Orthopedic Metal Artifact Reduction Research Articles

Image quality and metal artifact reduction in total hip arthroplasty CT: deep learning-based algorithm versus virtual monoenergetic imaging and orthopedic metal artifact reduction

BackgroundTo compare image quality, metal artifacts, and diagnostic confidence of conventional computed tomography (CT) images of unilateral total hip arthroplasty patients (THA) with deep learning-based metal artifact reduction (DL-MAR) to conventional CT and 130-keV monoenergetic images with and without orthopedic metal artifact reduction (O-MAR).MethodsConventional CT and 130-keV monoenergetic images with and without O-MAR and DL-MAR images of 28 unilateral THA patients were reconstructed. Image quality, metal artifacts, and diagnostic confidence in bone, pelvic organs, and soft tissue adjacent to the prosthesis were jointly scored by two experienced musculoskeletal radiologists. Contrast-to-noise ratios (CNR) between bladder and fat and muscle and fat were measured. Wilcoxon signed-rank tests with Holm-Bonferroni correction were used.ResultsSignificantly higher image quality, higher diagnostic confidence, and less severe metal artifacts were observed on DL-MAR and images with O-MAR compared to images without O-MAR (p < 0.001 for all comparisons). Higher image quality, higher diagnostic confidence for bone and soft tissue adjacent to the prosthesis, and less severe metal artifacts were observed on DL-MAR when compared to conventional images and 130-keV monoenergetic images with O-MAR (p ≤ 0.014). CNRs were higher for DL-MAR and images with O-MAR compared to images without O-MAR (p < 0.001). Higher CNRs were observed on DL-MAR images compared to conventional images and 130-keV monoenergetic images with O-MAR (p ≤ 0.010).ConclusionsDL-MAR showed higher image quality, diagnostic confidence, and superior metal artifact reduction compared to conventional CT images and 130-keV monoenergetic images with and without O-MAR in unilateral THA patients.Relevance statementDL-MAR resulted into improved image quality, stronger reduction of metal artifacts, and improved diagnostic confidence compared to conventional and virtual monoenergetic images with and without metal artifact reduction, bringing DL-based metal artifact reduction closer to clinical application.Key points• Metal artifacts introduced by total hip arthroplasty hamper radiologic assessment on CT.• A deep-learning algorithm (DL-MAR) was compared to dual-layer CT images with O-MAR.• DL-MAR showed best image quality and diagnostic confidence.• Highest contrast-to-noise ratios were observed on the DL-MAR images.Graphical

Utility of spectral CT with orthopedic metal artifact reduction algorithms for 125I seeds implantation in mediastinal and hepatic tumors.

Virtual monochromatic image (VMI) combined with orthopedic metal artifact reduction algorithms (VMI + O-MAR) can effectively reduce artifacts caused by metal implants of different types. Nevertheless, so far, no study has systematically evaluated the efficacy of VMI + O-MAR in reducing various types of metal artifacts induced by 125I seeds. The aim of this study was to assess the effectiveness of combining spectral computed tomography (CT) images with O-MAR in reducing metal artifacts and improving the image quality affected by artifacts in patients after 125I radioactive seeds implantation (RSI). A total of 45 patients who underwent dual-layer detector spectral CT (DLCT; IQon, Philips Healthcare) scanning of mediastinal and hepatic tumors after 125I RSI were retrospectively included. Spectral data were reconstructed into conventional image (CI), VMI, CI combined with O-MAR (CI + O-MAR), and VMI + O-MAR to evaluate the de-artifact effect and image quality improvement. Objective indicators included signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and artifact index (AI) of lesions affected by artifacts. Subjective indicators included assessment of overcorrected artifacts and new artifacts, different morphology of artifacts, and overall image quality. In artifact-affected lesion areas, SNR and CNR in the CI/VMI + O-MAR groups were better than those in CI groups (all P values <0.05). The AI showed a downward trend as VMI keV increased (all P values <0.001). The AI values of the CI/VMI (50-150 keV) group were all higher than the groups of CI/VMI + O-MAR (50-150 keV) (P<0.001). Overcorrection artifacts and new artifacts were concentrated in the VMI50/70 keV groups. In the evaluation of artifact morphology, as the VMI keV increased, the number of near-field banding artifacts in hyperdense artifacts gradually decreased, whereas the number of minimal or no artifacts increased, and the total number of hyperdense artifacts were decreased. The diagnostic and image quality scores of hyperdense artifacts were higher than those of hypodense artifacts as VMI keV increased. High VMI level combined with O-MAR substantially improve objective and subjective image quality, lesion display ability, and diagnostic confidence of CT follow-up after 125I RSI, especially at the VMI + O-MAR 150 keV level.

Dosimetric impact of CT metal artifact reduction for spinal implants in stereotactic body radiotherapy planning.

