Metal Artifact Research Articles

The Nature of Metal Artifacts in X-ray Computed Tomography and Their Reduction by Optimization of Tomography Systems Parameters

A significant gap in the known methods for assessing the levels of metal artifacts in X-ray computed tomography and approaches to their reduction is an almost complete disregard for the physical nature of this artifact—the proximity to zero of radioscopic transparency. The proposed work fills this gap. A mathematical model has been developed for evaluating metal artifacts in X-ray computed tomography as applied to the geometry of a parallel beam. The simulation model was transformed into an algorithm, and a Mathcad program was designed to simulate images of the internal structure of the test objects. The algorithm for estimating the studied artifact includes the stages of generating sinograms and estimating the distributions of the linear coefficient over the sections of the object based on the back projection method with filtering. The efficiency of the metal artifacts simulation algorithm is demonstrated in the example of symmetric and asymmetric objects with low- and high-density inclusions and inclusions from materials with high atomic number values. The possibility of reducing metal artifacts with the help of a rational choice of the maximum energy of X-ray radiation and the ADC bit depth is illustrated. For example, for an aluminum cylinder 200 mm in diameter with a central cylindrical cavity 80 mm in diameter, cylindrical inserts 12 mm in diameter with material densities from 1.5 g/cm3 to 10 g/cm3, and effective atomic numbers of materials from 13 to 47, the numerical simulation method proved the following: it is practically unattainable to significantly reduce the level of metal artifacts by increasing the ADC capacity to the maximum X-ray energy of 160 keV; the desired effect is achieved by simultaneously increasing the maximum X-ray energy to 225 keV and the ADC capacity to 24 or 32; increasing the maximum X-ray energy from 160 keV to 225 keV leads to an increase in the energy absorbed in the material of the test object by 26%. The results of this research can be used at the design stage of X-ray computed tomography systems designed to control objects with fragments of low radiation transparency.

Integration of Laboratory and Field Measurements on Soil and Bronze Artifacts: Facilitating Conservation Treatment and Management of Archaeological Collections

ABSTRACT Chloride ion, pH, and voltage (redox potential) measurements were conducted in the field and conservation laboratory on soil and copper alloy artifacts deriving from two archaeological sites of the Japanese Institute of Anatolian Archaeology, Kaman-Kalehöyük (Kırşehir) and Büklükale (Kirikkale), in Central Anatolia, Turkey. The project established the impact of the burial environmental conditions on the state of the recovered metal artifacts and applied this information to the subsequent conservation management of the metal artifacts in the collection. These measurements may be used to determine the degree of stability of the metal artifacts for their long-term preservation. Based on the test results a conservation plan may be drafted according to three options: (1) active conservation intervention (e.g., treating with a chemical corrosion inhibitor or desalination); (2) preventive conservation through control of the environment; and (3) no protective measures necessary. Recommendations for conservators include simple tests on soil and representative artifacts as a guide to predict decay behavior for post-excavation collection management. These test protocols may be applied to the interpretation of material degradation at all archaeological sites and may be adapted for other porous materials. A decision-making model is provided in a flow chart.

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

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

First results of metallographic analysis and absolute dating of iron finds from Nowe Brzesko, site 26, Proszowice District

AbstractThis paper presents the results of analyses of metal artefacts discovered at a multiphase site in Nowe Brzesko, Małopolskie Voivodeship, Poland. Fieldwalking prospection led to the discovery of steely iron objects, ploughed out on the site among other numerous archeological finds. A prospecting sondage yielded more corroded metal artefacts, identified mainly as agricultural tools (e.g. sickles, scythes). These chronologically nondistinctive artefacts could be assigned to the third to fourth century AD using radiocarbon dating, complemented by metallurgical analysis. The results open up new research perspectives on the economy and society of the Przeworsk culture in the Late Roman period.

