Artifact Volume Research Articles

Reducing Metal Artifacts in Clinical Photon Counting Detector Computed Tomography-A Phantom Study of an Exemplary Total Hip Arthroplasty.

To examine how different photon-counting detector (PCD) CT scanning and reconstruction methods affect the volume of metal artifacts and image quality for a hip prosthesis phantom. A titanium and cobalt-chromium-molybdenum-alloy total hip prosthesis phantom was scanned using a clinical PCD-CT with a constant tube potential (140kV) and Computed-Tomography-Dose- Index (7mGy). Different scan settings were used: with/without tin-filter (Sn), with/without ultra-high resolution (UHR), both individually and combined, resulting in four modes: Quantumplus (Standard), UHR Quantumplus (HighRes), QuantumSn (Standard-Tin) and UHR QuantumSn (HighRes-Tin). Reconstructions included virtual monoenergetic images (VMI) spanning 40-190keV and polychromatic images, with/without iterative metal artifact reduction (MAR). Artifact volumes rendered in a 3D-printing software were quantified in milliliters (ml), and image quality was evaluated using a Likert score. Polychromatic reconstruction: Tin-filter reduced artifact volumes (298 (Standard-Tin) vs. 347ml (Standard) and 310 (HighRes-Tin) vs. 360ml (HighRes)). The smallest artifact volume was measured in HighRes MAR (150ml). VMI reconstruction: The smallest artifact volume was measured in Standard 130keV (150ml) and HighRes 130keV (164ml) and in Standard-Tin 120keV (169ml) and HighRes-Tin 120keV (172ml). MAR further reduced the artifact volumes to 130ml (Standard 150keV MAR) and 140ml (HighRes 160keV MAR). Image quality was rated best for Standard 65keV MAR, polychromatic HighRes MAR, Standard 100keV MAR, polychromatic Standard-tin MAR, HighRes-tin 100keV and polychromatic HighRes-tin. Combining tin-filter, UHR and MAR in VMI or polychromatic images achieve the strongest artifact reduction.

4DCT image artifact detection using deep learning.

Four-dimensional computed tomography (4DCT) is an es sential tool in radiation therapy. However, the 4D acquisition process may cause motion artifacts which can obscure anatomy and distort functional measurements from CTscans. We describe a deep learning algorithm to identify the location of artifacts within 4DCT images. Our method is flexible enough to handle different types of artifacts, including duplication, misalignment, truncation, andinterpolation. We trained and validated a U-net convolutional neural network artifact detection model on more than 23000 coronal slices extracted from 98 4DCT scans. The receiver operating characteristic (ROC) curve and precision-recall curve were used to evaluate the model's performance at identifying artifacts compared to a manually identified ground truth. The model was adjusted so that the sensitivity in identifying artifacts was equivalent to that of a human observer, as measured by computing the average ratio of artifact volume to lung volume in a givenscan. The model achieved a sensitivity, specificity, and precision of 0.78, 0.99, and 0.58, respectively. The ROC area-under-the-curve (AUC) was 0.99 and the precision-recall AUC was 0.73. Our model sensitivity is 8% higher than previously reported state-of-the-art artifact detectionmethods. The model developed in this study is versatile, designed to handle duplication, misalignment, truncation, and interpolation artifacts within a single image, unlike earlier models that were designed for a single artifact type.

Nonmetallic Carbon Fiber-Reinforced Polyetheretherketone Implants Vs Titanium Implants: Analysis of Clinical Outcomes and Influence on Postoperative Radiotherapy Planning in Metastatic Spine Tumor Surgery.

