Severe metallosis following catastrophic failure of total shoulder arthroplasty - a case report.

Metallosis is an unusual but consequential complication arising from orthopedic hardware implantation, characterized by the deposition of metallic particles in the periprosthetic soft tissues. The incidence of metallosis associated with shoulder arthroplasties is exceptionally rare since the shoulder is not a weight-bearing joint, making it less susceptible to mechanical wear and, consequently, to conditions like particle disease and metallosis. Nevertheless, anomalous metal-on-metal interactions can develop in total shoulder arthroplasties if the polyethylene component fails due to wear, fracture, or dissociation. If left unaddressed, metallosis can incite an adverse immune-mediated local tissue response, culminating in joint destruction and adjacent soft tissues and muscle necrosis. In this case report, the diagnosis of metallosis was made in a patient with an anatomic total shoulder arthroplasty using a state-of-the-art photon counting detector CT supplemented by post-processing metal artifact reduction algorithms. This advanced imaging approach was effective in discerning the source of implant failure and in identifying manifestations of severe metallosis including osteolysis and pseudotumor formation. Advanced imaging methods can accurately characterize the severity and extent of metallosis, thereby helping guide surgical planning to mitigate serious complications associated with this condition.

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

PURPOSE: 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. METHODS: 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. RESULTS: 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). CONCLUSION: Varian's HyperSight MAR reconstruction algorithm shows a reduction in metal artifact metrics, motivating the use of MAR reconstruction for patients with metal implants.

Dual-energy CT in musculoskeletal imaging: technical considerations and clinical applications.

Dual-energy CT stands out as a robust and innovative imaging modality, which has shown impressive advancements and increasing applications in musculoskeletal imaging. It allows to obtain detailed images with novel insights that were once the exclusive prerogative of magnetic resonance imaging. Attenuation data obtained by using different energy spectra enable to provide unique information about tissue characterization in addition to the well-established strengths of CT in the evaluation of bony structures. To understand clearly the potential of this imaging modality, radiologists must be aware of the technical complexity of this imaging tool, the different ways to acquire images and the several algorithms that can be applied in daily clinical practice and for research. Concerning musculoskeletal imaging, dual-energy CT has gained more and more space for evaluating crystal arthropathy, bone marrow edema, and soft tissue structures, including tendons and ligaments. This article aims to analyze and discuss the role of dual-energy CT in musculoskeletal imaging, exploring technical aspects, applications and clinical implications and possible perspectives of this technique.

Performance of different cone-beam computed tomography scan modes with and without metal artifact reduction in detection of recurrent dental caries under various restorative materials.

Purpose: We aimed to compare the diagnostic performance of different cone-beam computed tomography (CBCT) scan modes with and without the application of a metal artifact reduction (MAR) option under 5 different restorative materials. Material and methods: Our research was an in vitro study with 150 caries-free premolars and molars. The teeth were randomly divided into experimental (with artificially induced caries, n = 75) and control (without caries, n = 75) groups and were prepared based on 5 types of restorative materials, including conventional composites (Filtek Z250, Gradia), flow composite, glass ionomer, and amalgam. The teeth were examined under 2 CBCT scan modes (high-resolution [HIRes] and standard) with and without MAR application. Finally, the diagnostic accuracy index values (area under the receiver operating characteristic curve [AUC], sensitivity, and specificity) were calculated. Results: The AUC of standard scan mode with the MAR option was significantly lower than that of HIRes with MAR (p = 0.018) and without MAR option (p = 0.011) in detecting recurrent caries. Also, without MAR option, the diagnostic accuracy (AUC) of the standard mode was significantly lower than that of the HIRes (p = 0.020). Similar findings were observed for sensitivity and specificity. Moreover, diagnostic performance of standard and HIRes scan modes with and without MAR in the amalgam group was lower than that in other restorative material groups. Conclusions: Diagnostic performance of HIRes CBCT mode was higher than that of standard mode for recurrent caries and remained unaffected by MAR application. However, the accuracy in detecting recurrent caries was lower in the amalgam group compared with other restorative material groups.

