A Feasibility Study on Quantifying Cortical Bone Free Water Longitudinal Relaxation Time Employing Short-TE MRI Technique at 3T

Abstract

Introduction: Aging is an important factor affecting bone quality, culminating in cortical bone thinning, increasing the number and size of the pores. As a consequence of these alterations, the free water molecules mobility augments and their longitudinal relaxation time (T1) increases. An MRI with its sensitivity to capture signal from hydrogen proton would be the best candidate to assess the bone quality during aging. By employing an appropriate pulse sequence with a short TE which is capable of acquiring a signal from hydrogen molecules of cortical bone pores before decaying, valuable information about the bone structure was extracted. Materials and Methods: Five healthy volunteers (3f/2m) were undergone a short TE MR imaging with dual-TR technique at 3T in order to calculate the cortical bone free water T1 . For T1 calculation, the mean signal intensity of the whole cortical bone in long-TR image was divided by the short-TR image to acquire an ‘r’ ratio. This ratio value was used in an equation (described further) to calculate T1 value. The process of cortical bone segmentation was performed manually due to the intense care that it needed for the discrimination of soft tissue from the bone tissue. Results: The longitudinal relaxation time of human cortical bone free water was quantified using two Gradient Echo STE-MR images differing in TR values and the average of the obtained T1 values was reported to be 589.32 ± 231.52 ms which was in a good agreement with previously reported values in the literature. Conclusion: The result suggests a successful application of STE-MRI for an accurate quantification of cortical bone T1 -values, with the advantage of widespread clinical availability and a cost-effective procedure.

Keywords

• Cortical Bone
• Short Time of Echo (TE)
• Bone water
• Longitudinal Relaxation Time