Image Modulation Transfer Function Research Articles

Super-agile satellites imaging mission planning method considering degradation of image MTF in dynamic imaging

Super-agile satellites with dynamic imaging capabilities can significantly improve the imaging efficiency of space-borne Earth observation. However, the image modulation transfer function (image MTF) of dynamic imaging varies dramatically with changes in the attitude maneuver status while improving observation efficiency. Therefore, both the observation efficiency and image MTF should be considered in the imaging mission planning of super-agile satellites. Existing imaging mission planning methods are mainly aimed at traditional agile satellites that are not capable of dynamic imaging, and the mainly optimization objectives are coverage revenue, spatial resolution, and task performance time, without considering the observation efficiency and image MTF as the optimization objectives. To overcome the problem of image MTF degradation caused by dynamic imaging, a mission planning method which considers the degradation of the image MTF and observation efficiency was proposed. Firstly, a mapping relationship between the angular velocity of the attitude maneuvering and the image MTF was constructed. On this basis, a Pareto multi-objective imaging mission planning model of partial order based was established. Considering the particularity of the model, the non-dominated sorting strategy of the NSGA-II algorithm was redesigned when solving the model using NSGA-II algorithm. Finally, the imaging tasks of different scales in single satellite and multi-satellite simulation scenes were set, and the proposed imaging mission planning method was verified. The planning results showed that the proposed method can achieve a balanced optimization of the image MTF and task efficiency under the premise of ensuing maximum observation coverage revenue.

Analysis of the Neutron Radiographic Image Quality and Beam Intensity Produced by a Compact Multichannel Collimator

We investigate the image quality and beam intensity of thermal neutron radiography after replacing a standard single-channel neutron collimator with a compact array of microcollimators. In this study, the MCNP6 Monte Carlo computer code was used to simulate a 2 × 2-cm-area isotropic thermal neutron source, which then was collimated by an array of micron-sized neutron collimators that measured 29.8 μm in diameter and with lengths that varied from 0.6 to 3 mm. These microcollimators were spaced 30 μm apart and assembled into a 2 × 2-cm array. The image quality of the neutron beams produced by the resulting collimator arrays was assessed by imaging the edge of a very thin (~0.01-mm) gadolinium foil to obtain the image Modulation Transfer Function (MTF). The MCNP6 resulting flux map from each simulation then was converted into a grayscale .tiff image and the image’s resulting MTF obtained using the ImageJ computer program with the imaging beam geometric unsharpness, which is a limiting factor in the image resolution determined at the 10% value of the MTF curve. In this study, we found that a 2 × 2× 0.298-cm microcollimator, corresponding to a length-to–hole diameter ratio of 100:1 and a collimator length of 2.98 mm produced a beam with a geometric unsharpness of 32 μm. Compared to a standard single-channel collimator with a 2 × 2-cm aperture, the single-channel collimator would need to be 660 cm long to produce an equivalent geometric sharpness. Yet because of its shorter length, the imaging beam intensity from our 2.98-mm-thick collimator array was approximately 50 times greater than that of an equivalent single-channel collimator.

Optical satellite image MTF compensation for remote-sensing data production

Modulation Transfer Function (MTF) compensation had been widely used in Remote-Sensing (RS) imagery processing for texture feature enhancement and high-frequency details restoration. In this paper, we propose an optical satellite MTF Compensation (MTFC) method for engineering applications and RS data production. The framework mainly includes Point Spread Function (PSF) model estimation and non-blind image deconvolution. In PSF estimation, we used the iterative total variation algorithm and 2D Gaussian model fitting to reduce the dependence on slant-edge quality and improve the efficiency of PSF measurement. The PSF model estimation error is less than 3% using the results from standard commercial software as an evaluation benchmark. In image deconvolution, we adopted a regularisation-based non-blind deconvolution method using hyper-Laplacian prior. Compared with the widely used methods, the MTF has been improved more than double in high-frequency part. Its processing efficiency and image quality can meet the requirements of RS image products. These results can effectively prove the engineering application value of our proposed method.

