Purpose To assess image quality, noise reduction, and radiation dose using sinogram affirmed iterative reconstruction vs filtered back projection of lumbar spine CT with semiautomated attenuation-based tube potential selection. Materials & Methods One hundred and seven patients (mean age 57.8 years, body mass index, BMI 24.57 k/m2) were underwent 128 slice dual source lumbar CT using semiautomated tube potential selection algorithm (CARE kV), which optimizes tube-potential as 100 kV and tube-current (range 248 - 416 mAs) based on the attenuation profile of the topogram. CT was reconstructed with regular filtered back projection (FBP) and sinogram affirmed iterative reconstruction (SAFIRE). Objective noise was measured by 1.0 cm2 region of interest at aorta, psoas muscle, and thecal sac on L3-4 level(Fig.1). Subjective image quality was evaluated by scoring of noise (1: little noise, 2: average noise, 3: high noise), visibility of structure (1: excellent visible, 2: marginal blurring, 3: unacceptable poorly visible), and confidence of diagnosis (1: complelely confident, 2: probable confident, 3: limited or low confident) at the margin of disc and thecal sac, nerve, cortical bone, and facet joint on L3-4 level by two musculoskeletal radiologists in agreement(Fig.2). The CT dose index (CTDI vol) was compared with CTDI vol of BMI matched standard 120kV protocol(Fig.3). Fig.3.pptx Results Objective image noise was significantly reduced in SAFIRE group compared with FBP group (p<0.001) in all areas. But subjective image quality by scoring of noise, visibility of structure and confidence of diagnosis was not significantly different in both groups . CTDIvol (mean 12.77 mGy) was significantly decreased when using this CARE kV algorithm compared with the standard 120 kV protocol (mean 21.78 mGy), corresponding to an overall dose reduction of 41%. Conclusion Semiautomated attenuation-based tube potential selection based on the attenuation profile of the topogram using SAFIRE provides a subjective diagnostic image quality of lumbar CT and reduces overall radiation dose by 41 % as compared with a standard protocol with 120 kV. References 1. Winklehner A, Goetti R, Baumueller S, et al. Automated attenuation-based tube potential selection for thoracoabdominal computed tomography angiography. Invest Radiol 2011;46:767-773. 2. Pontana F, Pagniez J, Flohr T, et al. Chest computed tomography using iterative reconstruction vs filtered backprojection (Part 1): evaluation of image noise reduction in 32 patients. Eur Radiol 2011;21:627-635. 3. Prakash P, Kalra MK, Ackman JB, et al. Diffuse lung disease: CT of the chest with adaptive statistical Iterativ reconstruction technique. Radiology 2010; 256:261-269.