CT scans through metal scanning technique versus hardware composition

Metal Artifact Reduction in Photon-Counting Detector CT: Quantitative Evaluation of Artifact Reduction Techniques

OBJECTIVES

With the introduction of clinical photon-counting detector computed tomography (PCD-CT) and its novel reconstruction techniques, a quantitative investigation of different acquisition and reconstruction settings is necessary to optimize clinical acquisition protocols for metal artifact reduction.

MATERIALS AND METHODS

A multienergy phantom was scanned on a clinical dual-source PCD-CT (NAEOTOM Alpha; Siemens Healthcare GmbH) with 4 different central inserts: water-equivalent plastic, aluminum, steel, and titanium. Acquisitions were performed at 120 kVp and 140 kVp (CTDI vol 10 mGy) and reconstructed as virtual monoenergetic images (VMIs; 110-150 keV), as T3D, and with the standard reconstruction "none" (70 keV VMI) using different reconstruction kernels (Br36, Br56) and with as well as without iterative metal artifact reduction (iMAR). Metal artifacts were quantified, calculating relative percentages of metal artifacts. Mean CT numbers of an adjacent water-equivalent insert and different tissue-equivalent inserts were evaluated, and eccentricity of metal rods was measured. Repeated-measures analysis of variance was performed for statistical analysis.

RESULTS

Metal artifacts were most prevalent for the steel insert (12.6% average artifacts), followed by titanium (4.2%) and aluminum (1.0%). The strongest metal artifact reduction was noted for iMAR (with iMAR: 1.4%, without iMAR: 10.5%; P < 0.001) or VMI (VMI: 110 keV 2.6% to 150 keV 3.3%, T3D: 11.0%, and none: 16.0%; P < 0.001) individually, with best results when combining iMAR and VMI at 110 keV (1.2%). Changing acquisition tube potential (120 kV: 6.6%, 140 kV: 5.2%; P = 0.33) or reconstruction kernel (Br36: 5.5%, Br56: 6.4%; P = 0.17) was less effective. Mean CT numbers and standard deviations were significantly affected by iMAR (with iMAR: -3.0 ± 21.5 HU, without iMAR: -8.5 ± 24.3 HU; P < 0.001), VMI (VMI: 110 keV -3.6 ± 21.6 HU to 150 keV -1.4 ± 21.2 HU, T3D: -11.7 ± 23.8 HU, and none: -16.9 ± 29.8 HU; P < 0.001), tube potential (120 kV: -4.7 ± 22.8 HU, 140 kV: -6.8 ± 23.0 HU; P = 0.03), and reconstruction kernel (Br36: -5.5 ± 14.2 HU, Br56: -6.8 ± 23.0 HU; P < 0.001). Both iMAR and VMI improved quantitative CT number accuracy and metal rod eccentricity for the steel rod, but iMAR was of limited effectiveness for the aluminum rod.

CONCLUSIONS

For metal artifact reduction in PCD-CT, a combination of iMAR and VMI at 110 keV demonstrated the strongest artifact reduction of the evaluated options, whereas the impact of reconstruction kernel and tube potential was limited.

Advanced Imaging of Total Knee Arthroplasty

The prevalence of total knee arthroplasty (TKA) is increasing with the aging population. Although long-term results are satisfactory, suspected postoperative complications often require imaging with the implant in place. Advancements in computed tomography (CT), such as tin prefiltration, metal artifact reduction algorithms, dual-energy CT with virtual monoenergetic imaging postprocessing, and the application of cone-beam CT and photon-counting detector CT, allow a better depiction of the tissues adjacent to the metal. For magnetic resonance imaging (MRI), high bandwidth (BW) optimization, the combination of view angle tilting and high BW, as well as multispectral imaging techniques with multiacquisition variable-resonance image combination or slice encoding metal artifact correction, have significantly improved imaging around metal implants, turning MRI into a useful clinical tool for patients with suspected TKA complications.

Quantitative Assessment of Lipiodol-Related Artifact Reduction for Dual-Energy Computed Tomography After Transcatheter Arterial Chemoembolization: A Phantom Study Evaluating the Use of Metal Artifact Reduction Algorithms

OBJECTIVE

This study used metal artifact reduction (MAR) software to examine the computed tomography (CT) number of dual-energy CT (DECT) of hepatocellular carcinoma after transcatheter arterial chemoembolization.

METHODS

Hollow columnar acrylic phantoms were filled with lipiodol and inserts of 2 sizes (large and small) were used to simulate liver tumors on a Revolution GSI CT scanner. The CT numbers of a single test object were collected twice: once with and once without the MAR algorithm. Lipiodol beam-hardening artifacts were quantified by measuring CT numbers in a region of interest around the tumor-simulating insert.

RESULTS

The virtual monochromatic CT numbers of large and small tumors were closely related to energy. For small tumors, CT numbers increased with energy. For large tumors, CT numbers increased with energy at 1 cm from the margin but decreased with an increase in energy at 5 cm. Regardless of the size, distance, or location of the tumor, the CT numbers fluctuated more at low energy levels.

CONCLUSIONS

At 1 cm from the margin, the CT numbers with MAR were significantly different from those without MAR. Low-energy CT numbers with MAR were near reference values. Metal artifact reduction exhibited superior performance for small tumors. Tumor margin images are affected by artifacts caused by Lipiodol. However, with MAR, CT numbers can be effectively calibrated, thus enabling clinicians to more accurately evaluate hepatocellular carcinoma development and identify residual tumors and recurrent or metastatic lesions.

[Postoperative imaging of the musculoskeletal system : Clinical aspects]

BACKGROUND

Postoperative imaging in trauma surgery is an essential part of documenting optimal osteosynthetic care. A precise and goal-oriented analysis with a justifiable indication is essential. The clinical information has a great impact on the quality of imaging. An objective evaluation and structured reporting complete the postoperative imaging procedure.

MATERIALS AND METHODS

Conventional x‑rays in two planes is the standard of postoperative imaging in musculoskeletal surgery. In specific anatomic structures, additional images may be necessary. The postoperative x‑ray is the simplest way to visualize a successful osteosynthesis and combines the most important points of postoperative management. Computed tomography (CT) is mostly used in emergencies, but also in the postoperative management of some elective procedures, including patients with surgery of the spine, hip or to the proximal long bones of the extremities. Furthermore, CT is useful in postoperative imaging of complicated ankle fractures. Magnetic resonance imaging (MRI) plays a modest role in postoperative imaging and is mostly used in musculoskeletal cancer surgery. Ultrasound rather plays a subordinated role in postoperative management, but it is increasingly becoming established as a tool for postoperative quality control. The great advantage is dynamic visualization in real time.

