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Objectives:
Metal artefacts present challenges to both radiologists and clinicians during post-operative imaging. Such artefacts reduce the diagnostic effectiveness of computed tomography (CT) scans and mask findings that could be vital for patient management. Thus, a powerful artefact reduction tool is necessary when imaging patients with metal i...
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M...
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A common complication, related to the use of nasogastric tube during the 1st day of life, is the necrosis of the columella. Esthetic damage in the early age typically leads to a healing request with very high result expectations.
Aims
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Settings and Design
We used our technique i...
Introduction: Facial fractures can result in limitation of mouth opening range, which consequently leads to functional impairments. Objective: To identify the influence of facial fractures and their corrective surgery on mouth opening range. Material and methods: Consecutive patients submitted to maxillofacial surgery had their mouth opening range...
Background: Artificial Neural Network (ANN) is relatively crude electronic model based on the neural structure of human brain which was used in the field of medicine in different purposes. It can be used for many medical branches especially for estimating the course of a certain disorder or treatment procedure. The aim of this study is to use ANN i...
Citations
... Although easy to recognize on NECT, artefacts in the skull base or orbits represent a potential source of overestimation of penumbral volume (55, 104). Iterative metal artifact reduction algorithms (iMAR, Siemens Healthcare) have been introduced during the past decade and have shown to significantly reduce metal artefacts in different body parts (see, e.g., (108,109), and most importantly in brain NECT and CTA after coiling or clipping [see, e.g., (110)(111)(112),]. More recently, the iMAR algorithm has been applied also to CTP, with favorable results (113). ...
CT perfusion (CTP) images can be easily and rapidly obtained on all modern CT scanners and have become part of the routine imaging protocol of patients with aneurysmal subarachnoid haemorrhage (aSAH). There is a growing body of evidence supporting the use of CTP imaging in these patients, however, there are significant differences in the software packages and methods of analysing CTP. In. addition, no quantitative threshold values for tissue at risk (TAR) have been validated in this patients’ population. Here we discuss the contribution of the technique in the identification of patients at risk of aSAH-related delayed cerebral ischemia (DCI) and in the assessment of the response to endovascular rescue therapy (ERT). We also address the limitations and pitfalls of automated CTP postprocessing that are specific to aSAH patients as compared to acute ischemic stroke (AIS).
... Dental implants can introduce severe metal artifacts due to high density and angular shape. All commercial MAR algorithms (O-MAR, iMAR, SEMAR and Smart-MAR) are able to reduce these metal artifacts, reduce noise, improve image quality and improve assessment of anatomical structures [48][49][50][51][52][53][54][55]. Reduction of metal artifacts by iMAR, SEMAR and Smart-MAR results in improved tumor visibility when compared to images without MAR [51,52,56]. ...
... Large and high-density implants Severe artifacts Hip arthroplasty [32][33][34][35][36][37][38][39][40][41][42]44,[73][74][75][76][77]84,85,92,101,106,[108][109][110][111][112][113][114][115][116][117] 120-200 keV ++ +++ 140 keV + MAR Knee arthroplasty [34,36,43,[78][79][80]112] 120-140 keV + +++ Shoulder arthroplasty [32,33,45,46,118] 130 keV ++ +++ Ankle arthroplasty [47,85,92] 105-150 keV ++ +++ Dental [23,[48][49][50][51][52][53][54][55][56]73,[81][82][83]110,119] 130-200 keV + +++ ...
... Several techniques have been developed to mitigate these artifacts, most commonly based on iterative reconstruction algorithms, 10,11 virtual monoenergetic imaging (VMI) reconstructions from multienergy imaging data, 4,5,12,13 or a combination thereof. [14][15][16][17] The recently introduced photon-counting detector CT (PCD-CT) technology is especially promising in this regard because of its routine acquisition of spectral data. ...
