Underneath the Arches, no. 61, October 24, 1968

Underneath the Arches was Grand Valley State\u27s faculty and staff newsletter, published from 1963 to 1971. It was a precursor to the Forum

Comparison and Combination of Dual-Energy- and Iterative-Based Metal Artefact Reduction on Hip Prosthesis and Dental Implants

<div><p>Purpose</p><p>To compare and combine dual-energy based and iterative metal artefact reduction on hip prosthesis and dental implants in CT.</p><p>Material and Methods</p><p>A total of 46 patients (women:50%,mean age:63±15years) with dental implants or hip prostheses (n = 30/20) were included and examined with a second-generation Dual Source Scanner. 120kV equivalent mixed-images were derived from reconstructions of the 100/Sn140kV source images using no metal artefact reduction (NOMAR) and iterative metal artefact reduction (IMAR). We then generated monoenergetic extrapolations at 130keV from source images without IMAR (DEMAR) or from source images with IMAR, (IMAR+DEMAR). The degree of metal artefact was quantified for NOMAR, IMAR, DEMAR and IMAR+DEMAR using a Fourier-based method and subjectively rated on a five point Likert scale by two independent readers.</p><p>Results</p><p>In subjects with hip prosthesis, DEMAR and IMAR resulted in significantly reduced artefacts compared to standard reconstructions (33% vs. 56%; for DEMAR and IMAR; respectively, p<0.005), but the degree of artefact reduction was significantly higher for IMAR (all p<0.005). In contrast, in subjects with dental implants only IMAR showed a significant reduction of artefacts whereas DEMAR did not (71%, vs. 8% p<0.01 and p = 0.1; respectively). Furthermore, the combination of IMAR with DEMAR resulted in additionally reduced artefacts (Hip prosthesis: 47%, dental implants 18%; both p<0.0001).</p><p>Conclusion</p><p>IMAR allows for significantly higher reduction of metal artefacts caused by hip prostheses and dental implants, compared to a dual energy based method. The combination of DE-source images with IMAR and subsequent monoenergetic extrapolation provides an incremental benefit compared to both single methods.</p></div

Three dimensional mesh model of a right coronary artery.

<p>Panel (A) shows the inflow (arrow) at the ostium of a right coronary artery and outflows of two small side branches (chevrons). Panel (B) shows a magnification of the outflow shown in panel (A). Notice the three boundary layers with small cell size (arrow head), necessary to accurately calculate ESS. Towards the inner lumen of the vessel, cell size increases to reduce the total number of cells and thus computation time.</p

Wall thickness.

<p>Mean wall thickness was highest in quartile 1 (low endothelial shear stress (ESS)) and lowest in quartiles 2 and 3 (intermediate ESS). Vessel wall thickness in quartile 4 (high ESS) was in between. Differences were not significant between quartile 2 and 3 (p = 0.15). All other differences were statistically significant (p < 0.001).</p><p>SD: standard deviation</p><p>Wall thickness.</p

Color encoded illustration of endothelial shear stress (ESS) on a 3D model of a right coronary artery obtained by coronary computed tomography angiography.

<p>After segmentation side branches were cut 1–2 cm from the branching point. The volume mesh consisted of about 400,000 polyhedral cells. The Navier-Stokes equations were solved by the finite element method. The level of ESS increases from blue to red as shown in the color map on the left.</p

Distribution of plaque tissue composition in areas exposed to different levels of endothelial shear stress (ESS).

<p>Panel (A) shows an example of an early, panel (B) an example of a more advanced atherosclerotic lesion as assessed by intravascular ultrasound radiofrequency data analysis. Fibrous tissue is represented by dark green, fibrofatty tissue by light green, necrotic tissue by red and calcified tissue by white colour. We observed a significantly higher amount of fibrofatty (*) tissue in areas exposed to the lowest level of ESS (quartile 1) in comparison to low-intermediate ESS (quartile 2), intermediate-high ESS (quartile 3) or high ESS (quartile 4) (p≤0.023) (C). There was no difference in the amount of other tissue types depending on the level of ESS (p≥0.061).</p

Bar-graphs demonstrating the association between the different MAR approaches applied and quantitative reduction of metal artefacts (averaged sums of amplitudes of the lower frequencies) representing streaking artefacts from hip prosthesis and metallic dental implants.

<p>NOMAR = no metal artefact reduction, DEMAR = dual-energy metal artefact reduction, IMAR = iterative metal artefact reduction, IMAR+DEMAR = sequential combination of iterative and dual-energy metal artefact reduction.</p

Patient Demographics and Imaging Parameters of the 46 subjects included in the analysis.

<p>Data is given ± standard deviation.</p

Applied method for quantitative image analysis with A) polygon placement around metallic implant to extract circular pixel information and B) results of discrete Fourier transform.

<p>Analysing amplitudes of low frequencies (red box) permits information on the degree of metal artefacts.</p

Plaque prevalence.

<p>There was a significantly higher prevalence of atherosclerotic plaques in areas of very low (quartile 1) and very high (quartile 2) endothelial shear stress (ESS) as compared to areas of intermediate ESS (quartile 2 and 3) (p < 0.001). Furthermore plaque prevalence was higher in quartile 1 compared to quartile 4 (p < 0.001). Differences between quartile 2 and 3 were not significant (p = 0.56).</p><p>Plaque prevalence.</p