Metal artifacts due to spinal implants may affect the accuracy of dose calculation for radiotherapy. However, the dosimetric impact of metal artifact reduction (MAR) for spinal implants in stereotactic body radiotherapy (SBRT) plans has not been well studied. The objective of this study was to evaluate the dosimetric impact of MAR in spinal SBRT planning with three clinically common dose calculation algorithms. Gammex phantom and 10 patients' computed tomography (CT) images were studied to investigate the effects of titanium implants. A commercial orthopedic MAR algorithm was employed to reduce artifacts. Dose calculations for SBRT were conducted on both artifact-corrected and uncorrected images using three commercial algorithms [analytical anisotropic algorithm (AAA), Acuros XB (AXB), and Monte Carlo (MC)]. Dose discrepancies between artifact-corrected and uncorrected cases were appraised using a dose-volume histogram (DVH) and 3-dimensional (3D) gamma analysis with different distance to agreement (DTA) and dose difference criteria. The gamma agreement index (GAI) was denoted as G(∆D, DTA). Statistical analysis of t-test was utilized to evaluate the dose differences of different algorithms. The phantom study demonstrated that titanium metal artifacts can be effectively reduced. The patient cases study showed that dose differences between the artifact-corrected and uncorrected datasets were small evaluated by gamma index and DVH. Gamma analysis found that even the strict criterion local G(1,1) had average values ≥93.9% for the three algorithms. For all DVH metrics, average differences did not exceed 0.7% in planning target volume (PTV) and 2.1% in planning risk volume of spinal cord (PRV-SC). Statistical analysis showed that the observed dose differences of MC method were significantly larger than those of AAA (P<0.01 for D98% of PTV and P<0.001 for D0.1cc of spinal cord) and AXB methods (P<0.001 for D98% and P<0.0001 for D0.1cc). Dosimetric impact of artifacts caused by titanium implants is not significant in spinal SBRT planning, which indicates that dose calculation algorithms might not be very sensitive to CT number variation caused by titanium inserts.

Is AI the way forward for reducing metal artifacts in CT? Development of a generic deep learning-based method and initial evaluation in patients with sacroiliac joint implants

PurposeTo develop a deep learning-based metal artifact reduction technique (dl-MAR) and quantitatively compare metal artifacts on dl-MAR-corrected CT-images, orthopedic metal artifact reduction (O-MAR)-corrected CT-images and uncorrected CT-images after sacroiliac (SI) joint fusion. Methodsdl-MAR was trained on CT-images with simulated metal artifacts. Pre-surgery CT-images and uncorrected, O-MAR-corrected and dl-MAR-corrected post-surgery CT-images of twenty-five patients undergoing SI joint fusion were retrospectively obtained. Image registration was applied to align pre-surgery with post-surgery CT-images within each patient, allowing placement of regions of interest (ROIs) on the same anatomical locations. Six ROIs were placed on the metal implant and the contralateral side in bone lateral of the SI joint, the gluteus medius muscle and the iliacus muscle. Metal artifacts were quantified as the difference in Hounsfield units (HU) between pre- and post-surgery CT-values within the ROIs on the uncorrected, O-MAR-corrected and dl-MAR-corrected images. Noise was quantified as standard deviation in HU within the ROIs. Metal artifacts and noise in the post-surgery CT-images were compared using linear multilevel regression models. ResultsMetal artifacts were significantly reduced by O-MAR and dl-MAR in bone (p < 0.001), contralateral bone (O-MAR: p = 0.009; dl-MAR: p < 0.001), gluteus medius (p < 0.001), contralateral gluteus medius (p < 0.001), iliacus (p < 0.001) and contralateral iliacus (O-MAR: p = 0.024; dl-MAR: p < 0.001) compared to uncorrected images. Images corrected with dl-MAR resulted in stronger artifact reduction than images corrected with O-MAR in contralateral bone (p < 0.001), gluteus medius (p = 0.006), contralateral gluteus medius (p < 0.001), iliacus (p = 0.017), and contralateral iliacus (p < 0.001). Noise was reduced by O-MAR in bone (p = 0.009) and gluteus medius (p < 0.001) while noise was reduced by dl-MAR in all ROIs (p < 0.001) in comparison to uncorrected images. Conclusiondl-MAR showed superior metal artifact reduction compared to O-MAR in CT-images with SI joint fusion implants.

