MRI of the Spine¶
Definition¶
Magnetic resonance imaging (MRI) of the spine is the gold standard for evaluating soft tissue structures including the spinal cord, intervertebral discs, ligaments, and nerve roots. It uses strong magnetic fields and radiofrequency pulses to produce high-resolution, multiplanar images without ionizing radiation.
Technique¶
Basic Physics¶
- MRI exploits the magnetic properties of hydrogen protons in body tissues
- A strong static magnetic field aligns hydrogen protons; radiofrequency pulses then perturb them
- As protons return to equilibrium, they emit signals that are detected and converted into images
- Different tissues (fat, water, muscle, bone marrow) produce different signal intensities based on their proton density and relaxation properties (T1 and T2)
Standard Spine MRI Protocol¶
| Sequence | Plane | Key Utility |
|---|---|---|
| Sagittal T1 | Sagittal | Anatomy, marrow evaluation, foraminal fat |
| Sagittal T2 | Sagittal | CSF ("myelographic" effect), disc hydration, cord signal, stenosis |
| Sagittal STIR | Sagittal | Edema detection, marrow pathology, ligamentous injury |
| Axial T2 | Axial | Canal and foraminal stenosis, disc herniations, cord morphology |
| Axial T1 | Axial | Anatomy, epidural fat |
| Post-contrast T1 (with fat sat) | Sagittal + Axial | Tumor, infection, post-surgical enhancement |
Coil Selection¶
- Cervical: head/neck coil or dedicated cervical spine coil
- Thoracic/Lumbar: spine phased-array coil (built into the table on most modern systems)
- Surface coils provide better signal-to-noise ratio for superficial structures
Field Strength¶
- 1.5 Tesla: standard clinical field strength; good balance of image quality and artifact management
- 3.0 Tesla: higher signal-to-noise ratio; better for small structures; more susceptibility artifacts near hardware
- Open/low-field MRI (0.2–0.7T): lower image quality but accommodates claustrophobic or large patients
Indications¶
- Disc disease: herniation, degeneration, annular tears
- Spinal stenosis: central, foraminal, and lateral recess
- Spinal cord pathology: myelopathy, syrinx, demyelination, cord compression, intramedullary tumors
- Infection: discitis, osteomyelitis, epidural abscess
- Neoplasm: primary spinal tumors, metastatic disease, intradural lesions
- Trauma: ligamentous injury, cord contusion, epidural hematoma
- Post-surgical: recurrent herniation vs. scar tissue (with contrast)
- Inflammatory disease: ankylosing spondylitis, rheumatoid arthritis
Signal Characteristics of Key Structures¶
| Structure | T1 Signal | T2 Signal |
|---|---|---|
| Normal marrow (adult) | Bright (fatty) | Intermediate |
| CSF | Dark | Bright |
| Intervertebral disc (healthy) | Intermediate | Bright (hydrated nucleus) |
| Intervertebral disc (degenerated) | Intermediate | Dark (desiccated) |
| Spinal cord | Intermediate | Intermediate |
| Ligaments | Dark | Dark |
| Epidural fat | Bright | Intermediate-bright |
| Cortical bone | Dark | Dark (no signal) |
Clinical Pearl
The single most important sequence in spine MRI is the sagittal T2. It provides a natural "myelographic" effect — the bright CSF silhouettes the cord and nerve roots — making it ideal for detecting stenosis, cord compression, and disc herniations at a glance. Always start your review with the sagittal T2 for a global overview before examining individual levels on axial images.
Limitations¶
- Contraindications: non-MRI-conditional pacemakers/defibrillators, certain metallic implants, metallic foreign bodies (especially orbital)
- Claustrophobia: affects ~5–10% of patients; may require sedation or open MRI
- Motion artifact: patient movement degrades image quality; acquisition times are longer than CT
- Metal artifact: hardware from prior surgery causes signal dropout and distortion
- Cost and availability: more expensive and less available than CT or radiography
- Cannot evaluate cortical bone detail as well as CT
Key Points¶
- MRI is the gold standard for evaluating the spinal cord, discs, ligaments, and nerve roots
- No ionizing radiation — safe for repeated use and in pregnancy (after first trimester, with caution)
- Sagittal T2 is the most important sequence for overall spine evaluation
- Contrast (gadolinium) is used for tumor, infection, and post-surgical evaluation
- MRI is complementary to CT — CT for bone, MRI for soft tissue
- Always check for MRI contraindications before scanning
References¶
- Gaillard F, et al. Lumbar spine protocol (MRI). Radiopaedia.org. Available at: https://radiopaedia.org/articles/lumbar-spine-protocol-mri
- Eisenmenger LB, Peret A, Roberts GS, et al. Focused Abbreviated Survey MRI Protocols for Brain and Spine Imaging. RadioGraphics. 2023;43(6):e220147. doi:10.1148/rg.220147. Available at: https://pubmed.ncbi.nlm.nih.gov/37167089/
- Mazurek MH, Abruzzo AR, King AH, et al. Implementation of a Survey Spine MR Imaging Protocol for Cord Compression in the Emergency Department: Experience at a Level 1 Trauma Center. AJNR Am J Neuroradiol. 2024;45(9):1378-1384. Available at: https://pubmed.ncbi.nlm.nih.gov/38702066/
- Mathieu J, Talbott JF. Magnetic Resonance Imaging for Spine Emergencies. Magn Reson Imaging Clin N Am. 2022;30(3):383-407. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC9926664/
- Shapiro M. Imaging of the spine at 3 Tesla. Neuroimaging Clin N Am. 2012;22(2):315-341. Available at: https://pubmed.ncbi.nlm.nih.gov/22548935/
- Patel ND, Broderick DF, Burns J, et al. ACR Appropriateness Criteria Low Back Pain. J Am Coll Radiol. 2016;13(9):1069-1078. Available at: https://pubmed.ncbi.nlm.nih.gov/27496288/