Feasibility of low-dose contrast media in run-off CT angiography on dual-layer spectral detector CT

Abstract

Background: The aim of the present study was to assess the feasibility of applying low-dose contrast media (CM), and to explore the optimal virtual monoenergetic images (VMIs) in run-off computed tomography (CT) angiography (CTA) on dual-layer spectral detector CT (SDCT).

Methods: Forty patients were randomly assigned into a control group using routine volume CM (group A) and an experimental group using half-volume CM (group B). In groups A and B, 120 kVp polychromatic conventional images were generated via hybrid iterative reconstruction algorithm defined as A1 and B1, respectively. Additionally, in group B, VMIs (range, 40-120 keV) were reconstructed via a spectral reconstruction algorithm defined as B2-B10. Vascular attenuation, noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and radiation dose were evaluated. Subjective evaluation was performed using a 5-point scale.

Results: The patient demographics and radiation dose demonstrated no significant difference between groups A and B [dose length product (DLP): 1,823.45±512.68 vs. 2,014.40±453.25 mGy·cm, P=0.229; volume CT dose index: 14.92±3.40 vs. 16.26±2.85 mGy, P=0.208; the effective dose (ED): 10.82±3.02 vs. 11.88±2.67 mSv, P=0.229]. The mean vascular attenuation was higher in group B2 (40 keV) and was lower in group B3 (50 keV) in comparison with that in group A1 (487.07±154.21 vs. 414.35±71.66 HU, 329.90±100.25 vs. 414.35±71.66 HU, P>0.05). Compared with group A1, the mean noise was similar in group B2 (40 keV) and was lower in group B1 and groups B3-B10 (50-120 keV) (14.81±5.67 vs. 17.29±4.70 HU, P>0.05; 6.75±1.23-11.26±3.24 vs. 17.29±4.70 HU, P<0.05). The mean SNR and CNR in group B2 (40 keV), as well as the mean SNR in group B3 (50 keV), were significantly higher than those of group A1 (38.21±7.52 vs. 28.25±7.20, 32.70±7.79 vs. 24.54±6.60, 32.85±7.10 vs. 28.25±7.20, P<0.05), and the mean CNR in group B3 (50 keV) was similar to that in group A1 (26.66±7.32 vs. 24.54±6.60, P>0.05). Scores of subjective image quality (IQ) in group B2 (40 keV) and B3 (50 keV) were similar to those in group A1 {5 [4.25, 5] vs. 5 [4, 5], 5 [5, 5] vs. 5 [4, 5], P>0.05}, and showed a declining trend in group B4 (60 keV) {4 [4, 5] vs. 5 [4, 5], P>0.05}.

Conclusions: It is feasible to perform run-off CTA using low-dose CM with VMI on SDCT. The VMIs at 40-50 keV were the optimal choice and did not compromise IQ.

Keywords: Spectral detector computed tomography; contrast media (CM); lower extremity; virtual monoenergetic images (VMIs).

Figure 1

Graphs showing the results of mean vascular attenuation (A), noise (B), signal-to-noise ratio (SNR) (C), and contrast-to-noise ratio (CNR) (D). A1, 120 kVp polychromatic conventional images using routine volume contrast media; B1 and B2–B10, 120 kVp polychromatic conventional images and virtual monoenergetic images (40–120 keV), respectively, using half-volume contrast media. The difference was significant except between groups A1 and B1–B10 (*).

Figure 2

Transverse image example of left middle popliteal arteries for objective image quality analysis. (A1) 120 kVp polychromatic conventional images of a 65-year-old man using routine volume contrast media; (B1 and B2–B10) 120 kVp polychromatic conventional images and virtual monoenergetic images (40–120 keV), respectively, of a 71-year-old man using half-volume contrast media.

Figure 3

Maximum intensity projection images for subjective image quality (IQ) analysis. (A1) 120 kVp polychromatic conventional images of a 65-year-old man using routine volume contrast media; (B1 and B2–B10) 120 kVp polychromatic conventional images and virtual monoenergetic images (40–120 keV), respectively, of a 71-year-old man using half-volume contrast media.