concentration became lower, whereas CTVNC form blood plus iodine inserts were stable regardless of low iodine concentration. As iodine diameter became smaller, CTVNC increased remarkably. CTVNC remained steady even though reconstruction parameters were varied. In our study, the VNC image reconstruction using DLIR algorithm was affected by various conditions such as iodine concentration and size. In particular, its accuracy was reduced by the size of target.

Evaluation of thyroid radiation dose during abdominal Computed Tomography procedures and dose reduction effectiveness of thyroid shielding

IntroductionDuring abdominal Computed Tomography (CT) studies, vicinity organs receive a dose from scatter radiation. The thyroid is considered an organ at greater risk due to high radiosensitivity. MethodsThe primary objective of this study was to determine the entrances surface dose (ESD) to the thyroid during abdominal CT studies and to evaluate the efficiency of dose reduction by lead shielding. The calibrated thermoluminescence dosimeter (TLD) chips were used to measure the ESD during 180 contrast-enhanced (CE) and non-contrast-enhanced (NC) abdominal CT studies in the presence and absence of lead shielding. ResultsThyroid shielding reduces the ESD by 72.3% (0.55 mGy), 86.5% (2.95 mGy) and 64.0% (2.24 mGy) during NC, 3–phase and 4–phase abdominal CT scans. Also, the patient height was identified as a parameter that inversely influenced the thyroid dose, proving that the taller patients receive less dose to the thyroid. Regardless, the scan parameters such as time and display field of view (DFOV) positively impact the thyroid dose. ConclusionLead shielding can prevent the external scatter reaching the thyroid region by 64%–87% during the non-vicinity scans such as abdomen CT. However, the actual dose saving lies between 0.2% and 0.4%, compared to the total effective dose of the whole CT procedure. Implications for practiceThe thyroid shield can effectively reduce external scatter radiation during abdominal CT procedures. However, the dose saving is insignificant compared to the total effective dose from the whole examination. Therefore, the use of thyroid shielding should be carefully evaluated during CT abdomen procedures.

Impact of Image Reconstruction Parameters on Abdominal Aortic Calcification Measurement Using Abdominal Computed Tomography.

Abdominal aortic calcification (AAC) is correlated with cardiovascular outcomes independent of traditional risk factors. Quantification of AAC on computed tomography (CT) has not been standardized. Reconstruction parameters have been shown to impact coronary calcium scores. The aim of our study was to assess the impact of abdominal CT reconstruction parameters, slice thickness (ST), and display field of view (DFOV) on AAC quantitative scoring on abdominal CT examinations. We retrospectively measured AAC on noncontrast CT of 46 patients (mean age, 64.1 years; 35 males) using 5 different reconstruction protocols with a range of ST and DFOV: protocol A, 2.5 mm ST, 35 cm DFOV; protocol B, 2.5 mm ST, 50 cm DFOV; protocol C, 2.5 mm ST, 25 cm DFOV; protocol D, 5 mm ST, 35 cm DFOV; and protocol E: 0.625 mm ST, 35 cm DFOV. The AAC scores from each protocol were compared using concordance correlation coefficient and Bland-Altman agreement analyses. The AAC mean (SD) scores for each protocol were as follows: A, 2022 (2418); B, 2022 (2412); C, 1939 (2310); D, 2220 (2695); and E, 1862 (2234). The AAC mean score differences between protocols and reference protocol A were -0.47, 82.01, -198.94, and 160 for protocols B, C, D, and E, respectively, with differences between protocols C to E statistically significantly different (P < 0.05). The different protocols showed overall excellent correlation (concordance correlation coefficient, >0.9) between AAC scores. Slice thickness and DFOV can impact AAC score measurement. A description of reconstruction parameters is important to allow comparisons across different cohorts.

EVALUATION OF THE RADIATION EXPOSURE IN SEQUENTIAL HEAD TOMOGRAPHIC EXAMS OF PATIENTS WITH TRAUMATIC BRAIN INJURY AND DECOMPRESSIVE CRANIECTOMY.

Brain trauma patients who underwent decompressive craniectomy make several computed tomography (CT) scans until cranioplasty. Despite several recommendations to avoid unnecessary radiological exposure, few studies systematically analyzed the technical parameters employed. CT exams of 14 patients were retrospectively analyzed to find display field of view (DFOV), dose length product (DLP), volume computed tomography dose index (CTDIvol) and effective dose (ED). The values obtained were: 120 kVp [95% confidence interval (CI) of 0.5], 297mA (95% CI of 5.6), scan range 20.8cm (95% CI of 1.3), DFOV 24.5cm (95% CI of 1.6), CTDIvol 67.5mGy (95% CI of 10.17), DLP 1404.8mGy.cm (95% CI of 235.0) and ED 2.9mSv (95% CI of 0.5). In conclusion, these values were above the recommendations of several guidelines and raise concern for excessive radiological exposure in trauma patients despite being previously reported in the literature.

