Gain In Image Quality Research Articles

Research on the use of AI for Selecting Abstractions for Natural Language Image Generation Tools

The article describes a method of image generation with Artificial Intelligence services using text abstraction retrieved using Artificial Intelligence services Dall-e, MidJourney and Stable Diffusion, that works with natural language. The implementation of the new approach gives a significant gain in image quality and consistency with analysed text. The methodology is based on using neural network API service instead of commonly used natural language algorithms to extract keywords or sentences. Proposed evaluation is applied to the generated images. An analysis of evaluation options is carried out depending on algorithm and Artificial Intelligence service, based on the tested book, length of result abstract and number of errors for each type. The evaluation results show that the new approach can provide better quality images that relate more with the text compared to natural language algorithms. For example, the average score of images generated by abstractions for GPT3 - 7.13 and GPT4 - 7.3, compared to natural language algorithms CO semantic - 5.43, TextRank - 4.98, TF-DF keywords - 4.74, WE spaCy - 3.04, WordNet - 4.34 for MidJourney generated images. Although results show most of the best results were generated for abstract with text length 20-40 words, meantime images generated for abstract with less or more words show much less consistency with text.

Time of Flight in Perspective: Instrumental and Computational Aspects of Time Resolution in Positron Emission Tomography.

The first time-of-flight positron emission tomography (TOF-PET) scanners were developed as early as in the 1980s. However, the poor light output and low detection efficiency of TOF-capable detectors available at the time limited any gain in image quality achieved with these TOF-PET scanners over the traditional non-TOF PET scanners. The discovery of LSO and other Lu-based scintillators revived interest in TOF-PET and led to the development of a second generation of scanners with high sensitivity and spatial resolution in the mid-2000s. The introduction of the silicon photomultiplier (SiPM) has recently yielded a third generation of TOF-PET systems with unprecedented imaging performance. Parallel to these instrumentation developments, much progress has been made in the development of image reconstruction algorithms that better utilize the additional information provided by TOF. Overall, the benefits range from a reduction in image variance (SNR increase), through allowing joint estimation of activity and attenuation, to better reconstructing data from limited angle systems. In this work, we review these developments, focusing on three broad areas: 1) timing theory and factors affecting the time resolution of a TOF-PET system; 2) utilization of TOF information for improved image reconstruction; and 3) quantification of the benefits of TOF compared to non-TOF PET. Finally, we offer a brief outlook on the TOF-PET developments anticipated in the short and longer term. Throughout this work, we aim to maintain a clinically driven perspective, treating TOF as one of multiple (and sometimes competitive) factors that can aid in the optimization of PET imaging performance.

A Radio-Nano-Platform for T1/T2 Dual-Mode PET-MR Imaging.

PurposeThis study aimed to develop a chelate-free radiolabeled nanoparticle platform for simultaneous positron emission tomography (PET) and magnetic resonance (MR) imaging that provides contrast-enhanced diagnostic imaging and significant image quality gain by integrating the high spatial resolution of MR with the high sensitivity of PET.MethodsA commercially available super-paramagnetic iron oxide nanoparticle (SPION) (Feraheme®, FH) was labeled with the [89Zr]Zr using a novel chelate-free radiolabeling technique, heat-induced radiolabeling (HIR). Radiochemical yield (RCY) and purity (RCP) were measured using size exclusion chromatography (SEC) and radio-thin layer chromatography (radio-TLC). Characterization of the non-radioactive isotope 90Zr-labeled FH was performed by transmission electron microscopy (TEM). Simultaneous PET-MR phantom imaging was performed with different 89Zr-FH concentrations. The MR quantitative image analysis determined the contrast-enhancing properties of FH. The signal-to-noise ratio (SNR) and full-width half-maximum (FWHM) of the line spread function (LSF) were calculated before and after co-registering the PET and MR image data.ResultsHigh RCY (92%) and RCP (98%) of the [89Zr]Zr-FH product was achieved. TEM analysis confirmed the 90Zr atoms adsorption onto the SPION surface (≈ 10% average radial increase). Simultaneous PET-MR scans confirmed the capability of the [89Zr]Zr-FH nano-platform for this multi-modal imaging technique. Relative contrast image analysis showed that [89Zr]Zr-FH can act as a dual-mode T1/T2 contrast agent. For co-registered PET-MR images, higher spatial resolution (FWHM enhancement ≈ 3) and SNR (enhancement ≈ 8) was achieved at a clinical dose of radio-isotope and Fe.ConclusionOur results demonstrate FH is a highly suitable SPION-based platform for chelate-free labeling of PET tracers for hybrid PET-MR. The high RCY and RCP confirmed the robustness of the chelate-free HIR technique. An overall image quality gain was achieved compared to PET- or MR-alone imaging with a relatively low dosage of [89Zr]Zr-FH. Additionally, FH is suitable as a dual-mode T1/T2 MR image contrast agent.