Single-Energy Metal Artifact Reduction (SEMAR) in Ultra-High-Resolution CT Angiography of Patients with Intracranial Implants

To evaluate the effects of single-energy metal artifact reduction (SEMAR) on image quality of ultra-high-resolution CT-angiography (UHR-CTA) with intracranial implants after aneurysm treatment. Image quality of standard and SEMAR-reconstructed UHR-CT-angiography images of 54 patients who underwent coiling or clipping was retrospectively evaluated. Image noise (i.e., index for metal-artifact strength) was analyzed in close proximity to and more distally from the metal implant. Frequencies and intensities of metal artifacts were additionally measured and intensity-differences between both reconstructions were compared in different frequencies and distances. Qualitative analysis was performed by two radiologists using a four-point Likert-scale. All measured results from both quantitative and qualitative analysis were then compared between coils and clips. Metal artifact index (MAI) and the intensity of coil-artifacts were significantly lower in SEMAR than in standard CTA in close vicinity to and more distally from the coil-package (p < 0.001, each). MAI and the intensity of clip-artifacts were significantly lower in close vicinity (p = 0.036; p < 0.001, respectively) and more distally from the clip (p = 0.007; p < 0.001, respectively). In patients with coils, SEMAR was significantly superior in all qualitative categories to standard images (p < 0.001), whereas in patients with clips, only artifacts were significantly less (p < 0.05) for SEMAR. SEMAR significantly reduces metal artifacts in UHR-CT-angiography images with intracranial implants and improves image quality and diagnostic confidence. SEMAR effects were strongest in patients with coils, whereas the effects were minor in patients with titanium-clips due to the absent of or minimal artifacts.

Visual and quantitative assessment of hip implant-related metal artifacts at low field MRI: a phantom study comparing a 0.55-T system with 1.5-T and 3-T systems

BackgroundTo investigate hip implant-related metal artifacts on a 0.55-T system compared with 1.5-T and 3-T systems.MethodsTotal hip arthroplasty made of three different alloys were evaluated in a water phantom at 0.55, 1.5, and 3 T using routine protocols. Visually assessment (VA) was performed by three readers using a Likert scale from 0 (no artifacts) to 6 (extremely severe artifacts). Quantitative assessment (QA) was performed using the coefficient of variation (CoV) and the fraction of voxels within a threshold of the mean signal intensity compared to an automatically defined region of interest (FVwT). Agreement was evaluated using intra/inter-class correlation coefficient (ICC).ResultsInterreader agreement of VA was strong-to-moderate (ICC 0.74−0.82). At all field strengths (0.55-T/1.5-T/3-T), artifacts were assigned a lower score for titanium (Ti) alloys (2.44/2.9/2.7) than for stainless steel (Fe-Cr) (4.1/3.9/5.1) and cobalt-chromium (Co-Cr) alloys (4.1/4.1/5.2) (p < 0.001 for both). Artifacts were lower for 0.55-T and 1.5-T than for 3-T systems, for all implants (p ≤ 0.049). A strong VA-to-QA correlation was found (r = 0.81; p < 0.001); CoV was lower for Ti alloys than for Fe-Cr and Co-Cr alloys at all field strengths. The FVwT showed a negative correlation with VA (-0.68 < r < -0.84; p < 0.001).ConclusionsArtifact intensity was lowest for Ti alloys at 0.55 T. For other alloys, it was similar at 0.55 T and 1.5 T, higher at 3 T. Despite an inferior gradient system and a larger bore width, the 0.55-T system showed the same artifact intensity of the 1.5-T system.

Photon-Counting Detector CT for Musculoskeletal Imaging: A Clinical Perspective.

Photon-counting detector (PCD) CT has emerged as a novel imaging modality that represents a fundamental shift in the way that CT systems detect x-rays. After pre-clinical and clinical investigations showed benefits of PCD CT for a range of imaging tasks, the U.S. FDA in 2021 approved the first commercial PCD CT system for clinical use. The technologic features of PCD CT are particularly well suited for musculo-skeletal imaging applications. Advantages of PCD CT compared with conventional energy-integrating detector (EID) CT include smaller detector pixels and excellent geometric dose efficiency that enable imaging of large joints and central skeletal anatomy at ultrahigh spatial resolution; advanced multienergy spectral postprocessing that allows quantification of gout deposits and generation of virtual noncalcium images for visualization of bone edema; improved metal artifact reduction for imaging of orthopedic implants; and higher CNR and suppression of electronic noise. Given substantially improved cortical and trabecular detail, PCD CT images more clearly depict skeletal abnormalities, including fractures, lytic lesions, and mineralized tumor matrix. The purpose of this article is to review, by use of clinical examples comparing EID CT and PCD CT, the technical features of PCD CT and their associated impact on musculoskeletal imaging applications.

