Effect Of Metal Artifact Reduction Research Articles

Effect of metal artifact reduction level on the assessment of dental implant positioning by cone-beam computed tomography.

This study evaluated the effect of metal artifact reduction (MAR) level and tube current on the assessment of dental implant positioning relative to the mandibular canal (MC) through cone-beam computed tomography (CBCT). Titanium dental implants were placed in dried mandibles at 0.5 mm superior to the MC (Group 1/n = 8), 0.5 mm inside the MC with perforation of the cortex (Group 2/n = 10). CBCT scans were obtained with different levels of MAR (off, medium and high) and two tube currents (4 mA and 8 mA). Four examiners analyzed the images and scored the contact between the implant and the MC using a 5-point scale. Sensitivity, specificity, area under receiver operating characteristic curve (ROC) and frequency of scores were calculated. Data were compared with ANOVA two-way and Tukey's test and scores with Chi-Square test. Specificity and area under ROC curve decreased significantly when MAR level was high compared with MAR-medium and MAR-off. The frequency of score 3 (inconclusive) was the highest, and scores 1 and 5 (definitely no contact and definitely contact, respectively) were the lowest with MAR-high, regardless of the tube current. When MAR was off, there were higher frequencies of scores 1 and 5. The level of MAR influences the assessment of the relationship between the dental implant and the MC. MAR-high led to lower diagnostic accuracy compared with MAR-medium and off. This paper shows that high level of MAR can interfere in the diagnostic of dental implant positioning relative to the mandibular canal, decreasing its accuracy.

Do metal artifact reduction algorithms influence the detection of implant-related injuries to the inferior alveolar canal in CBCT images?

BackgroundThe routine application of dental implants for replacing missing teeth has revolutionized restorative and prosthetic dentistry. However, cone beam computed tomography (CBCT) evaluations of structures adjacent to the implants are limited by metal artifacts. There are several methods for reducing metal artifacts, but this remains a challenging task. This study aimed to examine the effectiveness of metal artifact reduction (MAR) algorithms in identifying injuries of implants to the inferior alveolar canal in CBCT images.MethodIn this in vitro study, mono-cortical bone windows were created and the inferior alveolar canal was revealed. Using 36 implants, pilot drill and penetration damage of the implant tip into the canal was simulated and compared to the control implants with distance from the canal. CBCT images were evaluated by four experienced observers with and without the MAR algorithm and compared to direct vision as the gold standard. The values of accuracy, sensitivity, and specificity were obtained and compared by receiver operating characteristic (ROC) curve (α = 0.05).ResultThe area under the ROC curve values for detection of pilot drill injuries varied between 0.840–0.917 and 0.639–0.854 in the active and inactive MAR conditions, respectively. The increase in ROC area was only significant for one of the observers (P = 0.010). For diagnosing penetrative injuries, the area under the ROC curve values was between 0.990–1.000 and 0.722–1.000 in the active and inactive MAR conditions, respectively. The improvement of ROC curve values in active MAR mode was only significant for one of the observers (P = 0.006).ConclusionActivation of MAR improved the diagnostic values of CBCT images in detecting both types of implant-related injuries to the inferior alveolar canal. However, for most observers, this increase was not statistically significant.

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. This study compared 1.5-T and 3-T compressed sensing slice encoding for metal artifact correction (CS-SEMAC) MRI for diagnosing periprosthetic abnormalities around hip, knee, and ankle arthroplasty implants. Methods. Forty-five participants (mean age ± SD, 71 ± 14 years; 26 women, 19 men) with symptomatic lower extremity arthroplasty (hip, knee, and ankle, 15 each) prospectively underwent consecutive 1.5- and 3-T MRI with intermediate-weighted (IW) and STIR CS-SEMAC sequences. Using a Likert scale, three radiologists evaluated presence or absence of periprosthetic abnormalities, including bone marrow edema-like signal, osteolysis, stress reaction/fracture, synovitis, 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 CS-SEMAC MRI were interchangeable. Across all three joints, 3 T produced lower noise than 1.5 T (median IW/STIR score at 3 T vs 1.5 T, 4/4 [range, 2-5/3-5] vs 3/3 [2-5/2-4]; p < .01 for both), sharper edges (4/4 [both 2-5] vs 3/3 [2-4/2-5]; p < .02/p < .05), and more effective metal artifact reduction (4/4 [3-5/2-5] vs 4/4 [both 3-5]; p < .02/p = .72). Agreement was moderate to substantial for image contrast (IW/STIR, 0.66/0.54 [95% CI, 0.41-0.91/0.29-0.80]; p = .58/p = .16) and joint capsule visualization (0.57/0.70 [0.32-0.81/0.51-0.89]; p = .16/p = .19). The bone-implant interface was more visible at 1.5 T (median IW/STIR score, 4/4 [range, both 2-5] at 1.5 T vs 3/3 [both 2-5] at 3 T; p = .08/p = .58), but periprosthetic tissues had superior visibility at 3 T (4/4 [both 3-5] at 3 T vs 4/4 [2-5/3-5] at 1.5 T; p = .07/p = .19). Conclusion. Optimized 1.5-T and 3-T CS-SEMAC MRI are interchangeable for diagnosing periprosthetic abnormalities, although metallic artifacts are larger at 3 T. Clinical Impact. With CS-SEMAC MRI, lower extremity arthroplasty implants can be scanned at 3 T rather than 1.5 T.

