====== Single-photon emission computed tomography ======

[[Single-photon emission]] [[computed tomography]] ([[SPECT]], or less commonly, SPET) is a [[nuclear medicine]] tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera. However, it is able to provide true 3D information. This information is typically presented as cross-sectional slices through the patient but can be freely reformatted or manipulated as required.

The technique requires the delivery of a gamma-emitting radioisotope (a radionuclide) into the patient, normally through injection into the bloodstream. On occasion, the radioisotope is a simple soluble dissolved ion, such as a radioisotope of gallium(III). Most of the time, though, a marker radioisotope is attached to a specific ligand to create a radioligand, whose properties bind it to certain types of tissues. This marriage allows the combination of ligand and radiopharmaceutical to be carried and bound to a place of interest in the body, where the ligand concentration is seen by a gamma-camera.


===== 🔬 Common SPECT Modalities by Organ/System =====

🦴 [[Bone SPECT]]
Tracer: 99mTc-MDP or 99mTc-HDP

Use: Bone metastases, occult fractures, osteomyelitis, prosthetic joint evaluation

🧠 Brain SPECT
Tracer: 99mTc-HMPAO or 99mTc-ECD

Use: Epilepsy localization (ictal/interictal), dementia (Alzheimer’s, frontotemporal), cerebrovascular reserve assessment, traumatic brain injury

❤️ Cardiac SPECT (Myocardial Perfusion Imaging)
Tracer: 99mTc-sestamibi or 99mTc-tetrofosmin

Use: Coronary artery disease (ischemia vs infarction), myocardial viability, stress/rest perfusion studies

🦠 Infection/Inflammation SPECT
Tracer: 99mTc-HMPAO-labeled leukocytes or 99mTc-sulesomab

Use: Suspected osteomyelitis, infected prosthesis, fever of unknown origin

🦴 Parathyroid SPECT
Tracer: 99mTc-sestamibi

Use: Localization of parathyroid adenomas in hyperparathyroidism (often SPECT/CT)

🦋 Thyroid SPECT
Tracer: 99mTc-pertechnetate or 123I

Use: Nodular thyroid disease, functional status, ectopic thyroid tissue

🧠 Dopaminergic SPECT (DaTSCAN)
Tracer: 123I-ioflupane

Use: Differentiating Parkinson’s disease from essential tremor or atypical parkinsonism

🧠 Cerebral Perfusion in Brain Death
Tracer: 99mTc-HMPAO

Use: Demonstrates absence of cerebral perfusion

see [[CBF SPECT]]

[[Tc-99m ECD SPECT]]

===== Indications =====

Single-photon emission computed tomography (SPECT) traditionally has been the most sensitive modality for diagnosing active (early) [[spondylolysis]]. More recently, high signal change (HSC) in the [[pedicle]] or [[pars interarticularis]] on fluid-specific (T2) magnetic resonance imaging (MRI) has been shown to be important in the diagnosis of early spondylolysis.