Computed tomography, more commonly know as a CT or CT scan, is an X-ray technique that is used to produce very detailed images of internal organs located in various parts of the body, such as the head, chest, and abdomen. Doctors use the images produced through this procedure to help diagnose and treat diseases. Other terms for the technique are also called computerized tomography or computerized axial tomography (CAT). While conventional X-ray exams produce two-dimensional images, CT scans uses an X-ray-sensing unit that rotates around your body and a large computer to create cross-sectional images of the inside of your body. This paper will address vital educational information including a brief history, uses for computed tomography, and the effects that it may have on the patient. Computed Tomography

Brief History

British engineer, Godfrey Hounsfield of EMI Laboratories, England and Allan Cormack of Tufts University in Massachusetts invented computed tomography. Their work led to the installation of the first clinical CT scanners between the years 1974-1976. The original systems were limited to only taking images of the head, but soon "whole body" systems with larger patient openings became offered. The use of Cat Scans was in wide use beginning in 1980. There are now about 6,000 CT scanners installed in the United States and about 30,000 installed worldwide.

The first CT scanner developed by Hounsfield in his lab took several hours to acquire the raw data for a single scan or "slice" and took days to reconstruct a single image from this raw data. This is a far cry from the efficient imaging of the latest multi-slice CT systems that now have the capability to collect up to four "slices of data" in about 350 milliseconds and then reconstruct a matrix image from millions of data points in less than a second. For example, an entire chest image can be scanned in five to ten seconds using the most advanced multi-slice CT system.

During its brief history, advancements for computerized tomography have made great improvements in speed, patient comfort, and resolution. As scan times have gotten faster, more anatomy can be scanned more quickly and more efficiently. The extreme speed of scanning allows the elimination of artifacts from patient motion such as normal breathing. Faster scanning helps to eliminate artifacts from patient motion such as breathing or peristalsis. CT exams are even now quicker and more patient friendly than ever before. Tremendous research and development has been made to provide exceptional image quality for a diagnostic guarantee of the lowest possible x-ray dose.

Benefits for Computed Tomography

Computed tomography has been a powerful tool for more than thirty years and the benefits of a CaT scan include many. It is also a noninvasive way to "see" one's internal organs and tissues. "Advances with helical and subsequent multidetector technology have offered expanding and diverse opportunities" (Frush, 2003) where doctors use CaT scans to diagnose many conditions, such as tumors, infections, blood clots, and broken bones. (MayoClinic.com, 2003). A CaT scan also helps in diagnosing some diseases that might otherwise require surgery. For example, doctors can use a CaT scan to guide catheters to an abscess in the body and then drain pus from the infected area.

Computed tomograpy is used for various reasons and include:

Diagnose muscle and bone disorders, such as osteoporosis

Bone disorders are easier to detect than with traditional x-ray technology. Many hairline fractures may now be detected that previously were overlooked, thus possibly causing loss of bone area since it remained untreated.

Pinpoint the location of a tumor, infection or blood clot

Guide procedures such as surgery, biopsy and radiation therapy

Detect and monitor diseases such as cancer or heart disease, and monitor the progression of a disease

Detect internal injuries and internal bleeding

Revolutionized the surgical approaches to the posterior-ethmoid sinuses since the introduction of computed tomography

There are many revolutionary advances in the field of sinus surgical procedures. When the introduction of computer-aided image guidance in 1993, the endoscopic view and the CT view have been united to provide a three-dimensional triplanar perspective to the surgical anatomy, thus allowing computer-aided imaging to become an invaluable aspect of crucial anatomic regions such as the sphenoid sinus (Wagner & Conti, 1991).

They state, "that the sphenoid sinus, located in the recessed position in the skull base and surrounded by a host of vital neurologic structures, may be amenable to image-guided surgery in both primary and revision...

Laterally, the sphenoid sinus is flanked by the cavernous sinus, which houses the oculomotor nerve, the trochlear nerve, the ophthalmic division of the cranial nerve, and the internal carotid artery."
Usually, the sphenoid sinus was accessed by two principal methods being bicoronal craniotomy or a through the nose entry also known as transnasal entry. Both approaches may produce many risks and there are usually expected post-operative problems such as brain retraction and possibly permanent anosmia. However, with the use of computer tomography, "the anatomy of the paranasal sinuses constitutes a complex three-dimensional structure that deserves the accurate spatial representation afforded by computer-aided image-guided endoscopic sinus surgery to avoid surgical pitfalls" (Wagner & Conti, 1991).

Computed tomography exams can be done even if the patient already has a pacemaker or cardioverter defibrillator that has been implanted in the chest to help regulate the heartbeat. Also, if the patient is pregnant or thinks that they might be, their doctor should be informed because it might become suggested to postpone the procedure or choose an alternative exam that doesn't involve radiation. A variety of procedures are also used on healthy people. Many people who are healthy will undergo whole-body CaT scans to detect cancer and other medical conditions in the earliest stages, before any symptoms develop. Early detection is the key to a healthy life.

Cancer screening has also benefited from the use of CaT scans. Wagner and Conti (1991) state that lesions may not appear on traditional scans such as an MRI, and lesions of disparate pathology may also appear similar. The superior image quality, however, ensures that the experience will be sought and that MRI will find increasing use." The data produced by the CaT scan is more accurate thus showing that the biochemical function of the brain can be provided by positron emission tomography and single photon emission tomography. Emissions from radioactive tracers can be utilized to construct an image of where the tracers are concentrated in living tissue. Through the appropriate tracer, detailed information about the location of key biochemical processes may be obtained. These imaging technologies, used to complement one another, will yield information about cancer in its living, dynamic state, and complement the pathological analysis of processed tissue specimens (Wagner and Conti, 1991).

How Does Computer Tomography Work?

Imaginis.com (2000) explains that "computed tomography is based on the x-ray principal: as x-rays pass through the body they are absorbed or weakened at differing levels creating a matrix or profile of x-ray beams of different strength. This x-ray profile is registered on film, thus creating an image. In the case of CaT, the film is replaced by a banana shaped detector which measures the x-ray profile."

The CaT scan is performed in a hospital or an outpatient clinic. The duration of the X-ray imaging may last about 45 minutes to an hour. There are various levels of preparation that must be made in order to prepare for the scan, depending upon the patient's needs. The scan itself may only last up to several minutes. The patient may not have any metal zippers, snaps, and buttons on their clothing that would interfere with the CaT scan. A hospital gown will be worn if the patient's clothing does not comply with the CaT equipment. The patient will lie on a narrow table that moves in or out of the opening of the gantry or front area. The patient is not to move during this time and should become as comfortable as possible for the duration of the procedure; however, the table can be raised, lowered or tilted without any concern. Straps and pillows are provided to help the patient stay in position. During a head CaT, the table may be fitted with a special cradle that holds the head when imaging occurs (Mayo Clinic, 2000).

The table is positioned so that the organ to be scanned lies in the center of the gantry. A tube on the entrance beams X-rays through the patient's body and into special detectors that analyze the image produced. The gantry then rotates around the patient to obtain many images from different angles. The X-ray tube rotates around the body, while the table slowly moves through the opening. While the table is moving, there is a variety of motion taking place. The patient may realize that they might need to hold your breath to avoid blurring the images. The patient will begin to hear clicking and whirring noises and with each rotation, there are many images of thin slices of your body being conducted. The technologist remains in an adjoining room conducting the CaT scan and monitors the images as they appear on the computer screen. The technologist is also…