Inside Radiology

Contrast and Dyes

The best dye is no dye at all. Physicians would rather not use it, but in certain situations it is necessary. Contrast agents provide information that could not have been obtained otherwise. Contrast agents used in radiology run the gamut from dyes that are used to image the stomach and rectum to dyes that can be injected into the spinal canal. Barium is safe. Iodine-based dyes which are the only dyes used intravenously for x-ray, are also safe, but there may be a rare complication or two.

Many questions surround the use of intravenously given iodine-based dyes or so-called IVP dye. The same contrast agent is used for all the CT scans as well. Some of the questions concerning the use of contrast agents include when to use them, which of them to use, and what dosages. The only fact that is uncontested is that sometimes the contrast agents provide physicians with information that they could not have without them and that information is often very important.

How do radiologists use contrast agents? Very briefly, materials of certain atomic numbers interact with radiation in predictable ways. Barium, for example, is very similar to calcium in its atomic makeup and looks dense on an x-ray just like the bones that are made with calcium. So when you put barium into a tube, you can see the outline of the tube, actually, the "inline." Iodine is similar. Not quite as dense, but unlike barium, iodine is intravenously acceptable. By convention, radiologists assign the dense barium and less dense iodine to the whitest parts of the gray scale. Wherever this dye appears in any concentration, it looks white like the bones.

If you have to have an imaging test with a contrast agent, what does that mean to you? First of all, you will have to have a needle inserted into a vein in your arm, hand, or wrist. Then someone will inject the dye. You could have a reaction, even a serious one, rarely do such reactions lead to death.

Below is a frequently asked questions (FAQ) list that answers many questions surrounding the use of contrast agents in radiology.

FAQs

General

1. Why do radiologists need to use contrast agents at all? Contrast agents improve our images and allow us to see things that we might not have seen without them. Dyes do not necessarily make every study better, but they help with many. Remember, we are imaging the body indirectly and need all the help we can get.
2. Is "dye" the wrong word? It's not exactly wrong, but it's not as accurate as contrast agent or contrast material. The word dye conjures up a box of Rit and brightly colored Easter eggs. Also at issue is the word’s homonym, "die." In radiology we like to maintain a more upbeat, optimistic attitude.
3. Who pays for the contrast agent? Guess. You do! Before the days of expensive dyes, way back in the 80s of the last century, the hospitals paid the contrast bills without squawking. After the more expensive dyes were developed, the juggling act began, from the hospital to the insurance company/HMO to the patient. Of course, the situation will depend on your individual circumstances.
4. Do I have any choice over which contrast agent is used? Radiologists are trained to understand dyes completely. Of course, they'll listen to any suggestion. One choice you may have to make is the choice of which iodine-based agent will be used for intravenous injection. See below under FAQs/Iodine.
5. I am supposed to have an imaging test, but now I have a cold. Should I cancel or should I go? A minor cold is not reason enough to avoid radiology. It will not affect the test one iota.
6. The preparation says that I am to take nothing by mouth. Does that include my medications? No. Take your medications with as little water as possible. Take your calcium pills later.

Barium

1. Can't you do anything about the taste of the barium? It's really not that bad (it's better cold). Unfortunately, what is unpleasant about it is what makes it work. It is a lot better than the iodine-based dyes.
2. Barium is used for upper GI series, barium enemas, CT scans. Can it be used intravenously? Never, never, never. Though inert, insoluble barium in the vascular system acts just like a blood clot and can cause very serious damage.
3. Is barium safe? Fortunately, barium is as inert as a substance can be. Except for its slightly unpleasant taste and its propensity to become impacted if left around in the large bowel for a few days, it is the perfect contrast agent. It is also universally well tolerated.
4. Are there any complications to barium? While barium is a terrific agent in the gastrointestinal tract, it is a bull in the china shop when it gets into places it doesn't belong. It is an absolute no-no to inject barium in any form intraveniously. The key issue is to keep the barium inside the GI tube. Barium that leaks into the peritoneal space through a perforation in the stomach or duodenum, or into the sigmoid colon,diverticulitis may be serious, even catastrophic.
5. In these situations are there alternatives to barium? Yes, very good ones. If a perforation is suspected in the upper tract, the radiologist may want to use a water-soluble iodine-based agent. Leakage of this material is of no major concern because it is just reabsorbed back into the vascular system and then excreted by the kidneys; the inert barium would just sit there forever. Similarly, in the large bowel, if a perforation is suspected, the radiologist may choose to use a water-soluble agent rather than barium.
6. Is the barium used for an upper GI (UGI) series and for CT scans the same? Yes and no. It is still barium, but the density is very different. The UGI barium is thick and dense, so it can be seen on conventional x-ray and fluoroscopy; while the stuff used in CT is quite a bit less dense (and easier to tolerate). The thin barium is too thin to be seen well enough on x-rays; the thick barium, on the other hand, is so dense that it confounds the CT scanner and can ruin the image.

