Fundamentals of single-photon emission computed tomography (SPECT) and SPECT/CT imaging

Introduction Nuclear medicine imaging employs the administration of trace amounts of compounds labeled with radioactivity (radionuclides) that are used to provide diagnostic information in a wide range of disease states [1]. Special imaging instruments (e.g., gamma cameras, positron emission tomography (PET) scanners) detect the emitted photons from these nuclides following radioactive decay and provide non-invasive means to image physiological and pathological states within the body (Figure 6.1). Detection of disease with anatomical imaging methods often requires gross structural changes to be apparent before the diagnosis is definitive. The reliance on anatomical information for diagnosis also makes it difficult to monitor the response of diseased and normal tissues in the critical post-therapy period. In comparison, radiotracer imaging methods such as single-photon emission computed tomography (SPECT) and PET are well suited to provide critical information about the functional, metabolic, and molecular status of tissues and organs. SPECT is a technique widely used in nuclear medicine for the imaging of many organs including the skeleton, heart, lungs, kidneys, and brain, as well as for whole-body imaging [2, 3]. The study is obtained by moving a gamma camera on a gantry in a circular or elliptical orbit around the patient, obtaining information from different angles, which is then combined into a 3-dimensional (3D) volume. SPECT studies are normally viewed as a set of slices cut in the transaxial, sagittal, and coronal planes, with optional 3-dimensional interactive views. As opposed to 2-dimensional (2D) images, SPECT imaging provides higher contrast, depth information, and optional quantification. Brain SPECT is used mainly for perfusion or receptor imaging of the brain. Frequently brain pathology will manifest itself as functional changes before anatomical changes have taken place. The use of tracers of cerebral perfusion and brain neurotransmitter systems has resulted in the development of a number of applications for brain SPECT in neurology and psychiatry [4-6]. Common indications include dementia, epilepsy, neurovascular disorders, parkinsonism, and following minor head trauma. It also has the potential to be a valuable research tool for the study of in vivo brain function.