MR Image Quality Research Articles

Virtual phantom magnetic resonance imaging (ViP MRI) on a clinical MRI platform.

The purpose of this study was to implement Virtual Phantom Magnetic Resonance Imaging (ViP MRI), a technique that allows for generating reference signals in MR images using radiofrequency (RF) signals, on a clinical MR system and to test newly designed virtual phantoms. MRI experiments were conducted on a 1.5 T MRI scanner. Electromagnetic modelling of the ViP system was done using the principle of reciprocity. The ViP RF signals were generated using a compact waveform generator (dimensions of 26 cm × 18 cm × 16 cm), connected to a homebuilt 25 mm-diameter RF coil. The ViP RF signals were transmitted to the MRI scanner bore, simultaneously with the acquisition of the signal from the object of interest. Different types of MRI data acquisition (2D and 3D gradient-echo) as well as different phantoms, including the Shepp-Logan phantom, were tested. Furthermore, a uniquely designed virtual phantom - in the shape of a grid - was generated; this newly proposed phantom allows for the investigations of the vendor distortion correction field. High quality MR images of virtual phantoms were obtained. An excellent agreement was found between the experimental data and the inverse cube law, which was the expected functional dependence obtained from the electromagnetic modelling of the ViP system. Short-term time stability measurements yielded a coefficient of variation in the signal intensity over time equal to 0.23% and 0.13% for virtual and physical phantom, respectively. MR images of the virtual grid-shaped phantom were reconstructed with the vendor distortion correction; this allowed for a direct visualization of the vendor distortion correction field. Furthermore, as expected from the electromagnetic modelling of the ViP system, a very compact coil (diameter ~ cm) and very small currents (intensity ~ mA) were sufficient to generate a signal comparable to that of physical phantoms in MRI experiments. The ViP MRI technique was successfully implemented on a clinical MR system. One of the major advantages of ViP MRI over previous approaches is that the generation and transmission of RF signals can be achieved with a self-contained apparatus. As such, the ViP MRI technique is transposable to different platforms (preclinical and clinical) of different vendors. It is also shown here that ViP MRI could be used to generate signals whose characteristics cannot be reproduced by physical objects. This could be exploited to assess MRI system properties, such as the vendor distortion correction field.

Comparison of prostate distortion by inflatable and rigid endorectal MRI coils in permanent prostate brachytherapy imaging

PurposeTo study the deformation of the prostate by a rigid reusable endorectal coil and a balloon-type endorectal coil (BTC) during MRI of the prostate in brachytherapy imaging. Methods and MaterialsThe prostate gland was contoured on 157 MRI scans from 52 prostate cancer patients undergoing brachytherapy. The curvature of the posterior prostate surface deformation was computed as a measure of prostate distortion and compared between scans with a BTC, rigid endorectal coil (REC), or no endorectal coil. For the nine patients who had MRIs with all three endorectal scenarios, a mean prostate deformation vector was also calculated between scenarios using deformable image registration. These measures of prostate distortion were compared with the prostate anterior-to-posterior to left-to-right ratio (AP/LR) on the largest prostate axial slice. ResultsSignificant differences in prostate curvature were found between scans without an endorectal coil versus a REC versus a BTC (p < 0.001). The mean prostate deformation was 3.9 mm due to the BTC and 2.0 mm for the REC (p = 0.012). The mean AP/LR ratio was 0.62 with a BTC versus 0.76 without a coil or 0.73 with a REC (p < 0.001), but no difference existed between scans with a REC versus no coil (p = 0.7). The AP/LR ratio showed moderate correlation with prostate curvature (r = 0.48), and with mean prostate deformation (r = −0.64 to 0.68). ConclusionsThe REC caused minimal deformation of the prostate compared with a BTC with adequate MR image quality, and calculation of the cross-sectional AP/LR ratio on the largest axial prostate slice can serve as a simple measure of prostate distortion.