General Modulation Transfer Function Fitting Equation for Human Eye with Contact Lens

In this research, a general equation was derived to represent the modulation transfer function (MTF) of the human eye with the presence of the contact lenses (CL) and during the vision with monochrome or multi-wavelength (polychromatic) light. This equation was used to fit the MTF's curves for the eye with pupil diameters (EPD) (2.5, 4, 6, and 8 mm). The fitting equation accuracy was revealed by using the standard deviation (STD). The results indicated that the image MTF is sensitive to (EPD). Moreover, eye vision degrades as (EPD) increases due to the increased spherical and chromatic aberrations. The new equation consists of two exponential terms in addition to a correction polynomial function (H) to fit the EPD effect. The results showed that H function with power two is sufficient to give a good accuracy when the EPD is less than 4 mm, while H with power five is necessary when the EPD is larger or equal to 5 mm. The equation gives a high accuracy also in the case of vision with white light for the eye with a contact lens.

Image Motion Measurement and Image Restoration System Based on an Inertial Reference Laser.

Satellites have many high-, medium-, and low-frequency micro vibration sources that lead to the optical axis jitter of the optical load and subsequently degrade the remote sensing image quality. To address this problem, this paper developed an image motion detection and restoration method based on an inertial reference laser, and describe edits principle and key components. To verify the feasibility and performance of this method, this paper also built an image motion measurement and restoration system based on an inertial reference laser, which comprised a camera (including the inertial reference laser unit and a Hartmann wavefront sensor), an integrating sphere, a simulated image target, a parallel light pope, a vibration isolation platform, a vibration generator, and a 6 degrees of freedom platform. The image restoration principle was also described. The background noise in the experiment environment was measured, and an image motion measurement accuracy experiment was performed. Verification experiments of image restoration were also conducted under various working conditions. The experiment results showed that the error of image motion detection based on the inertial reference laser was less than 0.12 pixels (root mean square). By using image motion data to improve image quality, the modulation transfer function (MTF) of the restored image was increased to 1.61–1.88 times that of the original image MTF. The image motion data could be used as feedback to the fast steering mirror to compensate for the satellite jitter in real time and to directly obtain high-quality images.

Influence of incident angle, anisotropy, and floating distance on aerial imaging resolution

We measure the image resolution of aerial images formed with an AIRR (aerial imaging by retro-reflection) system. Using three different types of retro-reflectors inside the AIRR system, we measure the aerial image modulation transfer function (MTF) via the slanted knife edge method, showing that the resolution of depends on the angle of incidence on the retro-reflector, the retro-reflector's anisotropy, and the aerial image's floating distance.

Automated MTF measurement in CT images with a simple wire phantom

Abstract This study developed a simple wire phantom and an algorithm to automatically measure the modulation transfer function (MTF) in computed tomography (CT) and implemented it to evaluate the effect of focal spot size and reconstruction filter type. The phantom consisted of a resin cylinder filled with water, with a tin wire of diameter 0.1 mm positioned along the center of the cylinder. The automated MTF algorithm used an axial image of the phantom and comprised several steps. The center position of a region of interest (ROI) was automatically determined at the center of the wire image. The pixels were then summed along the y-direction to obtain the profile of the pixel values at a point along the x-direction. Following this, both edges of the profile were made equal to zero. The profile curve was then normalized so that the total of all the data was equal to unity. The normalized profile curve is the line spread function (LSF), and the MTF curve was obtained by taking its Fourier transform. Our system (phantom and algorithm) is able to differentiate the MTFs of CT images from different focal sizes and reconstruction filter types.

Modulation transfer function measurements of Type-II mid- wavelength and long-wavelength infrared superlattice focal plane arrays

