Uniformity Correction Research Articles

Application of non-uniformity correction framework in digital breast tomosynthesis by incorporating a total variation penalty

Digital breast tomosynthesis (DBT) is well-established in breast imaging modality to overcome the loss of depth-information in a three-dimension (3D) object in 2D mammography. However, the reconstructed DBT images suffer from shading artifacts caused by scatter radiation, beam-hardening effect, and unique geometric conditions. In this study, we investigated the application of a non-uniformity correction framework with TV-penalty in the DBT system for substantial improvement of its image visibility. We modeled a modified solver to estimate the non-uniformity field component, which is inspired by the normalized intensity-gradient joint-histogram-based energy minimization. The proposed framework was compared to the reference slice with only primary component in Monte-Carlo simulation and the uniformity was experimentally improved using the projection at low exposure condition. To quantitative evaluate image performance, percent integral uniformity (PIU) was calculated in acquired images. Our results indicated that the proposed framework well-operated to compensate for distorted flatness due to beam hardening, scatter, and unique DBT geometry. Especially, the measured PIU value of the corrected DBT slice was 14.2, it is almost same compared to that of mono-energy DBT slice (primary only) in simulation study. Moreover, the profile flatness of the corrected DBT slice was significantly improved from conventional DBT slice with much noise component. The uniformity correction of the DBT slice is necessary to reduce the misdiagnosis. Consequently, our results demonstrate that the proposed framework successfully corrects the non-uniformity at low X-ray exposure condition, and its scheme is expected to be applicable for efficient DBT imaging performance.

Attenuation correction using deep learning for brain perfusion SPECT images.

Non-uniform attenuation correction using computed tomography (CT) improves the image quality and quantification of single-photon emission computed tomography (SPECT). However, it is not widely used because it requires a SPECT/CT scanner. This study constructs a convolutional neural network (CNN) to generate attenuation-corrected SPECT images directly from non-attenuation-corrected SPECT images. We constructed an auto-encoder (AE) using a CNN to correct the attenuation in brain perfusion SPECT images. SPECT image datasets of 270 (44,528 slices including augmentation), 60 (5002 slices), and 30 (2558 slices) cases were used for training, validation, and testing, respectively. The acquired projection data were reconstructed in three patterns: uniform attenuation correction using Chang's method (Chang-AC), non-uniform attenuation correction using CT (CT-AC), and no attenuation correction (No-AC). The AE learned an end-to-end mapping between the No-AC and CT-AC images. The No-AC images in the test dataset were loaded into the trained AE, which generated images simulating the CT-AC images as output. The generated SPECT images were employed as attenuation-corrected images using the AE (AE-AC). The accuracy of the AE-AC images was evaluated in terms of the peak signal-to-noise ratio (PSNR) and the structural similarity metric (SSIM). The intensities of the AE-AC and CT-AC images were compared by voxel-by-voxel and region-by-region analysis. The PSNRs of the AE-AC and Chang-AC images, compared using CT-AC images, were 62.2, and 57.9, and their SSIM values were 0.9995 and 0.9985, respectively. The AE-AC and CT-AC images were visually and statistically in good agreement. The proposed AE-AC method yields highly accurate attenuation-corrected brain perfusion SPECT images.

Method for illumination uniformity correction in the illumination system of lithography

A method for correcting the illumination uniformity error in the illumination optical system of lithography is proposed. By analyzing the optical characteristic of the uniformity correction system, a mathematical model of the correction system is established based on the principle of linear invariant system and convolution. This model has the characteristics of bidirectional calculation, that is, the intensity distribution on the correction plane can be calculated from the distribution on the mask plane, and the intensity distribution of the mask surface can also be calculated from the distribution of the compensation surface. Then a method of uniformity correction device design is proposed based on this model and it is used to design a uniformity correction device in an actual lithography illumination system. Measurement results of the transmittance distribution and correction effect of the designed uniformity correction device validates that the correcting method established previously is correct and effective.