Titanium has been the conventional implant material of choice for fixation in both primary and metastatic spine tumor surgeries (MSTS). However, these implants result in artifact generation during postoperative computed tomography or magnetic resonance imaging, resulting in poor planning of radiotherapy (RT) and suboptimal tumor surveillance. Carbon fiber-reinforced polyetheretherketone (CFR-PEEK) implants have gained momentum for instrumentation in MSTS due to their radiolucent properties. In this study, the perioperative outcomes, postoperative imaging artifacts, and dosimetric data of CFR-PEEK implants to titanium implants were compared to assess for potential benefits in postoperative RT planning in patients undergoing MSTS. This is a retrospective study involving 62 patients who underwent operations for MSTS. The cohort of CFR-PEEK fixations (n = 20) was compared with a series of patients operated using titanium implants (n = 42). Patient-related data, including demographics, tumor pathology and extent of morbidity, intraoperative data, functional outcome, and RT-related data, were recorded for both groups. Primary outcome measures for RT data were amount of artifact generated on postoperative imaging and the time taken to contour them. All patients were followed up postoperatively for a minimum of 2 years or until death, whichever was earlier. Both groups had similar clinical outcomes for pain and overall survival predictability preoperatively (P = 0.786). The mean number of levels instrumented by titanium screws was 5.69 ± 2.64, while for CFR-PEEK screws it was 4.26 ± 1.05. Mean volume of artifact generated during postoperative computed tomography was 73.4 ± 50.43 mm3 in the titanium group and 20.0 ± 20.7 mm3 in the CFR-PEEK group (P < 0.001). The mean time taken to contour the artifacts was 17.3 ± 5.84 minutes in titanium group and 9.60 ± 7.17 minutes in CFR-PEEK group (P = 0.049). Our study confirms that CFR-PEEK screws significantly reduce artifact generation and the time taken to contour them during postoperative RT planning while delivering equivalent clinical and functional outcomes as compared with standard titanium implants.

Evaluation of a Metal Artifact Reduction Algorithm for Image Reconstruction on a Novel CBCT Platform.

The presence of metal implants can produce artifacts and distort Hounsfield units (HU) in patient computed tomography (CT) images. The purpose of this work was to characterize a novel metal artifact reduction (MAR) algorithm for reconstruction of CBCT images obtained by the HyperSight imaging system. Three tissue-equivalent phantoms were fitted with materials commonly used in medical applications. The first consisted of a variety of metal samples centered within a solid water block, the second was an Advanced Electron Density phantom with metal rods, and the third consisted of hip prostheses positioned within a water tank. CBCT images of all phantoms were acquired and reconstructed using the MAR and iCBCT Acuros algorithms on the HyperSight system. The signal-to-noise ratio (SNR), artifact index (AI), structural similarity index measure (SSIM), peak signal-to-noise ratio (PSNR), and mean-square error (MSE) were computed to assess the image quality in comparison to artifact-free reference images. The mean HU at various VOI positions around the cavity was calculated to evaluate the artifact dependence on distance and angle from the center of the cavity. The artifact volume of the phantom (excluding the cavity) was estimated by summing the volume of all voxels with HU values outside the 5th and 95th percentiles of the phantom CBCT with no artifact. The SNR, AI, SSIM, PSNR, and MSE metrics demonstrated significantly higher similarity to baseline when using MAR compared to iCBCT Acuros for all high-density materials, except for aluminum. Mean HU returned to expected solid water background at a shorter distance from metal sample in the MAR images, and the standard deviation remained lower for the MAR images at all distances from the insert. The artifact volume decreased using the novel MAR algorithm for all metal samples excluding aluminum (p<0.001) and all hip prostheses (p<0.05). Varian's HyperSight MAR reconstruction algorithm shows a reduction in metal artifact metrics, motivating the use of MAR reconstruction for patients with metal implants.

MRI susceptibility artefacts caused by orthodontic wire.

To evaluate magnetic susceptibility artefacts produced by orthodontic wires on MRI and the influence of wire properties and MRI image sequences on the magnitude of the artefact. Arch form orthodontic wires [four stainless steels (SS), one cobalt chromium (CC) alloy, 13 titanium (Ti) alloys] were embedded in a polyester phantom, and scanned using a 1.5-T superconducting magnet scanner with an eight-channel phased-array coil. All wires were scanned with T1-weighted spin echo (SE) and gradient echo (GRE) sequences according to the American Society for Testing and Materials (ASTM) F2119-07 standard. The phantom also scanned other eight sequences. Artefacts were measured using the ASTM F2119-07 definition and OsiriX software. Artefact volume was analysed according to metal composition, wire length, number of wires, wire thickness, and imaging sequence as factors. With SE/GRE, black/white artefacts volumes from all SS wires were significantly larger than those produced by CC and Ti wires (P < .01). With the GRE, the black artefacts volume was the highest with the SS wires. With the SE, the black artefacts volume was small, whereas white artefacts were noticeable. The cranio-caudal extent of the artefacts was significantly longer with SS wires (P < .01). Although a direct relationship of wire length, number of wires, and wire thickness with artefact volume was noted, these factors did not influence artefact extension in the cranio-caudal direction. Ferromagnetic/paramagnetic orthodontic wires create artefacts due to local alteration of magnetic field homogeneity. The SS-type wires produced the largest artefacts followed by CC and Ti.

