MRI with Nanoparticles Detects Tiny Tumors

Specifically designed nanoparticles can reveal very small tumors that are invisible by ordinary measures of detection, according to a new study.

Investigators have shown that tiny human melanoma tumors growing in mice--indistinguishable from the neighboring tissue by direct magnetic resonance imaging (MRI)--could be "lit up” and easily detected as quickly as 30 minutes after the mice were injected with the nanoparticles.

"One of the best advantages of the particles is that we designed them to detect tumors using the same MRI equipment that is in standard use for heart or brain scans,” remarked Gregory Lanza, M.D., Ph.D., associate professor of medicine at Washington University School of Medicine (St. Louis, MO, USA), and senor author of the study.

The effectiveness of the technology will be assessed in clinical trials in approximately one and one-half years. The spherical nanoparticles are a few thousand times smaller than
the dot about a typewritten i; however, each can carry approximately 100,000 molecules of the metal used to provide contrast for the MR images. This creates a very high density of contrast agent, and when the particles bind to a certain region, that site glows brightly in MRI scans.

In this study, MRI captured tumors that were only a couple of millimeters wide. Tiny, quickly growing tumors cause growth of new blood vessels, which then feed the tumors, a process called angiogenesis. Nanoparticles are very useful since they are so adaptive, according to Dr. Lanza. "We can also make these particles so that they can be seen with nuclear imaging, CT [computed tomography] scanning, and ultrasound imaging,” said Dr. Lanza.

Utilizing nanoparticles, drug doses could be much small than those commonly used in chemotherapy, making the procedure potentially safer. The nanoparticles may also allow for more effective follow-up since clinicians could use them to decipher whether a tumor was still growing after chemotherapy or radiation therapy. The scientists believe the technology should work for most solid tumors, because all tumors must enlist new blood vessels to attain nutrients as they grow.

Melanoma has a horizontal stage, when it metastasizes across the skin surface, and a vertical stage, when goes deep into the body and grows rapidly. "With the nanoparticles, we believe we would be able to see the smallest melanoma tumors when they are just large enough to begin new blood vessel formation,” said Dr. Lanza. The researchers published their findings in the March 2005, issue of the journal Magnetic Resonance in Medicine.