Hyo-Jin Kang1,2, Se Hyung Kim3,4, Cheong-Il Shin1,2, Ijin Joo1,2, Hwaseong Ryu5, Sang Gyun Kim6, Jong Pil Im6, Joon Koo Han1,2,7. 1. Department of Radiology, Seoul National University Hospital, 101 Daehangno, Jongno-gu, Seoul, 03080, Korea. 2. Department of Radiology, Seoul National University College of Medicine, 101 Daehangno, Jongno-gu, Seoul, 03080, Korea. 3. Department of Radiology, Seoul National University Hospital, 101 Daehangno, Jongno-gu, Seoul, 03080, Korea. shkim7071@gmail.com. 4. Department of Radiology, Seoul National University College of Medicine, 101 Daehangno, Jongno-gu, Seoul, 03080, Korea. shkim7071@gmail.com. 5. Pusan National University Yangsan Hospital, Yangsan, Korea. 6. Department of Internal medicine, Seoul National University Hospital, Seoul, Korea. 7. Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Korea.
Abstract
OBJECTIVES: To assess the feasibility of ultra-low dose computed tomography colonography (CTC) using knowledge-based iterative reconstruction (IR) and to determine its effect on polyp detection. METHODS: Forty-nine prospectively-enrolled patients underwent ultra-low dose CTC in the supine (100 kVp/20 mAs) and prone positions (80 kVp/20 mAs), followed by same-day colonoscopy. Thereafter, images were reconstructed using filtered back projection (FBP) and knowledge-based IR (IMR; Philips Healthcare, Best, Netherlands) algorithms. Effective radiation dose of CTC was recorded. Pooled per-polyp sensitivity and positive predictive value of three radiologists was analysed and compared between FBP and IMR. Image quality was assessed on a five-point scale and image noise was recorded using standard deviations. RESULTS: Mean effective radiation dose of ultra-low dose CTC was 0.90 ± 0.06 mSv. Eighty-nine polyps were detected on colonoscopy (mean, 8.5 ± 4.7 mm). The pooled per-polyp sensitivity for polyps 6.0-9.9 mm (n = 22) on CTC reconstructed with IMR (36/66, 54.5%) was not significantly different with that using FBP algorithm (34/66, 51.5%) (p = 0.414). For polyps ≥10 mm (n = 35), however, the pooled per-polyp sensitivity on CTC with IMR (73/105, 69.5%) was significantly higher than that with FBP (55/105, 52.4%) (p < 0.001). In particular, the difference of per-polyp sensitivity was statistically significant in intermediate (p = 0.014) and novice (p = 0.003) reviewers. Furthermore, mean image noise of IMR (8.4 ± 6.2 HU) was significantly lower than that of FBP (37.5 ± 13.9 HU) (p < 0.001) and image quality with IMR was significantly better than with FBP in all evaluated segments in all reviewers (all ps < 0.001). CONCLUSIONS: Sub-mSv CTC reconstructed with IMR was feasible for the detection of clinically significant polyps, demonstrating 70% per-polyp sensitivity of polyps ≥10 mm, while allowing significant noise reduction and improvement in image quality compared with FBP reconstruction. KEY POINTS: • Sub-mSv CTC using IMR demonstrated 70% per-polyp sensitivity for polyps ≥10 mm. • CTC using IMR significantly outperformed CTC reconstructed with FBP. • IMR allows significantly more noise reduction and improvement in image quality than FBP.
OBJECTIVES: To assess the feasibility of ultra-low dose computed tomography colonography (CTC) using knowledge-based iterative reconstruction (IR) and to determine its effect on polyp detection. METHODS: Forty-nine prospectively-enrolled patients underwent ultra-low dose CTC in the supine (100 kVp/20 mAs) and prone positions (80 kVp/20 mAs), followed by same-day colonoscopy. Thereafter, images were reconstructed using filtered back projection (FBP) and knowledge-based IR (IMR; Philips Healthcare, Best, Netherlands) algorithms. Effective radiation dose of CTC was recorded. Pooled per-polyp sensitivity and positive predictive value of three radiologists was analysed and compared between FBP and IMR. Image quality was assessed on a five-point scale and image noise was recorded using standard deviations. RESULTS: Mean effective radiation dose of ultra-low dose CTC was 0.90 ± 0.06 mSv. Eighty-nine polyps were detected on colonoscopy (mean, 8.5 ± 4.7 mm). The pooled per-polyp sensitivity for polyps 6.0-9.9 mm (n = 22) on CTC reconstructed with IMR (36/66, 54.5%) was not significantly different with that using FBP algorithm (34/66, 51.5%) (p = 0.414). For polyps ≥10 mm (n = 35), however, the pooled per-polyp sensitivity on CTC with IMR (73/105, 69.5%) was significantly higher than that with FBP (55/105, 52.4%) (p < 0.001). In particular, the difference of per-polyp sensitivity was statistically significant in intermediate (p = 0.014) and novice (p = 0.003) reviewers. Furthermore, mean image noise of IMR (8.4 ± 6.2 HU) was significantly lower than that of FBP (37.5 ± 13.9 HU) (p < 0.001) and image quality with IMR was significantly better than with FBP in all evaluated segments in all reviewers (all ps < 0.001). CONCLUSIONS: Sub-mSv CTC reconstructed with IMR was feasible for the detection of clinically significant polyps, demonstrating 70% per-polyp sensitivity of polyps ≥10 mm, while allowing significant noise reduction and improvement in image quality compared with FBP reconstruction. KEY POINTS: • Sub-mSv CTC using IMR demonstrated 70% per-polyp sensitivity for polyps ≥10 mm. • CTC using IMR significantly outperformed CTC reconstructed with FBP. • IMR allows significantly more noise reduction and improvement in image quality than FBP.
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