CONCLUSION

Postoperative imaging remains challenging, but can detect most issues regarding osteosynthesis, which can be then be treated or monitored. Various imaging modalities are available to make reliable statements on osteosynthetic material, bone and soft tissue.

Methods to address metal artifacts in post-processed CT images - A do-it-yourself guide for orthopedic surgeons

Computed tomography (CT) scans are often used for postoperative imaging in orthopedics. In the presence of metallic hardware, artifacts are generated, which can hamper visualization of the CT images, and also render the study ineffective for 3-D printing. Various solutions are available to minimize metal artifacts, and radiologists can employ these before or after processing the CT study. However, the orthopedic surgeon may be faced with situations where the metal artifacts were not addressed. To counter such problems, we present three do-it-yourself (DIY) techniques that can be used to manage metal artifacts.

Assessment of the efficiency of a pre- versus post-acquisition metal artifact reduction algorithm in the presence of 3 different dental implant materials using multiple CBCT settings: An in vitro study

Purpose

The aim of this study was to assess artifacts generated in cone-beam computed tomography (CBCT) of 3 types of dental implants using 3 metal artifact reduction (MAR) algorithm conditions (pre-acquisition MAR, postacquisition MAR, and no MAR), and 2 peak kilovoltage (kVp) settings.

Materials and Methods

Titanium-zirconium, titanium, and zirconium alloy implants were placed in a dry mandible. CBCT images were acquired using 84 and 90 kVp and at normal resolution for all 3 MAR conditions. The images were analyzed using ImageJ software (National Institutes of Health, Bethesda, MD) to calculate the intensity of artifacts for each combination of material and settings. A 3-factor analysis of variance model with up to 3-way interactions was used to determine whether there was a statistically significant difference in the mean intensity of artifacts associated with each factor.

Results

The analysis of all 3 MAR conditions showed that using no MAR resulted in substantially more severe artifacts than either of the 2 MAR algorithms for the 3 implant materials; however, there were no significant differences between pre- and post-acquisition MAR. The 90 kVp setting generated less intense artifacts on average than the 84 kVp setting. The titanium-zirconium alloy generated significantly less intense artifacts than zirconium. Titanium generated artifacts at an intermediate level relative to the other 2 implant materials, but was not statistically significantly different from either.

Conclusion

This in vitro study suggests that artifacts can be minimized by using a titanium-zirconium alloy at the 90 kVp setting, with either MAR setting.

Metal artifact reduction for improving quantitative SPECT/CT imaging

OBJECTIVE

This study aimed to evaluate the effect of the metal artifact reduction (MAR) method on quantitative single-photon emission computed tomography (SPECT)/computed tomography (CT) to reveal the usefulness of MAR in patients with metal implants.

METHODS

We performed a phantom experiment simulating patients with artificial hip prostheses using SPECT/CT equipped with the iterative MAR (iMAR). The phantom was filled with Tc-99m solution (29.5 kBq/mL). For the CT scan conditions, tube current time products were applied to obtain volume CT dose indexes (CTDIvols) of 1.4, 2.8, and 5.6 mGy. Six types of quantitative SPECT images were reconstructed using data from different doses of CT processed with and without iMAR for CT attenuation correction. Thirty circular regions of interest (ROIs) were placed in each of the dark-band artifact areas, the white-streak artifact areas, and the non-artifact areas. We calculated radioactivity concentrations from quantitative SPECT images with and without iMAR to evaluate the quantitative accuracy. The differences of the effect of iMAR with different CT doses were also evaluated.

RESULTS

The results obtained using CT data with a CTDIvol of 2.8 mGy are described below. For quantitative SPECT data without iMAR, we observed the underestimation of radioactivity concentration in the dark-band artifact areas and overestimation in the white-streak artifact areas. We observed quantification errors ranging from - 41.1% to + 20.0% without iMAR, depending on the ROI localization. When iMAR was used, these errors were reduced to a range of - 22.8% to + 14.2%. The mean absolute error from the true value in the artifact regions was also significantly reduced from 4.00 to 1.74 kBq/mL. In the non-artifact areas, the radioactivity concentrations obtained from the quantitative SPECT data with and without iMAR were equivalent to the true value and did not differ significantly between the two conditions. Similar results were observed for procedures with CTDIvols of 1.4 and 5.6 mGy.

CONCLUSIONS

This study indicated that iMAR could improve the quantitative accuracy of SPECT/CT independent of the CT dose. iMAR can serve as a practicable technique for quantitative SPECT/CT in patients with metal implants.

36M-pixel synchrotron radiation micro-CT for whole secondary pulmonary lobule visualization from a large human lung specimen

A micro-CT system was developed using a 36M-pixel digital single-lens reflex camera as a cost-effective mode for large human lung specimen imaging. Scientific grade cameras used for biomedical x-ray imaging are much more expensive than consumer-grade cameras. During the past decade, advances in image sensor technology for consumer appliances have spurred the development of biomedical x-ray imaging systems using commercial digital single-lens reflex cameras fitted with high megapixel CMOS image sensors. This micro-CT system is highly specialized for visualizing whole secondary pulmonary lobules in a large human lung specimen. The secondary pulmonary lobule, a fundamental unit of the lung structure, reproduces the lung in miniature. The lung specimen is set in an acrylic cylindrical case of 36 mm diameter and 40 mm height. A field of view (FOV) of the micro-CT is 40.6 mm wide × 15.1 mm high with 3.07 μm pixel size using offset CT scanning for enlargement of the FOV. We constructed a 13,220 × 13,220 × 4912 voxel image with 3.07 μm isotropic voxel size for three-dimensional visualization of the whole secondary pulmonary lobule. Furthermore, synchrotron radiation has proved to be a powerful high-resolution imaging tool. This micro-CT system using a single-lens reflex camera and synchrotron radiation provides practical benefits of high-resolution and wide-field performance, but at low cost.

Clinical application of multi-material artifact reduction (MMAR) technique in Revolution CT to reduce metallic dental artifacts

Background

This study aimed to explore the performance of Revolution CT virtual monoenergetic images (VMI) combined with the multi-material artifact reduction (MMAR) technique in reducing metal artifacts in oral and maxillofacial imaging.

