(MPI) The myocardial perfusion scan is the most common nuclear medicine procedure in cardiac imaging and allows assessing the blood-flow patterns to the heart muscles. The comparison of the radiopharmaceutical distribution after stress and at rest provides information on myocardial viability and cardiac perfusion abnormalities. ECG-gated myocardial perfusion imaging allows the assessment of global and regional myocardial function such as wall motion abnormalities.
The diagnostic accuracy of myocardial perfusion scintigraphy (also abbreviated MPS) allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularization. MPI also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly, and those with diabetes. The use of this type of cardiac scintigraphy is associated with greater cost effectiveness of treatment, in terms of life-years saved, particularly in these special patient groups.
Myocardial perfusion scintigrams are acquired with a gamma camera. Single photon emission computed tomography (SPECT) is preferred over planar imaging because of the three dimensional nature of the images and their superior contrast resolution.
Common MPI radiopharmaceuticals, approved by the U.S. Food and Drug Administration (FDA) include: Tl-201 and the Tc-99m-labeled radiopharmaceuticals, such as sestamibi, tetrofosmin, and teboroxime for single-photon imaging. Rb-82 is used for positron emission tomography (PET) imaging.

See also Gated Blood Pool Scintigraphy, Myocardial Late Enhancement, Cardiac MRI and Echocardiography.

(CT or CAT scan) Computed tomography is a diagnostic imaging technique, previously also known as computerized axial tomography (CAT), computer-assisted tomography (CAT), computerized tomographic imaging, and reconstructive tomography (RT).
A CT scan is based on the measurement of the amount of energy that a tissue absorbs as a beam of radiation passes through it from a source to a detector. As the patient table moves through the CT scanner, the CT tube rotates within the circular opening and the set of x-ray detectors rotate in synchrony. The narrow, fan-shaped x-ray beam has widths ranging from 1 to 20 mm. The large number of accurate measurements with precisely controlled geometry is transformed by mathematical procedures to image data. Corresponding to CT slices of a certain thickness, a series of two-dimensional cross-sectional images is created.
A CT is acquired in the axial plane, while coronal and sagittal images can be rendered by computer reconstruction. Although a conventional radiography provides higher resolution for bone x-rays, CT can generate much more detailed images of the soft tissues. Contrast agents are often used for enhanced delineation of anatomy and allow additional 3D reconstructions of arteries and veins.
CT scans use a relatively high amount of ionizing radiation compared to conventional x-ray imaging procedures. Due to widespread use of CT imaging in medicine, the exposure to radiation from CT scans is an important issue. To put this into perspective, the FDA considers the risk of absorbed x-rays from CT scans to be very small. Even so, the FDA recommends avoiding unnecessary exposure to radiation during diagnostic imaging procedures, especially for children.
CT is also used in other than medical fields, such as nondestructive testing of materials including rock, bone, ceramic, metal and soft tissue.

See also Contrast Enhanced Computed Tomography.

(CTA) A computed tomographic angiography or computerized tomography angiogram is a diagnostic imaging test that combines conventional CT technique with that of traditional angiography to create images of the blood vessels in the body - from brain vessels to arteries of the lungs, kidneys, arms and legs.
High resolution CT scans with thin slices and intravenous injection of iodinated contrast material provide detailed images of vascular anatomy and the adjacent bony structures. CTA requires rapid scanning as the imaging data are typically acquired during the first pass of a bolus of contrast medium. The selection of acquisition timing is important to optimize the contrast enhancement, which is dependent on contrast injection methods, imaging techniques and patient variations in weight, age and health. CT angiography is less invasive compared to conventional angiography and the data can be rendered in three dimensions.

CTA techniques are commonly used to:
See also Cardiovascular Imaging, Magnetic Resonance Angiography MRA, Coronary Angiogram, Computed Tomography Dose Index and Computed or Computerized Axial Tomography.

(CTE) Computed tomography enterography is an imaging procedure to evaluate diseases affecting the mucosa and bowel wall of the small intestine. CTE uses oral contrast agents to improve bowel wall visualization. Several studies established that small bowel distention using negative oral contrast agent increases diagnostic performance of some abdomen CT studies.
The multi-detector row CT (MDCT) improves temporal and spatial resolution and 3D imaging processes offer a full examination of the small bowel with surrounding structures, depicting the small bowel inflammation associated with Crohn's disease by displaying mural hyperenhancement, stratification, and thickening.
CT enterography versus capsule endoscopy provides a non invasive study with comparable sensitivity, high specificity and overall accuracy.

See also Colonoscopy and Virtual Colonoscopy.

A computed tomography (CT) of the abdomen images the region from the thoracic diaphragm to the pelvic groin. The computed tomography technique uses x-rays to differentiate tissues by their different radiation absorption rates.
Oral contrast material can be given to opacify the bowel before scanning. An i.v. injection of a contrast agent (x-ray dye) improves the visualization of organs like liver, spleen, pancreas and kidneys and provides additional information about the blood supply.
Spiral- or helical CT, including improvements in detector technology support faster image acquisition with higher quality. Advanced CT systems can usually obtain a CT scan of the whole abdomen during a single breath hold. This speed increases the detection of small lesions (caused by differences in breathing on consecutive scans) and is beneficial especially in pediatric, elderly or critically-ill patients.
Changes in patient weight require variations in x-ray tube potential to maintain constant detector energy fluence. An increased x-ray tube potential improves the contrast to noise resolution (CNR).

An abdominal CT is typically used to help diagnose the cause of abdominal pain and diseases such as:
Other indications for CT scanning of the abdomen/pelvis include planning radiation treatments, guide biopsies and other minimally invasive procedures. Advanced techniques include for example 3D CT angiography, multiphasic contrast-enhanced imaging, virtual cystoscopy, virtual colonoscopy, CT urography and CT densitometry.

See also Contrast Enhanced Computed Tomography.