... For each patient, 4 axial series were reconstructed using the "SPP" DICOM file format ("Spectral Post-Processing," Siemens Healthineers), which fully preserves spectral information: series 1 and 2 were generated using a medium soft tissue kernel without and with IMAR (Qr40; Qr40 IMAR ); series 3 and 4 using a bone kernel without and with IMAR (Qr60; Qr60 IMAR ). The IMAR algorithm ("iMAR," Siemens Healthineers) used in this study combines 2 methods, the normalized and frequency split metal artifact reduction, 11 and has been published previously. 20,21 For all series, slice thickness and increment were 1.5 mm and 1.0 mm, respectively, matrix size was 512 pixels, and size and position of the field of view covered the whole head. ...
Objective:
The aim of this study was to compare the effectiveness of common strategies for artifact reduction of dental material in photon-counting detector computed tomography data sets.
Materials and methods:
Patients with dental material who underwent clinically indicated CT of the neck were enrolled. Image series were reconstructed using a standard and sharp kernel, with and without iterative metal artifact reduction (IMAR) (Qr40, Qr40IMAR, Qr60, Qr60IMAR) at different virtual monoenergetic imaging (VMI) levels (40-190 keV). On representative slice positions with and without dental artifacts, mean and standard deviation of CT values were measured in all series at identical locations. The mean absolute error of CT values () and the artifact index (AIX) were calculated and analyzed focusing on 3 main comparisons: (a) different VMI levels versus 70 keV, (b) standard versus sharp kernel, and (c) nonuse or use of IMAR reconstruction. The Wilcoxon test was used to assess differences for nonparametric data.
Results:
The final cohort comprised 50 patients. Artifact measures decreased for VMI levels >70 keV, yet only significantly so for reconstructions using IMAR (maximum reduction, 25%). The higher image noise of the sharp versus standard kernel is reflected in higher AIX values and is more pronounced in IMAR series (maximum increase, 38%). The most profound artifact reduction was observed for IMAR reconstructions (maximum reduction : 84%; AIX: 90%).
Conclusions:
Metal artifacts caused by large amounts of dental material can be substantially reduced by IMAR, regardless of kernel choice or VMI settings. Increasing the keV level of VMI series, on the other hand, only slightly reduces dental artifacts; this effect, however, is additive to the benefit conferred by IMAR reconstructions.
... Pada penelitian sebelumnya yang dilakukan oleh Lee et al. (2007) bahwa artefak logam dapat dikurangi dengan mengoptimalkan parameter CT-scan seperti kVp, mAs, slice thickness, coliimation, dan rekonstruksi algoritma atau penggunaan kernel yang dilakukan sebelum pemeriksaan. Penelitian Hakim et al. (2017) menggunakan metode iMAR pada CT 128 slice Siemens untuk mengurangi artefak logam. Studi lain oleh Gjesteby et al. (2016) menggunakan MAR pada CT 128 slice GE juga dapat mengurangi artefak logam dan sebuah studi oleh Utaminingrum and Prijono (2007) menggunakan metode multistage adaptive wiener lebih baik dibandingkan dengan median dan average filter untuk mereduksi derau. ...
Background: One of the artifacts found on the CT scan is a metal artifact. Metal artifacts are caused by metal objects present in patients’ bodies. The file of metal artifacts can cover the organ that will be evaluated, and it can be inferred with the pixel value (CT number) assessment of the tissue around the metal. Purpose: To determine the effect of the band pass median filter and find the optimal filter to reduce metal artifacts on the head CT scan. Method: A total of 43 samples of patients’s files from head CT-scan without any contrast were reconstructed using four band pass median filters and obtained R1, R2, R5, and R10 filters. Two radiology specialists were assessed for the reduction of metal artifacts using the ImageJ application. Result: Four variations of the filter affected the reduction of metal artifacts because the band pass median filter maintained a point that was close to its neighboring points and points that were different from its neighboring points by replacing the value of the pixel with the median value of the grey level of neighboring pixels. The optimal filter recommendation is the R1 filter because it has the largest SNR value (16.9773) and the smallest RMSE value (8.57501) so that the result of the image is more informative and has a diagnostic value. Conclusion: The four filter variations were affected by reducing metal artifacts. Images with substantial SNR and fractional RMSE values produced an image that was more informative and still had diagnostic value.