Metal artifacts and artifact reduction of neurovascular coils in photon-counting detector CT versus energy-integrating detector CT - in vitro comparison of a standard brain imaging protocol.

OBJECTIVES: Photon-counting detector computed tomography (PCD-CT) is a promising new technique for CT imaging. The aim of the present study was the in vitro comparison of coil-related artifacts in PCD-CT and conventional energy-integrating detector CT (EID-CT) using a comparable standard brain imaging protocol before and after metal artifact reduction (MAR). METHODS: A nidus-shaped rubber latex, resembling an aneurysm of the cerebral arteries, was filled with neurovascular platinum coils and inserted into a brain imaging phantom. Image acquisition and reconstruction were repeatedly performed for PCD-CT and EID-CT (n = 10, respectively) using a standard brain imaging protocol. Moreover, linear interpolation MAR was performed for PCD-CT and EID-CT images. The degree of artifacts was analyzed quantitatively (standard deviation in a donut-shaped region of interest) and qualitatively (5-point scale analysis). RESULTS: Quantitative and qualitative analysis demonstrated a lower degree of metal artifacts in the EID-CT images compared to the total-energy PCD-CT images (e.g., 82.99 ± 7.89 Hounsfield units (HU) versus 90.35 ± 6.28 HU; p < 0.001) with no qualitative difference between the high-energy bin PCD-CT images and the EID-CT images (4.18 ± 0.37 and 3.70 ± 0.64; p = 0.575). After MAR, artifacts were more profoundly reduced in the PCD-CT images compared to the EID-CT images in both analyses (e.g., 2.35 ± 0.43 and 3.18 ± 0.34; p < 0.001). CONCLUSION: PCD-CT in combination with MAR have the potential to provide an improved option for reduction of coil-related artifacts in cerebral imaging in this in vitro study. KEY POINTS: • Photon-counting detector CT produces more artifacts compared to energy-integrating detector CT without metal artifact reduction in cerebral in vitro imaging after neurovascular coil-embolization. • Spectral information of PCD-CT provides the potential for new post-processing techniques, since the coil-related artifacts were lower in PCD-CT images compared to EID-CT images after linear interpolation metal artifact reduction in this in vitro study.

Compressed Sensing SEMAC MRI of Hip, Knee, and Ankle Arthroplasty Implants: A 1.5-T and 3-T Intrapatient Performance Comparison for Diagnosing Periprosthetic Abnormalities.

