Distortion Artifacts Research Articles

A Novel SAO-based Filtering Technique for Reduction in Temporal Flickering Artifacts in H.265/HEVC

This paper presents a novel filtering technique based on sample adaptive offset (SAO) in H.265/high-efficiency video coding (HEVC) for reduction in the temporal flickering artifacts and improving the coding performance. SAO is a newly introduced technique for in-loop filtering in H.265/HEVC, which derives the offsets independently for each frame in the spatial domain without considering temporal frame correlation. As a result, the temporal distortion artifacts which will have a negative effect on the subjective quality, such as flickering artifacts, cannot be effectively addressed. In this paper, the rate-distortion optimization of the newly developed SAO method, referred to as Inter-SAO, is performed on the residual samples between adjacent frames. Inter-SAO and SAO in the reference software of H.265/HEVC (i.e., the test model HM) are then combined to form the novel in-loop filter-based method, denoted as 3D-SAO filtering method, where both spatial information and temporal information are effectively utilized to reduce the overall distortion in reconstructed videos. Compared with the SAO in HM, 3D-SAO has demonstrated its advanced performance for flickering artifacts suppression. Furthermore, 3D-SAO improves the coding efficiency compared with the SAO in HM with a performance gain of up to 0.91 dB in $$\Delta PSNR$$ΔPSNR, 1.74 dB in $$\Delta PSPNR$$ΔPSPNR and 7.33 % in BD-rate reduction.

Spatial Distortion in MRI-Guided Stereotactic Procedures: Evaluation in 1.5-, 3- and 7-Tesla MRI Scanners

Background: Magnetic resonance imaging (MRI) is replacing computed tomography (CT) as the main imaging modality for stereotactic transformations. MRI is prone to spatial distortion artifacts, which can lead to inaccuracy in stereotactic procedures. Objective: Modern MRI systems provide distortion correction algorithms that may ameliorate this problem. This study investigates the different options of distortion correction using standard 1.5-, 3- and 7-tesla MRI scanners. Methods: A phantom was mounted on a stereotactic frame. One CT scan and three MRI scans were performed. At all three field strengths, two 3-dimensional sequences, volumetric interpolated breath-hold examination (VIBE) and magnetization-prepared rapid acquisition with gradient echo, were acquired, and automatic distortion correction was performed. Global stereotactic transformation of all 13 datasets was performed and two stereotactic planning workflows (MRI only vs. CT/MR image fusion) were subsequently analysed. Results: Distortion correction on the 1.5- and 3-tesla scanners caused a considerable reduction in positional error. The effect was more pronounced when using the VIBE sequences. By using co-registration (CT/MR image fusion), even a lower positional error could be obtained. In ultra-high-field (7 T) MR imaging, distortion correction introduced even higher errors. However, the accuracy of non-corrected 7-tesla sequences was comparable to CT/MR image fusion 3-tesla imaging. Conclusion: MRI distortion correction algorithms can reduce positional errors by up to 60%. For stereotactic applications of utmost precision, we recommend a co-registration to an additional CT dataset.

Adaptive Feedback Cancellation for Realistic Hearing Aid Applications

Acoustic feedback is a well-known phenomenon in hearing aids. Under certain conditions it causes the so-called howling effect, which is highly annoying for the hearing aid user and limits the maximum amplification of the hearing aid. The standard adaptive feedback cancellation algorithms suffer from a biased adaptation if the input signal is spectrally colored, as it is for speech and music signals. Due to this bias distortion artifacts (entrainment) are generated. In this paper, we present a sub-band feedback cancellation system which combines decorrelation methods with a new realization of a known non-parametric variable step size. To apply this step size in the context of adaptive feedback cancellation, a method to estimate the signal power of the desired input signal, i.e., without feedback, is necessary. A major part of this paper is spent with the theoretical derivation of this estimate. Furthermore, the complete system is evaluated extensively for several speech and music signals as well as for different feedback scenarios in simulations with feedback paths measured in concrete applications as well as for real-time simulations with hearing aid dummies. Both use hearing loss compensation methods as applied in physical hearing aids. The performance is measured in terms of being able to prevent entrainment and to react to feedback path changes. For both simulation setups the system shows a good performance with respect to the two performance measures. Furthermore, the overall feedback cancellation method relies only on few parameters, shows a low computational complexity, and therefore has a strong practical relevance.

