Received: 19 March 2009, Revised: 23 November 2009, Accepted: 24 November 2009, Published online in Wiley InterScience: 19 February 2010 Monitoring of the effect of intervertebral disc nucleus pulposus ablation by MRI Galit Saar a , Yoram Zilberman b , Hadassah Shinar a , Keren Keinan-Adamsky a , Gadi Pelled b,c , Dan Gazit b,c and Gil Navon a * In order to investigate intervertebral disc (IVD) degeneration and repair, a quantitative non-invasive tool is needed. Various MRI methods including qCPMG, which yields dipolar echo relaxation time (T DE ), magnetization transfer contrast (MTC), and 1 H and 2 H double quantum filtered (DQF) MRI were used in the present work to monitor changes in rat IVD after ablation of the nucleus pulposus (NP), serving as a model of severe IVD degeneration. In the intact IVD, a clear distinction between the annulus fibrosus (AF) and the NP is obtained on T 2 and T DE weighted images as well as on MTC maps, reflecting the high concentration of ordered collagen fibers in the AF. After ablation of the NP, the distinction between the compartments is lost. T 2 and T DE relaxation times are short throughout the disc and MTC is high. 1 H and 2 H DQF signal, which in intact discs is obtained only for the AF, is now observable throughout the tissue. These results indicate that after ablation, there is an ingression of collagen fibers from the AF into the area that was previously occupied by the NP, as was confirmed by histology. Copyright ß 2010 John Wiley & Sons, Ltd. Keywords: intervertebral disc; MRI; nucleus pulposus; annulus fibrosus; double quantum filtered MRI; MTR maps INTRODUCTION Intervertebral disc (IVD) degeneration is a very common pathology frequently causing severe back pain (1,2). It disrupts the patients’ well being and presents an enormous economical burden. The IVD is composed of three regions: the nucleus pulposus (NP) – a gelatinous core containing proteoglycans (PG), elastin and type-II collagen; the annulus fibrosus (AF) – the outer ring composed of type-I collagen arranged in a series of concentric lamellae, with the collagen fibers lying parallel within each lamella. The fibers are orienting at approximately 608 to the vertical axis, alternating to the left and right of it in adjacent lamellae (3,4), and the cartilaginous end plates that separate the disc from the vertebral bodies. The etiology of IVD degeneration is not clear. However, it is well accepted that aging, mechanical loads, genetic factors and disruption of disc nutrition through the vertebra’s end plates play an important role in the degeneration of the IVD (5). Disc degeneration is characterized by the loss of PG from the NP, which results in reduced water content, reduction of disc volume and disorganization of the AF (3,6,7). IVD degeneration starts at the NP. Several approaches for a biological treatment have been suggested for NP regeneration: intradiscal injections of growth factors such as osteogenic protein (OP)-1 and growth differentiation factor (GDF)-5 were able to induce disc regeneration in rabbit (8,9) and rat (10) models of disc degeneration. Gene therapy approaches have been tried, with adenoviruses delivering the Lim mineralization protein (LMP)-1 (11) or transforming growth factor (TGF)-b1 (12) into the NP, with beneficial results. However, both strategies rely on the presence of sufficient stem cells in the NP that will be able to respond or to produce the growth factor. Mesenchymal stem cells (MSCs) are good candidates to achieve IVD regeneration, based on their availability and multipotential differentiation capability (5,7,13). One of the major goals in tissue regeneration research is the establishment of valid imaging modalities that will provide a solid quantitative analytical tool for the evaluation of the repair processes. For example, we have previously shown that double quantum filtered (DQF) MRI, is an effective tool in monitoring the reorganization of collagen fibers in MSC-based tendon regen- eration (14). The rat tail provides an attractive model for disc degeneration since the discs are accessible to interventions and the injury can be done in a very precise manner with a minimal risk of damage to the surrounding tissues and minimal influence to the normal physiological function. It was recently reported that mammalian discs, including ones from the rat tail, can serve as a reference to human discs in terms of axial mechanics (15). Indeed, several studies have utilized the rat tail disc for the investigation of IVD degeneration (16–19) and regeneration (20). In this study, we simulated severe IVD degeneration by needle puncture and aspiration of the NP content from rat tail discs. (www.interscience.wiley.com) DOI:10.1002/nbm.1493 Research Article * Correspondence to: G. Navon, School of Chemistry, Tel Aviv University, Ramat Aviv, Tel-Aviv 69978, Israel. E-mail: navon@post.tau.ac.il a G. Saar, H. Shinar, K. Keinan-Adamsky, G. Navon School of Chemistry, Tel Aviv University, Tel Aviv, Israel b Y. Zilberman, G. Pelled, D. Gazit Skeletal Biotech Laboratory, Hebrew University - Hadassah Medical Campus, Jerusalem, Israel c G. Pelled, D. Gazit Department of Surgery, Cedars Sinai Medical Center, Los Angeles, CA, USA Contract/grant sponsor: The European PF7 program ENCITE. Abbreviations used: AF, annulus fibrosus; DE, dipolar echo; DQF, double quantum filtered; IVD, intervertebral disc; MSME, multi-slice multi-echo; MT, magnetization transfer; MTC, MT contrast; MTR, MT ratio; NP, nucleus pulpo- sus; PD, Proton Density; PG, proteoglycans. NMR Biomed. 2010; 23: 554–562 Copyright ß 2010 John Wiley & Sons, Ltd. 554