CAT scan

Principle

CT scanning combines x-rays and computer to produce precisely detailed cross-sectional images of the organs.

A thin x-ray beam rotates around the patient.
Detectors measure the amount of x-rays that make it through a particular area of interest.

CAT scans are enhanced by using intravenous iodinated contrast material to delineate vascular structure and function of certain organs, e.g. kidneys.

Normal enhancement of lung parenchyma can be compared to increased enhancement of the tumor.

When necessary, reconstructed images can create three-dimensional models of organs.

The patient lies on a narrow table that slides into the center of the scanner.
IV access will be required if contrast media needs to be administered.
For abdominal and pelvic CT’s, oral contrast may also need to be swallowed or given by NG tube .
Patient will be required to hold their breath for approximately 5-10 seconds and not move, as motion causes blurred images.
Scan time varies depending on the type of scanner and required studies.

The newest multidetector scanners can image from head to toe, in less than 30 seconds.
Spiral scanners can scan from lung apex to symphysis pubis in one breath holding.

CT scan is helpful in delineating the precise anatomy and location of pathology.
Three-dimensional reconstructions studies add information about blood supply and provide "road maps" for planning surgeries.

CT is often utilized in the trauma setting to evaluate the brain, chest, and abdomen as the first diagnostic procedure.
CT is done routinely in patients with cancer to evaluate the mass its extension and metastatic nodes.
CT can be used to guide interventional procedures, such as biopsies and placement of drainage tubes.

Table cannot fit very obese patients > 450 lbs.
Some patients cannot lie supine or remain still.
There are issues with contrast allergy in some patients, but there are protocols to follow using steroid and antihistamines prior to exam to limit a reaction if the CT is absolutely necessary.
Radiation exposure.
Requires IV access to inject contrast.
May only be able to do CT without IV contrast for patients in renal failure or with renal insufficiency.
Medications may need to be held prior to CT (i.e. metformin).