Advanced Imaging of the Spine - the MSK Perspective

Back and neck pain are among the most common reasons to seek medical advice, causing health care costs exceeding $ 80 billion annually in the US alone. It is established knowledge that short term back pain can be managed conservatively when no red flag symptoms are present, and clear cut guidelines for the utilization of cross-sectional imaging in the diagnostic work-up do exist. The clinical reality, however, shows ever-increasing numbers in CT and MRI exams used in the context of back pain (1). This is despite the fact that multiple studies have shown a poor correlation between imaging findings and patients’ symptoms as well as that there are high rates of false positive imaging findings (2). MRI with its superior soft tissue contrast is the preferred cross sectional modality in imaging for back pain, but in order to better serve patients different tools are needed to complement existing imaging approaches and improve the diagnostic information gain. In this talk, some of the potential problem solvers for spinal imaging will be reviewed, including their advantages and disadvantages.Kinematic MRI (kMRI) has been shown to help in individual cases of back pain in the setting of “normal” conventional supine MRI (3). Drawbacks of kMRI include the scarcity of vertically open MRI scanners and lack of existing standards, but kMRI is to some extent even possible in closed high field MRI scanners using axial load devices (4). In high field strength scanners, 3D isotropic resolution fast spin echo sequences available from virtually every vendor have reached a level that allows for their use in the clinical routine setting (5). They allow for creating multiplanar reformations which can help, e.g., in the setting of foraminal stenoses. The combination with Dixon-based fat/water separation methods can deliver water-weighted, in phase, out of phase, and fat-weighted images with one single sequence acquisition.Adding diffusion-weighted sequences for optimal nerve visualization to complement standard spine MRI protocols can be valuable and help identify pain generators (6). Diffusion-weighted sequences have also been shown to be valuable in the evaluation of infectious processes and tumors of the spine (7).In the post-surgical setting, novel sequences that allow the imaging around metal implants have been proven very helpful by reducing metal-induced susceptibility and spatial distortion artifacts (6).Entirely new opportunities arise with the arrival of PET/MRI, which combines the excellent spatial resolution, and soft tissue contrast of MRI with the molecular information of PET. While not widely available yet and still reserved to the setting of clinical studies, this new diagnostic tool offers a more “holistic” approach which may be very advantageous in the diagnostic work-up of back pain. Clinical pilot studies demonstrated some of potential of [18F] FDG PET/MRI in select cases of chronic cases of back pain and sciatica (8). In addition, novel tracers that are more specific for pain applications are under development, such as [18F]FTC-146 (9).

Acknowledgements

Thanks to my colleagues Drs. Kate Stevens, Dr. Nancy Fischbein, Dr. Sandip Biswal and Dr. Daehyun Yoon for contributing cases.