Whole-Brain In-vivo Measurements of the Axonal G-Ratio in a Group of 37 Healthy Volunteers.

The g-ratio, quantifying the ratio between the inner and outer diameters of a fiber, is an important microstructural characteristic of fiber pathways and is functionally related to conduction velocity. We introduce a novel method for estimating the MR g-ratio non-invasively across the whole brain using high-fidelity magnetization transfer (MT) imaging and single-shell diffusion MRI. These methods enabled us to map the MR g-ratio in vivo across the brain's prominent fiber pathways in a group of 37 healthy volunteers and to estimate the inter-subject variability. Effective correction of susceptibility-related distortion artifacts was essential before combining the MT and diffusion data, in order to reduce partial volume and edge artifacts. The MR g-ratio is in good qualitative agreement with histological findings despite the different resolution and spatial coverage of MRI and histology. The MR g-ratio holds promise as an important non-invasive biomarker due to its microstructural and functional relevance in neurodegeneration.

In vivo high angular resolution diffusion-weighted imaging of mouse brain at 16.4 Tesla.

Magnetic Resonance Imaging (MRI) of the rodent brain at ultra-high magnetic fields (> 9.4 Tesla) offers a higher signal-to-noise ratio that can be exploited to reduce image acquisition time or provide higher spatial resolution. However, significant challenges are presented due to a combination of longer T 1 and shorter T 2/T2* relaxation times and increased sensitivity to magnetic susceptibility resulting in severe local-field inhomogeneity artefacts from air pockets and bone/brain interfaces. The Stejskal-Tanner spin echo diffusion-weighted imaging (DWI) sequence is often used in high-field rodent brain MRI due to its immunity to these artefacts. To accurately determine diffusion-tensor or fibre-orientation distribution, high angular resolution diffusion imaging (HARDI) with strong diffusion weighting (b >3000 s/mm2) and at least 30 diffusion-encoding directions are required. However, this results in long image acquisition times unsuitable for live animal imaging. In this study, we describe the optimization of HARDI acquisition parameters at 16.4T using a Stejskal-Tanner sequence with echo-planar imaging (EPI) readout. EPI segmentation and partial Fourier encoding acceleration were applied to reduce the echo time (TE), thereby minimizing signal decay and distortion artefacts while maintaining a reasonably short acquisition time. The final HARDI acquisition protocol was achieved with the following parameters: 4 shot EPI, b = 3000 s/mm2, 64 diffusion-encoding directions, 125×150 μm2 in-plane resolution, 0.6 mm slice thickness, and 2h acquisition time. This protocol was used to image a cohort of adult C57BL/6 male mice, whereby the quality of the acquired data was assessed and diffusion tensor imaging (DTI) derived parameters were measured. High-quality images with high spatial and angular resolution, low distortion and low variability in DTI-derived parameters were obtained, indicating that EPI-DWI is feasible at 16.4T to study animal models of white matter (WM) diseases.

SU‐E‐J‐207: Effect of Pulse Sequence Parameters On Geometric Distortions Induced by a Titanium Brachytherapy Applicator

Purpose:To investigate the effect of readout bandwidth and voxel size on the appearance of distortion artifacts caused by a titanium brachytherapy applicator.Methods:An acrylic phantom was constructed to rigidly hold a MR conditional, titanium Fletcher‐Suit‐Delclos‐style applicator set (Varian Medical Systems) for imaging on CT (Philips Brilliance) and 1.5T MRI (Siemens Magnetom Aera). Several variants of MRI parameters were tried for 2D T2‐weighted turbo spin echo imaging in comparison against the standard clinical protocol with the criteria to keep relative SNR loss less than 20% and imaging time as short as possible. Two 3D sequences were also used for comparison with similar parameters. The applicator tandem was segmented on axial CT images (0.4×0.4×1.5mm 3 resolution) and the CT images were registered to the 3D MR images in Eclipse (Varian). The applicator volume was then overlaid on all MRI sets in 3D‐Slicer and distances were measured from the tandem tip to the MRI artifact edge in right/left/superior and anterior/posterior/superior directions from coronal and sagittal 2D acquisitions, respectively, or 3D data reformats. Artifact regions were also manually contoured in coronal/sagittal orientations for area measurements.Results:As would be expected, reductions in voxel size and increases in readout bandwidth reduced artifact size (average max artifact length decreased by 0.95 mm and average max area decrease by 0.27 cm2). Interestingly, bandwidth increases yielded reductions in area (0.19 cm2) and in distance measurements (1 mm) even with voxel increases, as compared to a standard protocol. This could be useful when high performance protocols are not feasible due to long imaging times.Conclusion:We have characterized artifacts caused by cervical brachytherapy applicator across multiple sequence parameters at 1.5T. Future work will focus on finalizing an optimal protocol that balances artifact reduction with imaging time and then testing this new protocol in patients.

