Improved image quality in abdominal CT in patients who underwent treatment for hepatocellular carcinoma with small metal implants using a raw data-based metal artifact reduction algorithm

Radiotherapy planning of spine and pelvis using single-energy metal artifact reduction corrected computed tomography sets

Metal artifacts produce incorrect Hounsfield units and impact treatment planning accuracy. This work evaluates the use of single-energy metal artifact reduction (SEMAR) algorithm for treatment planning by comparison to manual artifact overriding. CT datasets of in-house 3D-printed spine and pelvic phantoms with and without metal insert(s) and two treated patients with metal implants were analysed. CT number accuracy improved with the use of SEMAR filter: root mean square deviation (RMSD) from reference (without metal) reduced by 35.4 in spine and 98.8 in hip. The plan dose volume histograms (DVHs) and dosimetric measurements showed comparable results. SEMAR reconstruction improved planning efficiency.

Lateral Position With Gantry Tilt Further Improves Computed Tomography Image Quality Reconstructed Using Single-Energy Metal Artifact Reduction Algorithm in the Oral Cavity

OBJECTIVE

To assess the limitations of single-energy metal artifact reduction algorithm in the oral cavity and evaluate the availability of a solution by setting the patient in a lateral position (LP) with the use of a gantry tilt (GT).

METHODS

We analyzed 88 patients with dental metals retrospectively in study 1, and 74 patients prospectively in study 2. Patients were classified: metal I with dental metals in 1 region, metal II in 2 regions, and metal III in 3 regions. Patients underwent neck computed tomography examinations in a supine position (SP) in study 1, and 2 positions, an LP with a GT and an SP, in study 2. All images were reconstructed with this algorithm. Image quality was scored using a 4-point scale: 1 = severe artifact, 2 = moderate artifact, 3 = slight artifact, 4 = no artifact. The scores were compared between metal I, metal II, and metal III using the Mann-Whitney U test in study 1, and between an LP with a GT and an SP using the Wilcoxon signed ranks test in study 2.

RESULTS

The scores outside the dental arch were significantly higher in metal I than in metal II and metal III (3.0 ± 0.6 vs 2.3 ± 0.5 vs 2.2 ± 0.4; P < 0.0001 for metal I vs metal II and for metal I vs metal III) and significantly higher in an LP with a GT than an SP (3.2 ± 0.4 vs 2.3 ± 0.4; P < 0.0001).

CONCLUSIONS

Single-energy metal artifact reduction algorithm could reduce metal artifacts adequately in patients with dental metals in 1 region, but not in 2 or more regions. However, even for the latter, combination of this algorithm and an LP with a GT could further improve the image quality.

Application of Iterative Metal Artifact Reduction Algorithm to CT Urography for Patients With Hip Prostheses

OBJECTIVE. The purpose of this study is to retrospectively assess the impact of iterative metal artifact reduction (IMAR) with iterative reconstruction (IR) on the image quality and diagnostic performance of CT urography in the evaluation of patients with hip prostheses, compared with IR alone. MATERIALS AND METHODS. CT urography examinations that were reconstructed using IR with and without IMAR were analyzed for 57 patients (29 women and 28 men; mean age, 74 years [range, 22-94 years]) with hip prostheses (40 unilateral and 17 bilateral). For quantitative analysis, image noise within the bladder was measured. Two radiologists (radiologist 1 [RAD1] and radiologist 2 [RAD2]) qualitatively evaluated the images using both a 5-point scale to assess the degree of visualization of artifacts and a 6-point scale to determine diagnostic confidence in visualization of the bladder, ureters, prostate or uterus, pelvic calcifications, and genitourinary abnormalities involving the bladder, distal ureters, prostate, uterus, and ovaries. RESULTS. The combination of IMAR and an IR technique provided improvement in quantitative and qualitative measurements (p < 0.05). Forty-three genitourinary abnormalities were detected in 29 patients. Quantitative and qualitative comparisons of scans obtained with and without the use of IMAR, respectively, revealed image noise of 99.6 versus 173.3 HU and the following radiologist scores: for improvement of artifacts, 3.2 versus 1.6 (for RAD1) and 3.1 versus 1.6 (for RAD2); for visualization of the bladder, 3.6 versus 1.5 (RAD1) and 3.8 versus 1.6 (RAD2); visualization of the ureters, 3.8 versus 1.6 (RAD1) and 3.9 versus 1.7 (RAD2); visualization of the uterus, 4.3 versus 2.8 (RAD1) and 4.3 versus 2.6 (RAD2); visualization of the prostate, 4.5 versus 2.3 (RAD1) and 4.5 versus 2.2 (RAD2); diagnostic confidence for calcifications, 4.7 versus 3.5 (RAD1) and 4.7 versus 3.3 (RAD2); and diagnostic confidence for genitourinary abnormalities, 5.0 versus 3.2 (RAD1) and 4.8 versus 2.9 (RAD2), respectively. CONCLUSION. The addition of IMAR to IR led to statistically significant improvement in the retrospective diagnostic performance and image quality of CT urography for patients with hip prostheses, compared with IR alone.