SpinoBot: An MRI-Guided Needle Positioning System for Spinal Cellular Therapeutics.

The neurodegenerative disease amyotrophic lateral sclerosis (ALS) results in the death of motor neurons in voluntary muscles. There are no cures for ALS and few available treatments. In studies with small animal models, injection of cellular therapeutics into the anterior horn of the spinal cord has been shown to inhibit the progression of ALS. It was hypothesized that spinal injection could be made faster and less invasive with the aid of a robot. The robotic system presented-SpinoBot-uses MRI guidance to position a needle for percutaneous injection into the spinal cord. With four degrees of freedom (DOF) provided by two translation stages and two rotational axes, SpinoBot proved capable of advanced targeting with a mean error of 1.12mm and standard deviation of 0.97mm in bench tests, and a mean error of 2.2mm and standard deviation of 0.85mm in swine cadaver tests. SpinoBot has shown less than 3% signal-to-noise ratio reduction in 3T MR imaging quality, demonstrating its compliance to the MRI environment. With the aid of SpinoBot, the length of the percutaneous injection procedure is reduced to less than 60min with 10min for each additional insertion. Although SpinoBot is designed for ALS treatment, it could potentially be used for other procedures that require precise access to the spine.

Mechanical Validation of an MRI Compatible Stereotactic Neurosurgery Robot in Preparation for Pre-Clinical Trials.

The use of magnetic resonance imaging (MRI) for guiding robotic surgical devices has shown great potential for performing precisely targeted and controlled interventions. To fully realize these benefits, devices must work safely within the tight confines of the MRI bore without negatively impacting image quality. Here we expand on previous work exploring MRI guided robots for neural interventions by presenting the mechanical design and assessment of a device for positioning, orienting, and inserting an interstitial ultrasound-based ablation probe. From our previous work we have added a 2 degree of freedom (DOF) needle driver for use with the aforementioned probe, revised the mechanical design to improve strength and function, and performed an evaluation of the mechanism's accuracy and effect on MR image quality. The result of this work is a 7-DOF MRI robot capable of positioning a needle tip and orienting it's axis with accuracy of 1.37 ± 0.06mm and 0.79° ± 0.41°, inserting it along it's axis with an accuracy of 0.06 ± 0.07mm, and rotating it about it's axis to an accuracy of 0.77° ± 1.31°. This was accomplished with no significant reduction in SNR caused by the robot's presence in the MRI bore, ≤ 10.3% reduction in SNR from running the robot's motors during a scan, and no visible paramagnetic artifacts.

Development of patient-controlled respiratory gating system based on visual guidance for magnetic-resonance image-guided radiation therapy.

The aim of this study is to develop a visual guidance patient-controlled (VG-PC) respiratory gating system for respiratory-gated magnetic-resonance image-guided radiation therapy (MR-IGRT) and to evaluate the performance of the developed system. The near-real-time cine planar MR image of a patient acquired during treatment was transmitted to a beam projector in the treatment room through an optical fiber cable. The beam projector projected the cine MR images inside the bore of the ViewRay system in order to be visible to a patient during treatment. With this visual information, patients voluntarily controlled their respiration to put the target volume into the gating boundary (gating window). The effect of the presence of the beam projector in the treatment room on the image quality of the MRI was investigated by evaluating the signal-to-noise ratio (SNR), uniformity, low-contrast detectability, high-contrast spatial resolution, and spatial integrity with the VG-PC gating system. To evaluate the performance of the developed system, we applied the VG-PC gating system to a total of seven patients; six patients received stereotactic ablative radiotherapy (SABR) and one patient received conventional fractionated radiation therapy. The projected cine MR images were visible even when the room light was on. No image data loss or additional time delay during delivery of image data were observed. Every indicator representing MRI quality, including SNR, uniformity, low-contrast detectability, high-contrast spatial resolution, and spatial integrity exhibited values higher than the tolerance levels of the manufacturer with the VG-PC gating system; therefore, the presence of the VG-PC gating system in the treatment room did not degrade the MR image quality. The average beam-off times due to respiratory gating with and without the VG-PC gating system were 830.3±278.2s and 1264.2±302.1s respectively (P=0.005). Consequently, the total treatment times excluding the time for patient setup with and without the VG-PC gating system were 1453.3±297.3s and 1887.2±469.6s, respectively, on average (P=0.005). The average number of beam-off events during whole treatment session was reduced from 457±154 times to 195±90 times by using the VG-PC gating system (P<0.001). The developed system could improve treatment efficiency when performing respiratory-gated MR-IGRT. The VG-PC gating system could be applied to any kind of bore-type radiotherapy machine.

