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Feasibility of ultra-low kVp CT colonography

Philips CT Clinical Science Philips Healthcare • USA

Effect of different iterative reconstruction algorithms on radiologists’ performance

Shin CI, Kim SH, Lee ES, Lee DH, Hwang EJ, Chung SY, Lee JM, Han JK, Choi BI.

To analyze the effect of a decrease in tube voltage from 100~120 kVp to 80 kVp in CT colonography (CTC) on dose, image noise, and diagnostic performance using anthropomorphic phantoms and to assess the effect of two different iterative reconstruction algorithms on radiologists’ performance.

Method and Materials
Seven colon phantoms with 68 simulated polyps = 6 mm were scanned at different kVp settings (80, 100, and 120 kVp) and 10 mAs. Images were reconstructed using filtered back projection (FBP), statistical model-based iterative reconstruction (iDose⁴), and knowledge-based iterative reconstruction algorithm (IMR). Nine datasets for each phantom according to three kVp settings and three reconstruction algorithms yielded 63 CTC datasets. Volume CT dose index (CTDIvol) and image noise were recorded and compared. Two readers blinded to kVp and reconstruction algorithm independently reviewed CTC using primary 3D method. Per-polyp sensitivity was compared among the datasets.

Decreasing tube voltage from 120 and 100 to 80 kVp resulted in 70.7% and 50.5% significant reduction in CTDIvol, respectively (P=0.014). Effective radiation dose of 80 kVp CTC was 0.17 mSv. With FBP reconstruction, image noise in 80 kVp FBP significantly increased by 67.8% and 45.5%, respectively (P=0.018) and per-polyp sensitivity of both reviewers (14.7%, 7.4%) was significantly lower than those in 100 kVp FBP (57.4%, 39.7%) and 120 kVp FBP (85.3%, 83.8%)(P<0.0001). With iDose⁴, image noise in 80 kVp iDose⁴ significantly drop to 52.6% compared to that in 80 kVp FBP (P=0.018) but, per-polyp sensitivity (79.4%, 66.2%) in 80 kVp iDose⁴ was still significantly lower than those of 100 kVp iDose⁴ (95.6%, 86.8%) and 120 kVp iDose⁴ (98.5%, 89.7%)(P<0.002). With IMR, per-polyp sensitivity (98.5%, 95.6%) in 80 kVp IMR was not significantly different from those in 100 kVp IMR (100%, 95.6%) and 120 kVp IMR (100%, 95.6%) for both reviewers (P>0.05).

A decrease in tube voltage to 80 kVp results in a significant reduction of radiation dose to 0.17 mSv at a cost of significant deterioration in image noise and diagnostic performance. With application of knowledge-based iterative reconstruction algorithm, radiologists’ performance of 80 kVp CTC is acceptable and is on par with 100 or 120 kVp CTC.

Clinical Relevance/Application
Ultra-low kVp CT colonography with 80 kVp can be feasible with an application of knowledge-based iterative reconstruction algorithm, significantly lowering the radiation dose with sub-mSv.

Legal Note - The results described in this abstract are for this case only and do not claim to represent universal results. 

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Jan 21, 2014

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abdomen, Body, colon, dose, FBP reconstruction, iDose4, IMR, iterative model reconstruction, iterative reconstruction, phantom, polyps

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