Influence of field of view size and reconstruction methods on single-energy metal artifact reduction: a phantom study

The purpose of this study was to evaluate the effect of single-energy metal artifact reduction (SEMAR) for metal artifacts using CT images reconstructed with adaptive iterative dose reduction three dimensional (AIDR3D) and advanced intelligent clear-IQ engine (AiCE) in calibration-field of view of various sizes. A prosthetic hip joint was arranged at the center of the phantom. The phantom images were scanned by changing calibration-field of view of 320mm and 500mm, and were reconstructed using filtered back-projection (FBP), AIDR3D, and AiCE with and without SEMAR, respectively. The metal artifact reduction with SEMAR was evaluated by calculated the relative artifact index value and visual scores in degree of artifact by seven radiology technologists. Relative artifact index of FBP, AIDR3D, and AiCE with 320mm/500mm calibration-field of views were 10.2/10.0, 16.3/16.4, and 17.8/17.9 without SEMAR, 3.3/3.1, 2.6/2.5, and 2.3/2.0 with SEMAR, respectively. Visual scores were not significantly different between 320 and 500mm calibration-field of views in all reconstruction methods. The effect of metal artifact reduction was not affected by calibration-field of view sizes in the SEMAR combined with AIDR3D or AiCE.

[Evaluation of the Effect of Tube Voltage on Metal Artifact Reduction in Cone Beam Computed Tomography].

The purpose of this study was to evaluate the effectiveness of metal artifact reduction (MAR) processing in cone beam computed tomography angiography using the relative artifact index (AIr) and the difference due to tube voltage. A water phantom was imaged to obtain noise images. Next, a platinum alloy embolic coil was installed in the central part of the water phantom and the peripheral part, and then artifact images were acquired. The tube voltages were 70 kV and 109 kV, and four types of artifact images were acquired (with and without MAR). In all, 10 images in the z-direction from each image series were acquired (total: 40 images). The AIr value was calculated by setting a region of interest in the images, and multiple comparisons were made between the imaging conditions (significance level set at p<0.05). The AIr values were significantly lower by MAR, and MAR significantly reduced metal artifacts regardless of tube voltage (p<0.001). This study's results show that MAR with cone beam CT can reduce metal artifacts by more than 91%, and the effect is comparable regardless of tube voltage.

Metal Artifact Reduction With Tin Prefiltration in Computed Tomography: A Cadaver Study for Comparison With Other Novel Techniques.

With the aging population and thus rising numbers of orthopedic implants (OIs), metal artifacts (MAs) increasingly pose a problem for computed tomography (CT) examinations. In the study presented here, different MA reduction techniques (iterative metal artifact reduction software [iMAR], tin prefilter technique, and dual-energy CT [DECT]) were compared. Four human cadaver pelvises with OIs were scanned on a third-generation DECT scanner using tin prefilter (Sn), dual-energy (DE), and conventional protocols. Virtual monoenergetic CT images were generated from DE data sets. Postprocessing of CT images was performed using iMAR. Qualitative (bony structures, MA, image noise) image analysis using a 6-point Likert scale and quantitative image analysis (contrast-to-noise ratio, standard deviation of background noise) were performed by 2 observers. Statistical testing was performed using Friedman test with Nemenyi test as a post hoc test. The iMAR Sn 150 kV protocol provided the best overall assessability of bony structures and the lowest subjective image noise. The iMAR DE protocol and virtual monochromatic image (VMI) ± iMAR achieved the most effective metal artifact reduction (MAR) (P < 0.05 compared with conventional protocols). Bony structures were rated worse in VMI ± iMAR (P < 0.05) than in tin prefilter protocols ± iMAR. The DE protocol ± iMAR had the lowest contrast-to-noise ratio (P < 0.05 compared with iMAR standard) and the highest image noise (P < 0.05 compared with iMAR VMI). The iMAR reduced MA very efficiently. When considering MAR and image quality, the iMAR Sn 150 kV protocol performed best overall in CT images with OI. The iMAR generated new artifacts that impaired image quality. The DECT/VMI reduced MA best, but experienced from a lack of resolution of bony fine structures.

