Objective Image Quality Evaluation Research Articles

The effects of joint optimization of CT scanning-modes and CT angiography starting-modes on image quality and patients' radiation dose in cervicocerebral CT angiography

Objective To study the effects of joint optimization of CT scanning-modes and CTA starting-modes on the image quality, the patients' radiation doses and contrast volumes in cervicocerebral CTA. Method According to the date of examination from December 2013 to January 2014, 188 consecutive patients were prospectively selected and underwent cervicocerebral CTA using different CT scanning-modes and CTA starting-modes. These patients wererandomly divided into 4 groups: A1 (45 cases), A2 (48 cases), B1 (45 cases) and B2 (50 cases). Group A1 were Flash mode combined with test bolus, Group A2 were Flash mode combined with bolus tracking, group B1 were the common spiral scanning mode combined with test bolus and group B2 were the common spiral scanning mode combined with bolus tracking. The objective image quality evaluation criteria included the CT value comparison at the aortic arch(Pa1), carotid artery bifurcation (Pa2), basal artery (Pa3), superior vena cava (Pv1), internal jugular (pv2), transverse sinus (Pv3) and image objective noise. The subjective image quality assessments criteria included the contrast hardening artifact and diagnose acceptability. The radiation dose and contrast volumes of every patient were recorded and analyzed. The analysis of variance, the chi-square tests and the rank sum tests (Kruskal-Wallis) were used for data statistics. Results There were significant differences on the CT value at transverse sinus among the four groups, they were (124±30), (151±34), (130±37) and (160±37) HU, and different starting-modes had impacts on venous reflux (P 0.05). The image noise had significant differences in four groups (P 0.05), however there were significant differences on contrast hardening artifacts (P< 0.05) among the four groups. With the same scanning mode, the artifacts of group A1 were more serious than A2 and B1 were more serious than B2.There were significant differences on the patients' contrast volumes in the four groups (P<0.05), they were (45±5), (49±4), (35±4) and (35±4) ml, the contrast volumes in groups A1 and B1 were more than groups A2 and B2. There were significant differences among the four groups on patients' ED (P<0.05), which were (0.79±0.07), (0.81±0.08), (1.49±0.11) and (1.51±0.12) mSv. The radiation dose in groups A1, A2 were lower than those in B1 and B2. Conclusion The joint use of Flash mode and bolus tracking technique is recommended in application of cervicocerebral CTA, for its advantages of better image quality, good diagnosis acceptability, the patient's low radiation dose and low contrast volumes. Key words: Angiography; Tomography,X-ray computed; Radiation dosage; Contrast media; Comparative study

Subjective and objective evaluation of image quality in biplane cerebral digital subtraction angiography following significant acquisition dose reduction in a clinical setting

ObjectiveDifferent technical and procedural methods have been introduced to develop low radiation dose protocols in neurointerventional examinations. We investigated the feasibility of minimizing radiation exposure dose by simply decreasing the...

Objective evaluation of computer-generated hologram image quality

Objective evaluation of computer-generated hologram image quality

Realization of High Dynamic Range Imaging in the GLORIA Network and Its Effect on Astronomical Measurement

Citizen science project GLORIA (GLObal Robotic-telescopes Intelligent Array) is a first free- and open-access network of robotic telescopes in the world. It provides a web-based environment where users can do research in astronomy by observing with robotic telescopes and/or by analyzing data that other users have acquired with GLORIA or from other free-access databases. Network of 17 telescopes allows users to control selected telescopes in real time or schedule any more demanding observation. This paper deals with new opportunity that GLORIA project provides to teachers and students of various levels of education. At the moment, there are prepared educational materials related to events like Sun eclipse (measuring local atmosphere changes), Aurora Borealis (calculation of Northern Lights height), or transit of Venus (measurement of the Earth-Sun distance). Student should be able to learn principles of CCD imaging, spectral analysis, basic calibration like dark frames subtraction, or advanced methods of noise suppression. Every user of the network can design his own experiment. We propose advanced experiment aimed at obtaining astronomical image data with high dynamic range. We also introduce methods of objective image quality evaluation in order to discover how HDR methods are affecting astronomical measurements.

