Artifact Size Research Articles

Image quality comparisons of coil setups in 3T MRI for brain and head and neck radiotherapy simulations.

MRI is increasingly used for brain and head and neck radiotherapy treatment planning due to its superior soft tissue contrast. Flexible array coils can be arranged to encompass treatment immobilization devices, which do not fit in diagnostic head/neck coils. Selecting a flexible coil arrangement to replace a diagnostic coil should rely on image quality characteristics and patient comfort. We compared image quality obtained with a custom UltraFlexLarge18 (UFL18) coil setup against a commercial FlexLarge4 (FL4) coil arrangement, relative to a diagnostic Head/Neck20 (HN20) coil at 3T. The large American College of Radiology (ACR) MRI phantom was scanned monthly in the UFL18, FL4, and HN20 coil setup over 2 years, using the ACR series and three clinical sequences. High-contrast spatial resolution (HCSR), image intensity uniformity (IIU), percent-signal ghosting (PSG), low-contrast object detectability (LCOD), signal-to-noise ratio (SNR), and geometric accuracy were calculated according to ACR recommendations for each series and coil arrangement. Five healthy volunteers were scanned with the clinical sequences in all three coil setups. SNR, contrast-to-noise ratio (CNR) and artifact size were extracted from regions-of-interest along the head for each sequence and coil setup. For both experiments, ratios of image quality parameters obtained with UFL18 or FL4 over those from HN20 were formed for each coil setup, grouping the ACR and clinical sequences. Wilcoxon rank-sum tests revealed significantly higher (p<0.001) LCOD, IIU and SNR, and lower PSG ratios with UFL18 than FL4 on the phantom for the clinical sequences, with opposite PSG and SNR trends for the ACR series. Similar statistical tests on volunteer data corroborated that SNR ratios with UFL18 (0.58±0.19) were significantly higher (p<0.001) than with FL4 (0.51±0.18) relative to HN20. The custom UFL18 coil setup was selected for clinical application in MR simulations due to the superior image quality demonstrated on a phantom and volunteers for clinical sequences and increased volunteer comfort.

Safety and Feasibility of a Sheath Cryoprobe for Bronchoscopic Transbronchial Biopsy: The FROSTBITE Trial

Background: Bronchoscopic lung biopsy is typically performed using transbronchial forceps. However, this method is limited by small sample size and presence of crush artifact. Cryobiopsy offers the potential to overcome these limitations with larger artifact-free samples but has not been widely adopted due to concerns over increased rates of bleeding and pneumothorax. A new, smaller 1.1-mm cryoprobe has been developed that operates in a similar fashion to forceps, though the safety profile of this cryoprobe has not yet been prospectively studied. Objective: The aim of this study was to investigate the safety of transbronchial biopsy using a novel 1.1-mm cryoprobe. Methods: This prospective, single-arm study enrolled patients referred for transbronchial biopsy. All procedures were performed using the 1.1-mm cryoprobe with oversheath. The primary outcome was the composite of significant complications related to the cryobiopsy procedure (bleeding Grade ≥3, pneumothorax Grade ≥2, and respiratory failure). Bleeding and pneumothorax were graded according to previously published scales. Results: Fifty participants from two academic medical centers underwent transbronchial cryobiopsy. Indications for biopsy included evaluation of lung transplant allograft (50%), diffuse lung disease (44%), and pulmonary parenchymal lesion (6%). There were two pneumothoraces (4%), neither of which required aspiration or chest tube placement. There were no Grade 3 or 4 bleeding events. Mild bleeding (Grade ≤2) was observed in 25 cases (50%). No complications occurred that met the a priori primary outcome of bleeding Grade ≥3, pneumothorax Grade ≥2, and respiratory failure. Conclusions: Transbronchial cryobiopsy using a 1.1-mm cryoprobe is feasible with an acceptable safety profile.