Effectiveness of orthopedic metal artifact reduction among patients undergoing computed tomography at a tertiary setting – A cross-sectional study

Background: In computed tomography (CT), metal implants increase the inconsistencies between the measured data and the linear assumption of the radon transform made by the analytic CT reconstruction algorithm. Aims and Objectives: The aims of this study was to evaluate the effectiveness of orthopedic metal artifact reduction (O-MAR) among patients undergoing CT at a tertiary setting. Materials and Methods: A cross-sectional observational study was conducted on 30 subjects attending the department of radiology for CT scan for 1 year from December 2018 to 2019. The CT scan was performed in 64 detector row (PHILIPS INGENUITY CORE 128 slice) scanner. The patient was asked for the presence of metallic objects/history of implants, and the topo gram confirms it. Image noise was considered as the primary outcome variable. The statistical analysis was performed using the coGuide software and P&lt;0.005. Results: All the thirty participants were analyzed finally. Image noise in plain image type was 79.5 SD of Hounsfield units, and in O-MAR image type, it was 44.01 SD of Hounsfield units denoting a higher percentage of SD in plain than O-MAR images. Conclusion: The O-MAR application helped in improving image quality of CT for patients in the aspect of metal artifact reduction and soft-tissue profile. However, it can also improve diagnostic quality in the evaluation of patients with severe metallic artifacts by decreasing the negative impacts of orthopedic metals.

Metal artifact reduction in computed tomography: Is it of benefit in evaluating sacroiliac joint fusion?

PurposeThe aim of this study was to compare image quality of computed tomography (CT) images with and without orthopedic metal artifact reduction (O-MAR) in the follow-up of patients after sacroiliac (SI) joint fusion. MethodsThirty-six consecutive patients (31 females and 5 males) undergoing CT within 24 h after SI joint fusion were included. CT images were reconstructed with and without O-MAR and scored by two radiologists with over 20 years of experience using a six-point ordinal scale. Images were scored on overall image quality and five criteria that are important to the clinician for the follow-up of patients after SI joint fusion. In addition, images were scored on how well four bony structures could be delineated. Wilcoxon signed-ranks tests with Holm-Bonferroni correction were used to test for differences between the radiologists’ scores on CT images with and without O-MAR. ResultsBoth radiologists scored overall image quality significantly higher (p < 0.05) on the images without O-MAR than on the images with O-MAR. In addition, two of the follow-up criteria, delineation of the sacrum and delineation of the implanted ilium were scored significantly higher (p < 0.05) on the images without O-MAR. Neither radiologist scored the images with O-MAR significantly higher than the images without O-MAR for any of the criteria. ConclusionCT imaging without O-MAR provided higher image quality and better assessment of SI joint fusion follow-up criteria compared to CT imaging with O-MAR in the follow-up of patients after SI joint fusion.

Comparison of Metal Artifact Reduction Algorithms in Patients with Hip Prostheses: Virtual Monoenergetic Images vs. Orthopedic Metal Artifact Reduction.

To assess the usefulness of various metal artifact reduction (MAR) methods in patients with hip prostheses. This retrospective study included 47 consecutive patients who underwent hip arthroplasty and dual-energy CT. Conventional polyenergetic image (CI), orthopedic-MAR (O-MAR), and virtual monoenergetic image (VMI, 50-200 keV) were tested for MAR. Quantitative analysis was performed in seven regions around the prostheses. Qualitative assessments included evaluation of the degree of artifacts and the presence of secondary artifacts. The lowest amount of image noise was observed in the O-MAR, followed by the VMI. O-MAR also showed the lowest artifact index, followed by high-keV VMI in the range of 120-200 keV (soft tissue) or 200 keV (bone). O-MAR had the highest contrast-to-noise ratio (CNR) in regions with severe hypodense artifacts, while VMI had the highest CNR in other regions, including the periprosthetic bone. On assessment of the CI of pelvic soft tissues, VMI showed a higher structural similarity than O-MAR. Upon qualitative analysis, metal artifacts were significantly reduced in O-MAR, followed by that in VMI, while secondary artifacts were the most frequently found in the O-MAR (p < 0.001). O-MAR is the best technique for severe MAR, but it can generate secondary artifacts. VMI at high keV can be advantageous for evaluating periprosthetic bone.

Quantitative analysis of metal artifact reduction in total hip arthroplasty using virtual monochromatic imaging and orthopedic metal artifact reduction, a phantom study

ObjectiveTo quantify metal artifact reduction using 130 keV virtual monochromatic imaging (VMI) with and without orthopedic metal artifact reduction (O-MAR) in total hip arthroplasty.MethodsConventional polychromatic images and 130 keV VMI of a phantom with pellets representing bone with unilateral or bilateral prostheses were reconstructed with and without O-MAR on a dual-layer CT. Pellets were categorized as unaffected, mildly affected and severely affected.ResultsWhen 130 keV VMI with O-MAR was compared to conventional imaging with O-MAR, a relative metal artifact reduction in CT values, contrast-to-noise (CNR), signal-to-noise (SNR) and noise in mildly affected pellets (67%, 74%, 48%, 68%, respectively; p < 0.05) was observed but no significant relative metal artifact reduction in severely affected pellets. Comparison between 130 keV VMI without O-MAR and conventional imaging with O-MAR showed relative metal artifact reduction in CT values, CNR, SNR and noise in mildly affected pellets (92%, 72%, 38%, 51%, respectively; p < 0.05) but negative relative metal artifact reduction in CT values and noise in severely affected pellets (− 331% and -223%, respectively; p < 0.05), indicating aggravation of metal artifacts.ConclusionOverall, VMI of 130 keV with O-MAR provided the strongest metal artifact reduction.