MODEL-BASED ITERATIVE RECONSTRUCTION ENABLES THE EVALUATION OF THIN-SLICE COMPUTED TOMOGRAPHY IMAGES WITHOUT DEGRADING IMAGE QUALITY OR INCREASING RADIATION DOSE.

Computed tomography (CT) is one of the most important modalities in a radiological department. This technique not only produces images that enable radiological reports with high diagnostic confidence, but it may also provide an elevated radiation dose to the patient. The radiation dose can be reduced by using advanced image reconstruction algorithms. This study was performed on a Brilliance iCT, equipped with iDose(4) iterative reconstruction and an iterative model-based reconstruction (IMR) method. The purpose was to investigate the effect of reduced slice thickness combined with an IMR method on image quality compared with standard slice thickness with iDose(4) reconstruction. The results of objective and subjective image quality evaluations showed that a thinner slice combined with IMR can improve the image quality and reduce partial volume artefacts compared with the standard slice thickness with iDose(4) In conclusion, IMR enables reduction of the slice thickness while maintaining or even improving image quality versus iDose(4).

Real-time transmission of panoramic images for a telepresence wheelchair.

This paper proposes an approach to transmit panoramic images in real-time for a telepresence wheelchair. The system can provide remote monitoring and assistive assistance for people with disabilities. This study exploits technological advancement in image processing, wireless communication networks, and healthcare systems. High resolution panoramic images are extracted from the camera which is mounted on the wheelchair. The panoramic images are streamed in real-time via a wireless network. The experimental results show that streaming speed is up to 250 KBps. The subjective quality assessments show that the received images are smooth during the streaming period. In addition, in terms of the objective image quality evaluation the average peak signal-to-noise ratio of the reconstructed images is measured to be 39.19 dB which reveals high quality of images.

Texture and object related image analysis in microscopic images

Background Tissue based diagnosis or surgical diagnostic pathology undergoes significant changes and focuses on image content analysis in our days. Herein we describe and discuss new approaches of content image analysis and compare their applications, benefits and constraints. Theory Any useful microscopic image contains information that can be evaluated and transferred into a tissue-based diagnosis. A correctly derived diagnosis depends upon the image information and the pathologist’s knowledge, i.e. his ability to recognize and transfer the image content information into clinical application. Thus, image information is related to external “disease” information and “pure” image content information. Application of external image information requires a separation of objects from the background, or segmentation procedures. “Pure” image information is solely pixel based. It can be analyzed using different approaches, such as entropy measure, construction of image primitives and their spatial distribution, or image similarity operations. Our approach uses entropy calculations dependent upon all possible gray value thresholds in combination with syntactic analysis of pixel based image primitives. Implementation Virtual slides underwent the evaluation of regions of interest (ROI) as described previously. ROIs were interactively controlled and subject for application of developed image analysis procedures. The “classic method” of object recognition and syntactic structure analysis is applied too. Trials were performed on antie Her2_new stained, DAB visualized, and glycohistochemically stained, AP visualized slides. The images were measured at magnifications, which correspond to x20, and x40 objectives. Results The algorithm displayed only weak changes of the evaluated gray level based structural entropy (GL-MST)-entropy in the selected ROIs in contrast to the whole image. In addition, significant differences could be obtained when the measures were associated to the clinical impact (diagnosis, fetal developing stage). Conclusions: Images textures and pixel primitives can serve for evaluating “pure” image content information. They do not require segmentation and additional external information for measurement. Interpretation of the measures, i.e. external information can be implemented at a later stage. The described algorithm is probably applicable for image analysis of different fields such as histology, forests, traffic, or can serve for objective image quality evaluation.