BACKGROUND. The utility of 3-T MRI for diagnosing joint disorders is established, but its performance for diagnosing abnormalities around arthroplasty implants is unclear. OBJECTIVE. The purpose of this study was to compare 1.5-T and 3-T compressed sensing slice encoding for metal artifact correction (SEMAC) MRI for diagnosing peri-prosthetic abnormalities around hip, knee, and ankle arthroplasty implants. METHODS. Forty-five participants (26 women, 19 men; mean age ± SD, 71 ± 14 years) with symptomatic lower extremity arthroplasty (hip, knee, and ankle, 15 each) prospectively underwent consecutive 1.5- and 3-T MRI examinations with intermediate-weighted (IW) and STIR compressed sensing SEMAC sequences. Using a Likert scale, three radiologists evaluated the presence or absence of periprosthetic abnormalities, including bone marrow edema-like signal, osteolysis, stress reaction/fracture, synovitis, and tendon abnormalities and collections; image quality; and visibility of anatomic structures. Statistical analysis included nonparametric comparison and interchangeability testing. RESULTS. For diagnosing periprosthetic abnormalities, 1.5-T and 3-T compressed sensing SEMAC MRI were interchangeable. Across all three joints, 3-T MRI had lower noise than 1.5-T MRI (median IW and STIR scores at 3 T vs 1.5 T, 4 and 4 [range, 2-5 and 3-5] vs 3 and 3 [range, 2-5 and 2-4]; p < .01 for both), sharper edges (median IW and STIR scores at 3 T vs 1.5 T, 4 and 4 [both ranges, 2-5] vs 3 and 3 [range, 2-4 and 2-5]; p < .02 and p < .05), and more effective metal artifact reduction (median IW and STIR scores at 3 T vs 1.5 T, 4 and 4 [range, 3-5 and 2-5] vs 4 and 4 [both ranges, 3-5]; p < .02 and p = .72). Agreement was moderate to substantial for image contrast (IW and STIR, 0.66 and 0.54 [95% CI, 0.41-0.91 and 0.29-0.80]; p = .58 and p = .16) and joint capsule visualization (IW and STIR, 0.57 and 0.70 [range, 0.32-0.81 and 0.51-0.89]; p = .16 and p = .19). The bone-implant interface was more visible at 1.5 T (median IW and STIR scores, 4 and 4 [both ranges, 2-5] at 1.5 T vs 3 and 3 [both ranges, 2-5] at 3 T; p = .08 and p = .58), but periprosthetic tissues had superior visibility at 3 T (IW and STIR, 4 and 4 [both ranges, 3-5] at 3 T vs 4 and 4 [ranges, 2-5 and 3-5] at 1.5 T; p = .07 and p = .19). CONCLUSION. Optimized 1.5-T and 3-T compressed sensing SEMAC MRI are interchangeable for diagnosing periprosthetic abnormalities, although metallic artifacts are larger at 3 T. CLINICAL IMPACT. With compressed sensing SEMAC MRI, lower extremity arthroplasty implants can be imaged at 3 T rather than 1.5 T.

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.

State-of-the-art magnetic resonance imaging sequences for pediatric body imaging.

Longer examination time, need for anesthesia in smaller children and the inability of most children to hold their breath are major limitations of MRI in pediatric body imaging. Fortunately, with technical advances, many new and upcoming MRI sequences are overcoming these limitations. Advances in data acquisition and k-space sampling methods have enabled sequences with improved temporal and spatial resolution, and minimal artifacts. Sequences to minimize movement artifacts mainly utilize radial k-space filling, and examples include the stack-of-stars method for T1-weighted imaging and the periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER)/BLADE method for T2-weighted imaging. Similarly, the sequences with improved temporal resolution and the ability to obtain multiple phases in a single breath-hold in dynamic imaging mainly use some form of partial k-space filling method. New sequences use a variable combination of data sampling methods like compressed sensing, golden-angle radial k-space filling, parallel imaging and partial k-space filling to achieve free-breathing, faster sequences that could be useful for pediatric abdominal and thoracic imaging. Simultaneous multi-slice method has improved diffusion-weighted imaging (DWI) with reduction in scan time and artifacts. In this review, we provide an overview of data sampling methods like parallel imaging, compressed sensing, radial k-space sampling, partial k-space sampling and simultaneous multi-slice. This is followed by newer available and upcoming sequences for T1-, T2- and DWI based on these other advances. We also discuss the Dixon method and newer approaches to reducing metal artifacts.

Significantly Worse Fixation of Cemented Patellar Components on Multiacquisition Variable-Resonance Image Combination Magnetic Resonance Imaging Compared to Femoral and Tibial Components: A Cause for Concern?