The Use of Portable, Very Low-field (0.064T) MRI to Image Cochlear Implants: Metallic Image Artifact in Comparison to Traditional, Stationary 3T MRI.

To assess image artifact when imaging a cochlear implant (CI) with a conventional 3T MRI machine compared with a very low-field (0.064T) MRI. None. Diagnostic study. Image artifact size associated with the CI affixed to an MRI phantom at very low-field 0.064T MRI versus 3T MRI. The longest diameter of the image artifact was 125 mm for the 3T MRI and 86 mm for the 0.064T MRI, representing 45% longer image artifact generated in the 3T MRI. The actual volume of the imaging phantom was 1371 cm3. The volume of the image artifact was measured as 379 cm3 in the 3T MRI, representing a loss of 27.6% of the actual volume of the imaging phantom. The volume of image artifact was measured as 170 cm3 in the 0.064T MRI, representing a loss of 12.4% of the phantom volume. 3T MRI had better image quality. This result was not surprising given that larger magnetic field strength is known to provide higher resolution. There was 15% less image artifact generated in the very low-field MRI machine compared with a conventional 3T device. And there was also subjectively increased distortion of the imaging phantom at 3T MRI compared with the 0.064T MRI. With minimized safety concerns and a much lower cost than conventional 3T machines, very low-field scanners may find expanded clinical uses. This preclinical study explores the potential utility of very low-field MRI in scanning CI recipients.

Automated motion artifact detection in early pediatric diffusion MRI using a convolutional neural network.

Diffusion MRI (dMRI) is a widely used method to investigate the microstructure of the brain. Quality control (QC) of dMRI data is an important processing step that is performed prior to analysis using models such as diffusion tensor imaging (DTI) or neurite orientation dispersion and density imaging (NODDI). When processing dMRI data from infants and young children, where intra-scan motion is common, the identification and removal of motion artifacts is of the utmost importance. Manual QC of dMRI data is (1) time-consuming due to the large number of diffusion directions, (2) expensive, and (3) prone to subjective errors and observer variability. Prior techniques for automated dMRI QC have mostly been limited to adults or school-age children. Here, we propose a deep learning-based motion artifact detection tool for dMRI data acquired from infants and toddlers. The proposed framework uses a simple three-dimensional convolutional neural network (3DCNN) trained and tested on an early pediatric dataset of 2,276 dMRI volumes from 121 exams acquired at 1 month and 24 months of age. An average classification accuracy of 95% was achieved following four-fold cross-validation. A second dataset with different acquisition parameters and ages ranging from 2-36 months (consisting of 2,349 dMRI volumes from 26 exams) was used to test network generalizability, achieving 98% classification accuracy. Finally, to demonstrate the importance of motion artifact volume removal in a dMRI processing pipeline, the dMRI data were fit to the DTI and NODDI models and the parameter maps were compared with and without motion artifact removal.

Evaluation of a Novel Metal Artifact Reduction Algorithm for Reconstruction of Cone Beam CT (CBCT) Images Acquired on a New Imaging System

