Measuring internal body temperatures with an MRI is a novel proposition. But it is not without merit. Reporting in the latest Science, using a process called HOT thermometry, researchers at Duke University have outlined the process of precisely measuring internal body heat by using a conventional MRI machine. The method is reportedly five to ten times more accurate than any current ones. Why is this needed? Well, properly heated cancer cells are more susceptible to radiation treatment and an elevated temperature can also potentiate certain cancer drugs delivered to the region.
From the Duke press release about the work of Dr. Warren Warren, a Duke chemistry professor, and his colleagues:
The Duke group’s approach involves selective detection of what are called “intermolecular multiple quantum coherences (iMQCs)” in hydrogen atoms. Warren said the use of iMQCs is an application of his lab’s 1998 correction of an early “subtle mistake” in the way MRI’s inventors exploited quantum mechanical theory
While MRI theory sees nuclei of hydrogen as miniscule bar magnets spinning in characteristic ways within magnetic fields, it originally ignored certain interactions between those spins, Warren said. “We had to completely rewrite the theory of magnetic resonance to figure out where the mistake was made,” he added.
By incorporating these missing interactions, the Duke chemists refinied both the electronics and interpretation of data from MRI scans to improve heat measurements.
The Duke method exploits three sets of facts: First, water and fat never mix. Secondly, hydrogen atoms in water respond to heat changes but those in fat don’t. Thirdly, water and fat molecules in the body are likely to be positioned within tens of millionths of a meter (or microns) of each other.
Fat and water molecules occurring so close together are subjected to the same magnetic conditions, the Duke chemists reasoned. So the differences between the two types of MRI signals they emit should represent the effect of temperature changes on the hydrogen in water. Calculating the effects of iMQCs — the subtle interactions between atomic spins — further improves the accuracy of the comparison.
“So the difference between water and fat is an absolute magnetic resonance thermometer,” Warren said.
The Duke team’s report notes that the technique has been demonstrated in live rodents, including obese animals whose cells mimic those in fatty breast tissue. Because of fat cells’ effects on magnetic fields, breast tissue cannot be temperature-checked using conventional MRI, the report also noted.
Abstract: Accurate Temperature Imaging Based on Intermolecular Coherences in Magnetic Resonance Science 17 October 2008: Vol. 322. no. 5900, pp. 421 – 424
Press release: Duke Innovations Improve Accuracy Of MRI As Internal “Thermometer”…
Image credit: Wellcome images: Transverse MRI scan of a normal head at the level of the orbits….
