## 3 Results  
A typical time course of various patient's breath parameters during the lung imaging experiment is shown in Figure 4. Directed by a beep signal accompanied with a verbal instruction, a volunteer takes one normal breath of nitrogen to flush his lungs, and right after exhaling it, he inhales 300 mL of the HP gas of about 10% polarization, supplemented by 700 mL of nitrogen to fill the entire lung volume. The breath is held for several seconds to perform imaging experiments. Afterwards three full exhalations are collected to the metalized bag for later helium gas recovery.  
The black vertical lines in Figure 4 indicate the moments when the ventilator valves are switched. After initial breath stabilization, the nitrogen gas is applied (the first line from the left). Next switching corresponds to the application of HP gas. After emptying the HP storage bag, the system switches the valves again to deliver nitrogen, so that the volunteer may continue the inhalation until his lungs are full. At this moment the system opens the valve to the collector bag, to let the volunteer exhale the gas (the third line). After holding the breath for a few seconds and subsequently completing three full respiration cycles, the collector bag is closed (the fourth line), and the ventilation procedure is complete.  
The \({}^{3}\)He signal obtained in a single pulse NMR (Nuclear Magnetic Resonance)experiment as well as the proton image of the phantom showed no interference effects that might have been caused by the presence of the ventilator in the scanner room and its operation. The polarization losses of the helium gas during its transfer from the polarizer to the Tedlar bag inside the pressure chamber of the ventilator turned out to be negligible. They are of the same order as the relaxation during storage of the polarized gas in the container made of such material and placed in a homogeneous magnetic field.  
Typical results of the lung imaging experiments using the high field \({}^{3}\)He polarizer and the ventilator are presented in Figure 5. The volunteer was a healthy heavy smoker, who used to smoke a pack of cigarettes a day for more than ten years. Five coronal and one transversal slices indicate  
Figure 4: Time dependence of the respiration process during the lung imaging procedure. Respiration pressure (y * 20 mbar), respiration flow (y * 2 dm\({}^{3}\)/s), helium pressure (y * 150 mbar), inhalation threshold (y * 20 mbar), and exhalation threshold (y * 20 mbar) are shown in red, blue, black, green, and yellow, respectively.  
generally healthy lung parenchyma together with dark areas representing blood vessels. Slight ventilation defects in peripheral regions can be observed.  
The experiments with the same healthy heavy smoker were repeated after two weeks, and the images shown in Figure 5 were reproducible, confirming their diagnostic value.  
The dark stripes that are observed in the transversal slice are the interesting demonstration of the unique property of MRI using a hyperpolarized gas: The nuclear magnetization in the areas that were addressed in preceding experiments does not recover. This feature can be used to study the long-range diffusion in the lungs and has some potential diagnostic value [25].