Mid-wavelength Infrared (MWIR) and long-wavelength infrared (LWIR) Barrier Infrared Detector (BIRD) based on Antimonides Type-II superlattice detector array material are hybridized to 640 × 512, 1024 × 1024 and 1344 × 784 pixels format read out integrated circuits. The focal plane arrays (FPAs) Noise Equivalent Temperature Difference (NEΔT), Quantum Efficiency (η), Dark Current Density (JD), and Modulation Transfer Function (MTF) performance were measured at operating temperatures. High performance 640 × 512 array format MWIR High Operating Temperature (HOT) FPA has typical NEΔT ∼ 19 mK, JD ∼ 6.2 × 10−7 A/cm2, and η ∼ 53% using 3–5 μm band pass filter at 115 K operating temperatures. Best performance 640 × 512 array format LWIR FPA has NEΔT ∼ 25 mK, JD ∼ 2.5 × 10−5 A/cm2 and η ∼ 41% using 8–9.4 μm band pass filter at 60 K operating temperatures. For MTF investigation, a novel direct one-to-one image approach of Line Spread Function (LSF) and Edge Spread Function (ESF) are patterned onto substrate-removed FPAs. The direct LSF and ESF image are produced by 1000 A° thick gold layer deposition. The direct image horizontal and vertical MTFs are compared with projected knife-edge ESF-derived MTFs and results indicate that direct image MTFs have higher values compared to projected knife-edge ESF-derived MTFs at a Nyquist frequency. However, direct image MTF requires no lens MTF correction. The only relevant requirement for the direct image MTF is for the deposited pattern and substrate to be extremely thinned in which the HOT-BIRD FPAs fulfilled for this investigation.

Photon Counting Computed Tomography With Dedicated Sharp Convolution Kernels: Tapping the Potential of a New Technology for Stent Imaging.

The aims of this study were to assess the value of a dedicated sharp convolution kernel for photon counting detector (PCD) computed tomography (CT) for coronary stent imaging and to evaluate to which extent iterative reconstructions can compensate for potential increases in image noise. For this in vitro study, a phantom simulating coronary artery stenting was prepared. Eighteen different coronary stents were expanded in plastic tubes of 3 mm diameter. Tubes were filled with diluted contrast agent, sealed, and immersed in oil calibrated to an attenuation of -100 HU simulating epicardial fat. The phantom was scanned in a modified second generation 128-slice dual-source CT scanner (SOMATOM Definition Flash, Siemens Healthcare, Erlangen, Germany) equipped with both a conventional energy integrating detector and PCD. Image data were acquired using the PCD part of the scanner with 48 × 0.25 mm slices, a tube voltage of 100 kVp, and tube current-time product of 100 mAs. Images were reconstructed using a conventional convolution kernel for stent imaging with filtered back-projection (B46) and with sinogram-affirmed iterative reconstruction (SAFIRE) at level 3 (I463). For comparison, a dedicated sharp convolution kernel with filtered back-projection (D70) and SAFIRE level 3 (Q703) and level 5 (Q705) was used. The D70 and Q70 kernels were specifically designed for coronary stent imaging with PCD CT by optimizing the image modulation transfer function and the separation of contrast edges. Two independent, blinded readers evaluated subjective image quality (Likert scale 0-3, where 3 = excellent), in-stent diameter difference, in-stent attenuation difference, mathematically defined image sharpness, and noise of each reconstruction. Interreader reliability was calculated using Goodman and Kruskal's γ and intraclass correlation coefficients (ICCs). Differences in image quality were evaluated using a Wilcoxon signed-rank test. Differences in in-stent diameter difference, in-stent attenuation difference, image sharpness, and image noise were tested using a paired-sample t test corrected for multiple comparisons. Interreader and intrareader reliability were excellent (γ = 0.953, ICCs = 0.891-0.999, and γ = 0.996, ICCs = 0.918-0.999, respectively). Reconstructions using the dedicated sharp convolution kernel yielded significantly better results regarding image quality (B46: 0.4 ± 0.5 vs D70: 2.9 ± 0.3; P < 0.001), in-stent diameter difference (1.5 ± 0.3 vs 1.0 ± 0.3 mm; P < 0.001), and image sharpness (728 ± 246 vs 2069 ± 411 CT numbers/voxel; P < 0.001). Regarding in-stent attenuation difference, no significant difference was observed between the 2 kernels (151 ± 76 vs 158 ± 92 CT numbers; P = 0.627). Noise was significantly higher in all sharp convolution kernel images but was reduced by 41% and 59% by applying SAFIRE levels 3 and 5, respectively (B46: 16 ± 1, D70: 111 ± 3, Q703: 65 ± 2, Q705: 46 ± 2 CT numbers; P < 0.001 for all comparisons). A dedicated sharp convolution kernel for PCD CT imaging of coronary stents yields superior qualitative and quantitative image characteristics compared with conventional reconstruction kernels. Resulting higher noise levels in sharp kernel PCD imaging can be partially compensated with iterative image reconstruction techniques.