The presence of metal implants, dental work or prosthetics can produce image artifacts and distort Hounsfield units (HU) in patient CBCT images. The purpose of this work was to characterize a novel metal artifact reduction (MAR) algorithm for reconstruction of CBCT images obtained by a new imaging system and compare improvements in image quality with a conventional iterative reconstruction algorithm. Preliminary analyses show that the novel reconstruction algorithm implemented on the new imaging system produces image quality and HU comparable to standard fan-beam CT MATERIALS/METHODS: A 30 cm (length) x 30 cm (width) x 11 cm (depth) solid water phantom was fitted with a central cavity measuring 5.5 cm x 5.5 cm x 0.5 cm. Metal inserts of copper, aluminum, stainless steel, and titanium (5.5 cm x 5.5 cm x 1 - 5 mm in thickness) and sample dental implant materials (Amalgam, Au, Co-Cr, and Ti 6Al-Yv) were sequentially used to fill the cavity. CBCT images were acquired and reconstructed using the novel MAR and conventional iterative algorithms both on the on the new system. Images were also taken with the cavity filled with solid water for comparison. Eight image quality metrics were measured in six volumes of interest (VOIs) surrounding the cavity and compared to baseline VOI metrics for solid water-only images: HU mean, signal-to-noise ratio, contrast-to-noise ratio, artifact index, standard deviation, range, skewness, and kurtosis. The mean and standard deviation of HU within a shell-structure surrounding the cavity were calculated to evaluate the dependence of these values on distance from the center of the cavity. The artifact volume of the phantom (excluding the cavity) was estimated by calculating the 5th and 95th percentiles of HU in the CBCT of the phantom with the solid water insert, then summing the volume of all voxels with HU values outside this range. The eight image quality metrics extracted from the chosen VOIs were closer to baseline when using the novel MAR compared to conventional iterative reconstruction. It was also determined that mean HU returned to expected solid water background at a shorter distance from metal sample in the novel MAR images, and the standard deviation remained lower for the novel MAR images at all distances from the insert. These experimental outcomes were obtained for all high-density material inserts except for aluminum. The artifact volume was decreased using the novel MAR algorithm for all metal inserts excluding aluminum (p = 0.00013), and all dental implants (p = 0.00028). The novel MAR reconstruction algorithm shows a much lower sensitivity to metal artifacts, and significant improvement in image quality for all metal samples except for aluminum. These results justify the use of the novel MAR reconstruction for patients with metal implants and highlight advantages of the new CBCT imaging system for more accurate imaging and targeted treatment.

Artifacts in magnetic resonance imaging of the head and neck: Unwanted effects caused by implant-supported restorations fabricated with different alloys

Implant-supported restorations may cause artifacts in magnetic resonance imaging (MRI) of the head and neck area. However, the effect of different alloys remains unclear. The purpose of this in vitro study was to assess artifacts in head and neck MRI caused by implant-supported restorations with different alloys. Three dry mandibles were prepared to receive bilateral dental implants at the second premolar and second molar sites. Different alloy combinations were evaluated: titanium implants+cobalt chromium restorations; titanium-zirconium implants+cobalt chromium restorations; and zirconia implants+ceramic restorations. Specimens were imaged by using a 3-Tesla magnetic resonance scanner system (Achieva 3.0T TX; Philips GmbH) with a turbo-spin-echo sequence. Scan protocols were adjusted to optimize metal artifact reduction and shorten scan time. Artifact volumes were assessed and statistically analyzed by using the Kruskal-Wallis and Spearman tests (α=.05). A statistically significant difference was found among artifact volume caused by different materials (P=.002). The presence of titanium alloy was correlated with the artifact volume (r=-.87). Artifacts were greater for titanium and fewer for titanium-zirconium alloys, whereas zirconia implants found only minimal artifacts. The dimension of artifacts produced by implant-supported restorations varied according to the material.

Volumetric analysis of artifacts from fiducial markers under cone beam computed tomography

Computer aided implant surgery has been widely adopted in modern implant dentistry. However, absence of reliable anatomic landmarks for superimposing digital data sets for patients with terminal dentition or complete edentulism remained challenging. Utilization of additional fiducial markers intraorally as the reference points for the improvement of accuracy became crucial in implant digital workflow. Nevertheless, the choice of the material for fiducial markers should present the least radiographic artifacts under cone beam computed tomography (CBCT) for better accuracy. The aim of this invitro study was to investigate the volume of radiographic artifacts generated through different materials under the image of CBCT. Fifteen dental materials were selected and configured into cubic shape. All the materials were scanned initially with the laboratory scanner as the control groups. The samples were scanned by CBCT machine as test groups and the volume of artifact generated under CBCT images were compared and analyzed using 3D modeling software. Eleven out of fifteen materials could be recognized under CBCT images. Volumetric analysis reported that statistically significant differences among the materials could be noted, and the flowable composite resin presented the least volumetric difference. Lithium disilicate glass-ceramic, flowable composite resin, and gutta-percha presented the least deformation and maintained their cubic shapes. The results of the present study may imply that flowable composite resin compared to all ceramic materials, amalgam and gutta-percha may be a preferable choice when utilized as fiducial markers under CBCT images.