... However, the primary tumor is often non-assessable on CT due to dental artifacts. The metallic artifact reduction (MAR) algorithm is an effective artifact reduction technique for CT [9][10][11][12][13][14][15][16][17]. Although it is well-established that the MAR algorithm improves the imaging quality of the oral cavity [11][12][13][14][15][16][17], there are numerous cases in which tongue cancer cannot be clinically delineated despite the use of MAR. ...
... The metallic artifact reduction (MAR) algorithm is an effective artifact reduction technique for CT [9][10][11][12][13][14][15][16][17]. Although it is well-established that the MAR algorithm improves the imaging quality of the oral cavity [11][12][13][14][15][16][17], there are numerous cases in which tongue cancer cannot be clinically delineated despite the use of MAR. ...
... The MAR algorithm, which replaces corrupted projections by interpolation from uncorrupted projections, is effective for reducing artifacts due to photon starvation causing pronounced metal artifacts [9]. Several studies have reported that CT with the MAR algorithm improved the imaging quality and detectability of lesions in the oral region [11][12][13][14][15][16][17]. Previous studies have indicated that CT with the MAR algorithm was able to detect 22-56% more tumors compared with conventional CT [12,13]. ...
Purpose
Tumor size and depth of invasion (DOI) are mandatory assessments for tumor classification in tongue cancer but are often non-assessable on CT due to dental artifacts. This study investigated whether subtraction iodine imaging (SII) would improve tumor delineation and measurability.
Materials and methods
Fifty-seven consecutive patients with tongue cancer, who underwent scanning with a 320-row area detector CT with contrast administration and were treated with surgical resection, were retrospectively evaluated. CT was reconstructed with single-energy projection-based metallic artifact reduction (sCT). SII was generated by subtracting the pre-contrast volume scans from the post-contrast volume scans using a high-resolution deformable registration algorithm. MRI scans were also evaluated for comparing the ability of measurements. Two radiologists visually graded the tumor delineation using a 5-point scale. Tumor size and DOI were measured wherever possible. The tumor delineation score was compared using the Wilcoxon signed-rank method. Spearman’s correlations between imaging and pathological measurements were calculated. Intraclass correlation coefficients of measurements between readers were estimated.
Results
The tumor delineation score was greater on sCT-plus-SII than on sCT alone (medians: 3 and 1, respectively; p < 0.001), with higher number of detectable cases observed with sCT-plus-SII (36/57 [63.2%]) than sCT alone (21/57 [36.8%]). Tumor size and DOI measurability were higher with sCT-plus-SII (29/57 [50.9%]) than with sCT alone (17/57 [29.8%]). MRI had the highest detectability (52/57 [91.2%]) and measurability (46/57 [80.7%]). Correlation coefficients between radiological and pathological tumor size and DOI were similar for sCT (0.83–0.88), sCT-plus-SII (0.78–0.84), and MRI (0.78–0.90). Intraclass correlation coefficients were higher than 0.95 for each modality.
Conclusions
SII improves detectability and measurability of tumor size and DOI in patients with oral tongue squamous cell carcinoma, thus increasing the diagnostic potential. SII may also be beneficial for cases unevaluable on MRI due to artifacts or for patients with contraindications to MRI.
... With time, researchers have described the remarkable ability of MAR to enhance the visualization of various target lesions by reducing metallic artifacts. 18,[22][23][24][25][26][27][28][29] Therefore, the intended effect of MAR has been established, and the use of CT with MAR comprises the current clinical standard. ...
... Prior studies indicated a superior reduction of dental artifacts caused by dental hardware or diverse maxillofacial metal implants when several MAR algorithms from major vendors were used, compared with standard reconstruction. [24][25][26][27][28][29] However, MAR algorithms may introduce new artifacts into the image. These new artifacts can appear as defects or blurring around metal hardware in the bone window. ...