Results

There were significant differences in image quality scores between VMI + MMAR images and VMI+MARS (multiple artifact reduction system) images at each monochromatic energy level (p = 0.000). Compared with the MARS technology, the MMAR technology further reduced metal artifacts and improved the image quality. At VMI_{90 keV} and VMI_{110 keV}, the SD, CNR, and AI in the Revolution CT group were significantly lower than in the Discovery CT, but no significant differences in these parameters were found between two groups at VMI_{50 keV}, VMI_{70 keV}, and VMI_{130 keV} (p > 0.05). The attenuation was comparable between two groups at any energy level (p > 0.05).

Conclusions

Compared with the MARS reconstruction technique of Discovery CT, the MMAR technique of Revolution CT is better to reduce the artifacts of dental implants in oral and maxillofacial imaging, which improves the image quality and the diagnostic value of surrounding soft tissues.

Metal implants influence CT scan parameters leading to increased local radiation exposure: A proposal for correction techniques

Metal implants not only deteriorate image quality, but also increase radiation exposure. The purpose of this study was to evaluate the effect of metal hip prosthesis on absorbed radiation dose and assess the efficacy of organ dose modulation (ODM) and metal artifact reduction (MAR) protocols on dose reduction. An anthropomorphic phantom was scanned with and without bilateral metal hip prostheses, and surface and deep level radiation doses were measured at the abdomen and pelvis. Finally, the absorbed radiation doses at pelvic and abdominal cavities in the reference, ODM, and two MAR scans (Gemstone spectral imaging, GE) were compared. The Mann Whitney-U test and Kruskal-Wallis test were performed to compare the volume CT dose index (CTDI_vol) and mean absorbed radiation doses. Unilateral and bilateral metal hip prostheses increased CTDI_VOL by 14.4% and 30.5%, respectively. MAR protocols decreased absorbed radiation doses in the pelvis. MAR showed the most significant dose reduction in the deep pelvic cavity followed by ODM. However, MAR protocols increased absorbed radiation doses in the upper abdomen. ODM significantly reduced absorbed radiation in the pelvis and abdomen. In conclusion, metal hip implants increased radiation doses in abdominopelvic CT scans. MAR and ODM techniques reduced absorbed radiation dose in abdominopelvic CT scans with metal hip prostheses.

Prior-Guided Metal Artifact Reduction for Iterative X-Ray Computed Tomography

High-attenuation materials pose significant challenges to computed tomographic imaging. Formed of high mass-density and high atomic number elements, they cause more severe beam hardening and scattering artifacts than do water-like materials. Pre-corrected line-integral density measurements are no longer linearly proportional to the path lengths, leading to reconstructed image suffering from streaking artifacts extending from metal, often along highest-density directions. In this paper, a novel prior-based iterative approach is proposed to reduce metal artifacts. It combines the superiority of statistical methods with the benefits of sinogram completion methods to estimate and correct metal-induced biases. Preliminary results show minimized residual artifacts and significantly improved image quality.

Dual-energy CT and ceramic or titanium prostheses material reduce CT artifacts and provide superior image quality of total knee arthroplasty

PURPOSE

To evaluate the influence of different scan parameters for single-energy CT and dual-energy CT, as well as the impact of different material used in a TKA prosthesis on image quality and the extent of metal artifacts.

METHODS

Eight pairs of TKA prostheses from different vendors were examined in a phantom set-up. Each pair consisted of a conventional CoCr prosthesis and the corresponding anti-allergic prosthesis (full titanium, ceramic, or ceramic-coated) from the same vendor. Nine different (seven dual-energy CT and two single-energy CT) scan protocols with different characteristics were used to determine the most suitable CT protocol for TKA imaging. Quantitative image analysis included assessment of blooming artifacts (metal implants appear thicker on CT than they are, given as virtual growth in mm in this paper) and streak artifacts (thick dark lines around metal). Qualitative image analysis was used to investigate the bone-prosthesis interface.

RESULTS

The full titanium prosthesis and full ceramic knee showed significantly fewer blooming artifacts compared to the standard CoCr prosthesis (mean virtual growth 0.6-2.2 mm compared to 2.9-4.6 mm, p < 0.001). Dual-energy CT protocols showed less blooming (range 3.3-3.8 mm) compared to single-energy protocols (4.6-5.5 mm). The full titanium and full ceramic prostheses showed significantly fewer streak artifacts (mean standard deviation 77-86 Hounsfield unit (HU)) compared to the standard CoCr prosthesis (277-334 HU, p < 0.001). All dual-energy CT protocols had fewer metal streak artifacts (215-296 HU compared to single-energy CT protocols (392-497 HU)). Full titanium and ceramic prostheses were ranked superior with regard to the image quality at the bone/prosthesis interface compared to a standard CoCr prosthesis, and all dual-energy CT protocols were ranked better than single-energy protocols.

CONCLUSIONS

Dual-energy CT and ceramic or titanium prostheses reduce CT artifacts and provide superior image quality of total knee arthroplasty at the bone/prosthesis interface. These findings support the use of dual-energy CT as a solid imaging base for clinical decision-making and the use of full-titanium or ceramic prostheses to allow for better CT visualization of the bone-prosthesis interface.

Current and Novel Techniques for Metal Artifact Reduction at CT: Practical Guide for Radiologists

Artifacts caused by metallic implants appear as dark and bright streaks at computed tomography (CT), which severely degrade the image quality and decrease the diagnostic value of the examination. When x-rays pass through a metal object, depending on its size and composition, different physical effects negatively affect the measurements in the detector, most notably the effects of photon starvation and beam hardening. To improve image quality and recover information about underlying structures, several artifact reduction methods have been introduced in modern CT systems. Projection-based metal artifact reduction (MAR) algorithms act in projection space and replace corrupted projections caused by metal with interpolation from neighboring uncorrupted projections. MAR algorithms primarily suppress artifacts that are due to photon starvation. The dual-energy CT technique is characterized by data acquisition at two different energy spectra. Dual-energy CT provides synthesized virtual monochromatic images at different photon energy (kiloelectron volt) levels, and virtual monochromatic images obtained at high kiloelectron volt levels are known to reduce the effects of beam hardening. In clinical practice, although MAR algorithms can be applied after image acquisition, the decision whether to apply dual-energy CT for the patient usually needs to be made before image acquisition. Radiologists should be more familiar with the clinical and technical features of each method and should be able to choose the optimal method according to the clinical situation. ^©RSNA, 2018.

