Elsevier

European Journal of Radiology

Volume 81, Issue 12, December 2012, Pages 3905-3911
European Journal of Radiology

The optimal dose reduction level using iterative reconstruction with prospective ECG-triggered coronary CTA using 256-slice MDCT

https://doi.org/10.1016/j.ejrad.2012.06.022Get rights and content

Abstract

Aim

To assess the image quality (IQ) of an iterative reconstruction (IR) technique (iDose4) from prospective electrocardiography (ECG)-triggered coronary computed tomography angiography (coronary CTA) on a 256-slice multi-detector CT (MDCT) scanner and determine the optimal dose reduction using IR that can provide IQ comparable to filtered back projection (FBP).

Method and materials

110 consecutive patients (69 men, 41 women; age: 54 ± 10 years) underwent coronary CTA on a 256-slice MDCT (Brilliance iCT, Philips Healthcare). The control group (Group A, n = 21) were scanned using the conventional tube output (120 kVp, 210 mAs) and reconstructed using FBP. The other 4 groups were scanned with the same kVp but successively reduced tube output as follows: B[n = 15]: 125 mAs; C[n = 22]: 105 mAs; D[n = 36]: 84 mAs: E[n = 16]: 65 mAs) and reconstructed using IR levels of L3 (Group B), L4 (Group C) and L5 (Groups D and E), to compensate for the noise increase. All images were reconstructed using the same kernel (XCB). Two radiologists graded IQ in a blinded fashion on a 4-point scale (4 – excellent, 3 – good, 2 – fair and 1 – poor). Quantitative measurements of CT values, image noise and contrast-to-noise (CNR) were measured in each group. A receiver-operating characteristic (ROC) analysis was performed to determine a radiation reduction threshold up to which excellent IQ was maintained.

Results

There were no significant differences in objective noise, SNR and CNR values among Groups A, B, C, D, and E (P = 0.14, 0.09, 0.17, respectively). There were no significant differences in the scores of the subjective IQ between Group A, and Groups B, C, D, E (P = 0.23–0.97). Significant differences in image sharpness and study acceptability were observed between groups A and E (P < 0.05). Using the criterion of excellent IQ (score 4), the ROC curve of dose levels and IQ acceptability established a reduction of 60% of tube output (Group D) as optimum cutoff point (AUC: 0.72, 95% CI: 0.59–0.86). Group D (84 mAs with L5) provided equivalent subjective image ranking (with lumen sharpness taken into account) and objective IQ measurements (noise: 36.5 ± 10.7; SNR: 13.6 ± 4.9; CNR: 16.28 ± 5.4) compared with FBP images in Group A (noise: 35.5 ± 9.4; SNR: 12.4 ± 2.5; CNR: 15.4 ± 3.2) (P = 0.14, 0.09, 0.17, respectively). The effective dose (ED) of Group D was 63% lower than that of Group A (1.2 ± 0.1 mSv versus 3.2 ± 0.6 mSv).

Conclusion

Iterative reconstruction techniques can provide 63% ED reduction in prospectively-triggered coronary CTA using 256-slice MDCT while maintaining excellent image quality.

Introduction

Recent technological advancements in multidetector computed tomography (MDCT) have enabled coronary computed tomography angiography (coronary CTA) to become a preferred non-invasive alternative to coronary catheterization for ruling out significant coronary artery stenosis [1], [2], [3]. However, owing to radiation dose concerns commonly associated with coronary CTA using traditional techniques such as retrospectively electrocardiography (ECG)-gated scans, efforts have been undertaken to lower radiation associated, such as optimization of scan length, ECG-dependent tube current modulation, and reduced tube voltage, resulting in an effective radiation dose in the range of 9–14.6 mSv [4]. Further reductions in radiation dose were achieved by the use of prospective gating resulting in a radiation dose in the range of 2.1–3.6 mSv [5], [6], [7].

To date, studies at lowering radiation exposure from coronary CTA have mostly focused on the image acquisition techniques. Further attempts to reduce radiation dose via tube potential (kVp) or output (mA) are impacted by the limitations of reconstructions based on conventional filtered back projection (FBP) algorithms, resulting in an increase in the image noise, thus affecting image quality. A new reconstruction algorithm — iterative reconstruction (IR) has recently been introduced to address these shortcomings. Early investigations have shown that compared with FBP, IR can improve image quality (IQ) by lowering image noise in thoracic and abdominal CT scans [8], [9], [10], [11], [12], [13], [14], [15], while at the same time also enabling a reduction in radiation dose in the range of 32–65% depending on patient's body mass [10]. These benefits have also been extended to chest CT exams [8], [11], [12], and coronary CTA scans, with a coronary CTA multi-center study reporting a radiation dose reduction of 44% with the use of IR without impacting study interpretability [13]. The use of IR in coronary CTA has also been shown to reduce image noise compared to FBP [14].

As the X-ray examination should follow the principle radiation dose of as low as reasonably achievable (ALARA), it is necessary to explore the maximum dose reduction caused by IR. A newer hybrid IR technique (iDose4, Philips Healthcare, Cleveland, OH, USA) was recently introduced, the performance characteristics of which have been investigated in detail in prior work [15]. However, there is limited clinical data available investigating its performance in coronary CTA [16]. We aim to compare the performance of this technique with regards to IQ and radiation dose with FBP reconstruction algorithms in 256-slice prospectively-triggered axial coronary CTA. We compare the images reconstructed using FBP from scans performed at ‘routine’ tube output (i.e., ‘regular’ radiation dose) with IR from scans performed at progressively reduced tube output in cohorts demographically matched according to age and body-mass-index (BMI) to investigate the potential of reducing the radiation dose in prospectively-triggered axial coronary CTA while maintaining diagnostic image quality.

Section snippets

Subjects

Between June and July 2011, chronological data from 110 consecutive subjects (69 male, 41 female; mean age 54 ± 10 years; range 28–87 years; BMI 24.7 ± 2.8, who underwent coronary CTA was analyzed. Subjects were excluded from coronary CTA scans if they presented with any of the following criteria at baseline: severe renal inadequacy (creatinine clearance rate ≤120 μmol/L); pregnant; known allergies to iodinated contrast agent; severe arrhythmia; cardiac function or TIMI flow < Grade III after coronary

Results

Coronary CTA was successfully performed in all patients. No adverse events were observed. There were no significant differences in the patient demographics, heart rate, heart rate variability and the acquisition lengths among the groups (P > 0.05) (Table 1).

Discussion

This is the first experience of iDOSE4 in patients using prospectively-gated 256-slice MDCT coronary CTA. We investigated the performance of an IR technique (iDose4) in maintaining IQ in prospectively-gated coronary CTA scans compared to filtered backprojection (FBP), with progressive reduction in the tube output in patient cohorts demographically matched to age and BMI. Our study has demonstrated that the use of IR results in cardiac IQ that is comparable to FBP while at the same time

Conflict of interest

Authors who are not employees of Philips Healthcare controlled the inclusion of all data and information that might have represented a conflict of interest for the authors who are employees of that company.

Acknowledgments

The presented work was supported by two provincial government funds – Innovative Research Team of Liaoning Educational Committee (LT2010105) and Liaoning Doctoral Science Foundation (20071048).

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