Depth-of-Field Segmentation for Near-lossless Image Compression and 3D Reconstruction

Over the years, photometric three-dimensional (3D) reconstruction gained increasing importance in several disciplines, especially in cultural heritage preservation. While increasing sizes of images and datasets enhanced the overall reconstruction results, requirements in storage got immense. Additionally, unsharp areas in the background have a negative influence on 3D reconstructions algorithms. Handling the sharp foreground differently from the background simultaneously helps to reduce storage size requirements and improves 3D reconstruction results. In this article, we examine regions outside the Depth of Field (DoF) and eliminate their inaccurate information to 3D reconstructions. We extract DoF maps from the images and use them to handle the foreground and background with different compression backends, making sure that the actual object is compressed losslessly. Our algorithm achieves compression rates between 1:8 and 1:30 depending on the artifact and DoF size and improves the 3D reconstruction.

Histological assessment of new cholangioscopy-guided forceps in ERCP biliary stricture sampling: a blinded comparative study.

Background and study aims Obtaining quality tissue during ERCP biliary stricture sampling is of paramount importance for a timely diagnosis. While single-operator cholangioscopy (SOC)-guided biopsies have been suggested to be the superior biliary tissue acquisition modality given direct tissue visualization, less is known about the specimen histological quality. We aimed to analyze the specimen quality of SOC biopsies and compare the new generation forceps with prior “legacy” forceps. Patients and methods Patients who underwent SOC from January 2017-August 2021 for biliary sampling were reviewed. In February 2020, the SOC-guided biopsy forceps were changed from legacy SpyBite to the SpyBite Max forceps (max). Specimens were assessed by blinded pathologists for crush artifact (none, mild, or severe) and gross size (greatest dimension in mm). Crush artifact and gross size were compared between the two groups. The diagnostic performance characteristics for cholangiocarcinoma (CCA), were assessed in an exploratory fashion. Results Eighty-one patients (max = 27, legacy = 54) with similar baseline characteristics were included in this study. On blinded pathological assessment, 58 % had crush artifact, without significant differences between the two groups (Max 63 % vs. Legacy 56 %; P = 0.64). A similar mean specimen size was found (max 3 mm vs. legacy 3.2 mm; P = 0.24). The overall prevalence of CCA was 40 %. The sensitivity, specificity, positive predictive value, and negative predictive value of the entire cohort using a combination of cytology, fluorescence in situ hybridization, and SOC-guided biopsies were 78.1 %, 91.8 %, 86.2 %, and 86.5 %, respectively. No difference between legacy or max groups was found. Conclusions A high rate of crush artifact was found in SOC-guided biopsy specimens. Further investigation regarding proper biopsy technique and handling is necessary to increase the diagnostic yield with SOC-guided biopsies.

The Impact of View- Angle Tilting and Slice Encoding for Metal Artifact Correction Methods on the Metal Artifact Reduction in Magnetic Resonance Imaging of the Knee Prosthesis

Purpose: At Magnetic Resonance Imaging (MRI), artifacts arising from metal implants are an obstacle to obtaining optimal images. This study aimed to evaluate the impact of View-Angle Tilting (VAT) and Slice Encoding for Metal Artifact Correction (SEMAC) techniques for the artifact reduction of patients during knee MRI with metal implants.&#x0D; Materials and Methods: The MR images without any intervention of the knee from 20 patients with knee prostheses were used. The VAT and SEMAC metal artifact reduction techniques were applied to all the MR images. Volume and mass of the metal prosthesis were quantified using the MATLAB program and compared with the real measurements using nonparametric Wilcoxon tests in SPSS software. The qualitative analysis was performed by two blinded observers regarding the score of artifact size, distortions, image quality, and visualization of bone marrow and soft tissues adjacent to metal implants. In addition, Cohen’s kappa values were used for inter-observer agreement.&#x0D; Results: The average volume of the platinum based on the conventional, VAT, and SEMAC methods was estimated at 14.22 ± 0.43, 14.05 ± 0.4, and 13.3 ± 0.45 cm3, respectively. The statistical analysis showed no significant difference (P &gt; 0.05) between the mean value of the platinum volume for the SEMAC method and the real measurement (13.6 ± 0.33 cm3). Furthermore, regarding the conventional, VAT, and SEMAC sequences, the mean mass of the platinum was obtained at 305.02 ± 9.22, 301.37 ± 8.58, and 285.28 ± 9.65 g, respectively, with the P-Value of 0.005, 0.009, and 0.268, compared to the real measurements (286.81±8.75 g). Notably, the blinded readers demonstrated that the SEMAC method was remarkably superior quality compared with VAT and conventional acquisitions (P-Value&lt; 0.05).&#x0D; Conclusion: The knee prosthesis metal artifact was reduced using the VAT and SEMAC techniques, in a way that, the reduction was significant by the SEMAC method. In addition, concerning the qualitative observer analysis, the application of the SEMAC technique provides improved visualization of tissue structures adjacent to metal implants.

