A Nondestructive Method to Distinguish the Internal Constituent Architecture of the Intervertebral Discs Using 9.4 Tesla Magnetic Resonance Imaging.

The intervertebral disc (IVD) plays a crucial role in the biomechanics of the spine, allowing articulation between the vertebrae. Even minor changes in the IVD, whether biological or structural, have the potential to cascade into greater irregularities and significantly affect the biomechanical functions of the spine. Consequently, it is one of the major sites for back pain, which approximately 70% of the population will experience at some point in their lives.1 Detailed information on the substructure of the IVD is usually obtained from histological slices.2,3 This technique has limitations due to being 2-dimensional (2D) and destructive. 2D micrographs cannot provide accurate height-width-depth as well as spatial orientation details due to sectioning plane alignment and orientation. Hence, there is an element of “educated guesswork” involved in understanding such information, which may affect the reliability and consistency of the interpretations. Lack of coherent information along the 3rd direction is particularly disadvantageous when characterizing highly 3-dimensional (3D) structures such as IVDs. For instance, the lamellae in the annulus fibrosus (AF) are curved in their macro state and there exists an alternating fiber pattern in the adjoining lamellae. This fiber orientation is nearly impossible to visualize on a 2D histological section. A 3D method could provide clearer and further information, for example on the morphology of the lamellae within the AF, or the location of annular tears, and could have diagnostic applications if it were nondestructive. Such a technique could also be used preclinically during in vitro testing in which different interventions are compared, or for generating accurate computational models of the IVD. Ultrahigh-field strength magnetic resonance imaging (MRI) systems (4–9.4 T) are an emerging technology for clinical applications. Their capabilities, such as improved signal-to-noise ratio (SNR) and higher spatial resolution, have potential for improved imaging of tissues. The high-field technology has been shown to produce favorable results for imaging of brain tissue, but cardiac and abdominal applications have posed a greater challenge.4–8 As yet, the use of ultrahigh-field MRI for spinal applications has been relatively limited. Therefore there is a need to examine this imaging methodology for spinal tissue structures, to assess the feasibility of obtaining relevant structural and biological information, as well as identifying suitable imaging protocols. Visualization of the IVD would benefit from higher resolution due to the multiple structurally distinctive constituents. The hydrated nucleus pulposus (NP) provides a high signal. The AF consists of multiple lamellae and the fiber orientation is completely different in these alternating layers, exhibiting a criss-cross pattern. Consequently, the signal intensity will change depending on the fiber direction. The IVD endplate (EP) also gives rise to different signal intensities due to its cartilaginous and bony components. The aim of this study was to investigate the potential of ultrahigh-field strength MRI to obtain higher quality 3D volumetric MRI data sets of the IVD in order to better distinguish structural details. 2 potentially suitable protocols were investigated and comparisons were made with histological imaging of the same IVD.