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Sub-mSv radiation dose coronary CTA

Abstract
Philips CT Clinical Science Philips Healthcare • USA

Clinical impact of IMR with low kVp scans

Nakaura T, Tokuyasu S, Kidoh M, Nakamura S, Harada K, Yamashita Y, Itatani R.

Purpose 
Recently, the submillisievert radiation dose coronary CT angiography becomes clinically available by the techniques such as the iterative reconstruction technique, prospective ECG gating and low kVp setting. However, increased image noise is a problem except the extremely small body size patients. The purpose of this study was to evaluate the usefulness of the recent introduced iterative model reconstruction (IMR, Philips Healthcare) in ultra-low dose cardiac CT.

Method and Materials
This prospective study received institutional review board approval; prior informed consent to participate was obtained from all patients. We performed submillisievert radiation dose coronary CT angiography (CTA) to 25 patients who had suspicious or past history of the ischemic heart disease. We also performed phantom study to evaluate the influence of object size with AEC phantom (CT-AEC Cone Phantom, Kyoto Kagaku). We reconstructed clinical and phantom studies with filtered back projection (FBP), hybrid-iterative reconstruction (iDose⁴) and IMR. We compared CT number, image noise and contrast noise ratio (CNR) in ascending aorta of each reconstruction technique. We compared relationship between image noise and body mass index (BMI) for clinical study, and object size for phantom study.

Results 
Calculated effective dose of patients was 0.98 mSv. The image noise of IMR reconstructed images is significantly lower than that of FBP and iDose⁴ reconstructed images (IMR: 16.7±2.8; FBP: 67.5±14.5; iDose⁴: 28.3±5.9, respectively) (p<0.01). There were moderate correlations between image noise and BMI in FBP (r = 0.54, p < 0.01) and iDose⁴ (r = 0.42, p < 0.01); however, this correlation was not significant in IMR reconstruction technique (r = 0.31, p = 0.14). The phantom study suggested that there are the exponential regressions between image noise and object size in each reconstruction technique, and image noise of IMR reconstructed images were about 36% less influenced by the object size than that of FBP and iDose⁴ reconstructed images.

Conclusion
The IMR reconstruction offers stable and dramatic noise reduction in ultra low dose cardiac CT in various patient size as compared with FBP and iDose⁴ reconstruction.

Clinical Relevance/Application
The IMR reconstruction offers stable and dramatic noise reduction, and it might offer submillisievert radiation dose coronary CTA for most patients with diagnostic image quality.


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Abstract
aorta, Cardiac, coronary angiography, coronary arteries, dose, ECG-gated chest, FBP reconstruction, iDose4, image quality, IMR, IMR Platinum, iterative model reconstruction, iterative reconstruction, phantom, prospective, prospective gating, Vascular
 

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