Evaluation of a metal artifact reduction algorithm and an adaptive image noise optimization filter in the estimation of peri-implant fenestration defects using cone beam computed tomography: an in-vitro study.

The aim of this study is to assess the effects of metal artifact reduction (MAR) and adaptive image noise enhancer (AINO) in CBCT imaging on the detection accuracy of artificially created fenestration defects in proximity to titanium and zirconium implants in sheep jaw. Six zirconium and 10 titanium implants were planted on mandibular jaws of three sheep, and artificial defects were created. All images were obtained with a standard voxel size (0.150 mm3) and with 4 scan modes: (1) without MAR/without AINO; (2) with MAR/without AINO; (3) without MAR/with AINO; and (4) with MAR/with AINO during CBCT scanning. A total of 60 CBCT scans were produced. For all types of implants, intra- and inter-observer kappa values were the highest for MAR filter. The scan mode of with MAR filter was found to have the highest area under the curve (AUC), whereas the scan mode of without both MAR and AINO filters was found to have the lowest AUC values with statistical significance (p ≤ 0.05). Titanium implants were found to have higher AUC values than zirconium (p ≤ 0.05). Both MAR module and AINO filters enhance the accuracy of the detection of peri-implant fenestrations; however, the use of MAR filter solely can be recommended for detection of peri-implant fenestrations.

Measurement of Peri-Implant Bone Width with and without Metal Artifact Reduction Algorithm Using Two Cone-Beam Computed Tomography Software Programs

Objective:  To assess the effect of metal artifact reduction (MAR) algorithm of two cone-beam computed tomography (CBCT) software programs on the accuracy of peri-implant bone width measurements .  Material and Methods:  This in vitro study evaluated 35 bovine rib bone blocks measuring 8 x 8 x 11 mm. Titanium implants were inserted in bone blocks and placed in a wax model of mandible. CBCT scans were obtained with ProMax 3D and Cranex 3D CBCT systems with and without the MAR algorithm. The width of buccal and lingual bone plates surrounding the implant was measured on CBCT scans by two observers. The Cronbach’s alpha was calculated to assess inter-observer agreement. The area under the curve (AUC), sensitivity and specificity values were calculated and compared.  Results: The two observers had an excellent agreement. The accuracy of Cranex 3D was higher than that of ProMax 3D (p<0.05). Both CBCT systems showed higher accuracy when the MAR algorithm was not used (p<0.05). Both CBCT systems showed higher accuracy for measuring the width of the lingual plate than buccal plate (p<0.05) .  Conclusion:  The application of MAR algorithm did not notably increase the measurement accuracy in any CBCT system. Cranex 3D showed generally higher measurement accuracy than ProMax 3D.

Comparison of metal artifact reduction using single-energy CT and dual-energy CT with various metallic implants in cadavers

ObjectivesThe purpose of this study was to compare the effectiveness of metal artifact reduction using Single Energy Metal Artifact Reduction (SEMAR) and Dual Energy CT (DECT). Materials and methodsSix cadavers containing metal implants in the head, neck, abdomen, pelvis, and extremities were scanned with Standard, SEMAR, and DECT protocols on a 320-slice CT scanner. Four specialized radiologists blinded to acquisition methods rated severity of metal artifacts, visualization of anatomic structures, diagnostic interpretation, and image preference with a 5-point grading scale. ResultsScores were significantly better for SEMAR than Standard images in the hip, knee, pelvis, abdomen, and maxillofacial scans (3.25 ± 0.88 versus 2.14 ± 0.93, p < 0.001). However, new reconstruction artifacts developed in SEMAR images that were not present in Standard images. Scores for severity of metal artifacts and visualization of smooth structures were significantly better for DECT than Standard images in the cervical spine (3.50±0.50 versus 2.0±0.58, p < 0.001) and was preferred over Standard images by one radiologist. In all other cases, radiologists preferred the Standard image over the DECT image due to increased image noise and reduced low-contrast resolution with DECT. In all cases, SEMAR was preferred over Standard and DECT images. ConclusionSEMAR was more effective at reducing metal artifacts than DECT. Radiologists should be aware of new artifacts and review both the original and SEMAR images. When the anatomy or implant is relatively small, DECT may be superior to SEMAR without additional artifacts. However, radiologist should be aware of a reduction in soft tissue contrast.

