Cryogenics for Medical Imaging

Creare is leading the way to making a new lung imaging procedure using hyperpolarized noble gases widely available. An innovative application of cryogenic technology to biomedical engineering promises to make recycling of the extremely rare and expensive isotopes ³He and ¹²⁹Xe possible. This breakthrough will make high resolution images of the lungs and airways economical for doctors to use in treating patients with lung disorders.

It is nearly impossible to make high quality images of lungs using conventional techniques such as MRI or CAT scans due to the very low density of lung tissue. Recent technological advances significantly improve lung imaging, however, by using isotopes of noble gases. These isotopes can be treated so that their nuclear spins are aligned or “hyperpolarized.” Hyperpolarized gas atoms provide an extremely strong MRI signal—five orders of magnitude larger than the protons used in conventional MRI. The gas becomes a highly effective contrast agent for patients who breathe a small amount of hyperpolarized gas, enabling doctors to make images of their lungs with unprecedented clarity. However, the only two isotopes that can be hyperpolarized are ³He and ¹²⁹Xe. These isotopes are extremely rare, and their high cost can severely limit the availability of this procedure.

Currently these rare gases are used only once, then released into the atmosphere as the patient exhales. Creare’s innovation is to collect exhaled breath after an imaging procedure, then separate and purify the imaging gas using cryogenic separation processes. These recycled gas atoms can then be re-polarized and used for imaging over and over again without harm to patients, making this breakthrough technology an affordable diagnostic tool.

Recycling processes must recover nearly all of the noble gas atoms with almost zero concentration of any other gases. Cryogenic separation processes ensure purity since the thermodynamic properties of the noble gas atoms differ from those of the other gases present in exhaled breath. Under the proper conditions of pressure and temperature, the valuable noble gas atoms can be condensed and/or frozen while leaving impurities in the gas phase. Tests in our laboratories have demonstrated that this cryogenic separation approach recovers the noble gas atoms with impurity concentrations of less than ten parts per million.

Creare’s efforts are sponsored by both the National Heart, Lung, and Blood Institute (NHLBI) and the National Institute of Biomedical Imaging and Bioengineering (NIBIB). These efforts culminated in 2003 with the demonstration of a complete, prototype gas recovery system. By recycling the rare gases, we hope to reduce costs by over an order of magnitude and make high resolution lung imaging widely available.