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The impact of the number of projections on image quality in Compton scatter tomography
摘要： The availability of high resolution, energy discriminating photon counting detectors should make it possible to use Compton scattered photons to improve the diagnostic capability of computed tomography (CT). With high, spatial and energy resolution detectors Compton scatter tomography (CST) images of adequate quality can be obtained with a single projection. In practice, the limitations of realistic detectors require multiple projections for good quality images. The relationship between the number of projections used for reconstruction and the reconstructed image quality obtained for conventional CT does not necessarily apply to multi-projection Compton scatter tomography (MPCST). The purpose of this work was to investigate the dependence of the reconstructed image quality on the number of projections for MPCST. Analytical simulations and reconstructions were used to evaluate the contrast and spatial resolution for images reconstructed with one to 720 projections. Contrast-to-noise ratios (CNR) and the modulation transfer functions (MTF) demonstrated that the contrast increases monotonically with the number of projections while spatial resolution was independent of the number of projections. The contrast initially increases rapidly with projection number, becoming more gradual as the number of projections increase, with the rate of change being a function of fluence. The number of projections required to asymptotically approach the maximum contrast decreases as the fluence increases, with no indication of an optimal value for the range of fluences and projections investigated. For the projections considered, an increase in the number of projections increases the CNR even though the number of photons per projection decreases.
关键词： Compton scatter tomography,number of projections
更新于2025-09-23 15:22:29
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Relationship between Peripapillary Retinal Nerve Fiber Layer Thickness Measured by Optical Coherence Tomography and Visual Field Severity Indices
摘要： Purpose: Though there are many reports regarding the structure-function relationship in glaucoma, they are too complicated to apply to the routine clinical setting. The aim of this study was to investigate the direct relationship between peripapillary retinal nerve fiber layer (RNFL) thickness measured by optical coherence tomography (OCT) and visual field (VF) severity indices computed by standard automated perimetry. Methods: This cross-sectional comparative study included 104 glaucomatous patients and 59 healthy subjects. Peripapillary RNFL thickness was measured by spectral domain (SD) and time domain (TD) OCTs. Four glaucoma VF severity indices, including mean deviation (MD), pattern standard deviation (PSD), Collaborative Initial Glaucoma Treatment Study (CIGTS) VF score, and Advanced Glaucoma Intervention Study (AGIS) VF score, were calculated using standard automated perimetry. The Pearson’s correlation coefficients (r) between the average and quadrants of peripapillary RNFL thicknesses and the four VF severity indices were calculated. Results: In glaucomatous eyes, the r value between the average RNFL thickness measured by SD OCT and each VF severity index were 0.562, -0.514, -0.577, and -0.567 for the MD, PSD, CIGTS VF score, and AGIS VF score, respectively (all p < 0.001). Among each quadrant, the inferior RNFL thickness showed the largest r value; 0.587, -0.552, -0.613, and -0.598 for the MD, PSD, CIGTS VF score, and AGIS VF score, respectively (all p < 0.001). Measurements by TD OCT showed similar strengths of association with SD OCT. Conclusions: Moderate correlation was identified between peripapillary RNFL thicknesses measured by SD/TD OCT and glaucoma VF severity indices. Among each quadrant, the inferior RNFL thickness showed the greatest association with glaucoma VF severity indices. There was no significant difference according to the type of VF severity index or the type of OCTs.
关键词： Glaucoma,Retinal nerve fiber layer thickness,Optical coherence tomography,Visual fields
更新于2025-09-23 15:22:29
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A Single Simulation Platform for Hybrid Photoacoustic and RF-Acoustic Computed Tomography
摘要： In recent years, multimodal thermoacoustic imaging has demonstrated superior imaging quality compared to other emerging modalities. It provides functional and molecular information, arising due to electromagnetic absorption contrast, at ultrasonic resolution using inexpensive and non-ionizing imaging methods. The development of optical- as well as radio frequency (RF)-induced thermoacoustic imaging systems would benefit from reliable numerical simulations. To date, most numerical models use a combination of different software in order to model the hybrid thermoacoustic phenomenon. Here, we demonstrate the use of a single open source finite element software platform (ONELAB) for photo- and RF-acoustic computed tomography. The solutions of the optical diffusion equation, frequency domain Maxwell’s equations, and time-domain wave equation are used to solve the optical, electromagnetic, and acoustic propagation problems, respectively, in ONELAB. The results on a test homogeneous phantom and an approximate breast phantom confirm that ONELAB is a very effective software for both photo- and RF-acoustic simulations, and invaluable for developing new reconstruction algorithms and hardware systems.
