Bland & Altman plot of the ASPECTS score of the NECT analysis in comparison to the “best contrast” image analysis.

<p>Bland & Altman plot of the ASPECTS score of the NECT analysis in comparison to the “best contrast” image analysis.</p

Schematic illustration of the “best contrast” (BC) post-processing.

<p>The center is defining the attenuation level, at which image information is highlighted. By adjustment of the slope and delta of the attenuation curve, the expression of the post-processing can be modulated.</p

64 year-old male patient with ischemic stroke of the right cerebral hemisphere due to an isolated occlusion of the right internal carotid artery.

<p>While the NECT (A) only give an idea of a slight dedifferentiation of gray and white matter at the insular cortex, the “best contrast” image (B) shows a great delineated infarction (long arrows) with involvement of the internal capsule (short arrow). The diagnosis was confirmed on follow-up CT, which shows that the BC image reflects the infarct size more accurately (C).</p

50-year-old male patient with ischemic stroke of the left hemisphere due to occlusion of the left internal carotid artery (ICA).

<p>The NECT (A) does not show a significant infarct demarcation, whilst the “best contrast” optimized images (B) show a demarcation of the left basal ganglia and the insular cortex (arrows), which was confirmed by follow-up CT (C).</p

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

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

Cohens kappa show interrater reliability of MAR methods stratified by hip prosthesis and dental implants.

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

Qualitative image analysis is based on 5 point Likert scales taking into account the degree of artefact as well as diagnostic impact on adjacent and distant tissue for both hip prosthesis (A to D) and dental implants (E to H).

<p>A and E) massive artefacts (4 points), B and F) pronounced streaks (3 points), C and G) intermediate streaks (2 points), D and H) minimal streaks (1 point).</p

Bar-graphs demonstrating qualitative assessment of impact on metal artefacts of the different MAR approaches applied A) hip prosthesis and B) dental implants based on 5 point Likert scales.

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