Effect of acquisition techniques, latest kernels, and advanced monoenergetic post-processing for stent visualization with third-generation dual-source CT

Abstract

PURPOSE The purpose of this study is to systematically evaluate the effect of tube voltage, current kernels, and monoenergetic post-processing on stent visualization. METHODS A 6 mm chrome-cobalt peripheral stent was placed in a dedicated phantom and scanned with the available tube voltage settings of a third-generation dual-source scanner in single-energy (SE) and dual-energy (DE) mode. Images were reconstructed using the latest convolution kernels and monoenergetic reconstructions (40-190 keV) for DE. The sharpness of stent struts (S), struts width (SW), contrast-to-noise-ratios (CNR), and pseudoenhancement (PE) between the vessel with and without stent were analyzed using an in-house built automatic analysis tool. Measurements were standardized through calculated z-scores. Z-scores were combined for stent (SQ), luminal (LQ), and overall depiction quality (OQ) by adding S and SW, CNR and SW and PE, and S and SW and CNR and PE. Two readers rated overall stent depiction on a 5-point Likert-scale. Agreement was calculated using linear-weighted kappa. Correlations were calculated using Spearman correlation coefficient. RESULTS Maximum values of S and CNR were 169.1 HU/pixel for [DE; 100/ Sn 150 kV; Qr59; 40 keV] and 50.0 for [SE; 70 kV; Bv36]. Minimum values of SW and PE were 2.615 mm for [DE; 80 to 90/ Sn 150 kV; Qr59; 140 to 190 keV] and 0.12 HU for [DE; 80/ Sn 150 kV; Qr36; 190 keV]. Best combined z-scores of SQ, LQ, and OQ were 4.53 for [DE; 100/ Sn 150 kV; Qr 59; 40 keV], 1.23 for [DE; 100/ Sn 150 kV; Qr59; 140 keV] and 2.95 for [DE; 90/ Sn 150 kV; Qr59; 50 keV]. Best OQ of SE was ranked third with 2.89 for [SE; 90 kV; Bv59]. Subjective agreement was excellent (kappa=0.86; P < .001) and correlated well with OQ (rs=0.94, P < .001). CONCLUSION Combining DE computed tomography (CT) acquisition with the latest kernels and monoenergetic post-processing allows for improved stent visualization as compared with SECT. The best overall results were obtained for monoenergetic reconstructions with 50 keV from DECT 90/Sn 150 kV acquisitions using kernel Qr59.

Figure 1.

a, b. Visualization of quantitative image analysis. (a) Seven consecutive images containing the stent were averaged. Pixel data were extracted from 2 lines crossing the center of the stent and the stent struts. The profiles were angulated horizontally and vertically to obtain more robust data. (b) The resulting graph with fitted curve. The slope (oblique dashed line) was calculated representing the sharpness of the stent depiction. FWHM was used as an approximated measure of the stent width. FWHM was calculated from the stent wall’s maximum attenuation toward the background and the contrast-enhanced lumen of the stent. FMWH, full width at half maximum; CT, computed tomography.

Figure 2.

a-c. Ranking of acquisition and reconstruction parameters. The image in (a) represents the best overall z-scores (lumen and stent z-score). The image in (b) shows the best z-score for the depiction of the stent (sharpness and stent width z-score) and the best z-score for the visualization of the lumen (lumen width, CNR, and pseudoenhancement). The image in (c) shows the best z-scores for the categories: sharpness, lumen width, stent width, CNR, and pseudoenhancement. Z-scores were obtained statistically by standardization. In square brackets listed are [the mode of acquisition; the monoenergetic photon energy setting in case of DE; the tube voltage; the reconstruction kernel]. CNR, contrast-to-noise ratio; DE, dual-energy; SE, single-energy; Sn, tin-filtered.

Figure 3.

a-f. Exemplary images of the stent and vessel phantom for the 3 best combinations of acquisition and reconstruction parameters based on a combined z-score of measured sharpness, stent strut width, contrast-to-noise ratio, and pseudoenhancement (difference of vessel attenuation inside and outside of the stent). For (a), (b), and (e), window levels are adjusted for luminal depiction. For (b), (d), and (f), window levels are adjusted for stent visualization. (a, b), (c, d), and (e, f) represent [DE; 90/ Sn 150 kV; Qr59; 50 keV], [DE; 100/ Sn 150 kV; Qr59; 60 keV], and [SE; 90 kV; Bv59] as best single-energy images.

Figure 4.

Illustration of acquisition parameters on combined stent, lumen, and overall z-score. Z-scores are based on standardized measurements. The stent z-score is a combination of sharpness and stent width. The lumen z-score is a representation of stent width, CNR, pseudoenhancement (measured enhancement within the stent minus enhancement of the vessel model outside the stent). The overall z-score consists of sharpness, stent width, CNR, and pseudoenhancement.