Surface Micro-Reflector Array for Augmented Reality Display

Geometric optical waveguide display can significantly miniaturize the augmented reality eyeglasses, but suffers from the ghost image. In this paper, a method using surface micro-reflector array is proposed, which can dramatically suppress the ghost image. The transmission and expansion of the light bearing image are completed by using planar waveguide and micro-reflector array embedded in the surface layer of waveguide. The image quality is improved by using the dual channel to eliminate ghost image. The imaging process of optical system is modeled and simulated. The surface micro-reflector array waveguide element of 3 mm thickness is prepared for verification. The whole optical system has the advantages of simple structure, easy preparation and high structural strength. The display field of view is shown to be 25° × 25°, and the size of the full field of view area is 15 mm with even light distribution. What's more, the uniformity of imaging intensity is better than 20%, and the image is clear without ghost image, which can effectively realize the fusion of the virtual image and the real environment. Thus, the efficiency of augmented reality is greatly improved, and the danger of human eye safety is effectively avoided.

Quantitative Analysis of Emphysema in Ultra-high-resolution CT by Using Deep Learning Reconstruction: Comparison with Hybrid Iterative Reconstruction

The noise generated in ultra-high-resolution computed tomography (U-HRCT) images affects the quantitative analysis of emphysema. In this study, we compared the physical properties of reconstructed images for hybrid iterative reconstruction (HIR) and deep learning reconstruction (DLR), which are reconstruction methods for reducing image noise. Using clinical evaluation, we evaluated the correlation between low attenuation volume (LAV) % obtained by CT and forced expiratory volume in 1 s per forced vital capacity (FEV1/FVC) obtained by respiratory function tests. CT data obtained by HIR and DLR were used for analysis (matrix size: 1024´1024, slice thickness: 0.25 mm). The physical characteristics were evaluated for the modulation transfer function (MTF) and noise power spectrum (NPS). Display-field of view (D-FOV) was analyzed by varying between 300 mm and 400 mm. The clinical data evaluated the relationship between LAV% and FEV1/FVC by Spearman's correlation coefficient. The 10% MTFs were 1.3 cycles/mm (HIR) and 1.3 cycles/mm (DLR) at D-FOV 300 mm, and 1.2 cycles/mm (HIR) and 1.1 cycles/mm (DLR) at D-FOV 400 mm. The NPS had less noise in DLR than HIR in all frequency ranges. The correlation coefficients between LAV% and FEV1/FVC were 0.64 and 0.71, respectively, in HIR and DLR. There was no difference in the resolution characteristics of HIR and DLR. DLR had better noise characteristics than HIR. The correlation between LAV% measured by HIR and DLR and FEV1/FVC is equivalent. The noise characteristics of the DLR enable the reduction of exposure to emphysema quantitative analysis by CT.

Influence of metabolic syndrome on thigh intermuscular fat in older adults with knee osteoarthritis

Influence of metabolic syndrome on thigh intermuscular fat in older adults with knee osteoarthritis

The Effect of Head Tracking on the Degree of Presence in Virtual Reality

ABSTRACT The performance of a virtual reality (VR) system can be assessed from two aspects in the human-VR interaction loop. One aspect is the degree of immersion, which objectively quantifies the performance of the VR system using metrics such as the display field of view or the refresh rate. The other aspect is presence, which measures the user response to the VR system. This article presents a study that compares the impact on presence by changing immersion through enabling and disabling of the head tracking ability on a VR headset. The study quantitatively assesses this change by taking objective measurements of posture and subjective ratings of the VR experience, in terms of presence and motion sickness, after participants have gone through two versions of a roller coaster simulation; one with head tracking on and the other with head tracking off. The results indicate that a loss of immersion, caused by turning the head tracking feature off, results in a significant reduction in postural sway. This loss of immersion also affected presence, as shown through the user surveys. The survey responses indicate that the simulation with head tracking off was less enjoyable and caused more motion sickness compared to when head tracking is kept on.

Study of Preoperative 3D-CT Angiography of Uterine Artery in Patients with Uterine Cervical Cancer.

