Chronic pulmonary disease is an immense and growing global problem. Respiratory diseases like chronic obstructive pulmonary disease (COPD), and asthma continue to grow in prevalence and healthcare burden, even as we make enormous strides in slowing the advances of other diseases. Why is so little progress being made in treating chronic pulmonary disease? Consider that the primary diagnostic technology used today to diagnose, differentiate and monitor patients, is over 100 years old. Pulmonary function testing is the oldest diagnostic technique still used in modern medicine. Therefore, today a doctor must evaluate his/her patients’ lungs as a “black box” based on exhaled gas flow dynamics and make best guesses about what’s happening within. As illustrated above, hyperpolarized gas MRI can directly visualize a patient’s response to therapy. This technology has the potential to revolutionize how we care for patients suffering from pulmonary disease as well as accelerating the pace with which new therapies can be evaluated through clinical trials.
The power of MRI is in its exquisite ability to generate different forms of contrast that allow visualization of different types of pathology. This is also the case for hyperpolarized 129Xe MRI. In the example above, images have been acquired with diffusion-weighted contrast, which highlights portions of the lung where 129Xe mobility is higher due to airspace enlargement resulting from emphysema. Thus, in addition to imaging the distribution of ventilation, a deeper insight can be gained into lung function by evaluating whether all ventilated areas have healthy microstructure. In the example above, portions of the lung depicted in red are ventilated, but have very likely emphysema and therefore do not contribute productively to pulmonary gas exchange.
Perhaps the most fundamental aspect of pulmonary function is gas exchange – the transfer of oxygen into the pulmonary blood and the removal of CO2. 129Xe possesses unique biological properties that make it ideally suited for imaging pulmonary gas exchange. Xenon is soluble in blood and tissues, and moreover exhibits its signal at a distinct frequency when it is dissolved. Thus, dissolved 129Xe can be imaged separately from xenon remaining in the airspaces. Together this provides a view of pulmonary gas exchange.