Coronary computed tomographic angiography in coronary artery bypass grafts: comparison between low-concentration Iodixanol 270 and Iohexol 350.

The aim of this study was to evaluate the feasibility of low-concentration iso-osmolar Iodixanol 270 compared with Iohexol 350 in patients with coronary artery bypass grafts (CABGs) undergoing coronary computed tomographic angiography (CCTA). A total of 80 consecutive patients undergoing CABG follow-up with the use of CCTA were prospectively enrolled, with 40 patients assigned to Iodixanol 270 and 40 patients assigned to Iohexol 350. In both groups, the contrast medium was injected at an injection rate of 4.5 mL/s in the patients with a body mass index of greater than 24 kg/m2 and 3.5 mL/s in the patients with a body mass index of 24 kg/m2 or lower. The contrast volume was determined by the flow rate and scan time. Image quality score and visualization of bypass grafts were evaluated. Subjective assessment of image quality for each coronary artery segment was determined using a 4-point grading scale by 2 reviewers, whereas objective evaluation of image quality was conducted by measuring the mean CT attenuation values (hounsfield unit [HU]) in terms of SD, contrast-noise ratio, and signal-noise ratio in the ascending aorta. The mean (SD) contrast volume for the Iodixanol 270 and Iohexol 350 groups was 66.28 (12.00) and 64.98 (8.12) mL, respectively, with no significant difference (P = 0.57). The mean (SD) CT attenuation value in the Iodixanol 270 group was 414.72 (101.47), which was lower than in the Iohexol 350 group, which was 478.85 (108.73) (P = 0.01). The subjective image quality for the Iodixanol 270 group was superior to that for the Iohexol 350 group in the arterial graft vessels (P = 0.027), whereas there was no significant difference between the 2 groups in the venous graft vessels (P = 0.377). There was no significant difference in terms of SD of the ascending aorta, signal-noise ratio, and contrast-noise ratio between the 2 groups. Low-concentration iso-osmolar Iodixanol 270 provides image quality comparable with that of Iohexol 350, allowing diagnostic CCTA follow-up of patients with CABGs.

Influence of selective photon shield combined with sinogram affirmed iterative reconstruction on image quality and radiation dose of dual-energy CT angiography for the diagnosis of intracranial aneurysms

Objective To investigate the influence of selective photon shield combined with sinogram affirmed iterative reconstruction(SAFIRE) on image quality and radiation dose of dual-energy CTA for the diagnosis of intracranial aneurysms. Methods The study retrospectively analyzed 80 patients with spontaneous subarachnoid hemorrhage, who were diangosed having intracranial aneurysms by three-dimensional DSA and surgery and underwent cerebral CTA examination. According to CTA scanning method, the patients were divided into conventional group and experimental group (n=40 for each). All patients underwent head CTA in dual energy mode with selective photon shield (SPS) technology. The scanning protocols of conventional group were tube voltages 80 kV and sn 140 kV, tube currents 300 mAs and 150 mAs, filtered back projection (FBP) reconstruction. The scanning protocols of experimental group were tube voltages 80 kV, sn 140 kV, tube currents 200 mAs, 100 mAs, SAFIRE reconstruction. Objective image quality evaluation indexes included the average CT value of all parts (occipital lobe, the anterior cerebral artery, middle cerebral artery and posterior cerebral artery), the background noise, the signal-to-noise ratio (SNR) and contrast to noise ratio (CNR), and subjective image quality was also assessed. Radiation dose was recorded. With 3D DSA or operation findings as gold standard, coincidence rate of intracranial aneurysm detection was calculated both in experimental group and conventional group. Objective image quality evaluation index and radiation dose both in conventional group and experimental group were compared with two independent two-sample t test, subjective image scores with non parameter test of independent samples. Results The noise of occipital lobe, the anterior cerebral artery, middle cerebral artery and posterior cerebral artery were (5.34±1.22), (39.94±15.96), (39.94±15.96) and (23.17± 5.51) HU in conventional group, (4.44 ± 1.08), (24.91 ± 9.36), (35.03 ± 13.65) and (20.61 ± 5.08) in experimental group (the value of t test were 2.508,3.742,2.788 and 2.563, P 0.05). Image quality scores of the conventional group and experimental group were (4.86± 0.07) and (4.67±0.21) without statistical difference (Z=- 0.443,P=0.621). CTDIvol and ED were (20.61 ± 1.07) mGy and (0.79 ± 0.04) mSv in conventional group and (13.59 ± 1.27) mGy and (0.54 ± 0.06) mSv in experimental group (the value of t test were 24.039 and 15.813, P<0.01). With 3D DSA or operation findings as gold standard, intracranial aneurysm diagnosis coincidence of experimental group was 100.0% (29/29), while coincidence rate of conventional group was 96.0% (25/26). Conclusion SPS combined with SAFIRE techniques applied in dual energy CTA for the diagnosis of intracranial aneurysms could improve the quality of CT image and reduce the radiation dosage and have a high diagnosis accuracy. Key words: Intracranial aneurysm; Tomography, X-ray computed; Radiation dosage; Image quality

