Validation of noninvasive quantification of bone marrow fat volume with microCT in aging rats Oddom Demontiero, Wei Li, Emma Thembani, Gustavo Duque ⁎ Ageing Bone Research Program, Sydney Medical School-Nepean, The University of Sydney, PO Box 63, Penrith, NSW, 2751, Australia abstract article info Article history: Received 8 December 2010 Received in revised form 5 January 2011 Accepted 12 January 2011 Available online 20 January 2011 Section Editor: Dr. Christiaan Leeuwenburgh Keywords: Marrow fat MicroCT Aging Osteoporosis Reliability Marrow fat infiltration is one of the hallmarks of age-related bone loss. This fat infiltration has been quantified by invasive and noninvasive methods. However, the validity of the noninvasive methods has not been correlated with a gold standard. In this study we aim to validate the usefulness of marrow fat quantification by correlating microCT (μCT) images with histology analysis. Fat volume (FV) and bone volume (BV) of distal femora of young (4 months) and old (27 months) Louvain/c (LOU) rats (n = 22) were quantified by histology and compared with μCT images analyzed by an image analysis software (SliceOMatic). We found that for SliceOMatic/μCT the intra-rater reliability for duplicate measurements was 0.94 (p b 0.001) and the inter-rater reliability for FV/BV ratio in young and old rats was 98% and 99% respectively. Both methods showed a significant increase (~2 fold) in the FV/BV ratio in the old rats as compared with their young counterparts (p b 0.001). A significantly higher correlation (r2 = 0.85) in the old rats was found between our noninvasive method and histology. Furthermore, our noninvasive method showed good agreement with histology. In conclusion, noninvasive quantification of FV/BV ratio using an image analysis software is as reliable as histology for identifying age related marrow fat changes with high inter and intra-rater reliability. These findings provide a new noninvasive method for quantifying marrow fat, which is useful and can be tested not only in animals but also in human studies. © 2011 Elsevier Inc. All rights reserved. 1. Introduction Osteoporosis and its most devastating sequelae, fractures, is a rising global health, economic and social burden. Thus the early detection and treatment of individuals at risk of fractures is a priority before the fragility fracture cascade sets in. Bone Mineral Density (BMD) and Dual Energy X-ray Absorptiometry (DXA) have long been the recommended fracture surrogate and non-invasive tool respec- tively that estimate fracture risk. However, there is evidence that BMD alone, as defined by the World Health Organization (WHO), does not reliably predict fractures (Marshall et al., 1996), does not identify the majority who are at moderate risk (Pasco et al., 2006), and is limited for monitoring the effect of drug therapy (Delmas and Seeman, 2004). This has led to the development of clinical tools for predicting fracture risks such as the WHO Fracture Risk Assessment Tool (FRAX) (Kanis et al., 2005) and the Garvan fracture risk calculator (Nguyen et al., 2007). However, the validity of a purely clinical tool to predict fractures is still controversial (Leslie and Hans, 2009) and its accuracy may be limited by differences between cohorts (Sandhu et al., 2010). In recent years it is increasingly recognized that trabecular microarchitecture confers bone its strength (Seeman and Delmas, 2006) and hence may explain the discrepancy between BMD and fracture risk (Delmas and Seeman, 2004). Several non-invasive methods [e.g. magnetic resonance imaging (MRI), and computed tomography (CT) scan] have been used to assess the microarchitec- ture of the different components of bone (Brandi, 2009). However despite their usefulness, there are other components of bone microarchitecture that have not been fully assessed. One of them is the presence of increasing levels of marrow fat (Burkhardt et al., 1987). In contrast to menopausal bone loss, age-related bone loss is not only associated with high levels of bone resorption, but also with increased adipogenesis (Rozman et al., 1989) and reduced osteoblas- togenesis (Zhou et al., 2008), which affects bone mass. Biopsy studies have shown significant increase in marrow fat with age (Tanaka and Inoue, 1976), as well as an inverse relationship between fat volume (FV) and bone volume that was independent of sex and correlated with the changes seen in people with osteoporosis (Justesen et al., 2001). Currently there are few non-invasive methods that have quanti- fied marrow fat in humans. Among them, magnetic resonance imaging (MRI) has been the main modality showing increased marrow fat in older subjects (Schellinger et al., 2001) and in osteoporotic individuals (Yeung et al., 2005). However the Experimental Gerontology 46 (2011) 435–440 ⁎ Corresponding author at: Ageing Bone Research Program, Sydney Medical School- Nepean, The University of Sydney, PO Box 63 Penrith NSW 2751, Australia. Tel.: +61 2 4734 4278; fax: +61 2 4734 2614. E-mail address: gduque@med.usyd.edu.au (G. Duque). 0531-5565/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.exger.2011.01.001 Contents lists available at ScienceDirect Experimental Gerontology journal homepage: www.elsevier.com/locate/expgero