Concepts in Image Sticking Measurements: Temporal Alignment, Uniformity Correction and Grey Level Dependency

Concepts in Image Sticking Measurements: Temporal Alignment, Uniformity Correction and Grey Level Dependency

Comparison of three different correction trajectories for foot and ankle deformity treated by supramalleolar osteotomy using a novel external fixator.

Based on the principle of distraction osteogenesis, external fixators are widely used in deformity correction of the foot and ankle. In this study, a novel ankle external fixator is proposed to correct complex multiplane deformities, especially for supramalleolar osteotomy to correct distal tibia deformities. The relatively simple structure and fewer struts in the proposed fixator reduce the complexity of adjusting the external fixator. Based on two existing adjustment strategies, a new strategy taking into account the orientation and shortest path of the ankle joint center is proposed, which is named joint adjustment for equal bone distraction. By proposing the inverse kinematic solutions of the novel external fixator, mathematical derivations of the bone trajectory and modelling of the bone shape for the three distraction strategies are performed. The results obtained by comparative analysis indicate that a uniformly spaced path of the ankle joint center can be acquired, and a smooth and uniform correction trajectory of the distal tibia end can be obtained using the new adjustment strategy. It can avoid bone end interference and only generates a maximum deviation 0.66% greater than the currently optimal 1 mm/day. The new strategy can perform multiplane corrections simultaneously, which shortens the correction time and reduces the patient's pain.

Characterization of a new scintillation imaging system for proton pencil beam dose rate measurements

The goal of this work was to create a technique that could measure all possible spatial and temporal delivery rates used in pencil-beam scanning (PBS) proton therapy. The proposed system used a fast scintillation screen for full-field imaging to resolve temporal and spatial patterns as it was delivered. A fast intensified CMOS camera used continuous mode with 10 ms temporal frame rate and 1 × 1 mm2 spatial resolution, imaging a scintillation screen during clinical proton PBS delivery. PBS plans with varying dose, dose rate, energy, field size, and spot-spacing were generated, delivered and imaged. The captured images were post processed to provide dose and dose rate values after background subtraction, perspective transformation, uniformity correction for the camera and the scintillation screen, and calibration into dose. The linearity in scintillation response with respect to varying dose rate, dose, and field size was within 2%. The quenching corrected response with varying energy was also within 2%. Large spatio-temporal variations in dose rate were observed, even for plans delivered with similar dose distributions. Dose and dose rate histograms and maximum dose rate maps were generated for quantitative evaluations. With the fastest PBS delivery on a clinical system, dose rates up to 26.0 Gy s−1 were resolved. The scintillation imaging technique was able to quantify proton PBS dose rate profiles with spot weight as low as 2 MU, with spot-spacing of 2.5 mm, having a 1 × 1 mm2 spatial resolution. These dose rate temporal profiles, spatial maps, and cumulative dose rate histograms provide useful metrics for the potential evaluation and optimization of dose rate in treatment plans.