Chalcolithic copper production and use in the western end of the Iberian Peninsula: The testimony of Castro de Chibanes (Portugal)

Recent archaeological excavations identified a prehistoric occupation at Castro de Chibanes (Setúbal Peninsula, Portugal) displaying ceramic crucibles and metal artefacts in stratigraphic levels assigned to 2500–1900 cal BC. Apart from basic tools such as flat axes and awls, the collection includes ceramic crucibles, with emphasis to an uncommon example with a pouring lip and four feet. The studied set was completed with metal prills and artefacts from neighbouring Chalcolithic settlements of Rotura and Pedrão. The studied collection was characterised by chemical and microstructural techniques (p-EDXRF, micro-PIXE, optical microscopy and SEM-EDS). Overall, the results point to a local production of copper with variable arsenic contents, agreeing with the composition of artefacts (Cu with 0.14 to 4.4 wt% As), whose post-casting manufacture included hammering and annealing (recrystallized grains and annealing twins), although with incipient conditions that prevented a full compositional homogenisation. These results were compared with the Chalcolithic metallurgy of southwestern Iberian Peninsula, allowing to integrate the Setúbal Peninsula region into a wider context of metal production and use during the 3rd millennium BC. Finally, a supposed Bell Beaker “tanged dagger” was found to be composed by a leaded bronze alloy with a worked microstructure exhibiting Cu-Fe sulphides with high Se contents. The contradiction between analytical features and ancient chronology led to a revision of the typology and chronology of this bronze, showing the importance of the integration of analytical and archaeological research.

Evaluation of Carbon Fiber and Titanium Surgical Implants for Proton and Photon Therapy

Impending and actual pathologic fractures secondary to metastatic bone disease, lymphoma, or multiple myeloma often require intramedullary fixation followed by radiation therapy. Because of carbon's low atomic number, there are reduced computed tomography (CT) imaging artifacts and dose perturbation when planning postoperative radiation for carbon fiber (CF) rods. Herein, we characterize the dosimetric properties of CF implants compared with titanium alloy (TA) for proton and photon. TA and CF samples were acquired from an implant manufacturer. Material characteristics were evaluated by CT scans with and without metal artifact reduction (MAR). Relative stopping power (RSP) was determined from the range pull-back of each sample in a 20-cm range proton beam. Photon transmission measurements were made in a solid water phantom and compared with the modeled dosimetry from the RayStation planning system. CF caused no visible CT artifacts, and MAR was not necessary for Hounsfield unit (HU) determination (median, 364 HU) or contouring, whereas TA (median, 3071 HU) caused substantial artifacts, which were improved, but not eliminated by MAR. The proton RSP was measured as 3.204 for TA and 1.414 for CF. For 6 MV photons, the measured transmission was 89.3% for TA and 98% for CF. CF RSP calculation and transmission from CT HU showed a physical density overestimate compared with measurements, which would cause a slight, but acceptable, dose uncertainty (<10% proton range or 1% photon transmission). With a density similar to bone, CF implants did not cause imaging artifacts and minimal dose perturbation compared with TA. Although the CF proton RSP is underestimated and the photon attenuation is overestimated by the HU, both effects are relatively small and may be most easily accounted for by planning with a 2-mm expansion around organs at risk beyond or in close proximity to the implant.

Letter: Arthrodesis With Titanium Implants: A Different Picture.