Applications of cryobiopsy in airway, pleural, and parenchymal disease

Introduction :Cryobiopsy is a novel diagnostic technique for thoracic diseases which has been extensively investigated over the past 20 years. It was originally proposed for the diagnosis of endobronchial lesions and diffuse parenchymal lung disease due to limitations of conventional sampling techniques including small size and presence of artifacts. Areas covered :We will review recent evidence related to the expanding use of cryobiopsy in thoracic diseases. To identify references, the MEDLINE database was searched from database inception until May 2022 for case series, cohort studies, randomized controlled trials, systematic reviews and meta-analyses related to cryobiopsy. Expert opinion Cryobiopsy has expanding applications in the field of thoracic diseases. Evidence to support transbronchial cryobiopsy as an alternative to surgical lung biopsy is increasing and was recently endorsed as a conditional recommendation by the latest American Thoracic Society guideline update for Idiopathic Pulmonary Fibrosis. Developments in technology and technique, in particular the availability of a 1.1 mm flexible cryoprobe, have extended applications to pulmonary diseases, including diagnosis of interstitial lung diseases, peripheral pulmonary lesions, and lung transplant rejection.

MRI compatibility of orthodontic brackets and wires: systematic review article

BackgroundBefore the magnetic resonance imaging (MRI) examination fixed orthodontic devices, such as brackets and wires, cause challenges not only for the orthodontist but also for the radiologist. Essentially, the MRI-safe scan of the fixed orthodontic tools requires a proper guideline in clinical practice. Therefore, this systematic review aimed to examine all aspects of MRI-safe scan, including artifact, thermal, and debonding effects, to identify any existing gaps in knowledge in this regard and develop an evidence-based protocol.MethodsThe Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) statement was used in this study. The clinical question in “PIO” format was: “Does MRI examination influence the temperature of the orthodontic devices, the size of artifacts, and the debonding force in patients who have fixed orthodontic bracket and/or wire?” The search process was carried out in PubMed, PubMed Central, Scopus, and Google Scholar databases. The search resulted in 1310 articles. After selection according to the eligibility criteria, 18 studies were analyzed by two reviewers. The risk of bias was determined using the Quality In Prognosis Studies tool.ResultsOut of the eligible 18 studies, 10 articles examined the heating effect, 6 were about the debonding effect, and 11 measured the size of artifact regarding brackets and wires. Considering the quality assessment, the overall levels of evidence were high and medium.The published studies showed that heating and debonding effects during MRI exposure were not hazardous for patients. As some wires revealed higher temperature changes, it is suggested to remove the wire or insert a spacer between the appliances and the oral mucosa. Based on the material, ceramic and plastic brackets caused no relevant artifact and were MRI-safe. Stainless steel brackets and wires resulted in susceptibility artifacts in the orofacial region and could cause distortion in the frontal lobe, orbits, and pituitary gland. The retainer wires showed no relevant artifact.ConclusionsIn conclusion, the thermal and debonding effects of the fixed orthodontic brackets and wires were irrelevant or resoluble; however, the size of the artifacts was clinically relevant and determined most significantly the feasibility of fixed brackets and wires in MRI examination.

Photon-Counting Detector CT Virtual Monoengergetic Images for Cochlear Implant Visualization-A Head to Head Comparison to Energy-Integrating Detector CT.

