Brain cancer is one of the most difficult types of cancer to treat because different brain tumors respond differently to treatments and it is hard for doctors to predict what will work. Currently, doctors give people an MRI brain scan before treatment and again after treatment to see if the tumor has shrunk. But that whole cycle can take up to three months or longer. Now researchers from the University of Michigan School of Medicine may have figured out a way to predict in just three weeks whether a patient's brain cancer treatment is working by using an MRI machine that measures the flow of water through cells, called a diffusion MRI.

What the researchers wanted to know: Can diffusion MRI be used to predict whether a brain cancer treatment is working?

What they did: The researchers gave 20 patients with brain tumors a diffusion MRI and traditional MRI before they started treatment. Then, after being treated with radiation therapy, chemotherapy, or both for three weeks, they gave the patients another diffusion MRI. They guessed that if the treatment were working, the cell densities near the tumor would change, causing water to flow through those areas faster or slower depending on the type of change. Then, as is standard practice, the patients had a traditional MRI about a month after the completion of their treatment to see if the tumors had changed size.

What they found: The researchers were able to predict, with 100 percent accuracy, which patients would have shrinking tumors (6 of the 20), which would have no change in tumor size (6 of the 20), and which would have growth in their tumors (8 of the 20). Any change in the rate at which water flowed through these areas, as revealed with the diffusion MRI, meant that the tumor was responding to the treatment, says one of the researchers on the project. More water diffusion could mean that the tumor was shrinking, and less might mean that the tumor is swelling, as some tend to before the malignant cells die.

What it means to you: Because brain cancer tends progress rapidly, knowing quickly whether or not a treatment is working can be very important. This finding, if confirmed, could be used to switch patients off an ineffective treatment as well as spare them the nasty side effects of cancer therapies that aren't working. The diffusion MRI technique these researchers used is available on most newer MRI machines, the researchers say, so this technique could be used on current patients.

Caveats: This study used a small number of patients. To confirm the effectiveness of diffusion MRI scans, another study should be done with more participants.

Find out more: The American Cancer Society has basic information about brain tumors.

The American Brain Tumor Association has a more comprehensive guide, a downloadable book available on its site.

Read the article: Moffot, B.A. et al. "Functional Diffusion Map: A Noninvasive MRI Biomarker for Early Stratification of Clinical Brain Tumor Response." Proceedings of the National Academy of Sciences. Published online March 28, 2005.