Depiction of the fine vessel can provide useful preoperative information for patients with uterine cervical cancer. Although angiography can visualize vessels in detail, it is invasive. MR-angiography is a minimally invasive method to depict vessels, but the resolution of images is insufficient for preoperative evaluation. In this study, we used less invasive three-dimensional CT angiography (3D-CTA) and reconstructed images of adaptive iterative dose resolution 3D (AIDR 3D) with display field of view (D-FOV), which are suitable for arteries with large and small diameters, and created the fusion images. Created images allowed the observation of vessel branch in wide area compared with angiography, and it was less invasive. We evaluated the utility of 3D-CTA for visualizing fine vessels branching from uterine artery as preoperative evaluation for radial hysterectomy. 3D-CTA was obtained in nine patients. Conventional reconstruction and magnification reconstruction (D-FOV: 320‒360 mm, 150 mm) was made using arterial phase. Normal volume rendering image (N-VR) was made from conventional reconstruction image, and hybrid volume rendering image (H-VR) was made from conventional and magnification reconstruction image. Visual evaluation of each VR image was performed by 5 trained radiologists. A Wilcoxon rank sum test was performed for each result. No statistical significance was found in the visualization of vessels with large diameter (p=0.81), but statistical significance was detected in the visualization of the uterine artery and its ascending/descending branches (p<0.05). H-VR could visualize fine vessels clearer than N-VR, and H-VR could depict a vascular map including fine vessels in a large field. Therefore, H-VR could provide useful information for surgical operation. Additional depiction of vein and ureter could clearly visualize the anatomical relationship of each structure, and new clinical finding of anatomical relationship between uterine artery and ureter was suggested. This new clinical finding was useful in radical hysterectomy in which crossing site of the uterine artery and ureter is dissected. This method is simple to create and useful for various clinical surgery.

Influence of the Pixel Sizes of Reference Computed Tomography on Single-photon Emission Computed Tomography Image Reconstruction Using Conjugate-gradient Algorithm.

The frame-of-reference using computed-tomography (CT) coordinate system on single-photon emission computed tomography (SPECT) reconstruction is one of the advanced characteristics of the xSPECT reconstruction system. The aim of this study was to reveal the influence of the high-resolution frame-of-reference on the xSPECT reconstruction. 99mTc line-source phantom and National Electrical Manufacturers Association (NEMA) image quality phantom were scanned using the SPECT/CT system. xSPECT reconstructions were performed with the reference CT images in different sizes of the display field-of-view (DFOV) and pixel. The pixel sizes of the reconstructed xSPECT images were close to 2.4 mm, which is acquired as originally projection data, even if the reference CT resolution was varied. The full width at half maximum (FWHM) of the line-source, absolute recovery coefficient, and background variability of image quality phantom were independent on the sizes of DFOV in the reference CT images. The results of this study revealed that the image quality of the reconstructed xSPECT images is not influenced by the resolution of frame-of-reference on SPECT reconstruction.

Triple rule-out CT angiography protocol with restricting field of view for detection of pulmonary thromboembolism and aortic dissection in emergency department patients: simulation of modified CT protocol for reducing radiation dose

Background Triple rule-out computed tomography (TRO CT) is a CT protocol designed to simultaneously evaluate the coronary, aorta, and pulmonary arteries. Purpose To evaluate potential diagnostic performance of TRO CT with restricted volume coverage for detection of pulmonary thromboembolism (PTE) and aortic dissection (AD). Material and Methods This study included 1224 consecutive patients with acute chest pain who visited the emergency department and underwent TRO CT using a 128-slice dual-source CT. Image data were reconstructed according to the display field of view (DFOV) of coronary CT angiography (CCTA) and TRO CT protocols in each patient. The presence of PTE and AD was evaluated by independent observers in each DFOV. The radiation dose was calculated to evaluate the potential benefits by restricting z-axis coverage to cardiac scan range instead of the whole thorax. Results Among all patients, 22 cases with PTE (1.9%) and nine cases with AD (0.8%) were found. Except for one PTE case, all cases were detected on both DFOV of TRO CT and CCTA. Mean effective dose for evaluation of entire thorax and cardiac scan coverage were 5.9 ± 1.1 mSv and 3.5 ± 0.7 mSv, respectively. Conclusion Isolated PTE and AD outside the CCTA DFOV rarely occur. Therefore, modified TRO CT protocol using cardiac scan coverage can be adopted to detect PTE and AD with reduced radiation dose.