Cochlear implants (CIs) are the primary treatment method in patients with profound sensorineural hearing loss. Interpretation of postoperative imaging with conventional energy-integrating detector computed tomography (EID-CT) following CI surgery remains challenging due to metal artifacts. Still, the photon-counting detector (PCD-CT) is a new emerging technology with the potential to eliminate these problems. This study evaluated the performance of virtual monoenergetic (VME) EID-CT images versus PCD-CT in CI imaging. In this cadaveric study, two temporal bone specimens with implanted CIs were scanned with EID-CT and PCD-CT. The images were assessed according to the visibility of interelectrode wire, size of electrode contact, and diameter of halo artifacts. The visibility of interelectrode wire sections was significantly higher when reviewing PCD-CT images. The difference in diameter measurements for electrode contacts between the two CT scanner modalities showed that the PCD-CT technology generally led to significantly larger diameter readings. The larger measurements were closer to the manufacturer’s specifications for the CI electrode. The size of halo artifacts surrounding the electrode contacts did not differ significantly between the two imaging modalities. PCT-CT imaging is a promising technology for CI imaging with improved spatial resolution and better visibility of small structures than conventional EID-CT.

Experimental and Modeling Based Investigations of Process Parameters on a Novel, 3D Printed and Self-Insulated 24-Well, High-Throughput 3D Microelectrode Array Device for Biological Applications

We have investigated the effect of printing angle and device orientation on the development of high-throughput (HT), self-insulated, 3D printed 3D Microelectrode Arrays (HT-3DMEAs) for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro</i> biotechnology applications and its repercussions for optical, mechanical, and electrical properties of the final device. Makerspace based development using micro-Stereolithography ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\mu }$ </tex-math></inline-formula> SLA) 3D printing and ink casting technique were carried out to develop a 24-well device with self-insulated 3D microelectrodes, with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100% yield and 7 microtowers per well</i> acting as supports for the microelectrodes. These MEAs were further characterized by Optical Microscopy, Electrical Impedance Spectroscopy (EIS), Laser Scanning Confocal Microscopy, Scanning Electron Microscopy (SEM), and UV-Vis Spectroscopy. Surface flatness required for the microelectrode formation was obtained for 0° tilt printed version at top-side orientation. The process optimization and results were interpreted using established <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\mu }$ </tex-math></inline-formula> SLA theory and COMSOL modeling. Artifact size determination with a maximum 6% error was predicted. Experimental finding on the microelectrode formation, i.e., a potentially useful microbullet shape was observed and confirmed using Laser Confocal and SEM microscopy characterization and COMSOL simulation. These results allow for greater understanding of the device-process relationships for HT-3DMEAs and paves the pathway towards scalability, denser electrodes and even higher well counts for HT screening in biotechnology. [2021-0201]

STEAM-DWI as a robust alternative to EPI-DWI: Evaluation in pediatric brain MRI

PurposeDiffusion-weighted imaging (DWI) is an essential element of almost every brain MRI examination. The most widely applied DWI technique, a single-shot echo-planar imaging DWI (EPI-DWI) sequence, suffers from a high sensitivity to magnetic field inhomogeneities. As an alternative, a single-shot stimulated echo acquisition mode diffusion-weighted MRI (STEAM-DWI) has recently been re-introduced after it became significantly faster. The aim of the study was to investigate the applicability of STEAM-DWI as a substitute to EPI-DWI in a daily routine of pediatric radiology.MethodsRetrospectively, brain MRI examinations of 208 children with both EPI-DWI and STEAM-DWI were assessed. Visual resolution and diagnostic confidence were evaluated, the extent of susceptibility artifacts was quantified, and contrast-to-noise ratio was calculated in case of diffusion restriction. Furthermore, the correlation of apparent diffusion coefficient values between STEAM-DWI and EPI-DWI was tested.ResultsSTEAM-DWI was inferior to EPI-DWI in visual resolution but with higher diagnostic confidence and lower artifact size. The apparent diffusion coefficient values of both sequences demonstrated excellent correlation. The contrast-to-noise ratio of STEAM-DWI was only half of that of EPI-DWI (58% resp. 112%).ConclusionSTEAM-DWI is a robust alternative to EPI-DWI when increased susceptibility artifacts are to be expected. Drawbacks are a lower contrast-to-noise ratio and poorer visual resolution.

Re-Do endoscopic third ventriculostomy. Retrospective analysis of 13 patients.