BACKGROUND: The etiology of anterior knee pain after total knee arthroplasty (TKA) remains unclear. Few studies have examined patellar fixation quality. The purpose of the present study was to evaluate the patellar cement-bone interface after TKA on magnetic resonance imaging (MRI) and to correlate the patella fixation grade with the incidence of anterior knee pain. METHODS: We retrospectively reviewed 279 knees undergoing metal artifact reduction MRI for either anterior or generalized knee pain at least 6 months after cemented, posterior-stabilized TKA with patellar resurfacing with one implant manufacturer. MRI cement-bone interfaces and percent-integration of the patella, femur, and tibia were assessed by a fellowship-trained senior musculoskeletal radiologist. The grade and character of the patella interface were compared to the femur and tibia. Regression analyses were used to determine the association between patella integration with anterior knee pain. RESULTS: There were more patellar components with ≥75% zones of fibrous tissue (50%) compared to the femur (18%) or tibia (5%) (P < .001). There were a greater number of patellar implants with poor cement integration (18%) compared to the femur (1%) or tibia (1%) (P < .001). MRI findings showed more evidence of patellar component loosening (8%) compared to the femur (1%) or tibia (1%) (P < .001). Anterior knee pain was correlated with worse patella cement integration (P = .01), with women predicted to have better integration (P < .001). CONCLUSION: The quality of the patellar cement-bone interface after TKA is worse compared to the femoral or tibial component interface. Poor patellar cement-bone interface may be a source of anterior knee pain after TKA, but further investigation is required.

Metal Artifact Reduction in Dental CBCT Images Using Direct Sinogram Correction Combined with Metal Path-Length Weighting.

Metal artifacts in dental computed tomography (CT) images, caused by highly X-ray absorbing objects, such as dental implants or crowns, often more severely compromise image readability than in medical CT images. Since lower tube voltages are used for dental CTs in spite of the more frequent presence of metallic objects in the patient, metal artifacts appear more severely in dental CT images, and the artifacts often persist even after metal artifact correction. The direct sinogram correction (DSC) method, which directly corrects the sinogram using the mapping function derived by minimizing the sinogram inconsistency, works well in the case of mild metal artifacts, but it often fails to correct severe metal artifacts. We propose a modified DSC method to reduce severe metal artifacts, and we have tested it on human dental images. We first segment the metallic objects in the CT image, and then we forward-project the segmented metal mask to identify the metal traces in the projection data with computing the metal path length for the rays penetrating the metal mask. In the sinogram correction with the DSC mapping function, we apply the weighting proportional to the metal path length. We have applied the proposed method to the phantom and patient images taken at the X-ray tube voltage of 90 kVp. We observed that the proposed method outperforms the original DSC method when metal artifacts were severe. However, we need further extensive studies to verify the proposed method for various CT scan conditions with many more patient images.

The anatomical location of cystic pseudotumors and muscle atrophy in metal-on-metal resurfacing hip arthroplasty is related to the surgical approach used for implantation. A subgroup analyses of a randomized controlled trial.

BACKGROUND: Pseudotumors and muscle atrophy have been associated with metal-on-metal (MoM) resurfacing hip arthroplasty (RHA). We aimed to investigate the influence of the anterolateral (AntLat) and the posterior (Post) surgical approach on the location, grade and prevalence of pseudotumors and muscle atrophy in MoM RHA. PATIENTS AND METHODS: Forty-nine patients were randomized to MoM RHA by the AntLat (n = 25) or the Post (n = 24) approach at Aarhus University Hospital. Patients underwent metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) scans for investigation of location, grade and prevalence of pseudotumors and muscle atrophy. Plain radiographs, metal-ions concentrations and clinical outcome scores were evaluated to compare outcomes of the surgical approaches. RESULTS: MRI-detected pseudotumors were seen in 7 of 18 patients (39%) in the AntLat group and in 12 of 22 patients (55%) in the Post group (p = 0.33). Pseudotumors were mainly located anterolaterally to the hip joint in the AntLat group and postero-lateral to the hip joint in the Post group. Higher grades of muscle atrophy of the caudal part of the gluteus medius and minimus (p < 0.004) were seen in the AntLat group, and higher grades of muscle atrophy of the small external rotators were seen in the Post group (p < 0.001). The AntLat group had higher anteversion angles of mean 15.3° (range 6.1-7.5) versus mean 11.5° (range 4.9-22.5) in the Post group (p = 0.02). Metal-ion concentrations and clinical outcome scores were similar between groups (p > 0.08). CONCLUSION: Muscle atrophy and pseudotumor location after MoM RHA follow the surgical approach used for implantation. This knowledge may help differentiate between "normal postoperative appearance" and "MoM disease."

