If you’re asking yourself this question, “Can I refuse contrast dye for MRI scans?,” you no longer need to wonder!
The easy answer is of course you can. The better question? SHOULD you refuse contrast agents? In this article, I’ll cover everything you need to know about MRI contrast material.
What is an MRI Contrast Agent?
Intravenous MRI contrast agents do exactly what their name implies: they add contrast (our ability to tell two adjacent things apart from one another such as a tumor in the liver from normal liver tissue – see example below) to MRI images.
Gadolinium, a rare earth metal naturally occurring on Earth, is the element that adds contrast to MRI images and is actually used in ionic form (meaning it’s missing a few electrons and has a positive charge). This is why MRI contrast is often referred to as “gadolinium based contrast agents.”
Gadolinium is a unique element that has ideal properties for MRI, which greatly improves our ability to see abnormalities on MRI scans.
- ‘Our’ refers to radiologists – the physicians who interpret the MRI exams.
- Unsure if you really need an MRI scan or if a CT would suffice? Check out my article CT Scan vs MRI: What’s the Difference? to find out.
Gadolinium agents actually contain only a very small amount of gadolinium and exist as clear liquids. These types of contrast material are administered by injection through a peripheral IV (or occasionally into a joint) and imaging is performed prior to and after the injection of the contrast.
The gadolinium ion is “held” onto by something called a “chelator.” Each different cegfrontrast agent has a different chelator, which is what differentiates contrast agents from one another. Some are “linear” with the gadolinium ion next to it (like a sunset with the sun [gadolinium] sitting on top of the water [linear chelator]) and others are “macrocyclic” with a circular/spherical chelator surrounding the gadolinium ion (the chelator tightly “hugs” the gadolinium). The macrocyclic agents generally hold on to the gadolinium more tightly than the linear agents.
The Different Gadolinium Agents
Gadolinium-based agents are split into three different groups.
Group 1 Agents
- gadodiamide (Omniscan®)
- gadopentetate dimeglumine (Magnevist®)
- gadoversetamide (OptiMARK®)
These are the earliest MRI contrast agents and the least safe. Because of this, they are no longer used as intravenous (IV) agents. These are the contrast agents that led to concerns of nephrogenic systemic fibrosis (NSF), which we’ll cover below.
Group 2 Agents
- gadobenate dimeglumine (MultiHance®)
- gadobutrol (Gadovist®, Gadavist®)
- gadoterate meglumine (Dotarem®)
- gadoteridol (ProHance®)
These are the safest agents and the ones currently used in practice today. They have been associated with minimal, if any, cases of NSF and are considered to be safe, even in patients with chronic kidney disease.
Group 3 Agents
- gadoxetic acid disodium salt (Eovist®, Primovist® )
This agent is one of the newer agents and there currently isn’t enough data to determine the safety at this time. Until that data exists, it will be treated conservatively and only given in patients with adequate kidney function (eGFR >30 mL/min/1.73 m2).
What is the Purpose of Contrast in a MRI Scan?
Everything we do in medicine has an underlying purpose. For MRI contrast, that purpose is to aid physicians, such as radiologists, in identifying pathology – abnormal processes that occur in the human body that can cause symptoms in a patient. Not all pathology causes symptoms (e.g., many cancers cause no symptoms early on, but can be diagnosed with imaging).
The contrast dye makes pathological processes stand out in organs and tissues that would otherwise be invisible or unclear. It aids in the diagnosis of many conditions and is particularly helpful in evaluating cancer, inflammation, infection, and blood vessels.
MRI contrast agents play a crucial role in the diagnosis of many cancers with MRI being used to stage various cancers, guide treatment (surgery and/or chemotherapy), and evaluate a tumor’s response to treatment. MRI contrast agents allow us to make diagnoses that we would otherwise be unable to make.
Are MRI Contrast Agents Safe?
Yes. MRI contrast agents are some of the safest drugs in medicine.
Every doctor, physician assistant, and nurse practitioner is expected to perform a cost versus benefit analysis when ordering an imaging exam. Radiologists and MRI technologists will protocol your MRI scan to see if contrast is necessary. In general, we reserve contrast only for those indications where we expect to see a substantial benefit from the contrast.
What are the Potential Harms of Contrast?
Adverse reactions are uncommon, occurring in 0.7-2.4% of patients and consist of warmth, cold, pain at the injection site, nausea, vomiting, dizziness, tingling, and headache. Most patients do not experience any symptoms.
Similar to CT contrast, the most common issue with MRI contrast is an allergic-like reaction, which is not a true allergy though, for all intents and purposes, behaves like and can be treated like an allergic reaction. These are idiosyncratic, meaning they happen randomly and just because you had one reaction doesn’t mean you’ll definitely have a reaction the second or third time. Reactions are quite rare (~0.15%), mostly mild with hives. Moderate and severe reactions are incredibly rare.
In the past, NSF was an incredibly important harm that was found to be caused by older agents (group 1 agents), which is discussed further below. NSF has essentially disappeared after discovering that it only occurred in patients with very poor kidney function (eGFR < 30 mL/min/1.73 m2). NSF does not appear to occur with the newer agents currently in use.
What is eGFR?
Estimated glomerular filtration rate (eGFR) is a measurement of our kidneys’ ability to filter out waste from the body – it’s a marker of our kidney function. eGFR is measured in mL/min/1.73 m2 – the volume of fluid filtered per minute in a normal size adult with a mean body surface area of 1.73 square meters.
What is Nephrogenic Systemic Fibrosis (NSF)?
NSF is a horrible disease that was caused by “loose” gadolinium escaping from the chelator in older agents. The gadolinium would circulate in patients with significant kidney disease and deposit in soft tissues, frequently skin, and som