PET/CT – What is it For?
Symptoms of cancer may be general and non-specific e.g. fatigue, loss of appetite, or weight loss, or specific to the impact of the cancer upon the organ in which the cancer arises e.g. obstruction, pain, blood loss. Cancer is characterized by the presence of a space-occupying lesion, hence the use of spatial (anatomic) imaging, e.g. X-rays, CT, MRI to demonstrate the presence, location, size, distribution, and relationships of a cancer to surrounding normal structures. However, spatial imaging does not tell you what is occupying the space. To interpret what is occupying the space requires a different type of image—a functional image—as provided by PET, often in conjunction with CT to provide a concurrent picture of both space and function.
The conditions for which functional imaging is adding significantly to our knowledge include Alzheimer’s disease and dementias (cognitive disorders); traumatic brain injury, including chronic traumatic encephalopathy as experienced through repeated head trauma in athletes or through sports injuries; and post-traumatic stress disorder in those surviving acutely stressful situations; complex neuro-psychiatric conditions; movement disorders e.g. Parkinson’s disease; and treatment-refractory epilepsy. Unlike cancer, the underlying problem is not space-occupation (anatomical change) causing functional change, but functional change initially without any change in anatomy. Such functional changes can include memory loss, speech disturbance, withdrawal and isolation, behavior change, and depression. These more subtle changes can be present on functional images before any structural changes become evident on anatomic images (CT, MRI). Although treatment interventions are not yet available to reverse these conditions, there is much that can be done to benefit patients and caregivers if the correct diagnosis is known, interventions to slow the progress of the disease are initiated, and the condition is addressed before neurological function is irretrievably lost.
Declining heart function reflects the inability of the heart to function effectively as the pump to circulate blood throughout the organs of the body. As heart function declines, so to does the function of other organs. Heart function decline may be due to anatomic abnormalities present from birth or acquired throughout life, or they may be functional abnormalities secondary to blood vessel disorders (ischaemic heart disease) or to conditions directly impairing heart muscle function (e.g. infiltrative, metabolic, inflammatory, or degenerative disorders). Heart size, impacts of abnormal pump function and coronary blood vessel integrity can be imaged with anatomic, spatial imaging. PET measures the metabolic and functional activity of the heart, the presence and distribution of damaged or dead heart muscle, and the selection and monitoring of appropriate interventions, including cardiac surgery.