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Iodine

1. I am about to have the contrast material injected and need to know if I could really die from this? The tech made it sound awful! Do I really have something to worry about? Not really. The chances that any given patient will have a reaction are very, very small. The reason that technicians make it sound awful is that they are just doing their job in obtaining "informed consent." To do so they needed to inform you about all the risks, which, though alarming, is a better alternative than not informing patients about potential dangers.
2. How much of an ordeal will the injection be? Usually very little, depending on how good your veins are and how skilled the injector is. Generally speaking, most x-ray dyes can be injected through relatively skinny butterfly needles or small plastic tubes (catheters) that are not difficult to insert.
3. What's the most common adverse reaction? Hives are seen now and then in an x-ray department. This urticarial rash is composed of small wheals of skin that are raised and itch. Hives are a very common allergic reaction to any number of things. They may be solitary, in a bunch, or very rarely all over your body. A few hives may not be treated at all, and they will subside by themselves. If they get more widespread, a small dose of antihistamine may be needed. Very, very rarely, epinephrine may be required.
4. Are there different kinds of intravenous dyes? There are many different kinds and different brands. There are two main categories of iodinated dye for intravenous injection, high osmolarity contrast agents and low osmolarity contrast agents, so called HOCA and LOCA, respectively. The HOCA dyes are the older of the two and are inexpensive ($5-$10 per study). LOCA dyes are relatively new on the scene. They are much more expensive ($50 or so per study) but are somewhat better tolerated.
5. I have heard that you can be premedicated with steroids and antihistamines to prevent adverse reactions. Does that work? Yes, there has been work that suggests that premedication may reduce the incidence of reactions. The problem is that a program of premedication is a logistical nightmare for any department, and given the somewhat limited benefit, if any, most do not premedicate.
6. Can I be asked to be premedicated? Certainly. But again, given the safety of contrast agents, especially LOCA, the small additional benefit that premedication affords seems small.
7. If I had a reaction before, is it more likely that I'll have a reaction now? Yes, but much greater for HOCA than LOCA. The problem is that the second reaction can be worse than the first.
8. I am an asthmatic, so can I still have the dye? Guidelines and risk figures vary. Many radiologists are hesitant to use any form of iodinated dye, HOCA or LOCA, in severe asthmatics, such as those who use inhalers several times a day. If a no contrast scan is acceptable, so much the better, or if ultrasound and/or MRI can provide similar information so much the better. If you really need the contrast, we'd have to decide on a case-by-case basis how much you really need the study versus what the risk is to you.
9. I have renal disease, so can I have the contrast? It depends. Iodinated dye is just a bit toxic to the kidneys as it passes through. This is not a major concern if you don't have the dye every other day and if your kidneys are functioning well. Normally functioning kidneys do just fine in filtering the dye and excreting it out through the urine. For kidneys not functioning at their best, however, the additional dye load may be just the thing that tips them over to a point where they stop functioning altogether (renal shutdown). To prevent this circumstance, we push liquids so that the patient is hydrated, and we never give the dye if the lab values suggest significant renal impairment.
10. I take medications, so are there any that interact with the dye? There are a few interactions that require caution. For example, if you are taking glucophage, you must stop taking it a few days before the test. There are guidelines, so you should check with your particular radiology department.
11. Can I die from the injection? The short answer is yes. But you must put this fact into perspective. The chance of having a severe anaphylactic reaction that results in death is extremely rare—less than one hundredth of one percent.
12. Will my personal physician be around if there are any problems? Patients often panic when they find out that their personal physicians may not be in the department when they are going to have a test requiring dye. The fact is that the personal physician may not even be in the hospital when you are having the test. If there is a rare reaction that needs to be dealt with, an organized team of physicians will surface in the blink of an eye.
13. If not my own physician, who would respond to a severe reaction? If there is a rare reaction that needs to be dealt with, an organized team of physicians will surface in the blink of an eye. Some radiology departments are adjacent to the emergency department. But not all departments are so blessed. You should ask about a department's plan for emergencies. Just make sure that a qualified physician is immediately available to provide resuscitation should you have that very, very rare severe reaction.
14. Does it feel different when one or the other dye is injected? Yes, that is often the case: the LOCA and HOCA dyes feel different. As a general rule, patients injected with LOCA feel nothing while those injected with HOCA may experience a variety of unpleasant side effects. Though disputed, it is generally accepted that LOCA is safer to use because of a lower incidence of adverse reactions such as hives and asthma and cardiovascular collapse. LOCA also seems to cause less of the minor but often unpleasant reactions such as the nausea and vomiting. For a more detailed look at how it feels, click on IVP.
15. What dye will they use on me? HOCA or LOCA? The U.S. government provides nothing but the best for its VA hospitals where only LOCA is available. There are many other institutions that follow the same policy. Most institutions follow the guidelines of the American College of Radiology which recommends use of LOCA in some patients but allows HOCA for others.
16. Would it be out of line for me to ask the radiologist what dye he would ask for if he were having the test? No. I would have LOCA in a heartbeat, and I don't resent the question if put nicely. Other radiologists may respond otherwise, but I would think that you should be entitled to an honest answer before you sign an informed consent.
17. Who pays for it? Who foots the bill for the fancy dye varies. It could be you, could be your insurance company, or the hospital. Traditionally, hospitals have been stuck with the bill, but since you pay for the hospitals, I guess you pay for it indirectly.
18. I've been told that my urine will change color from the dye. Is that true? This question comes up because of our use of the word dye. IV dyes used in x-ray are crystal clear going and coming out. Your body will not excrete or secrete any colorful liquids.
19. I have heard that occasionally patients get strange sensations in their genitals from the dye injection. Is this true? It is uncommon, but not unheard of for patients to have a pleasant feeling of warmth in their anal and genital regions. Women, in particular, seem to be prone to this reaction. I can clearly remember an elderly dowager well into her eighties suddenly grinning from ear to ear as though she had just rediscovered an old friend.
20. Will I be able to drive after a contrast injection? Only if you could before the injection. The contrast material should in no way alter your ability to drive. If you are queasy from the injection and the test itself, sit in the department for a few minutes. Ask someone for a cup of water before you head out. If you have had an antihistamine because of a minor reaction, you should not drive home by yourself.
21. Are there delayed reactions to the dye?They are very rare and mostly have to do with small problems at the injection site.
22. If I had a reaction, what do I do? Assuming that the reaction has been treated and subsided, the proper caution is add a note to your records for future reference. You should enter the same caution into your records as well. Some people even wear a dog-tag or bracelet that announces an allergy to iodine.

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