Radiographic distortion artifact of circular external fixators.

Circular external fixators are commonly used to surgically treat a variety of orthopedic conditions. However, distortion artifact may mislead the radiographic interpreter as to the true anatomic location of the transfixing wires and either negatively impact patient healing or lead to unnecessary procedures. Distortion is due to unequal magnification of different parts of an object. The purpose of this study was to assess distortion of three circular external fixator apparatuses with the transfixing wires at 30, 60, and 90°. Distortion was greatest with all three apparatuses at 10° of rotation from parallel to the central X-ray beam. When comparing distortion between the three apparatuses, distortion was greatest with the transfixing wires at 30°. The study authors concluded that distortion artifact is most severe when the transfixing wires are at smaller angles and when they are farther from the X-ray table. The circular external fixator should be placed in the center of, and parallel to, the primary X-ray beam and as close to the table as possible to reduce/prevent distortion artifact and possible radiographic misinterpretation of transfixing wire location.

Robotic system for MRI-guided stereotactic neurosurgery.

Stereotaxy is a neurosurgical technique that can take several hours to reach a specific target, typically utilizing a mechanical frame and guided by preoperative imaging. An error in any one of the numerous steps or deviations of the target anatomy from the preoperative plan such as brain shift (up to mm), may affect the targeting accuracy and thus the treatment effectiveness. Moreover, because the procedure is typically performed through a small burr hole opening in the skull that prevents tissue visualization, the intervention is basically “blind” for the operator with limited means of intraoperative confirmation that may result in reduced accuracy and safety. The presented system is intended to address the clinical needs for enhanced efficiency, accuracy, and safety of image-guided stereotactic neurosurgery for deep brain stimulation lead placement. The study describes a magnetic resonance imaging (MRI)-guided, robotically actuated stereotactic neural intervention system for deep brain stimulation procedure, which offers the potential of reducing procedure duration while improving targeting accuracy and enhancing safety. This is achieved through simultaneous robotic manipulation of the instrument and interactively updated in situ MRI guidance that enables visualization of the anatomy and interventional instrument. During simultaneous actuation and imaging, the system has demonstrated less than 15% signal-to-noise ratio variation and less than 0.20 geometric distortion artifact without affecting the imaging usability to visualize and guide the procedure. Optical tracking and MRI phantom experiments streamline the clinical workflow of the prototype system, corroborating targeting accuracy with three-ax- s root mean square error 1.38 ± 0.45 mm in tip position and 2.03 ± 0.58° in insertion angle.

Hierarchical Pictorial Structures for Simultaneously Localizing Multiple Organs in Volumetric Pre-Scan CT.

Parsing volumetric computed tomography (CT) into 10 or more salient organs simultaneously is a challenging task with many applications such as personalized scan planning and dose reporting. In the clinic, pre-scan data can come in the form of very low dose volumes acquired just prior to the primary scan or from an existing primary scan. To localize organs in such diverse data, we propose a new learning based framework that we call hierarchical pictorial structures (HPS) which builds multiple levels of models in a tree-like hierarchy that mirrors the natural decomposition of human anatomy from gross structures to finer structures. Each node of our hierarchical model learns (1) the local appearance and shape of structures, and (2) a generative global model that learns probabilistic, structural arrangement. Our main contribution is two fold. First we embed the pictorial structures approach in a hierarchical framework which reduces test time image interpretation and allows for the incorporation of additional geometric constraints that robustly guide model fitting in the presence of noise. Second we guide our HPS framework with the probabilistic cost maps extracted using random decision forests using volumetric 3D HOG features which makes our model fast to train and fast to apply to novel test data and posses a high degree of invariance to shape distortion and imaging artifacts. All steps require approximate 3 mins to compute and all organs are located with suitably high accuracy for our clinical applications such as personalized scan planning for radiation dose reduction. We assess our method using a database of volumetric CT scans from 81 subjects with widely varying age and pathology and with simulated ultra low dose cadaver pre-scan data.

