Comparison of hybrid and pure iterative reconstruction techniques with conventional filtered back projection: dose reduction potential in the abdomen

Sarabjeet Singh, Mannudeep K Kalra, Synho Do, Jean Baptiste Thibault, Homer Pien, Owen J O'Connor, Owen O J Connor, Michael A Blake
Journal of Computer Assisted Tomography 2012, 36 (3): 347-53

PURPOSE: Assess the effect of filtered back projection (FBP) and hybrid (adaptive statistical iterative reconstruction [ASIR]) and pure (model-based iterative reconstruction [MBIR]) iterative reconstructions on abdominal computed tomography (CT) acquired with 75% radiation dose reduction.

MATERIALS AND METHODS: In an institutional review board-approved prospective study, 10 patients (mean [standard deviation] age, 60 (8) years; 4 men and 6 women) gave informed consent for acquisition of additional abdominal images on 64-slice multidetector-row CT (GE 750HD, GE Healthcare). Scanning was repeated over a 10-cm scan length at 200 and 50 milliampere second (mA s), with remaining parameters held constant at 120 kilovolt (peak), 0.984:1 pitch, and standard reconstruction kernel. Projection data were deidentified, exported, and reconstructed to obtain 4 data sets (200-mA s FBP, 50-mA s FBP, 50-mA s ASIR, 50-mA s MBIR), which were evaluated by 2 abdominal radiologists for lesions and subjective image quality. Objective noise and noise spectral density were measured for each image series.

RESULTS: Among the 10 patients, the maximum weight recorded was 123 kg, with maximum transverse diameter measured as 43.7 cm. Lesion conspicuity at 50-mA s MBIR was better than on 50-mA s FBP and ASIR images (P < 0.01). Image noise was rated as suboptimal on low-dose FBP and ASIR but deemed acceptable in MBIR images. Objective noise with 50-mA s MBIR was 2 to 3 folds lower compared to 50-mA s ASIR, 50-mA s FBP, and 200-mA s FBP (P < 0.0001). Noise spectral density analyses demonstrated that ASIR retains the noise spectrum signature of FBP, whereas MBIR has much lower noise with a more regularized noise spectrum pattern.

CONCLUSION: Model-based iterative reconstruction renders acceptable image quality and diagnostic confidence in 50- mA s abdominal CT images, whereas FBP and ASIR images are associated with suboptimal image quality at this radiation dose level.

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