ABBREVIATION: DECT Dual-energy computed tomography. To the Editor: Psuedoarthrosis is a commonly known complication of trying to achieve solid body spinal fusion (arthrodesis) in the setting of spine surgery. Although recent advances in spinal surgery instrumentation, imaging, biologics, and management have occurred, it is still a prominent complication with significant morbidity and high cost burden.1 Deciding when to operate on these patients is variable and is primarily dependent on clinician gestalt regarding degree of intervention, physical examination findings, and the presence or lack of boney bridge formation across interbody implantation. Complicating this matter even further is the presence of psuedoarthrosis in the setting of no clinical symptoms. As it stands, computed tomography (CT) is the gold standard for detecting the presence of psuedoarthrosis. When evaluating multiple modalities of imaging for effectiveness in evaluating psuedoarthrosis, Peters et al found the pooled CT odds ratio to be highest in comparison with other modalities such as flexion/extension radiography, magnetic resonance, and scintigraphy. Furthermore, the authors went on to cite several instances in the literature where psuedoarthrosis was not detected through radiographic means but was detected by unveiling motion between adjacent segments.2 Although CT imaging may be a useful tool in imaging operated vertebrae with polyetheretherketone, carbon fiber, metal alloy, or other radiolucent implants, it can be less than reliable in titanium implants which often display significant artifact. Similar artifacts are seen on magnetic resonance imaging, posing an obstacle for thorough postoperative evaluation. Altogether, these findings illustrate the necessity of alternative modalities to better evaluate arthrodesis in the setting of spine surgery using titanium implants. Dual-energy CT (DECT) may prove a step in the right direction for evaluating psuedoarthrosis. In opposition to conventional CT imaging which uses a single image set, DECT uses 2 separate x-ray photon energy spectra; thus, allowing the interrogation of different attenuation properties at different energies.3 Artifact secondary to metal prosthesis (ie, titanium spinal interbody implants) typically occurs when low-energy photons within a polychromatic x-ray beam scatter radiation and abut image quality. Using DECT, these low-energy photons are removed; thus, limiting artifact. As of now, artifact in conventional CT is a major limitation in the evaluation of arthrodesis because initial boney bridge formation can be subtle or absent. To date, several articles have investigated the use of DECT in the setting of spinal fusion. Zeng et al4 in a retrospective review of 40 patients who underwent DECT after lumbar internal fixation found superior image quality with metal artifact reduction compared with conventional methods. Srinivasan et al5 in a retrospective review analyzing transpedicular screw interfacing noted the beneficial effects of metallic streak artifact reduction alongside better visualization of the hardware-bone interface. To our knowledge, there have been no prospective studies that study the differences between DECT and non-DECT images of the same patients. Several radiological fusion scales exist for the grading and measurement of fusion including a quantitative scale such as CT-Hounsfield Unit and qualitative scales such as the Lenke, Bridwell, and Brantigan, Steffe, Fraser scales.6,7 However, these are limited in that they are significantly dependent on subjective interpretation by an individual clinician and limited in their utility in assessment of titanium implants that present with significant artifact. Taken together, these findings highlight the need for a novel, quantized scale for assessing fusion with titanium implants using DECT.

Sensitivity and specificity for detecting pseudotumors in patients with hip resurfacing arthroplasty, metal-on-metal or metal-on-polyethylene total hip arthroplasty-MRI versus ultrasonography performed by an orthopedic surgery resident.

Metal artifact reduction sequence magnetic resonance imaging (MRI) scan is a common method to detect adverse reaction to metal debris in total hip arthroplasty (THA). It might be quicker and cheaper if ultrasonography (US) could screen for the need for an MRI. However, both require trained personnel. We aimed to investigate the sensitivity and specificity of US for detecting pseudotumors (PT) when performed by an orthopedic surgery resident compared to MRI. We also investigated the sensitivity and specificity of US to detect PTs in obese and non-obese patients. We examined 205 patients with hip resurfacing arthroplasty, metal-on-metal or metal-on-polyethylene THA with both MRI and US. US was performed by an orthopedic surgery resident who was trained according to a standardized training program in musculoskeletal US. Results from MRI were used as gold standard. US had a sensitivity of 0.92 (95% CI 0.81-0.98) and specificity of 0.94 (95% CI 0.89-0.97) for detecting PT. It had a positive predictive value of 0.84 (95% CI 0.73-0.91) and a negative predictive value of 0.97 (95% CI 0.93-0.99). US performed similarly in obese and non-obese patients. US had a high sensitivity and specificity for detecting PT when performed by an orthopedic surgery resident. Trained orthopedic surgeons could screen for the need of an MRI scan when searching PTs.

Deep Learning Image Reconstruction for CT: Technical Principles and Clinical Prospects.

Filtered back projection (FBP) has been the standard CT image reconstruction method for 4 decades. A simple, fast, and reliable technique, FBP has delivered high-quality images in several clinical applications. However, with faster and more advanced CT scanners, FBP has become increasingly obsolete. Higher image noise and more artifacts are especially noticeable in lower-dose CT imaging using FBP. This performance gap was partly addressed by model-based iterative reconstruction (MBIR). Yet, its "plastic" image appearance and long reconstruction times have limited widespread application. Hybrid iterative reconstruction partially addressed these limitations by blending FBP with MBIR and is currently the state-of-the-art reconstruction technique. In the past 5 years, deep learning reconstruction (DLR) techniques have become increasingly popular. DLR uses artificial intelligence to reconstruct high-quality images from lower-dose CT faster than MBIR. However, the performance of DLR algorithms relies on the quality of data used for model training. Higher-quality training data will become available with photon-counting CT scanners. At the same time, spectral data would greatly benefit from the computational abilities of DLR. This review presents an overview of the principles, technical approaches, and clinical applications of DLR, including metal artifact reduction algorithms. In addition, emerging applications and prospects are discussed.

