This revolution has already begun, as explained in detail in the May issue of the European Respiratory Journal by three teams from Germany, the United Kingdom and Canada.

For a very long time, respiratory medicine had to make do with images obtained either by X-ray (simple thoracic radiography or scanner images, both of which reveal lung morphology) or scintigraphy (the use of radioactive tracers that show the functioning of the respiratory system and its ability to oxygenate the blood properly).

And, while MRI provided highly valuable results in other fields of medicine, it barely gained a foothold in chest medicine.

This was particularly regrettable given that MRI does not expose the patient to any radiation, offers a high level of resolution and provides access to functional information.

The reason MRI was marginalized in this way was basically technical. Classical MRI visualizes protons, i.e. hydrogen nuclei -- in other words, essentially water. While water is a major component of the human body (two thirds of body weight), it is not present inside the lungs. The air that we inhale also contains very few protons.

Hence, traditional MRI had relatively few applications in chest medicine.

Things have started to change. "Today, this obstacle has been overcome and MRI has become a pneumological reality", explains Hans-Ulrich Kauczor, first author of the article published in the May issue of the European Respiratory Journal (ERJ), the peer-review publication of the European Respiratory Society (ERS).

Substantial progress has already been made, in two directions in particular.

First, the traditional techniques have been refined to the point that they are now sensitive enough to detect the very low level of protons present in air in the lungs in such a way that computers can now generate images.

The mere fact of changing the oxygen concentration in the air inhaled (ambient air as against pure oxygen) makes it possible, for example, to view pulmonary ventilation on the base of just two comparative images and some computer calculations.

While this information is not dynamic, it provides information regarded by the article's authors as extremely valuable, since until now neither radiological techniques nor traditional functional respiratory tests provided information on the distribution of air in the lungs.

This means that "today we can easily distinguish the areas of the lungs that function normally from those that do not contribute to global respiratory function", explains Edwin J.R. van Beek, of Sheffield, one of the article's co-authors.

Second, there are now new agents available, mainly contrast, especially using gases, which, once inhaled, fill the lung cavity and make it possible to view the distribution of air masses during breathing.

But the new MRI techniques have a value far beyond simply increasing understanding of respiratory physiology. Enormous progress can be expected in terms of the diagnosis, understanding and treatment of lung diseases, a fact of particular interest given the great social and financial burden that these diseases represent.

The revolution has come at the right time. In the past, neither doctors nor patients lost much from the fact that MRI was poorly developed in respiratory medicine, for the available treatments could do little to influence the evolution of pulmonary ventilation.

Today, though, organ transplants and operations to reduce lung volume reduction used as a treatment for emphysema have become much more common. If these costly operations are to be targeted at the patients best able to benefit, sophisticated information is needed, and this is what the new MRI techniques can provide.

There will soon be even more spectacular developments in connection with the application of MRI in pneumology: these are currently undergoing initial clinical trials.

A number of teams are already working on non-protonic techniques, based on the use of either inert gases (such as Helium-3 or Xenon-129) or fluorinated gases such as sulfur hexafluoride. Helium-3 possesses the particular advantage of having no toxic or anaesthetic effects on the body.

"But the density of gases in the natural state is too low to give a detectable signal," explains one of the article's co-authors, the physicist X. Josette Chen, of Toronto. "So we need artificially to increase the amount of polarization by unit volume, using optical pumping techniques developed forty years ago to study neutrons. This allows us to produce what is known as hyperpolarized gases".

As reported in the article in the May ERJ, in a pilot study using ten subjects, MRI with hyperpolarized Helium-3 revealed undeniable differences between apparently healthy adults who smoked and their non-smoking counterparts, though traditional measurement methods would have indicated that both sets had identical, normal lung function.

What the study showed was that smokers presented minor ventilation defects not found in non-smokers, and, importantly, that those changes did not depend on the number of cigarettes smoked.

Kauczor and his colleague, Wolfgang G. Schreiber, the study's founders, perceive a clear link between the defects and the inflammation caused by tobacco smoking: "This should allow us to identify the 20 to 25% of smokers whose airways become severely inflamed as a result of cigarette smoking".

The many developments in MRI bode well for the various branches of respiratory medicine.

For example, in the treatment of chronic bronchitis -- which specialists prefer to call COPD (for chronic obstructive pulmonary disease) -- the new MRI techniques will make it easier to distinguish the zones contributing to exchange between the blood and the lungs and hence to oxygenation of the blood.

The information provided by these new images will allow personalized treatment. It will be possible to judge the need for the treatment itself on the basis of the type and size of the anomalies revealed, which will indicate whether the selected treatment can lead to an improvement.

On the basis of these images and the anomalies revealed, it will also be possible either to limit the treatment to simple bronchodilators (designed to ease breathing) or, on the contrary, where subjects have significant anomalies, to consider the application of corticosteroids, which combat inflammation.

The progress in MRI should also bring benefits in terms of asthma detection, particularly by allowing the identification of asymptomatic subjects, and in the management of cystic fibrosis, whose evolution will be able to be monitored much more precisely.

Techniques using oxygen have the advantage of being simple and inexpensive. Their main disadvantage, though, is the fact that they provide relatively little functional dynamic information.

MRI using hyperpolarized Helium-3 seems at present to be the most favored option, given the amount of functional information it can provide. Moreover, it is currently undergoing a number of advanced clinical tests. The main problem here is the rarity of the gas used: Helium-3 is a byproduct of tritium decay, and is not available in large quantities.

Xenon-129 might have the edge over the alternatives. While the relevant technique is still at the experimental stage and no clinical tests have yet been completed, it seems promising.

There are abundant quantities of Xenon in the air and it presents the additional advantage of being soluble in blood and in lipid-rich tissues, which means it can be used as a tracer in perfusion studies.

The four authors of the ERJ study conclude that the revolution is on the way: "With the unique possibility of mapping functional information, an exciting new field of interdisciplinary research has emerged. More sensitive techniques might change the indications for treatment or certain treatment options".

[Contact: Hans-Ulrich Kauczor MD]

09-May-2001