Modified-BRISQUE as no reference image quality assessment for structural MR images

An effective and practical Image Quality Assessment (IQA) model is needed to assess the image quality produced from any new hardware or software in MRI. A highly competitive No Reference – IQA (NR – IQA) model called Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE) initially designed for natural images were modified to evaluate structural MR images. The BRISQUE model measures the image quality by using the locally normalized luminance coefficients, which were used to calculate the image features. The modified-BRISQUE model trained a new regression model using MR image features and Difference Mean Opinion Score (DMOS) from 775 MR images. Two types of benchmarks: objective and subjective assessments were used as performance evaluators for both original and modified-BRISQUE models. There was a high correlation between the modified-BRISQUE with both benchmarks, and they were higher than those for the original BRISQUE. There was a significant percentage improvement in their correlation values. The modified-BRISQUE was statistically better than the original BRISQUE. The modified-BRISQUE model can accurately measure the image quality of MR images. It is a practical NR-IQA model for MR images without using reference images.

RFID-Based Real-Time Navigation for Interventional Magnetic Resonance Imaging: Development and Evaluation of a Novel Tracking System

The purpose of this study was to evaluate the suitability of a novel radio-frequency identification (RFID)-based tracking system for intraoperative magnetic resonance imaging (MRI). A RFID tracking system was modified to fulfill MRI-compatibility and tested according to ASTM and NEMA. The influence of the RFID tracking system on MRI was analyzed in a phantom study using a half-Fourier acquisition single-shot turbospin echo (HASTE) and true fast imaging with steady-state precession sequence (TrueFISP) sequence. The RFID antenna was gradually moved closer to the isocenter of the MR scanner from 90 to 210 cm to investigate the influence of the distance. Furthermore, the RF was gradually changed between 865 and 869 MHz for a distance of 90 cm, 150 cm, and 210 cm to the isocenter of the magnet to investigate the influence of the frequency. The specific spatial resolution was measured with and without a permanent line of sight (LOS). After the modification of the reader, no significant change of the signal-to-noise ratio (SNR) could be observed with increasing distance of the RFID tracking system to the isocenter of the MR scanner. Also, different radio frequencies of the RFID tracking system did not influence the SNR of the MR-images significantly. The specific spatial resolution deviated on average by 8.97 ± 7.33 mm with LOS and 11.23 ± 12.03 mm without LOS from the reference system. The RFID tracking system had no relevant influence on the MR-image quality. RFID tracking solved the LOS problem. However, the spatial accuracy of the RFID tracking system has to be improved for medical usage.

Fully integrated 3D high-resolution multicontrast abdominal PET-MR with high scan efficiency.