Metallic Artifact Reduction in Midfacial CT Scans Using Patient-Specific Polymer Implants Enhances Image Quality.

Midfacial reconstruction after tumor resection surgery is commonly conducted by using autologous bone grafts or alloplastic implants. Titanium is the most frequently used osteosynthesis material in these cases but causes disturbing metallic artifacts in CT imaging. The purpose of this experimental study was to evaluate whether the use of midfacial polymer implants reduces metallic artifacts in CT imaging to improve image quality. Zygomatic titanium (n = 1) and polymer (n = 12) implants were successively implanted in a human skull specimen. Implants were analyzed for their effect on Hounsfield Unit values (streak artifacts) and virtual growth in CT images (blooming artifacts) as well as image quality. Multi-factorial ANOVA and Bonferroni's post hoc test were used. Titanium (173.7 HU; SD ± 5.1) and hydroxyapatite containing polymers (155.3 HU; SD ± 5.9) were associated with significantly more streak artifacts compared to all other polymer materials. There was no significant difference in blooming artifacts between materials. The metallic artifact reduction algorithm showed no significant difference. Image quality was slightly better for polymer implants compared to titanium. Personalized polymer implants for midfacial reconstruction significantly reduce metallic artifacts in CT imaging which improves image quality. Hence, postoperative radiation therapy planning and radiological tumor aftercare around the implants are facilitated.

Uncertainty of Quantitative X-ray Fluorescence Micro-Analysis of Metallic Artifacts Caused by Their Curved Shapes.

This paper summarizes the effects of irregular shape on the results of a quantitative X-ray fluorescence (XRF) micro-analysis. These effects become relevant when an XRF analysis is performed directly on an investigated material. A typical example is XRF analyses of valuable and historical objects whose measurements should be performed non-destructively and non-invasively, without taking samples. Several measurements and computer simulations were performed for selected metallic materials and shapes to evaluate the accuracy and precision of XRF. The described experiments and the corresponding Monte Carlo simulations were related to the XRF device designed and utilized at the Czech Technical University. It was found that the relative uncertainty was typically about 5-10% or even higher in quantitative analyses of minor elements due to irregular shapes of surfaces. This must be considered in cases of the interpretation of XRF results, especially in the cultural heritage sciences. The conclusions also contain several recommendations on how to measure objects under hard-to-define geometric conditions with respect to reduction in the surface effect in quantitative or semi-quantitative XRF analyses.

Quantitative evaluation of the reduction of distortion and metallic artifacts in magnetic resonance images using the multiacquisition variable‑resonance image combination selective sequence.

Magnetic resonance imaging (MRI) is superior to computed tomography (CT) in determining changes in tissue structure, such as those observed following inflammation and infection. However, when metal implants or other metal objects are present, MRI exhibits more distortion and artifacts compared with CT, which hinders the accurate measurement of the implants. A limited number of reports have examined whether the novel MRI sequence, multiacquisition variable-resonance image combination selective (MAVRIC SL), can accurately measure metal implants without distortion. Therefore, the present study aimed to demonstrate whether MAVRIC SL could accurately measure metal implants without distortion and whether the area around the metal implants could be well delineated without artifacts. An agar phantom containing a titanium alloy lumbar implant was used for the present study and was imaged using a 3.0 T MRI machine. A total of three imaging sequences, namely MAVRIC SL, CUBE and magnetic image compilation (MAGiC), were applied and the results were compared. Distortion was evaluated by measuring the screw diameter and distance between the screws multiple times in the phase and frequency directions by two different investigators. The artifact region around the implant was examined using a quantitative method following standardization of the phantom signal values. It was revealed that MAVRIC SL was a superior sequence compared with CUBE and MAGiC, as there was significantly less distortion, a lack of bias between the two different investigators and significantly reduced artifact regions. These results suggested the possibility of utilizing MAVRIC SL for follow-up to observe metal implant insertions.