Indication for endoscopic third ventriculostomy (ETV) in the treatment for noncommunicating hydrocephalus is widely accepted. There is controversy regarding the indication of a second procedure (re-ETV) when the first has failed. The objective of this work is to revise ETV failures in a series in which re-ETV was performed and to describe the factors related to its prognosis. Retrospective study of pediatric patients with ETV failure treated by re-ETV between 2003 and 2018. Gender, age in first and second ETV, time to failure of first ETV, etiology of hydrocephalus, previous presence of shunt, ETV-SS in the first and second ETV, intraoperative findings, success of the second procedure and follow-up were collected. The ETV-SS result was grouped into high (≥80), moderate (50-70) or low (≤40) scores. Endoscopic procedure failure was considered clinical worsening or the absence of radiological criteria for improvement (reduction in ventricular size or presence of ETV flow artifact in the floor of third ventricle). Of 97 ETV carried out in this period, 47 failures were registered, with 13 re-ETV performed. Of these, 8 were classified as successful (61.53%). Re-ETV was successful in 4/4 cases in which etiology was tectal tumor or aqueduct stenosis. In the group with a high ETV-SS score there was a higher rate of success (75%) than in the group with a moderate score (40%). 9 patients presented shunt prior to first ETV and in them, success was 66.6% compared to 50% in the group without prior shunt. All re-ETV were performed without complications. In 11 of the 13 procedures a closed stoma was found and the remaining 2 cases, we found a punctate opening. The mean follow-up after re-ETV was 61.23 months. The selection of patients for re-VET should be cautious. Factors such as age, etiology, and previous shunt (ETV-SS factors) have prognostic influence. However, there are specific factors which indicate favorable prognostic for re-VET such as a longer time to failure of the first procedure, the finding of a closed/punctate stoma or the loss of flow artifact in the follow-up MRI.

Characterizing Cochlear Implant Magnet-Related MRI Artifact.

To evaluate cochlear implant (CI) magnet-related MRI artifact shape and size, as well as imaging indications and clinical adequacy of scans. A retrospective chart review was performed for patients undergoing CI and subsequent MRI head imaging from 2014 to 2020 at a single institution. Indications and adequacy of each scan was recorded, and interpretability compared by indication. Magnet-related artifact size was determined by performing ellipsoid modeling at axial slice of greatest signal loss. Artifact radius in centimeters was calculated for 5 sequence categories, and size compared between sequences, manufacturers, and by time from implantation. Twenty patients underwent 58 head MRI scans. Approximately 76% of MRIs (n = 44) for 70% of patients (n = 14) were performed for indications known of prior to implantation; the remainder were performed during workup of new issues. Desired structures were interpretable in 23 (52%) of known-indication MRIs and 8 (57%) of new-indication MRIs, without significant difference (P = .751). Magnet-related artifact magnitude, compared to the reference T1-weighted fast spin echo (FSE) (4.47 cm), was similar in T2 FSE (4.57 cm, P = .068) and T1 gradient echo (GRE) sequences (4.79 cm, P = .28), but significantly greater in T2 GRE (6.86, P < .0001) and DWI (7.56 cm, P < .0001) sequences. DWI and T2 GRE sequences are less useful in MRI evaluation of CI patients. With a more favorable artifact profile, T1 FSE, T2 FSE, and T1 GRE sequences more likely yield clinically useful information. The large proportion of scans performed for known pathology represents an opportunity to optimize for magnet location preoperatively.

New-Generation Low-Field Magnetic Resonance Imaging of Hip Arthroplasty Implants Using Slice Encoding for Metal Artifact Correction: First In Vitro Experience at 0.55 T and Comparison With 1.5 T.