Prostate radiotherapy in the setting of bilateral hip prostheses: All commonly used photon-based radiation approaches are feasible.

The prevalence of hip prostheses is increasing. Prostate radiation delivery in the setting of hip prostheses is complicated by both imaging artifacts that interfere with volume delineation and dosimetric effects that must be addressed in the planning process. We hypothesized that with specialized planning, any photon-based definitive prostate radiotherapy approach may be utilized in patients with bilateral hip prostheses. Imaging data from sequential patients with prostate cancer and bilateral hip prostheses treated definitively with radiation were retrospectively reviewed. Bimodality imaging was used to define targets and organs at risk (OARs) along with specialized MRI sequences and/or orthopedic metal artifact reduction (OMAR) for MRI and CT artifact suppression, respectively. Multiple VMAT plans were generated for each set of patient images to include three fractionation schemes (conventional, hypofractionated, and SBRT), each with hip avoidance and with simulated normal hip. The ability to meet standard dose constraints was assessed for each plan type. Differences in target and OAR dosing between plans accounting for prosthetic hips via avoidance vs plans with simulated absence of prosthetic hip were also assessed. T-tests were used to compare dosimetric parameters. Ten patients with bilateral hip prostheses were identified, and 6 plans were created for each patient for a total of 60 radiation plans. Prosthetic hip avoidance did not result in failure to meet dose constraints for any patient. Hip avoidance resulted in minimal increases in high dose to the rectum and bladder (increases in mean V80%, V90%, and V95% ranged from 0.1% to 2.4%). Larger increases were seen at lower dose levels, with rectal V50% significantly increased in all three plan types with hip avoidance (conventional: 26.0% [standard deviation, SD 13.9] vs 16.9% [SD 10.2, p = 0.003]; hypofractionation: 26.4% [SD 13.3] vs 17.1% [SD 10.1, p = 0.002]; SBRT: 18.3% [SD 10.7] vs 10.5% [SD 6.9, p = 0.008]). Similarly, hip avoidance resulted in increases in bladder V50% to 31.7% (SD 16.8) vs 23.3% (SD 14.0, p = 0.001), 31.3% (SD 17.0) vs 23.3% (SD 13.8, p = 0.002), and 22.7% (SD 12.3) vs 16.5% (SD 12.6, p < 0.001) for conventional, hypofractionated, and SBRT plans, respectively. Hydrogel spacer resulted in reductions in rectal dose. For example, V70% for hip avoidance plans decreased with spacer presence to 8.3% (SD 6.7) vs 21.1% (SD 5.8, p = 0.021), 8.6% (SD 6.5) vs 21% (SD 5.7, p = 0.022), and 3.7% (SD 3.2) vs 15% (SD 8.2, p = 0.010) for conventional, hypofractionated, and SBRT plans, respectively. Any photon-based definitive prostate radiotherapy approach can be used with bimodality imaging for target and OAR definition and planning techniques to avoid dose attenuation effects of hip prostheses. Hydrogel spacer is a useful adjunct.

Evaluation of radiation treatment planning by computed tomography metal artifact reduction algorithm

Introduction: The objective of this study was to evaluate the usefulness of Computed Tomography(CT) images acquired through repeated subtraction reconstruction algorithms to reduce metal artifacts in CT Treatment Planning System(TPS).Materials and methods: Origin images of Gammex phantom and Rando phantom and non orthopedic metal artifact reduction(O-MAR) images were obtained after high density implantation. O-MAR applied images were also obtained. For evaluation of images, regions of interest(ROI) were set at five tissue rods and three points directly affected by artifacts in Gammex phantom. CT number and noise were compared and analyzed. To investigate dose change according to CT number change of the surrounding artifact, a three virtual cylindrical target volume was formed on Rando phantom CT images. The average dose was then compared and analyzed.Results: CT number difference according to the application of O-MAR showed significant difference among lung and bone rod and 3 ROI directly affected. Noise difference according to O-MAR application was significantly different in rod except for bone rod. In the treatment plan using Rando phantom, non-O-MAR and O-MAR images showed -4.3 ~ 1.9% and -0.4 ~ 2.3% dose differences, respectively.Conclusion: Applying a metal artifact reduction reconstruction algorithm can reduce image distortion due to high density implantation, improve image quality, and correct CT number.

A dosimetry study of post-mastectomy radiation therapy with AeroForm tissue expander.

