Common Questions and Answers
> About Contrast Materials
> About CT scan Diagnostics
> About CT Scans and Pacemakers
> About CT Scans and Radiation
> About Whole-Body CT Scans
About Contrast Materials
Q1: I have a posterior cervical mass. I am very concerned about getting a CT scan, because I was told that they will most likely inject "dye" or contrast material. What are the odds of it affecting me? Do most patients get ill from it? If so, what kinds of symptoms do they experience?
A1: The vast majority of people have no adverse reaction to the contrast material used during CT scans. You are most likely one of them. When contrast material is injected, you may feel a fleeting sensation of warmth and get a metallic taste in your mouth, but these are harmless symptoms. Also we use the term contrast agent or contrast material to refer to the substance that is injected rather than the term "dye." It is a clear colorless fluid. Dyes, by definition, have a color to them.
In very rare cases, people develop an allergic reaction to contrast material which can consist of nausea, vomiting, and/or shortness of breath. All symptoms should be reported to the technologist monitoring the examination.
Q2: I had a CT Scan two days ago. I drank 3 glasses of what I believe was diluted iodine and was given an IV with another tracking substance at the time of the scan. Yesterday evening, I began to have diarrhea. It has continued today. I have done nothing different from my normal routine and have not eaten anything unusual. Is the diarrhea most likely a side effect of the formula I was given?
A2: Yes, the diarrhea is most likely a harmless side effect of the iodine solution that you drank prior to the CT examination. The iodine solution is thicker than water. We also use a solution containing barium that may not cause diarrhea. The iodine solution makes the bowel show up more clearly on the CT images, so that it can be more easily differentiated from other organs in your abdomen. Therefore, the fluid tends to remain in your bowel rather than being absorbed by the body. The presence of extra fluid in the bowel may cause diarrhea. This type of diarrhea is usually very mild and should resolve within a day or two, after all the iodine has been excreted.
Q3: What would happen if contrast material "leaked" from the injection site? For example, if the IV needle was not in the vein properly, and the contrast material was injected into the surrounding tissues of the hand or arm—how would it affect the nearby tissue? How could it affect the rest of the body? Are there any long-term effects? Could the patient still have the CT scan done that same day, or would it have to be rescheduled?
A3: Although such a case is extremely rare, it is possible that an IV needle may not be optimally located within the vein or may become dislodged when the patient lies down on the examination table. When the contrast material is injected during the exam, it leaks into the surrounding tissue (a process called "paravasation"). Paravasation maybe painful. If this occurs, please notify the technologist immediately. It may require treatment.
Even if a full dose of contrast material is injected into the tissue surrounding a vein, however, long-term damage is extremely unlikely to occur. Usually the contrast material is fully absorbed by the body within a day without any residues.
Normally there is also no need to reschedule the examination. It can be completed on that day.
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About CT Scan Diagnostics
Q1: Can CT be used to diagnose Parkinson's disease? Is it typically used?
A1: CT is not used to diagnose Parkinson's disease. In Parkinson’s disease, a certain type of cell found in the brainstem degenerates over time. The changes associated with Parkinson's disease are too subtle to be seen on a CT scan. Parkinson's disease is usually diagnosed based on clinical assessment by a neurologist, not based on images of the brain.
Q2: Following a pelvic CT scan, my mother-in-law was told that two nodules in her lower left lung are metastatic cancer. Is it possible to make such a specific diagnosis based on a CT scan?
A2: A CT scan is an extremely accurate tool for exploring a patient’s body. You are correct, however, to question the diagnosis. These two nodules in the lung, found unexpectedly on a CT scan of the abdomen and pelvis, could be anything. They could indeed represent metastatic disease (cancer that has "spread" to a new location). It is even more likely, however, that the nodules are just benign residues of a small, localized pneumonia.
The only way to be sure is to have further tests. Your doctor may want to check for any cancer somewhere else in the body. In general, we recommend, a full CT scan of the lungs be performed after three months to determine if the nodules are growing. If they have not grown, they most likely represent benign changes.
Q3: My sister died of stomach cancer. She had endoscopy and a CT scan but neither of these tests showed any tumors. I saw the ultrasound of the cancer all in her abdomen when she was diagnosed. When she was operated on just days before her death, her disease was confirmed that cancer filled her abdomen. Why had the CT scan not shown any disease?
