Robarts Research Institute imaging scientists Robert Bartha, PhD, and Nevin McVicar, PhD Candidate, are using a novel MRI technique to show the exact pH in specific areas of the brain. This opens up a whole new way of measuring disease progression and guiding treatment specifically for things like stroke and brain cancer.
“People have developed methods to show relative differences in pH,” said Bartha. “But we are the first to give an actual number to the pH using MRI.”
“Typically MRI is anatomical, but this is now bringing metabolic imaging to the MRI,” said McVicar who is the lead author of the study published in February’s edition of the Journal of Cerebral Blood Flow & Metabolism.
Using mouse models of stroke, Bartha and McVicar applied a unique MRI technique to measure absolute pH in the brains of the mice. By taking a series of MRI images designed to highlight changes in pH and taking the ratio of the signal changes within each pixel, they were able to colour code the brains of the stroke-model mice based on the pH in each area.
Because tissue pH is an indicator of altered cellular metabolism in diseases including stroke and cancer, they believe that this technique will have practical applications to guide both diagnostics and treatment for these patients.
“When you sprint, your muscles build up lactic acid because your muscles can’t breathe. It’s the same with the brain. If the blood flow is cut off, then the pH changes,” said McVicar.
In stroke patients, this can help clinicians to have an exact picture of which parts of the brain are dead or dying and may be able to provide a threshold pH indicator that demonstrates at what point the tissue can be saved or at what point it is too far gone to be salvageable.
In brain tumour patients, they are hoping that by using drugs that modify pH in cancer cells but not in normal brain tissue they will be able to show exactly where the tumour is located in the brain based on the pH. After radiation treatment, it may also help physicians to differentiate between what is a tumour and what is damaged tissue as a result of the radiation.
“One of the hardest things for a radiologist to tell after radiation and chemotherapy is whether or not the bright spot is the tumour coming back, or damage to the tissue from the radiation therapy,” said Bartha. He expects that this technique will clearly show the difference between the two because of the way the pH level will respond to the drug in the tumour cells versus the damaged cells in the brain.
The development of this unique technique began by scanning egg whites at different pH levels in the MRI. Now Bartha’s team is working on moving their studies into human brain tumour patients. They say they couldn’t have gotten to this point so quickly if they weren’t part of the community at Robarts Research Institute.
“The resources we have here at Robarts is key,” said McVicar. A Robarts scientist built specific hardware that they needed for the scanner and the team collaborated with both the Vania and Marco Prado's lab and Susan Meakin’s lab for the stroke and brain cancer models.
“Honestly, we wouldn’t have been able to do this if didn’t have these collaborations in place,” said McVicar. “I would have been stuck with the egg.”