Improvement of Image Quality in the Axial Section Using High-resolution Scan Mode and Hybrid Iterative Reconstruction in Ultra-high-resolution Computed Tomography

The purpose of this study is to compare the physical characteristics and visibility of high-resolution and conventional images acquired with the same X-ray dose, and to investigate the superiority of super high-resolution imaging. A Catphan phantom was scanned in the normal resolution (NR), high-resolution (HR), and super high-resolution (SHR) modes of ultra-high-resolution computed tomography at 120 kV and 75 mAs. All images were reconstructed into a 5-mm thick image slices with filtered back-projection (FBP) and hybrid image reconstruction (HIR), which included normal and enhanced adaptive iterative dose reduction 3D (AIDR and eAIDR, respectively). The modulation transfer function (MTF) and noise power spectrum (NPS) were measured using the circular edge method and radial frequency method, respectively. The signal-to-noise ratio (SNR) was then calculated. High-contrast resolution and low-contrast detectability were evaluated visually by five radiological technologists. The MTFs of HReAIDR and HRFBP images were higher than those of NRFBP images. However, the NPSs of HReAIDR and HRFBP images were larger than those of NRFBP images. The SNR of HReAIDR images was higher than that of NRFBP and HRFBP images. The scores of high-contrast resolution of HReAIDR, NRFBP, and HRFBP images were 13, 8, and 13 cycles/cm, respectively, and the scores of low-contrast detectability were 5, 5, and 6 mm, respectively. Hence, an improvement in high-contrast resolution of signal more than 400 HU in the axial section can be achieved without increasing the radiation dose and decreasing low-contrast detectability with 10 HU using the HR mode and eAIDR.

Optical bench performance of a novel trifocal intraocular lens compared with a multifocal intraocular lens.

PurposeThe purpose of this study is to compare the optical characteristics of the novel PanOptix presbyopia-correcting trifocal intraocular lens (IOL) and the multifocal ReSTOR +3.0 D IOL, through in vitro bench investigations.MethodsThe optical characteristics of AcrySof® IQ PanOptix™ (PanOptix) and AcrySof® IQ ReSTOR +3.0 D (ReSTOR +3.0 D) IOLs were evaluated by through-focus Badal images, simulated headlight images, and modulation transfer function (MTF) measurements which determine resolution, photic phenomena, and image quality. Through-focus Badal images of an Early Treatment of Diabetic Retinopathy Study chart were recorded at both photopic and mesopic pupil sizes. Simulated headlight images were taken on an MTF bench with a 50-μm pinhole target and a 5.0 mm pupil at the distance focus of the IOL. MTF curves were measured with a 3.0 mm pupil, and spatial frequencies equivalent to 20/40 and 20/20 visual acuities were recorded to illustrate the through-focus MTF curves. Far-, intermediate-, and near-focus MTF values were obtained.ResultsBench Badal image testing and MTF measurements showed that PanOptix has a near focus at a distance of 42 cm and an additional intermediate focus at a distance of about 60 cm. The near focus for ReSTOR +3.0 D is at 45 cm. PanOptix and ReSTOR +3.0 D have comparable photopic distances and near MTF values. Additionally, PanOptix provided a substantial continuous range of vision from distance to intermediate and to near compared with ReSTOR +3.0 D. The halo propensity for PanOptix was slightly higher than that for ReSTOR +3.0 D.ConclusionLaboratory-based in vitro simulations showed that PanOptix trifocal IOL has comparable resolution and image quality performance in distance and near foci compared with ReSTOR +3.0 D IOL. PanOptix showed better resolution and image quality performance at the intermediate focus than ReSTOR +3.0 D IOL.