Combination of Iterative Metal Artifact Reduction and Virtual Monoenergetic Reconstruction Using Split-Filter Dual-Energy CT in Patients With Dental Artifact on Head and Neck CT.

BACKGROUND. Head and neck CT can be limited by dental hardware artifact. Both postprocessing-based iterative metal artifact reduction (IMAR) and virtual monoenergetic imaging (VMI) reconstruction in dual-energy CT (DECT) can reduce metal artifact. Their combination is poorly described for single-source DECT systems. OBJECTIVE. The purpose of this study was to compare metal artifact reduction between VMI, IMAR, and their combination (VMIIMAR) in split-filter single-source DECT of patients with severe dental hardware artifact. METHODS. This retrospective study included 44 patients (nine woman, 35 men; mean age, 66.0 ± 10.4 years) who underwent head and neck CT and had severe dental hardware artifact. Standard, VMI, IMAR, and VMIIMAR images were generated; VMI and VMIIMAR were performed at 40, 70, 100, 120, 150, and 190 keV. ROIs were placed to measure corrected attenuation in pronounced hyperattenuating and hypoattenuating artifacts and artifact-impaired soft tissue and to measure corrected artifact-impaired soft-tissue noise. Two radiologists independently assessed soft-tissue interpretability (1-5 scale), and pooled ratings were analyzed. Readers selected the preferred reconstruction for each patient. RESULTS. Mean hyperattenuating artifact-corrected attenuation was 521.0 HU for standard imaging, 496.4-892.2 HU for VMI, 48.2 HU for IMAR, and 32.8-91.0 HU for VMIIMAR. Mean hypoattenuating artifact-corrected attenuation was -455.1 HU for standard imaging, -408.5 to -679.9 HU for VMI, -37.3 for IMAR, and -17.8 to -36.9 HU for VMIIMAR. Mean artifact-impaired soft tissue-corrected attenuation was 10.8 HU for standard imaging, -0.6 to 24.9 HU for VMI, 4.3 HU for IMAR, and -2.0 to 7.8 HU for VMIIMAR. Mean artifact-impaired soft tissue-corrected noise was 58.7 HU for standard imaging, 38.2 to 129.7 HU for VMI, 11.0 HU for IMAR, and 5.8 to 45.6 HU for VMIIMAR. Median soft-tissue interpretability was 1.2 for standard imaging, 1.1-1.2 for VMI, 3.7 for IMAR, and 2.0-3.8 for VMIIMAR. Artifact-impaired soft tissue-corrected attenuation and soft-tissue interpretability significantly improved (p < .05) for VMIIMAR versus IMAR only at 100 keV. The two readers preferred VMIIMAR at 100 keV in 56.8% and 59.1% of examinations. CONCLUSION. For reducing severe artifact due to dental material, IMAR has greater effect than VMI. Though the results for IMAR and VMIIMAR were similar overall, VMIIMAR had a small benefit at 100 keV. CLINICAL IMPACT. VMI and IMAR techniques in split-filter DECT may be combined for clinical head and neck imaging to reduce artifact from dental hardware and improve image quality.

Impact of metal artifact reduction algorithm on gross tumor volume delineation in tonsillar cancer: reducing the interobserver variation.

