What is scintigraphy?

What is Scintigraphy?

Scintigraphy is a diagnostic nuclear medicine imaging technique that uses small amounts of radioactive materials (radiopharmaceuticals) to evaluate organ function and structure by detecting radiation emitted from the body after administration of these substances. 1

Basic Principles of Scintigraphy

• Scintigraphy involves the intravenous injection of radioactive tracers that accumulate in specific target organs or tissues, allowing visualization of their function and structure 1, 2
• The gamma rays emitted by these radiopharmaceuticals are detected by specialized equipment called gamma cameras, which create images through a process called collimation 2
• The resulting images represent the distribution of the radioactive tracer in the body, reflecting physiological and metabolic processes rather than just anatomical structures 3
• Resolution of scintigraphic images decreases with distance from the detector, with typical resolution of 5-10mm for structures being imaged 2

Types of Scintigraphy

Myocardial Perfusion Scintigraphy (MPS)

• Used to evaluate coronary heart disease by assessing blood flow to the heart muscle 1
• Involves injection of tracers like thallium-201 or technetium-99m compounds during cardiovascular stress 1
• Helps diagnose coronary stenosis, assess disease severity, and evaluate myocardial viability 1
• Particularly valuable for patients who cannot undergo exercise stress testing, using pharmacological stress agents instead 1

Bone Scintigraphy

• Highly sensitive for detecting skeletal abnormalities including metastases, fractures, and inflammatory conditions 1, 4
• Uses phosphates or diphosphonates labeled with technetium-99m that accumulate in areas of increased bone turnover 5
• Can detect bone metastases 3-6 months earlier than conventional radiographs, with 15-25% of cancer patients having positive scans despite normal X-rays 5
• Particularly useful in evaluating patients with cancer (especially breast, prostate, and lung) for bone metastases 4, 5

White Blood Cell (WBC) Scintigraphy

• Valuable for diagnosing inflammatory bowel disease and evaluating its extent and activity 1
• Uses radiolabeled leukocytes to detect areas of inflammation 1
• Particularly useful in children due to relatively low radiation exposure (2-4 mSv/exam) 1

Advanced Scintigraphic Techniques

• Single Photon Emission Computed Tomography (SPECT): Creates three-dimensional images by reconstructing data from multiple planar images taken as the gamma camera rotates around the patient 2
• SPECT/CT: Combines functional information from SPECT with anatomical detail from CT for improved diagnostic accuracy 4
• Positron Emission Tomography (PET): Uses positron-emitting radionuclides to create higher resolution images (approximately 5mm) through coincidence detection techniques 2

Clinical Applications

• Cancer diagnosis and staging: Particularly valuable for detecting bone metastases before they appear on conventional radiographs 5, 6
• Fracture detection: Highly sensitive for stress fractures, occult fractures, and trauma evaluation 1, 6
• Cardiac assessment: Evaluates coronary artery disease, myocardial viability, and cardiac function 1
• Infection and inflammation: Detects osteomyelitis, inflammatory bowel disease, and other inflammatory conditions 1, 6
• Pediatric applications: Useful in suspected child abuse cases to detect occult fractures 1

Safety Considerations

• Radiation exposure varies by procedure: 10 mSv for tetrofosmin studies, 12 mSv for MIBI studies, and 18 mSv for thallium studies in cardiac imaging 1
• This radiation exposure is comparable to CT scans and coronary angiography 1
• The benefit of diagnostic information typically outweighs the small radiation risk, especially in older patients and those with known disease 1
• Complications are rare, with pharmacological stress agents having complication rates of at most 0.01% deaths and 0.02% morbidity 1

Limitations

• While highly sensitive, scintigraphy often lacks specificity for certain conditions 1
• Cannot detect soft tissue abnormalities in some applications (e.g., wrist pain evaluation) 1
• Resolution is lower than some other imaging modalities like MRI 2
• May require sedation in young patients or those unable to remain still 1