Though CT scans and MRI scans are often ordered for the same reasons, intravenous contrast affects MRI examinations much differently than CT scans, so the indications for contrast MRI examinations are different from the indications for contrast CT scans.
It is safe to assume in most cases that a non-contrast MRI is a very effective evaluation for most body organs in most situations and with most patients, though contrast MRI can be helpful in some specific situations. Contrast should be considered for most CT scans.
MRI has naturally superior contrast to CT scans. A CT scan without contrast may miss more than one half of the pathology in many body organs. However MRI detects most pathology within most body organs without intravenous contrast and in some cases pathology may be less visible on a contrast MRI than on the non-contrast part of the MRI study whereas pathology is almost always more visible on a contrast CT than a non-contrast CT.
The main usage of intravenous contrast in MRI is in the detecting of benign or malignant tumors and for the staging of tumors of the central nervous system and major body organs. Bone tumors are often less visible with contrast on MRI examinations.
Though stroke can be diagnosed with a contrast MRI, there are specific MRI pulse sequences that are of greater sensitivity for stroke diagnoses without contrast. The main reason for ordering a contrast MRI in a stroke patient is to rule out a brain tumor or aneurysm. After those unexpected diagnoses are ruled out, a stroke patient can be successfully followed with non-contrast MRI.
Benign and malignant pituitary disease requires intravenous contrast for MRI examination. Acoustic neuromas, central nervous system aneurysms, vascular malformations, and causes for seizures are more completely evaluated with contrast on MRI examinations. Meningitis can benefit from contrast MRI in diagnosis and follow up.
Sports injuries, work related injuries, and back pain do not require intravenous contrast MRI examinations and intravenous contrast usually adds nothing to the examination. There has been some research regarding some specific uses of intravenous contrast for sports injuries, but the vast majority of cases can be completely evaluated without intravenous contrast.
Multiple sclerosis can be easily detected and followed without contrast. Detection and follow up of multiple sclerosis has historically been a common reason for ordering contrast MRI examinations. However experience over many years of MS patient follow up has found that contrast is of very limited use in MS, mainly to rule out an unexpected tumor or aneurysm.
Back surgery that was performed over one year prior to a patient’s symptoms does not require a contrast MRI. A patient with new or recurrent back problems days, weeks, or a few months after back surgery can benefit from MRI intravenous contrast to differentiate between contrast enhancing surgical scar and a new or recurrent non-enhancing disk herniation. However surgical scar enhances with contrast for only a limited of time after surgery, making intravenous contrast useless after a period of time.
Osteomyelitis does not require intravenous contrast for an MRI examination. Many of these patients are diabetics or have other major multi-organ diseases. Intravenous contrast in some cases may be harmful to these patients since they may have undiagnosed kidney disease which is the most common cause of side effects to intravenous contrast. Osteomyelitis is usually less visible on intravenous contrast images in MRI.
Podiatrists may desire a contrast MRI of the foot to rule out a neuroma or other tumor of the foot. Though contrast may be helpful in these cases, most tumors of the foot do not enhance with contrast and are effectively diagnosed without contrast.
One reason that intravenous contrast may be less helpful for MRI examinations is that enhancing lesions on an intravenous contrast MRI present as increased signal intensity on T1 images, causing “bright spots” on the MRI. However most pathology on T1 MRI is diagnosed as low signal intensity, causing “dark spots” on the T1 examination. Therefore, the brightness of contrast in MRI can increase the brightness of a dark spot, making that dark spot less visible. An intravenous contrast MRI is helpful only if it makes a lesion much brighter than normal body structures. Unfortunately some lesions are just made “less dark” on T1 MRI, so are less visible.
Congratulations if you have read this far through a long article. The conclusions are the same as detailed at the beginning of the article. Most MRI examinations are excellent without IV contrast and can be ordered with confidence. Intravenous contrast can be very helpful for a few specific indications listed above.
by: Scott Wiedenmann, MD
Copyright A1 Imaging Centers, LLC 2013