Characterisation of a hand-held CZT-based gamma camera for 177Lu imaging

BackgroundCurrently, hand-held gamma cameras are being developed for 99mTc imaging, mainly for sentinel lymph node detection. These cameras offer advantages, such as mobility and ease of access, and may be useful also for other applications such as biokinetic studies in animals or for imaging of small, superficial structures in patients. In this work, the suitability of a CZT-based hand-held camera for 177Lu imaging is investigated. The energy response of CZT-based detectors combined with the multiple photon emissions of 177Lu poses new challenges compared to 99mTc imaging, and a thorough camera characterisation is thus warranted.MethodsThree collimators (LEHR, LEHS, and MEGP) and three energy windows (55 keV, 113 keV, and 208 keV) are investigated. Characterised camera properties include the system spatial resolution, energy resolution, sensitivity, image uniformity, septal penetration, and temperature dependence. Characterisations are made starting from NEMA guidelines when applicable, with adjustments made when required. The applicability of the camera is demonstrated by imaging of a superficially located tumour in a patient undergoing [177 Lu]Lu-DOTA-TATE therapy.ResultsOverall, the results are encouraging. Compared to a conventional gamma camera, the hand-held camera generally has a higher sensitivity for a given collimator. For source-collimator distances below 3 cm, the spatial resolution FWHM is within 6 mm for the LEHR and MEGP collimators. Before uniformity correction, the central field-of-view integral uniformity shows best results for the 113-keV window, with values obtained between 11 and 14%. The corresponding values after uniformity correction are within 3%. Effects of septal penetration are observed but are manageable with a proper combination of collimator and energy window setting. Septal penetration and collimator scatter not only affect the 208-keV window but also contribute with counts in lower windows due to energy-tailing effects. The patient study revealed non-uniform uptake patterns in a region that appeared uniform in a conventional gamma camera image.ConclusionsThe results show that the hand-held camera can be used for 177Lu imaging. A 113-keV energy window combined with LEHR or MEGP collimators provides the best image system characteristics.

Establishment of a clinical SPECT/CT protocol for imaging of 161Tb

BackgroundIt has been proposed, and preclinically demonstrated, that 161Tb is a better alternative to 177Lu for the treatment of small prostate cancer lesions due to its high emission of low-energy electrons. 161Tb also emits photons suitable for single-photon emission computed tomography (SPECT) imaging. This study aims to establish a SPECT protocol for 161Tb imaging in the clinic.Materials and methodsOptimal settings using various γ-camera collimators and energy windows were explored by imaging a Jaszczak phantom, including hollow-sphere inserts, filled with 161Tb. The collimators examined were extended low-energy general purpose (ELEGP), medium-energy general purpose (MEGP), and low-energy high resolution (LEHR), respectively. In addition, three ordered subset expectation maximization (OSEM) algorithms were investigated: attenuation-corrected OSEM (A-OSEM); attenuation and dual- or triple-energy window scatter-corrected OSEM (AS-OSEM); and attenuation, scatter, and collimator-detector response-corrected OSEM (ASC-OSEM), where the latter utilized Monte Carlo-based reconstruction. Uniformity corrections, using intrinsic and extrinsic correction maps, were also investigated. Image quality was assessed by estimated recovery coefficients (RC), noise, and signal-to-noise ratio (SNR). Sensitivity was determined using a circular flat phantom.ResultsThe best RC and SNR were obtained at an energy window between 67.1 and 82.1 keV. Ring artifacts, caused by non-uniformity, were removed with extrinsic uniformity correction for the energy window between 67.1 and 82.1 keV, but not with intrinsic correction. Analyzing the lower energy window between 48.9 and 62.9 keV, the ring artifacts remained after uniformity corrections. The recovery was similar for the different collimators when using a specific OSEM reconstruction. Recovery and SNR were highest for ASC-OSEM, followed by AS-OSEM and A-OSEM. When using the optimized parameter setting, the resolution of 161Tb was higher than for 177Lu (8.4 ± 0.7 vs. 10.4 ± 0.6 mm, respectively). The sensitivities for 161Tb and 177Lu were 7.41 and 8.46 cps/MBq, respectively.ConclusionSPECT with high resolution is feasible with 161Tb; however, extrinsic uniformity correction is recommended to avoid ring artifacts. The LEHR collimator was the best choice of the three tested to obtain a high-resolution image. Due to the complex emission spectrum of low-energy photons, window-based scatter correction had a minor impact on the image quality compared to using attenuation correction only. On the other hand, performing attenuation, scatter, and collimator-detector correction clearly improved image quality. Based on these data, SPECT-based dosimetry for 161Tb-labeled radiopharmaceuticals is feasible.

