Spine SPECT

Principle and hybrid imaging

Classic radionuclide scintigraphy provides only a two-dimensional representation of tracer uptake. SPECT uses a rotating gamma camera that takes slices to form a full 3D model of the radiopharmaceutical distribution. In the absence of other pathologies, local accumulations of the tracer directly indicate areas of increased bone metabolism: sites of mechanical stress, healing, or active degeneration.

However, isolated SPECT has a major drawback—low spatial resolution, which makes it extremely difficult to precisely correlate an identified lesion with a specific spinal segment. This problem is solved by hybrid imaging—SPECT/CT (SPECT/CT).

The role of computed tomography in hybrid imaging:

• Provides high spatial resolution (up to 1 mm).
• Enables precise fusion of the metabolic map with anatomical structures.
• Improves the quality of the SPECT image itself through soft-tissue attenuation correction algorithms.

Depending on the clinical task, the hybrid study can be supplemented with either low-dose or full diagnostic dose CT.

Indications and clinical use

Adding metabolic imaging to traditional radiological anatomy radically changes the diagnostic workflow in a number of conditions.

Degenerative spine diseases While standard CT and MRI brilliantly demonstrate structural changes (e.g., osteochondrosis or arthrosis), SPECT allows the identification of the active phase of the disease. The method specifically highlights areas of bone stress—active facet joint arthropathy or progressive intervertebral disc degeneration.

Traumatic injuries The study is indispensable for the differential diagnosis of vertebral body compression fractures. By the presence or absence of active bone metabolism, the physician can reliably distinguish an acute vertebral collapse from an old, chronic fracture.

Spondylolysis evaluation In defects of the pars interarticularis, SPECT helps differentiate an old, clinically "silent" defect from active spondylolysis. In the latter case, tomograms show an intense hot spot, indicating active inflammation or microfractures, which is often the true source of pain.

Postoperative follow-up In patients who have undergone surgical stabilization (spinal fusion), SPECT/CT outperforms other diagnostic imaging modalities in assessing the condition of hardware. The method effectively detects pedicle screw loosening and other fixation elements, and also helps diagnose occult postoperative infections.

How the scan is performed

The procedure takes time and consists of several successive stages:

1. Preparation and injection: a small dose of a radioactive tracer is injected intravenously (usually into the cubital vein). The type of drug is selected based on clinical indications.
2. Waiting period: a pause is required for the radiopharmaceutical to distribute through the bloodstream and accumulate in target tissues.
3. SPECT scan: a gamma camera rotates 360 degrees around the patient, taking projections at 3 to 6-degree steps.
4. CT scan: computed tomography is performed across the exact same anatomical region of interest.
5. Processing and reconstruction: specialized software fuses the two datasets, correcting for patient motion artifacts if necessary. Ultimately, the physician receives multiplanar images (in axial, sagittal, and coronal planes), standard bone window CT reconstructions, and maximum intensity projections (MIP).

Role among other imaging modalities

SPECT complements but does not replace standard Imaging Techniques, each of which has its own strengths.

• Plain radiography (Plain radiography): in modern practice, it is being superseded by CT and MRI. Its main advantage is the ability to take images in the erect position. In trauma, it helps assess the level of injury, but it is important to remember that routine radiography misses up to 55% of cervical spine fractures.
• Computed tomography (CT): excellently assesses the bone anatomy of posterior vertebral structures, facet joints, as well as fractures and their stability. It adequately demonstrates spinal cord compression.
• MRI (MRI): the gold standard for soft tissues. In evaluating the postoperative state, it outperforms CT in detecting scar tissue and adhesions (fibrosis). The basic MRI protocol includes sagittal T1, T2, fat-suppressed T2 (STIR), and axial T2. Axial T1 with contrast (gadolinium) is added postoperatively.
• Digital subtraction angiography (DSA): remains the unsurpassed standard for studying spinal arteries due to its exceptionally high spatial resolution.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Radiological features of spondylolysis on CT and SPECT/CT
• Differential diagnosis of compression fractures: acute vs. chronic
• Routine MRI protocols for the spine (T1, T2, STIR)
• Principles of assessing pedicle screw placement on CT
• The challenge of diagnosing cervical spine injuries

Other topics in the "Spine" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.