by the number of regions measured (four in this study). The
MTRh metric ranges from 0 (homogenous) to 1 (anisotropic).
MTR and MTRh mean values and standard deviations were
calculated for each group and the primary outcomes for this
pilot study were purely descriptive.
Table 1 details demographic data of all participants. MTRh
across the entire cord appeared similar between groups.
However, differences were observed between the WAD group
and the controls as well as the WAD and recovered group.
Additionally, MTRh differences between the recovered and
healthy control subjects appeared similar. A higher anisotropy
in MTRh values across the cord at C5 were present in the WAD
group with an average ± standard deviation MTRh of 0.23 ±
0.07, versus 0.13 ± 0.03 for the recovered group and 0.10 ± 0.05
for the control group (Table 1).
This preliminary investigation details the potential use of MT
imaging toward identifying regional changes in cord anatomy
that may be related to a whiplash event. The MT characteristics of the whole cord, which lacks specificity for pathway
changes, were similar across all three groups likely because
of local changes in MT signal being masked by averaging the
volume across the entire cord.
Cohen-Adad and colleagues noted that when comparing
MTR values across the different aspects of the cord, tract-
specific information could be derived to predict sensory and
motor disability in patients with traumatic SCI. 26 Such findings
from the spinal cord are consistent with other brain-based
investigations involving populations with known neurologic
pathologies (eg, multiple sclerosis27 or traumatic brain in-
jury28). While region-specific data from the cord can be col-
lected with relative ease (four minutes total scan time), MTR
comparison between subjects is not straight-forward. When
conducting a simple MT experiment, multiple confounding
factors, such as subject size, transmitter load, receiver coil load
and MT pulse parameters, modulate the M T effect, hindering
direct subject-to-subject comparison of MTR.
Here we proposed a scalar insensitive, subject-normalized
metric, the MTRh, as a potential solution to identify within
cord changes that may be related to fiber damage, the severity
or significance of which cannot be determined at this stage.
However, the MTRh metric demonstrated changes in a small
sample of subjects with chronic WAD compared to those who
self-reported recovery suggesting mechanical consequences
of the injury could affect a small number of fibers in specific
regional pathways. This MTRh-based method had high resolution, high signal-to-noise ratio, and excellent myelin contrast
allowing investigation at a fine scale (eg, a voxel size of 0.5
x 0.5 x 4 mm). Future prospective studies investigating the
registered data on a voxel by voxel basis are warranted and
Edema and hemorrhage, a characteristic sign of SCI in the
acute state, are typically visible via signal abnormalities on T2
weighted MRI. 32 However, such findings from conventional
imaging applications are typically not present in cases of acute
whiplash suggesting the possibility of a more subtle, yet nonetheless significant, injury involving the spinal cord and potentially specific ascending/descending pathways. Accordingly,
Figure 3 details how a high-resolution M T sequence could be
a means of further characterizing WAD by identifying regions
of cord involvement33 in tandem with known risk factors of
recovery. 22, 23, 34-36 Before stronger conclusions can be drawn
about the utility of M TRh as a diagnostic marker, larger scaled
prospective studies involving participants with varying levels
of pain-related disability following whiplash are required
and are now underway. Positive findings would then provide
foundation for more informed treatment protocols, such as
specific exercise, and pharmacological and psychological pain
management strategies consistent with current best practice
for patients with motor and/or sensory incomplete SCI.
Current Concepts | Section Feature Article
Table 1. Demographics (Mean [SD]) for Control,
Recovered and Chronic WAD Groups
Descriptive Control Recovered WAD
Age (yr) 41. 8 ( 11. 1) 27.0 ( 3. 6) 37. 4 ( 9.0)
Body mass index
25.0 ( 4. 9) 26. 1 ( 3. 8) 30.0 ( 4. 2)
NDI (%) 0 (0) 1. 2 ( 1. 2) 44. 4 ( 10. 9)
35.0 ( 4. 2) 34. 9 ( 7. 5) 34. 1 ( 8. 1)
WM MTRh 0.10 (0.05) 0.13 (0.03) 0.23 (0.07)
Figure 2: Standard images are shown above along with magnetization
transfer contrast images and magnetization transfer ratio maps for
control, recovered, and subjects with chronic whiplash-associated
disorders. The observed magnetization transfer images were found
to be similar between groups.