Magic Angle in Cardiac CT: Eliminating Clinically Relevant Metal Artifacts in Pacemaker Leads with a Lead-Tip/Gantry Angle of ≤70°

RATIONALE AND OBJECTIVE

To identify the influence of various parameters for reducing artifacts in computed tomography (CT) of commonly used pacemakers or implantable cardioverter-defibrillator (ICD) lead tips.

MATERIALS AND METHODS

This ex vivo phantom study compared two CT techniques (Dual-Energy CT [DECT] vs. Dual-Source CT [DSCT]), as well as the influence of incremental alterations of current-time product and pacemaker lead-tip angle with respect to the gantry plane. Four pacemaker leads and one ICD lead were evaluated. The images were assessed visually on a five-point Likert scale (1 = artifact free to 5 = massive artifacts). Likert values 1-3 represent clinically relevant, diagnostic image quality.

RESULTS

344 of 400 total images were rated with diagnostic image quality. The DECT and dual-source DSCT technique each scored 86% diagnostic image quality. Statistically, DECT images showed significantly improved image quality (P < .05). Concerning the current-time product, no statistically significant change was found. Regarding lead-tip positioning, an angle of ≤70° yielded 100% diagnostic image quality. Pacemaker and ICD leads were assessed to have statistically significant differences.

CONCLUSIONS

Surprisingly, the lead-tip angle of 70° has been established as the key angle under which diagnostic image quality is always ensured, regardless of the imaging technique. Thus, we call 70° the "Magic angle" in CT pacemaker imaging.

The utility of dual-energy CT for metal artifact reduction from intracranial clipping and coiling

OBJECTIVE

To assess the ability of dual-energy CT (DECT) to reduce metal-related artifacts in patients with clips and coils in head CT angiography, and to analyze the differences in this reduction between both type of devices.

MATERIALS AND METHODS

Thirteen patients (6 clips, 7 coils) were selected and retrospectively analized. Virtual monoenergetic images (MEI) with photon energies from 40 to 150 keV were obtained. Noise was measured at the area of maximum artifact. Subjective evaluation of streak artifact was performed by two radiologists independently. Differences between noise values in all groups were tested by using the ANOVA test. Mann-Whitney U test was used to compare the differences between clips and coils. Coheńs κ statistic was used to determine interobserver agreement.

RESULTS

The lowest noise value was observed at high energy levels (p<0,05). Noise was higher in the coil group than in the clip group (p<0.001). Interobserver agreement was good (κ=0.72).

CONCLUSIONS

TCED with MEI helps to minimize the artifact from clips ands coils in patients who undergo head CT angiography. The reduction of the artifact is greater in patients with surgical clipping than in patients with endovascular coiling.

Dual-Energy CT for the Musculoskeletal System

The principal advantages of dual-energy computed tomography (CT) over conventional CT in the musculoskeletal setting relate to the additional information provided regarding tissue composition, artifact reduction, and image optimization. This article discusses the manifestations of these in clinical practice-urate and bone marrow edema detection, metal artifact reduction, and tendon analysis, with potential in arthrography, bone densitometry, and metastases surveillance. The basic principles of dual-energy CT physics and scanner design will also be discussed. ^© RSNA, 2016.

Impact of iterative metal artifact reduction on diagnostic image quality in patients with dental hardware

Background Metal artifacts often impair diagnostic accuracy in computed tomography (CT) imaging. Therefore, effective and workflow implemented metal artifact reduction algorithms are crucial to gain higher diagnostic image quality in patients with metallic hardware. Purpose To assess the clinical performance of a novel iterative metal artifact reduction (iMAR) algorithm for CT in patients with dental fillings. Material and Methods Thirty consecutive patients scheduled for CT imaging and dental fillings were included in the analysis. All patients underwent CT imaging using a second generation dual-source CT scanner (120 kV single-energy; 100/Sn140 kV in dual-energy, 219 mAs, gantry rotation time 0.28-1/s, collimation 0.6 mm) as part of their clinical work-up. Post-processing included standard kernel (B49) and an iterative MAR algorithm. Image quality and diagnostic value were assessed qualitatively (Likert scale) and quantitatively (HU ± SD) by two reviewers independently. Results All 30 patients were included in the analysis, with equal reconstruction times for iMAR and standard reconstruction (17 s ± 0.5 vs. 19 s ± 0.5; P > 0.05). Visual image quality was significantly higher for iMAR as compared with standard reconstruction (3.8 ± 0.5 vs. 2.6 ± 0.5; P < 0.0001, respectively) and showed improved evaluation of adjacent anatomical structures. Similarly, HU-based measurements of degree of artifacts were significantly lower in the iMAR reconstructions as compared with the standard reconstruction (0.9 ± 1.6 vs. -20 ± 47; P < 0.05, respectively). Conclusion The tested iterative, raw-data based reconstruction MAR algorithm allows for a significant reduction of metal artifacts and improved evaluation of adjacent anatomical structures in the head and neck area in patients with dental hardware.

Performances of low-dose dual-energy CT in reducing artifacts from implanted metallic orthopedic devices

OBJECTIVES

The objective was to evaluate the performances of dose-reduced dual-energy computed tomography (DECT) in decreasing metallic artifacts from orthopedic devices compared with dose-neutral DECT, dose-neutral single-energy computed tomography (SECT), and dose-reduced SECT.

MATERIALS AND METHODS

Thirty implants in 20 consecutive cadavers underwent both SECT and DECT at three fixed CT dose indexes (CTDI): 20.0, 10.0, and 5.0 mGy. Extrapolated monoenergetic DECT images at 64, 69, 88, 105, 120, and 130 keV, and individually adjusted monoenergy for optimized image quality (OPTkeV) were generated. In each group, the image quality of the seven monoenergetic images and of the SECT image was assessed qualitatively and quantitatively by visually rating and by measuring the maximum streak artifact respectively.

RESULTS

The comparison between SECT and OPTkeV evaluated overall within all groups showed a significant difference (p <0.001), with OPTkeV images providing better images. Comparing OPTkeV with the other DECT images, a significant difference was shown (p <0.001), with OPTkeV and 130-keV images providing the qualitatively best results. The OPTkeV images of 5.0-mGy acquisitions provided percentages of images with scores 1 and 2 of 36 % and 30 % respectively, compared with 0 % and 33.3 % of the corresponding SECT images of 10- and 20-mGy acquisitions. Moreover, DECT reconstructions at the OPTkeV of the low-dose group showed higher CT numbers than the SECT images of dose groups 1 and 2.