Searching algorithm of theodolite auto-focusing based on compound focal judgment

Abstract Focusing of search judgment is one of the important parts of theodolite image measurement. Traditional hill-climbing search algorithm cannot usually focus accurately due to the interference of the evaluation function of the local extremum affected by measuring environment, such as light illumination. A compound auto-focal judgment combining image definition evaluation function and modulation transfer function (MTF) auxiliary function was introduced to improve the hill-climbing method. Definition evaluation function and MTF values of images were considered to judge the search direction together. Slanted-edge method was improved to calculate the image MTF values accurately based on the auto-selection of slanted-edge area. Lastly, the principle and implementation of the improved algorithm were given. In the theodolite auto-focusing system, the system imaging effect was validated, and different initial position and circumstances were considered using the proposed searching algorithm. The experiment results of theodolite auto-focus system show that the improved hill-climbing search algorithm can effectively eliminate the local extremum disturbance and make the system search focusing accurate and reliable.

MTFフラクタル次元によるX線画像の画質評価

Objective evaluation, e.g., using the modulation transfer function (MTF) or the noise power spectrum (NPS) of an X-ray imaging system may not correctly correspond to the subject's evaluation, e.g., when using the receiver operating characteristic (ROC). Moreover, it is difficult to measure MTF or NPS from clinical images. We therefore applied MTF fractal dimension to an X-ray imaging system. The MTF fractal dimension includes the frequency properties of the human eye in addition to quantitative complexity. In this study, we demonstrated a relationship between basic image quality and MTF fractal dimension using simulated and actual X-ray images.

Optical performance of hydrophobic acrylic intraocular lenses with surface light scattering

To evaluate the potential effect of surface light scattering on the optical performance of hydrophobic acrylic intraocular lenses (IOLs) made of Acrysof material. Alcon Laboratories, Inc., Fort Worth, Texas, USA. Experimental study. Explanted IOLs from cadaver eyes with more than 50 computer-compatible tape (CCT) units of scatter were selected, yielding 7 IOLs. Clinically explanted IOLs (n = 4) were obtained after IOLs had been implanted 8.5 to 10.5 years. Explanted IOLs were matched to unused control IOLs. After proteins were removed, scatter was measured for IOLs dry, wetted (2 minutes in a balanced salt solution), and hydrated (24 hours). Badal imaging, ultraviolet-visible transmission, and modulation transfer function (MTF) measurements were performed with hydrated IOLs. Hydrated scatter values ranged from 80 to 221 CCT for explanted IOLs and 2 to 7 CCT for controls. No differences in Badal image resolution were observed between explanted IOLs and controls. The mean MTF values at 100 line pairs per mm (representing 20/20 visual acuity) were similar between explanted IOLs and controls. Over the range of 400 to 700 nm, a small reduction (mean 2.1% ± 1.4% [SD]) in transmission was observed. Surface light scattering of explanted IOLs did not affect image resolution or MTF values. Although light transmission was slightly decreased, the magnitude appeared to be inconsequential for optical performance.

Spatial Quality Assessment of Pan-Sharpened High Resolution Satellite Imagery Based on an Automatically Estimated Edge Based Metric

Most of the existing pan-sharpening quality assessment methods consider only the spectral quality and there are just few investigations, which concentrate on spatial characteristics. Spatial quality of pan-sharpened images is vital in elaborating the capability of object extraction, identification, or reconstruction, especially regarding man-made objects and their application for large scale mapping in urban areas. This paper presents an Edge based image Fusion Metric (EFM) for spatial quality evaluation of pan-sharpening in high resolution satellite imagery. Considering Modulation Transfer Function (MTF) as a precise measurement of edge response, MTFs of pan-sharpened images are assessed and compared to those obtained from the original multispectral or panchromatic images. Spatial quality assessment of pan-sharpening is done by comparison of MTF curves of the pan-sharpened and reference images. The capability of the proposed method is evaluated by quality assessment of two different residential and industrial urban areas of WorldView-2 pan-sharpened images. Obtained results clearly show the wide spatial discrepancy in quality of Pan-sharpened images, resulting from different fusion methods, and confirm the need for spatial quality assessment of fused products. The results also prove the capability of the proposed EFM as a powerful tool for evaluation and comparison of different image fusion techniques and products.