PurposeTo evaluate the dosimetric effects of the AeroFormTM (AirXanpders®, Palo Alto, CA) tissue expander in‐situ for breast cancer patients receiving post‐mastectomy radiation therapy.Methods and MaterialsA film phantom (P1) was constructed by placing the metallic canister of the AeroForm on a solid water phantom with EBT3 films at five depths ranging from 2.6 mm to 66.2 mm. A breast phantom (P2), a three‐dimensional printed tissue‐equivalent breast with fully expanded AeroForm in‐situ, was placed on a thorax phantom. A total of 21 optical luminescent dosimeters (OLSDs) were placed on the anterior skin–gas interface and the posterior chest wall–metal interface of the AeroForm. Both phantoms were imaged with a 16‐bit computed tomography scanner with orthopedic metal artifact reduction. P1 was irradiated with an open field utilizing 6 MV and 15 MV photon beams at 0°, 90°, and 270°. P2 was irradiated using a volumetric modulated arc therapy plan with a 6 MV photon beam and a tangential plan with a 15 MV photon beam. All doses were calculated using Eclipse (Varian, Palo Alto, CA) with AAA and AcurosXB (AXB) algorithms.ResultsThe average dose differences between film measurements and AXB in the region adjacent to the canister in P1 were within 3.1% for 15 MV and 0.9% for 6 MV. Local dose differences over 10% were also observed. In the chest wall region of P2, the median dose of OLSDs in percentage of prescription dose were 108.4% (range 95.4%–113.0%) for the 15MV tangential plan and 110.4% (range 99.1%–113.8%) for the 6MV volumetric modulated arc therapy plan. In the skin–gas interface, the median dose of the OLSDs were 102.3% (range 92.7%–107.7%) for the 15 MV plan and 108.2% (range 97.8–113.5%) for the 6 MV plan. Measured doses were, in general, higher than calculated doses with AXB calculations. The AAA dose algorithms produced results with slightly larger discrepancies between measurements compared with AXB.ConclusionsThe AeroForm creates significant dose uncertainties in the chest wall–metal interface. The AcurosXB dose calculation algorithm is recommended for more accurate calculations. If possible, post‐mastectomy radiation therapy should be delivered after the permanent implant is in place.

Metal Artifact Reduction for Orthopedic Prosthesis in Lower Extremity CT Venography: Evaluation of Image Quality and Vessel Conspicuity

This study evaluates the image quality of lower extremity CT venography reconstructed with orthopedic metal artifact reduction (O-MAR) in patients with unilateral or bilateral metallic prostheses in the hip or knee. This retrospective study was approved by our institutional review board, and informed consent was waived. Twenty-nine patients of lower extremity CT with 51 metallic hip or knee prostheses were reconstructed to both standard CT images and O-MAR images. The subjective image quality and vessel conspicuity for both images were evaluated by two readers using five-point scales (0-4). Vessel conspicuity scores of 3 or 4 were considered diagnostically acceptable. Image noise was measured in the air and subcutaneous fat. O-MAR images showed significantly higher scores of subjective image quality (p < .001) and vessel conspicuity (p = .002) than standard CT images. Diagnostic acceptance of vessel conspicuity was not significantly different between O-MAR images and standard CT images (p = 1.000). O-MAR images showed significantly less image noise than conventional CT images (p < .001 for both air and subcutaneous fat). O-MAR may be an effective solution for the metal artifacts in lower extremity CT venography; however, the distance between prostheses and vessels affects the diagnostic acceptance in patients with metallic hip or knee prostheses. Level 4, Case Series.

The effects of the orthopedic metal artifact reduction (O-MAR) algorithm on contouring and dosimetry of head and neck radiotherapy patients

Metallic objects, such as dental fillings, cause artifacts in computed tomography (CT) scans. We quantify the contouring and dosimetric effects of Orthopedic Metal Artifact Reduction (O-MAR), in head and neck radiotherapy.The ease of organ contouring was assessed by having a radiation oncologist identify the CT data set with or without O-MAR for each of 28 patients that was easier to contour. The effect on contouring was quantified further by having the physician recontour parotid glands, previously drawn by him on the O-MAR scans, on uncorrected scans, and calculating the Dice coefficent (a measure of overlap) for the contours.Radiotherapy plans originally generated on scans reconstructed with O-MAR were recalculated on scans without metal artifact correction. The study was done using the Analytical Anisotropic Algorithm (AAA) dose calculation algorithm. The 15 patients with a planning target volume (PTV) extending to the same slice as the artifacts were used for this part of the study.The normal tissue doses were not significantly affected. The PTV mean dose and V95 were not affected, but the cold spots became less severe in the O-MAR corrected plans, with the minimum point dose on average being 4.1% higher. In 79% of the cases, the radiation oncologist identified the O-MAR scan as easier to contour; in 11% he chose the uncorrected scan and in 11% the scans were judged to have equal quality. A total of nine parotid glands (on both scans—18 contours in total) in 5 patients were recontoured. The average Dice coefficient for parotids drawn with and without O-MAR was found to be 0.775 +/− 0.045.The O-MAR algorithm does not produce a significant dosimetric effect in head and neck plans when using the AAA dose calculation algorithm. It can therefore be used for improved contouring accuracy without updating the critical structure tolerance doses and target coverage expectations.