关键词： tomography,thermoacoustic,radio frequency,photoacoustic imaging
更新于2025-09-23 15:22:29
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Receive Beam-Steering and Clutter Reduction for Imaging the Speed-of-Sound Inside the Carotid Artery
摘要： Handheld imaging of the tissue’s speed-of-sound (SoS) is a promising multimodal addition to diagnostic ultrasonography for the examination of tissue composition. Computed ultrasound tomography in echo mode (CUTE) probes the spatial distribution of SoS, conventionally via scanning the tissue under a varying angle of ultrasound transmission, and quantifying—in a spatially resolved way—phase variations of the beamformed echoes. So far, this technique is not applicable to imaging the lumen of vessels, where blood ?ow and tissue clutter inhibit phase tracking of the blood echoes. With the goal to enable the assessment of atherosclerotic plaque composition inside the carotid artery, we propose two modi?cations to CUTE: (a) use receive (Rx) beam-steering as opposed to transmit (Tx) beam-steering to increase acquisition speed and to reduce ?ow-related phase decorrelation, and (b) conduct pairwise subtraction of data obtained from repetitions of the scan sequence, to highlight blood echoes relative to static echo clutter and thus enable the phase tracking of blood echoes. These modi?cations were tested in a phantom study, where the echogenicity of the vessel lumen was chosen to be similar to the one of the background medium, which allows a direct comparison of SoS images obtained with the different techniques. Our results demonstrate that the combination of Rx-steering with the subtraction technique results in an SoS image of the same quality as obtained with conventional Tx-steering. Together with the improved acquisition speed, this makes the proposed technique a key step towards successful imaging of the SoS inside the carotid artery.
关键词： atherosclerosis,clutter reduction,plaque characterisation,multimodal imaging,ultrasound tomography
更新于2025-09-23 15:22:29
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[ACM Press the 3rd International Conference - Seoul, Republic of Korea (2018.08.22-2018.08.24)] Proceedings of the 3rd International Conference on Biomedical Signal and Image Processing - ICBIP '18 - Noise and Resolution Performance Evaluation for Statistical and Non-Statistical Iterative CBCT Reconstruction Methods
摘要： Non-statistical iterative and statistical iterative reconstruction (SIR) methods establish different models for Cone-beam computed tomography (CBCT) image reconstruction, which possibly produce different performance outcomes in reconstructed images. This paper presents a method to evaluate the noise and resolution properties of statistical and non-statistical iterative conditions. An algorithms EGSnrc/BEAMnrc Monte Carlo (MC) system was built for generating CBCT projections of a digital water phantom. SIR based OSC-TV (ordered subsets convex via total variation minimization) algorithm was selected to compare with non-statistical ASD-POCS (adaptive steepest descent-projection onto convex sets) algorithm and conventional FDK algorithm. The results demonstrate that ASD-POCS algorithm achieved a higher modulation transfer function than SIR based OSC-TV algorithm at the price of a higher image noise, while OSC-TV algorithm yielded best noise equivalent quanta performance among the three algorithms. The results of our study could guide a better evaluation and optimization of reconstruction algorithms for CBCT imaging.
关键词： Noise equivalent quanta,Image quality assessment,Noise power spectrum,Modulation transfer function,Computed tomography
更新于2025-09-23 15:22:29
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<sup>18</sup> F-Fluoride Signal Amplification Identifies Microcalcifications Associated With Atherosclerotic Plaque Instability in Positron Emission Tomography/Computed Tomography Images
摘要： BACKGROUND: Microcalcifications in atherosclerotic plaques are destabilizing, predict adverse cardiovascular events, and are associated with increased morbidity and mortality. 18F-fluoride positron emission tomography (PET)/computed tomography (CT) imaging has demonstrated promise as a useful clinical diagnostic tool in identifying high-risk plaques; however, there is confusion as to the underlying mechanism of signal amplification seen in PET-positive, CT-negative image regions. This study tested the hypothesis that 18F-fluoride PET/CT can identify early microcalcifications. METHODS: 18F-fluoride signal amplification derived from microcalcifications was validated against near-infrared fluorescence molecular imaging and histology using an in vitro 3-dimensional hydrogel collagen platform, ex vivo human specimens, and a mouse model of atherosclerosis. RESULTS: Microcalcification size correlated inversely with collagen concentration. The 18F-fluoride ligand bound to microcalcifications formed by calcifying vascular smooth muscle cell derived extracellular vesicles in the in vitro 3-dimensional collagen system and exhibited an increasing signal with an increase in collagen concentration (0.25 mg/mL collagen ?33.8×102±12.4×102 counts per minute; 0.5 mg/mL collagen ?67.7×102±37.4×102 counts per minute; P=0.0014), suggesting amplification of the PET signal by smaller microcalcifications. We further incubated human atherosclerotic endarterectomy specimens with clinically relevant concentrations of 18F-fluoride. The 18F-fluoride ligand labeled microcalcifications in PET-positive, CT-negative regions of explanted human specimens as evidenced by 18F-fluoride PET/CT imaging, near-infrared fluorescence, and histological analysis. Additionally, the 18F-fluoride ligand identified micro and macrocalcifications in atherosclerotic aortas obtained from low-density lipoprotein receptor-deficient mice. CONCLUSIONS: Our results suggest that 18F-fluoride PET signal in PET-positive, CT-negative regions of human atherosclerotic plaques is the result of developing microcalcifications, and high surface area in regions of small microcalcifications may amplify PET signal.