To provide 3D multicontrast anatomical MR with high isotropic resolution and metabolic positron emission tomography (PET) images using a respiratory motion-compensated simultaneous PET-MR examination with high scan efficiency. Standard abdominal PET-MR examinations combine MR data obtained during multiple breath-holds with free-breathing PET acquisitions, limiting the achievable image resolution and potentially causing misalignment errors between breath-hold and free-breathing data. Here, a 3D free-breathing PET-MR acquisition is presented, yielding T1 and T2 -weighted MR images with an isotropic resolution of 1.5 mm3 . In addition, nonrigid respiratory motion information and respiratory-resolved attenuation-correction maps are obtained without an increase in scan time. Motion information is used in motion-compensated image reconstructions to improve MR and PET image quality while shortening scan times. The proposed approach was evaluated in 11 oncology patients and provided respiratory motion information with an accuracy of 1.3 ± 0.1 mm. Sharpness of anatomical features was increased by 19 ± 13% compared with the uncorrected MR images in a 54 ± 26% shorter scan time than a gated MR acquisition. The MR-based motion information improved uptake values (75 ± 94%) and resolution (16 ± 27%) of simultaneously acquired PET images. The proposed method provides motion-compensated 3D high-quality MR and PET images in a comprehensive and highly efficient examination. Magn Reson Med 79:900-911, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Synthetic MRI for Clinical Neuroimaging: Results of the Magnetic Resonance Image Compilation (MAGiC) Prospective, Multicenter, Multireader Trial

Synthetic MR imaging enables reconstruction of various image contrasts from 1 scan, reducing scan times and potentially providing novel information. This study is the first large, prospective comparison of synthetic-versus-conventional MR imaging for routine neuroimaging. A prospective multireader, multicase noninferiority trial of 1526 images read by 7 blinded neuroradiologists was performed with prospectively acquired synthetic and conventional brain MR imaging case-control pairs from 109 subjects (mean, 53.0 ± 18.5 years of age; range, 19-89 years of age) with neuroimaging indications. Each case included conventional T1- and T2-weighted, T1 and T2 FLAIR, and STIR and/or proton density and synthetic reconstructions from multiple-dynamic multiple-echo imaging. Images were randomized and independently assessed for diagnostic quality, morphologic legibility, radiologic findings indicative of diagnosis, and artifacts. Clinical MR imaging studies revealed 46 healthy and 63 pathologic cases. Overall diagnostic quality of synthetic MR images was noninferior to conventional imaging on a 5-level Likert scale (P < .001; mean synthetic-conventional, -0.335 ± 0.352; Δ = 0.5; lower limit of the 95% CI, -0.402). Legibility of synthetic and conventional morphology agreed in >95%, except in the posterior limb of the internal capsule for T1, T1 FLAIR, and proton-density views (all, >80%). Synthetic T2 FLAIR had more pronounced artifacts, including +24.1% of cases with flow artifacts and +17.6% cases with white noise artifacts. Overall synthetic MR imaging quality was similar to that of conventional proton-density, STIR, and T1- and T2-weighted contrast views across neurologic conditions. While artifacts were more common in synthetic T2 FLAIR, these were readily recognizable and did not mimic pathology but could necessitate additional conventional T2 FLAIR to confirm the diagnosis.

Super-pixel algorithm and group sparsity regularization method for compressed sensing MR image reconstruction

Exploiting the sparsity of MR signals, Compressed Sensing MR imaging (CS-MRI) is one of the most promising approaches to good quality MR image reconstruction from highly under-sampled k-space data. The group sparse method, which exploits additional sparse representations of the spatial group structure, can increase the overall degrees of sparsity, thereby leading to better reconstruction performance. In this work, an efficient superpixel/group assignment method, simple linear iterative clustering (SLIC), is incorporated to CS-MRI studies. A variable splitting strategy and classic alternating direct method are employed to solve the group sparse problem. This approach, termed Group Sparse reconstructions using Super-Pixel or SP-GS algorithm, was tested on three different types of MR images with different undersampling rates to validate its performance in reconstruction accuracy and computational efficiency. The results indicate that the proposed SP-GS method is capable of achieving significant improvements in reconstruction accuracy and computation efficiency when compared with the state-of-the-art reconstruction methods.