BACKGROUND: Patients with tonsillar cancer (TC) often have dental fillings that can significantly degrade the quality of computed tomography (CT) simulator images due to metal artifacts. We evaluated whether the use of the metal artifact reduction (MAR) algorithm reduced the interobserver variation in delineating gross tumor volume (GTV) of TC. METHODS: Eighteen patients with TC with dental fillings were enrolled in this study. Contrast-enhanced CT simulator images were reconstructed using the conventional (CTCONV) and MAR algorithm (CTMAR). Four board-certified radiation oncologists delineated the GTV of primary tumors using routine clinical data first on CTCONV image datasets (GTVCONV), followed by CTCONV and CTMAR fused image datasets (GTVMAR) at least 2 weeks apart. Intermodality differences in GTV values and Dice similarity coefficient (DSC) were compared using Wilcoxon's signed-rank test. RESULTS: GTVMAR was significantly smaller than GTVCONV for three observers. The other observer showed no significant difference between GTVCONV and GTVMAR values. For all four observers, the mean GTVCONV and GTVMAR values were 14.0 (standard deviation [SD]: 7.4) cm3 and 12.1 (SD: 6.4) cm3, respectively, with the latter significantly lower than the former (p < 0.001). The mean DSC of GTVCONV and GTVMAR was 0.74 (SD: 0.10) and 0.77 (SD: 0.10), respectively, with the latter significantly higher than that of the former (p < 0.001). CONCLUSIONS: The use of the MAR algorithm led to the delineation of smaller GTVs and reduced interobserver variations in delineating GTV of the primary tumors in patients with TC.

Reliability and benefits of single-energy projection-based metallic artifact reduction (SEMAR) in the different orthopedic hardware for the hip.

OBJECTIVE: To evaluate the performance and reliability of the single-energy metal artifact reduction (SEMAR) algorithm in patients with different orthopedic hardware at the hips. MATERIALS AND METHODS: A total of 153 patients with hip instrumentation who had undergone CT with adaptive iterative dose reduction (AIDR) 3D and SEMAR algorithms between February 2015 and October 2019 were included retrospectively. Patients were divided into 5 groups by the hardware type. Two readers with 21 and 13 years of experience blindly reviewed all image sets and graded the extent of artifacts and imaging quality using 5-point scales. To evaluate reliability, the mean densities and image noises were measured at the urinary bladder, veins, and fat in images with artifacts and the reference images. RESULTS: No significant differences were found in the mean densities of the urinary bladder, veins, and fat between the SEMAR images with artifacts (7.57 ± 9.49, 40.29 ± 23.07, 86.78 ± 38.34) and the reference images (7.77 ± 6.2, 40.27 ± 8.66, 89.10 ± 20.70) (P = .860, .994, .392). Image noises of the urinary bladder in the SEMAR images with artifacts (14.25 ± 4.50) and the SEMAR reference images (9.69 ± 1.29) were significantly higher than those in the AIDR 3D reference images (9.11 ± 1.12) (P < .001; P < .001). All AIDR 3D images were non-diagnostic (overall quality ≤ 3) and less than a quarter of the SEMAR images were non-diagnostic (16.7-23.7%), mainly in patients with prostheses [reader 1: 91.7% (22/24); reader 2: 92.6% (25/27)]. CONCLUSION: The SEMAR algorithm significantly reduces metal artifacts in CT images, more in patients with internal fixations than in patients with prostheses, and provides reliable attenuation of soft tissues.

Dual energy CT in musculoskeletal applications beyond crystal imaging: bone marrow maps and metal artifact reduction.

Dual energy CT (DECT) is becoming increasingly popular and valuable in the domain of musculoskeletal imaging. Gout maps and crystal detection have been predominant indications for about a decade. Other important indications of bone marrow maps and metal artifact reduction are also frequent with added advantages of detection and characterization of bone marrow lesions similar to MR imaging and diagnosis of hardware related complications, respectively. This article discusses technical considerations and physics of DECT imaging and its role in musculoskeletal indications apart from crystal imaging with respective case examples and review of the related literature. DECT pitfalls in these domains are also highlighted and the reader can gain knowledge of above concepts for prudent use of DECT in their musculoskeletal and general practices.

Accuracy Assessment of Percutaneous Pedicle Screw Placement Using Cone Beam Computed Tomography with Metal Artifact Reduction.