Reducing artifacts from total hip replacements in dual layer detector CT: Combination of virtual monoenergetic images and orthopedic metal artifact reduction

PurposeTo evaluate the reduction of artifacts caused by total hip replacements (THR) in dual-layer DECT (DLCT) provided by the combination of virtual monoenergetic images (VMI) and orthopedic metal artifact reduction (MAR). Materials and MethodsA total of 24 consecutive patients carrying THR, who received DLCT, were included. Four different images were reconstructed from the same CT dataset: a) conventional images (CI), b) conventional images with orthopedic metal artifact reduction (CIMAR) c) VMI and d) VMI combined with orthopedic metal artifact reduction (VMIMAR). VMI and VMIMAR were reconstructed at 140 keV, 160 keV, 180 keV and 200 keV. Attenuation (HU) and noise (SD) were measured in order to evaluate reduction of hypodense and hyperdense artifacts, evaluate reduction of image noise as well as to calculate contrast-to-noise ratios (CNR). Image quality was additionally rated with regard to: a) extent of artifact reduction and assessment of b) pelvic organs, c) bone and d) muscle adjacent to the metal implants. Statistical analysis was performed using Wilcoxon test. ResultsVMIMAR at high keV, 140, 160, 180 and 200 keV, led to the greatest reduction of hypodense artifacts in comparison to plain VMI or CIMAR (p < 0.01), while in comparison to CI hyperdense artifacts were significantly reduced in all reconstructions (p < 0.05). Accordingly, subjective analysis found VMIMAR to be superior in reducing hypodense artifacts in comparison to VMI and CIMAR (p < 0.05), while hyperdense artifacts were equally reduced in all reconstructions compared to CI (p < 0.0001). Additionally, assessment of the pelvic organs and adjacent bone was significantly improved in VMIMAR in comparison to VMI and CIMAR (p < 0.05). In contrast, muscles adjacent to the metal implants were significantly better assessable in all reconstructions compared to CI (p < 0.01). ConclusionThe combination of VMI and MAR yields strongest reduction of hypo- and hyperdense artifacts caused by total hip replacements in staging DLCT in comparison to each technique by itself.

Metal Artifact Reduction of Dental Fillings in Head and Neck CT Images

Introduction: The issue of metal artifact and its reduction is as old as the clinical use of computed tomography itself. When metal objects such as dental fillings, hip prostheses or surgical clips are present in the computed tomography (CT) field of view (FOV), make severe artifacts that reduce the image quality and accuracy of CT numbers. They can lead to unreliable clinical results due to inability in true tumor volume delineation and uncertainty in dose calculation of treatment planning software. So far, no generally accepted solution to this problem, especially for small size dental fillings, has been found. Herein, an approach is presented to reduce the dental filling artifacts in CT images of head and neck patients with multiple dental fillings. The proposed approach is compared with the commercial orthopedic metal artifact reduction (O-MAR) algorithm by Philips company. Materials and Methods: Our algorithm consists of six steps: 1) metallic object segmentation by thresholding, 2) obtaining the prior image by multi thresholding of the initial image, 3) normalization of the original image sinogram by prior image, 4) interpolation (replacing the affected projection data by previous slice unaffected projection data, 5) denormalization of the corrected sinogram and 6) application of a two dimensional adaptive filter to the final image. The forth step can be implemented by substitution of affected projections with opposite view projections. Both methods were tested and previous slice substitution was superior. Quantitative evaluation of the commercial and proposed algorithms was done in terms of peak signal-to-noise ratio (PSNR), signal-to- noise ratio (SNR) and structural similarity index (SSIM) on a CT image of a head and neck patient with four dental fillings. The posterior part of the head in original image was considered as the reference image. Also two uniform regions of interest (ROI) were considered in the image. ROI1 was posterior region of the head away from dental fillings, while ROI2 was restricted to the tongue region near to the dental fillings. Results: The PSNR, SNR, SSIM values obtained by the proposed method and O-MAR algorithm were 37.05, 36.13, 22.29, 21.37, 0.93 and 0.84, respectively. Using our approach, the standard deviation of CT numbers in ROI1 was 27 times less than the original image and 7% better than the commercial competitor. However, for ROI2 the commercial algorithm was 36% more successful in reduction of variations due to metal artifact. Conclusion: The proposed approach can be applied successfully for dental filling artifact reduction in head and neck patients. Although the performance of the commercial method was superior to ours in near dental regions, for the farther regions with more critical organs was vice versa. However, weighting the interpolation and adaptive filtering steps may result in even better results.