Reconfigurable multi‐channel RF crossbar switch matrix for MRI receiver front‐end

In this Letter, a highly reconfigurable crossbar transmission line switch matrix for magnetic resonance imaging (MRI) system is proposed. Unlike the conventional M × N crossbar switch configuration, the proposed structure can manipulate 2M × N matrix without doubling the area occupancy. Also, the proposed structure includes the signal loss-compensation circuitry based on inductor banks to enhance signal-to-noise ratio (SNR). Thus, for any required numbers of input and output channels, the proposed structure can reduce the overall size, the number of required component, and even increase the quality of MR images by SNR enhancement. The proposed structure was implemented and verified at 4-Tesla (170 MHz) MR system through the comparison of RF path loss, SNR and phantom test image qualities.

Cardiac and Respiratory Motion Correction for Simultaneous Cardiac PET/MR

Cardiac PET is a versatile imaging technique providing important diagnostic information about ischemic heart diseases. Respiratory and cardiac motion of the heart can strongly impair image quality and therefore diagnostic accuracy of cardiac PET scans. The aim of this study was to investigate a new cardiac PET/MR approach providing respiratory and cardiac motion-compensated MR and PET images in less than 5 min. Methods: Free-breathing 3-dimensional MR data were acquired and retrospectively binned into multiple respiratory and cardiac motion states. Three-dimensional cardiac and respiratory motion fields were obtained with a nonrigid registration algorithm and used in motion-compensated MR and PET reconstructions to improve image quality. The improvement in image quality and diagnostic accuracy of the technique was assessed in simultaneous 18F-FDG PET/MR scans of a canine model of myocardial infarct and was demonstrated in a human subject. Results: MR motion fields were successfully used to compensate for in vivo cardiac motion, leading to improvements in full width at half maximum of the canine myocardium of 13% ± 5%, similar to cardiac gating but with a 90% ± 57% higher contrast-to-noise ratio between myocardium and blood. Motion correction led to an improvement in MR image quality in all subjects, with an increase in sharpness of the canine coronary arteries of 85% ± 72%. A functional assessment showed good agreement with standard MR cine scans with a difference in ejection fraction of -2% ± 3%. MR-based respiratory and cardiac motion information was used to improve the PET image quality of a human in vivo scan. Conclusion: The MR technique presented here provides both diagnostic and motion information that can be used to improve MR and PET image quality. Reliable respiratory and cardiac motion correction could make cardiac PET results more reproducible.

The pilot study of radiology nursing intervention in abdominal 3-T Magnetic Resonance examination.

The aim of this study was to investigate the effect of radiology nursing intervention in abdominal examination at 3-T MRI. 60 patients with abdominal diseases were divided into two groups randomly: MR nursing intervention group and control group. All the patients underwent abdominal MR examination at 3-T. The MR nursing interventions were performed in nursing intervention group. The outcomes, including one-time success rate, the ratio of diagnosable MR images and the points of image quality, were compared between these two groups. The one-time success rates in control group and MR nursing intervention group were 66.67% and 96.67% with significant difference ( χ2 =9.017, P<0.05). The ratios of diagnosable images in the two groups were 76.67% and 96.67% with significant difference (χ2 =5.192, P<0.05). The points of MR image quality in the two groups were 1.87±0.86 and 2.33±0.55, respectively. There was significant difference between these two groups (t=-2.508, P<0.05). The effective nursing intervention can make the patients cooperation better in abdominal MR examination and improve the image quality significantly.

Analyzing Wavelet and Bidimensional Empirical Mode Decomposition of MRI Segmentation using Fuzzy C-Means Clustering

Image segmentation is a vital step in medical image processing. Magnetic resonance imaging (MRI) is used for brain tissues extraction in white and gray matter. These tissues extraction help in image segmentation applications such as radiotherapy planning, clinical diagnosis, treatment planning. This paper presents utilization of fuzzy C-means (FCM) clustering by using wavelet and bidimensional empirical mode decomposition (BEMD) to improve the quality of noisy MR images. The signal to noise ratio (SNR) value is calculated from FCM clustering data to examine the best segmentation technique. The experiment with synthetic Brain Web images has demonstrated the efficiency and robustness of the appropriate approach in segmenting medical MRI.