... These new artifacts can appear as defects or blurring around metal hardware in the bone window. 26,27 Recently, several clinical studies reported that the combination of spectral detector CT (or dualenergy CT) with virtual monoenergetic images and MAR provided optimal artifact reduction and improved diagnostic imaging assessments in patients with dental implants and bridges or metallic dental prostheses. 36,37 As noted previously, the MBIR algorithm is a revolutionary reconstruction technology that uses various models and repeats the subtraction of original raw data after forward projection to yield a reconstructed image that differs minimally from the raw data. ...
Background and purpose:
Metal artifacts reduce the quality of CT images and increase the difficulty of interpretation. This study compared the ability of model-based iterative reconstruction and hybrid iterative reconstruction to improve CT image quality in patients with metallic dental artifacts when both techniques were combined with a metal artifact reduction algorithm.
Materials and methods:
This retrospective clinical study included 40 patients (men, 31; women, 9; mean age, 62.9 ± 12.3 years) with oral and oropharyngeal cancer who had metallic dental fillings or implants and underwent contrast-enhanced ultra-high-resolution CT of the neck. Axial CT images were reconstructed using hybrid iterative reconstruction and model-based iterative reconstruction, and the metal artifact reduction algorithm was applied to all images. Finally, hybrid iterative reconstruction + metal artifact reduction algorithms and model-based iterative reconstruction + metal artifact reduction algorithm data were obtained. In the quantitative analysis, SDs were measured in ROIs over the apex of the tongue (metal artifacts) and nuchal muscle (no metal artifacts) and were used to calculate the metal artifact indexes. In a qualitative analysis, 3 radiologists blinded to the patients' conditions assessed the image-quality scores of metal artifact reduction and structural depictions.
Results:
Hybrid iterative reconstruction + metal artifact reduction algorithms and model-based iterative reconstruction + metal artifact reduction algorithms yielded significantly different metal artifact indexes of 82.2 and 73.6, respectively (95% CI, 2.6-14.7; P < .01). The latter algorithms resulted in significant reduction in metal artifacts and significantly improved structural depictions(P < .01).
Conclusions:
Model-based iterative reconstruction + metal artifact reduction algorithms significantly reduced the artifacts and improved the image quality of structural depictions on neck CT images.
... Likert scale (Table 1) was used in the 3 regions (R1-R3) 8 . An RR was selected from another slice that did not contain metal and was rated using the same 4-point Likert scale. ...
... Previous studies have shown the efficiency of iMAR in different body regions 8,20 . Other studies have evaluated the performance of iMAR in non-contrast CT and CTA during follow-up after coiling or clipping [21][22][23][24][25] . ...
Metal artifacts resulting from coiling or clipping of a brain aneurysm degrade image quality and reduce diagnostic usefulness of computed tomography perfusion CTP. Our aim was to assess the diagnostic value of the iterative metal artifact reduction algorithm (iMAR) in CTP studies after coiling or clipping of ruptured intracranial aneurysms. Fifty-eight CTP exams performed in 32 patients were analysed. iMAR was applied to the source images from the CT scanner. Perfusion maps were generated from datasets both with and without iMAR, and both datasets were compared qualitatively and quantitatively. Qualitative analysis included evaluation of intensity of artifacts, image quality, presence of new artifacts, and the reader’s confidence in their diagnosis as well as diagnostic impression. Quantitative analysis included evaluation of tissue attenuation curves, evaluation of region of interest (ROI)-based measurement of perfusion values at levels that do and do not contain metal, compared to previously published reference ranges of perfusion values. Our results showed that application of iMAR reduced artifacts and significantly improved image quality. New artifacts were observed adjacent to metallic implants, but did not limit the evaluation of other regions. After correction for artifact readers’ confidence in their diagnosis increased from 41.3% to 87.9%, and the diagnostic impression changed in 31% of the exams. No difference between tissue attenuation curves was found. For slices without metal, no difference was noted between values measured before and after iMAR, and the total number of ROIs in the reference range of perfusion values was unchanged. At the level of the metal implant, 89.85% of ROIs obtained before using iMAR showed calculation errors. After using iMAR, only 1.7% showed errors. Before iMAR 3.1% of values were in the reference range, whereas after iMAR this increased to 33.1%. In conclusion, our results show that iMAR is an excellent tool for reducing artifacts in CTP. It is therefore recommended for use in clinical practice, particularly when severe artifacts are present, or when hypoperfusion is suspected at the level of the coil or clip. After the application of iMAR, the perfusion values at the level of the metal can be better calculated, but may not lie within the reference range; therefore, quantitative analysis at the level of artifacts is not advisable.
