Advancing imaging technologies for patients with spinal pain: with a focus on whiplash injury

Abstract

Background context: Radiological observations of soft-tissue changes that may relate to clinical symptoms in patients with traumatic and non-traumatic spinal disorders are highly controversial. Studies are often of poor quality and findings are inconsistent. A plethora of evidence suggests some pathoanatomical findings from traditional imaging applications are common in asymptomatic participants across the life span, which further questions the diagnostic, prognostic, and theranostic value of traditional imaging. Although we do not dispute the limited evidence for the clinical importance of most imaging findings, we contend that the disparate findings across studies may in part be due to limitations in the approaches used in assessment and analysis of imaging findings.

Purpose: This clinical commentary aimed to (1) briefly detail available imaging guidelines, (2) detail research-based evidence around the clinical use of findings from advanced, but available, imaging applications (eg, fat and water magnetic resonance imaging and magnetization transfer imaging), and (3) introduce how evolving imaging technologies may improve our mechanistic understanding of pain and disability, leading to improved treatments and outcomes.

Study design/setting: A non-systematic review of the literature is carried out.

Methods: A narrative summary (including studies from the authors' own work in whiplash injuries) of the available literature is provided.

Results: An emerging body of evidence suggests that the combination of existing imaging sequences or the use of developing imaging technologies in tandem with a good clinical assessment of modifiable risk factors may provide important diagnostic information toward the exploration and development of more informed and effective treatment options for some patients with traumatic neck pain.

Conclusions: Advancing imaging technologies may help to explain the seemingly disconnected spectrum of biopsychosocial signs and symptoms of traumatic neck pain.

Keywords: Biopsychosocial; Imaging; Low back pain; MRI; Neck pain; Whiplash.

Fig. 1.

Basic physics underlying magnetization transfer imaging. Typical magnetic resonance imaging (MRI) draws its signal from protons associated with free water. There is also a pool of protons bound to macromolecules—such as the myelin surrounding an axon. If one compares the resonance spectra of these two pools, free water has a sharp resonance peak and long T2, whereas macromolecular protons have a broad spectrum and an ultra-short T2 (~100 μs), making imaging of this group difficult. By use of an off-resonance radiofrequency pulse before imaging, one can selectively saturate the macromolecular pool of protons. Although the relaxation will not be visible, magnetization of the bound pool will partially exchange with the surrounding free water, degrading the local free water signal in proximity to macromolecules, as shown by the dashed line. This exchange between pools of magnetization allows for the indirect study of the bound protons, and thus the density and stability of macromolecular content of a given imaging voxel. This technique is often reported as the magnetization transfer ratio or MTR, the signal change in free water caused by magnetization exchange.

Fig. 2.

(A) A native sagittal T2-weighted image of a participant with spinal cord injury. (B) Native axial T2-weighted images through the spinal cord lesion. (C) The lesion filled image was then straightened along the spinal cord and registered to the MNI-Poly-AMU spinal cord template. The mean and standard deviation (SD) of the voxel intensities were then calculated within a non-lesioned 1-cm axial cross section of the spinal cord immediately superior to the lesion. The maximum intensity projection image was then thresholded at two SDs above the mean to define the lesion. (D) The extent of spinal cord damage was then quantified in the axial plane as the ratio of the spinal cord that was lesioned across the total cord and within the right and left lateral corticospinal tracts (LCST) and gracile fasciculi (GF). One representative participant is shown. The right and left LCST and GF are shown in green and light blue, respectively.