Magnetic Resonance Guided Radiation Therapy: Feasibility Study of a Linear Accelerator and Magnetic Resonance-on-Rails System

Comprehensive technical assessment of a MR-guided radiation therapy system, design, and integration of clinical workflows. A therapy vault was designed to house a Linac conventional setup and at the same time to allow a 1.5T MR-on-rails scanner to travel inside the vault at a pre-defined imaging location in the vicinity of the Linac. The Linac is a 6X FF/FFF system with a standard patient treatment table. The MR can travel on ceiling-mounted rails between a dedicated MR simulation suite and the Linac vault, the two rooms being separated by radiation and RF shielding doors. To allow MR imaging in the vault, the Linac and the patient table are stored behind specially designed RF doors. The separation between the Linac and MR was chosen to allow for a full magnetic field decoupling between all sub-components. With the MR at the imaging position the Linac/couch can be operated independently without posing safety risks or sub-optimal performance of the Linac/couch or MR scanner. The patient is moved between MR diagnostic table and Linac table via a patient transfer system operated as a hovercraft device. The MR/Linac configuration was assessed by considering the following aspects: a) magnetic field decoupling by experimental measurements – i.e. field mapping with Hall probes, magnetic pull forces on the Linac table, radiation beam specifications - output/flatness/symmetry, Linac on-board imaging, MR shimming and overall imaging performance – b) RF noise isolation (survey, MR testing), c) safety systems (interlocking system, redundancy measures), d) RT workflows (patient transfer, MR data flow, MR to kV matching), and QC procedures (MR image quality and B0 mapping, Linac/MR). Numerical simulations based on finite elements methods were also performed to model the entire MR-Linac environment including the Linac table. The MR scanner field was generated using a LP optimization technique and the Linac/table was represented as full-scale CAD geometries. The Linac beam performance and its kV imaging system were found to be unaffected by the MR presence in the treatment vault. The effects were measured and monitored over one year. The MR scanner was tested for optimal performance - the shimming and standard imaging procedures passed the clinical requirements. The numerical simulations and associated measurements for the magnetic field decoupling were in good agreement (forces, field mapping). RT workflows utilizing the kV and MR in-room imaging (independent and combined) are currently under development to facilitate the clinical integration of the system. Targeted applications are MR-based RT (adaptive) planning and guidance, fast imaging for the quantification of organ motion. Integrated quality control procedures were also developed for routine monitoring (MR shimming, image distortions – scanner-related and patient-induced, MR-to-kV matching). All aspects investigated support the feasibility of the MR-guided RT system for clinical deployment.

MR Performance Comparison of a PET/MR System Before and After SiPM-Based Time-of-Flight PET Detector Insertion

A silicon photomultiplier (SiPM)-based time-of-flight capable PET detector has been integrated with a 70 cm wide-bore 3T MR scanner for simultaneous whole-body imaging (MR750w, GE Healthcare, Waukesha, WI). After insertion of the PET detector, the final PET/MR bore is 60 cm wide (SIGNA PET/MR, GE Healthcare, Waukesha, WI). The MR performance was compared before and after the PET ring insertion. ${\rm B}_0$ homogeneity, ${\rm B}_1^ + $ uniformity of the body coil along with peak ${\rm B}_1^ + $ , coherent noise, and FBIRN (Function Biomedical Informatics Research Network) tests are used to compare the MR performance. It is shown that ${\rm B}_0$ homogeneity and coherent noise have not changed according to the system specifications. Peak ${\rm B}_1^ + $ is increased by 33% and ${\rm B}_1^ + $ inhomogeneity is increased by 4% after PET ring insertion due to a smaller diameter body coil design. The FBIRN test shows similar temporal stability before and after PET ring insertion. Due to a smaller body coil on the PET/MR system, the signal fluctuation to noise ratio (SFNR) and SNR for body receive coil, are improved by ${\sim} 40\%$ and ${\sim} 160\%$ for Echo Planar Imaging (EPI) and spiral sequences respectively. Comparison using RF- and gradient-intensive clinical sequences shows inserting the PET detectors into the wide-bore MRI has not compromised the MR image quality according to these tests.

