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Can I Eat Before A Ct Scan

by Lyndon Langley
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Can I Eat Before A Ct Scan

Can I Eat Before A Ct Scan

Patients often ask me about eating before testing at the hospital. The general rule is that patients should not eat anything at least six hours before their tests (unless they have been fasting). There is some controversy over this because there are certain types of testing where it may be OK to eat. For instance, most people know that it’s generally OK to go ahead with breakfast on an MRI, as long as you don’t lie down in bed for the duration of the test. But what does this mean when it comes to other types of imaging? What are the rules? Here’s what we do know…
CT Scans – Patients should not eat anything at all at least 6 hours before their test. If possible, however, try to get up right before the test and then sit upright during the test. This will help reduce motion artifacts from food going through the intestines. It will also keep you awake longer since you won’t need to hold yourself upright throughout the entire test. If you absolutely must eat something, make sure it doesn’t contain calcium, such as yogurt or milk. Calcium can cause bloating and gas. You should also avoid greasy and spicy foods. These items tend to slow down intestinal peristalsis (the movement of the bowel wall muscles) which causes smearing of the images and reduces image quality. Finally, you should limit fluids so that they aren’t swallowed accidentally. Try to drink water instead of liquids like soda or coffee. Carbonated drinks can create bubbles in the stomach which can lead to air swallowing during the scan and possibly even vomiting afterwards.
Ultrasound – Some ultrasound procedures require patients to fast for about 4-6 hours prior to the exam. Ultrasounds use sound waves to produce images. Since sound travels faster than light, these sound waves travel faster than food can pass through the digestive system. As a result, food moving through the digestive tract can appear blurred by the time it reaches the end of the colon (ultrasound uses high frequency sounds, whereas X-rays use low frequencies). In addition, ultrasound machines generate heat which makes the small intestine expand. When food enters the expanded small intestine, it tends to hang up and become “stuck.” Food that gets stuck in the small intestine means that it cannot move into the large intestine where it could be digested properly. Also, the stomach fills with fluid during the procedure and puts pressure on surrounding organs, including the liver and spleen. This can cause pain and discomfort. Because of all these risks, patients undergoing ultrasounds should not eat within four hours of the exam.
Magnetic Resonance Imaging (MRI) – Patients should not eat at least eight hours prior to their exams. However, if possible, try to get up right before the test and then sit upright during the test. This will help reduce motion artifacts from food going through the intestines. It will also keep you awake longer since you won’t need to hold yourself upright throughout the entire test. To prevent food from getting stuck in the small intestine, take antacids containing magnesium hydroxide and aluminum hydroxide (such as Maalox) 24 hours beforehand. Magnesium and aluminum bind to fatty acids and thus block them from being absorbed.
Positron Emission Tomography (PET) / Single Photon Emission Computed Tomography (SPECT) – Patients should not eat solid foods for 2 hours prior to their test if they are having a PET scan (this includes both PET and SPECT scans), or if they are having any PET for which intravenous contrast will be injected. Contrast agents used in PET scanning can sometimes cause nausea. Therefore, patients who receive intravenously injected contrast agents should not eat 1 hour beforehand.
Dental Procedures – Patients should not eat 6 hours before dental procedures. Dental procedures involve the injection of local anesthesia which contains benzene. Benzene has been shown to cause cancer in laboratory animals exposed to very small quantities. Although there hasn’t been conclusive evidence that patients actually absorb enough of the toxin to cause harm, it is still best to stay away from food for 6 hours.
In summary, the following are good recommendations for patients regarding eating before various types of tests:
CT Scans – Patients should not eat anything at all at least 6 hours before their test. If possible, however, try to get up right before the test and then sit upright during the test. This will help reduce motion artifacts from food going through the intestines. It will also keep you awake longer since you won’t need to hold yourself upright throughout the entire test. If you absolutely must eat something, make sure it doesn’t contain calcium, such as yogurt or milk. Calcium can cause bloating and gas. You should also avoid greasy and spicy foods. These items tend to slow down intestinal peristalsis (the movement of the bowel wall muscles) which causes smearing of the images and reduces image quality. Finally, you should limit fluids so that they aren’t swallowed accidentally. Try to drink water instead of liquids like soda or coffee. Carbonated drinks can create bubbles in the stomach which can lead to air swallowing during the scan and possibly even vomiting afterwards.
Ultrasound – Some ultrasound procedures require patients to fast for about 4-6 hours prior to the exam. Ultrasounds use sound waves to produce images. Since sound travels faster than food can pass through the digestive tract, these sound waves travel faster than food can pass through the digestive tract. As a result, food moving through the digestive tract can appear blurred by the time it reaches the end of the colon (ultrasound uses high frequency sounds, whereas X-rays use low frequencies). In addition, ultrasound machines generate heat which makes the small intestine expand. When food enters the expanded small intestine, it tends to hang up and become “stuck.” Food that gets stuck in the small intestine means that it cannot move into the large intestine where it could be digested properly. Also, the stomach fills with fluid during the procedure and puts pressure on surrounding organs, including the liver and spleen. This can cause pain and discomfort. Because of all these risks, patients undergoing ultrasounds should not eat within four hours of the exam.
Magnetic Resonance Imaging (MRI) – Patients should not eat at least eight hours prior to their tests. However, if possible, try to get up right before the test and then sit upright during the test. This will help reduce motion artifacts from food going through the intestines. It will also keep you awake longer since you won’t need to hold yourself upright throughout the entire test. To prevent food from getting stuck in the small intestine, take antacids containing magnesium hydroxide and aluminum hydroxide (such as Maalox) 24 hours beforehand. Magnesium and aluminum bind to fatty acids and thus block them from being absorbed.
Positron Emission Tomography (PET) / Single Photon Emission Computed Tomography (SPECT) – Patients should not eat solid foods for 2 hours prior to their test if they are having a PET scan (this includes both PET and SPECT scans), or if they are having any PET for which intravenous contrast will be injected. Contrast agents used in PET scanning can sometimes cause nausea. Therefore, patients who receive intravenously injected contrast agents should not eat 1 hour beforehand.
Dental Procedures – Patients should not eat 6 hours before dental procedures. Dental procedures involve the injection of local anesthesia which contains benzene. Benzene has been shown to cause cancer in laboratory animals exposed to very small quantities. Although there hasn’t been conclusive evidence that patients actually absorb enough of the toxin to cause harm, it is still best to stay away from food for 6 hours.

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