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MSK · SPECT/CT

Bone SPECT/CT

Snapshot

Bone SPECT/CT fuses the 3-D distribution of osteoblastic activity with the CT anatomy of the same region. It turns a sensitive but non-specific hot spot into a specific diagnosis (facet arthropathy or metastasis, an active pars defect, a painful ossicle, a loose prosthesis) and raises reader confidence and agreement. The EANM guideline recommends it for abnormal or equivocal planar findings, trauma, small bones of the hand and foot, osteoid osteoma, painful prostheses and pain after orthopaedic surgery.

Planar images superimpose structures; SPECT separates them but has few anatomical landmarks; CT supplies the substrate (sclerosis, lysis, fracture line, osteophyte, lucency around an implant) and the attenuation map. The CT can be a low-dose localisation scan or a diagnostic-quality scan of a limited field when the question needs it.

κ 0.43 → 0.87Reader agreement, planar → SPECT/CT
61% → 8%Equivocal lesions (prostate)
< 0.1 mSvCT dose, extremities
Reference values
  • Adult activity: 500 MBq (300–740 MBq) ⁹⁹ᵐTc-MDP or HDP, or 8–10 MBq/kg (11–13 MBq/kg if obese); children by the EANM dosage card, minimum 40 MBq.
  • Effective dose 0.0057 mSv/MBq: about 2.9 mSv for 500 MBq.
  • Delayed images 2–5 h after injection (up to 24 h if needed); encourage 1 L or more of fluid and frequent voiding.
  • SPECT: 128 × 128 matrix, 60–64 frames per head over 360°, 10–30 s per frame.
  • CT: 80–130 kV, 2.5–300 mAs; slices 0.33–2 mm for extremities, 0.33–5 mm for spine.
  • CT dose: extremities < 0.1 mSv; diagnostic-quality spine or hip CT 4–10 mSv.
  • Normal adult spine and pelvis (⁹⁹ᵐTc-MDP, 500 patients): SUVbw 4.6 ± 2.0; values depend on scanner, reconstruction and site.
Indications and evidence
  • Back pain: SPECT can find active facet joints. In a randomised study, 13 of 15 patients injected at scan-positive facets improved at 1 month, against 2 of 16 with negative scans and 5 of 16 injected on clinical grounds, and the number of facets injected fell from 60 to 27 (Pneumaticos 2006).
  • Spondylolysis in young athletes: SPECT shows an active pars stress reaction; CT shows whether there is a fracture line and whether it is healing. A pars defect without uptake is chronic.
  • Foot and ankle: localises active arthritis among many small joints, stress fractures, osteochondral lesions and painful accessory ossicles; intraobserver κ was 0.86, with better interobserver agreement than bone scan and CT read separately, especially at the naviculocuneiform and tarsometatarsal joints (Pagenstert 2009).
  • Hand and wrist: occult carpal fractures and small-joint problems where radiographs are normal.
  • After surgery: painful arthroplasty (loosening, and CT for component position), suspected non-union after spinal fusion, residual pain after foot or knee surgery. For infection, see Prosthetic joint infection.
  • Oncology: in prostate cancer, SPECT/CT cut equivocal lesions from 61% (planar and SPECT) to 8% (Helyar 2010); fused images raised the area under the ROC curve for benign versus malignant from 0.59–0.77 to 0.95–0.97 (Utsunomiya 2006).
  • Osteoid osteoma: an intense focus (the nidus) within a wider zone of lesser uptake; CT shows the lucent nidus and guides ablation.

Acquisition

  • Whole-body or regional planar images first; SPECT/CT of the region the planar scan or clinical question points to, including adjacent levels in the spine.
  • Match the CT to the question: low-dose CT for localisation and attenuation correction; diagnostic-quality CT (thin slices, bone kernel) when fracture lines or implant–bone interfaces must be judged and no recent CT exists.
  • Reconstruct iteratively with CT attenuation and scatter correction; review fused images in three planes with a maximum-intensity projection.
  • Near metal, use metal-artefact reduction and review non-attenuation-corrected SPECT, because streaks corrupt the attenuation map.

Quantitative bone SPECT

  • Absolute quantification needs a calibrated camera (sensitivity factor cross-calibrated with the dose calibrator), CT attenuation and scatter correction and resolution modelling; results are given as SUV, like PET.
  • Vendor methods such as xSPECT Quant (calibrated SUV) and xSPECT Bone (CT-derived tissue zones that sharpen bone edges) are examples; SUVs are not interchangeable between systems.
  • Normal bone SUV varies widely (coefficient of variation about 40% in the spine and pelvis), so compare with the same patient, the contralateral side or a reference region rather than a fixed cut-off.
  • Possible uses include response of bone metastases and side-to-side comparison; the EANM guideline states that its routine role is yet to be determined.

