When Do I Need an MRI Study of My Body? A Discussion Guide for Patients and Caregivers

Richard C. Semelka, MD


September 12, 2005

In This Article

Body MRI: What Your Doctor May Not Know

Over the last 20-25 years, the classic approach that referring physicians and radiologists have formulated to decide which imaging modality should be used for which application has been to primarily focus on diagnostic accuracy, ie, how good the modality is at findings abnormalities and describing what they are. Important additional considerations include the cost of the imaging modality and how quickly the study can be done to find out information on the patient's physical condition upon which to base medical management. With the exception of imaging the fetus, considerations of safety generally have not been a major focus. Hence, fetal imaging is performed with ultrasound, which has not been associated with the development of cancer. The safety of individuals other than fetuses generally has not been emphasized either by referring physicians or by radiologists, which reflects in part the lack of information or training of the potential hazards of radiation. This concern has been brought to the fore this year with the first-ever Department of Health and Human Services inclusion that x-rays are acknowledged as a known human carcinogen. In the forward-looking new imaging paradigm, the 2 major criteria for performing a diagnostic study should be diagnostic accuracy coupled with patient safety, with the ancillary consideration of cost. CT is an excellent modality in many settings, but careful thought about its benefits must be balanced against the potentially harmful effects of radiation exposure.[1,2]

In evaluating whether an imaging study should be performed, one can approach it from the classic consideration, which is evaluating diagnostic accuracy, and also check it against the new imaging paradigm, which is diagnostic accuracy and safety. In some organ systems, MRI is overwhelmingly the most diagnostically accurate modality, even without having to consider safety. Prior to emphasizing the potential hazards of radiation, major indications for performing body MRI have been patients with serious allergies or kidney failure, due to the greater safety of contrast agents used by MRI compared with those used by CT.

The liver is the prime example of an organ that, like the central nervous system (CNS, which is brain and spinal cord) and the musculoskeletal system, is much better studied by MRI, compared with CT or ultrasound. MRI should be considered the study of choice for all imaging investigations that are focused on the liver.[3]

Even in the hands of inexperienced radiologists, MRI employing serial postgadolinium intravenous contrast agent is the most diagnostically accurate test. Because MRI is more complicated to perform and interpret than CT, other organ systems may require more expertise on the part of the radiologist to interpret well. In experienced hands, imaging of the pancreas is also better performed with MR than CT,[4,5] but in the setting of limited experience, CT may be a better choice. This same weighing of considerations may also have to be employed for other organ systems for which MRI is superior, such as female and male pelvic organs. Another factor that must be considered is whether more than one region of the body has to be studied at the same time, which is more complex and time-consuming with MRI than with CT.

Imaging territories of the body are generally separated into 3 regions: the abdomen, pelvis, and chest. On an individual region basis, MRI is generally more diagnostically accurate than CT in the abdomen and pelvis, so a combined abdomen/pelvis MRI study seems appropriate; CT, however, is a superior modality for imaging the chest, which explains why many physicians may opt for a CT study, even when optimal-quality MRI is available, if they are studying the chest, abdomen, and pelvis. This also makes perfect sense when the highest likelihood of disease process may be in the chest. An alternative approach that may be used occurs in the scenario of chest disease and liver disease that are approximately equivalent, in which case a chest study with CT and an abdominal study with MRI may be performed.It can be cumbersome for many patients to have to undergo 2 different studies. Therefore, the fact that CT is excellent for the chest and quite good for the abdomen and pelvis is a reasonable argument for studying all of these regions with CT.

The kidneys, adrenal glands, and spleen show slight advantages in diagnostic accuracy for MRI in comparison to CT, and yet CT is often done because the differences are minimal, CT is slightly less expensive, CT studies can generally be acquired sooner, and physicians have more familiarity with CT images. In the proposed new imaging paradigm, many of these patients should undergo MRI. MRI is only marginally superior diagnostically to CT; however, it is safer and therefore should be used preferentially.


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