Evaluation of phase retrieval approaches in magnified X-ray phase nano computerized tomography applied to bone tissue.

X-ray phase contrast imaging offers higher sensitivity compared to conventional X-ray attenuation imaging and can be simply implemented by propagation when using a partially coherent synchrotron beam. We address the phase retrieval in in-line phase nano-CT using multiple propagation distances. We derive a method which extends Paganin's single distance method and compare it to the contrast transfer function (CTF) approach in the case of a homogeneous object. The methods are applied to phase nano-CT data acquired at the voxel size of 30 nm (ID16A, ESRF, Grenoble, France). Our results show a gain in image quality in terms of the signal-to-noise ratio and spatial resolution when using four distances instead of one. The extended Paganin's method followed by an iterative refinement step provides the best reconstructions while the homogeneous CTF method delivers quasi comparable results for our data, even without refinement step.

Predicted accommodative response from image quality in young eyes fitted with different dual-focus designs.

To investigate the separated and combined influences of inner zone (IZ) diameter and effective add power of dual-focus contact lenses (CL) in the image quality at distance and near viewing, in a functional accommodating model eye. Computational wave-optics methods were used to define zonal bifocal pupil functions, representing the optic zones of nine dual-focus centre-distance CLs. The dual-focus pupil functions were defined having IZ diameters of 2.10 mm, 3.36 mm and 4.00 mm, with add powers of 1.5 D, 2.0 D and 2.5 D (dioptres), for each design, that resulted in a ratio of 64%/36% between the distance and treatment zone areas, bounded by a 6 mm entrance pupil. A through-focus routine was implemented in MATLAB to simulate the changes in image quality, calculated from the Visual Strehl ratio, as the eye with the dual-focus accommodates, from 0 to -3.00 D target vergences. Accommodative responses were defined as the changes in the defocus coefficient, combined with a change in fourth and sixth order spherical aberration, which produced a peak in image quality at each target vergence. Distance viewing image quality was marginally affected by IZ diameter but not by add power. Near image quality obtained when focussing the image formed by the near optics was only higher by a small amount compared to the other two IZ diameters. The mean ± standard deviation values obtained with the three adds were 0.28 ± 0.02, 0.23 ± 0.02 and 0.22 ± 0.02, for the small, medium and larger IZ diameters, respectively. On the other hand, near image quality predicted by focussing the image formed by the distance optics was considerably lower relatively to the other two IZ diameters. The mean ± standard deviation values obtained with the three adds were 0.15 ± 0.01, 0.38 ± 0.00 and 0.54 ± 0.01, for the small, medium and larger IZ diameters, respectively. During near viewing through dual-focus CLs, image quality depends on the diameter of the most inner zone of the CL, while add power only affects the range of clear focus when focussing the image formed by the CL near optics. When only image quality gain is taken into consideration, medium and large IZ diameters designs are most likely to promote normal accommodative responses driven by the CL distance optics, while a smaller IZ diameter design is most likely to promote a reduced accommodative response driven by the dual-focus CL near optics.

Prospective PET image quality gain calculation method by optimizing detector parameters.