CONCLUSIONS

This study demonstrates that low-dose DECT permits a reduction of artifacts due to metallic implants to be obtained in a similar manner to neutral-dose DECT and better than reduced or neutral-dose SECT.

Getting the Most From Your Dual-Energy Scanner: Recognizing, Reducing, and Eliminating Artifacts

OBJECTIVE

Dual-energy CT (DECT) is an innovative imaging modality that allows superior detection of pulmonary embolism, enhanced detection of urate in gout, and improved assessment of metal prostheses when compared with conventional CT.

CONCLUSION

The primary aim of this review is to describe these DECT protocols and compare each to its respective diagnostic reference standards. Moreover, this review will describe how to recognize, reduce, and eliminate DECT artifacts, thereby maximizing its diagnostic capabilities.

Computed tomography dose optimisation in cystic fibrosis: A review

Cystic fibrosis (CF) is the most common autosomal recessive disease of the Caucasian population worldwide, with respiratory disease remaining the most relevant source of morbidity and mortality. Computed tomography (CT) is frequently used for monitoring disease complications and progression. Over the last fifteen years there has been a six-fold increase in the use of CT, which has lead to a growing concern in relation to cumulative radiation exposure. The challenge to the medical profession is to identify dose reduction strategies that meet acceptable image quality, but fulfil the requirements of a diagnostic quality CT. Dose-optimisation, particularly in CT, is essential as it reduces the chances of patients receiving cumulative radiation doses in excess of 100 mSv, a dose deemed significant by the United Nations Scientific Committee on the Effects of Atomic Radiation. This review article explores the current trends in imaging in CF with particular emphasis on new developments in dose optimisation.

Use of cone-beam computed tomography in early detection of implant failure

Preimplant planning with complex imaging techniques has long been a recommended practice for assessing the quality and quantity of alveolar bone before dental implant placement. When maxillofacial imaging is necessary, static film or digital images lack the depth and dimension offered by computed tomography. Cone-beam computed tomography (CBCT) offers the dentist not only a radiographic volumetric view of alveolar bone but also a 3-dimensional reconstruction. This article reviews the use of CBCT for assessing implant placement and early detection of failure, and compares the performance of CBCT with that of other imaging modalities in the early detection of implant failure.

[Imitation of an Anderson type II dens fracture by a motion artefact in computed tomography : Four case examples]

Computed tomography (CT) is the method of choice in the diagnosis and classification of odontoid fractures with a sensitivity of more than 99 % and a specificity almost equally as high. In this article we report on four cases where CT-generated motion artefacts exactly mimicked an Anderson type II fracture of the dens axis, initially leading to a wrong diagnosis. Although this seems to be a very rare event, these cases indicate that overlooked CT motion artefacts can lead to severe consequences and attention must be paid to the radiological signs outlined in this report.

Value of monoenergetic dual-energy CT (DECT) for artefact reduction from metallic orthopedic implants in post-mortem studies

OBJECTIVES

The aim of this ex vivo study was to assess the performance of monoenergetic dual-energy CT (DECT) reconstructions to reduce metal artefacts in bodies with orthopedic devices in comparison with standard single-energy CT (SECT) examinations in forensic imaging. Forensic and clinical impacts of this study are also discussed.

MATERIALS AND METHODS

Thirty metallic implants in 20 consecutive cadavers with metallic implants underwent both SECT and DECT with a clinically suitable scanning protocol. Extrapolated monoenergetic DECT images at 64, 69, 88, 105, 120, and 130 keV and individually adjusted monoenergy for optimized image quality (OPTkeV) were generated. Image quality of the seven monoenergetic images and of the corresponding SECT image was assessed qualitatively and quantitatively by visual rating and measurements of attenuation changes induced by streak artefact.

RESULTS

Qualitative and quantitative analyses showed statistically significant differences between monoenergetic DECT extrapolated images and SECT, with improvements in diagnostic assessment in monoenergetic DECT at higher monoenergies. The mean value of OPTkeV was 137.6 ± 4.9 with a range of 130 to 148 keV.

CONCLUSIONS

This study demonstrates that monoenergetic DECT images extrapolated at high energy levels significantly reduce metallic artefacts from orthopedic implants and improve image quality compared to SECT examination in forensic imaging.

[CT and MRI of hip arthroplasty]

Metal-induced artifacts impair image quality of computed tomography (CT) and magnetic resonance imaging (MRI) in patients with hip prostheses. Due to new developments in metal artifact reduction both methods can now be used for evaluation of a painful hip prosthesis. Iterative reconstruction algorithms and dual-energy scans are among the newer CT techniques for artifact reduction, while slice-encoding for metal artifact correction (SEMAC) and multi-acquisition variable-resonance image combination (MAVRIC) have introduced substantial improvements for MRI. Loosening of the hip prosthesis, osteolysis from small wear particles and pseudotumors in metal-on-metal prostheses are specific pathologies in patients with total hip arthroplasty. Other causes of painful hip prostheses are infections, fractures, tendinopathies, tendon ruptures, muscle and nerve alterations and heterotopic ossifications.

Metal artifact reduction: standard and advanced magnetic resonance and computed tomography techniques

An increasing number of joint replacements are being performed in the United States. Patients undergoing these procedures can have various complications. Imaging is one of the primary means of diagnosing these complications. Cross-sectional imaging techniques, such as computed tomography (CT) and MR imaging, are more sensitive than radiographs for evaluating complications. The use of CT and MR imaging in patients with metallic implants is limited by the presence of artifacts. This review discusses the causes of metal artifacts on MR imaging and CT, contributing factors, and conventional and novel methods to reduce the effects of these artifacts on scans.

Assessment of metal artefact reduction around dental titanium implants in cone beam CT

OBJECTIVES

The aim of this study was to investigate if the metal artefact reduction (MAR) tool used in the software of the ORTHOPANTOMOGRAPH(®) OP300 (Instrumentarium Dental, Tuusula, Finland) can improve the gray value levels in post-operative implant scans.