Establishing the suitability of quantitative optical CT microscopy of PRESAGE® radiochromic dosimeters for the verification of synchrotron microbeam therapy

Previous research on optical computed tomography (CT) microscopy in the context of the synchrotron microbeam has shown the potential of the technique and demonstrated high quality images, but has left two questions unanswered: (i) are the images suitably quantitative for 3D dosimetry? and (ii) what is the impact on the spatial resolution of the system of the limited depth-of-field of the microscope optics? Cuvette and imaging studies are reported here that address these issues. Two sets of cuvettes containing the radiochromic plastic PRESAGE® were irradiated at the ID17 biomedical beamline of the European Synchrotron Radiation facility over the ranges 0–20 and 0–35 Gy and a third set of cuvettes was irradiated over the range 0–20 Gy using a standard medical linac. In parallel, three cylindrical PRESAGE® samples of diameter 9.7 mm were irradiated with test patterns that allowed the quantitative capabilities of the optical CT microscope to be verified, and independent measurements of the imaging modulation transfer function (MTF) to be made via two different methods. Both spectrophotometric analysis and imaging gave a linear dose response, with gradients ranging from 0.036–0.041 cm−1 Gy−1 in the three sets of cuvettes and 0.037 (optical CT units) Gy−1 for the imaging. High-quality, quantitative imaging results were obtained throughout the 3D volume, as illustrated by depth–dose profiles. These profiles are shown to be monoexponential, and the linear attention coefficient of PRESAGE® for the synchrotron-generated x-ray beam is measured to be (0.185 ± 0.02) cm−1 in excellent agreement with expectations. Low-level (<5%) residual image artefacts are discussed in detail. It was possible to resolve easily slit patterns of width 37 µm (which are smaller than many of the microbeams used on ID-17), but some uncertainty remains as to whether the low values of MTF for the higher spatial frequencies are scanner related or a result of genuine (but non-ideal) dose distributions. We conclude that microscopy images from our scanner do indeed have intensities that are proportional to spectrophotometric optical density and can thus be used as the basis for accurate dosimetry. However, further investigations are necessary before the microscopy images can be used to make the quantitative measures of peak-to-valley ratios for small-diameter microbeams. We suggest various strategies for moving forward and are optimistic about the future potential of this system.

Investigation of image lag and modulation transfer function in fluoroscopy images obtained with a dynamic flat-panel detector

Digital imaging with a dynamic flat-panel detector (FPD) is commonly used in clinical practice. However, several factors reduce the accuracy of target tracking in fluoroscopic imaging, including image lag and blurring. There have been several reports focusing on the modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) in different types of FPD. However, there have been no studies comparing image lag and MTF properties in dynamic images obtained with indirect- and direct-conversion FPDs. We investigated the image lag and MTF under several imaging conditions in fluoroscopic images obtained with an indirect-conversion and a direct-conversion FPD system. The measurements of image lag and MTF were obtained under several conditions according to IEC 62220-1-3 standards. We examined whether the image lag and MTF were influenced by the dose level and target movement speed. Indirect-conversion FPD showed dependence on the dose level, which was not observed for direct-conversion FPD. Furthermore, there were large differences in MTF between images of static and moving plate with indirect-conversion FPD in comparison to the differences observed with direct-conversion FPD. These results will be useful for the determination of imaging conditions for target tracking and other types of dynamic imaging.

Removing atmospheric MTF and establishing an MTF compensation filter for the HJ-1A CCD camera

The total image modulation transfer function (MTF) comprises imaging system MTF and atmospheric MTF, both of which can produce blurring effects in remote-sensing images. Imaging system MTF, one of the important specifications of the imaging system, is used to characterize the radiometric response of the sensor. Atmospheric MTF, which consists of aerosol MTF and turbulence MTF, usually changes with external atmospheric conditions. To obtain the MTF of the imaging system, the atmospheric MTF has to be removed from the total image MTF. This study aims to determine a method for removing the atmospheric MTF for the charge-coupled device (CCD) camera on-board the Huanjing 1A satellite (HJ-1A). The aerosol MTF and the turbulence MTF in the CCD images were first predicted based on the aerosol optical depth (AOD) derived by dark target and reanalysis of data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). Then, the MTFs of the CCD camera were retrieved by removing the aerosol and turbulence MTFs from the total on-orbit image MTFs that were calculated from the linear features on CCD images. For the HJ-1A CCD camera, results show that the MTF values at Nyquist frequency increased by about 10% after the atmospheric MTFs were removed. The total image MTF became degraded by about 50% when AOD was high or turbulence was strong. Furthermore, this study has established an MTF compensation (MTFC) filter for the HJ-1A by modifying the ‘modified inverse filter (MIF)’ approach. Results illustrate that the effective instantaneous field of view (EIFOV) of the restored image improved from 78 to 41 m, while the noise level of the model was well controlled. This research demonstrates that the modified approach is effective for sensors with low MTF values.

