Diagnostic imaging—magnetic resonance imaging (MRI) and computerized tomography (CT) scans—do not use radiation and allow for superior images of soft tissue structures.
MRI
Magnetic resonance imaging (MRI) is a relatively new imaging study that is widely available in hospitals and outpatient radiology facilities. An MR unit is very similar in appearance to a CT or PET scanner, although there are some differences. MR does not use radiation, and it allows superior images of soft tissue structures, such as the neck.
What to expect
- The MR technologists will give you all the instructions for your MR scan. The total time to perform the MR scan, excluding waiting for your turn on the scanner and registration, is approximately 30 minutes.
- In brief, you will lie on a table and the table will be positioned within the MR scanner's opening. Then, automatically, the machine will move in order for images to be obtained of the entire area of interest. During the procedure, you will hear a knocking sound, which is normal. There is no pain.
- After completion of your images, but before you leave, a radiologist will usually review your images in order to determine if any repeat or extra images are needed. However, do not be concerned if repeat or extra images are performed. Repeat or extra views are frequently necessary, and they do not necessarily mean that the radiologist has found something of concern.
- After completion of the images, the MR technician will release you. As a rule, the radiologist does not review the results with you, but will send a report to your physician.
How do I prepare for the procedure?
- It is very important to inform the technician before the procedure as to whether there is any metal in your body. Because of the powerful magnetic fields created by the MR, only certain kinds of metal can be allowed in the machine. Be sure to tell your doctor and technician about any metal you may have in your body. Only they can decide if it is safe.
- You will be asked to change into a dressing gown and to remove all your jewelry, if you are wearing any. There are two kinds of MRs: contrast and non-contrast. If you are having a contrast MR you will be given the contrast material through an IV placed in your arm.
How is the procedure performed?
You will be led into a room where the MR, a large machine that looks like a giant cube, is housed. You will be asked to lie down onto an open tube attached to the machine and you will be moved inside the cube. The technician will then leave the room and the test will begin. All you have to do is stay as still as possible, so the pictures will be of the best quality.
Will it hurt?
The MR test does not hurt at all, but the machine makes a loud "clanging" noise while taking the pictures. This can be bothersome to some. Some patients, especially those who are claustrophobic, may be bothered by lying still for so long in an enclosed space. Open MRs may be options for these patients, as well as taking some medicine before the test in order to relax you. You should discuss these options with your doctor.
CT scan
Computerized tomography (CT) scans first became routinely used in the 1970s, and the quality of CT images continues to improve.
A CT scan is frequently performed with an injection of a material called "contrast." Before receiving the contrast injection, check with your endocrinologist, nuclear medicine physician, or nuclear radiologist to ensure that you are permitted to receive the contrast. If you are not sure, do not take the contrast.
In most cases, you may assume that your endocrinologist does not want you to be given contrast. Contrast contains large amounts of iodine, which may slow or significantly reduce the uptake of radioiodine by thyroid tissue. This could affect the quality of your radioiodine whole body scan or the effectiveness of your treatment.
What to expect
- Typically, you will not receive any injection. As noted above, if the CT technician or radiologist wishes to give you an injection, make sure that your referring physician has approved this injection.
- The CT technologists will give you all the instructions for your CT scan. The total time to perform the CT scan (excluding waiting for your turn on the scanner and registration) is usually less than 30 minutes.
- In brief, you will lie on a table, and the table will be positioned within the CT scanner's opening. Then, automatically, the table will move in order for images to be obtained of the entire area of interest. There is no pain.
- After completion of your images but before you leave, a radiologist will usually review your images in order to determine whether any repeat or extra images are needed. However, do not be concerned if any repeat or extra images are performed. Repeat or extra views are frequently necessary, and they do not necessarily mean that the radiologist has found something of concern.
- After completion of the images, the CT technician will release you. As a rule, the radiologist does not review the results with you, but will send a report to your physician.
How should I prepare for the procedure?
- You should wear comfortable, loose-fitting clothing for your CT exam. It is best not to wear clothes with metal, like zippers and snaps, as this can affect the images.
- You may also be asked to remove hairpins, jewelry, eyeglasses, hearing aids, and any removable dental work, depending on the part of the body that is being scanned.
- You may be asked not to eat or drink anything for one or more hours before the exam.
Will it hurt?
How is the procedure done?
A small amount of radiation is passed through the patient, and a small X-ray image is obtained and stored on a computer. By performing this same process many times around the outside of the body in a circular motion, the computer obtains an "image-in-the-round" of the body.
Through computer processing, these images allow the construction of highly detailed cross-sectional images of many of the organs and structures in the area. This would be the same if one took multiple little X-rays around a loaf of bread, and then, with computer processing, an image is displayed showing you the details of one of the slices of bread in the loaf. The image of that one slice of bread from the middle of the loaf is a cross-sectional image.
Although this analogy is not completely accurate, it does convey a general concept of how CT scans obtain cross-sectional images. CT scans do use X-rays; however, the amount of radiation is low.
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