Despite significant progress, artifact-free visualization of the bone and soft tissues around hip arthroplasty implants remains an unmet clinical need. New-generation low-field magnetic resonance imaging (MRI) systems now include slice encoding for metal artifact correction (SEMAC), which may result in smaller metallic artifacts and better image quality than standard-of-care 1.5 T MRI. This study aims to assess the feasibility of SEMAC on a new-generation 0.55 T system, optimize the pulse protocol parameters, and compare the results with those of a standard-of-care 1.5 T MRI. Titanium (Ti) and cobalt-chromium total hip arthroplasty implants embedded in a tissue-mimicking American Society for Testing and Materials gel phantom were evaluated using turbo spin echo, view angle tilting (VAT), and combined VAT and SEMAC (VAT + SEMAC) pulse sequences. To refine an MRI protocol at 0.55 T, the type of metal artifact reduction techniques and the effect of various pulse sequence parameters on metal artifacts were assessed through qualitative ranking of the images by 3 expert readers while taking measured spatial resolution, signal-to-noise ratios, and acquisition times into consideration. Signal-to-noise ratio efficiency and artifact size of the optimized 0.55 T protocols were compared with the 1.5 T standard and compressed-sensing SEMAC sequences. Overall, the VAT + SEMAC sequence with at least 6 SEMAC encoding steps for Ti and 9 for cobalt-chromium implants was ranked higher than other sequences for metal reduction ( P < 0.05). Additional SEMAC encoding partitions did not result in further metal artifact reductions. Permitting minimal residual artifacts, low magnetic susceptibility Ti constructs may be sufficiently imaged with optimized turbo spin echo sequences obviating the need for SEMAC. In cross-platform comparison, 0.55 T acquisitions using the optimized protocols are associated with 45% to 64% smaller artifacts than 1.5 T VAT + SEMAC and VAT + compressed-sensing/SEMAC protocols at the expense of a 17% to 28% reduction in signal-to-noise ratio efficiency. B 1 -related artifacts are invariably smaller at 0.55 T than 1.5 T; however, artifacts related to B 0 distortion, although frequently smaller, may appear as signal pileups at 0.55 T. Our results suggest that new-generation low-field SEMAC MRI reduces metal artifacts around hip arthroplasty implants to better advantage than current 1.5 T MRI standard of care. While the appearance of B 0 -related artifacts changes, reduction in B 1 -related artifacts plays a major role in the overall benefit of 0.55 T.

Optimised passive marker device visibility and automatic marker detection for 3-T MRI-guided endovascular interventions: a pulsatile flow phantom study

BackgroundPassive paramagnetic markers on magnetic resonance imaging (MRI)-compatible endovascular devices induce susceptibility artifacts, enabling MRI-visibility and real-time MRI-guidance. Optimised visibility is crucial for automatic detection and device tracking but depends on MRI technical parameters and marker characteristics. We assessed marker visibility and automatic detection robustness for varying MRI parameters and marker characteristics in a pulsatile flow phantom.MethodsGuidewires with varying iron(II,III) oxide nanoparticle (IONP) concentration markers were imaged using gradient-echo (GRE) and balanced steady-state free precession (bSSFP) sequences at 3 T. Furthermore, echo time (TE), slice thickness (ST) and phase encoding direction (PED) were varied. Artifact width was measured and contrast-to-noise ratios were calculated. Marker visibility and image quality were scored by two MRI interventional radiologists. Additionally, a deep learning model for automatic marker detection was trained and the effects of the parameters on detection performance were evaluated. Two-tailed Wilcoxon signed-rank tests were used (significance level, p < 0.05).ResultsMedan artifact width (IQR) was larger in bSSFP compared to GRE images (12.7 mm (11.0–15.2) versus 8.4 mm (6.5–11.0)) (p < 0.001) and showed a positive relation with TE and IONP concentration. Switching PED and doubling ST had limited effect on artifact width. Image quality assessment scores were higher for GRE compared to bSSFP images. The deep learning model automatically detected the markers. However, the model performance was reduced after adjusting PED, TE, and IONP concentration.ConclusionMarker visibility was sufficient and a large range of artifact sizes was generated by adjusting TE and IONP concentration. Deep learning-based marker detection was feasible but performance decreased for altered MR parameters. These factors should be considered to optimise device visibility and ensure reliable automatic marker detectability in MRI-guided endovascular interventions.

Effective magnetic susceptibility of 3D-printed porous metal scaffolds.