A3: We are sorry to hear of your sister's death from stomach cancer. There are many possible explanations why the CT scan had apparently shown no tumor, but when she was explored at surgery, there was tumor present. One explanation might be that CT scans may not detect some tumors that involve the inner lining of the abdomen, called the "peritoneum." We are working on ways to improve our ability to detect cancer in that location. PET scanning may be one such solution, and now we can obtain images that combine PET scanning and CT together, called "PET/CT." Your testimony will be remembered as we strive to research better ways to detect cancers.
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About CT Scan and Pacemakers
Q1: Can a person who has a pacemaker have a CT scan?
A1: CT scanners use X-rays to generate images; a person who has a pacemaker can undergo a CT scan safely.
Another type of imaging, a technique called Magnetic Resonance Imaging (MRI), uses a strong magnetic field to generate images of the human body. The magnetic field generated by the MRI machine can interfere with a metallic pacemaker. People with pacemakers should not even get close to an MRI scanner.
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About CT Scan and Radiation
Q1: My toddler (20 months old) came down with a stomach virus. Within an hour or so of first showing symptoms, he was slumped in his car seat with his eyes rolled back; he was unresponsive. I immediately took him to the emergency room, where he quickly came around. The doctors checked him out carefully, and everything was normal. A CT scan was obtained as part of the examination. I am glad he was examined thoroughly, but I have heard that CT scan in children may be related to the development of cancer later in life. Should I have not allowed them to take a CT scan of my child? I did ask if the level of radiation was reduced for children, and they told me that it was. What information can you provide on this subject?
A1: CT images are generated using a special X-ray technique. Therefore, there is a certain level of radiation involved. For a routine CT scan, the level of radiation to the patient is about four times higher than the normal annual radiation dose from natural sources (sun, soil, food, water) to which the patient is exposed. The level of radiation can be adjusted based on body size, so that only the amount of radiation necessary for getting an accurate image is used.
At large academic centers, like ours, special care is taken to keep the radiation dose to an absolute minimum for all patients. We use only what is necessary to get a clear picture and make an accurate diagnosis. The level of radiation is adapted to patients with a smaller body size, children in particular. As a cutting edge radiology department, we use only state-of-the-art CT scanners that work with a fraction of the radiation dose of older machines.
It is known that high levels of radiation may cause cancer. It is highly unlikely that the level of radiation used for a CT scan would cause cancer at some later date. If a doctor thinks that a CT scan is necessary to rule out a serious injury or disease, there is usually a good reason for it. It can be very dangerous to delay the diagnosis of a serious injury or illness. You are at much greater risk of causing permanent damage by not getting the proper diagnosis than by sustaining a one-time exposure to the radiation of a CT scan.
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About Whole-Body CT Scans
Q1: A few weeks ago, (a popular TV talk show) featured the whole-body CT scan as a general health exam. In her discussion, the talk-show host said that the CT scanner they used for the exam is fairly new and that there are only about seven of them around the US. Can you tell me if this is the kind of machine you have? I would like to know what hospital in my area might have one—could you tell me where to find that information?
A1: The type of scanner used for the whole-body CT scan is a “multidetector-row CT scanner.“ We have six scanners of this type at Brigham and Women’s hospital. The real advantage of this scanner type is its speed. It collects data so quickly that the entire body can be scanned—with very good image quality—while the patient holds his/her breath. These scanners help doctors provide fast and accurate diagnoses to injured or critically ill patients.
Some use this newer scanner to sell full body investigations to healthy people, calling the procedure "full body screen", "wellness imaging", "health scan" or something similar. There is no evidence that this kind of investigation has a beneficial impact on the health or life expectancy of people that undergo the test. Most things that are found on such a scan are meaningless to a person’s overall health and only serve to generate anxiety or to prompt additional, potentially dangerous tests. There is scientific evidence that CT scans of the colon (“virtual colonoscopy"), the lung (“lung cancer screening"), and the heart (“coronary screening“; "coronary calcium screening“) may be beneficial for healthy people who are at an increased risk for getting a particular disease (colon cancer, lung cancer, heart attack). These kinds of focused tests are therefore offered, some on an investigational basis.
It is also important to remember that a full body CT scan is not a "free lunch.“ CT examinations do involve radiation. And though it is a relatively low dose, radiation should only be used when necessary.
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This page was last modified on 10/19/2011