Lutetium-based scintillators with high-performance electronics introduced time-of-flight (TOF) reconstruction in the clinical setting. Let G' be the total signal to noise ratio gain in a reconstructed image using the TOF kernel compared with conventional reconstruction modes. G' is then the product of G1 gain arising from the reconstruction process itself and (n-1) other gain factors (G2, G3, … Gn) arising from the inherent properties of the detector. We calculated G2 and G3 gains resulting from the optimization of the coincidence and energy window width for prompts and singles, respectively. Both quantitative and image-based validated Monte Carlo models of Lu2SiO5 (LSO) TOF-permitting and Bi4Ge3O12 (BGO) TOF-nonpermitting detectors were used for the calculations. G2 and G3 values were 1.05 and 1.08 for the BGO detector and G3 was 1.07 for the LSO. A value of almost unity for G2 of the LSO detector indicated a nonsignificant optimization by altering the energy window setting. G' was found to be ∼1.4 times higher for the TOF-permitting detector after reconstruction and optimization of the coincidence and energy windows. The method described could potentially predict image noise variations by altering detector acquisition parameters. It could also further contribute toward a long-lasting debate related to cost-efficiency issues of TOF scanners versus the non-TOF ones. Some vendors re-engage nowadays to non-TOF product line designs in an effort to reduce crystal costs. Therefore, exploring the limits of image quality gain by altering the parameters of these detectors remains a topical issue.

A source-channel coding approach to digital image protection and self-recovery.

Watermarking algorithms have been widely applied to the field of image forensics recently. One of these very forensic applications is the protection of images against tampering. For this purpose, we need to design a watermarking algorithm fulfilling two purposes in case of image tampering: 1) detecting the tampered area of the received image and 2) recovering the lost information in the tampered zones. State-of-the-art techniques accomplish these tasks using watermarks consisting of check bits and reference bits. Check bits are used for tampering detection, whereas reference bits carry information about the whole image. The problem of recovering the lost reference bits still stands. This paper is aimed at showing that having the tampering location known, image tampering can be modeled and dealt with as an erasure error. Therefore, an appropriate design of channel code can protect the reference bits against tampering. In the present proposed method, the total watermark bit-budget is dedicated to three groups: 1) source encoder output bits; 2) channel code parity bits; and 3) check bits. In watermark embedding phase, the original image is source coded and the output bit stream is protected using appropriate channel encoder. For image recovery, erasure locations detected by check bits help channel erasure decoder to retrieve the original source encoded image. Experimental results show that our proposed scheme significantly outperforms recent techniques in terms of image quality for both watermarked and recovered image. The watermarked image quality gain is achieved through spending less bit-budget on watermark, while image recovery quality is considerably improved as a consequence of consistent performance of designed source and channel codes.

Sci-Fri AM: Mountain - 02: A comparison of dose reduction methods on image quality for cone beam CT

Modern radiotherapy uses highly conformai dose distributions and therefore relies on daily image guidance for accurate patient positioning. Kilovoltage cone beam CT is one technique that is routinely used for patient set-up and results in a high dose to the patient relative to planar imaging techniques. This study uses an Elekta Synergy linac equipped with XVI cone beam CT to investigate the impact of various imaging parameters on dose and image quality. Dose and image quality are assessed as functions of x-ray tube voltage, tube current and the number of projections in the scan. In each case, the dose measurements confirm that as each parameter increases the dose increases. The assessment of high contrast resolution shows little dependence on changes to the image technique. However, low contrast visibility suggests a trade off between dose and image quality. Particularly for changes in tube potential, the dose increases much faster as a function of voltage than the corresponding increase in low contrast image quality. This suggests using moderate values of the peak tube voltage (100 – 120 kVp) since higher values result in significant dose increases with little gain in image quality. Measurements also indicate that increasing tube current achieves the greatestmore » degree of improvement in the low contrast visibility. The results of this study highlight the need to establish careful imaging protocols to limit dose to the patient and to limit changes to the imaging parameters to those cases where there is a clear clinical requirement for improved image quality.« less