3D-printed porous metal scaffolds are a promising emerging technology in orthopedic implant design. Compared to solid metal implants, porous metal implants have lower magnetic susceptibility values, which have a direct impact on imaging time and image quality. The purpose of this study is to determine the relationship between porosity and effective susceptibility through quantitative estimates informed by comparing coregistered scanned and simulated field maps. Five porous scaffold cylinders were designed and 3D-printed in titanium alloy (Ti-6Al-4V) with nominal porosities ranging from 60% to 90% using a cellular sheet-based gyroid design. The effective susceptibility of each cylinder was estimated by comparing acquired B0 field maps against simulations of a solid cylinder of varying assigned magnetic susceptibility, where the orientation and volume of interest of the simulations was informed by a custom alignment phantom. Magnitude images and field maps showed obvious decreases in artifact size and field inhomogeneity with increasing porosity. The effective susceptibility was found to be linearly correlated with porosity (R2 =0.9993). The extrapolated 100% porous (no metal) magnetic susceptibility was -9.9ppm, closely matching the expected value of pure water (-9ppm), indicating a reliable estimation of susceptibility. Effective susceptibility of porous metal scaffolds is linearly correlated with porosity. Highly porous implants have sufficiently low effective susceptibilities to be more amenable to routine imaging with MRI.

Artifact reduction of coaxial needles in magnetic resonance imaging-guided abdominal interventions at 1.5 T: a phantom study

Needle artifacts pose a major limitation for MRI-guided interventions, as they impact the visually perceived needle size and needle-to-target-distance. The objective of this agar liver phantom study was to establish an experimental basis to understand and reduce needle artifact formation during MRI-guided abdominal interventions. Using a vendor-specific prototype fluoroscopic T1-weighted gradient echo sequence with real-time multiplanar acquisition at 1.5 T, the influence of 6 parameters (flip angle, bandwidth, matrix, slice thickness, read-out direction, intervention angle relative to B0) on artifact formation of 4 different coaxial MR-compatible coaxial needles (Nitinol, 16G–22G) was investigated. As one parameter was modified, the others remained constant. For each individual parameter variation, 2 independent and blinded readers rated artifact diameters at 2 predefined positions (15 mm distance from the perceived needle tip and at 50% of the needle length). Differences between the experimental subgroups were assessed by Bonferroni-corrected non-parametric tests. Correlations between continuous variables were expressed by the Bravais–Pearson coefficient and interrater reliability was quantified using the intraclass classification coefficient. Needle artifact size increased gradually with increasing flip angles (p = 0.002) as well as increasing intervention angles (p < 0.001). Artifact diameters differed significantly between the chosen matrix sizes (p = 0.002) while modifying bandwidth, readout direction, and slice thickness showed no significant differences. Interrater reliability was high (intraclass correlation coefficient 0.776–0.910). To minimize needle artifacts in MRI-guided abdominal interventions while maintaining optimal visibility of the coaxial needle, we suggest medium-range flip angles and low intervention angles relative to B0.

Development and evaluation of a numerical simulation approach to predict metal artifacts from passive implants in MRI

ObjectiveThis study presents the development and evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment that can be applied to improve the testing procedure for MR image artifacts in medical implants according to ASTM F2119.MethodsThe numerical approach is validated by comparing simulations and measurements of two metallic test objects made of titanium and stainless steel at three different field strengths (1.5T, 3T and 7T). The difference in artifact size and shape between the simulated and measured artifacts were evaluated. A trend analysis of the artifact sizes in relation to the field strength was performed.ResultsThe numerical simulation approach shows high similarity (between 75% and 84%) of simulated and measured artifact sizes of metallic implants. Simulated and measured artifact sizes in relation to the field strength resulted in a calculation guideline to determine and predict the artifact size at one field strength (e.g., 3T or 7T) based on a measurement that was obtained at another field strength only (e.g. 1.5T).ConclusionThis work presents a novel tool to improve the MR image artifact testing procedure of passive medical implants. With the help of this tool detailed artifact investigations can be performed, which would otherwise only be possible with substantial measurement effort on different MRI systems and field strengths.