Anomaly Kriging Helps to Remove Bias in Spatial Model Runoff Estimates

AbstractThe low spatial density of streamflow gauging stations limits the accuracy of spatial streamflow estimates in many parts of the world. Strategies to improve runoff estimates in the absence of dense measurements have tended to focus on estimating parameters of runoff models in ungauged regions, through so‐called parameter regionalization methods. However, parameter regionalization can be affected by overdependence on calibration at gauged sites, model parameter equifinality, and ensuing estimation errors. As a result, spatial model runoff estimates typically exhibit spatially correlated biases. This analysis attempts to enhance the use of observations in spatial runoff estimation. Specifically, we assessed the potential to reduce systematic errors by spatially interpolating residuals (i.e., errors) between prior grid‐based streamflow estimates for Australia at 0.05° × 0.05° grid from the Australian Bureau of Meteorology's calibrated, operational Australian Water Resources Assessment Landscape model (AWRA‐L) and streamflow gauging records from 780 unimpeded, relatively small catchments. We analyzed spatial autocorrelation in residuals and tested an efficient two‐step correction approach involving a uniform correction and subsequent kriging of residuals. The approach removed an average of 41% of systematic bias in the model estimates and also improved other model performance measures. Further reduction in errors at shorter timescales may be achievable through a temporally hierarchical correction scheme.

Osprey: Open-source processing, reconstruction & estimation of magnetic resonance spectroscopy data

BackgroundProcessing and quantitative analysis of magnetic resonance spectroscopy (MRS) data are far from standardized and require interfacing with third-party software. Here, we present Osprey, a fully integrated open-source data analysis pipeline for MRS data, with seamless integration of pre-processing, linear-combination modelling, quantification, and data visualization. New MethodOsprey loads multiple common MRS data formats, performs phased-array coil combination, frequency-and phase-correction of individual transients, signal averaging and Fourier transformation. Linear combination modelling of the processed spectrum is carried out using simulated basis sets and a spline baseline. The MRS voxel is coregistered to an anatomical image, which is segmented for tissue correction and quantification is performed based upon modelling parameters and tissue segmentation. The results of each analysis step are visualized in the Osprey GUI. The analysis pipeline is demonstrated in 12 PRESS, 11 MEGA-PRESS, and 8 HERMES datasets acquired in healthy subjects. ResultsOsprey successfully loads, processes, models, and quantifies MRS data acquired with a variety of conventional and spectral editing techniques. Comparison with Existing Method(s)Osprey is the first MRS software to combine uniform pre-processing, linear-combination modelling, tissue correction and quantification into a coherent ecosystem. Compared to existing compiled, often closed-source modelling software, Osprey’s open-source code philosophy allows researchers to integrate state-of-the-art data processing and modelling routines, and potentially converge towards standardization of analysis. ConclusionsOsprey combines robust, peer-reviewed data processing methods into a modular workflow that is easily augmented by community developers, allowing the rapid implementation of new methods.

