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Computed tomography, or CT, is another technique used to image the heart. CT utilizes radiation to create slices of the heart. If one decides to take a heart, and cut it, the resulting two-dimensional image is called a slice. CT techniques can produce horizontal and vertical slices.
How is CT imaging any different from x-ray imaging? Although both systems use x-rays, CT continually scans the patient at multiple angles. Unlike x-ray imaging, a computer interprets CT information to create a picture of a heart. CT scans utilize a detector array which sends information about the x-ray absorption to a computer. X-ray scans image directly to film without using a computer.
There are many different types of computed tomography. One type is the electron beam computed tomography (EBCT), also called the ultrafast computed tomography. The EBCT creates x-rays using an electron gun. Usually, x-rays are created using x-ray tubes. The EBCT scans create many images within a single heartbeat and therefore decrease the time a scan takes. The EBCT also eliminate other problems associated with regular CT scans. Since the EBCT is so quick, images usually made blurry by the beating of the heart become clear. The EBCT is able to image calcium buildup in the arteries, which can be an indication of heart disease. Another type of CT scanning is called spiral or helical CT scan. Spiral or helical CT scanning provides many of the same advantages as EBCT. Spiral/helical CT is made possible by the power slip ring, which allows continuous scanning of the chest. The data can be used to construct three dimensional representations.
CT scans utilize high-powered x-rays to image the body. CT scans, though, are far more detailed than chest x-rays. CT scans tend to minimize a patient’s exposure to the damaging x-rays with quick scans.
CT is the fastest scanning technique available today. A CT scan can gather thousands and thousands of images in just 12 to 15 seconds. Some models can even image in 5 seconds! CT can measure volume of heart cavities and the ejection fraction, the percent blood squeezed from the heart after a contraction (though not as well as MRI). The CT is the best technique for clear images and qualitative studies.
In the lab...
Radiation Amount: As with x-rays, the radiation exposure is minimal.
Safety Precautions: Almost none. The CT scans do not require extensive abstinence from certain foods or drinks, like other scans. A bismuth medication, such as Pepto-Bismol, should not be taken before a CT scan.
Orientation of Patient: The patient lies down on a sliding bed. The patient is scanned through a doughnut-shaped machine. The machine can be open on both sides. The patient should hold his or her breath while the scanning takes place. Sometimes, a contrast material is injected into the patient’s vessels to allow doctors to visualize the blood vessels better.
Length of Scan: Using the newest technology, CT scanning can be very short. The fastest CT model can image the heart in 5 seconds. Usually, a CT scan takes 12 to 15 seconds.
Computed tomography has only been around for the past 25 years, which means CT is a relatively recent technology. CT also utilizes x-rays.
1972 – Computed tomography is invented by Godfrey Hounsfield, a British scientist.
1979 – The Nobel Prize for medicine is given to Hounsfield and Cormack, another scientist, for the invention of computed tomography.
1980s – CT scanning becomes popularized.
As with x-ray imaging, CT scans use radiation which always poses a risk. The fetus of a pregnant woman is especially susceptible to the dangers of x-rays. The injection of the contrast material can make patients feel uncomfortable or hot. Some patients may have allergic reactions to the contrast materials.