Poster — Thur Eve — 05: Objective phantom‐based and porcine model comparison of filtered back projection, adaptive statistical iterative reconstruction and model based iterative reconstruction algorithms

We performed objective image quality evaluation of three commercial reconstruction algorithms available on a GE DiscoveryCT750HD multi‐detector CT (MDCT) scanner at different dose levels. Using a Catphan500 phantom and a freshly euthanized pig carcass (∼ 36kg), we evaluated the noise and contrast‐to‐noise ratio (CNR) for the three reconstruction algorithms: filtered back‐projection (FBP), adaptive statistical iterative reconstruction (ASIR™) and model based iterative reconstruction (code named VEO™). At a dose of ∼ 1.5 mGy, ASIR™ offers noise reduction up to 54% with the phantom, while VEO™ reduces noise by up to 70% with the porcine model. At low doses, VEO™ offers better noise reduction capabilities over FBP and ASIR™, depending on helical pitch. The level of noise reduction increases as pitch increases. Similar trend was observed with CNR increases as VEO™ offered significantly better CNR over FBP and ASIR™. Compared to FBP, iterative algorithms reduce image noise and increase CNR. The model‐based iterative algorithm (VEO™) produced better noise and contrast resolution in both phantom and porcine images compared to FBP and ASIR™.

Methods for clinical evaluation of noise reduction techniques in abdominopelvic CT.

Most noise reduction methods involve nonlinear processes, and objective evaluation of image quality can be challenging, since image noise cannot be fully characterized on the sole basis of the noise level at computed tomography (CT). Noise spatial correlation (or noise texture) is closely related to the detection and characterization of low-contrast objects and may be quantified by analyzing the noise power spectrum. High-contrast spatial resolution can be measured using the modulation transfer function and section sensitivity profile and is generally unaffected by noise reduction. Detectability of low-contrast lesions can be evaluated subjectively at varying dose levels using phantoms containing low-contrast objects. Clinical applications with inherent high-contrast abnormalities (eg, CT for renal calculi, CT enterography) permit larger dose reductions with denoising techniques. In low-contrast tasks such as detection of metastases in solid organs, dose reduction is substantially more limited by loss of lesion conspicuity due to loss of low-contrast spatial resolution and coarsening of noise texture. Existing noise reduction strategies for dose reduction have a substantial impact on lowering the radiation dose at CT. To preserve the diagnostic benefit of CT examination, thoughtful utilization of these strategies must be based on the inherent lesion-to-background contrast and the anatomy of interest. The authors provide an overview of existing noise reduction strategies for low-dose abdominopelvic CT, including analytic reconstruction, image and projection space denoising, and iterative reconstruction; review qualitative and quantitative tools for evaluating these strategies; and discuss the strengths and limitations of individual noise reduction methods.