The Role of SGS1 Helicase in Mismatch Repair During Single Strand Annealing

In humans, interspersed repeated sequences constitute at least 35% of the genome. Single Strand Annealing (SSA) is a repair pathway which occurs when a double strand break is produced between homologous repeats. The product of SSA is a single copy of one of the homologous repeats. As such SSA is a highly mutagenic repair pathway. If an SSA event occurs and consequently deletes important genes such as BRAC2, which itself contains repeats, the result can be catastrophic.To study mismatch correction (MMC) during SSA, a yeast strain was created to have 7 mismatches (6 base‐pair substitutions and 1‐bp insertion/deletion), resulting in a 3% divergence between the repeats. Previous results show that strains with 3% divergence between the repeats, designated as the F‐A strain, reduced SSA two‐fold compared to the identical strains, designated as the A‐A strain. This reduction in SSA is due to heteroduplex rejection which occurs when the mismatch repair complex, MSH2‐MSH6, recognizes the mismatches in the DNA‐duplex and stimulates the unwinding of the DNA via SGS1 helicase, resulting in cell death. In the absence of heteroduplex, MSH2‐MSH3 will bind branched SSA intermediate, and recruit RAD1‐RAD10 to remove the non‐homologous tails.Sgs1Δ results in a very efficient SSA repair, with 2 folds increased viability, in both F‐A and A‐A strains, compared to WT strains as SGS1 is required for heteroduplex rejection. Sequencing analysis of sgs1Δ F‐A strain shows an asymmetric gradient of correction favoring the F fragment, similar to the WT strain, suggesting that SGS1 has minimal effects on MMC outcomes. In both sgs1Δ and WT strains tailless strains, there is a uniform correction of MMs, suggesting that the non‐homologous tails influence MMC. All together current data suggests that MMC is more likely to occur during replication, once the SSA repair is completed. Future directions include knocking‐out MLH1, a mismatch repair protein shown to interact with SGS1, and investigating if sectored colonies, cells with unrepaired mismatches is due to replication.Support or Funding InformationBrandeis Division of Science Summer Research Fellowship

Variability - Surface intensity distribution of large-area reference sources

In this paper we present the impact of variability, a surface source parameter, on the efficiency evaluation of surface contamination monitors. This study was based on two source uniformity correction methodologies and data from real surface source distributions. Surface source intensity distribution has been changed by rearranging the cells (portions of the active area of each LARS) while keeping the same source uniformity value. Instrument efficiencies have been calculated for different sets of uniformities and variabilities. This study led to emphasize the importance of variability, a differential source intensity distribution parameter, over the uniformity, an integral source intensity distribution parameter, and reinforced the importance of the source uniformity correction procedure on the course of surface contamination monitor calibration.

Dwelling time calculation for film uniformity correction by ion beam sputtering process on larger optical materials

It is difficult to obtain film with uniform thickness and constant performance for optical components with larger diameter. It is a critical technology to improve the film uniformity during the deposition process. The ion beam sputtering system was used to prepare the film on the surface of large-aperture optical elements. The performance of film including thickness and roughness were measured by step profiler and optical profilometer instrument. The film thickness correction model was proposed in this paper. The optimized dwell time ratio was obtained by the film thickness data obtained from former experiments, and the dwell time distribution was calculated, after several iteration with the model, uniform film can be achieved on optical elements over 300mm in diameter. Taking the Si film on the surface of fused silica as an example. The research results show that, different film thickness between 100nm and 400nm can be obtained, when the film thickness is more than 200 nm, the film uniformity from more than 13% to less than 0.5%. The surface roughness variation of optical material before and after film deposition were studied, which provide stable process for obtaining high performance film on larger optical components.

Technical Note: Long-term stability of Hounsfield unit calibration for cone beam computed tomography.

The goal of this study was to investigate the stability of a phantom-based Hounsfield unit (HU) calibration for cone beam CT (CBCT). Three consecutive scans of a large phantom configuration and a small phantom configuration were acquired and reconstructed with a uniform scatter correction method. The CBCT gray values of the phantom inserts were measured and the three values of each insert averaged. The linear calibration curve was determined and its slope and intercept were evaluated. This procedure was performed for three CBCT scanners (Elekta Synergy) over a period of 10 months with 1, 2, or 4 weeks between measurements. A dosimetric estimation of the HU fluctuations was carried out. The CBCT HUs were stable over time with only small variations in slope and intercept resulting in HU differences on the water level, that is, intercepts, of less than 7HU (standard deviation). Therefore, the dosimetric influence of these HU differences was limited. The inter-scanner disparities (up to~16HU) were larger than the intra-scanner ones (up to~7HU). Stable HUs were observed over a period of 10 months. Due to the differences between the CBCT scanners, scanner-specific calibration curves are necessary.