... DECT with GSI-MARS resulted in less severe metal artifacts and improved the delineation of the prosthesis and periprosthetic region [12]; increased diagnostic confidence in pelvic cavity assessment [13]; and reduced the severity metal artifacts on cerebral CT angiography after intracranial aneurysm clipping regardless of the location and number of clips [14]. The IMAR algorithm, used for CT in patients after deep brain stimulation (DBS) implantation, efficiently reduced the number of metal artifacts near DBS electrodes [15] and led to artifact reduction, image quality improvement, and increased diagnostic utility in the imaging of patients with maxillofacial metal implants [16]. OMAR greatly improved ability to delineate tumors and surrounding organs during the planning of radiation therapy [17] and resulted in use of a lower radiation dose in the CT imaging of a total hip arthroplasty phantom [18]. ...
A metal implant was placed in an acrylic phantom to enable quantitative analysis of the metal artifact reduction techniques used in computed tomography (CT) scanners from three manufacturers. Two titanium rods were placed in a groove in a cylindrical phantom made by acrylic, after which the groove was filled with water. The phantom was scanned using three CT scanners (Toshiba, GE, Siemens) under the abdomen CT setting. CT number accuracy, contrast-to-noise ratio, area of the metal rods in the images, and fraction of affected pixel area of water were measured using ImageJ. Different iterative reconstruction, dual energy, and metal artifact reduction techniques were compared within three vendors. The highest contrast-to-noise ratio of three scanners were 85.7 ± 8.4 (Toshiba), 85.9 ± 11.7 (GE), and 55.0 ± 14.8 (Siemens); and the most correct results of metal area were 157.1 ± 1.4 mm² (Toshiba), 155.0 ± 1.0 (GE), and 170.6 ± 5.3 (Siemens). The fraction of affected pixel area obtained using single-energy metal artifact reduction of Toshiba scanner was 2.2% ± 0.7%, which is more favorable than 4.1% ± 0.7% obtained using metal artifact reduction software of GE scanner (p = 0.002). Among all quantitative results, the estimations with fraction of affected pixel areas matched the effect of metal artifact reduction in the actual images. Therefore, the single-energy metal artifact reduction technique of Toshiba scanner had a desirable effect. The metal artifact reduction software of GE scanner effectively reduced the effect of metal artifacts; however, it underestimated the size of the metal rods. The monoenergetic and dual energy composition techniques of Siemens scanner could not effectively reduce metal artifacts.
... scanning is a more sensitive and reproducible tool to evaluate some postoperative placement features, but it remains a 2-dimensional (2D) representation; it is also limited because of metal artifacts. 14 For preoperative planning and evaluation, recent literature has recommended 3-dimensional (3D) CT reconstruction over 2D CT or plain radiographs for a more reliable anatomic understanding and measurements, particularly when the anatomy is severely altered by osteoarthritis. 3,10,15,18 Postoperatively, the main limiting factor in using 3D CT reconstruction for evaluating implant placement has been metal artifacts caused by the implant. ...
... However, technical progress in improving the image acquisition process and reconstruction approaches is necessary before it is more widely applied. 13,14,28 The results of the new method demonstrated in this study, using 3D CT registration of postoperative to preoperative anatomy for evaluating RSA glenoid implant and screw positioning, suggest that it is possible to overcome the metal-artifact limitation of a 3D CT postoperative evaluation. ...
