Practical T2 Mapping of Cartilage in a Rabbit Model of Hemophilic Arthropathy

Introduction: Hemophilia is an inherited bleeding disorder caused by deficiencies of clotting factors VIII and IX, respectively. Cartilage degeneration contributes to most of the disease morbidity. Early treatment of hemophilia has been shown to reduce long-term joint morbidity [1]. Novel functional MR imaging techniques hold the potential for being ideal diagnostic and prognostic tools for assessment of early cartilaginous changes in hemophilic arthropathy, prior to the development of cartilaginous abnormalities. Specifically, T2 mapping is known to be sensitive to alterations in collagen structure that result from ingrowth of reparative fibrocartilage and/or fibrous tissue [2]. The mapping could therefore be used as a proxy of collagen organization in the articular cartilage of hemophilic arthritis. Unfortunately, conventional T2 mapping techniques using multiecho spin-echo pulse sequences can be very time consuming and non-feasible in clinical practice. To address this problem, we employed a new short-TR spin echo T2 mapping technique. In this technique by keeping TR-TE constant, undesired T1 weighting is eliminated from the T2 weighting. This maintains the accuracy of the T2 measurement [3]. In addition to cartilage alterations, another important characteristic of hemophilia is the presence of active macrophages in the joint synovium. To detect this activity, the use of ultrasmall paramagnetic iron oxide contrast-enhanced MRI (USPIO CE MRI) has been proposed. However, the presence of USPIO may alter the T2 maps. The objectives of this study were therefore: 1) to validate the use of a new short-TR T2 map technique (constant TR-TE values) for assessment of early cartilaginous changes over time in knees of a rabbit model of hemophilic arthritis, and 2) to determine whether the use of USPIO CE MRI prior to acquisition of T2 maps alter the T2 values.