3D high-resolution diffusion-weighted MRI at 3T: Preliminary application in prostate cancer patients undergoing active surveillance protocol for low-risk prostate cancer.

To improve spatial resolution and image quality of diffusion-weighted (DW) MRI in detecting low-risk prostate cancer (lrPC) in patients undergoing active surveillance protocol (AS-PC), we propose the application of a diffusion-prepared balanced steady-state free precession (bSSFP) technique capable of multishot acquisition. Diffusion-prepared bSSFP was compared with single-shot DW echo planar imaging (SS-DW-EPI) at two prescribed resolutions (2.1 × 2.1 × 3.5mm(3) , 0.9 × 0.9 × 3.5 mm(3) ) in nine healthy subjects and nine AS-PC patients. Geometric distortion and susceptibility artifacts were quantitatively assessed in all subjects. In AS-PC patients, lesion detection via blinded multiparametric MRI including T1-weighted, T2-weighted, dynamic contrast-enhanced imaging, and along with either of two DW methods were evaluated against 12-point biopsy. Geometric distortion and susceptibility artifacts were significantly less for diffusion-prepared bSSFP at both prescribed spatial resolutions than SS-DW-EPI. Apparent diffusion coefficients of healthy prostate tissue were concordant between the two DW methods at both spatial resolutions. In AS-PC patients, multiparametric MRI with diffusion-prepared bSSFP had greater sensitivity (94%, 63%), accuracy (76%, 67%), positive-predictive value (54%, 48%), negative-predictive value (97%, 82%), and area under the curve (0.80, 0.67) than with SS-DW-EPI. The proposed diffusion-prepared technique with higher spatial resolution and improved image quality over SS-DW-EPI resulted in better multiparametric MRI detection of lrPC in AS-PC patients.

Detection of myocardial edema with diffusion weighted imaging in patients with acute myocarditis

Methods We have analyzed 26 consecutive patients: 22 male, average age: 27 years (range 13-43) with clinical diagnosis of acute myocarditis. The CMR examinations were performed on a 1,5 T scanner using an eight-channel phasedarray coil combined with 4-6 elements of spinal coil. All patients underwent assessment of myocardial oedema: T2weighted triple inversion recovery (STIR), T1-weighted turbo spin echo pre and post contrast, function (cine Steady State Free Precession) and scar (Late Gadolinium Enhancement). Additionally DWI EPI sequence with b = 50 sec/mm was acquired before contrast administration. The sequence parameters were as follows: slice thickness 10 mm, repetition time (depending on patient breath cycle) 3-4 s, echo time 78 ms, bandwidth 1,736 Hz/Px. The DWI sequence was ECG-gated and synchronized to the respiratory cycle using PACE technique. For all patients T1 and T2 ratio were calculated and presence of LGE areas were reported. For STIR and DWI contrast between healthy myocardium and edema was calculated as a difference between edematous and normal myocardial muscle divided by standard deviation of image noise. Results We managed to acquired good quality DWI images in all 26 patients, average acquisition time was 120s per slice, distortion artifacts occurred in 5 patients but did not impaired diagnostic value of analyzed images. Increased signal intensity in DWI images occurred in all patients in the area of LGE enhancement and were consistent with areas of increased signal in STIR. All patients met at least two out of three criteria for inflammatory activity and injury. T2 ratio was increased (≥ 2) in 24 patients, T1 ratio (≥ 4) in 23 cases, all patients had focal non ischemic enhancement in LGE. CNR was higher in DWI than in STIR: 23,8 vs. 17,6 respectively.

High-Pressure Freeze and Freeze Substitution Electron Microscopy in C. elegans.