METAL ARTIFACT REDUCTION IN STATIONARY INTRAORAL TOMOSYNTHESIS

<h3>Background</h3> The first generation stationary intraoral tomosynthesis (sIOT) device, developed at University of North Carolina (UNC), provides 3-D information in intraoral imaging with a speed and dose comparable with those of traditional intraoral radiography. Initial research shows promise in several diagnostic tasks, including caries and fracture detection. However, the original iterative reconstruction produces artifacts adjacent to metal restorations. Two new iterative reconstructions with metal artifact reduction (MAR1 and MAR2) have been developed. MAR1 segments the metal out before reconstruction and adds it back after reconstruction. MAR2 minimizes the artifact amplified at each iteration by dividing the projected error by the number of slices. <h3>Objective(s)</h3> The aim of this study was to compare the effectiveness of metal artifact reduction in tomosynthesis. <h3>Study Design</h3> Pilot samples of 2 extracted premolars with amalgam restorations were imaged by using the sIOT system. Reconstructions were generated using the original, MAR1, and MAR2 algorithms. Using line density plots, artifact pixel intensity and artifact width were measured for the original, MAR1, and MAR2 algorithms. <h3>Results</h3> The difference between average dentin pixel intensity and artifact pixel intensity for sample 1 was 8016, –5781, and 759 for the original, MAR1, and MAR2 reconstructions, respectively. Artifact width was 2.61 mm, 0.82 mm, and 1.38 mm, respectively. For sample 2, the difference in intensity was 8248, –5399, and 93, respectively. Artifact width was 1.71 mm, 1.06 mm, and 0.81 mm, respectively. <h3>Discussion/Conclusions</h3> MAR1 and MAR2 reduced the intensity of the artifacts; however, reduction by MAR2 was more pronounced. MAR1 produced radiopaque artifacts, whereas MAR2 produced radiolucent artifacts. MAR1 and MAR2 reduced the width of the artifacts, but the extent was reversed between the samples. The results support the value of MAR for tomosynthesis and suggests that MAR2 may be more effective. Continued development of artifact reduction techniques is needed with a more in-depth study using a larger sample size.

Quantitative assessment of three vendor’s metal artifact reduction techniques for CT imaging using a customized phantom

A metal implant was placed in an acrylic phantom to enable quantitative analysis of the metal artifact reduction techniques used in computed tomography (CT) scanners from three manufacturers. Two titanium rods were placed in a groove in a cylindrical phantom made by acrylic, after which the groove was filled with water. The phantom was scanned using three CT scanners (Toshiba, GE, Siemens) under the abdomen CT setting. CT number accuracy, contrast-to-noise ratio, area of the metal rods in the images, and fraction of affected pixel area of water were measured using ImageJ. Different iterative reconstruction, dual energy, and metal artifact reduction techniques were compared within three vendors. The highest contrast-to-noise ratio of three scanners were 85.7 ± 8.4 (Toshiba), 85.9 ± 11.7 (GE), and 55.0 ± 14.8 (Siemens); and the most correct results of metal area were 157.1 ± 1.4 mm2 (Toshiba), 155.0 ± 1.0 (GE), and 170.6 ± 5.3 (Siemens). The fraction of affected pixel area obtained using single-energy metal artifact reduction of Toshiba scanner was 2.2% ± 0.7%, which is more favorable than 4.1% ± 0.7% obtained using metal artifact reduction software of GE scanner (p = 0.002). Among all quantitative results, the estimations with fraction of affected pixel areas matched the effect of metal artifact reduction in the actual images. Therefore, the single-energy metal artifact reduction technique of Toshiba scanner had a desirable effect. The metal artifact reduction software of GE scanner effectively reduced the effect of metal artifacts; however, it underestimated the size of the metal rods. The monoenergetic and dual energy composition techniques of Siemens scanner could not effectively reduce metal artifacts.

