Contrast

CT contrast

There are several CT vascular contrast agents used today, all of which contain iodine. Iodine attenuates x-rays and shows up very bright, or hyperdense, on CT. Contrast is used in conventional contrast enhanced CT and CT angiography. The same contrast agents are used in conventional angiography. Allergic reaction and renal toxicity are the primary safety concerns specific to CT contrast. As always, if there is concern for either, it should be asked if the clinical question can be answered without the use of contrast or with an alternative study. A radiologist would be happy to discuss this with you.

Allergic reactions to CT contrast can range from minor itching or flushing to serious anaphalaxis and airway compromise. A patient who has previously had an allergic reaction is obviously at risk. Other patients with increased risk for allergic reaction include those with other allergies, allergic asthma, debilitated patients, and recent IL-2 therapy. It is often asked if patients with a seafood allergy can be at higher risk for a contrast reaction. It is generally thought that there is no increased risk directly correlated to seafood allergy. If a study needs to be performed with contrast and no alternative is acceptable (ie MRI) a patient with a minor allergy can be pre-medicated and monitored closely for a reaction. Treatment guidelines are available in the "Contrast Corner" (see link at bottom of this page).

Nephrotoxitcity is of concern in certain patient populations. This includes diabetics, those with acute or chronic renal failure, patients on Metformin (this can be held prior to contrast to limit risk), patients with gout, and patients with multiple myeloma. CT contrast is generally contraindicated in acute renal failure unless the reward heavily outweighs the risk and it is understood that the kidneys may never recover from potential damage. For patients with chronic renal failure we use creatinine and eGFR levels to determine which type of contrast can be used if at all. If a patient at risk for contrast induced nephropathy is still to be scanned with IV contrast after discussion with the radiologist, pretreatment with hydration and bicarbonate is often prescribed if time permits. The protocol for pretreatment at UW can be found through the link at the bottom of this page.

Patients with pheochromocytoma are risk of developing a hypertensive crisis after CT IV contrast administration. Blood pressure for these patients needs to be closely monitored prior to, during, and after IV contrast administration.

MR Contrast

There are several formulations of MRI contrast, all of which boil down to the element gadolinium (Gd, atomic number 64). In neuro imaging at UW we use gadobenate dimeglumine, trade name MultiHance. MultiHance is considered to be very safe but patients can still have allergies to MRI contrast. Reactions occur less frequently compared to iodinated CT contrast. Allergic reactions to MR contrast also range from itching to anaphalaxis. Known serious allergies such as anaphalaxis generally contraindicate the use of contrast. If a contrast study is medically necessary in a patient with a minor allergy, pre-treated can often be offered. Nephrogenic systemic fibrosis (NSF) is a rare but serious complication of gadolinium use. NSF leads to fibrosis of skin, joints, eyes, and internal organs. In general, outpatients are considered to be at no to very low risk. Inpatients with renal failure in combination with a serious systemic illness, vasculopathy, or recent major surgery need to be screened very carefully. For patients at risk there will often be a conversation between the radiologist and the patient's physician regarding the medical necessity of contrast and risk factors.