Contrast Guidelines / Q&A’s
For a complete overview of current contrast media and other radiological pharmaceuticals administration guidelines per the American College of Radiology, we have included the 2012 Contrast Media Manual.
This is a basic guide to understanding Intra-Vascular Contrast Agents and their use at the Center for Diagnostic Imaging.
When medical imaging studies for cross sectional examinations of the body, (i.e., Computed Tomography (CT), Magnetic Resonance Imaging (MRI) are ordered by referring physicians, a question that frequently arises is – “Do I order this With, Without, or With AND Without Contrast?”
To answer the question, we must first define what ordering “contrast” means, what IV contrast is and what it does, and specific safety issues to be addressed when considering the use of IV contrast agents.
What does it mean when I order an exam “With” contrast?
Ordering an examination with contrast for an MRI or CT study means you are specifying that you want Intra Vascular Contrast (IVC) to be used. As opposed to barium sulfate Oral Contrast Media (OCM), which is chemically inert and is administered parenterally, IVC is administered via IV at the time of the exam.
IVC agents are a regulated drug class, and can be only administered by prescription, just like any other controlled medication, this is why the use of IV contrast must be specified or indicated by the physician ordering the examination. The radiology department may alter the prescribed use of IV contrast per department protocol, radiologist orders, or by other safety concerns, but the initial request for the use of IVC must come from the physician ordering the examination.
What is “IV Contrast”?
Intra Vascular Contrast media (IVC) come in two broad categories, those used for MRI, commonly called paramagnetic contrast agents, and those used for CT or diagnostic radiography, also called iodinated contrast agents.
For MRI, IVC are composed of organically bound gadolinium or iron in solution, and are designed to greatly increase the number of protons available in the region of interest being scanned in MRI, so as to make differences in signal intensity between tissues more readily apparent.
A prime example of this would be in a patient undergoing an MRI of the lumbar spine, where the patient has had a prior history of back surgery or current history of a suspected soft tissue mass. In both cases, the need to differentiate between normal, healthy tissue and that of old scar tissue or neoplasm would indicate the use of MR IVC. If the patient has neither history of suspected mass, nor a history of prior surgery in the region of interest, then MR IVC would not be indicated.
In general, MR IVC should only be ordered for:
- Brain studies where a mass, aneurysm, or other demyelenating process is suspected.
- Spine studies where a para spinal soft tissue mass is suspected, for demyelenating disease processes, and for patients with <10 year pat history of having surgery in the region of interest.
- Vascular studies, such as carotid, renal, or peripheral arteriography.
- Evaluation of soft tissue masses in solid organs, such as the liver, or muscle tissue masses such as rhabdosarcoma.
Routine MRI for spine for pain, radiculopathy, DJD, DDD and the like should be performed without. If need be, IVC can be considered should any incidental findings require it.
Routine MRI for joints should be perform without IVC, as there is usually very good differentiation between tissues within joint capsules, i.e. bone from cartilage, tendons from bone, etc.
For CT scan, IVC is composed of an organically bound iodine / benzene compound in a saline solution, and are designed to make blood and organs more radio-opaque by absorbing a small percentage of X-rays that would normally pass through the body. CT scan images are projected in thousands of shades of gray, whereas the human brain can only discern between 40 and 100 shades. IVC changes the density of tissues, and therefore the perceived image is rendered in what looks to be a more “black and white” image. With increased contrast comes increased visualization between adjacent structures observed in a CT scan image.
A prime example of the use of IVC in CT would be during contrasted studies of the thorax, where there is a need to distinguish between arterial and venous vascular structures of the heart and lungs when looking for pulmonary emboli, or to evaluate blood vessels vs. enlarged lymph nodes in a patient with lymphoma.
In general, CT IVC can be used for any CT study such as:
- Head, neck, and thoracic imaging for suspected mass, lymphadenopathy, vascular injuries such as aneurysm, and CVA.
- Abdomen, Pelvic imaging for same.
- CT angiography, for evaluation of vascular structures.
Routine CT scanning where IVC is not indicated would be:
- Any examination where the patient has a known history of Iodine or IVC allergies.
- Bone or joint imaging.
- Imaging for kidney stones.
- Spine imaging where there is no history of suspected soft tissue mass.
Brands of IVC used at CDI and our safety policy regarding their administration.
CDI uses GE Healthcare’s line of contrast agents for use in the CT and MRI modalities. GE (formerly Amersham) products were selected over all others due to:
- Safety: Omnipaque and Omniscan have been used for nearly 20 years with an unparalleled safety record.
- Patient tolerance: IV administration of Omnipaque, Visipaque, and Omniscan is met with little or no adverse reactions in patients such as nausea, vomiting, or shortness of breath.
- Technical factors, such as Omniscan being the only MRI agent approved for rapid bolus injection, a necessity for MRA, or Visipaque, being the only iso-osmolar contrast agent for CT, making it ideal for cardiac and “routine” CT Angiography studies.
- Omniscan is the paramagnetic, gadolinium based contrast agent used for MRI and MRA applications here at CDI.
Omnipaque and Visipaque are iodinated contrast agents used for CT and CTA applications. Omnipaque is used for routine CT and low volume CTA (Circle of Willis, Carotid) studies, while Visipaque is used for high volume CTA (aortography, lower extremity runoffs), and in patients whose EGFR is between 30 and 50ml/min.
All patients aged 65 and older, and any patient with a known history of renal dysfunction are required to have a recent (<30 day old) serum creatinine in order to establish that the patient has sufficient renal function to clear the IV contrast from the bloodstream without incurring damage to the kidneys.
For any patient that has an EGFR of less than 30mg/ml, for either CT or MRI, the technologist will consult with the radiologist to determine if the requested exam can be performed without IV contrast, or if another imaging modality would be more appropriate.
Patients who are already on dialysis may receive IVC, but we will schedule the exam to be performed just prior to their scheduled dialysis appointment. Dialysis will remove over 93% of IVC agents in the first pass.
There will be NO exceptions to the 30ml/min. EGFR rule without written consent of the referring physician and the radiologist.
For any questions in regards to the use of IV contrast when ordering a contrasted exam, please feel free to contact your CT or MRI technologist. If they cannot answer your questions, they will refer you to a MRG radiologist.
CT / MRI Technologist: 541-472-5154 ext. 105
Medford Radiological Group work center: 541-773-5773