Computer axial tomography scans are also called CAT scans and CT scans. Starting in the 1970s, this technology became wildly popular as more and more hospitals sought to expand their imaging capabilities. The CT scan was a revolutionary advance over conventional imaging techniques which produced only two-dimensional images. The advance was so astounding that Allan Cormack and Godfrey Hounsfield shared the Nobel Prize 1979 for their work in developing the CT scan.
3-D Imaging
CT scans rely upon a series of X-ray views taken from many different angles. A computer integrates these views to create a sequence of cross-sectional views. These images are put together to create a three-dimensional view of both hard and soft tissues. For example, PhysicsCentral.org reports that modern scanners can "image the entire abdomen and pelvis of most adults, making a total of 80 CT images in less than 30 seconds."
The images can be manipulated by the computer so that the doctor can see precisely the tissues he is interested in. Prior to the CT scan, doctors lacked the ability to see a cross section of a tissue. Longtitudinal X-ray images were all that was available.
Non-Invasive
Since CT scans can detect or confirm the presence of a tumor that could previously only be detected by surgery, they minimize the need for exploratory surgery. Substituting a noninvasive procedure for an invasive one requiring anesthesia provides better patient outcomes. Virtual colonoscopies eliminate the risks associated with conventional colonoscopies.
In addition to supplanting exploratory surgery, CT scans can be used to target treatment more effectively. For example, the National Cancer Institute notes that CT scans can also be used to "plan radiation therapy" and "guide a biopsy" with far more specificity than was previously available.
Soft Tissues
Conventional X-rays had very limited capability to create images of soft tissues. In conventional imaging, bone appears in white, air in black, and soft tissue as grey. It is very difficult and often impossible to distinguish between soft tissues at all. While some radiologists get good at interpreting shadows on X-rays, it's important to remember that these shadows are all they are seeing.
CT technology allows detailed imaging of lungs, kidneys and brains. Cancers can be diagnosed with more certainly because the tumor itself can be imaged.
Resolution
The amount of detail that can be imaged in a CT scan made after 2000 is far greater than conventional X-rays or even CT scans made in the 1970s. According to PhysicsCentral.org, a 1970 CT scanner recorded 6,400 pixels per image. This increased to 256,000 pixels per image in 2001. Not only has the number of pixels increased, but the size of them has decreased. Whereas in 2001, a pixel was 3mm by 3mm, by 2001, pixel size decreased to 0.5mm by 0.5mm.
This increased resolution means that subtle details such as calcification in an artery can be picked up on a CT scan. This is just not possible using a conventional X-ray, which often suffers from high signal-to-noise ratio issues.
Other Techniques
The advantages associated with CT scans have a downside in that CT scans expose patients to a higher level of radiation than X-rays. For this reason, doctors must weigh the benefits of CT scans against radiation risks.
While this remains a concern, the amount of radiation needed for a CT scan has come down since the 1970s. A study reported on June 21, 2010, on MedlinePlus, a publication of the National Institutes of Health, discusses a new software program that effectively cuts the radiation required in half. Implementation of such software could make CT scans safer.
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