A quality assurance framework for the fully automated and objective evaluation of image quality in cone‐beam computed tomography

Thousands of cone-beam computed tomography (CBCT) scanners for vascular, maxillofacial, neurological, and body imaging are in clinical use today, but there is no consensus on uniform acceptance and constancy testing for image quality (IQ) and dose yet. The authors developed a quality assurance (QA) framework for fully automated and time-efficient performance evaluation of these systems. In addition, the dependence of objective Fourier-based IQ metrics on direction and position in 3D volumes was investigated for CBCT. The authors designed a dedicated QA phantom 10 cm in length consisting of five compartments, each with a diameter of 10 cm, and an optional extension ring 16 cm in diameter. A homogeneous section of water-equivalent material allows measuring CT value accuracy, image noise and uniformity, and multidimensional global and local noise power spectra (NPS). For the quantitative determination of 3D high-contrast spatial resolution, the modulation transfer function (MTF) of centrally and peripherally positioned aluminum spheres was computed from edge profiles. Additional in-plane and axial resolution patterns were used to assess resolution qualitatively. The characterization of low-contrast detectability as well as CT value linearity and artifact behavior was tested by utilizing sections with soft-tissue-equivalent and metallic inserts. For an automated QA procedure, a phantom detection algorithm was implemented. All tests used in the dedicated QA program were initially verified in simulation studies and experimentally confirmed on a clinical dental CBCT system. The automated IQ evaluation of volume data sets of the dental CBCT system was achieved with the proposed phantom requiring only one scan for the determination of all desired parameters. Typically, less than 5 min were needed for phantom set-up, scanning, and data analysis. Quantitative evaluation of system performance over time by comparison to previous examinations was also verified. The maximum percentage interscan variation of repeated measurements was less than 4% and 1.7% on average for all investigated quality criteria. The NPS-based image noise differed by less than 5% from the conventional standard deviation approach and spatially selective 10% MTF values were well comparable to subjective results obtained with 3D resolution pattern. Determining only transverse spatial resolution and global noise behavior in the central field of measurement turned out to be insufficient. The proposed framework transfers QA routines employed in conventional CT in an advanced version to CBCT for fully automated and time-efficient evaluation of technical equipment. With the modular phantom design, a routine as well as an expert version for assessing IQ is provided. The QA program can be used for arbitrary CT units to evaluate 3D imaging characteristics automatically.

Despeckle filtering software toolbox for ultrasound imaging of the common carotid artery

Ultrasound imaging of the common carotid artery (CCA) is a non-invasive tool used in medicine to assess the severity of atherosclerosis and monitor its progression through time. It is also used in border detection and texture characterization of the atherosclerotic carotid plaque in the CCA, the identification and measurement of the intima-media thickness (IMT) and the lumen diameter that all are very important in the assessment of cardiovascular disease (CVD). Visual perception, however, is hindered by speckle, a multiplicative noise, that degrades the quality of ultrasound B-mode imaging. Noise reduction is therefore essential for improving the visual observation quality or as a pre-processing step for further automated analysis, such as image segmentation of the IMT and the atherosclerotic carotid plaque in ultrasound images. In order to facilitate this preprocessing step, we have developed in MATLAB® a unified toolbox that integrates image despeckle filtering (IDF), texture analysis and image quality evaluation techniques to automate the pre-processing and complement the disease evaluation in ultrasound CCA images. The proposed software, is based on a graphical user interface (GUI) and incorporates image normalization, 10 different despeckle filtering techniques (DsFlsmv, DsFwiener, DsFlsminsc, DsFkuwahara, DsFgf, DsFmedian, DsFhmedian, DsFad, DsFnldif, DsFsrad), image intensity normalization, 65 texture features, 15 quantitative image quality metrics and objective image quality evaluation. The software is publicly available in an executable form, which can be downloaded from http://www.cs.ucy.ac.cy/medinfo/. It was validated on 100 ultrasound images of the CCA, by comparing its results with quantitative visual analysis performed by a medical expert. It was observed that the despeckle filters DsFlsmv, and DsFhmedian improved image quality perception (based on the expert's assessment and the image texture and quality metrics). It is anticipated that the system could help the physician in the assessment of cardiovascular image analysis.

