Inside view

ever since the invention of x -rays about 100 years ago, medical imaging technology has undergone several changes. cat -scans, pet scanning and mri scanning have helped physicians learn a great deal about the human body without surgical intervention. But there remain some parts of the body, such as lungs, which are still not clearly visible in these images. Now, several researchers are exploring a new mri technique that could provide high-resolution images of lungs.

The idea behind the new mri scanning technique is that some unusual isotopes of rare gases like xenon or helium, which have been 'hyperpolarised' with the help of laser beams, can provide a much stronger signal for the mri machine. Thus, if the patient inhales a lung-full of this isotope and retains the gas in his/her lungs while the scan is taken, the mri signal is almost 100,000 times stronger than the signal obtained from water. With the stronger signal, the lungs can be better imaged with a much greater resolution. The challenge has been to make enough of the polarised gas.

In the 1990s, miti , a us company, developed a machine to make the polarised isotopes in enough quantities to be useful for mri scans of lungs. This machine uses a laser to first polarise rubidium atoms in vapour. The rubidium atoms then give up their spin to the helium atoms, which have been mixed in the rubidium vapour. This method has been tested on many volunteers to obtain much clearer images of their lungs. Researchers say that the technique could also be useful in colon imaging ( Scientific American , June 1999, p33).

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