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A polarizer (Model IGI.9600, GE Healthcare, Waukesha, WI) is available to polarize about 1200 ml of 3He to about 35% polarization in several hours through a process known as optical pumping and spin transfer. This is about 10,000 times as much polarization as can be achieved using the MRI system alone. These high levels of polarization allow acquisition of images with very high signal-to-noise ratios. When inhaled, the polarized 3He enters areas of the lungs that are ventilated, but is prevented from entering areas of the lungs that are not well ventilated. Using various MRI imaging methods, this process can be used to evaluate lung anatomy and function.

A second GE polarizer (XenoSpin) is capable of producing 1000 ml of 129Xe polarized to 10% in about 60 minutes. This gas, which is also used for lung imaging, offers the capability to perform pulmonary studies with a gas that is more readily available. In addition, 129Xe dissolved in tissue or blood exhibits a chemical shift, so an appropriately designed MRI sequence can be used to study gas transfer between pulmonary gas spaces and the bloodstream.

Imaging Equipment

A 1.5-T MRI scanner (HDx, GE Healthcare, Waukesha, WI) is available for whole body human scanning in the Pulmonary Imaging Center. It was first installed in January 2009 and has since been upgraded to a 60-cm bore. The system has 8 receivers and a variety of radiofrequency transmit and/or receive coils. It is fully loaded with all of the available software applications. It also is equipped with multi-nuclear spectroscopy capability.

A fully-redesigned, revolutionary 3.0-T MRI scanner (MR750, GE Healthcare, Waukesha, WI) containing the latest advances in radiofrequency and gradient coil hardware, receiver electronics, reconstruction engines, and acquisition, processing, and interface software is available for whole body human scanning. The maximum gradient strength is 50 mT/m and the time necessary to achieve this maximum strength is 250 microseconds, for a gradient slew rate of 200 mT/m/ms. The bore diameter is 60 cm. The system is equipped with 32 receivers and is expandable to 128.

A state-of-the-art CT scanner (GE Discovery 750HD, 64 slice volumetric scanner) dedicated for clinical research use is housed adjacent to our MRI facilities to ease multi-modality imaging.

The proximity of these scanners to our polarizer lab is shown in the following detail of our building floor plan.

RF Coils

Several commercial coils for chest imaging are available from Clinical MR Solutions (CMRS). Two transmit receive 1.5T coils, one tuned to 3He (48.6 MHz, panel B in the figure above) and one tuned to 129Xe (17.6 MHz) are used routinely for ongoing clinical research studies of asthma and cystic fibrosis in children and adults. A third 1.5T transmit/receive 3He coil is built on an elliptical rigid birdcage design (panel A above) by Rapid Biomedical. Also, 129Xe coil designed for pediatric imaging at 3.0T is also manufactured by CMRS. This coil is unique in that it has a quadrature transmit/receive capability integrated with an 8-channel proton phased array for high resolution proton imaging of the chest in conjunction with hyperpolarized 129Xe MRI. The 129Xe transmit/receive component of this coil is shown in panel C above.

Hyperpolarized Gas Delivery

For delivery of polarized gas to human subjects, we use the delivery assembly shown in the left panel above. The polarized gas dose is dispensed into the fluoropolymer dose delivery bag through a valve containing no metal parts. The valve attaches to the mouthpiece assembly with a quick-disconnect fitting. The mouthpiece assembly contains one-way valves which allow the volunteer to inhale through the tube to the right of the mouthpiece and exhale through the long tube on the left. The fittings are open when disconnected so the volunteer naturally breathes room air while the team is preparing for the MRI scan. The panel at right above shows two lab members demonstrating the use of this assembly in the MRI scanner. The dose delivery bag is being attached to the mouthpiece assembly, after which the valve would be opened and the volunteer would be instructed to inhale as deeply as possible. When the researcher in the scan room observes that the dose bag has completely collapsed, he or she signals the MRI technologist in the control room to begin the scan.

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