3D-OSEM and FP-CIT SPECT quantification

Dopamine transporter imaging with single-photon emission computed tomography (SPECT) is a valuable tool for both clinical routine and research studies. Recently, it was found that the image quality could be improved by introduction of the three-dimensional ordered subset expectation maximization (3D-OSEM) reconstruction algorithm, which provides resolution recovery. The aim of this study was to systematically evaluate the potential benefits of 3D-OSEM in comparison with 2D-OSEM under critical imaging conditions, for example, scans with a high radius of rotation. Monte Carlo simulation scans of a digital brain phantom with various disease states and different radii of rotation ranging from 13 to 30 cm were reconstructed with both 2D-OSEM and 3D-OSEM algorithms. Specific striatal binding and putamen-to-caudate ratios were determined and compared with true values in the phantom. The percentage recovery of true striatal binding was similar between both reconstruction algorithms at the minimum rotational radius; however, at the maximum rotational radius, it decreased from 53 to 43% for 3D-OSEM and from 52 to 26% for 2D-OSEM. 3D-OSEM matched the true putamen-to-caudate ratios more closely than did 2D-OSEM in scans with high SPECT rotation radii. 3D-OSEM offers a promising image quality gain. It outperforms 2D-OSEM, particularly in studies with limited resolutions (such as scans acquired with a high radius of rotation) but does not improve the accuracy of the putamen-to-caudate ratios. Whether the benefits of better recovery in studies with higher radii of rotation could potentially increase the diagnostic power of dopamine transporter SPECT in patients with borderline striatal radiotracer binding, however, needs to be further examined.

Pattern-based video coding with dynamic background modeling

The existing video coding standard H.264 could not provide expected rate-distortion (RD) performance for macroblocks (MBs) with both moving objects and static background and the MBs with uncovered background (previously occluded). The pattern-based video coding (PVC) technique partially addresses the first problem by separating and encoding moving area and skipping background area at block level using binary pattern templates. However, the existing PVC schemes could not outperform the H.264 with significant margin at high bit rates due to the least number of MBs classified using the pattern mode. Moreover, both H.264 and the PVC scheme could not provide the expected RD performance for the uncovered background areas due to the unavailability of the reference areas in the existing approaches. In this paper, we propose a new PVC technique which will use the most common frame in a scene (McFIS) as a reference frame to overcome the problems. Apart from the use of McFIS as a reference frame, we also introduce a content-dependent pattern generation strategy for better RD performance. The experimental results confirm the superiority of the proposed schemes in comparison with the existing PVC and the McFIS-based methods by achieving significant image quality gain at a wide range of bit rates.

Image quality for advanced iterative reconstruction schemes with SPECT/CT

Background Advanced iterative reconstruction methods are now widely used for SPECT-CT. The aim of this study was to evaluate the gain in image quality for clinical settings currently used for brain and body SPECT studies. Material and methods Data from the IEC image quality head and body phantoms were obtained with different SPECT/CT systems. Spheres (inner diameters varying from 10 to 37 mm) were filled with Tc-99 m for spheres to background contrasts of 4:1 and 6:1 and the ‘body’ filled with 150 MBq. Camera settings were those used routinely for brain and body SPECT studies except pixel size that was adjusted as close as 3 mm. SPECT data were reconstructed with clinical parameters for OSEM (number of iterations and subsets, post-filter) using CT-based attenuation correction and scatter compensation based on multiple windowing estimates and nonuniform collimator response compensation for recovering isotropic resolution. Image quality was assessed following NEMA NU2-2007 definitions for hot spheres percent contrasts and background variability for the 37 mm sphere for 24 background ROIS (8 ROIs on three slices). Results Visual analysis exhibited that all spheres were detected in brain studies whereas in body studies, in one case the smaller sphere was not visible for the 4:1contrast. Spatial distorsions due to incomplete collimator response correction were present in all body transaxial images. Image noise was substantially decreased with resolution recovery correction. Despite different reconstruction parameters depending on manufacturers recommendations, hot sphere contrasts were quite similar from one system to the other and exhibited strong variations with sphere size (from 10% for 10 mm to 66% for 37 mm). Contrast recovery was mainly affected by post filtering. Conclusion We proposed an image quality test for evaluation of image quality and contrast recovery in SPECT-CT. Advanced iterative reconstructions including collimator modelling demonstrated important spatial distorsions for body like studies and limitations of contrast recovery.