METHODS

20 potential implant sites were selected from 5 edentulous human dry mandibles. Each mandible was scanned by a CBCT scanner, and images were produced under three different conditions: implant sites drilled but no implants inserted, implants inserted without application of MAR and implants inserted with application of MAR. Using Geomagic(®) Studio 2012 (Geomagic, Morrisville, NC) and 3Diagnosys(®) v. 5.3.1 (3Diemme(®) SRL, Cantù, Italy) software, three scans of each mandible were superimposed. The mean gray value of identical regions of bone around the implants was derived for each condition. The differences between gray value measurements at implant sites derived from different conditions were assessed.

RESULTS

A significant difference was found between mean gray values from the scans with no implants inserted and with implants inserted (with and without MAR) (p = 0.012). No significant difference was revealed for gray values measured from scans with and without MAR (p = 0.975).

CONCLUSIONS

The MAR tool in the software of the ORTHOPANTOMOGRAPH OP300 CBCT scanner does not significantly correct the voxel gray values affected by the metal artefact in the vicinity of an implant in human dry mandibles.

Peering through the glare: using dual-energy CT to overcome the problem of metal artefacts in bone radiology

OBJECTIVE

Imaging of patients with large metal implants remains one of the most difficult endeavours for radiologists. This article reviews the theory of dual-energy CT (DECT) and its ability to reduce metal artefact, thus enhancing the diagnostic value of musculoskeletal imaging. The strengths, weaknesses, and alternative applications of DECT, as well as areas requiring further research, will also be reviewed.

CONCLUSION

Currently, DECT stands as the frontier for metal artefact reduction in musculoskeletal imaging. DECT requires no additional radiation and provides significantly enhanced image acquisition. When considered along with its other capabilities, DECT is a promising new tool for musculoskeletal and trauma radiologists.

Bone quality evaluation at dental implant site using multislice CT, micro-CT, and cone beam CT

OBJECTIVES

The first purpose of this study was to analyze the correlation between bone volume fraction (BV/TV) and calibrated radiographic bone density Hounsfield units (HU) in human jaws, derived from micro-CT and multislice computed tomography (MSCT), respectively. The second aim was to assess the accuracy of cone beam computed tomography (CBCT) in evaluating trabecular bone density and microstructure using MSCT and micro-CT, respectively, as reference gold standards.

MATERIAL AND METHODS

Twenty partially edentulous human mandibular cadavers were scanned by three types of CT modalities: MSCT (Philips, Best, the Netherlands), CBCT (3D Accuitomo 170, J Morita, Kyoto, Japan), and micro-CT (SkyScan 1173, Kontich, Belgium). Image analysis was performed using Amira (v4.1, Visage Imaging Inc., Carlsbad, CA, USA), 3Diagnosis (v5.3.1, 3diemme, Cantu, Italy), Geomagic (studio(®) 2012, Morrisville, NC, USA), and CTAn (v1.11, SkyScan). MSCT, CBCT, and micro-CT scans of each mandible were matched to select the exact region of interest (ROI). MSCT HU, micro-CT BV/TV, and CBCT gray value and bone volume fraction of each ROI were derived. Statistical analysis was performed to assess the correlations between corresponding measurement parameters.

RESULTS

Strong correlations were observed between CBCT and MSCT density (r = 0.89) and between CBCT and micro-CT BV/TV measurements (r = 0.82). Excellent correlation was observed between MSCT HU and micro-CT BV/TV (r = 0.91). However, significant differences were found between all comparisons pairs (P < 0.001) except for mean measurement between CBCT BV/TV and micro-CT BV/TV (P = 0.147).

CONCLUSIONS

An excellent correlation exists between bone volume fraction and bone density as assessed on micro-CT and MSCT, respectively. This suggests that bone density measurements could be used to estimate bone microstructural parameters. A strong correlation also was found between CBCT gray values and BV/TV and their gold standards, suggesting the potential of this modality in bone quality assessment at implant site.

Total ankle arthroplasty: optimizing computed tomography imaging protocol

OBJECTIVE

To evaluate parameters and positioning when imaging total ankle prostheses on computed tomography (CT).

MATERIALS AND METHODS

An ankle prosthesis implanted into a pig's knee joint underwent 16 different CT imaging protocols. Four defects were drilled around prosthesis components simulating periprosthetic osteolytic lesions. The specimen with the implant was imaged in four different orientations with the tibial stem parallel to the table and at 25, 45, and 90° angles to it. The protocol consisted of scanning at 100, 120, and 140 kVp in every position with a pitch of 1.2. The scanning at 120 kVp in every position was repeated with a pitch of 1.0.

RESULTS

CT proved to be a reliable imaging modality when studying periprosthetic lesions adjacent to the ankle prosthesis when the tibial stem alignment was parallel to the table. When imaging at higher angles, metal artifacts distorted the image, making the analysis of periprosthetic bone structure unreliable. There were no statistically significant differences between different tube voltages or pitch in volume measurements of the osteolytic lesions.

CONCLUSIONS

CT is a reliable imaging method to evaluate periprosthetic bone structure around ankle prostheses when orientation of the prosthesis and acquisition parameters is optimized.

A questionnaire survey reviewing radiologists' and clinical specialist radiographers' knowledge of CT exposure parameters

Objective

To review knowledge of computed tomography (CT) parameters and their influence on patient dose and image quality amongst a cohort of clinical specialist radiographers (CSRs) and examining radiologists.

Methods

A questionnaire survey was devised and distributed to a cohort of 65 examining radiologists attending the American Board of Radiology exam in Kentucky in November 2011. The questionnaire was later distributed by post to a matching cohort of Irish CT CSRs. Each questionnaire contained 40 questions concerning CT parameters and their influence on both patient dose and image quality.

Results

A response rate of 22 % (radiologists) and 32 % (CSRs) was achieved. No difference in mean scores was detected between either group (27.8 ± 4 vs 28.1 ± 4, P = 0.87) although large ranges were noted (18–36). Considerable variations in understanding of CT parameters was identified, especially regarding operation of automatic exposure control and the influence of kilovoltage and tube current on patient dose and image quality. Radiologists were unaware of recommended diagnostic reference levels. Both cohorts were concerned regarding CT doses in their departments.

Conclusions

CT parameters were well understood by both groups. However, a number of deficiencies were noted which may have a considerable impact on patient doses and limit the potential for optimisation in clinical practice.

Key points

• CT users must adapt parameters to optimise patient dose and image quality.

• The influence of some parameters is not well understood.

• A need for ongoing education in dose optimisation is identified.