Combined application of virtual monoenergetic high keV images and the orthopedic metal artifact reduction algorithm (O-MAR): effect on image quality

To determine whether there is any additional metal artifact reduction when virtual monochromatic images (VMI) and metal artifact reduction for orthopedic implants (O-MAR) are applied together compared to their separate application in both phantom and clinical abdominopelvic CT studies. An agar phantom containing a spinal prosthesis was scanned using a dual-layer, energy CT scanner (IQon, Philips Healthcare), and reconstructed with the filtered back-projection algorithm without O-MAR (FBP), filtered back-projection algorithm with O-MAR (O-MAR), VMI140 without O-MAR (VMI140), and VMI140 with O-MAR (VMI140 + O-MAR). Abdominopelvic CT images of 47 patients with metallic prostheses were also reconstructed in the same manner for clinical study. Noise measured as the standard deviation of CT Hounsfield units was compared between the four reconstruction methods in both phantom and clinical studies. Improvements in metal artifact reduction, image quality, and diagnostic improvement were further analyzed in the clinical study. Noise was significantly decreased when both VMI and O-MAR were applied in conjunction compared to their separate application in both phantom (16.3 HU vs. 25.0 and 26.4 HU) and clinical studies (15.8 HU vs. 19.2 and 26.2 HU). In the clinical study, the qualitative degree of artifacts was also significantly reduced with VMI140 + O-MAR (2.85 and 2.87) compared to VMI140 (2.36 and 2.26) or O-MAR (2.13 and 2.04) alone for both reviewers (P < 0.001) and improvements in image quality were observed in all 47 patients, with actual diagnostic improvements observed in three. Metal artifacts can be additionally reduced by applying O-MAR and VMI in conjunction, compared to their separate application, thereby improving diagnostic performance.

Evaluation of Orthopedic Metal Artifact Reduction Application in Three-Dimensional Computed Tomography Reconstruction of Spinal Instrumentation: A Single Saudi Center Experience.

Aim of the Study:The aim of the study was to evaluate the commercially available orthopedic metal artifact reduction (OMAR) technique in postoperative three-dimensional computed tomography (3DCT) reconstruction studies after spinal instrumentation and to investigate its clinical application.Materials and Methods:One hundred and twenty (120) patients with spinal metallic implants were included in the study. All had 3DCT reconstruction examinations using the OMAR software after obtaining the informed consents and approval of the Institution Ethical Committee. The degree of the artifacts, the related muscular density, the clearness of intermuscular fat planes, and definition of the adjacent vertebrae were qualitatively evaluated. The diagnostic satisfaction and quality of the 3D reconstruction images were thoroughly assessed.Results:The majority (96.7%) of 3DCT reconstruction images performed were considered satisfactory to excellent for diagnosis. Only 3.3% of the reconstructed images had rendered unacceptable diagnostic quality.Conclusion:OMAR can effectively reduce metallic artifacts in patients with spinal instrumentation with highly diagnostic 3DCT reconstruction images.

Radiological Evaluation of Spinal Instrumentation as Treatment for Adolescent Idiopathic Scoliosis, a Single Saudi Center 5-Year Experience

Aim of the Study: The aim of this work is to radiologically evaluate the postoperative outcomes of spinal instrumentation performed as a treatment for Adolescent Idiopathic Scoliosis (AIS) on 5-year follow up basis, and to correlate with different clinical scenarios. Materials and Methods: One hundred (100) AIS consecutive patients treated with spinal instrumentation were included in this study. The study period was from 2012 to 2017. All patients had radiological evaluations including total spine x-rays, low dose CT scan using Orthopedic Metal Artifact Reduction (OMAR) software and MRI, after obtaining the informed consents and approval of the institution ethical board. Radiological evaluation included Cobb angle measurement assessed pre, postoperatively and at regular intervals within the 5-year period. Results: Of the 100 patients included, 24 were females and 76 were males. The average age at operation was 16.5 years. Sixty seven (67%) patients showed good correction and maintenance of the spinal curves where the mean Cobb angle was 68° preoperatively and 21° postoperatively, representing a correction rate of 74%. Thirty three (33%) patients showed complications including postoperative infection (13), surgical revision (4), pseudarthrosis (3), neurological deficits (5), screw loosening (7) and complete hardware failure (1); in whom the preoperative mean Cobb angle was 56° compared to the patients with no complications (p = 0.288). In males, there were postoperative complications in 27 out of 76 and in females 5 out of 24, (p = 0.027). The average duration of follow-up was 3.7 years for all cases. Conclusion: Five-year follow up of patients with AIS treated with spinal instrumentation demonstrates good improvement and maintenance of the corrected spinal curves in two thirds of patients, one third showed variable minor and major complications. Low dose CT scan with OMAR provided an effective modality for evaluation.