Operation of a layer-oriented multiconjugate adaptive optics system in the partial illumination regime

Multiconjugate adaptive optics (MCAO) promises uniform wide-field atmospheric correction. However, partial illumination of the layers at which the deformable mirrors are conjugated results in incomplete information about the full turbulence field. We report on a working solution to this difficulty for layer-oriented MCAO, including laboratory and on-sky demonstration with the LINC-NIRVANA instrument at the Large Binocular Telescope. This approach has proven to be simple and stable.

Percentage low-density lipoprotein-cholesterol response to a given statin dose is not fixed across the pre-treatment range: Real world evidence from clinical practice: Data from the ESC-EORP EUROASPIRE V Study.

Recent European guidelines recommend in patients with atherosclerotic cardiovascular disease to achieve a reduction of low-density lipoprotein-cholesterol of at least 50% if the baseline low-density lipoprotein-cholesterol level is between 1.8 and 3.5 mmol/L. Systematic reviews have associated a given statin/dose combination with a fixed percentage low-density lipoprotein-cholesterol response. Algorithms for detecting cases and estimating the prevalence of familial hypercholesterolaemia often rely on such fixed percentage reductions. We used data from 915 coronary patients participating in the EUROASPIRE V study in whom atorvastatin or rosuvastatin therapy was initiated at hospital discharge and who were still using these drugs at the same dose at a follow-up visit 6 or more months later. Pre and on-treatment low-density lipoprotein-cholesterol levels were compared across the full low-density lipoprotein-cholesterol range. The prevalence of FH was estimated using the Dutch Lipid Clinic Network criteria, once using observed pre-treatment low-density lipoprotein-cholesterol and once using imputed pre-treatment low-density lipoprotein-cholesterol by following the common strategy of applying fixed correction factors to on-treatment low-density lipoprotein-cholesterol. Inter-individual variation in the low-density lipoprotein-cholesterol response to a fixed statin and dose was considerable, with a strong inverse relation of percentage reductions to pre-treatment low-density lipoprotein-cholesterol. The percentage low-density lipoprotein-cholesterol response was markedly lower at the left end of the pre-treatment low-density lipoprotein-cholesterol range especially for levels less than 3 mmol/L. The estimated prevalence of familial hypercholesterolaemia was 2% if using observed pre-treatment low-density lipoprotein-cholesterol and 10% when using imputed low-density lipoprotein-cholesterol. The inter-individual variation in the percentage low-density lipoprotein-cholesterol response to a given dose of a statin is largely dependent on the pre-treatment level: the lower the pre-treatment low-density lipoprotein-cholesterol level the smaller the percentage low-density lipoprotein-cholesterol reduction. The use of uniform correction factors to estimate pre-treatment low-density lipoprotein-cholesterol is not justified.

Robust Optimization for Gynecological High-Dose Rate Interstitial BrachytherapyUsing Post-Hoc Uniformity Correction

Graphical optimization (GO) is commonly used during forward planning high-dose rate (HDR) interstitial brachytherapy (IB) to conform prescription dose to high-risk clinical target volume (HRCTV) while limiting organs-at-risk (OAR) doses. However, this typically Results in variations in dwell times between adjacent dwell positions even within an interstitial catheter (Figure 1a). When using IB for locally advanced/recurrent gynecological cancers, a common fractionation approach involves 5 fractions delivered twice daily over 3 days. During this time, day-to-day variations in internal normal tissue anatomy (bowel/bladder filling) can occur. Connecting and disconnecting transfer tubes for each treatment may result in longitudinal movement of individual catheters. Above factors could impact actual dose delivered. To mitigate the impact of these variations, we seek to explore the impact of a post-hoc uniformity correction (PHUC) on the GO plan and report an initial clinical experience with using this robust optimized (RO) approach.

