Nuclear Medicine — Bone Scan for Spine¶

Definition¶

A bone scan (skeletal scintigraphy) is a nuclear medicine imaging study that uses a radiotracer — typically technetium-99m methylene diphosphonate (⁹⁹ᵐTc-MDP) — to evaluate bone metabolism. Areas of increased osteoblastic activity (bone turnover) concentrate the radiotracer and appear as "hot spots" on the scan.

Technique¶

Procedure¶

Injection: ⁹⁹ᵐTc-MDP is administered intravenously (20–30 mCi for adults)
Uptake phase: 2–4 hours of waiting while the tracer distributes and binds to hydroxyapatite crystite in metabolically active bone
Imaging: whole-body planar images are acquired in anterior and posterior projections using a gamma camera
SPECT (Single Photon Emission Computed Tomography): can be added for cross-sectional imaging and better localization

Three-Phase Bone Scan¶

For suspected infection or complex regional pain syndrome, a three-phase study is performed:

Phase 1 (Flow/Angiographic): rapid sequential images during tracer injection — evaluates blood flow
Phase 2 (Blood Pool): images at 3–5 minutes — evaluates soft tissue hyperemia
Phase 3 (Delayed/Bone): images at 2–4 hours — evaluates osteoblastic activity
Positive all three phases: suggests infection or active inflammation
Positive delayed phase only: suggests bony pathology without active soft tissue inflammation

SPECT/CT¶

Combines functional SPECT data with anatomic CT in a single study
Dramatically improves localization — identifies the specific vertebra, facet joint, or pars defect responsible for increased uptake
Increasingly used for evaluating back pain, especially when standard imaging is equivocal

Indications¶

Metastatic disease screening — whole-body survey for osseous metastases (especially breast, prostate, lung)
Occult fractures — stress fractures, insufficiency fractures not visible on radiographs
Spondylolysis — active pars defect in young patients with back pain (SPECT is more sensitive than planar)
Infection — osteomyelitis, discitis (often combined with gallium or labeled WBC scans for specificity)
Post-surgical — pseudarthrosis, hardware loosening (increased uptake around hardware suggests non-union or loosening)
Paget disease — markedly increased uptake in affected vertebrae
Primary bone tumors — staging and monitoring

Imaging Findings¶

Finding	Bone Scan Appearance
Metastasis (blastic)	Focal hot spots, often multiple, randomly distributed
Acute fracture	Focal linear or band-like increased uptake
Spondylolysis	Focal uptake at the pars interarticularis (best seen on SPECT)
Paget disease	Markedly increased uptake expanding the vertebral body
Degenerative changes	Mild increased uptake at facet joints, endplates
"Superscan"	Diffusely increased skeletal uptake with absent renal activity — suggests widespread metastatic disease
"Cold" lesion	Photopenic defect — suggests aggressive lytic metastasis (myeloma, renal cell), avascular necrosis, or radiation therapy effect

Clinical Pearl

Bone scan has high sensitivity but low specificity for spinal pathology — any process that increases osteoblastic activity will produce a hot spot, including fracture, degeneration, infection, and tumor. SPECT/CT significantly improves specificity by correlating the hot spot with the precise anatomic structure involved. For evaluating active spondylolysis in young athletes, SPECT is more sensitive than planar bone scan and can detect stress reactions before a fracture line becomes visible on CT.

Limitations¶

Low specificity — cannot reliably distinguish tumor from fracture, degeneration, or infection on planar images alone
Low spatial resolution compared to CT or MRI
Radiation exposure — whole-body radiation dose (~6 mSv)
Purely lytic lesions may be "cold" — myeloma and some aggressive lytic metastases may not show increased uptake
Delayed imaging — 2–4 hour wait between injection and imaging
Pregnancy — contraindicated

Key Points¶

Bone scan detects areas of increased osteoblastic activity using ⁹⁹ᵐTc-MDP
High sensitivity but low specificity — SPECT/CT improves localization and specificity
Primary role: metastatic screening, occult fractures, active spondylolysis, and infection evaluation
Purely lytic lesions (myeloma) may be falsely negative
Three-phase bone scan adds specificity for infection (positive all three phases)
SPECT is superior to planar imaging for evaluating the spine

References¶

Gaillard F, et al. Bone scintigraphy. Radiopaedia.org. Available from: https://radiopaedia.org/articles/bone-scintigraphy-1
Adams C, Jensen J, Leslie SW. Bone Scan. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2026. Available from: https://www.ncbi.nlm.nih.gov/books/NBK531486/
Van den Wyngaert T, Strobel K, Kampen WU, et al. The EANM practice guidelines for bone scintigraphy. Eur J Nucl Med Mol Imaging. 2016;43(9):1723–1738. doi:10.1007/s00259-016-3415-4
Love C, Din AS, Tomas MB, Kalapparambath TP, Palestro CJ. Radionuclide bone imaging: an illustrative review. RadioGraphics. 2003;23(2):341–358. doi:10.1148/rg.232025103
Trout AT, Sharp SE, Anton CG, Gelfand MJ, Mehlman CT. Spondylolysis and beyond: value of SPECT/CT in evaluation of low back pain in children and young adults. RadioGraphics. 2015;35(3):819–834. doi:10.1148/rg.2015140092
Matesan M, Behnia F, Bermo M, Vesselle H. SPECT/CT bone scintigraphy to evaluate low back pain in young athletes: common and uncommon etiologies. J Orthop Surg Res. 2016;11(1):76. doi:10.1186/s13018-016-0402-1
Bellah RD, Summerville DA, Treves ST, Micheli LJ. Low-back pain in adolescent athletes: detection of stress injury to the pars interarticularis with SPECT. Radiology. 1991;180(2):509–512. PMID: 1829845
Lo SS, Lutz ST, Chang EL, et al; Expert Panel on Radiation Oncology-Bone Metastases. ACR Appropriateness Criteria® spinal bone metastases. J Palliat Med. 2013;16(1):9–19. doi:10.1089/jpm.2012.0376