Effect of brightness in the evaluation of lumbar pedicular screws position: clinical study

Artifact may lead to confusion when evaluating postoperative CT scans of lumbar pedicle screws. The aim of our study was to develop a specific metal artifact reduction image protocol, in order to reduce metal artifact caused by titanium pedicular screw in patients undergoing lumbar pathology by lumbar fusion. Therefore, the reduction in metal artifacts in lumbar pedicle screws allows surgeons to do an accurate diagnosis of the exact placement of inserted pedicle screws, minimizes false reexploration, and maximizes proper and prompt treatment of misplaced screw. In a first step, we performed a retrospective study of 103 titanium alloy pedicle screws in patients undergoing a lumbar instrumented fusion for treatment for degenerative disease. CT scan was performed postoperatively evaluating the possible overdimension caused by artifact. In a second step, a prospective study was performed using a 64-slice multidetector-row computed tomography (MDCT) in 104 titanium alloy pedicle screws in patients undergoing a lumbar instrumented fusion for treatment for degenerative disease. Our results show that on the group of sequential CT scan, mean overdimension (on each side) due to brightness was 1.045 mm (SD 0.45). On the group of 64-slice multichannel CT, mean overdimension (on each side) due to brightness was 0.005 mm at the proximal part of the screw and 0.025 mm at the distal part of the screw. The results observed suggest that beam-hardening artifacts caused by the screw on CT after lumbar fusion are dramatically reduced by using specific metal artifact reduction image protocol in a 64-slice MDCT.

Metal artifacts reduction using monochromatic images from spectral CT: evaluation of pedicle screws in patients with scoliosis

PURPOSE

To evaluate the effectiveness of spectral CT in reducing metal artifacts caused by pedicle screws in patients with scoliosis.

MATERIALS AND METHODS

Institutional review committee approval and written informed consents from patients were obtained. 18 scoliotic patients with a total of 228 pedicle screws who underwent spectral CT imaging were included in this study. Monochromatic image sets with and without the additional metal artifacts reduction software (MARS) correction were generated with photon energy at 65keV and from 70 to 140keV with 10keV interval using the 80kVp and 140kVp projection sets. Polychromatic images corresponded to the conventional 140kVp imaging were also generated from the same scan data as a control group. Both objective evaluation (screw width and quantitative artifacts index measurements) and subjective evaluation (depiction of pedicle screws, surrounding structures and their relationship) were performed.

RESULTS

Image quality of monochromatic images in the range from 110 to 140keV (0.97±0.28) was rated superior to the conventional polychromatic images (2.53±0.54) and also better than monochromatic images with lower energy. Images of energy above 100keV also give accurate measurement of the width of screws and relatively low artifacts index. The form of screws was slightly distorted in MARS reconstruction.

CONCLUSIONS

Compared to conventional polychromatic images, monochromatic images acquired from dual-energy CT provided superior image quality with much reduced metal artifacts of pedicle screws in patients with scoliosis. Optimal energy range was found between 110 and 140keV.

Clinical evaluation of the normalized metal artefact reduction algorithm caused by dental fillings in CT

OBJECTIVES

The aim of this study was to evaluate the performance of a normalized metal artefact reduction (NMAR) algorithm in patients with high-density dental fillings in CT images, and compare the results with weighted filtered back-projection (WFBP) and linear interpolation metal artefact reduction (MARli) algorithms.

METHODS

A total of 15 patients who had dental fillings were included in this study. The CT raw data sets were processed on an offline workstation. For each data set, one image series was reconstructed with WFBP, one with MARli and one with NMAR. Two observers qualitatively graded the severity of metal artefacts and their impacts on surrounding and distant soft tissue using a five-point scale. Six regions of interest were selected to measure the CT values and the standard deviation (SD) for quantitatively evaluating the effects of artefact reduction.

RESULTS

A total of 217 slices with metal artefacts from 15 patients were included in the qualitative analysis. The average score (mean ± SD) with the WFBP and MARli algorithms was 2.24 ± 1.06 and 2.71 ± 0.73, respectively. Image artefacts were significantly reduced using the NMAR algorithm compared with the other two algorithms, with an average score of 1.70 ± 0.83. The mean CT value in the most hypodense streak artefacts around the metal fillings was significantly improved with both MARli and NMAR. The mean SDs of measured CT values from surrounding or distant soft tissues were lower in NMAR images than in WFBP and MARli images.

CONCLUSIONS

The NMAR algorithm can significantly reduce the artefacts caused by dental fillings, compared with the WFBP and linear interpolation algorithms.

A comparison of MRI and CT imaging clarity of titanium alloy and titanium alloy with cobalt-chromium-alloy pedicle screw and rod implants in the lumbar spine

BACKGROUND

Magnetic resonance imaging (MRI) and computed tomography (CT) imaging are important postoperative diagnostic and evaluation tools, particularly in patients who have undergone spinal fusions. Advancements in materials and imaging techniques have lessened artifact and improved overall imaging results. Systems that combine titanium alloy and cobalt-chromium components have been introduced to reduce implant profile while maintaining strength. The objective of this study was to determine if there were any differences in the clarity of imaging between two types of implant materials in a lumbar spine construct model.

METHODS

One of two lumbar spine stabilization implant systems, titanium alloy (titanium) or titanium alloy with cobalt-chromium alloy (titanium-cobalt), was placed to simulate a four-level fusion construct in two human cadaveric spine segments, followed by MRI and CT imaging. The implant systems were then removed from each cadaver and implanted in the other cadaver. Nine physician graders from three subspecialties scored the images using a 5-point scale, with higher imaging scores indicating greater clarity of the region of interest. Physician-rated scores were compared across systems and between physician groups.

RESULTS

There were no significant differences in the overall mean total scores on the basis of construct material. Overall mean scores were 18.16 for titanium and 17.45 for titanium-cobalt (p = 0.275). Among images of the titanium-cobalt constructs, no significant differences in mean scores were found between specimens with use of MRI (p = 0.883) or with use of CT only (p = 0.274). Among images of the titanium system, a slightly significant difference was found between specimens with use of MRI (p = 0.044) but not with CT imaging (p = 0.837).

CONCLUSIONS

Overall image clarity scores were not significantly different between titanium and titanium-cobalt implant systems in the lumbar spine. Observation of pertinent anatomy in the regions of interest was not degraded by the presence of either system.

Metallic artefact reduction with monoenergetic dual-energy CT: systematic ex vivo evaluation of posterior spinal fusion implants from various vendors and different spine levels

OBJECTIVES

To evaluate optimal monoenergetic dual-energy computed tomography (DECT) settings for artefact reduction of posterior spinal fusion implants of various vendors and spine levels.