Towards task-based assessment of CT performance: System and object MTF across different reconstruction algorithms

To investigate a measurement method for evaluating the resolution properties of CT imaging systems across reconstruction algorithms, dose, and contrast. An algorithm was developed to extract the task-based modulation transfer function (MTF) from disk images generated from the rod inserts in the ACR phantom (model 464 Gammex, WI). These inserts are conventionally employed for HU accuracy assessment. The edge of the disk objects was analyzed to determine the edge-spread function, which was differentiated to yield the line-spread function and Fourier-transformed to generate the object-specific MTF for task-based assessment, denoted MTF(Task). The proposed MTF measurement method was validated against the conventional wire technique and further applied to measure the MTF of CT images reconstructed with an adaptive statistical iterative algorithm (ASIR) and a model-based iterative (MBIR) algorithm. Results were further compared to the standard filtered back projection (FBP) algorithm. Measurements were performed and compared across different doses and contrast levels to ascertain the MTF(Task) dependencies on those factors. For the FBP reconstructed images, the MTF(Task) measured with the inserts were the same as the MTF measured from the wire-based method. For the ASIR and MBIR data, the MTF(Task) using the high contrast insert was similar to the wire-based MTF and equal or superior to that of FBP. However, results for the MTF(Task) measured using the low-contrast inserts, the MTF(Task) for ASIR and MBIR data was lower than for the FBP, which was constant throughout all measurements. Similarly, as a function of mA, the MTF(Task) for ASIR and MBIR varied as a function of noise--with MTF(Task) being proportional to mA. Overall greater variability of MTF(Task) across dose and contrast was observed for MBIR than for ASIR. This approach provides a method for assessing the task-based MTF of a CT system using conventional and iterative reconstructions. Results demonstrated that the object-specific MTF can vary as a function of dose and contrast. The analysis highlighted the paradigm shift for iterative reconstructions when compared to FBP, where iterative reconstructions generally offer superior noise performance but with varying resolution as a function of dose and contrast. The MTF(Task) generated by this method is expected to provide a more comprehensive assessment of image resolution across different reconstruction algorithms and imaging tasks.

SU-E-I-54: Evaluation of High Contrast Resolution for Model Based Iterative Reconstruction of Sinus Examinations.

To evaluate high contrast resolution of Model Based Iterative Reconstruction used with typical sinus examination acquisition parameters. MBIR has recently become available as a recon option on a clinical scanner (Discovery HD750, GE Healthcare). In this work, we evaluate high contrast resolution for scan and reconstruction options that are available for sinus examinations. For this study we used our adult sinus CT protocol reconstructed with filtered back projection, and two alternative scans reconstructed with IR. Our conventional adult sinus CT protocol utilizes a high resolution scan mode which is not compatible with the scanner's IR recon option. The two additional scans are with high resolution option off, one with the head SFOV, and one with the body SFOV. Using IR and the head SFOV, reconstructed images have a 1024 × 1024 pixel matrix. Using IR and the body SFOV, reconstructed images have a 512 × 512 pixel matrix. Three evaluations of high contrast resolution are made for these images. A wire phantom is scanned for assessment of image modulation transfer function. The bar patterns of the ACR phantom are visually assessed for quality in both axial and coronal reformats. MTF curves show 50% values of 6.8, 7.5, and 7.7 lp/cm for Body IR 512 × 512, Head IR 1024 × 1024, and filtered back projection with HD Bone kernel. The 10% MFT curves for these reconstructions are 11.2, 11.9, and 12.1 lp/cm. Visual evaluation of the ACR phantom at 15 cm display field of view demonstrates resolution of the 10 lp/cm bar patterns for all reconstructions with better visualization of the axial versus coronal recons. MBIR reconstruction demonstrates high contrast resolution that is comparable with our conventional sinus examination.