MRI offers excellence in detecting bone mets.
What comes to mind when you hear “nuclear”? Some people might think of a nuclear family. Others might think of nuclear energy. For most people, nuclear medicine will hardly be the first expression to pop into their heads. Yet nuclear medicine – which is not yet even 100 years old – continues to offer great potential for detecting very small tumors using small amounts of radioactive material called radiotracers. Radiotracers are chemical compounds that consist of molecules that are preferentially attracted to cancer cells, and are bonded with radioactive isotopes. The small amount of radioactivity can be “seen” on certain kinds of medical imaging.
One application of such isotopes is detecting the early spread of a tumor cancer such as lung, breast or prostate cancer into the bones. Cancer cells that manage to travel to the bones (bone metastasis or bone mets) can lie dormant (inactive) while adapting the resources of healthy bone cells to their own selfish purposes. Once these opportunistic disease cells begin to flourish, the result is damage to the bones leading to breakage or pain. It is therefore important to identify bone mets as soon as possible, since there are various treatments that can minimize trauma to the bone.
The established nuclear imaging modality for bone mets is called bone scintigraphy. To accomplish bone scintigraphy, the patient is given an intravenous (IV) injection of a radiotracer that consists of a radioactive element (isotope) bonded to molecules favorable to collecting in the bone tumors. The radioactivity will rapidly give off radiation, or decay. When it settles in the bone tumor, a special type of camera captures the radioactivity from the decaying isotope. In the resulting skeletal image, bone mets show up as very dark spots.
Scintigraphy is therefore a very important tool for identifying bone mets. Some patients, however, don’t like the idea of radiation lingering in their bodies for the 2-3 days it takes for it to be completely gone. Although the merits of scintigraphy outweigh exposure to radiation, it is a test that is postponed if a woman is pregnant to avoid exposing the developing fetus to radiation; and if a woman is nursing a baby, she will be advised to bottle feed formula for 2-3 days while she pumps the breast milk and disposes of it.
MRI for detecting bone mets
Magnetic resonance imaging (MRI) is a non-radioactive imaging method that is quickly gaining ground as an alternative to scintigraphy. A recent (April 2017) published review of the professional research on MRI for the detection of bone mets in prostate cancer evaluated how well MRI compared with scintigraphy. In fact, the core question was whether MRI could “replace the role of bone scintigraphy.”i The authors reviewed previous studies in which MRI scans done on magnets with a strength of 1.5T or greater were used to detect prostate cancer bone mets. They chose articles that met additional criteria such as using biopsy as a reference standard. They chose 10 studies representing data on a total of 1031 patients. They found that MRI excelled in terms of correctly detecting the presence of bone mets, and accurately identifying the absence of mets (thus avoiding a false positive). When the imaging was done in two or more planes, the degree of accuracy was the highest. The authors concluded, “Contemporary MRI shows excellent sensitivity and specificity for detection of bone metastasis in patients with prostate cancer.”
Thus, if MRI can deliver comparable bone mets detection rates that are comparable to bone scintigraphy – without radiation exposure – it seems inevitable that it will become the preferred method of imaging. The Sperling Medical Group provides detection of bone mets using a powerful 3T magnet. In addition, our Medical Group offers MRI-guided Focused Ultrasound (MRgFUS) for the noninvasive treatment of painful bone mets. For more information, contact the Sperling Medical Group.
iWoo S, Suh CH, Kum SY, Cho JY, Kim SH. Diagnostic Performance of Magnetic Resonance Imaging for the Detection of Bone Metastasis in Prostate Cancer: A Systematic Review and Meta-analysis. Eur Urol. 2017 Apr 12. pii: S0302-2838(17)30273-7. doi: 10.1016/j.eururo.2017.03.042. [Epub ahead of print]
- Bone mets