CT 画像計測プログラムを用いた円形エッジ法における標的径とFOV に対するMTF 測定精度

The purpose of this study was to evaluate the effects of target diameter and display-field of view (D-FOV) in modulation transfer function (MTF) by circular edge strategy using the computed tomography (CT) image measurement program "CTmeasure". We calculated the MTF (MTF(edge)) using the circular edge strategy applied to cylindrical phantom (200 mmφ) that inserted with cylinders have 10, 20, 30, and 40 mm diameters. The phantom images were reconstructed using filtered back projection method varied with D-FOV (240, 320, 400, and 500 mm). The study compared both MTF(edge) and MTF(wire) at MTF50% and MTF(10%) for target diameter and D-FOV, respectively. The MTF(edge) by the different of target diameter indicated in rough compatibility. However, MTF(edge) of D-FOV diameters (320, 400, and 500 mm) decreased in the high frequency range. The circular edge strategy for MTF depended on the D-FOV, however, it was little dependent on target diameter using the CT image measurement program "CTmeasure".

Method of Individual Adjustment for 3D CT Analysis: Linear Measurement.

Introduction. We aim to regularize measurement values in three-dimensional (3D) computed tomography (CT) reconstructed images for higher-precision 3D analysis, focusing on length-based 3D cephalometric examinations. Methods. We measure the linear distances between points on different skull models using Vernier calipers (real values). We use 10 differently tilted CT scans for 3D CT reconstruction of the models and measure the same linear distances from the picture archiving and communication system (PACS). In both cases, each measurement is performed three times by three doctors, yielding nine measurements. The real values are compared with the PACS values. Each PACS measurement is revised based on the display field of view (DFOV) values and compared with the real values. Results. The real values and the PACS measurement changes according to tilt value have no significant correlations (p > 0.05). However, significant correlations appear between the real values and DFOV-adjusted PACS measurements (p < 0.001). Hence, we obtain a correlation expression that can yield real physical values from PACS measurements. The DFOV value intervals for various age groups are also verified. Conclusion. Precise confirmation of individual preoperative length and precise analysis of postoperative improvements through 3D analysis is possible, which is helpful for facial-bone-surgery symmetry correction.

Ultra-High-Resolution Computed Tomography of the Lung: Image Quality of a Prototype Scanner.

PurposeThe image noise and image quality of a prototype ultra-high-resolution computed tomography (U-HRCT) scanner was evaluated and compared with those of conventional high-resolution CT (C-HRCT) scanners.Materials and MethodsThis study was approved by the institutional review board. A U-HRCT scanner prototype with 0.25 mm x 4 rows and operating at 120 mAs was used. The C-HRCT images were obtained using a 0.5 mm x 16 or 0.5 mm x 64 detector-row CT scanner operating at 150 mAs. Images from both scanners were reconstructed at 0.1-mm intervals; the slice thickness was 0.25 mm for the U-HRCT scanner and 0.5 mm for the C-HRCT scanners. For both scanners, the display field of view was 80 mm. The image noise of each scanner was evaluated using a phantom. U-HRCT and C-HRCT images of 53 images selected from 37 lung nodules were then observed and graded using a 5-point score by 10 board-certified thoracic radiologists. The images were presented to the observers randomly and in a blinded manner.ResultsThe image noise for U-HRCT (100.87 ± 0.51 Hounsfield units [HU]) was greater than that for C-HRCT (40.41 ± 0.52 HU; P < .0001). The image quality of U-HRCT was graded as superior to that of C-HRCT (P < .0001) for all of the following parameters that were examined: margins of subsolid and solid nodules, edges of solid components and pulmonary vessels in subsolid nodules, air bronchograms, pleural indentations, margins of pulmonary vessels, edges of bronchi, and interlobar fissures.ConclusionDespite a larger image noise, the prototype U-HRCT scanner had a significantly better image quality than the C-HRCT scanners.

金属アーチファクト低減再構成技術におけるdisplay field of view(DFOV)の影響について

We evaluated the effect of orthopedic-metal artifact reduction (O-MAR) for metal artifact in computed tomography with 73 simulated seeds for brachytherapy in different sizes of display field of view (DFOV) obtained by helical scan under the same clinical scan condition. The metal artifacts were analyzed with the Gumbel's method by changing DFOV sizes 80 mm, 160 mm, and 320 mm. Gumbel distribution, scale parameter (γ), and location parameter (β) of the metal artifacts with O-MAR were compared with that of the metal artifacts with filtered back projection (FBP). In conclusion, it was considered that the effect of metal artifact reduction with O-MAR was influenced by DFOV size in this study. The reduction rates of scale parameter (γ) were 22.3%, 21.3%, and 10.0% in DFOV 80 mm, 160 mm, and 320 mm, respectively. The reduction rates of location parameter (β) were 27.4%, 23.4 %, and 9.8%. Therefore, the effect of metal artifact reduction with O-MAR showed the tendency of increasing with decreasing DFOV size.

