ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

3. METHODS
3.1 Specimen Preparation
The T13-L3 segment was dissected from the spine of a skeletally mature (aged 6 years)
ovine spine. The central disc of the specimen, L1L2, was studied throughout. All
muscle tissue and most ligament tissue was removed from the specimens whilst
avoiding damage to the discs. The transverse processes were removed, as were the
posterior elements and facet joints, by sawing through the centre of the spinal canal.
Both ends of the specimens were potted in PMMA cement to facilitate mounting in a
bespoke loading rig suitable for use in the MRI scanner. A marker was attached to the
specimen that contained a fluid (Ortho-Spots, Beekley Medical, USA) and a glass
component. This was designed to show on both the µCT and MRI scans to aid image
registration during post-processing. Throughout the dissection and potting process, the
hydration of the discs was maintained by wrapping the specimen in damp paper-tissue.
The specimen was sealed in two layers of polythene bags and stored in the freezer at -
20°C until use. Before scanning, the specimen was thawed at 2°C for 24 hours.
3.2 Imaging
To capture the vertebral geometry, a µCT scan was taken of each specimen in its
unloaded state (XtremeCT scanner, Scanco Medical, Switzerland), at a voxel size of
123µm and integration time of 300ms.
All MRI scans were taken using a 3T Siemens Verio. Two surface coils were placed
either side of the central disc (L1L2). A range of sequences were tried in the
development of the MR method with the aim of tuning the sequences to clearly show:
a) The geometry of the NP.
b) The geometry of the AF including individual lamellae.
The settings that were developed and used throughout the study are shown in Table 1.
NP scan AF scan
In plane resolution 0.31 mm 0.2mm
slice thickness 1.5mm 0.2mm
Scan type turbo spin echo flash
FoV 160 x 160 60 x 60
matrix size 512 x 512 256 x 256
TR 3200 50
TE 36 5
Flip angle n/a 30˚
number of averages 1 1
scan time approx 6 min approx 55 min
number of slices 20 300
Table 1 – Final settings used for NP and AF MRI scans.
During MRI scanning the specimens were mounted in the compression rig. The
specimen was imaged prior-to-loading and whilst under axial compression.
Compression was applied via a hand-tightened screw thread mechanism until the