The Effect of Cosmetics on Magnetic Resonance Imaging: Focusing on Eye Cosmetics

Magnetic susceptibility artifacts affect image quality and also affect patient safety. Most magnetic resonance imaging scans are conducted without removing makeup. However, cosmetics can contain metal ingredients which can cause magnetic susceptibility artifacts. This study aims to evaluate the effect of artifacts found in cosmetics on magnetic resonance imaging and compares them according to the type of cosmetic, magnitudes of magnetic fields, and sequences. A total of 32 target materials were used: 24 eyeshadows, 4 mascara, and 4 eyeliners. Experiments used four sequences: spin echo, turbo spin echo, gradient echo, and echo planar imaging to obtain coronal and axial plane images of each target material. In the coronary plane image, the target material was measured vertically from the attached surface to the point where the artifact reached. Magnetic susceptibility artifacts occurred in all 32 cosmetics used in the experiment. The maximum size of artifacts was seen in gradient echo and echo planar imaging. Magnetic susceptibility artifacts were larger at 3 T than at 1.5 T, with a maximum size of 9.05 mm at a gradient echo of 3.0 T. Therefore, in this study, we found that cosmetics affect images due to magnetic susceptibility artifacts, and that magnetic resonance imaging scans can be affected by these artifacts, especially around the eye, where makeup should be removed. In addition, because cosmetics produce magnetic susceptibility artifacts, there may be a risk of burns being caused by heat, therefore, it is necessary to guide the removal of makeup or check for abnormal reactions during magnetic resonance imaging scans.

Lattice continuum-limit study of nucleon parton quasidistribution functions

The parton quasidistribution functions approach provides a path to computing parton distribution functions (PDFs) using lattice QCD. This approach requires matrix elements of a power-divergent operator in a nucleon at high momentum and one generically expects discretization effects starting at first order in the lattice spacing $a$. Therefore, it is important to demonstrate that the continuum limit can be reliably taken and to understand the size and shape of lattice artifacts. In this work, we report a calculation of isovector unpolarized and helicity PDFs using lattice ensembles with ${N}_{f}=2+1+1$ Wilson twisted mass fermions, a pion mass of approximately 370 MeV, and three different lattice spacings. Our results show a significant dependence on $a$, and the continuum extrapolation produces a better agreement with phenomenology. The latter is particularly true for the antiquark distribution at small momentum fraction $x$, where the extrapolation changes its sign.

Re-Do endoscopic third ventriculostomy. Retrospective analysis of 13 patients

ObjetivesIndication for endoscopic third ventriculostomy (ETV) in the treatment for noncommunicating hydrocephalus is widely accepted. There is controversy regarding the indication of a second procedure (re-ETV) when the first has failed. The objective of this work is to revise ETV failures in a series in which re-ETV was performed and to describe the factors related to its prognosis. MethodRetrospective study of pediatric patients with ETV failure treated by re-ETV between 2003 and 2018. Gender, age in first and second ETV, time to failure of first ETV, etiology of hydrocephalus, previous presence of shunt, ETV-SS in the first and second ETV, intraoperative findings, success of the second procedure and follow-up were collected. The ETV-SS result was grouped into high (≥ 80), moderate (50−70) or low (≤ 40) scores. Endoscopic procedure failure was considered clinical worsening or the absence of radiological criteria for improvement (reduction in ventricular size or presence of ETV flow artifact in the floor of third ventricle). ResultsOf 97 ETV carried out in this period, 47 failures were registered, with 13 re-ETV performed. Of these, 8 were classified as successful (61.53%). Re-ETV was successful in 4/4 cases in which etiology was tectal tumor or aqueduct stenosis. In the group with a high ETV-SS score there was a higher rate of success (75%) than in the group with a moderate score (40%). 9 patients presented shunt prior to first ETV and in them, success was 66.6% compared to 50% in the group without prior shunt. All re-ETV were performed without complications. In 11 of the 13 procedures a closed stoma was found and the remaining 2 cases, we found a punctate opening. The mean follow-up after re-ETV was 61.23 months. ConclusionThe selection of patients for re-VET should be cautious. Factors such as age, etiology, and previous shunt (ETV-SS factors) have prognostic influence. However, there are specific factors which indicate favorable prognostic for re-VET such as a longer time to failure of the first procedure, the finding of a closed/punctate stoma or the loss of flow artifact in the follow-up MRI.