4.2 Spine Protocols

Spine Protocols

MRI of the spine is a common and vital diagnostic tool for evaluating degenerative disc disease, spinal stenosis, disc herniation, trauma, neoplasm, infection, and radiculopathy. Spine imaging is challenging due to the small, detailed structures of the spinal cord and nerve roots, as well as artifacts from swallowing, cardiac motion, respiration, and CSF pulsation.

Patient Positioning and Coil Selection

Spine imaging is performed with the patient in the supine position. Patients are placed head-first for cervical and thoracic spines, and either head- or feet-first for lumbar spine protocols. Phased-array spine coils embedded in the patient table are utilized to maximize SNR.

• Cervical Spine: Positioned in a dedicated neck/cervical coil. The laser alignment light is centered at the level of the thyroid cartilage (C4–C5 level).
• Thoracic Spine: Center of the coil and laser light are aligned at the mid-sternum (sternal angle or T4–T5 level).
• Lumbar Spine: Patient knees are flexed over a triangular sponge. This positioning flattens the lumbar lordotic curve, aligning the spine closer to the table, reducing patient discomfort, and minimizing involuntary motion. The laser light is centered at the level of the iliac crest (L4 level) or the xiphoid process (L3 level).
• Sacrum and Coccyx: Center of the coil and laser light are aligned at the level of the anterior superior iliac spine (ASIS) or pubic symphysis.

Slice Planning and Coverage

• Sagittal Spine Slices: Sagittal slices are planned on both coronal and axial localizers. Slices are aligned parallel to the spinal cord or vertebral bodies. Slice coverage must span from the left pedicle to the right pedicle. This ensures that the neural foramina are fully imaged, which is critical for evaluating nerve root exit pathways.
• Axial Spine Slices:
  • Cervical Spine: Axial slices are angled parallel to individual disc spaces (typically C2–C3 through C7–T1) in multiple angled stacks. This alignment ensures that the disc bulge and nerve root exit are visualized without obliquity.
  • Thoracic Spine: Slices are planned perpendicular to the spinal cord. They can be planned as a continuous block or angled parallel to specific disc spaces of interest.
  • Lumbar Spine: Axial slices are angled parallel to the lower three disc spaces (L3–L4, L4–L5, and L5–S1) in individual angled stacks. Coverage must include the entire spinal canal and the neural foramina.
  • Sacrum/Coccyx: Sagittal slices are planned parallel to the sacral midline. Axial-oblique slices are planned parallel to the sacrum (or perpendicular to the sacral canal) to evaluate the sacral nerve roots, and coronal-oblique slices are planned parallel to the sacrum.

Radiculopathy Protocols & Sequence Optimization

Radiculopathy refers to nerve root compression or inflammation. The standard protocol requires high-resolution sagittal and axial T2-weighted and T1-weighted sequences. In the cervical spine, axial T2 gradient-recalled echo (GRE)* (such as MEDIC or MERGE) is essential. Unlike spin echo sequences, T2* GRE is highly sensitive to magnetic susceptibility effects and provides excellent contrast between:

1. Cerebrospinal Fluid (CSF): Hyperintense (bright) due to long T2* relaxation.
2. Spinal Cord: Intermediate signal, showing gray and white matter differentiation.
3. Bone Osteophyte Complexes and Herniated Discs: Hypointense (dark) due to low proton density and susceptibility effects. This contrast allows the technologist to differentiate hard osteophytes (bone spurs) from soft disc herniations, which is critical for surgical planning.

Signal Optimization and Artifact Reduction

• Spatial Presaturation Bands (Sat Bands): Placing presaturation bands anterior to the vertebral bodies is essential. For cervical spine, a sat band suppresses motion from swallowing. For thoracic spine, sat bands suppress breathing and cardiac motion. For lumbar spine, sat bands suppress bowel peristalsis and pulsatile blood flow from the aorta and inferior vena cava. This prevents ghosting artifacts from projecting across the spinal canal.
• Phase Encoding Direction:
  • Sagittal Spine: The phase encoding direction must be set to Feet-to-Head (F/H). If oriented Anterior-to-Posterior (A/P), motion from the heart, aorta, and chest wall would propagate along the phase axis directly across the spinal cord, making the image non-diagnostic. F/H phase encoding directs these motion artifacts vertically. F/H phase direction also prevents aliasing (wrap-around) from the nose, chin, or chest.
  • Axial Spine: Typically set to Anterior-to-Posterior (A/P) (with flow artifacts directed laterally or anteriorly) or Right-to-Left (R/L) (using no-phase-wrap to prevent aliasing from the hips/arms).
• Gradient Flow Compensation: Also known as gradient nulling, this technique is utilized to reduce CSF pulsation artifacts in the spinal canal, which can mimic intradural pathology on T2-weighted images.

Summary of Spine Protocols