MR Technology Provides Radiation-Free Imaging of Childhood Tumors

A new imaging approach that searches young cancer patients’ bodies for tumors without exposing them to radiation has been devised that could reduce the children’s’ chance of developing secondary cancers later on in life. The new technique is a modification of magnetic resonance imaging (MRI) that used an innovative contrast agent to find tumors. The MRI-based technology is as effective as cancer-detection scans that use ionizing radiation, specifically, positron emission tomography/computed tomography (PET/CT).

Although whole-body PET-CT technology provides vital data for diagnosing cancer, it has one big downside: A single scan exposes the patient to as much radiation as 700 chest X-rays. This exposure is especially risky for children and teenagers, who are more susceptible to radiation than adults are because they are still growing. Children are also more likely to live long enough to develop a second cancer. “I’m excited about having an imaging test for cancer patients that requires zero radiation exposure,” said senior author Heike Daldrup-Link, MD, associate professor of radiology at Stanford University School of Medicine (Stanford, CA, USA). “That is a big deal.”

The investigators, who published their findings February 18, 2014, in the Lancet Oncology, compared the modified MRI technique to conventional PET-CTs in 22 patients ages 8 to 33 who had lymphoma or sarcoma.

Several obstacles in the past prevented physicians from using whole-body MRI scanning to look for tumors; the scans take up to two hours. A whole-body PET-CT, however, takes only a few minutes and involves capturing PET images monitoring the metabolism of radioactive glucose with CT images. More significantly, in many organs, MRI does not differentiate healthy from cancerous tissue. Furthermore, contrast agents now in use leave the tissues too quickly to be used in a lengthy, whole-body MRI.

To locate tumors using MRI, the researchers used a new contrast agent comprised of iron nanoparticles. Injections of these iron nanoparticles are approved by the US Food and Drug Administration (FDA) to treat anemia, and the researchers obtained FDA permission for the experimental use. The nanoparticles are retained in the body for many days. On MR images, they cause blood vessels to appear brighter, providing anatomic landmarks. The nanoparticles also cause healthy lymph nodes, bone marrow, liver, and spleen to appear darker, making tumors stand out.

The images generated from the research MRI scans provided comparable information to the PET-CT scans that study subjects received as part of their care. The PET-CTs detected 163 of 174 total tumors in the 22 patients; the MRIs found 158 of 174 tumors. The two methods had similar levels of sensitivity, specificity, and diagnostic accuracy. “We were able to find a new way to integrate anatomical and physiological MRI information and make it more efficient,” said Christopher Klenk, MD, a postdoctoral scholar and the study’s lead author.

None of the patients experienced adverse reactions to the iron nanoparticles, though the US Food and Drug Administration (FDA) has previously noted a small risk of allergic reaction to the nanoparticles’ coating. In addition, seldom do patients to have adverse reactions to other contrast agents.

Radiologists at several academic hospitals are looking for ways to reduce children’s radiation exposure, according to Dr. Daldrup-Link, adding that she is sharing the new technique with colleagues in the United States. “Some type of whole-body MRI imaging test is available at many big children’s hospitals right now,” she said, adding that for such techniques to be widely adopted, doctors are asking for evidence that whole-body MRI does the job. “It’s slowly entering clinical practice, but clinicians are cautious and want to be convinced, she added. The other hurdle to wide adoption of MRI-based scanning is lack of a billing code, a drawback the researchers hope will soon be fixed. But there are no technologic obstacles to use of the new technique. “It’s really exciting that this will soon be clinically applicable,” Dr. Daldrup-Link said.

Future studies, according to the investigators, will be done to confirm the MRI-based technology in larger, more diverse groups of cancer patients, as well as to study its possible use for monitoring tumors over the course of cancer treatment. Moreover, the MRI-based strategy has potential for scanning patients after their treatment is complete, when the ability to monitor them without radiation would be particularly beneficial.

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Stanford University School of Medicine