Quantitative evaluation of artifact expression in conebeam computed tomography of mesoporous calcium silicate nanoparticles as a promising root canal sealer

We aimed to quantitatively compare the area and volume of artifacts in cone beam computed tomography produced by mesoporous calcium silicate nanoparticles (MCSNs), AH Plus sealer, and iRoot SP sealer when used as root canal sealers. We prepared 40 single-rooted mandibular premolars and divided them into an MCSN sealer group, an AH Plus sealer group, an iRoot SP sealer group, and a no-sealer (control) group. We filled the canals with gutta-percha using the single-cone method and subjected them to conebeam computed tomography before and after the placement of root fillings using the same exposure parameters. We evaluated the images to quantify the areas of hyperdense and hypodense artifacts and non-affected teeth and reconstructed 3-dimensional image models of the materials to study volume distortion artifacts. The MCSN sealer group produced a significantly smaller hyperdense and volume distortion artifacts than the AH Plus and iRoot SP groups (P < .01), but the area and volume of hypodense artifacts did not differ significantly among the groups (P > .05). When used as a root canal sealer, MCSNs generate a significantly smaller area and volume of hyperdense artifacts than AH Plus and iRoot SP sealers. By significantly reducing the generation of high-density artifacts, MCSNs may facilitate the evaluation of root canal filling quality and the diagnosis of root canal abnormalities.

Semi-automatic artifact quantification in thermal ablation probe and algorithms for the evaluation of metal artifact reduction

Objectives To compare metal artifacts and evaluation of metal artifact reduction algorithms during probe positioning in computed tomography (CT)-guided microwave ablation (MWA), cryoablation (CRYO), and radiofrequency ablation (RFA). Materials and methods Using CT guidance, individual MWA, CRYO, and RFA ablation probes were placed into the livers of 15 pigs. CT imaging was then performed to determine the probe’s position within the test subject’s liver. Filtered back projection (B30f) and iterative reconstructions (I30-1) were both used with and without dedicated iterative metal artifact reduction (iMAR) to generate images from the initial data sets. Semi-automatic segmentation-based quantitative evaluation was conducted to estimate artifact percentage within the liver, while qualitative evaluation of metal artifact extent and overall image quality was performed by two observers using a 5-point Likert scale: 1-none, 2-mild, 3-moderate, 4-severe, 5-non-diagnostic. Results Among MWA, RFA, and CRYO, compared with non-iMAR in B30f reconstruction, the largest extent of artifact volume percentages were observed for CRYO (11.5–17.9%), followed by MWA (4.7–6.6%) and lastly in RFA (5.5–6.2%). iMAR significantly reduces metal artifacts for CRYO and MWA quantitatively (p = 0.0020; p = 0.0036, respectively) and qualitatively (p = 0.0001, p = 0.0005), but not for RFA. No significant reduction in metal artifact percentage was seen after applying iterative reconstructions (p > 0.05). Noise, contrast-to-noise-ratio, or overall image quality did not differ between probe types, irrespective of the application of iterative reconstruction and iMAR. Conclusion A dedicated metal artifact algorithm may decrease metal artifacts and improves image quality significantly for MWA and CRYO probes. Their application alongside with dedicated metal artifact algorithm should be considered during CT-guided positioning.

Diagnostic compatibility of various fixed orthodontic retainers for head/neck MRI and dental MRI