Visual attention pooling and understanding the structural similarity index in multi-scale analysis

We present a novel spatial pooling strategy and the results of an extensive multi-scale analysis of the well-known structural similarity index metric (SSIM) for objective image quality evaluation. We show, in contrast with some previous studies, that even relatively simple perceptual importance pooling strategies can significantly improve objective metric performance evaluated as the correlation with subjective quality assessment. In particular, we define an attention and quality driven pooling mechanism that focuses structural comparisons within the SSIM model to only those pixels exhibiting significant structural degradations. We show that optimal objective metric performance is achieved over very sparse spatial domains indeed that ignore most of the signal data. We also investigate an explicit breakdown of the structural models within SSIM and show that in combination with the proposed attention and quality driven pooling some of these models represent well performing metrics in their own right, when applied at appropriate scale for which there may not be a single optimal value. Our experiments demonstrate that the augmented SSIM metric using the proposed pooling model provides performance advantage on an extensive LIVE dataset covering hundreds of degraded images and 5 different distortion types compared to both conventional SSIM and state-of-the-art objective quality metrics.

Evaluation of high-pitch flash scan for pulmonary venous CTA on a 128-slice dual source CT: compared with prospective ECG-triggered sequence scan

To compare the image quality (IQ) and radiation dose of high-pitch scan and prospective ECG-triggered sequence scan on a 128-slice DSCT system for patients with atrial fibrillation (AF). Pulmonary venous (PV) CTA was performed with two protocols, including high-pitch scan and prospective ECG-triggered sequence scan. For each protocol, 20 sex, age and body-mass-index (mean 24.2 kg/m(2)) matched patients were identified. Two experienced radiologists, who were blinded to the scan protocols, independently graded the CT images of the two groups by a 5-point scale for subjective IQ assessment. Measured CT attenuation (Hounsfield units ± standard deviation), signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) at various anatomic locations were also recorded for objective IQ evaluation. Radiation exposure parameters [dose length product (DLP) and effective radiation dose (ERD)] were compared. Twenty-three patients (57.5 %) showed an ECG pattern of AF in total. Subjective IQ was rated excellent in 100 % for the high-pitch scan group, while minor step artifacts were observed in two patients (10 %) with arrhythmia for the prospective ECG-triggered sequence group. There was no significant difference on IQ, neither by subjective, nor by objective measures (SNR, CNR) between the two groups. The ERD of high-pitch flash scan and prospective ECG-triggered sequence scan were 0.9 (± 0.25) and 2.9 (± 0.69) mSv, respectively. Significantly lower radiation was achieved by using high-pitch flash scan (P < 0.05). High-pitch flash scan can provide similar subjective and objective IQ compared with prospective ECG-triggered sequence scan for PV CTA, while radiation exposure was significantly reduced.

A simple application of compressed sensing to further accelerate partially parallel imaging

