Positron emission tomography - computed tomography (better know by its acronym PET-CT) is a medical imaging device which combines in a single gantry system both a Positron Emission Tomography (PET) and an x-ray Computed Tomography, so that images acquired from both devices can be taken sequentially, in the same session from the patient and combined into a single superposed (co-registered) image. Thus, functional imaging obtained by PET, which depicts the spatial distribution of metabolic or biochemical activity in the body can be more precisely aligned or correlated with anatomic imaging obtained by CT scanning. Two- and three-dimensional image reconstruction may be rendered as a function of a common software and control system.

PET-CT has revolutionized many fields of medical diagnosis, by adding precision of anatomic localization to functional imaging, which was previously lacking from pure PET imaging. For example, in oncology, surgical planning, radiation therapy and cancer staging have been changing rapidly under the influence of PET-CT availability, to the extent that many diagnostic imaging procedures and centers have been gradually abandoning conventional PET devices and substituting them by PET-CTs. Although the combined device is considerably more expensive, it has the advantage of providing both functions as stand-alone examinations, being, in fact, two devices in one.

PET and PET/CT scans are performed to:

	Detect cancer.
	Determine whether a cancer has spread in the body.
	Assess the effectiveness of a treatment plan, such as cancer therapy.
	Determine if a cancer has returned after treatment.
	Determine blood flow to the heart muscle.
	Determine the effects of a heart attack, or myocardial infarction, on areas of the heart.
	Identify areas of the heart muscle that would benefit from a procedure such as angioplasty or coronary artery bypass surgery (in combination with a myocardial perfusion scan).
	Evaluate brain abnormalities, such as tumors, memory disorders and seizures and other central nervous system disorders.
	To map normal human brain and heart function.