Measuring lung surface-to-volume ratio with MagniXene™

One measure of lung health is the local surface-to-volume ratio, or S/V. Regions with healthy alveolar tissue have a high S/V. If disease, pollution, or smoking has caused tissue decay and erosion, the local S/V in that region should drop.

The solubility of xenon in tissues can be exploited to measure the local lung surface-to-volume ratio S/V. Once dissolved in tissues xenon exhibits a shift in its MR resonance frequency relative to the gas frequency. Consequently lung regions with inhaled MagniXene™ offer two frequency peaks: a gas peak which calibrates the volume under consideration, and a dissolved peak which measures the local surface area. The depth of penetration of the xenon saturating the tissues can be controlled by the timing. We first quench all the signal-producing xenon magnetization dissolved in the tissues, then measure how much has diffused back into the tissues only a short time later. In fact we can perform this measurement at several points in time: the signal strength present after a short time corresponds to a layer of xenon permeating only a thin region of the tissue surface, while measurements recorded after longer times represent a more complete saturation of xenon throughout the septal tissue volume.

Our collaboration has adapted S/V measurement techniques for human validation that were developed elsewhere using animals. We find these techniques to provide precise S/V measurements, and are therefore exquisitely sensitive to lung tissue surface area.