Monoenergetic reconstructions and iodine density maps for visualization of coronary artery stents using 8-cm dual-layer detector spectral computed tomography: an in vitro phantom study

Abstract

Background: The effectiveness of coronary computed tomography (CT) angiography in assessing stent restenosis is hindered by heavy metal artifacts. This study aimed to evaluate the image quality of monoenergetic reconstructions and iodine density map for coronary stent imaging using an 8-cm dual-layer detector spectral CT.

Methods: In this study, 8 stents with a diameter <3 mm (group A) and 10 with a diameter ≥3 mm (group B) were placed in plastic tubes filled with iodinated contrast media and scanned. The internal diameter of the prepared stents was then measured by intravascular ultrasound. The reconstructed images included iodine density maps, conventional images, and different energy levels. The visualization of the stent lumen and stent structure was subjectively assessed using a 4-point Likert scale. The objective evaluation was performed using the in-stent lumen signal-to-noise ratio (SNRis), non-stent lumen SNR (SNRns), internal diameter difference (IDD), and blooming artifact index (BAI). The Friedman test and analysis of variance were used for multiple comparisons.

Results: For lumen visualization, the optimal monoenergetic images received the highest score for both group A (2.56±0.51) and group B (3.1±0.55). Multiple comparisons showed that there were significant differences between the optimal monoenergetic images and iodine density maps. However, for stent structure, iodine density maps received the highest score for group A (3.0±0.52) and group B (3.8±0.41). For quantitative assessment, the optimal monoenergetic images had the highest SNRis and SNRns, while the iodine density maps had the lowest SNRis and SNRns. For IDD and BAI, the iodine density maps yielded the smallest value.

Conclusions: The monoenergetic images on the second-generation dual-layer detector CT provide better visualization of the lumen and higher SNR. However, iodine density maps are superior for evaluating stent structure and IDD and BAI compared to monoenergetic and conventional reconstructions.

Keywords: Computed tomography (CT); coronary artery disease; dual-layer detector; in-stent restenosis; stent.

Figure 1

Photographs of the phantom setup. (A,B) The vertical and front views of the prepared tubes arranged in two layers on a customized tray. (C) A container filled with homogenized vegetable oil to mimic epicardial adipose tissue.

Figure 2

ROIs for the quantitative evaluations. (A) A representation of the internal and external diameter measurements of the stent (number 12). (B) ROIs were placed for the measurement of mean attenuation and standard deviation of the in-stent and non-stent lumens. ROI, region of interest; Av, average; HU, Hounsfield unit; SD, standard deviation.

Figure 3

IVUS measurements of the inner diameter of the stent (number 12). IVUS, intravascular ultrasound.

Figure 4

Monoenergetic images at 40–200 keV (a 10 keV interval), conventional images, and iodine density maps of a stent in group A (number 11, row 1–2) and group B (number 12, row 3–4). Group A was the group with stents <3 mm in diameter, and group B was the group with stents ≥3 mm in diameter. Row 1 and row 3 show the stent lumen, while row 2 and row 4 show the stent structure. CON, conventional images; IDM, iodine density maps.

Figure 5

Subjective assessment score of stent lumen and structure. (A) Subjective score of stent lumen for group A. (B) Subjective score of stent lumen for group B. (C) Subjective score of stent structure for group A. (D) Subjective score of stent structure for group B. Group A was the group with stents <3 mm in diameter, and group B was the group with stents ≥3 mm in diameter. The dashed boxes indicate the energy level of optimal monoenergetic imaging. *, P<0.05; **, P<0.01.

Figure 6

The mean SNR_is, SNR_ns, IDD, and BAI of each image set for both stent groups. Group A was the group with stents <3 mm in diameter, and group B was the group with stents ≥3 mm in diameter. Note that the curves of SNR_ns are smoother than those of SNR_is. SNR_is, in-stent lumen signal-to-noise ratio; SNR_ns, non-stent lumen signal-to-noise ratio; IDD, internal diameter difference; BAI, blooming artifact index.