DTI of the Brain and Cervical Spine: Evaluation in Normal Subjects and Patients With Cervical Spondylotic Myelopathy

More than half of the middle-aged population has radiologic evidence of cervical spondylosis
and a subset of this population develops cervical spondylotic myelopathy (CSM), a condition
in which the spinal cord is impaired, either by direct mechanical compression or indirectly
by arterial deprivation and/or venous stasis. Although many operations are performed for
conditions related to CSM, no consensus exists regarding the timing of the surgical
intervention or how to select among the available surgical options for a given patient. Many
factors have been implicated in the propensity for CSM to develop including advanced age,
disability at presentation, cord diameter, cord area, altered cord signal on MRI (T2- and
T1- weighted images), increased cervical spinal mobility and a congenitally narrow spinal
canal. The same factors may also determine the response to surgery, either positively
(increased cervical mobility) or negatively (advanced age, congenitally narrow spinal
canal). The potential complications of surgical procedures are noteworthy. Although
incapacitating adverse effects are uncommon, their occurrence in a disease process with a
potentially benign course is of undoubted gravity. Finally, it should be noted that the
radiologic criteria of cervical root or cord compression on MRI are subjective and it is
uncertain that they correlate with the clinical symptoms.

Diffusion tensor imaging (DTI) is sensitive to the motion of water and is considered to be a
marker for axonal integrity in the brain. There has been much interest in applying the
technique to the spine and in particular to the evaluation of patients with CSM. In the
brain DTI is performed using a single shot echo planar imaging (SS-EPI) sequence which
acquires all of the data for a single slice following the application of a single excitation
pulse and diffusion gradients. While very efficient in terms of data collections there are
several problems with SS-EPI, notably that 1) It is best suited to the acquisition of
relatively small imaging matrices, resulting in either low spatial resolution or the use of
additional techniques to reduce the field of view (FOV). Increasing the number of echoes
acquired to increase the resolution does not produce an increase in the acquired resolution
since the decay of the signal during the longer echo train results in increased blurring of
the image. 2) The images are distorted by susceptibility gradients in areas close to the
interfaces between tissue and bone or osseous structures. These factors have made applying
DTI to clinical studies of the spine problematic. Specifically:-

1. The small size of the spinal cord means that high spatial resolution is required.

2. The susceptibility effects from the surrounding osseous structure result in image
distortion.

3. The motion of the cord during the cardiac cycle leads to artifacts.

Readout segmented EPI (RESOLVE or RS-EPI) sequence has been shown to be capable of obtaining
images with higher spatial resolution and reduced distortion in the brain. We have recently
demonstrated that the RESOLVE sequence can also be used to obtain high quality DTI images of
the cervical spine of volunteers (see figure 1) and can provide clinically useful
information in subjects with metastases in the spine. The RESOLVE sequence breaks the data
collection into several segments, resulting in reduced distortion and the potential to
obtain images with higher resolution, but at the cost of either increased scan time or a
reduced number of directions for the diffusion gradients (i.e. reduced signal to noise ratio
(SNR)). The RESOLVE sequence also incorporates real-time assessment of the data, enabling
data corrupted by motion to be rejected and then reacquired. We now wish to optimize, and
assess the clinical utility of, the RESOLVE sequence in patients with CSM by applying it to
a group of CSM patients and a group of aged matched control subjects. The raw diffusion
images are post-processed to yield parametric images which characterize the diffusivity
(mean, longitudinal and radial) and anisotropy (directional dependence) of the diffusion.
The anisotropy of the diffusion data is typically quantified using the fractional anisotropy
(FA) index, however, we have recently shown that two other quantities, the mode and
ellipsoidal area ratio (EAR) of the diffusion tensor, provide useful supplementary
information and we propose to use all three parameters when analyzing the anisotropy of the
diffusion data from this study.

Using the RESOLVE sequence address these first two of the "bullet" points listed above and
we found that in some subjects high quality DTI images of the spine can be obtained without
the use of cardiac gating, however, for a robust clinical sequence we, and other groups,
have found cardiac gating to be essential. Another issue to consider for DTI studies of the
spine is the orientation of the scan. Sagittal images provide coverage of the whole spine
with relatively few slices, which is particularly beneficial when cardiac gating is
employed. Axial slices have the advantage that the changes in the configuration of the spine
in the caudal-cranial direction are relatively slow, meaning that thicker slices can be used
without a significant loss of information. However, a relatively large number of slices are
still required to cover the entire C-spine resulting in a lengthy measurement time when
cardiac gating is used.

Objectives The investigators wish to try and answer the following questions for the
C-spine:-

1. What are the diffusion characteristic of the normal C-spine (spatial variation and age
dependence)?

2. How do the RESOLVE and SS-EPI images of the spine compare in terms of image quality?

3. What is the effect of changing the number of segments for the RESOLVE sequence?

4. When comparing SS-EPI and RESOLVE are there statistically significant differences in
the derived values of anisotropy or diffusivity?

5. Are the diffusion characteristics of the C-spine of subjects with CSM significantly
different from those of aged matched controls?

6. Can DTI of the spine be used to derive diagnostic information, either in terms of
prognostic information for individual CSM patients or the identification of sub-groups
of CSM patients? For the brain the question we would be addressing are:-

1) When comparing SS-EPI and RESOLVE are there statistically significant differences in the
derived values of anisotropy or diffusivity? 2) Is there a statistically significant
difference in the volume of the fiber tracts derived using the two sequences or between the
two groups? 3) Is the diffusion data from the brains of patients with CSM significantly
different from that of the controls?

Inclusion Criteria:

- 20 patients will be selected by an experienced team of orthopedic specialist from the
Emory Orthopaedics & Spine Center and will include patients suffering signs and
symptoms of cervical myelopathy and with evidence of radiographic cervical cord
compression with or without abnormal spinal cord signal intensity secondary to
spondylosis.

- 20 controls : Aged matched to the patient group. No history of CSM.

Exclusion Criteria:

- Any history of significant trauma implicating the brain or cervical spine, including
prior motor vehicle collision and history of prior brain, neck or cervical spine
surgery.

- Any history of neurological disease

- Dental braces or similar orthodontic devices.

- Claustrophobia