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Half contrast agent dose and low radiation dose protocol for abdominal dynamic CT

Philips CT Clinical Science Philips Healthcare • USA

Clinical impact of IMR for low kVp imaging

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

Low kilo-voltage (kVp) CT is well suited for low contrast and low radiation dose abdominal CT; however, increased image noise is a problem. The recent introduced iterative model reconstruction (IMR, Philips Healthcare) dramatically reduces the image noise and offers virtually noise free images. We evaluated the feasibility of a half contrast agent dose and low radiation dose protocol for abdominal dynamic CT using 80 kVp and the IMR technique.

Method and Materials
This prospective study received institutional review board approval; prior informed consent was obtained from all patients. We enrolled 30 patients who underwent abdominal dynamic CT using 80-kVp setting with a half contrast dose (300 mgI/kg) during 30 sec. We also enrolled 30 patients who were scanned with a standard 120-kVp protocol with filtered back projection (FBP) technique using the standard contrast dose of 600 mgI/kg during 30 sec as a control group. The 80-kVp images were reconstructed with FBP, hybrid-iterative reconstruction (iDose⁴) and IMR. We compared the effective dose (ED) of each protocol and evaluated image noise, CT numbers and the contrast to noise ratio (CNR) of 120 kVp and FBP-, iDose⁴-, IMR-reconstructed 80 kVp images at the abdominal aorta in hepatic arterial phase (HAP) and hepatic parenchyma in portal venous phase (PVP).

The total effective radiation dose was 42% lower with 80-kVp scan than with 120-kVp scan (9.0 mSv ± 1.3 vs 15.6 mSv ± 2.6). CT numbers with the half contrast dose 80 kVp protocol were significantly higher than with the 120 kVp protocol (abdominal aorta: 371.2 ± 65.1 vs 333.3 ± 46.9, p = 0.04; hepatic parenchyma: 121.1 ± 12.6 vs 107.7 ± 9.3, p < 0.01). IMR and iDose⁴ technique decreased mean image noise by 72% and 45% as compared with FBP technique at 80 kVp scan (IMR: 4.5 ± 0.7; iDose⁴: 8.8 ± 1.1; FBP: 15.8 ± 2.0; 120 kVp: 8.3 ± 1.6, respectively). The CNR of 80-kVp with IMR were significantly higher than 120-kVp protocols (abdominal aorta: 87.9 ± 19.8 vs 42.5 ± 10.8, p < 0.01; hepatic parenchyma: 26.3 ± 4.5 vs 13.2 ± 3.2, p < 0.01).

IMR is a promising technique to improve the image quality of the half contrast agent dose and low radiation dose protocol for abdominal dynamic CT with low kVp setting. 

Clinical Relevance/Application 
The contrast dose for abdominal dynamic CT can be reduced by 50% by using a 80 kVp setting with IMR with improved image quality and reduced radiation dose.

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Jan 14, 2014

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abdomen, aorta, Body, Dynamic, FBP reconstruction, iDose4, image quality, IMR, iterative model reconstruction, iterative reconstruction, low dose, prospective, Vascular

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