According to the report from the institute, the method uses a standard magnetic resonance imaging, or MRI, protocol to monitor changes over time in tumour blood volume within individual voxels of the image, rather than a composite view of average change within the tumour. This parametric response map allowed researchers to see specific areas in which tumour blood volume increased or decreased, that may have cancelled each other out when looking at the changes as an average.
Results of the study appear in the advance online edition of Nature Medicine.
"What we have potentially is a generalized analytical approach that we can use to quantify treatment intervention in patients," says study author Dr. Brian Ross, professor of radiology and biological chemistry at the U-M Medical School and co-director of the Molecular Imaging Program at the U-M Comprehensive Cancer Center.
The researchers looked at 44 people with high-grade glioma, a type of brain tumour, who were treated with chemotherapy and radiation. Each participant underwent MRIs before treatment, and one week and three weeks after starting treatment. The researchers then looked at the relative cerebral blood volume and the relative cerebral blood flow of the tumour to analyze voxel-wise changes among the serial scans.
Looking at standard comparisons using averages, the scans indicated no change one week and three weeks into treatment. But, using the parametric response map approach, the researchers were able to show changes in the tumour's blood volume and blood flow after one week that corresponded to the patient's overall survival.
"We're seeing treatment response earlier into the treatment, and responses that couldn't be detected at all looking at average changes. We could detect this after just one week, which is amazing for brain tumours," says study author Dr. Craig Galbán, assistant professor of radiology at the U-M Medical School.
High grade gliomas have a high mortality rate, with people surviving only an average of 12 months after diagnosis. Typically, patients receive six to seven weeks of treatment, followed by a traditional MRI scan six weeks after completing therapy to determine if the tumour shrank. If the cancer did not respond to the treatment, a new approach may be tried.
The researchers believe this approach might also be useful with other imaging techniques such as PET and CT scans.