While traditional chemical fixation methods for C. elegans electron microscopy (EM) have provided invaluable anatomical and structural information, the development of high-pressure freeze (HPF) and freeze substitution (FS) protocols offers advantages for high-resolution imaging. Specimens prepared using HPF methodology exhibit fewer distortion artifacts due to fixation and dehydration, have improved antigenicity, and result in a more physiologically accurate structural representation of the worm. In the HPF technique, freely moving worms are frozen at high-pressure (2100 bar) and low temperature (-180 °C) within milliseconds. These conditions prevent the formation of ice crystals that can damage cellular structures. Samples then undergo FS, during which worms are slowly brought to room temperature while substituting amorphous ice with organic solvents to preserve tissue in its near native state and provide contrast for imaging. FS can be performed in an automatic freeze substitution (AFS) machine or in makeshift, temperature controlled chambers. Fixed worms can be embedded in plastic resin and further processed for a variety of imaging techniques. Samples then viewed using scanning (SEM) or transmission electron microscopy (TEM) will show enhanced preservation of organelles, cell morphology, and antigenicity for immunocytochemistry.

Does a cleansing enema improve image quality of 3T surface coil multiparametric prostate MRI?

To assesses the utility of a preparatory enema in the interpretation of prostate multiparametric (MP) magnetic resonance imaging (MRI). Under a waiver from the Institutional Review Board (IRB), 32 patients without bowel preparation and 28 patients who underwent a self-administered enema were imaged consecutively with 3T MP-MRI over 6 months. Two blinded radiologists independently assessed image quality on T2 -weighted (T2 W), trace b 1000 mm(2) /sec echo-planar (EPI) and apparent-diffusion coefficient (ADC) and assessed for motion/blur on T2 W and distortion/blur on EPI and ADC. Radiologists also quantified rectal stool and gas. A third blinded radiologist generated contrast curves from dynamic contrast-enhanced (DCE) data at six locations and measured the number of corrupted data points, defined as >10% aberrant signal intensity change. Subjective scores were compared using Wilcoxon sign rank test. Rectal contents were correlated to artifact using Spearman correlation. Contrast curves were evaluated with independent t-tests. There was no difference in image quality on T2 W (P = 0.66-0.74), EPI (P = 0.13-0.36) or ADC (P = 0.49-0.59). There was less rectal stool in the enema group (P = 0.004) and amount of stool correlated with motion artifact on T2 W (r = 0.23, P = 0.02); however, there was no difference in motion artifact between groups (P = 0.47-0.94). Only a minority of patients in the non-enema group had moderate or large amounts of stool (16%) and none of these patients had severe or extensive artifact on T2 . There was less rectal gas in the enema group (P = 0.002); however, amount of gas did not correlate with distortion artifact on EPI or ADC (P = 0.17-0.41) and there was no difference in blur (P = 0.41-0.91) or distortion (P = 0.31-0.99) on EPI or ADC between groups. There was no difference in corrupted data points on DCE (P = 0.46). In this study the use of a preparatory enema did not improve image quality or reduce artifact in prostate MP-MRI.

Diffusion-weighted MRI of the prostate: advantages of Zoomed EPI with parallel-transmit-accelerated 2D-selective excitation imaging.

The purpose of our study was to evaluate the use of 2D-selective, parallel-transmit excitation magnetic resonance imaging (MRI) for diffusion-weighted echo-planar imaging (pTX-EPI) of the prostate, and to compare it to conventional, single-shot EPI (c-EPI). The MRI examinations of 35 patients were evaluated in this prospective study. PTX-EPI was performed with a TX-acceleration factor of 1.7 and a field of view (FOV) of 150 × 90 mm(2), whereas c-EPI used a full FOV of 380 × 297 mm(2). Two readers evaluated three different aspects of image quality on 5-point Likert scales. To quantify distortion artefacts, maximum diameters and prostate volume were determined for both techniques and compared to T2-weighted imaging. The zoomed pTX-EPI was superior to c-EPI with respect to overall image quality (3.39 ± 0.62 vs 2.45 ± 0.67) and anatomic differentiability (3.29 ± 0.65 vs 2.41 ± 0.65), each with p < 0.0001. Artefacts were significantly less severe in pTX-EPI (0.93 ± 0.73 vs 1.49 ± 1.08), p < 0.001. The quantitative analysis yielded a higher agreement of pTX-EPI with T2-weighted imaging than c-EPI with respect to coronal (ICCs: 0.95 vs 0.93) and sagittal (0.86 vs 0.73) diameters as well as prostate volume (0.94 vs 0.92). Apparent diffusion coefficient (ADC) values did not differ significantly between the two techniques (p > 0.05). Zoomed pTX-EPI leads to substantial improvements in diffusion-weighted imaging (DWI) of the prostate with respect to different aspects of image quality and severity of artefacts. Recent technical developments in MRI allow the use of accelerated, spatially-selective excitation (parallel-transmit, pTX). pTX can be used for zoomed echo-planar prostate imaging (pTX-EPI). pTX-EPI improves different aspects of image quality in prostate MRI. Distortion artefacts are reduced by the use of pTX-EPI in prostate MRI. Further studies should aim at assessing the diagnostic accuracy of pTX-EPI.

