Prospective ECG-triggered coronary CT angiography: clinical value of noise-based tube current reduction method with iterative reconstruction

Abstract

Objectives: To evaluate the clinical value of noise-based tube current reduction method with iterative reconstruction for obtaining consistent image quality with dose optimization in prospective electrocardiogram (ECG)-triggered coronary CT angiography (CCTA).

Materials and methods: We performed a prospective randomized study evaluating 338 patients undergoing CCTA with prospective ECG-triggering. Patients were randomly assigned to fixed tube current with filtered back projection (Group 1, n = 113), noise-based tube current with filtered back projection (Group 2, n = 109) or with iterative reconstruction (Group 3, n = 116). Tube voltage was fixed at 120 kV. Qualitative image quality was rated on a 5-point scale (1 = impaired, to 5 = excellent, with 3-5 defined as diagnostic). Image noise and signal intensity were measured; signal-to-noise ratio was calculated; radiation dose parameters were recorded. Statistical analyses included one-way analysis of variance, chi-square test, Kruskal-Wallis test and multivariable linear regression.

Results: Image noise was maintained at the target value of 35HU with small interquartile range for Group 2 (35.00-35.03HU) and Group 3 (34.99-35.02HU), while from 28.73 to 37.87HU for Group 1. All images in the three groups were acceptable for diagnosis. A relative 20% and 51% reduction in effective dose for Group 2 (2.9 mSv) and Group 3 (1.8 mSv) were achieved compared with Group 1 (3.7 mSv). After adjustment for scan characteristics, iterative reconstruction was associated with 26% reduction in effective dose.

Conclusion: Noise-based tube current reduction method with iterative reconstruction maintains image noise precisely at the desired level and achieves consistent image quality. Meanwhile, effective dose can be reduced by more than 50%.

Figure 1. Flow chart of patient inclusion. CCTA: Coronary CT Angiography; FBP: Filtered Back Projection; IR: Iterative Reconstruction; HR: Heart Rate.

Figure 2. Examples of different image quality scores.

Representative examples for different image quality scores. The examples show curved multiplanar reformations of left descending arteries of different patients. (a) impaired image quality, (b) reduced image quality, (c) adequate image quality, (d) good image quality, (e) excellent image quality.

Figure 3. Representative CCTA demonstrating image quality with different scan protocols.

57year old woman with body mass index of 26.49 kg/m² (a−c) and 42year old man with body mass index of 22.41 kg/m² (d−f). Curved multiplanar reformations of left descending arteries (a, d), left circumflex arteries (b, e), and right coronary arteries (c, f) of two patients demonstrating the same noise level (35HU) and qualitative image quality (score 3) obtained by the noise-based tube current with filtered back projection (328 mA, 120 kV, 2.02 mSv; a−c) and with iterative reconstruction (195 mA, 120 kV, 1.19 mSv; d-f), respectively.