Exploiting spatial sparsity for multiwavelength imaging in optical interferometry

Optical interferometers provide multiple wavelength measurements. In order to fully exploit the spectral and spatial resolution of these instruments, new algorithms for image reconstruction have to be developed. Early attempts to deal with multichromatic interferometric data have consisted in recovering a gray image of the object or independent monochromatic images in some spectral bandwidths. The main challenge is now to recover the full three-dimensional (spatiospectral) brightness distribution of the astronomical target given all the available data. We describe an approach to implement multiwavelength image reconstruction in the case where the observed scene is a collection of point-like sources. We show the gain in image quality (both spatially and spectrally) achieved by globally taking into account all the data instead of dealing with independent spectral slices. This is achieved thanks to a regularization that favors spatial sparsity and spectral grouping of the sources. Since the objective function is not differentiable, we had to develop a specialized optimization algorithm that also accounts for non-negativity of the brightness distribution.

Peripheral Aberrations and Image Quality for Contact Lens Correction

Contact lenses (CLs) reduced the degree of hyperopic field curvature present in myopic eyes and rigid CLs reduced spherocylindrical image blur on the peripheral retina, but their effect on higher order aberrations and overall optical quality of the eye in the peripheral visual field is still unknown. The purpose of our study was to evaluate peripheral wavefront aberrations and image quality across the visual field before and after CL correction. A commercial Hartmann-Shack aberrometer was used to measure ocular wavefront errors in 5° steps out to 30° of eccentricity along the horizontal meridian in uncorrected eyes and when the same eyes are corrected with soft or rigid CLs. Wavefront aberrations and image quality were determined for the full elliptical pupil encountered in off-axis measurements. Ocular higher order aberrations (HOA) increase away from fovea in the uncorrected eye. Third-order aberrations are larger and increase faster with eccentricity compared with the other HOA. CLs increase all HOA except third-order Zernike terms. Nevertheless, a net increase in image quality across the horizontal visual field for objects located at the foveal far point is achieved with rigid lenses, whereas soft CLs reduce image quality. Second-order aberrations limit image quality more than HOA in the periphery. Although second-order aberrations are reduced by CLs, the resulting gain in image quality is partially offset by increased amounts of HOA. To fully realize the benefits of correcting HOA in the peripheral field requires improved correction of second-order aberrations as well.

SPECT imaging of high energy isotopes and isotopes with high energy contaminants with rotating slat collimators

Quantitative SPECT imaging is limited by many factors, including penetration of high energy photons through the collimator. Even small peaks of high energy yield extensive contamination in the photopeak energy window. Rotating slat collimators typically offer a 40- to 50-fold increase in geometric detection efficiency compared to parallel hole collimators, while the amount of high-energy contamination is expected to remain the same. The aim of this study is to show that SPECT for isotopes with high energy peaks benefits from the use of a rotating slat collimator by significantly reducing the effect of high energy contamination. Monte Carlo simulations were performed for I-123 and I-131. The simulation of a single point source in a scattering medium was used to investigate the history of each detected photon both for the rotating slat and the parallel hole collimator. Next, realistic simulations of an image quality phantom in combination with iterative image reconstruction enabled us to study the gain in image quality which can be expected for the rotating slat collimator. The results show that the rotating slat collimator is able to reduce the contribution of high energy photons from about 60% to about 8% of all the detected photons in the photopeak energy window. This results in a recovered contrast gain of about 25%. For I-131, there was a reduction in contamination from 65% to 49% when using a rotating slat instead of a parallel hole collimator. This resulted in an average hot contrast improvement of 12% and average cold contrast improvement of 8% for tomographic images. Rotating slat collimators have an additional advantage regarding image quality for isotopes with high energy emissions, especially if the contamination arises from photons with energies higher than the main emission energy, due to the relatively lower number of measured collimator-penetrating photons with respect to geometrically collimated photons.

