DDIF: A novel contrast for MRI of trabecular bone

INTRODUCTION: Fragility fracture is a serious and costly public health issue [1] and improved methods for screening, diagnosis and treatment monitoring of metabolic bone disease are needed. In particular, there is strong interest in non-invasive, clinically applicable MRI methods to study trabecular bone structure in vivo [2, 3]. We employed a novel method, DDIF (Decay due to Diffusion in the Internal Field), to study (ex vivo) intact animal trabecular bone specimens of varying trabecular structure and porosity, containing marrow and blood, close to in vivo physiological conditions. The DDIF contrast is related to the surface-to-volume ratio of the porous structure of bones. DDIF has been studied for marrow-free trabecular bone [4, 5], but not in intact trabecular specimens containing marrow and surrounded by soft tissue. Bone marrow is comprised of slowly diffusing large lipid molecules (adipocytic, yellow, marrow) and fast diffusing watery haematopoietic red marrow containing iron-carrying hemoglobin. The two components differ in diffusion and relaxation time constants [6]. Water is by far the most diffusible molecule, and the dominant source of DDIF contrast. However, the reduction of water diffusion constant and of T1 in marrow compared to bulk water may reduce the DDIF contrast and make it harder to measure it experimentally. We examined the feasibility of DDIF is in realistic bone specimens, in view of in vivo application to humans.