How to read it

  • Match every focus to its CT correlate: osteophyte and facet arthropathy, endplate degeneration, fracture line, or a lytic or sclerotic lesion with cortical destruction.
  • Uptake without a CT correlate: early stress reaction, early marrow metastasis or bone bruise; MRI may help.
  • A CT abnormality without uptake (bone island, healed fracture, chronic pars defect) is inactive and unlikely to be the pain generator, but purely lytic tumours (myeloma, renal, thyroid) can be cold.
  • Grade intensity against normal bone and the opposite side, and state which lesion best explains the symptoms.
  • See also Bone scintigraphy and SPECT/CT physics.

Pitfalls

  • Misregistration from movement between SPECT and CT, especially in the hands and feet: check the fusion before reporting.
  • Degenerative uptake is common and often painless; name it the pain generator only when it fits the clinical picture.
  • Uptake around implants and fusions stays high for months to years after surgery; interpret with the time since surgery and a baseline if available.
  • The axial field of view is limited: a lesion outside it will be missed, so use planar images to choose the region.
  • CT adds dose: restrict the diagnostic-quality field to what the question needs.
In depth
  • Helyar 2010 (50 lesions in 40 prostate cancer patients): inter-reviewer κ 0.43 for planar, 0.56 for SPECT and 0.87 for SPECT/CT; SPECT/CT called 24% of lesions malignant and 68% benign.
  • Utsunomiya 2006: reading SPECT and CT side by side helped (AUC 0.83–0.89), but fused images helped more (0.95–0.97), mostly by making readers confident that lesions were benign.
  • Pneumaticos 2006: SPECT-guided facet injection also cut the Medicare cost per patient from $2191 to $1865.
  • Hou 2024: normal spine and pelvis SUVbw 4.57 ± 1.97 in 500 patients, correlating with age and CT density, which is why site-specific references are needed.
  • EANM 2016: CT for SPECT/CT uses 80–130 kV and 2.5–300 mAs; a low-dose localisation CT of the extremities adds under 0.1 mSv, while a diagnostic spine or hip CT adds 4–10 mSv, more than the bone scan itself (about 2.9 mSv).
  • Planar and SPECT show osteoblastic reaction, not tumour: a purely lytic, rapidly growing lesion may be cold, while healing fractures, arthropathy and Paget's disease are hot.

Sources: EANM bone scintigraphy guideline 2016 (PMID 27262701) · Helyar 2010 (PMID 20016889) · Utsunomiya 2006 (PMID 16304081) · Pneumaticos 2006 (PMID 16436824) · Hou 2024 (PMID 39154304)

Sources

  1. Van den Wyngaert T, Strobel K, Kampen WU, et al. The EANM practice guidelines for bone scintigraphy. Eur J Nucl Med Mol Imaging. 2016;43:1723–38.
  2. Bartel TB, Kuruva M, Gnanasegaran G, et al. SNMMI procedure standard for bone scintigraphy 4.0. J Nucl Med Technol. 2018;46:398–404.
  3. Delbeke D, Coleman RE, Guiberteau MJ, et al. Procedure guideline for SPECT/CT imaging 1.0. J Nucl Med. 2006;47:1227–34.
  4. Israel O, Pellet O, Biassoni L, et al. Two decades of SPECT/CT – the coming of age of a technology: an updated review of literature evidence. Eur J Nucl Med Mol Imaging. 2019;46:1990–2012.
  5. Helyar V, Mohan HK, Barwick T, et al. The added value of multislice SPECT/CT in patients with equivocal bony metastasis from carcinoma of the prostate. Eur J Nucl Med Mol Imaging. 2010;37:706–13.
  6. Utsunomiya D, Shiraishi S, Imuta M, et al. Added value of SPECT/CT fusion in assessing suspected bone metastasis: comparison with scintigraphy alone and nonfused scintigraphy and CT. Radiology. 2006;238:264–71.
  7. Pneumaticos SG, Chatziioannou SN, Hipp JA, et al. Low back pain: prediction of short-term outcome of facet joint injection with bone scintigraphy. Radiology. 2006;238:693–8.
  8. Pagenstert GI, Barg A, Leumann AG, et al. SPECT-CT imaging in degenerative joint disease of the foot and ankle. J Bone Joint Surg Br. 2009;91:1191–6.
  9. Hou X, He Y, Liu G, et al. SPECT/CT imaging: quantifying ⁹⁹ᵐTc-MDP concentration in the spine and pelvis. Ann Nucl Med. 2024;38:933–42.
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