Knee implant imaging at 3 Tesla using high-bandwidth radiofrequency pulses.

To investigate the impact of high-bandwidth radiofrequency (RF) pulses used in turbo spin echo (TSE) sequences or combined with slice encoding for metal artifact correction (SEMAC) on artifact reduction at 3 Tesla in the knee in the presence of metal. Local transmit/receive coils feature increased maximum B1 amplitude, reduced SAR exposition and thus enable the application of high-bandwidth RF pulses. Susceptibility-induced through-plane distortion scales inversely with the RF bandwidth and the view angle, hence blurring, increases for higher RF bandwidths, when SEMAC is used. These effects were assessed for a phantom containing a total knee arthroplasty. TSE and SEMAC sequences with conventional and high RF bandwidths and different contrasts were tested on eight patients with different types of implants. To realize scan times of 7 to 9 min, SEMAC was always applied with eight slice-encoding steps and distortion was rated by two radiologists. A local transmit/receive knee coil enables the use of an RF bandwidth of 4 kHz compared with 850 Hz in conventional sequences. Phantom scans confirm the relation of RF bandwidth and through-plane distortion, which can be reduced up to 79%, and demonstrate the increased blurring for high-bandwidth RF pulses. In average, artifacts in this RF mode are rated hardly visible for patients with joint arthroplasties, when eight SEMAC slice-encoding steps are applied, and for patients with titanium fixtures, when TSE is used. The application of high-bandwidth RF pulses by local transmit coils substantially reduces through-plane distortion artifacts at 3 Tesla.

Zoomed EPI-DWI of the head and neck with two-dimensional, spatially-selective radiofrequency excitation pulses.

To evaluate the feasibility of zoomed diffusion-weighted EPI (z-EPI) in the head and neck in a healthy volunteer population and to compare to conventional single-shot EPI (c-EPI). Nine volunteers were included in this prospective, IRB-approved study. Examinations were performed on a 3T-MR system equipped with a two-channel, fully-dynamic parallel transmit array. The acquired sequences consisted of a T2w-TSE, a c-EPI, and two z-EPI acquisitions. For quantitative assessment of distortion artefacts, DW images were fused with T2-TSE images. Misregistration of DW images with T2-TSE images was assessed in the cervical spine. For qualitative assessment, two readers ranked c-EPI and z-EPI sequences in terms of susceptibility artefacts, image blur, and overall imaging preference. ADC values of several anatomical regions were calculated and compared between sequences. Mean maximum distortion with the c-EPI was 5.9mm ± 1.6mm versus 2.4mm ± 1mm (p < 0.05) with z-EPI. Both readers found more blur and susceptibility artefacts in every case with c-EPI. No statistically significant differences in calculated ADC values were observed. z-EPI of the head and neck leads to substantial image quality improvements relative to c-EPI due to a reduction in susceptibility artefacts and image blur. • Zoomed DWI is feasible in the head and neck. • Image quality improves substantially with zoomed DWI of the neck. • Zoomed DWI exhibits markedly reduced susceptibility artefacts.

SU‐E‐J‐50: Does a Breathing Surrogate From a Point On the Abdominal Skin Represent the Organ Motion in Thorax for Phase‐Based 4D CT Sorting?