Real Time Non uniformity Correction Algorithm and Implementation in Reconfigurable Architecture for Infra red Imaging Systems

In modern electro-optical systems, infra-red (IR) imaging system is an essential sensor used for day and night surveillance. In recent years, advancements in IR sensor technology resulted the detectors having smaller pitch, better thermal sensitivity with large format like 640.512, 1024.768 and 1280.1024. Large format IR detectors enables realisation of high resolution compact thermal imager having wide field-of view coverage. However, the performance of these infrared imaging systems gets limited by non uniformity produced by sensing element, which is temporal in nature and present in spatial domain. This non uniformity results the fixed pattern noise, which arises due to variation in gain and offset components of the each pixel of the sensor even when exposed to a uniform scene. This fixed pattern noise limits the temperature resolution capability of the IR imaging system thereby causing the degradation in system performance. Therefore, it is necessary to correct the non-uniformities in real time. In this paper, non uniformity correction algorithm and its implementation in reconfigurable architectures have been presented and results on real time data have been described.

Proposition of a practical protocol for obtaining a valid radiology image using radiography tally of MCNPX Monte Carlo Code

Background and objectiveOver the past years, Monte Carlo codes have widespread use in the radiation research field. Radiography tally of MCNPX Monte Carlo code can be a popular and applicable tool for simulation of radiography images. However, validation is the most important prerequisite before using its results. MethodsHerein, validation of MCNPX radiography tally with experimental results based on the output image parameters has been investigated. Three cubic phantoms with different thicknesses and aluminum, water, and acrylic inserts were studied. The effects of uniformity correction, the detector efficiency of X-ray in different energies, as well as noise caused by a high statistical error in the simulation were also evaluated. ResultsBased on the proposed protocol to correct the error and uniformity of simulated images versus experimental ones, the maximum difference of less than 5% was achieved. ConclusionsConsequently, using the presented method with fewer steps than previous similar works, the MCNPX radiography tally of Monte Carlo code is a useful and validated tool for medical investigation of radiology images.

Uniform combined reconstruction of multichannel 7T knee MRI receive coil data without the use of a reference scan.

MR image intensity nonuniformity is often observed at 7T. Reference scans from the body coil used for uniformity correction at lower field strengths are typically not available at 7T. To evaluate the efficacy of a novel algorithm, Uniform Combined Reconstruction (UNICORN), to correct receive coil-induced nonuniformity in musculoskeletal 7T MRI without the use of a reference scan. Retrospective image analysis study. MRI data of 20 subjects was retrospectively processed offline. Field Strength/Sequence: Knees of 20 subjects were imaged at 7T with a single-channel transmit, 28-channel phased-array receive knee coil. A turbo-spin-echo sequence was used to acquire 33 series of images. Three fellowship-trained musculoskeletal radiologists with cumulative experience of 42 years reviewed the images. The uniformity, contrast, signal-to-noise ratio (SNR), and overall image quality were evaluated for images with no postprocessing, images processed with N4 bias field correction algorithm, and the UNICORN algorithm. Intraclass correlation coefficient (ICC) was used for measuring the interrater reliability. ICC and 95% confidence intervals (CIs) were calculated using the R statistical package employing a two-way mixed-effects model based on a mean rating (k = 3) for absolute agreement. The Wilcoxon signed-rank test with continuity correction was used for analyzing the overall image quality scores. UNICORN was preferred among the three methods evaluated for uniformity in 97.9% of the pooled ratings, with excellent interrater agreement (ICC of 0.98, CI 0.97-0.99). UNICORN was also rated better than N4 for contrast and equivalent to N4 in SNR with ICCs of 0.80 (CI 0.72-0.86) and 0.67 (CI 0.54-0.77), respectively. The overall image quality scores for UNICORN were significantly higher than N4 (P < 6 × 10-13 ), with good to excellent interrater agreement (ICC 0.90, CI 0.86-0.93). Without the use of a reference scan, UNICORN provides better image uniformity, contrast, and overall image quality at 7T compared with the N4 bias field-correction algorithm. 4 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1534-1544.