Compressed sensing (CS) and partially parallel imaging (PPI) enable fast magnetic resonance (MR) imaging by reducing the amount of k-space data required for reconstruction. Past attempts to combine these two have been limited by the incoherent sampling requirement of CS since PPI routines typically sample on a regular (coherent) grid. Here, we developed a new method, “CS+GRAPPA,” to overcome this limitation. We decomposed sets of equidistant samples into multiple random subsets. Then, we reconstructed each subset using CS and averaged the results to get a final CS k-space reconstruction. We used both a standard CS and an edge- and joint-sparsity-guided CS reconstruction. We tested these intermediate results on both synthetic and real MR phantom data and performed a human observer experiment to determine the effectiveness of decomposition and to optimize the number of subsets. We then used these CS reconstructions to calibrate the generalized autocalibrating partially parallel acquisitions (GRAPPA) complex coil weights. In vivo parallel MR brain and heart data sets were used. An objective image quality evaluation metric, Case-PDM, was used to quantify image quality. Coherent aliasing and noise artifacts were significantly reduced using two decompositions. More decompositions further reduced coherent aliasing and noise artifacts but introduced blurring. However, the blurring was effectively minimized using our new edge- and joint-sparsity-guided CS using two decompositions. Numerical results on parallel data demonstrated that the combined method greatly improved image quality as compared to standard GRAPPA, on average halving Case-PDM scores across a range of sampling rates. The proposed technique allowed the same Case-PDM scores as standard GRAPPA using about half the number of samples. We conclude that the new method augments GRAPPA by combining it with CS, allowing CS to work even when the k-space sampling pattern is equidistant.

Objective evaluation of acute adverse events and image quality of gadolinium-based contrast agents (gadobutrol and gadobenate dimeglumine) by blinded evaluation. Pilot study

PurposeThe purpose was to objectively evaluate a recently FDA-approved gadolinium-based contrast agent (GBCA) in comparison to our standard GBCA for acute adverse events and image quality by blinded evaluation. MethodsEvaluation was made of a recently FDA-approved GBCA, gadobutrol (Gadavist; Bayer), in comparison to our standard GBCA, gadobenate dimeglumine (MultiHance; Bracco), in an IRB- and HIPAA-compliant study. Both the imaging technologist and patient were not aware of the brand of the GBCA used. A total of 59 magnetic resonance studies were evaluated (59 patients, 31 men, 28 women, age range of 5–85 years, mean age of 52 years). Twenty-nine studies were performed with gadobutrol (22 abdominal and 7 brain studies), and 30 studies were performed with gadobenate dimeglumine (22 abdominal and 8 brain studies). Assessment was made of acute adverse events focusing on objective observations of vomiting, hives, and moderate and severe reactions. Adequacy of enhancement was rated as poor, fair and good by one of two experienced radiologists who were blinded to the type of agent evaluated. ResultsNo patient experienced acute adverse events with either agent. The target minor adverse events of vomiting or hives, and moderate and severe reactions were not observed in any patient. Adequacy of enhancement was rated as good for both agents in all patients. ConclusionsObjective, blinded evaluation is feasible and readily performable for the evaluation of GBCAs. This proof-of-concept study showed that both GBCAs evaluated exhibited consistent good image quality and no noteworthy adverse events.