关键词： molecular imaging,fluoride,atherosclerosis,positron emission tomography,microcalcification
更新于2025-09-23 15:22:29
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Comparison of Kang's and Littmann's Methods of Correction for Ocular Magnification in Circumpapillary Retinal Nerve Fiber Layer Measurement
摘要： PURPOSE. To assess and compare the accuracy of Kang’s method for ocular magnification correction in circumpapillary retinal nerve fiber layer (cpRNFL) thickness measurement with that of the currently used Littmann’s method. METHODS. A total of 148 eyes of 148 healthy participants underwent cpRNFL measurement without correction and with correction by Littmann’s method using spectral-domain optical coherence tomography. Correction of ocular magnification by Kang’s method is based on the observed uncorrected cpRNFL thickness. The accuracy of Kang’s method was compared with that of Littmann’s method for magnification correction by using the Pearson product-moment correlation coefficient (r) and Bland–Altman analysis. RESULTS. A total of 132 eyes were assessed. The two methods used to correct the global cpRNFL thickness were strongly correlated (r = 0.940, P < 0.01), and the mean difference between the two methods was -0.4 μm, with 95% limits of agreement (LoA) of –6 μm without systemic bias (P > 0.05). Although the cpRNFL thicknesses corrected with the two methods at quadrant and 12-o’clock sectors showed a strong correlation (r > 0.731, P < 0.01), high LoAs ranging from –13.3 to –27.9 and systemic biases were observed at nasal and inferior sectors. CONCLUSION. No difference was found between Kang’s and Littmann’s methods for correction of ocular magnification in global cpRNFL thickness measurement. However, with regard to magnification correction for sectoral cpRNFL thickness, further scrutiny of Kang’s method is warranted, even in healthy participants, because of the high variability between Littmann’s and Kang’s methods.
关键词： Littmann’s method,optical coherence tomography,magnification correction,circumpapillary retinal nerve fiber layer,Kang’s method
更新于2025-09-23 15:22:29
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Fast four-dimensional tensile test monitored via X-ray computed tomography: Elastoplastic identification from radiographs
摘要： A projection-based digital volume correlation method (presented in a companion paper) is extended to an integrated approach for the calibration of an elastoplastic law based on a single radiograph per loading step. Instead of following a two-step sequential procedure (i.e. first, measurement of the displacement field; second, identification), the integrated method aims at identifying few model parameters directly from the gray-level projections. The analysis of an in situ tensile test composed of 127 loading steps performed in 6 min is presented. An isotropic elastoplastic constitutive law with free-form hardening behavior (i.e. controlled by only eight parameters) is identified and shows a ductile behavior (up to 6.3% strain before failure). A large improvement on the residual quality is shown and validates the proposed model and procedure. The obtained displacement fields are similar to those measured with no mechanical integration. A different parameterization of the constitutive law provides a very close result, thereby assessing the robustness of the procedure.
关键词： inverse methods,in situ tests,Tomography,projection-based digital volume correlation,integrated digital volume correlation,four-dimensional measurement
更新于2025-09-23 15:22:29
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Optical coherence tomography and its use in optical neuritis and multiple sclerosis
摘要： Optical coherence tomography is a relatively new non-invasive imaging technique used for obtaining the images and quantifying the layers of the retina. It also provides information about optic nerve head topography, peripapillary retinal nerve fiber layer thickness, and macular volume which correlates with axonal loss. Until now, this method was used mainly in ophthalmology; now it has emerged as relevant in neurology as well. RNFL thickness is of particular interest in optic neuropathies and in multiple sclerosis. In sclerosis multiplex, axonal loss occurs as early as the first stages and the quantification of the RNFL thickness by OCT provides an indirect measure of axonal and neuronal loss in the anterior visual pathways. Because OCT is noninvasive, easy to obtain, and highly reproducible, it can be used as a marker of axonal loss and as an endpoint in clinical trials. This paper presents a comprehensive summary of the use of this new diagnostic method in multiple sclerosis patients (Fig. 1, Ref. 58). Text in PDF www.elis.sk.
关键词： multiple sclerosis,optical neuritis,optical coherence tomography
更新于2025-09-23 15:22:29
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Design Considerations for Murine Retinal Imaging Using Scattering Angle Resolved Optical Coherence Tomography
摘要： Optical coherence tomography (OCT), an optical imaging approach enabling cross-sectional analysis of turbid samples, is routinely used for retinal imaging in human and animal models of diseases affecting the retina. Scattering angle resolved (SAR-)OCT has previously been demonstrated as offering additional contrast in human studies, but no SAR-OCT system has been reported in detail for imaging the retinas of mice. An optical model of a mouse eye was designed and extended for validity at wavelengths of light around 1310 nm; this model was then utilized to develop a SAR-OCT design for murine retinal imaging. A Monte Carlo technique simulates light scattering from the retina, and the simulation results are confirmed with SAR-OCT images. Various images from the SAR-OCT system are presented and utility of the system is described. SAR-OCT is demonstrated as a viable and robust imaging platform to extend utility of retinal OCT imaging by incorporating scattering data into investigative ophthalmologic analysis.
关键词： angle resolved imaging,retinal imaging,optical coherence tomography,rodent imaging,scattering
更新于2025-09-23 15:22:29