11.1 Spine CT — Cervical, Thoracic & Lumbosacral Protocols

Why Spine CT Carries Exam Weight

Spine CT sits inside the Head, Spine, and Musculoskeletal subcategory, which alone accounts for 25 of the 71 Procedures questions (43% of the 165 total scored items) on the ARRT CT exam. Within that subcategory, the ARRT content outline lists spine as four numbered leaf items: cervical, thoracic, lumbosacral, and postmyelogram (covered in the next section). In practice, cervical spine trauma imaging is now one of the most common CT studies performed in any acute-care setting, because helical CT has replaced plain radiography as the first-line trauma imaging test for at-risk patients under validated clinical decision rules such as NEXUS and the Canadian C-Spine Rule. Expect the exam to test both the technical protocol (kernel, slice thickness, reformats) and the clinical reasoning behind ordering the study.

Core Anatomy and Protocol Terms

• Cervical spine: C1 (atlas) through C7 — 7 vertebrae — including the craniocervical junction (occiput-C1-C2) and the cervicothoracic junction (C7-T1).
• Thoracic spine: T1-T12 — 12 vertebrae, one per rib pair. Counting ribs on the scout/topogram is the standard way to confirm a thoracic level, since patient rotation can shift apparent vertebral position.
• Lumbosacral spine: L1-L5 plus the sacrum/S1. Watch for transitional anatomy — a lumbarized S1 (an extra mobile-appearing segment) or a sacralized L5 (a fused-appearing lowest lumbar vertebra) — a classic source of level-labeling errors on both radiographs and CT.
• Thin-section helical acquisition: commonly ≤1 mm slice thickness is standard for spine so the near-isotropic data set supports high-quality sagittal and coronal multiplanar reformation (MPR). Fracture lines, disc-space narrowing, and listhesis are far easier to see along the long axis of the spine than on axial images alone.
• Dual reconstruction algorithm: a sharp bone algorithm/kernel is reconstructed for cortical bone detail (fracture lines, facet joints), and a separate soft-tissue/standard kernel is reconstructed from the same raw data for paraspinal soft tissue, spinal cord region, and epidural space evaluation.
• Reconstruction interval: overlapping the reconstruction interval relative to the acquired slice thickness (for example, reconstructing every 0.5 mm from 1 mm raw data) reduces partial volume averaging and produces smoother MPR images without any added patient dose, since it reuses data already acquired.
• Field of view: spine studies use a small, tailored scan/display field of view centered on the spine rather than a full-body FOV, which keeps pixel size small and maximizes the spatial resolution needed for fine bone detail.

Table: Spine Region Quick Reference

Contrast Use in Spine CT

Most spine CT studies are performed without intravenous contrast, since bone detail and canal/foraminal narrowing are well seen on a noncontrast, bone-algorithm image set. Contrast is added when the clinical question moves beyond bone: a suspected vertebral artery injury or dissection after cervical trauma adds a CT angiography (CTA) component, and a suspected epidural abscess, discitis-osteomyelitis, or spinal tumor may call for contrast-enhanced soft-tissue sequences to evaluate for abnormal enhancement.

Patient-Specific and Oncologic Considerations

Spine protocols also flex for patient type and clinical question, echoing the blueprint's cross-cutting "patient considerations" focus theme. A pediatric spine trauma study should use a reduced mAs and, when possible, a smaller pitch adjustment appropriate to body size rather than an adult default technique, since children are more radiosensitive and their spines are still developing (incomplete ossification centers can mimic fracture lines to an inexperienced eye). In oncology patients, thoracic and lumbar spine CT is frequently ordered to characterize a compression fracture found on radiograph or bone scan — CT helps distinguish a benign osteoporotic compression fracture (preserved posterior vertebral body height, no destructive soft-tissue mass) from a pathologic fracture caused by metastatic disease (cortical destruction, an associated soft-tissue mass, or other vertebral lesions). Because vertebral metastases are common in breast, lung, and prostate cancer, spine CT in an oncology patient is rarely a pure "bone-only" question on the exam — expect the stem to combine anatomy with a pathologic-recognition detail.

Exam Scenario

A 24-year-old restrained driver arrives after a high-speed collision with midline cervical tenderness and a Glasgow Coma Scale score that makes clinical clearance unreliable. The trauma team orders a CT cervical spine. The technologist should plan a thin-section helical acquisition from the skull base through T1, reconstruct both bone- and soft-tissue-algorithm image sets, and generate sagittal and coronal reformats before calling the study complete. Axial-only images are considered an incomplete spine trauma study, because subtle listhesis and endplate compression fractures are easy to miss without the long-axis views.

A second, non-trauma scenario: a 68-year-old with known metastatic breast cancer develops new midline thoracic back pain. The ordering provider requests a noncontrast thoracic spine CT rather than starting with MRI because the patient has an MRI-incompatible device. The technologist should still apply the same thin-section, dual-algorithm, sagittal/coronal-reformat protocol used for trauma, since distinguishing a benign versus pathologic compression fracture depends on the same bone-detail and alignment information.

Common Traps

• Confusing thoracic level counting: always verify against ribs, not just position on the scout image.
• Skipping soft-tissue kernel reconstructions because "it's a bone study" — cord-region signal changes and epidural hematoma are missed without them.
• Treating cervical spine CT as a replacement for MRI in cord injury evaluation — CT excels at bone and alignment, but soft-tissue/cord contrast is MRI's strength; CT is the first-line trauma screen, not a soft-tissue substitute.