Currently, ultrasound is the preferred test for thyroid disease. Why do doctors sometimes recommend a magnetic resonance imaging (MRI) test?
Advantages and disadvantages of MRI
The biggest advantages of MRI are the lack of radiation, the high resolution of soft tissues (skin, subcutaneous tissue, muscles, tendons, ligaments, nerves, blood vessels, etc.), and the ability to do multi-directional, multi-sequence scans; with new technology, it is even possible to determine the blood supply and cellular metabolism within tumor tissue.
Thus, it can objectively and accurately show the morphology, borders, and signal changes of thyroid nodules that are different from normal thyroid tissue, in addition to better determining the extent of nodal invasion and lymph node metastasis.
Magnetic resonance is not dependent on iodine contrast and can be used in people who are allergic to iodine.
However, MRI is not as good at showing nodal calcification, blood flow within and around the lesion: it is not as good as B ultrasound for blood flow and CT for calcification, and because the thyroid is attached to the trachea, breathing and vascular pulsation can produce artifacts that may reduce image quality.
Therefore, magnetic resonance alone is not as diagnostic as ultrasound for thyroid nodules.
When does your doctor recommend an MRI?
MRI is not a routine test, but it has its place.
If your doctor suspects that a nodule is malignant and is ready for surgery, an MRI is usually needed to accurately assess the size of the nodule, surrounding tissue invasion, airway compression, extent of tumor growth behind the sternum, and metastases to the lymph nodes in the neck to assist in the surgical planning.
When used for preoperative evaluation, both CT and MRI are options, but MRI has a higher resolution of soft tissues and has better diagnostic value than CT for specific conditions (eg, tumor invasion of the pharynx, larynx, blood vessels, anterior cervical muscles, spine, etc).
In addition, if CT cannot be done because of allergy to contrast or concern about radiation damage, or if CT resolution is not sufficient, MRI may be an alternative.
Who should not have an MRI?
An MRI is usually safe for most people, but because of the strong magnetic field that MRI generates, it cannot be done if there are metal implants in the body, such as fixed dentures, metal stents, pacemakers, steel plates, and steel nails. In addition, patients in early pregnancy, suffering from claustrophobia, and critically ill patients with poor vital signs are not suitable for MRI.
Co-written by Dr. Yiming Cao, Cancer Hospital of Fudan University