ObjectivesTo evaluate the diagnostic MRI compatibility of different fixed orthodontic retainers using a high-resolution 3D-sequence optimized for artifact reduction.Materials and methodsMaxillary and mandibular retainers made of five different materials were scanned in vitro and in vivo at 3 T MRI using an MSVAT-SPACE sequence. In vitro, artifact volumes were determined for all maxillary and mandibular retainers (AVmax; AVmand). In vivo, two independent observers quantified the extent of artifacts based on the visibility of 124 dental and non-dental landmarks using a five-point rating scale (1 = excellent, 2 = good, 3 = acceptable, 4 = poor, 5 = not visible).ResultsRectangular-steel retainers caused the largest artifacts (AVmax/AVmand: 18,060/15,879 mm3) and considerable diagnostic impairment in vivo (mean landmark visibility score ± SD inside/outside the retainer areas: 4.8 ± 0.8/2.9 ± 1.6). Smaller, but diagnostically relevant artifacts were observed for twistflex steel retainers (437/6317 mm3, 3.1 ± 1.7/1.3 ± 0.7). All retainers made of precious-alloy materials produced only very small artifact volumes (titanium grade 1: 70/46 mm3, titanium grade 5: 47/35 mm3, gold: 23/21 mm3) without any impact on image quality in vivo (each retainer: visibility scores of 1.0 ± 0.0 for all landmarks inside and outside the retainer areas).ConclusionsIn contrast to steel retainers, titanium and gold retainers are fully compatible for both head/neck and dental MRI when using MSVAT-SPACE.Clinical relevanceThis study demonstrates that titanium and gold retainers do not impair the diagnostic quality of head/neck and dental MRI when applying an appropriate artifact-reduction technique. Steel retainers, however, are not suitable for dental MRI and can severely impair image quality in head/neck MRI of the oral cavity.

Dosimetric impact of using a commercial metal artifact reduction tool in carbon ion therapy in patients with hip prostheses

The study investigated the dosimetric impact of an iterative metal artifact reduction (iMAR) tool on carbon ion therapy for pelvic cancer patients with hip prostheses. An anthropomorphic pelvic phantom with unilateral and bilateral hip prostheses was used to simulate pelvic cancer patients with metal implants. The raw data obtained from phantom CT scanning were reconstructed with a regular filtered back projection (FBP) algorithm and then corrected with iMAR. The phantom without hip prosthesis was also scanned and used as a reference ground truth (GT). The CT images of three prostate and four sarcoma patients with unilateral hip prosthesis were also reconstructed by FBP and iMAR algorithm and compared. iMAR algorithm reduced the metal artifacts and the maximum WEPL deviation in phantom images from −19.1 to −0.4 mm. However, the CT numbers cannot be retrieved using iMAR for periprosthetic bone materials, eventually leading to a WEPL deviation of −3.6 mm. The use of iMAR improved large discrepancies in DVHs of PTVs and the gamma index between FBP and GT images but increased the difference in the bladder DVH for bilateral hip prostheses due to newly introduced artifacts. In the patient study, the discrepancies of dose distribution were small on iMAR images when compared with FBP images for most cases, except for two sarcoma cases where gamma analysis failed and dose coverage in 98% of the PTV maximally reduced due to large volume of dark metal artifacts. iMAR reduced the metal artifacts and improved dose distribution accuracy in carbon ion radiotherapy for pelvic cancer. However, the residual and newly introduced artifacts, especially with bilateral hip prostheses, may potentially increase WEPL inaccuracy and dose uncertainty. The use of iMAR has the potential to improve carbon ion treatment planning of pelvic cancer but should be used with caution.

Community Archaeology in Los Roques Archipielago National Park, Venezuela

Convinced that archaeology as a past‑ oriented discipline should exert a transformative impact on the present, we discuss a series of initiatives that aim at interweaving the past of the Los Roques Archipelago, located 135 km off the central coast of Venezuela, into its present‑ day community life. Pioneering archaeological research carried out on these islands since 1982 revealed an unexpectedly rich volume of diversified artifacts and contextual information on the Amerindian seamen who seasonally exploited the local natural resources between A.D. 1200 and 1500. We are confident that despite the historical discontinuity between the pre‑ Hispanic seamen and the current population of the archipelago, the vibrant and colorful archaeological past will reach the present‑ day inhabitants, enriching their socio‑ cultural identity and influencing their way of life that currently oscillates entrapped between fishing and tourism‑ oriented activities. We discuss the aims and methodology of community archeology activities that include talks, exhibits, publications, documentary films and – above all – archaeological workshops that bring together the archaeologists and Los Roques schoolchildren in experiential archaeological events.

Clinical and MRI Evaluation of Silicone Gel Implants with RFID-M Traceability System: A Prospective Controlled Cohort Study Related to Safety and Image Quality in MRI Follow-Up.