Improving the image quality of contrast-enhanced MR angiography by automated image registration: A prospective study in peripheral arterial disease of the lower extremities

Objective If a patient has moved during digital subtraction angiography (DSA), manual pixel shift can improve the image quality. This study investigated whether such image registration can also improve the quality of contrast-enhanced magnetic resonance angiography (MRA) in patients with peripheral arterial disease of the lower extremities. Materials and methods 404 leg MRAs of patients likely to have peripheral artery disease were included in this prospective study. The standard non-registered MRAs were compared to automatically linear, affine and warp registered MRAs by four image quality parameters, including the vessel detection probability (VDP) in maximum intensity projection (MIP) images and contrast-to-noise ratios (CNR). The different registration types were compared by analysis of variance. Results All studied image quality parameters showed similar trends. Generally, registration improved the leg MRA quality significantly ( P < 0.05). The 12% of lower legs with a body shift of 1 mm or more showed the highest gain in image quality when using linear registration instead of no registration, with an average VDP gain of 20–49%. Warp registration improved the image quality slightly further. Conclusion Automated image registration can improve the MRA image quality especially in the lower legs, which is comparable to the effect of pixel shift in DSA.

Fast 3D iterative image reconstruction for SPECT with rotating slat collimators

As an alternative to the use of traditional parallel hole collimators, SPECT imaging can be performed using rotating slat collimators. While maintaining the spatial resolution, a gain in image quality could be expected from the higher photon collection efficiency of this type of collimator. However, the use of iterative methods to do fully three-dimensional (3D) reconstruction is computationally much more expensive and furthermore involves slow convergence compared to a classical SPECT reconstruction. It has been proposed to do 3D reconstruction by splitting the system matrix into two separate matrices, forcing the reconstruction to first estimate the sinograms from the rotating slat SPECT data before estimating the image. While alleviating the computational load by one order of magnitude, this split matrix approach would result in fast computation of the projections in an iterative algorithm, but does not solve the problem of slow convergence. There is thus a need for an algorithm which speeds up convergence while maintaining image quality for rotating slat collimated SPECT cameras. Therefore, we developed a reconstruction algorithm based on the split matrix approach which allows both a fast calculation of the forward and backward projection and a fast convergence. In this work, an algorithm of the maximum likelihood expectation maximization (MLEM) type, obtained from a split system matrix MLEM reconstruction, is proposed as a reconstruction method for rotating slat collimated SPECT data. Here, we compare this new algorithm to the conventional split system matrix MLEM method and to a gold standard fully 3D MLEM reconstruction algorithm on the basis of computational load, convergence and contrast-to-noise. Furthermore, ordered subsets expectation maximization (OSEM) implementations of these three algorithms are compared. Calculation of computational load and convergence for the different algorithms shows a speedup for the new method of 38 and 426 compared to the split matrix MLEM approach and the fully 3D MLEM respectively and a speedup of 16 and 21 compared to the split matrix OSEM and the fully 3D OSEM respectively. A contrast-to-noise study based on simulated data shows that our new approach has comparable accuracy as the fully 3D reconstruction method. The algorithm developed in this study allows iterative image reconstruction of rotating slat collimated SPECT data with equal image quality in a comparable amount of computation time as a classical SPECT reconstruction.