Metal artefact reduction in digital tomosynthesis using component decomposition

We propose a technique for metal artefact reduction in digital tomosynthesis reconstruction. Although the problem was addressed earlier in the literature, we suggest another approach, which is, in our opinion, simpler, and easier to implement. It is a two-stage algorithm. At the first stage, attenuation images are segmented by decomposing their intensity distributions into gaussian-like components. Statistical information contained in each component is used for pixel classification. Components corresponding to metallic objects are identified, and a pixel threshold value separating regions occupied by metal objects from the rest of the image is found. Based on this value, at the second stage, a smooth mapping of image intensity is applied. This makes dense regions transparent, resulting in the artefact reduction in reconstruction. The methodology is demonstrated by several examples.

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

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

MFGAN: Multi-modal Feature-fusion for CT Metal Artifact Reduction Using GANs

Due to the existence of metallic implants in certain patients, the Computed Tomography (CT) images from these patients are often corrupted by undesirable metal artifacts, which causes severe problem of metal artifact. Although many methods have been proposed to reduce metal artifact, reduction is still challenging and inadequate. Some reduced results are suffering from symptom variance, second artifact, and poor subjective evaluation. To address these, we propose a novel method based on generative adversarial nets (GANs) to reduce metal artifacts. Specifically, we firstly encode interactive information (text) and imaging CT (image) to yield multi-modal feature-fusion representation, which overcomes representative ability limitation of single-modal CT images. The incorporation of interaction information constrains feature generation, which ensures symptom consistency between corrected and target CT. Then, we design an enhancement network to avoid second artifact and enhance edge as well as suppress noise. Besides, three radiology physicians are invited to evaluate the corrected CT image. Experiments show that our method gains significant improvement over other methods. Objectively, ours achieves an average increment of 7.44% PSNR and 6.12% SSIM on two medical image datasets. Subjectively, ours outperforms others in comparison in term of sharpness, resolution, invariance, and acceptability.

Path Tracing vs. Volume Rendering Technique in Post-Surgical Assessment of Bone Flap in Oncologic Head and Neck Reconstructive Surgery: A Preliminary Study.

This study aims to compare a relatively novel three-dimensional rendering called Path Tracing (PT) to the Volume Rendering technique (VR) in the post-surgical assessment of head and neck oncologic surgery followed by bone flap reconstruction. This retrospective study included 39 oncologic patients who underwent head and neck surgery with free bone flap reconstructions. All exams were acquired using a 64 Multi-Detector CT (MDCT). PT and VR images were created on a dedicated workstation. Five readers, with different expertise in bone flap reconstructive surgery, independently reviewed the images (two radiologists, one head and neck surgeon and two otorhinolaryngologists, respectively). Every observer evaluated the images according to a 5-point Likert scale. The parameters assessed were image quality, anatomical accuracy, bone flap evaluation, and metal artefact. Mean and median values for all the parameters across the observer were calculated. The scores of both reconstruction methods were compared using a Wilcoxon matched-pairs signed rank test. Inter-reader agreement was calculated using Spearman's rank correlation coefficient. PT was considered significantly superior to VR 3D reconstructions by all readers (p < 0.05). Inter-reader agreement was moderate to strong across four out of five readers. The agreement was stronger with PT images compared to VR images. In conclusion, PT reconstructions are significantly better than VR ones. Although they did not modify patient outcomes, they may improve the post-surgical evaluation of bone-free flap reconstructions following major head and neck surgery.

Effect of Dental Distance from Implant and MAR Algorithm on the Detection of Vertical Root Fracture in CBCT Images

Three-dimensional cone-beam computed tomography (CBCT) has an important role in the detection of vertical root fractures (VRFs). The effect of artifact generation by high-density objects like dental implants on image quality was well documented. This study aimed to assess the effect of tooth-implant distance and the application of metal artifact reduction (MAR) algorithm on the detection of VRFs on CBCT scans. This study was conducted on 20 endodontically treated single-rooted teeth. VRFs were induced in 10 teeth, while the other 10 remained intact. The implant was inserted in the right second premolar socket area, and two teeth were inserted in right canine and right first premolar sockets area randomly and underwent CBCT with and without the application of MAR algorithm. SPSS 21 was used to analyze the results (alpha=0.05). According to the findings of this study, all four variables of sensitivity, specificity, accuracy, and positive predictive values in diagnosis were higher in cases without MAR software at both close(roots in first premolar sockets) and far distances (roots in canine sockets) from the implant. However, the highest rate of diagnosis accuracy of the first and second radiologists was in the far distance group from the implant without MAR, and the lowest rate of diagnosis accuracy in the first and second radiologists was in the close distance to the implant. Applying MAR algorithm had no positive effect on detection of VRFs on CBCT scans in both close and distant scenarios.