SmoothSilk implants (SSI) are the first generation of implants to incorporate a radio-frequency identification device (RFID-M), a non-invasive traceability system. Although the RFID-M is considered compatible with magnetic resonance imaging (MRI), the size of the artifact and its influence on breast tissue vary. This prospective study assessed safety and MRI issues in a cohort of breast reconstruction patients. Forty-four SSI were used for breast reconstruction in patients undergoing treatment for breast cancer. All patients were evaluated for magnetic field interactions, MRI-related heating and artifacts in a 1.5-T MRI unit using standard T1/T2-weighted sequences utilized in clinical assessment of breast tissue/implants. Mean patient age was 41.5 years (27-53ys) and body mass index was 28+-6.44 kg/m2. In 18/22 patients (81.8%), mastectomies were unilateral. No patients reported local heat/discomfort. All implants showed RFID-M-related artifacts with an estimated mean volume in T1 of 42.9cm3 (26.2-63.6cm3; SD±8.6 and 95% CI, 40.37-45.45) and in T2 of 60.5cm3 (35.4-97.2cm3; SD±14.7 and 95% CI, 56.29-65.01). Artifact volume was smaller in T1 than in T2, to a statistically significant degree (p <0.001). There were no statistically significant differences in artifact volume according to surgical indication, breast side or implant volume. There were 4/44 (9%) cases of minor rotation (<45°). In all cases, adequate analysis of the breast tissue was performed. The results demonstrate that SSI with RFID-M technology presented an artifact volume of 42.9cm3 and 60.5cm3 in T1 and T2 images, respectively. Our findings provide detailed information on the quality and location of MRI artifacts in a reconstructed cohort which can help guide clinical decision-making for patients. To our knowledge, this is the first time RFID-M breast implants have been prospectively evaluated for clinical and MRI issues in a cohort of reconstructive patients. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Effectiveness of Commercial Software–Enhanced Image Artifact Reduction Software

IntroductionArtifact reduction (AR) software has been incorporated into some cone-beam computed tomographic (CBCT) systems to reduce the severity of beam hardening (BH) artifacts and improve image quality. This study quantifies BH artifact and evaluates the effectiveness of AR in 2 CBCT systems. MethodsPalatal roots of Dent-Alike (Dentsply Sirona, Tulsa, OK) teeth were prepared and root filled with gutta-percha and EndoSequence BC Sealer (Brasseler, Savannah, GA). Six teeth were imaged with and without AR software using the ProMax3D (Planmeca Oy, Helsinki, Finland) and the Pax-i3D (Vatech, Hwaseong-si, South Korea) systems. FSL (FMRIB, Oxford, UK) software was used to quantify the light and dark components of the BH artifact along the tooth root using a specific region of interest approach and an image-wide analysis approach. Statistical analysis was performed using paired t tests and corrected for multiple comparisons with cluster mass correction using a nonparametric statistical analysis to evaluate the differences in the artifact volumes and areas with and without AR. ResultsA significant reduction in the light artifact was observed with the Planmeca system (P < .05), but no significant differences were observed for either the light or dark artifacts with the Vatech system when AR was applied. There were also significant reductions in the volumes of light and dark artifacts along the entire root length when the AR was applied with the Planmeca system (cluster mass P < .05), but no significant differences were observed with the Vatech system. ConclusionsProprietary AR software is not equally effective in reducing the light and/or dark components of CBCT BH artifacts.

Comparison of the Quality of Various Polychromatic and Monochromatic Dual-Energy CT Images with or without a Metal Artifact Reduction Algorithm to Evaluate Total Knee Arthroplasty.

ObjectiveTo compare the quality of various polychromatic and monochromatic images with or without using an iterative metal artifact reduction algorithm (iMAR) obtained from a dual-energy computed tomography (CT) to evaluate total knee arthroplasty.Materials and MethodsWe included 58 patients (28 male and 30 female; mean age [range], 71.4 [61–83] years) who underwent 74 knee examinations after total knee arthroplasty using dual-energy CT. CT image sets consisted of polychromatic image sets that linearly blended 80 kVp and tin-filtered 140 kVp using weighting factors of 0.4, 0, and −0.3, and monochromatic images at 130, 150, 170, and 190 keV. These image sets were obtained with and without applying iMAR, creating a total of 14 image sets. Two readers qualitatively ranked the image quality (1 [lowest quality] through 14 [highest quality]). Volumes of high- and low-density artifacts and contrast-to-noise ratios (CNRs) between the bone and fat tissue were quantitatively measured in a subset of 25 knees unaffected by metal artifacts.ResultsiMAR-applied, polychromatic images using weighting factors of −0.3 and 0.0 (P−0.3i and P0.0i, respectively) showed the highest image-quality rank scores (median of 14 for both by one reader and 13 and 14, respectively, by the other reader; p < 0.001). All iMAR-applied image series showed higher rank scores than the iMAR-unapplied ones. The smallest volumes of low-density artifacts were found in P−0.3i, P0.0i, and iMAR-applied monochromatic images at 130 keV. The smallest volumes of high-density artifacts were noted in P−0.3i. The CNRs were best in polychromatic images using a weighting factor of 0.4 with or without iMAR application, followed by polychromatic images using a weighting factor of 0.0 with or without iMAR application.ConclusionPolychromatic images combined with iMAR application, P−0.3i and P0.0i, provided better image qualities and substantial metal artifact reduction compared with other image sets.

