What is CT?
Computed Tomography(CT), also known as CAT scan, uses a limited beam of x-ray to obtain image data. The data is then interpreted by a computer to show cross sectional images of the body tissues and organs. Dense tissues, such as bones, appear white in the pictures produced by a CT scan. Less dense tissues, such as brain tissue or muscles, appear in shades of gray. Air-filled spaces, such as in the bowel or lungs, appear black.
What does the CT scanner look like?
The CT scanner has a large opening in which a table moves up and slowly through. As the patient moves through the large opening, an x-ray tube rotates around the patient obtaining images, which are then sent to a computer for interpretation.
How should I come prepared for my CT?
Clothing should be free of metal in the region being scanned. For example, for scanning of the chest shirts should have no metal buttons and bras should have no metal clips or clasps. For scanning of the pelvis pants should not have zippers or metal buttons. You may also be asked to remove jewelry, hairpins, hearing aids, removable dental work, body piercings, or any other metal in the region being scanned. Correct attire is available with private changing rooms and secured lockers. You may also be asked to refrain from drinking or eating anything 1 hour or longer before your exam. Women should inform their physician or the technologist if there is a chance of pregnancy.
How long will my CT examination take?
Allowing for paperwork and patient care time the entire process will take an average of 40 minutes. In most cases the actual time to obtain the CT images can be done in 10 to 30 seconds. The quick scan time allows us to gather information without the chance of voluntary or involuntary motion, which can degrade the images.
Who interprets my CT examination and how do I get the results?
The radiologist on-site at AMI will interpret the CT exam. A radiologist is a physician who specializes in using CT and other radiologic examinations for the detection of abnormalities of the internal organs and bone structures. A signed report with the radiologist interpretation will then be available to your physician 24 hours after your exam. Your physician's office will inform you about how to obtain your results.
Contrast agents used in CT
There are two commonly used contrast media in CT. One commonly used contrast to opacify the GI tract (stomach, small bowel, colon) is barium sulfate. This is usually taken orally, but can be administered-in some cases-rectally. The volume of CT barium sulfate to be administered will depend on the degree and the extent of contrast required in the area under examination. Your physician will inform you of the amount and the time to drink your contrast when the exam is scheduled.
Another contrast medium that contains iodine is often injected into the blood intravenously (IV) during the scan. This contrast makes blood vessels and other structures or organs more visible on the CT images. It may also be used to evaluate blood flow, detect tumors, and locate areas of inflammation. Intravenous contrast material is often used to obtain images of the brain, chest, abdomen, and pelvis; an oral contrast material is commonly given for an abdominal and/or pelvis CT scan. Contrast material may be injected in to the area around the spinal cord (intrathecally) for spinal scans.
Before the administration of IV contrast the technologist will ask the patient if they have any medicine or iodine allergies. A patient who has allergies is at higher risk of allergic reaction with the administration of IV contrast. If the patient is over 65 years of age and is having a CT exam with IV contrast, we require lab test to evaluate kidney function within the last 30 days. Poor kidney function could cause potential problems in the elimination of the IV contrast from the patient's body. At the time your physician's office schedules the appointment, they will inform you if you need lab work.
Exams commonly performed in CT (Click exam type for a definition and example of the images)
One of the most classic applications for CT and 3D imaging is the evaluation of musculoskeletal trauma. CT can aid in the assessment of indeterminate fractures on plain x-ray films or aid in determining the extent of injury to allow for surgical or non-surgical planning. We are able to produce 3D imaging without additional radiation exposure to the patient. CT also is a valuable tool in evaluating disease process such as arthritis, degenerative joint disease, and oncologic applications.
CT of the Abdomen is done to evaluate for disease in the tissues and organs of the abdomen. CT abdomen demonstrates organs or tissue in the upper abdomen such as liver, kidneys, spleen, and pancreas. CT is often the preferred method for diagnosing many different cancers and inflammatory processes. In cases of acute abdominal distress, CT can quickly identify the source of the pain. To better visualize the vessels and organs in the abdomen a contrast material is given intravenously (IV) in most cases. To aid in the visualization of the stomach, small and large bowel a patient may receive instructions to drink oral contrast an hour before the procedure.
