Original Article Microdose acquisition in adolescent leg length discrepancy using a low-dose biplane imaging system Janni Jensen 1 , Bo R Mussmann 1,2 , John Hjarbæk 1,3 , Zaid Al-Aubaidi 1,* , Niels W Pedersen 4 , Oke Gerke 5,6 and Trine Torfing 1 Abstract Background: Children with leg length discrepancy often undergo repeat imaging. Therefore, every effort to reduce radiation dose is important. Using low dose preview images and noise reduction software rather than diagnostic images for length measurements might contribute to reducing dose. Purpose: To compare leg length measurements performed on diagnostic images and low dose preview images both acquired using a low-dose bi-planar imaging system. Material and Methods: Preview and diagnostic images from 22 patients were retrospectively collected (14 girls, 8 boys; mean age, 12.8 years; age range, 10–15 years). All images were anonymized and measured independently by two muscu- loskeletal radiologists. Three sets of measurements were performed on all images; the mechanical axis lines of the femur and the tibia as well as the anatomical line of the entire extremity. Statistical significance was tested with a paired t-test. Results: No statistically significant difference was found between measurements performed on the preview and on the diagnostic image. The mean tibial length difference between the observers was 0.06 cm (95% confidence interval [CI], 0.12 to 0.01) and 0.08 cm (95% CI, 0.21 to 0.05), respectively; 0.10 cm (95% CI, 0.02–0.17) and 0.06 cm (95% CI, 0.02 to 0.14) for the femoral measurements and 0.12 cm (95% CI, 0.05 to 0.26) and 0.08 cm (95% CI, 0.02 to 0.19) for total leg length discrepancy. ICCs were >0.99 indicating excellent inter- and intra-rater reliability. Conclusion: The data strongly imply that leg length measurements performed on preview images from a low-dose bi-planar imaging system are comparable to measurements performed on diagnostic images. Keywords Leg length inequality, pediatrics, radiology, observer variation Date received: 1 June 2016; accepted: 4 November 2016 Introduction Leg length discrepancy (LLD) is a common occurrence (1,2) and approximately one-third of all adolescents in Denmark have a LLD of less than 1 cm and approxi- mately 5–10% more than 1 cm (3). Many of these ado- lescents undergo serial radiologic assessment. LLD may be congenital, post-traumatic, or caused by disease (1). As LLD may be a predictor for prema- ture osteoarthritis (4), the importance of an early diag- nosis is imperative. The accuracy of measuring tools when assessing LLD was investigated in a review by Sabharwal and 1 Department of Radiology, Odense University Hospital, Odense, Denmark 2 Institute of Clinical Research, University of Southern Denmark, Odense, Denmark 3 Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark 4 Department of Orthopedics, Odense University Hospital, Odense, Denmark 5 Department of Nuclear Medicine, Odense University Hospital, Odense, Denmark 6 Centre of Health Economics Research, University of Southern Denmark, Odense, Denmark *Current affiliation: Consultant Pediatric Orthopedic Surgeon Corresponding author: Janni Jensen, OUH Department of Radiology, Odense University Hospital, Sdr. Boulevard 29, 5000 Odense, C Denmark. Email: janni.jensen@rsyd.dk Acta Radiologica 0(0) 1–7 ! The Foundation Acta Radiologica 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0284185116682381 acr.sagepub.com