Metal artifact reduction (MAR) algorithms are used with cone beam computed tomography (CBCT) during augmented reality surgical navigation for minimally invasive pedicle screw instrumentation. The aim of this study was to assess intra- and inter-observer reliability of pedicle screw placement and to compare the perception of baseline image quality (NoMAR) with optimized image quality (MAR). CBCT images of 24 patients operated on for degenerative spondylolisthesis using minimally invasive lumbar fusion were analyzed retrospectively. Images were treated using NoMAR and MAR by an engineer, thus creating 48 randomized files, which were then independently analyzed by 3 spine surgeons and 3 radiologists. The Gertzbein and Robins classification was used for screw accuracy rating, and an image quality scale rated the clarity of pedicle screw and bony landmark depiction. Intra-class correlation coefficients (ICC) were calculated. NoMAR and MAR led to similarly good intra-observer (ICC > 0.6) and excellent inter-observer (ICC > 0.8) assessment reliability of pedicle screw placement accuracy. The image quality scale showed more variability in individual image perception between spine surgeons and radiologists (ICC range 0.51−0.91). This study indicates that intraoperative screw positioning can be reliably assessed on CBCT for augmented reality surgical navigation when using optimized image quality. Subjective image quality was rated slightly superior for MAR compared to NoMAR.

Effects of metal implants and validation of four treatment planning methods used for radiotherapy dose calculation.

Background: The radiotherapy treatment planning process involves target delineation and dose calculation, both of which directly depend on image quality and Hounsfield unit (HU) accuracy of computed tomography (CT) images. CT images of patients having metal implants undergo image quality deterioration and show inaccurate HU values due to various artifacts. Metal artifact reduction (MAR) is used to improve the image quality. In this study, four treatment planning methods with and without MAR, in combination with actual and assigned HU values, were analyzed for dose calculation accuracy. The aim was to study the effects of metal implants on planning CT and to evaluate the dose calculation accuracy of four treatment planning methods for radiotherapy. Materials and methods: Two phantoms with six different metal inserts were scanned in the extended HU mode, with and without MAR. Geometry verification and HU analysis of the metals and the surrounding region were carried out. Water equivalent distance (WED) measurements and dose calculation for each metal insert were done in the treatment planning system (TPS) using the anisotropic analytical algorithm (AAA). Point dose and two-dimensional dose distribution were studied. Percentage variation analysis between calculated and measured doses and gamma evaluation were conducted to determine the most suitable method for treatment planning. Conclusion: This study concludes that an MARCT image with an assigned HU similar to that of the metal implant is better for contouring and high dose calculation accuracy. If MAR is not available, the actual HU value from the extended HU CT for the metal should be used for dose calculation.

Reduction of metal artifacts from knee tumor prostheses on CT images: value of the single energy metal artifact reduction (SEMAR) algorithm.

BACKGROUND: To evaluate the effect of the single energy metal artifact reduction (SEMAR) algorithm with a multidetector CT (MDCT) for knee tumor prostheses. METHODS: First, a phantom of knee tumor prosthesis underwent a MDCT scan. The raw data was reconstructed by iterative reconstruction (IR) alone and IR plus SEMAR. The mean value of the CT number and the image noise were measured around the prosthesis at the stem level and articular level. Second, 95 consecutive patients with knee tumor prostheses underwent MDCT scans. The raw data were also reconstructed by the two methods. Periprosthetic structures were selected at the similar two levels. Four radiologists visually graded the image quality on a scale from 0 to 5. Additionally, the readers also assessed the presence of prosthetic complication and tumor recurrence on a same scale. RESULTS: In the phantom, when the SEMAR was used, the CT numbers were closer to normal value and the noise of images using soft and sharper kernel were respectively reduced by up to 77.1% and 43.4% at the stem level, and by up to 82.2% and 64.5% at the articular level. The subjective scores increased 1 ~ 3 points and 1 ~ 4 points at the two levels, respectively. Prosthetic complications and tumor recurrence were diagnosed in 66 patients. And the SEMAR increased the diagnostic confidence of prosthetic complications and tumor recurrence (4 ~ 5 vs. 1 ~ 1.5). CONCLUSIONS: The SEMAR algorithm can significantly reduce the metal artifacts and increase diagnostic confidence of prosthetic complications and tumor recurrence in patients with knee tumor prostheses.

