Computerized Axial Tomography (CT) Services
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Computerized Axial Tomography, also known as a CT or CAT scan, is a diagnostic procedure which rotates an x-ray beam around the body and produces high resolution, cross sectional images. These images can be of the brain, spine, chest, abdomen, pelvis, lower extremities, or just about any body part.
How it Works
X-ray slice data is generated using an X-ray source that rotates around the patient. X-ray sensors are positioned on the opposite side of the circle from the X-ray source. Many data scans are progressively taken as the patient is gradually passed through the scanner opening. They are combined together by the mathematical procedure known as tomographic reconstruction to create an image that the radiologist can interpret.
Early Development
In the late 1980s, the first helical (spiral) computed tomography (CT) scanner for clinical applications was introduced. In these "single slice" systems, the x-ray photons are directed at the patient using a desired thickness and are received by a single-row detector array. By eliminating the relatively time-consuming stepwise patient positioning (the so-called "stop-and-shoot" method) associated with conventional CT scanners, scanning time was reduced and improved imaging speed while still maintaining satisfactory image quality.
Spiral CT scanners use a continuously rotating gantry and continuous movement of the table and patient in order to acquire data continuously and volumetrically during the scan sequence. Today, currently available spiral scanners use a multiple rows of x-ray detectors that acquire data from a tissue thickness determined by the width of the x-ray beam. The narrower the collimation, the higher the spatial resolution of the scan produced.
The advantages of speed and continuity can be seen in applications such as imaging of the lungs. The speed allows the complete data set to be acquired within one breath hold. This avoids the problem of parts of the lung being missed because the patient breathes differently in consecutive acquisitions.
Today's CT Scanner
Newer machines with faster computer systems and newer software strategies can process not only individual cross sections but continuously changing cross sections as the patient slowly slides through the X-ray circle. Most scanners in the market today are called helical or spiral CT machines. Their computer systems integrate the data of the moving individual slices to generate three dimensional volumetric information (3D-CT scan), in turn viewable from multiple different perspectives on attached CT workstation monitors.
Contrast Injections
Sometimes contrast materials such as intravenous iodinated contrast are used. This is useful to highlight structures such as blood vessels that otherwise would be difficult to delineate from their surroundings. Using contrast material can also help to obtain functional information about tissues.
The speed of acquisition also makes it possible to make better use of the contrast dynamics of intravenously administered contrast agents. This allows blood vessels to be imaged while they contain the maximum amount of contrast agent. It is also possible to obtain images of a complete organ in one or several specific phases of contrast enhancement, by scanning the volume repeatedly during a single contrast cycle.
Viewing
In spiral CT, several reconstructions are generally made per rotation of the tube. This leads to a large number of images, all of which have to be assessed. In order to speed assessment of the scan, and to reduce the quantity of films, the reporting is often done with a combination of a viewing workstation and films. Sequences of images can be displayed on the workstation in a 'movie' or 'cine' mode. This has the great advantage that structures can easily be followed through the various images. At Precision, a workstation is used for multiplanar eformatting (MPR). These images show planes through the patient in sagittal, coronal or oblique directions. They also help to provide a 3-dimensional impression of the patient.
The development of the spiral technology has led to a rapid increase in the speed of acquisition. This has increased the 'patient throughput' for examinations of the trunk, and has made it possible to apply new diagnostic procedures.
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CT Preparation
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