Assessing MRI susceptibility artefact through an indicator of image distortion

Abstract Susceptibility artefacts in magnetic resonance imaging (MRI) caused by medical devices can result in a severe degradation of the MR image quality. The quantification of susceptibility artefacts is regulated by the ASTM standard which defines a manual method to assess the size of an artefact. This means that the estimated artefact size can be user dependent. To cope with this problem, we propose an algorithm to automatically quantify the size of such susceptibility artefacts. The algorithm is based on the analysis of a 3D surface generated from the 2D MR images. The results obtained by the automatic algorithm were compared to the manual measurements performed by study participants. The results show that the automatic and manual measurements follow the same trend. The clear advantage of the automated algorithm is the absence of the inter- and intra-observer variability. In addition, the algorithm also detects the slice containing the largest artefact which was not the case for the manual measurements.

Unenhanced 3D turbo spin echo MR angiography of lower extremity arteries: comparison with 128-MDCT angiography.

This study aimed to investigate the feasibility and diagnostic power of unenhanced 3D turbo spin echo MR angiography sequence (a technique based on subtraction of corresponding images acquired in diastole and systole, Syngo Native Space-Siemens healthcare) to identify peripheral artery disease (PAD). Thirty patients (619 arterial segments in total) suspected with PAD and who were assessed with lower extremity MDCT angiography were examined starting from the level of aortic bifurcation for both lower extremities by 3D native space MR angiography. Two readers assessed the image quality of native space MR angiography and number of lesions, their degrees of stenosis and localizations. The differences and compliance between the readers in the parameters assessed were investigated. Out of 619 segments; Reader 1 considered 187 segments (30.2%) and Reader 2 considered 177 segments (28.6%) to have poor and inadequate MR image quality. When compared to CTA, sensitivity, specificity and diagnostic accuracy of native space MR angiography were calculated as 81.0, 83.1, 82.6%, respectively, by Reader 1, while the same parameters were calculated as 69.9, 92.6, 84.9%, respectively, by Reader 2. When the two readers were examined together, sensitivity, specificity, diagnostic accuracy were found to be 76.3, 88.1, 83.7%, respectively, and the positive predictive value and negative predictive value was 70.3 and 89.9%, respectively. A significantly better image quality was acquired with the age group below 50years (p=0.002). Native space MR angiography technique can be used as the first-step imaging technique before contrast-enhanced examinations in young and middle age patients with suspected PAD and for patients with the risk of nephrogenic systemic fibrosis in chronic renal failure.

Evaluation of motion and its effect on brain magnetic resonance image quality in children.

Motion artifacts pose significant problems for the acquisition of MR images in pediatric populations. To evaluate temporal motion metrics in MRI scanners and their effect on image quality in pediatric populations in neuroimaging studies. We report results from a large pediatric brain imaging study that shows the effect of motion on MRI quality. We measured motion metrics in 82 pediatric patients, mean age 13.4years, in a T1-weighted brain MRI scan. As a result of technical difficulties, 5 scans were not included in the subsequent analyses. A radiologist graded the images using a 4-point scale ranging from clinically non-diagnostic because of motion artifacts to no motion artifacts. We used these grades to correlate motion parameters such as maximum motion, mean displacement from a reference point, and motion-free time with image quality. Our results show that both motion-free time (as a ratio of total scan time) and average displacement from a position at a fixed time (when the center of k-space was acquired) were highly correlated with image quality, whereas maximum displacement was not as good a predictor. Among the 77 patients whose motion was measured successfully, 17 had average displacements of greater than 0.5mm, and 11 of those (14.3%) resulted in non-diagnostic images. Similarly, 14 patients (18.2%) had less than 90% motion-free time, which also resulted in non-diagnostic images. We report results from a large pediatric study to show how children and young adults move in the MRI scanner and the effect that this motion has on image quality. The results will help the motion-correction community in better understanding motion patterns in pediatric populations and how these patterns affect MR image quality.