4:03 PM Abstract No. 259 Utility of metal artifact reduction to improve visualization of therapeutic ice ball in CT-guided cryoablation of musculoskeletal metastases

To evaluate the effects of metal artifact reduction (MAR) on cryoprobe-induced artifact for improvement of therapeutic ice ball visualization in CT-guided cryoablation of musculoskeletal (MSK) metastases. An iterative MAR algorithm (Siemens, Germany) was retrospectively applied to 12 cases of CT-guided MSK cryoablation in 11 patients from November 2016 to August 2017. The final cryoablation CT image with greatest metal artifact caused by the cryoprobe was compared before and after application of MAR. Three experienced interventional radiologists performed a blinded, qualitative evaluation of side-by-side images with and without MAR using a modified 4-point scale (0-3; 0 denotes no artifact, 3 severe artifact). The metal artifact beyond and adjacent to the probe, metallic artifact compromising the ice ball margins, and visualization of critical structures within 1 cm of the margins was scored. Quantitative measurements of CT attenuation (Hounsfield Unit) and standard deviation (noise) were made in four locations: beyond the probe, directly overlying the probe tip, and within and outside of the ice ball margins. Wilcoxon signed-ranks test was used to compare variables. Qualitative analysis showed image quality improvement in MAR images beyond the probe tip (mean score 1.6/0.9, without MAR vs with MAR, p = 0.002), adjacent to the probe (0.8/0.4, p = 0.011), and ice ball conspicuity (1.1/0.5, p = 0.007). There was a trend towards improved visualization of critical structures within 1 cm of ice ball margins (0.8/0.4, p = 0.07). Quantitative analysis confirmed a noise decrease for MAR images beyond the probe (HU 90.5 ± 57.6, 64.8 ± 48.5, without MAR vs with MAR; p = 0.002) and within the ice ball (25.1 ± 8.7, 20.6 ± 7.0; p = 0.008). Noise overlying the probe tip and at critical structures was not significantly improved. MAR provides both qualitative and quantitative improvements for the visualization of the therapeutic ice ball during CT-guided cryoablation of musculoskeletal metastases.

[The Effect of Metal Artifact Reduction at Different Rotation Time in Computed Tomography].

The purpose of the study was to examine the metal artifact-reducing effects of single energy metal artifact reduction (SEMAR) at different rotation time. Helical and volume scans were employed to photograph a self-made phantom at various rotation time. Metal artifacts were examined using artifact index (AI) values and visual scores. At rotation times of 0.35, 0.4, 0.5, 0.6, 0.75, and 1.0 s/rotation on the helical scans (SEMAR-ON), AI values were 66.6, 64.3, 39.7, 39.7, 40.8, and 15.4, respectively, and visual scores were 3.2, 3.4, 3.0, 3.1, 3.0, and 2.8, respectively. Similar results were obtained on the volume scans. Specifically, the AI values reduced with a decreasing rotation time, although the visual scores did not significantly differ with a rotation time changes. The metal artifact-reducing effects of SEMAR are not altered by the rotation time.

Evaluation of digital tomosynthesis reconstruction algorithms used to reduce metal artifacts for arthroplasty: A phantom study

To investigate methods to reduce metal artifacts during digital tomosynthesis for arthroplasty, we evaluated five algorithms with and without metal artifact reduction (MAR)-processing tested under different radiation doses (0.54, 0.47, and 0.33mSv): adaptive steepest descent projection onto convex sets (ASD-POCS), simultaneous algebraic reconstruction technique total variation (SART-TV), filtered back projection (FBP), maximum likelihood expectation maximization (MLEM), and SART. The algorithms were assessed by determining the artifact index (AI) and artifact spread function (ASF) on a prosthesis phantom. The AI data were statistically analyzed by two-way analysis of variance. Without MAR-processing, the greatest degree of effectiveness of the MLEM algorithm for reducing prosthetic phantom-related metal artifacts was achieved by quantification using the AI (MLEM vs. ASD-POCS, SART-TV, SART, and FBP; all P<0.05). With MAR-processing, the greatest degree of effectiveness of the MLEM, ASD-POCS, SART-TV, and SART algorithms for reducing prosthetic phantom-related metal artifacts was achieved by quantification using the AI (MLEM, ASD-POCS, SART-TV, and SART vs. FBP; all P<0.05). When assessed by ASF, metal artifact reduction was largest for the MLEM algorithm without MAR-processing and ASD-POCS, SART-TV, and SART algorithm with MAR-processing. In ASF, the effect of metal artifact reduction was always greater at reduced radiation doses, regardless of which reconstruction algorithm with and without MAR-processing was used. In this phantom study, the MLEM algorithm without MAR-processing and ASD-POCS, SART-TV, and SART algorithm with MAR-processing gave improved metal artifact reduction.