Low-dose CT with metal artifact reduction in arthroplasty imaging: a cadaveric and clinical study.

OBJECTIVE: To determine whether a simulated low-dose metal artifact reduction (MAR) CT technique is comparable with a clinical dose MAR technique for shoulder arthroplasty evaluation. MATERIALS AND METHODS: Two shoulder arthroplasties in cadavers and 25 shoulder arthroplasties in patients were scanned using a clinical dose (140 kVp, 300 qrmAs); cadavers were also scanned at half dose (140 kVp, 150 qrmAs). Images were reconstructed using a MAR CT algorithm at full dose and a noise-insertion algorithm simulating 50% dose reduction. For the actual and simulated half-dose cadaver scans, differences in SD for regions of interest were assessed, and streak artifact near the arthroplasty was graded by 3 blinded readers. Simulated half-dose scans were compared with full-dose scans in patients by measuring differences in implant position and by comparing readers' grades of periprosthetic osteolysis and muscle atrophy. RESULTS: The mean difference in SD between actual and simulated half-dose methods was 2.42 HU (95% CI [1.4, 3.4]). No differences in streak artifact grades were seen in 13/18 (72.2%) comparisons in cadavers. In patients, differences in implant position measurements were within 1° or 1 mm in 149/150 (99.3%) measurements. The inter-reader agreement rates were nearly identical when readers were using full-dose (77.3% [232/300] for osteolysis and 76.9% [173/225] for muscle atrophy) and simulated half-dose (76.7% [920/1200] for osteolysis and 74.0% [666/900] for muscle atrophy) scans. CONCLUSION: A simulated half-dose MAR CT technique is comparable both quantitatively and qualitatively with a standard-dose technique for shoulder arthroplasty evaluation, demonstrating that this technique could be used to reduce dose in arthroplasty imaging.

Benefits of iterative metal artifact reduction and dual-energy CT towards mitigating artifact in the setting of total shoulder prostheses.

OBJECTIVE: To determine the utility of iterative metal artifact reduction and 130 keV dual-energy virtual monoenergetic images to improve bone and soft tissue visualization in CT scans affected by metal artifacts. MATERIAL AND METHODS: Thirteen females and 6 males with a history of total shoulder prosthesis who underwent dual-energy shoulder CT were included. Four sets of images were reconstructed for each patient: (1) original polychromatic kV images reconstructed with weighted filtered back projection; (2) polychromatic kV images with iterative metal artifact reduction; (3) 130 keV dual-energy virtual monoenergetic; (4) combined iterative metal artifact reduction and 130 keV dual-energy virtual monoenergetic. Three readers blindly reviewed all image sets and graded the extent of artifact and image quality. RESULTS: Mean artifact score and median overall image quality score were better in 130 keV dual-energy virtual monoenergetic with iterative metal artifact reduction compared with those in original polychromatic kV images (3.02 vs 4.28, P < 0.001 and 3.00 vs 4.33, P < 0.001, respectively). The median difference in CT numbers between regions affected by artifacts and normal regions was lowest in 130 keV dual-energy virtual monoenergetic with iterative metal artifact reduction compared with that in original polychromatic kV images (72.28 vs 252.08, P < 0.001 for bony regions and 15.09 vs 324.38, P < 0.001 for soft tissue). CONCLUSION: In patients with metal artifacts due to shoulder replacement surgery, the use of dual-energy monoenergetic images and iterative metal artifact reduction reconstruction significantly improves both subjective and objective indicators of image quality.