Background:
Long-term function and survival of reverse shoulder arthroplasties (RSAs) are reliant on component positioning and fixation. Conventional postoperative analysis is performed using plain radiographs or 2-dimensional (2D) computed tomography (CT) images. Although 3-dimensional (3D) CT would be preferred, its use is limited by metal artifacts. This study proposes a new 3D CT method for postoperative RSA evaluation and compares its interobserver reliability with conventional methods.
Materials and methods:
Preoperative and postoperative CT scans, as well as postoperative radiographs, were obtained from 18 patients who underwent RSA implantation; the scapula, implant, and screws were reconstructed as 3D CT models. The postoperative 3D scapula and implant were imported into preoperative coordinates and matched to the preoperative scapula. Standardized scapula coordinates were defined, in which the glenoid baseplate version and inclination angle were measured. The percentage of screw volume in bone was measured from a Boolean intersection operation between the preoperative scapula and screw models. Four independent reviewers performed the measurements using 3D CT and conventional 2D methods. Intraclass correlation coefficients (ICCs) were used to compare the reliability of the methods.
Results:
The 3D CT method showed excellent reliability (ICC > 0.75) in baseplate inclination (ICC = 0.92), version (ICC = 0.97), and screw volume in bone (ICC = 0.99). Conventional 2D methods demonstrated poor reliability (ICC < 0.4). For radiographs, inclination showed poor reliability (ICC = 0.09) and the screw percentage in bone showed fair reliability (ICC = 0.54). Version was not measured with plain radiographs. For 2D CT slice measurements, inclination showed poor reliability (ICC = 0.02), version showed excellent reliability (ICC = 0.81), and the screw percentage in bone showed poor reliability (ICC = 0.28).
Conclusion:
The new 3D CT-based method for evaluating RSA glenoid implant positioning and screw volume in bone showed excellent reliability and overcame the metal-artifact limitation of postoperative CT and 3D CT reconstruction.
... Another noteworthy technical advance was the introduction of new algorithms for artefact reduction, such as the iterative metal artefact reduction (iMAR) algorithm introduced by Siemens Healthcare, which has shown good results in artefact reduction in several body regions. 23 The primary aim of the present study was to evaluate the effects of in-plane shielding of the eye lens during perfusion imaging, particularly for perfusion maps. A second aim was to evaluate the ability of iMAR to reduce artefacts arising from orbit shielding. ...
Aim:
To evaluate the image quality and artefacts resulting from in-plane orbit shielding during computed tomography (CT) perfusion and to assess the possibility of artefact reduction using the iterative metal artefact reduction (iMAR) algorithm.
Materials and methods:
Twenty-eight perfusion CT examinations obtained from 20 patients using orbit shields were included in this study. Source images and perfusion maps were analysed retrospectively to detect the type and extent of artefacts. Original images were compared with images processed using the iMAR algorithm. The extent of artefacts was categorised into three groups: orbital/frontal, middle fossa, and posterior fossa. Types of artefacts in source images were categorised as noise, streak, beam hardening, or a combination of those, and types of artefacts in perfusion maps were categorised as: noise, image distortion, areas with missing colour codes, or incorrect colour-coding.
Results:
All source images evaluated showed artefacts related to orbit shielding and 85.7% reached the posterior fossa. In 92.8% of scans, perfusion maps showed artefacts, mostly as incorrect colour codes. Of the perfusion maps with artefacts, 92.3% reached the posterior fossa. After application of the iMAR algorithm, an increase in the extent of artefacts was observed in 93% of perfusion maps, and no improvement of image quality was noted.
Conclusion:
Orbit shields cause significant artefacts if used for in-plane shielding during whole-brain CT perfusion, and render areas at the level of the shield undiagnosable. Usage of an orbit shield during whole-brain CT perfusion is not recommended, so alternative methods for reducing the radiation dose are advisable.