The effects of metal artifact reduction on the retrieval ofattenuation values.

BackgroundThe quality of CT slices can be drastically reduced in the presence of high‐density objects such as metal implants within the patients’ body due to the occurrence of streaking artifacts. Consequently, a delineation of anatomical structures might not be possible, which strongly influences clinical examination.PurposeThe aim of the study is to clinically evaluate the retrieval of attenuation values and structures by the recently proposed Augmented Likelihood Image Reconstruction (ALIR) and linear interpolation in the presence of metal artifacts.Material and MethodsA commercially available phantom was equipped with two steel inserts. At a position between the metal rods, which shows severe streaking artifacts, different human tissue‐equivalent inserts are alternately mounted. Using a single‐source computer tomograph, raw data with and without metal rods are acquired for each insert. Images are reconstructed using the ALIR algorithm and a filtered back projection with and without linear interpolation. Mean and standard deviation are compared for a region of interest in the ALIR reconstructions, linear interpolation results, uncorrected images with metal rods, and the images without metal rods, which are used as a reference. Furthermore, the reconstructed shape of the inserts is analyzed by comparing different profiles of the image.ResultsThe measured mean and standard deviation values show that for all tissue classes, the metal artifacts could be reduced using the ALIR algorithm and the linear interpolation. Furthermore, the HU values for the different classes could be retrieved with errors below the standard deviation in the reference image. An evaluation of the shape of the inserts shows that the reconstructed object fits the shape of the insert accurately after metal artifact correction. Moreover, the evaluation shows a drop in the standard deviation for the ALIR reconstructed images compared to the reference images while reducing artifacts and keeping the shape of the inserts, which indicates a noise reduction ability of the ALIR algorithm.ConclusionHU values, which are distorted by metal artifacts, can be retrieved accurately with the ALIR algorithm and the linear interpolation approach. After metal artifact correction, structures, which are not perceptible in the original images due to streaking artifacts, are reconstructed correctly within the image using the ALIR algorithm. Furthermore, the ALIR produced images with a reduced noise level compared to reference images and artifact images. Linear interpolation results in a distortion of the investigated shapes and features remaining streaking artifacts.

The Effect of Metal Artifact Reduction at Different Calibrated and Display Field of Views in Computed Tomography.

The purpose of this study was to investigate the effects of the metal artifact reduction using single energy metal artifact reduction (SEMAR) with a prosthetic hip joint in different field of view (FOV). A prosthetic hip joint was arranged at the center of the phantom. The phantom images were scanned by changing calibrated-FOV (C-FOV) of 240, 320, 400, and 500 mm. Those images were reconstructed by changing the display-FOV (D-FOV) of 120, 180, 240, and 320 mm. The metal artifact reduction with the SEMAR was evaluated by calculating the artifact index (AI) and its decrease ratio. The AI of C-FOV (500 mm) and D-FOV (120, 180, 240, or 320 mm) were 15.8, 15.8, 15.7, and 14.4 with SEMAR. For changed C-FOV, the AI of C-FOV (240 mm) was significantly higher than any other C-FOVs. The AI of C-FOV (240 mm) was 29.8-30.0 and that of the other C-FOV were 12.4-15.8 with SEMAR. In addition, the decrease ratio of AI was 52.2-54.1% for C-FOV (240 mm) and 58.9-73.2% for the other C-FOVs. Although the SEMAR decreased the metal artifact, the effect of reducing the metal artifact was affected by C-FOV.

金属アーチファクト低減再構成技術におけるdisplay field of view(DFOV)の影響について

We evaluated the effect of orthopedic-metal artifact reduction (O-MAR) for metal artifact in computed tomography with 73 simulated seeds for brachytherapy in different sizes of display field of view (DFOV) obtained by helical scan under the same clinical scan condition. The metal artifacts were analyzed with the Gumbel's method by changing DFOV sizes 80 mm, 160 mm, and 320 mm. Gumbel distribution, scale parameter (γ), and location parameter (β) of the metal artifacts with O-MAR were compared with that of the metal artifacts with filtered back projection (FBP). In conclusion, it was considered that the effect of metal artifact reduction with O-MAR was influenced by DFOV size in this study. The reduction rates of scale parameter (γ) were 22.3%, 21.3%, and 10.0% in DFOV 80 mm, 160 mm, and 320 mm, respectively. The reduction rates of location parameter (β) were 27.4%, 23.4 %, and 9.8%. Therefore, the effect of metal artifact reduction with O-MAR showed the tendency of increasing with decreasing DFOV size.