Near-lossless spread spectrum watermarking for multispectral remote sensing images

Watermarking represents a potentially effective tool for the protection and verification of ownership rights in remotely sensed imagery. Such data however cannot undergo critical quality degradation processes, for they must ensure accurate extraction of thematic and scientific information. In this paper, we propose to adapt a state-of-the-art spread spectrum method found to be particularly powerful for real world images to make the watermark insertion process near-lossless while preserving most of its effective robustness capability. This is done by embedding the watermark in the middle-frequency range of the discrete cosine transform (DCT) domain instead of the low-frequency range. The exact position is determined by a numerical root-finding method, targeted to achieve a userspecified minimum level of robustness against a given ensemble of attacks. In this way, an optimal trade-off can be obtained between quality and robustness. Thorough experimental tests over a multispectral remote sensing image show that the proposed method allows to trade a contained loss in robustness with a significant gain in image quality, quantified in terms of both peak signal-to-noise ratio (PSNR) and impact on classification performance. In addition, they reveal an interesting property of the watermark insertion shifting into the middle-frequency range, consisting of a sharp increase in robustness to the widely used cropping operation, which is considered the most critical attack in remote sensing imagery.

Investigation of time-of-flight benefit for fully 3-DPET

The purpose of this paper is to determine the benefit that can be achieved in image quality for a time-of-flight (TOF) fully three-dimensional (3-D) whole-body positron emission tomography (PET) scanner. We simulate a 3-D whole-body time-of-flight PET scanner with a complete modeling of spatial and energy resolutions. The scanner is based on LaBr3 Anger-logic detectors with which 300ps timing resolution has been achieved. Multiple simulations were performed for 70-cm long uniform cylinders with 27-cm and 35-cm diameters, containing hot spheres (22, 17, 13, and 10-mm diameter) in a central slice and 10-mm diameter hot spheres in a slice at 1/4 axial FOV. Image reconstruction was performed with a list-mode iterative TOF algorithm and data were analyzed after attenuation and scatter corrections for timing resolutions of 300, 600, 1000 ps and non-TOF for varying count levels. The results show that contrast recovery improves slightly with TOF (NEMA NU2-2001 analysis), and improved timing resolution leads to a faster convergence to the maximum contrast value. Detectability for 10-mm diameter hot spheres estimated using a nonprewhitening matched filter (NPW SNR) also improves nonlinearly with TOF. The gain in image quality using contrast and noise measures is proportional to the object diameter and inversely proportional to the timing resolution of the scanner. The gains in NPW SNR are smaller, but they also increase with increasing object diameter and improved timing resolution. The results show that scan times can be reduced in a TOF scanner to achieve images similar to those from a non-TOF scanner, or improved image quality achieved for same scan times.

51.2: Mastering the Moving Image: Refreshing TFT-LCDs at 120 Hz

Moving image quality has been the Achilles' heel of TFT-LCDs. The switching speed of liquid crystals has been improved constantly, so that we now have reached to a point where further improvement does not translate into real image quality gain: LCDs are facing the final hurdle as a hold-type display. Two ways were proposed to overcome the problem. One is to introduce impulsive transmission and the other is to increase the refresh rate. The first approach was commercialized, with limited success. The second approach has been emulated with a high refresh-rate CRT. For the first time, we report a 40″ LCD-TV refreshed at 120 Hz. The higher refresh rate led to 25% reduction in the on + off response time and 50% reduction in the intergray response time. There was substantial video quality improvement as well as the nominal enhancement: images sweeping the whole screen horizontally in two seconds showed little deterioration in details.

Doppler imaging from artificial data

We present extensive numerical tests of our temperature-based image reconstruction code TempMap. Two test cases that represent a rapidly- rotating low-inclination star and a moderately-rotating high-inclination star are used for the forward problem. Tests are then made to recover the original input map and include data errors and input-parameter errors. The former include variations of photon noise, continuum displacement, continuum slopes, scattered light in the spectrograph, and phase gaps with and without con- tinuum information. The input-parameter tests include the confusion in the recovery of hot versus cool spots, uncertainties of atmospheric parameters such as radial- tangential macroturbulence and gravity, and the influence of line strength and line damping. In general, we nd that the geometric information is less dependent on photon noise and on input errors than the temperature information. Our test inversions also show that, at the v sini of these test cases, no signicant gain in image quality is achieved once S=N of 300:1 is surpassed.