Quantitative ultrashort echo time (UTE) MRI of human cortical bone: Correlation with porosity and biomechanical properties

Abstract

In this study we describe the use of ultrashort echo time (UTE) magnetic resonance imaging (MRI) to evaluate short and long T2* components as well as the water content of cortical bone. Fourteen human cadaveric distal femur and proximal tibia were sectioned to produce 44 rectangular slabs of cortical bone for quantitative UTE MR imaging, micro computed tomography (μCT), and biomechanical testing. A two-dimensional (2D) UTE pulse sequence with a minimal nominal TE of 8 μs was used together with bi-component analysis to quantify the bound and free water in cortical bone using a clinical 3T scanner. Total water concentration was measured using a 3D UTE sequence together with a reference water phantom. UTE MR measures of water content (total, free and bound), T2* (short and long), and short and long T2* fractions were compared to porosity assessed with μCT, as well as elastic (modulus, yield stress and strain) and failure (ultimate stress, failure strain and energy) properties, using Pearson correlation. Porosity significantly correlated positively with total (R2=0.23; P<0.01) and free (R2=0.31; P<0.001) water content as well as long T2* fraction (R2=0.25; P<0.001), and negatively with short T2* fraction and short T2* (R2=0.24; P<0.01). Failure strain significantly correlated positively with short T2* (R2=0.29; P<0.001), ultimate stress significantly correlated negatively with total (R2=0.25; P<0.001) and bound (R2=0.22; P<0.01) water content, and failure energy significantly correlated positively with both short (R2=0.30; P<0.001) and long (R2=0.17; P<0.01) T2* values. These results suggest that UTE MR measures are sensitive to the structure and failure properties of human cortical bone, and may provide a novel way of evaluating cortical bone quality.

Assessment of different fitting methods for in-vivo bi-component T2* analysis of human patellar tendon in magnetic resonance imaging

“…However, changes in T2 and T2* are nonspecific and can be caused by multiple factors including hydration, macromolecular content, and tissue anisotropy with comparable changes occurring in disparate settings [5][6][7][8][9] . Bi-component T2 and T2* mapping techniques have been used to improve the specificity of T2 analysis by assessing the individual water components of musculoskeletal tissues [10][11][12][13][14][15][16][17][18][19][20][21][22] . Bi-component T2 and T2* mapping methods have measured two distinct T2 components in cartilage assumed to represent short relaxing water bound to the macromolecular matrix and long relaxing bulk water [12][13][14]21,22 .…”

“…Bi-component T2 and T2* mapping methods have measured two distinct T2 components in cartilage assumed to represent short relaxing water bound to the macromolecular matrix and long relaxing bulk water [12][13][14]21,22 . Bi-component T2* mapping methods have been used in cortical bone to differentiate between water bound to the organic matrix and free water in the Haversian systems [15][16][17] , Bi-component T2 and T2* mapping methods have also been used in the meniscus to differentiate between macromolecular bound water and bulk water [18][19][20] . In tendon, recent studies using bi-component T2* mapping techniques have measured two distinct T2 components representing short relaxing water bound to the highly organized collagen fibers and long relax-…”

Acute and Stress-related Injuries of Bone and Cartilage: Pertinent Anatomy, Basic Biomechanics, and Imaging Perspective

“…Cortical bone fractures can be caused by either the application of a single highamplitude force (traumatic fracture), a subthreshold force applied to bone weakened from a pathologic process such as a neoplasm (pathologic fracture), or accumulative microdamage related to capacity of the cortex to tolerate stress (102). Cortical bone is stronger and has a higher capacity for load absorption, particularly in compression, than cancellous bone but it exhibits a higher modulus of elasticity, indicating it is stiffer and less flexible than cancellous bone, which can deform three to four times to a greater extent (38).…”

Magnetic resonance ultrashort echo time spin-echo imaging of the deepest layers of articular cartilage

“…By using half-sinc radiofrequency (RF) pulses, radial mapping of k-space, rapid transmit/receive switching, and variable rate selective excitation, nominal TEs as short as 8 μs have been achieved with ultrashort TE (UTE) imaging [9,10]. Therefore, the UTE pulse sequences make it possible to directly image tissues with very short T2 and their adjacent tissues [11]. Although short T2 tissues are detectable with UTE sequences, positive visualization of deep layers of cartilage is limited by the presence of high signals from long T2 water and fat.…”