In Germany, physicists Ernst Wilhelm Otten and Werner Heil from the Institute of Physics at Mainz University laid the foundations for the new process. In 1998, they received the Körber European Science Award. Now they are among the contenders for the German Future Prize 2000, with which since 1997 excellent achievements in science and technology have been awarded annually.
Unlike their colleagues from the American Princeton University and the State University of New York at Stony Brook, who created a tomogram of a prepared mouse lung in 1994 with the help of the polarized noble gas xenon-129, Otten and Heil chose the isotope helium-3 as a contrast agent for their attempts. From her point of view, xenon was not very well suited because it has a narcotic effect and is taken up by the patients' blood.
The two scientists, together with researchers from the Laboratoire Chancellor Brossel in Paris, have been working since the 1980s to produce polarized helium-3 in order to study the structure of nuclear particles. Through a variant of the so-called optical pumping, they managed to generate larger amounts of polarized helium-3 and to maintain the polarization over days. The aim of the experiments was originally basic research. Otten and Heil only came across the possibility of a medical application after reading an article in the journal "Nature", in which the experiments of the researchers from Princeton and Stony Brook were made public. display
With the Mainz radiologist Manfred Thelen and experts from the German Cancer Research Center in Heidelberg, Otten and Heil finally succeeded in depicting the exact distribution of air in the lungs through the combination of magnetic resonance imaging and polarized helium-3 as a contrast medium. The new method is so precise that in the case of a 30-year-old subject, the signs of a later pulmonary emphysema could be detected. And although the person smoked, but otherwise was very healthy and had no complaints with the lungs.
In collaboration with scientists from the Institute of Physics, as well as the clinics for radiology and anesthesia at the University of Mainz, several variants of the procedure have been developed. Using a newly developed gas application unit, a specified amount of polarized helium-3 can be injected into the respiratory flow of patients, tracked within the airway, and captured on film at tenths of a second. Other variants make it possible to determine the oxygen content and consumption of the lungs and detect destroyed or abnormally altered alveoli. Since the equipment for the polarization of the gas are currently too costly for clinics to acquire, Otten and Heil are planning a central distribution station for polarized helium-3. The gas is to be produced there in large quantities and delivered to hospitals. Transportation itself is still giving researchers a headache. The so-called "relaxation time" - the period until the polarization of helium-3 falls to a fraction of its original polarization - was initially only one hour. It has now been increased to 11.5 days in glass containers with a special coating.
Scientists in England and the US are taking a different approach. They have developed a device that allows polarized helium-3 to be produced locally in clinics. The apparatus is used so far but only for research purposes. Problems could also make the availability of helium possible in the future. The noble gas is rare in nature and currently comes mainly from the nuclear weapons production or from the destruction of nuclear weapons in the wake of the disarmament. According to the estimation of Werner Heil, one liter of the noble gas would be required for each patient in magnetic resonance imaging. At the moment, the first phase of certification of the new contrast agent is under way in the USA. To the surprise of the scientists, the US Food and Drug Administration (FDA) has classified helium-3 as a drug and therefore subjected the entire production and transport process of the gas to strict criteria. Already started tests with test subjects had to be discontinued in the USA. Werner Heil estimates that it will take another three to four years to get approval.
Frank Volke, the head of the Magnetic Resonance Research Group of the Fraunhofer Institute for Biomedical Engineering (IBMT) and his team have developed the first MRI-certified coil for magnetic resonance imaging. He also believes that it will be some time before the use of helium-3 in magnetic resonance tomography is suitable for mass application: "There are promising approaches both in Germany and in the USA. For example at the University of Virginia. The doctors are also putting pressure. However, a lot of work is still needed in order for the procedure to be used in clinics. The logistics have to be provided and it still has to be researched how helium-3 circulates in the lungs and how the tomography images can be medically interpreted. "Almut Bruschke-Reimer