Bone Matrix Imaged In Vivo by Water- and Fat-Suppressed Proton Projection MRI (WASPI) of Animal and Human Subjects

Purpose: To demonstrate water- and fat-suppressed proton projection MRI (WASPI) in a clinical scanner to visualize the solid bone matrix in animal and human subjects. Materials and Methods: Pig bone specimens and polymer pellets were used to optimize the WASPI method in terms of soft-tissue suppression, image resolution, signal-to-noise ratio, and scan time on a 3T MRI scanner The ankles of healthy 2-3-month-old live Yorkshire pigs were scanned with the optimized method. The method was also applied to the wrists of six healthy adult human volunteers to demonstrate the feasibility of the WASPI method in human subjects. A transmit/receive coil built with proton-free materials was utilized to produce a strong B-1 field. A fast transmit/receive switch was developed to reduce the long receiver dead time that would otherwise obscure the signals. Results: Clear 3D WASPI images of pig ankles and human wrists, showing only the solid bone matrix and other tissues with high solid content (eg, tendons), with a spatial resolution of 2.0 mm in all three dimensions were obtained in as briefly as 12 minutes. Conclusion: WASPI of the solid matrix of bone in humans and animals in vivo is feasible.