Purpose:This work aims (1) to determine the validity of the current practice of the phase‐based 4DCT sorting (abdomen signal) for thorax scans; (2) to assess the potential benefit of utilizing the 3D surface breathing surrogate of chest area for phase‐based 4DCT sorting.Methods:Dynamic 3D surface images over the chest and abdomen were acquired using 3D‐suface‐camera‐system (VisionRT Ltd., London, UK) for a total of 10 patients. The vertical motions of five regions‐of‐interest (ROIs): abdomen, mid‐sternum, lower‐, middle‐, and upper‐ ipsilateral‐chest were tracked. Based on our previous work, the main source of motion artifact is the variation‐of‐phase‐differences (VPD) between the breathing surrogate and the organ motion during scanning. Thus, we utilize VPD as a quantitative index of the variation of the resulting 4DCT images. The average VPD over a 60 second time‐period was calculated for each of the abdomen and ROI combination. A simulation study with a wire phantom was designed to demonstrate the resulting 4DCT images.Results:Simulation showed significant image distortion or motion artifacts when VPD is larger than 5% of breathing period. The average VPDs of individual ROIs of each patient indicates that 75%, 59% and 22% cases have VPD larger than 5%, 10% and 15% of period each cycle between the selected ROI and the abdominal motions patterns, respectively (10.1±6.0 %, minimum 1.0% to maximum 23.9 %). Overall, patients with less 3‐second breathing‐period present VPD larger than 10%. The correlations between the abdomen and individual chest ROIs motions as well as the motions among chest ROIs are highly case‐dependent.Conclusion:Abdominal motion does not represent the chest motions for some of the patients. This results in motion artifacts in the phase‐based 4DCT. Utilizing the surface surrogate of the chest region can potentially improve phase‐based 4DCT sorting for thorax 4DCT scan, especially for fast breathing patients.

Lens distortion correction and enhancement based on local self-similarity for high-quality consumer imaging systems

In this paper, a novel image enhancement system for a wide-angle lens camera is presented. The proposed system consists of; i) lens distortion correction using space-varying interpolation kernels and ii) image restoration based on the local self-similarity. The correction process for the geometric distortion produced by a wide-angle lens results in radial distortion artifacts caused by non-linear resampling. To reduce such artifacts, the proposed algorithm uses space-varying interpolation kernels derived from the lens calibration data. The corrected image is further enhanced using self-example-based image restoration. Experimental results demonstrate the proposed method can correctly remove the geometric distortion and further enhance the quality of the radially interpolated image.

A simple method to improve the quality of diffusion-weighted magnetic resonance imaging with rapid histologic correlation in a murine model.

Diffusion-weighted magnetic resonance imaging (DW-MRI) has been used extensively in biomedical research. However, this technique has often suffered from distortion artifacts because of the magnetic field inhomogeneity surrounding the tissues. Histology is important for validating MRI interpretations, but correlating MRIs with tissue samples is challenging. Here we propose a method to improve DW-MRI and facilitate the matching between MRIs and tissue samples. A cryostat embedding medium, optimal cutting temperature (OCT) compound, was used to cover the examined target during the MRI studies. Frozen OCT compound could aid the examined target to be sectioned in parallel with the imaging plane. Phantom experiments demonstrated that embedding in OCT compound improved the magnetic field inhomogeneity while maintaining the apparent diffusion coefficient. Animal experiments revealed significantly reduced distortions in DW images in both the axial and coronal planes. The in vivo MRIs were easily matched with histologic specimens in a slice-to-slice fashion to examine the corresponding tissue microenvironment. This simple method might improve the quality of DW-MRI and provide histologic information for MRI to serve as an image biomarker.

A hard tissue cephalometric comparative study between hand tracing and computerized tracing.

Aims:To analyze and compare the angular and linear hard tissue cephalometric measurements using hand-tracing and computerized tracings with Nemoceph and Dolphin software systems.Subjects and Methods:A total of 30 cephalograms were randomly chosen for study with the following criteria, cephalograms of patients with good contrast, no distortion, and minimal radiographic artifacts were considered using the digital method (Kodak 8000 C) with 12 angular and nine linear parameters selected for the study. Comparisons were determined by post-hoc test using Tukey HSD method. The N-Par tests were performed using Kruskal-Walli's method.Statistical Analysis Used:ANOVA and post-hoc.Results:The results of this study show that there is no significant difference in the angular and linear measurements recorded. The P values were significant at 0.05 levels for two parameters, Co-A and Co-Gn with the hand-tracing method. This was significant in ANOVA and post-hoc test by Tukey HSD method.Conclusions:This study of comparison provides support for transition from digital hand to computerized tracing methodology. In fact, digital computerized tracings were easier and less time consuming, with the same reliability irrespective of each method of tracing.