CT reconstruction techniques for improved accuracy of lung CT airway measurement.

To determine the impact of constrained reconstruction techniques on quantitative CT (qCT) of the lung parenchyma and airways for low x-ray radiation dose. Measurement of small airways with qCT remains a challenge, especially for low x-ray dose protocols. Images of the COPDGene quality assurance phantom (CTP698, The Phantom Laboratory, Salem, NY) were obtained using a GE discovery CT750 HD scanner for helical scans at x-ray radiation dose-equivalents ranging from 1 to 4.12 mSv (12-100 mA s current-time product). Other parameters were 40 mm collimation, 0.984 pitch, 0.5 s rotation, and 0.625 mm thickness. The phantom was sandwiched between 7.5 cm thick water attenuating phantoms for a total length of 20 cm to better simulate the scatter conditions of patient scans. Image data sets were reconstructed using STANDARD (STD), DETAIL, BONE, and EDGE algorithms for filtered back projection (FBP), 100% adaptive statistical iterative reconstruction (ASIR), and Veo reconstructions. Reduced (half) display field of view (DFOV) was used to increase sampling across airway phantom structures. Inner diameter (ID), wall area percent (WA%), and wall thickness (WT) measurements of eight airway mimicking tubes in the phantom, including a 2.5 mm ID (42.6 WA%, 0.4 mm WT), 3 mm ID (49.0 WA%, 0.6 mm WT), and 6 mm ID (49.0 WA%, 1.2 mm WT) were performed with Airway Inspector (Surgical Planning Laboratory, Brigham and Women's Hospital, Boston, MA) using the phase congruency edge detection method. The average of individual measures at five central slices of the phantom was taken to reduce measurement error. WA% measures were greatly overestimated while IDs were underestimated for the smaller airways, especially for reconstructions at full DFOV (36 cm) using the STD kernel, due to poor sampling and spatial resolution (0.7 mm pixel size). Despite low radiation dose, the ID of the 6 mm ID airway was consistently measured accurately for all methods other than STD FBP. Veo reconstructions showed slight improvement over STD FBP reconstructions (4%-9% increase in accuracy). The most improved ID and WA% measures were for the smaller airways, especially for low dose scans reconstructed at half DFOV (18 cm) with the EDGE algorithm in combination with 100% ASIR to mitigate noise. Using the BONE + ASIR at half BONE technique, measures improved by a factor of 2 over STD FBP even at a quarter of the x-ray dose. The flexibility of ASIR in combination with higher frequency algorithms, such as BONE, provided the greatest accuracy for conventional and low x-ray dose relative to FBP. Veo provided more modest improvement in qCT measures, likely due to its compatibility only with the smoother STD kernel.

Lessons learned: Evaluating visualizations for occluded objects in handheld augmented reality

Handheld devices like smartphones and tablets have emerged as one of the most promising platforms for Augmented Reality (AR). The increased usage of these portable handheld devices has enabled handheld AR applications to reach the end-users; hence, it is timely and important to seriously consider the user experience of such applications. AR visualizations for occluded objects enable an observer to look through objects. AR visualizations have been predominantly evaluated using Head-Worn Displays (HWDs), handheld devices have rarely been used. However, unless we gain a better understanding of the perceptual and cognitive effects of handheld AR systems, effective interfaces for handheld devices cannot be designed. Similarly, human perception of AR systems in outdoor environments, which provide a higher degree of variation than indoor environments, has only been insufficiently explored.In this paper, we present insights acquired from five experiments we performed using handheld devices in outdoor locations. We provide design recommendations for handheld AR systems equipped with visualizations for occluded objects. Our key conclusions are the following: (1) Use of visualizations for occluded objects improves the depth perception of occluded objects akin to non-occluded objects. (2) To support different scenarios, handheld AR systems should provide multiple visualizations for occluded objects to complement each other. (3) Visual clutter in AR visualizations reduces the visibility of occluded objects and deteriorates depth judgment; depth judgment can be improved by providing clear visibility of the occluded objects. (4) Similar to virtual reality interfaces, both egocentric and exocentric distances are underestimated in handheld AR. (5) Depth perception will improve if handheld AR systems can dynamically adapt their geometric field of view (GFOV) to match the display field of view (DFOV). (6) Large handheld displays are hard to carry and use; however, they enable users to better grasp the depth of multiple graphical objects that are presented simultaneously.