Prospective Study Evaluating Metal Artifact Reduction in MRI-Based Cervical Cancer Intracavitary Brachytherapy

The accuracy of MRI-based brachytherapy with titanium tandem and ovoid applicators for cervical cancer is affected by metal artifacts in imaging. We hypothesized that orthopedic metal artifact reduction (O-MAR) MRI may reduce artifact associated with the titanium tandem, and that variations in applicator reconstruction due to artifact can affect brachytherapy dosimetry. We performed a prospective clinical study to test these hypotheses. We enrolled 12 patients receiving brachytherapy for cervical cancer on a prospective institutional review board-approved imaging protocol. We intended for each patient to receive six MRI-based brachytherapy treatments interdigitated with intensity modulated radiation. After tandem and ovoid implantation, patients received MRI simulation on a 1.5 T scanner with T2-weighted (T2W), diffusion weighted imaging (DWI), proton density weighted imaging (PDW), and PDW with O-MAR. The O-MAR method incorporated slice-selective excitation pulses with large bandwidth, view angle tilting, and “weak” slice encoding for metal artifact correction with 7 z-phase encodes. The tumor was contoured on the DWI, bladder, and rectum on T2W, and the tandem was reconstructed based on the PDW. The primary endpoint was reduction in the dimensions of the “bloom” artifact associated with the tip of the titanium tandem as measured in the PDW and O-MAR images. We evaluated dosimetry effects of variations in reconstruction due to the artifact by creating mock brachytherapy plans in which the tandem and dwell positions were shifted distally by a distance equal to half the improvement in the artifact length in O-MAR compared to PDW. Values are reported as mean and range. Differences were evaluated using the paired t-test. We acquired 62 MRI simulation scans with O-MAR, out of 72 brachytherapy fractions. The tandem tip “bloom” artifact mean length was 6.7 mm (3.6-8.9) without O-MAR and 3.4 (1.4-6.7) with O-MAR (P < 0.01), and the artifact mean width was 7.5 mm (4.4-9.4) without O-MAR and 3.7 mm (1.8-5.9) with O-MAR (P < 0.01). The mock brachytherapy plan representing potential variation in tandem reconstruction was generated with a mean shift of 1.7 mm (0.6-3.0), and resulted in a mean decrease of 1.3% (-4.5 to 3.2) in point A dose (P < 0.01), 4.4% (-1.9 to 18) in mean tumor dose (P < 0.01), 1.5% (-8.9 to 7.4) in tumor D100% (P < 0.01), and 2.8% (-1.4 to 8.5) in tumor D90% (P < 0.01) compared to baseline plans. Additionally, the maximum bladder dose was not significantly changed (P = 0.08), but there was a mean decrease of 0.5% (-14 to 4.0) in mean bladder dose (P = 0.01), 1.2% (0.3 to 7.0) in maximum rectum dose (P < 0.01), and 1.1% (-2.9 to 2.9) in mean rectum dose (P < 0.01) compared to baseline plans. O-MAR decreases the artifact associated with the titanium tandem. Variability in reconstruction due to the artifact at the tip of a tandem may lead to a mean tumor dose of 4.4% less than expected, highlighting the importance of accurate applicator reconstruction in brachytherapy treatment planning.

Metal artifact reduction in MRI-based cervical cancer intracavitary brachytherapy

Magnetic resonance imaging (MRI) plays an increasingly important role in brachytherapy planning for cervical cancer. Yet, metal tandem, ovoid intracavitary applicators, and fiducial markers used in brachytherapy cause magnetic susceptibility artifacts in standard MRI. These artifacts may impact the accuracy of brachytherapy treatment and the evaluation of tumor response by misrepresenting the size and location of the metal implant, and distorting the surrounding anatomy and tissue. Metal artifact reduction sequences (MARS) with high bandwidth RF selective excitations and turbo spin-echo readouts were developed for MRI of orthopedic implants. In this study, metal artifact reduction was applied to brachytherapy of cervical cancer using the orthopedic metal artifact reduction (O-MAR) sequence. O-MAR combined MARS features with view angle tilting and slice encoding for metal artifact correction (SEMAC) to minimize in-plane and through-plane susceptibility artifacts. O-MAR improved visualization of the tandem tip on T2 and proton density weighted (PDW) imaging in phantoms and accurately represented the diameter of the tandem. In a pilot group of cervical cancer patients (N  =  7), O-MAR significantly minimized the blooming artifact at the tip of the tandem in PDW MRI. There was no significant difference observed in artifact reduction between the weak (5 kHz, 7 z-phase encodes) and medium (10 kHz, 13 z-phase encodes) SEMAC settings. However, the weak setting allowed a significantly shorter acquisition time than the medium setting. O-MAR also reduced susceptibility artifacts associated with metal fiducial markers so that they appeared on MRI at their true dimensions.