Detection and Diagnosis of Glaucoma: Ocular Imaging

Imaging is a valuable tool in the assessment of glaucoma and glaucoma progression. Although glaucoma is a clinical diagnosis—there is no blood test or definitive genetic test, for example, for the disease—the diagnosis has traditionally been subjective albeit based on certain physical characteristics of the patient. Over the years, the diagnosis has gone from a hard, blind, painful eye; to palpation indicating a hard eye associated with sudden pain or slow, painless visual loss; to a specifically described progressive optic neuropathy with characteristic neural damage and visual loss, sometimes associated with elevated intraocular pressure (IOP). In the mid-19th century, Helmholtz and Von Graefe enabled clinical assessment of the optic nerve head (ONH); later, fundus photography permitted objective recording of this physical parameter.1,2 Nevertheless, despite objective photographs of the ONH, subjective interpretation on the part of the clinician was necessary for identification of glaucomatous damage or progression. Different clinicians would provide discrepant interpretations of the optic nerve, and even the same observer would frequently characterize the disc differently on separate viewings of the same photograph.3 Measurement of ocular function is and has been similarly crude and subjective. From discriminating finger movement in different quadrants to discerning white objects on a black background to map the visual field in tangent screen perimetry, the patient must tell the examiner when a light or object is seen. The same is true of kinetic and static perimetry, both manual and automated. The patient must detect the object (or light) on the retina, realize that a light or object has been seen, and then inform the examiner of this fact. The evaluation is difficult as best, often tedious, and fraught with problems in reproducibility of findings. For these reasons, clinicians, scientists, and engineers have sought to objectively measure optic nerve structure and function both quantitatively and reproducibly, preferably without the requirement for patient input. In the assessment of optic nerve function, this has meant multifocal electroretinography,4 pattern electroretinography,5,6 multifocal visual evoked potential, and pattern visual evoked potential,7,8 among other tests.9 Unfortunately, none of these objective functional tests has been validated to the level of perimetry, which remains the clinical gold standard, despite its shortcomings. Automated objective, quantitative characterization of the optic nerve has been more successful. As mentioned above, the first step in this direction was optic nerve photography, particularly stereoscopic disc photography. This method enables objective recording, but still requires subjective interpretation. More sophisticated techniques, invented and/or developed in the past quarter century, include confocal scanning laser ophthalmoscopy (CSLO), scanning laser polarimetry (SLP), and optical coherence tomography (OCT). These systems capture, in different ways, objective, accurate, and precise quantitative information about optic nerve and retinal structure that does not require subjective input for measurement. Although there is objective image and segmentation algorithm quality evaluation, subjective quality assessment is still necessary to ensure that the image acquired is adequate for evaluation and that the analysis algorithm has functioned properly.

경계 기반의 깊이 영상 개선

Recently, 3D technology based on depth image is widely used in various fields including 3D space recognition, image acquisition, interaction, and games. Depth camera is used in order to produce depth image, various types of effort are made to improve quality of the depth image. In this paper, we suggests using area-based Canny edge detector to improve depth image in applying 3D technology based on depth camera. The suggested method provides improved depth image with pre-processing and post-processing by fixing image quality deterioration, which may take place in acquiring depth image in a limited environment. For objective image quality evaluation, we have confirmed that the image is improved by 0.42dB at maximum, by applying and comparing improved depth image to virtual view reference software. In addition, with DSCQS(Double Stimulus Continuous Quality Scale) evaluation method, we are reassured of the effectiveness of improved depth image through objective evaluation of subjective quality.

Optimization of Radiation Exposure and Image Quality of the Cone-beam O-arm Intraoperative Imaging System in Spinal Surgery

Retrospective study. To optimize the radiation doses and image quality for the cone-beam O-arm surgical imaging system in spinal surgery. Neurovascular compromise has been reported after screw misplacement during thoracic pedicle screw insertion. The use of O-arm with or without navigation system during spinal surgery has been shown to lower the rate of screw misplacement. The main drawback of such imaging surgical systems is the high radiation exposure. Chest phantom and cadaveric pig spine were examined on the O-arm with different scan settings: 2 were recommended by the O-arm manufacturer (120 kV/320 mAs, and 120 kV/128 mAs), and 3 low-dose settings (80 kV/80 mAs, 80 kV/40 mAs, and 60 kV/40 mAs). The radiation doses were estimated by Monte Carlo calculations. Objective evaluation of image quality included interobserver agreement in the measurement of pedicular width in chest phantom and assessment of screw placement in cadaveric pig spine. The effective dose/cm for 120 kV/320 mAs scan was 13, 26, and 69 times higher than those delivered with 80 kV/80 mAs, 80 kV/40 mAs, and 60 kV/40 mAs scans, respectively. Images with 60 kV/40 mAs were unreliable. Images with 80 kV/80 mAs were considered reliable with good interobserver agreement when measuring the pedicular width (random error 0.38 mm and intraclass correlation coefficient 0.979) and almost perfect agreement when evaluating the screw placement (κ value 0.86). The radiation doses of the O-arm system can be reduced 5 to 13 times without negative impact on image quality with regard to information required for spinal surgery.