METHODS

Posterior spinal fusion implants of five vendors for cervical, thoracic and lumbar spine were examined ex vivo with single-energy (SE) CT (120 kVp) and DECT (140/100 kVp). Extrapolated monoenergetic DECT images at 64, 69, 88, 105 keV and individually adjusted monoenergy for optimised image quality (OPTkeV) were generated. Two independent radiologists assessed quantitative and qualitative image parameters for each device and spine level.

RESULTS

Inter-reader agreements of quantitative and qualitative parameters were high (ICC = 0.81-1.00, κ = 0.54-0.77). HU values of spinal fusion implants were significantly different among vendors (P < 0.001), spine levels (P < 0.01) and among SECT, monoenergetic DECT of 64, 69, 88, 105 keV and OPTkeV (P < 0.01). Image quality was significantly (P < 0.001) different between datasets and improved with higher monoenergies of DECT compared with SECT (V = 0.58, P < 0.001). Artefacts decreased significantly (V = 0.51, P < 0.001) at higher monoenergies. OPTkeV values ranged from 123-141 keV. OPTkeV according to vendor and spine level are presented herein.

CONCLUSIONS

Monoenergetic DECT provides significantly better image quality and less metallic artefacts from implants than SECT. Use of individual keV values for vendor and spine level is recommended.

KEY POINTS

• Artefacts pose problems for CT following posterior spinal fusion implants. • CT images are interpreted better with monoenergetic extrapolation using dual-energy (DE) CT. • DECT extrapolation improves image quality and reduces metallic artefacts over SECT. • There were considerable differences in monoenergy values among vendors and spine levels. • Use of individualised monoenergy values is indicated for different metallic hardware devices.

Spinal fusion-hardware construct: Basic concepts and imaging review

The interpretation of spinal images fixed with metallic hardware forms an increasing bulk of daily practice in a busy imaging department. Radiologists are required to be familiar with the instrumentation and operative options used in spinal fixation and fusion procedures, especially in his or her institute. This is critical in evaluating the position of implants and potential complications associated with the operative approaches and spinal fixation devices used. Thus, the radiologist can play an important role in patient care and outcome. This review outlines the advantages and disadvantages of commonly used imaging methods and reports on the best yield for each modality and how to overcome the problematic issues associated with the presence of metallic hardware during imaging. Baseline radiographs are essential as they are the baseline point for evaluation of future studies should patients develop symptoms suggesting possible complications. They may justify further imaging workup with computed tomography, magnetic resonance and/or nuclear medicine studies as the evaluation of a patient with a spinal implant involves a multi-modality approach. This review describes imaging features of potential complications associated with spinal fusion surgery as well as the instrumentation used. This basic knowledge aims to help radiologists approach everyday practice in clinical imaging.

Metal artefact reduction with cone beam CT: an in vitro study

BACKGROUND

Metal in a patient's mouth has been shown to cause artefacts that can interfere with the diagnostic quality of cone beam CT. Recently, a manufacturer has made an algorithm and software available which reduces metal streak artefact (Picasso Master 3D® machine; Vatech, Hwaseong, Republic of Korea).

OBJECTIVES

The purpose of this investigation was to determine whether or not the metal artefact reduction algorithm was effective and enhanced the contrast-to-noise ratio.

METHODS

A phantom was constructed incorporating three metallic beads and three epoxy resin-based bone substitutes to simulate bone next to metal. The phantom was placed in the centre of the field of view and at the periphery. 10 data sets were acquired at 50-90 kVp. The images obtained were analysed using a public domain software ImageJ (NIH Image, Bethesda, MD). Profile lines were used to evaluate grey level changes and area histograms were used to evaluate contrast. The contrast-to-noise ratio was calculated.

RESULTS

The metal artefact reduction option reduced grey value variation and increased the contrast-to-noise ratio. The grey value varied least when the phantom was in the middle of the volume and the metal artefact reduction was activated. The image quality improved as the peak kilovoltage increased.

CONCLUSION

Better images of a phantom were obtained when the metal artefact reduction algorithm was used.

Quantification of metal artifacts on cone beam computed tomography images

OBJECTIVES

To quantify metal artifacts obtained from a wide range of cone beam computed tomography (CBCT) devices and exposure protocols, to compare their tolerance to metals of different densities, and to provide insights regarding the possible implementation of metal artifact analysis into a QC protocol for CBCT.

MATERIALS AND METHODS

A customized polymethyl methacrylate (PMMA) phantom, containing titanium and lead rods, was fabricated. It was scanned on 13 CBCT devices and one multi-slice computed tomography (MSCT) device, including high-dose and low-dose exposure protocols. Artifacts from the rods were assessed by two observers by measuring the standard deviation of voxel values in the vicinity of the rods, and normalizing this value to the percentage of the theoretical maximum standard deviation.

RESULTS

For CBCT datasets, artifact values ranged between 6.1% and 27.4% for titanium, and between 10.% and 43.7% for lead. Most CBCT devices performed worse than MSCT for titanium artifacts, but all of them performed better for lead artifacts. In general, no clear improvement of metal artifacts was seen for high-dose protocols, although certain devices showed some artifact reduction for large FOV or high exposure protocols.

CONCLUSIONS

Regions in the vicinity of the metal rods were moderately or gravely affected, particularly in the area between the rods. In practice, the CBCT user has very limited possibilities to reduce artifacts. Researchers and manufacturers need to combine their efforts in optimizing exposure factors and implementing metal artifact reduction algorithms.

Fast CT metal artefacts correction based on derivative and region-based filling

INTRODUCTION

Metal artefacts seriously degrade the quality of the CT images. Blurring around the junctions between metal and non-metal regions in CT images, metal artefacts often prevent right diagnoses, and even lead to misdiagnoses of patients. The aim of the study was to devise a fast and robust method to improve the quality of the artefact-contaminated CT images.

METHODS

The proposed artefact correction includes the following five steps: metal object segmentation, forward projection, region-based filling, adaptive scaling and final image reconstruction.

RESULTS

The feasibility of the proposed method in correcting metal artefacts was validated by experiments on both simulated and clinical images. Experiments showed the proposed correction could lead to fast and effective reduction of metal artefacts in CT images.

CONCLUSIONS

Compared with other methods, the proposed method has less computational cost and allows a feasible and easy implantation into current CT imaging systems.