Metal Artifact Reduction MRI of Total Ankle Arthroplasty

Category: Ankle Arthritis Introduction/Purpose: Total ankle arthroplasty (TAA) is an often successful treatment for end-stage ankle arthritis; however, a subset of patient presents with ankle pain following TAA and concern for early failure. Although radiographs are often diagnostic, patients with normal radiographs and continued pain pose a diagnostic challenge. In those patients, magnetic resonance imaging (MRI) may be helpful to evaluate periprosthetic bone and soft tissues. Traditional high-bandwidth (high-BW) metal artifact reduction sequence (MARS) MRI lessens metal artifacts, but image distortions remain with Cobalt-Chromium implants. Slice- Encoding-Metal-Artifact-Correction (SEMAC) is a recently FDA-approved, advanced MARS technique that promises more powerful metal suppression. Therefore, we prospectively tested the hypothesis that SEMAC MARS MRI facilitates better metal reduction and visibility of periprosthetic structures than does traditional MARS MRI in patients with TAA. Methods: In this IRB-approved study, 20 volunteers [10 females/10 males; age, 59 (41-73) years, 15 (3-24) months post- operatively] with TAA were prospectively enrolled. The research protocol consisted of high-BW and SEMAC MARS MRI using a clinical 1.5 Tesla MRI scanner and a dedicated boot-shaped MRI coil. For each technique, intermediate-weighted and fat- suppressed MR images were obtained in axial, sagittal and coronal orientation. Three observes (2 foot/ankle surgeons and 1 musculoskeletal radiologist) evaluated the high-BW and SEMAC MR images in an independent, random and blinded fashion. Equidistance 5-point Likert scales (1=non-diagnostic, 5=very good) were used to grade image quality as well as the quality of metal suppression and visibility of bone-metal interfaces, tendons, ligaments, bone and joints. Differences between the two MARS techniques were assessed with a Kruskall-Wallis test, and interobserver agreement was graded with Intraclass-Correlation- Coefficient (ICC). Bonferroni-corrected p-values ≤ 0.01 were considered significant. Results: All 20 subjects completed the research protocol. There was good agreement between observers (ICC = 0.79; 95% CI, 0.78-0.80). Image quality of high-BW and SEMAC MR images was similar for tissue contrast, fat suppression, and fluid brightness, whereas image sharpness was one interval higher on high-BW images than on SEMAC images (p &lt; 0.01). Metal reduction of TAA components was significantly better (p &lt; 0.01) on SEMAC images (very good) than on high-BW images (poor-to-adequate). At level of the implants, long flexor and peroneal tendons, deep deltoid, syndesmotic and lateral collateral ligaments, and medial and lateral gutters were significantly better seen (p &lt; 0.01) on SEMAC images (good-to-very good) than on high-BW images (poor-to- adequate). Similar visibility (good-to-very good) was found for the remainder of the tendons, ligaments, bones and joints. Conclusion: Based on the results of our study, we accept the hypothesis that SEMAC MARS MRI outperforms traditional high- BW MARS MRI in the degree of metal artifact reduction as well as visibility of bone implant interfaces and periprosthetic tendons and ligaments at level of the joint line. We believe advanced MARS MRI can be a valuable clinical tool to assess osseous integration and soft tissue lesions in patients following TAA.