CT of the spine is performed to evaluate the vertebral column. The adult vertebral column consists of 26 bones separated into 5 regions. First the cervical or neck region, which usually consist of 7 vertebrae, thoracic or middle region which consist of 12 vertebrae, and the lumbar or lower region which usually consist of 5 vertebrae, 1 sacrum made up of five fused vertebrae, and 1 coccyx “tailbone” is a fusion of 4 coccygeal vertebrae. CT images can be reconstructed to show many different angles of the spine. Intervertebral disc are located between the adjacent vertebrae. These fibrocartilage discs form strong joints and absorb spinal compression shock. Spinal CT is frequently used to detect spinal damage in patients who have had injuries, helpful in evaluating the spine before and after surgery, and can help detect various types of tumors in the vertebral column. To better look at the spinal canal CT may be used in conjuntion with a myelogram.
CT of the neck is done to evaluate for disease in the soft tissues of the neck. The exam is commonly done with intravenous (IV) contrast. The contrast material will show vascular structures within the neck.
CT of the Sinuses is used to evaluate the paranasal sinuses, which are, air filled cavities located in the facial region. CT demonstrates thickening of membranes, which cover the air filled cavities, and help to diagnosis sinusitis or inflammation caused from chronic infections. Ct of the paranasal sinus is a quick patient friendly exam.
CT of the head is performed to give the physicians a more detailed look at the brain and skull then plain x-rays. CT assists in the diagnosis of stroke, brain tumors, head injuries, and other brain diseases. It has the ability to show bone, soft tissues, and blood vessels on the same image. Head CT may be scanned with or without intravenous (IV) contrast depending on the patient's symptoms. The use of IV contrast is per the order of the physician.
Computed Tomography Angiography (CTA)
CT angiography or CTA is an examination to visualize blood flow in the major arteries throughout the body. An iodinated contrast is injected through a peripheral vein instead of an artery like in conventional catheter angiography. Scans are obtained in a quick and timely manner to help diagnose conditions such as aneurysms, pulmonary embolisms, and renal artery stenosis.
Exams commonly performed with CTA (Click exam type for a definition and example of the images)
CTA of the aorta brings oxygenated blood to all parts of the body. The largest artery in the human body, the aorta originates from the left ventricle of the heart travels through the chest down through the abdomen and divides into two vessels in the pelvis. The aorta brings oxygenated blood to all parts of the body. The aorta can be described in sections the ascending aorta which arise from the left ventricle upwards to the arch of the aorta to the descending aorta which goes downward to the chest and abdomen area.
CTA of the abdomen/renal arteries branch off the aorta and supply the kidneys with blood. Constriction or narrowing of the renal arteries (stenosis ) can be a cause for hypertension in certain patients and can be corrected. CTA of the renal arteries is a fast and accurate exam.
CTA of the chest/pulmonary arteries is used in the diagnosis of Pulmonary Embolism an obstruction or closing of the pulmonary arteries. The pulmonary arteries carry deoxygenated blood from the heart to the lungs. It occurs when a blood clot from the leg or vein in the pelvis are carried upwards towards the lungs. This is a serious but treatable condition.
At the base of the brain, the carotid and vertebrobasilar arteries form a circle of communicating arteries known as the circle of Willis. From this circle other arteries -- the anterior cerebral artery (ACA), the middle cerebral artery (MCA), the posterior cerebral artery (PCA) - arise and travel to all parts of the brain. Posterior Inferior Cerebellar Arteries (PICA). Because the carotid and vertebrobasilar arteries form a circle, if one of the main arteries is occluded, the distal smaller arteries that it supplies can receive blood from the other arteries (collateral circulation).