Assessing the advantages of CFR-PEEK over titanium spinal stabilization implants in proton therapy—a phantom study

High-density materials, such as titanium, used for spinal stabilization, introduces several critical issues in proton therapy (PT). Artefacts affect both contouring and dose calculation. Subsequently, artefacts need to be corrected which is a time-consuming process. Besides, titanium causes proton interactions that are unaccounted for in dose calculation. The result is a suboptimal treatment plan, and indeed decreased local controls have been reported for these patients. Carbon fiber reinforced polyetheretherketone (CFR-PEEK) implant material, which is of low density, potentially solves these issues. For this study, we designed a unique phantom to compare the effects of titanium and CFR-PEEK implants in PT. The phantom contains four interchangeable spinal inserts representing a native spine, and three different spinal stabilizations consisting of titanium only, CFR-PEEK only, and a combination of titanium and CFR-PEEK. All phantom scenarios received the standard treatment workup. Two planning approaches were investigated: a single field plan and a multi-field optimized plan with spinal cord sparing. For both plans we analyzed the following aspects: total volume of artefacts on CT images, time required for artefact correction, effect of planning CT correction on dose calculation, plan robustness to range and set up uncertainties, and finally the discrepancy between the calculated dose and the delivered dose with Gafchromic® film. The CFR-PEEK implant had a 90% reduction of artefacts on CT images and subsequently severely reduced the time for artefact correction with respect to the titanium-only implant. Furthermore, the CFR-PEEK as opposed to titanium did not influence the robustness of the plan. Finally, the titanium implants led to hardware-related discrepancies between the planned and the measured dose while the CFR-PEEK implant showed good agreement. As opposed to titanium, CFR-PEEK has none to minor effects on PT. The use of CFR-PEEK is expected to optimize treatment and possibly improve outcomes for patients that require spinal stabilization.

A semi-automated quantitative comparison of metal artifact reduction in photon-counting computed tomography by energy-selective thresholding

An evaluation of energy thresholding and acquisition mode for metal artifact reduction in Photon-counting detector CT (PCD-CT) compared to conventional energy-integrating detector CT (EID-CT) was performed. Images of a hip prosthesis phantom placed in a water bath were acquired on a scanner with PCD-CT and EID-CT (tube potentials: 100, 120 and 140 kVp) and energy thresholds (above 55–75 keV) in Macro and Chess mode. Only high-energy threshold images (HTI) were used. Metal artifacts were quantified by a semi-automated segmentation algorithm, calculating artifact volumes, means and standard deviations of CT numbers. Images of a human cadaver with hip prosthesis were acquired on the PCD-CT in Macro mode as proof-of-concept. Images at 140 kVp showed less metal artifacts than 120 kVp or 100 kVp. HTI (70, 75 keV) had fewer artifacts than low energy thresholds (55, 60, 65 keV). Fewer artifacts were observed in the Macro-HTI (8.9–13.3%) for cortical bone compared to Chess-HTI (9.4–19.1%) and EID-CT (10.7–19.0%) whereas in bone marrow Chess-HTI (19.9–45.1%) showed less artifacts compared to Macro-HTI (21.9–38.3%) and EID-CT (36.4–54.9%). Noise for PCD-CT (56–81 HU) was higher than EID-CT (33–36 HU) irrespective of tube potential. High-energy thresholding could be used for metal artifact reduction in PCD-CT, but further investigation of acquisition modes depending on target structure is required.