Photons of energy are given off by the tracer and are recorded by a gamma camera. Newer systems allow a larger field of view so that whole body scans are able to provide excellent images and may be preferable to limited regional studies for practical reasons.
Scintigraphy, a more formal name for bone scanning, using technetium 99m methylene diphosphonate (MDP) will reveal a variety of non-osseous disorders, including neoplastic, hormonal, inflammatory, ischemic, traumatic, and excretory. Soft tissue Tc99m MDP uptake can be observed in benign conditions, such as tumoral calcinosis or myositis ossificans, and in malignant conditions, such as sarcomas, adenocarcinomas, and metastases. Moreover, tissue damage (which may be due to inflammation, physical injury, or infection), generally results in localized hyperemia, edema, or calcium (and hemosiderin) deposition. These can also be visualized with scintigraphy.1
For deeper structures, single photon emission computed tomography (SPECT) can produce increased image contrast and improve spacial resolution.2 Limitations to imaging the cervical spine with SPECT include decreased resolution, as a result of the relatively low bone mass of the cervical spine, and the relatively large radius of rotation necessitated by the mass of the shoulders. Despite such limitations, a recent report reveals the usefulness of cervical SPECT in trauma cases; the authors were able to make the diagnosis of occult fractures not seen with conventional plain film, demonstrate periosteal injury, differentiate radiographic abnormalities from healed fractures, and identify active posttraumatic osteoarthritis superimposed on chronic degenerative disease.3 Their proposed algorithm for the diagnosis of cervical spine injury after trauma is presented in Figure 1.
| Figure 1 | Neck Trauma | |||
| | ||||
| | ||||
__________________ | Cervical spine series | _________________ | ||
| | | | | | ||
Negative fracture | | | Positive acute fracture | ||
Positive DDD(?) fracture | ||||
| | | | |||
| | | | | | ||
| | | | | | ||
| | | | | | ||
Persistent pain | Flexion/extension films | --Unstable-- | CT | |
| | | | | | ||
| | | | | | ||
| | Stable | | | ||
| | | | | | ||
| | | | | | ||
| | Persistent pain | Neurosurgery | ||
| | | | | | ||
SPECT | SPECT | | | ||
______ | ______ | _______ | _____ | | |
| | | | | | | | | |
| Positive | Negative | Positive | Negative | | |
| | | | | | | | Consider Bone SPECT |
| | | | | | | | |
| Consider CT, immobilization | Conservative treatment | CT | Conservative treatment | |
SPECT appears to be a promising method for the evaluation of mild traumatic brain injuries (MTBI). Measuring regional cerebral blood flow (rCBF), Nedd et al.4 compared the results of the SPECT study with CT findings and found intraparenchymal abnormalities with SPECT in 87.5 percent vs. only 37.5 percent with CT. Areas of involvement were larger in the SPECT studies and contrecoup lesions were detected more often with SPECT. All patients with skull fractures had normal CT (brain) scans in this series, whereas 43.7 percent had rCBF abnormalities on SPECT.
In a similar comparative study,5 this time for low back pain, SPECT was shown to be superior to both plain film radiology and CT in the identification of lesions. Eighty percent of the SPECT visualized lesions were seen on CT, but only 37 percent were seen on plain film studies. Another report suggests that SPECT may be more likely than CT to correlate with clinical findings in cases of spondylosis.6
About 90 percent of fractures will appear normal on bone scan within two years. They can be detected within hours of injury in the majority of cases. The occasional exception to this rule is in hip fractures in the elderly.
In many cases, bone scan can detect bone injuries which are too subtle for plain film radiography or CT -- modalities that detect fracture on the basis of absolute loss of bone crystal. Below is the list of the conditions detectable with scintigraphy.
Conditions Detectable with Radionuclide Imaging:
- Avulsion fractures
- Stress fractures
- Shin splints
- Insufficiency fractures
- Bone bruises (focal periosteal, cartilaginous, subchondral, or interosseous trauma)
- Pars defects
- Osteonecrosis
- Plantar fascitis
- Muscle Injuries
- Tendinitis
- Bursitis
- Frostbite
- Electrical burns
- Child abuse
- Chronic radiation injury
- Osteomyelitis
- Reflex sympathetic dystrophy
- Osteoarthritis and other arthritides (including those affecting the TM joint)
- Osteochondroses
- Osteochondroses
- CA
- Discitis
References
- Peller PJ, Ho VB, Kransdorf MJ. Extraosseous Tc-99m MDP uptake -- a pathophysiologic approach. Radiographics 13(4):715-734, 1993.
- Front D, Israel O, Jerushalmi J, et al. Quantitative bone scintigraphy using SPECT. J Nucl Med 30:240-245, 1989.
- Seitz JP, Unguez CE, Corbus HF, Wooten WW. SPECT of the cervical spine in the evaluation of neck pain after trauma. Clin Nuc Med 20(8):667-673, 1995.
- Nedd K, Sfakianakis G, Ganz W, et al. 99mTc-HMPAO SPECT of the brain in mild to moderate traumatic brain injury patients -- compared with CT -- a prospective study. Brain Injury 7(6):469-479, 1993.
- Ryan PJ, Evans PA, Gibson T, et al. Chronic low back pain -- comparison of bone SPECT with radiography and CT. Radiology 182(3):849-854, 1992.
- Raby N, Mathews S. Symptomatic spondylosis -- correlation of CT and SPECT with clinical outcome. Clin Radiology 48(2):97-99, 1993.
Arthur Croft, DC, MS, FACO
San Diego, California
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