Single-energy metal artifact reduction technique for reducing metallic coil artifacts on post-interventional cerebral CT and CT angiography

PURPOSE

To evaluate the effects of the single-energy metal artifact reduction (SEMAR) algorithm on image quality of cerebral CT and CT angiography (CTA) for patients who underwent intracranial aneurysm coiling.

METHODS

Twenty patients underwent cerebral CT and CTA using a 320-detector row CT after intracranial aneurysm coiling. Images with and without application of the SEMAR algorithm (SEMAR CT and standard CT images, respectively) were reconstructed for each patient. The images were qualitatively assessed by two independent radiologists in a blinded manner for the depiction of anatomical structures around the coil, delineation of the arteries around the coil, and the depiction of the status of coiled aneurysms. Artifact strength was quantitatively assessed by measuring the standard deviation of attenuation values around the coil.

RESULTS

The strength of artifacts measured in SEMAR CT images was significantly lower than that in standard CT images (25.7 ± 10.2 H.U. vs. 80.4 ± 67.2 H.U., p < 0.01, Student's paired t test). SEMAR CT images were significantly improved compared with standard CT images in the depiction of anatomical structures around the coil (p < 0.01, the sign test), delineation of the arteries around the coil (p < 0.01), and the depiction of the status of coiled aneurysms (p < 0.01).

CONCLUSION

The SEMAR algorithm significantly reduces metal artifacts from intracranial aneurysm coiling and improves visualization of anatomical structures and arteries around the coil, and depiction of the status of coiled aneurysms on post-interventional cerebral CT.

Utility of second-generation single-energy metal artifact reduction in helical lung computed tomography for patients with pulmonary arteriovenous malformation after coil embolization

PURPOSE

The quality of images acquired using single-energy metal artifact reduction (SEMAR) on helical lung computed tomography (CT) in patients with pulmonary arteriovenous malformation (PAVM) after coil embolization was retrospectively evaluated.

MATERIALS AND METHODS

CT images were reconstructed with and without SEMAR. Twenty-seven lesions [20 patients (2 males, 18 females), mean age 61.2 ± 11.0 years; number of embolization coils, 9.8 ± 5.0] on contrast-enhanced CT and 18 lesions of non-enhanced lung CT concurrently performed were evaluated. Regions of interest were positioned around the coils and mean standard deviation value was compared as noise index. Two radiologists visually evaluated metallic coil artifacts using a four-point scale: 4 = minimal; 3 = mild; 2 = strong; 1 = extensive.

RESULTS

Noise index was significantly improved with SEMAR versus without SEMAR (median [interquartile range]; 194.4 [161.6-211.9] Hounsfield units [HU] vs. 243.9 [220.4-286.0] HU; p < 0.001). Visual score was significantly improved with SEMAR versus without SEMAR (Reader 1, 3 [3] vs.1 [1]; Reader 2, 3 [3] vs.1 [1]; p < 0.001). Significant differences were similarly demonstrated on lung CT (p < 0.001).

CONCLUSION

SEMAR provided clear chest CT images in patients who underwent PAVM coil embolization.

Evaluation of CT Angiography Image Quality Acquired with Single-Energy Metal Artifact Reduction (SEMAR) Algorithm in Patients After Complex Endovascular Aortic Repair

Purpose

To evaluate the value of single-energy metal artifact reduction (SEMAR) algorithm on image quality in patients after complex endovascular aortic repair (EVAR) with fenestrated and branched devices.

Methods

Routine follow-up computed tomography angiography (CTA) examinations were performed between February 2016 and May 2017 in 18 patients who underwent a complex EVAR procedure at our institution. Objective analysis was performed by measuring the standard deviation (SD) of attenuation (Hounsfield Units), and the contrast-to-noise ratio (CNR) in regions of interests in the stented visceral arteries. Subjective analysis of the degree of artifacts and stent visualization was performed independently by two interventional radiologists, blinded to the image reconstruction.

Results

The SD of attenuation was significantly lower in all target visceral arteries (p < .001), the celiac artery (p = .002), the superior mesenteric artery (SMA; p = .043), and renal arteries (p < .001) in the CT images with SEMAR reconstruction. The CNR significantly increased in all SEMAR-reconstructed target visceral arteries (overall: p < .001, celiac artery: p = .009; SMA: p = .003; renal arteries: p < .001). The reviewers rated a significantly lower artifact degree in all target vessels (overall: p < .001, celiac artery: p = .001; SMA: p = .008; renal arteries: p < .001) and a significantly improved visualization of the stent patency in all target vessels (overall: p < .001, celiac artery: p = .031; SMA: p = .047; renal arteries: p < .001) in the SEMAR images. Overall preference of both reviewers was in favor of the SEMAR reconstruction in 15/18 cases (83%).

Conclusion

Reconstruction with SEMAR algorithm significantly improves CTA image quality in patients after complex EVAR.

Level of Evidence

Level 4, Case series.