The information obtained can help evaluate whether you are at increased risk for heart attack. Tell your doctor if there's a possibility you are pregnant and discuss any recent illnesses, medical conditions, medications you're taking, and allergies. You will be instructed not to eat or drink anything and to avoid caffeine and smoking for four hours prior to the exam. Leave jewelry at home and wear loose, comfortable clothing. You may be asked to wear a gown. Computed tomography, more commonly known as a CT or CAT scan, is a diagnostic medical test that, like traditional x-rays, produces multiple images or pictures of the inside of the body.
The cross-sectional images generated during a CT scan can be reformatted in multiple planes, and can even generate three-dimensional images. CT images of internal organs, bones, soft tissue and blood vessels provide greater detail than traditional x-rays, particularly of soft tissues and blood vessels. A cardiac CT scan for coronary calcium is a non-invasive way of obtaining information about the presence, location and extent of calcified plaque in the coronary arteries—the vessels that supply oxygen-containing blood to the heart muscle.
Calcified plaque results when there is a build-up of fat and other substances under the inner layer of the artery. This material can calcify which signals the presence of atherosclerosis, a disease of the vessel wall, also called coronary artery disease CAD.
People with this disease have an increased risk for heart attacks. In addition, over time, progression of plaque build up CAD can narrow the arteries or even close off blood flow to the heart. The result may be chest pain, sometimes called " angina ," or a heart attack. Because calcium is a marker of CAD, the amount of calcium detected on a cardiac CT scan is a helpful prognostic tool. The findings on cardiac CT are expressed as a calcium score. Another name for this test is coronary artery calcium scoring. The goal of cardiac CT scan for calcium scoring is to determine if CAD is present and to what extent, even if there are no symptoms.
It is a screening study that may be recommended by a physician for patients with risk factors for CAD but no clinical symptoms. No special preparation is necessary in advance of a cardiac CT examination. You should continue to take your usual medications, but should avoid caffeine and smoking for four hours prior to the exam. You should wear comfortable, loose-fitting clothing to your exam.
You may be given a gown to wear during the procedure. Metal objects, including jewelry, eyeglasses, dentures and hairpins, may affect the CT images and should be left at home or removed prior to your exam. You may also be asked to remove hearing aids and removable dental work. Women will be asked to remove bras containing metal underwire. You may be asked to remove any piercings, if possible. Women should always inform their physician and the CT technologist if there is any possibility that they may be pregnant.
See the Safety page for more information about pregnancy and x-rays. The CT scanner is typically a large, box-like machine with a hole, or short tunnel, in the center. You will lie on a narrow examination table that slides into and out of this tunnel. Rotating around you, the x-ray tube and electronic x-ray detectors are located opposite each other in a ring, called a gantry.
The computer workstation that processes the imaging information is located in a separate control room, where the technologist operates the scanner and monitors your examination in direct visual contact and usually with the ability to hear and talk to you with the use of a speaker and microphone. In many ways CT scanning works very much like other x-ray examinations.
Why it's done
X-rays are a form of radiation—like light or radio waves—that can be directed at the body. Different body parts absorb the x-rays in varying degrees. In a conventional x-ray exam, a small burst of radiation is aimed at and passes through the body, recording an image on photographic film or a special image recording plate. Bones appear white on the x-ray; soft tissue shows up in shades of gray and air appears black.
With CT scanning, numerous x-ray beams and a set of electronic x-ray detectors rotate around you, measuring the amount of radiation being absorbed throughout your body. The scanner will take a set of images and then the table will move axial scan. Sometimes the examination table will move during the scan so that the x-ray beam follows a spiral path spiral or helical scan.
A special computer program processes this large volume of data to create two-dimensional cross-sectional images of your body, which are then displayed on a monitor. CT imaging is sometimes compared to looking into a loaf of bread by cutting the loaf into thin slices. When the image slices are reassembled by computer software, the result is a very detailed multidimensional view of the body's interior. Refinements in detector technology allow new CT scanners to obtain multiple slices in a single rotation.
These scanners, called multislice CT or multidetector CT, allow thinner slices to be obtained in a shorter period of time, resulting in more detail and additional view capabilities. Modern CT scanners are so fast that they can scan through large sections of the body in just a few seconds. Such speed is beneficial for all patients but especially children, the elderly and critically ill. In EBCT, an electron beam is sent to a target ring located around the patient. The beam creates x-rays at the target rings, which radiate through the patient to the detector on the opposite end of the scan tube.
Because the machine has no moving parts, it can acquire as many as 20 images every second—fast enough so that it avoids any blurring caused by the beating of the heart. The technologist begins by positioning you on the CT examination table, usually lying flat on your back. Straps and pillows may be used to help you maintain the correct position and to help you remain still during the exam.
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Electrodes small, sticky discs will be attached to your chest and to an electrocardiograph ECG machine that records the electrical activity of the heart. This makes it possible to record CT scans when the heart is not actively contracting. Next, the table will move quickly through the scanner to determine the correct starting position for the scans. Then, the table will move slowly through the machine as the actual CT scanning is performed. Depending on the type of CT scan, the machine may make several passes. Patients are asked to hold their breath for a period of 10 to 20 seconds while images are recorded.
When the examination is completed, you will be asked to wait until the technologist verifies that the images are of high enough quality for accurate interpretation. For an EBCT scan, you will lie on a table under an arch-shaped scanner. You may remain clothed and your head will not be enclosed at any time.
During the scan, you will be asked to hold your breath at times to help you remain motionless. The procedure takes about 10 to 15 minutes, although the actual scanning time is only a few seconds. Though the scanning itself causes no pain, there may be some discomfort from having to remain still for several minutes and with placement of an IV. If you have a hard time staying still, are very nervous or anxious or have chronic pain, you may find a CT exam to be stressful. The technologist or nurse, under the direction of a physician, may offer you some medication to help you tolerate the CT scanning procedure.
For exams excluding head and neck your head will remain outside the hole in the center of the scanner.
The Current State of Cardiac CT Technology in 2018
The scanner is approximately 24 inches wide, therefore, your entire body will be "inside" the scanner at one time such as with MRI. The levels of radiation are considered safe for adults — there have been no documented side effects from low levels of radiation — but not for a developing fetus.
Your doctor will typically ask you to fast for four to eight hours before the scan. However, avoid caffeinated drinks since caffeine can affect your heart rate. Most people will be able to drive themselves home after the test. You may be given a beta-blocker before the scan.
This medication slows down your heart so that clearer pictures can be taken. Small, sticky discs called electrodes are placed onto your chest to record the scan. The radiology technician inserts an intravenous line IV into a vein so that they can inject the radioactive dye into your arm. You may feel warm or flushed briefly or have a temporary metallic taste in your mouth when they inject the dye. Before the start of the scan, you lie down on a bench, possibly in a specific position.
Cardiac CT Scan | National Heart, Lung, and Blood Institute (NHLBI)
The technician may use pillows or straps to ensure that you stay in the correct position for long enough to get a quality image. You may also have to hold your breath during brief individual scans, which last only 10 to 20 seconds. To start the scan, the technician moves the table — via a remote from a separate room — into the CT machine.
The CT machine looks like a giant doughnut made of plastic and metal. The dye will naturally work its way out of your body.
Drinking more water will help speed up this process. Your doctor or the technician will go over the results with you. Depending on what the images show, your doctor will advise you of any lifestyle changes , treatments, or procedures that need to be done.
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