Successive images of the heart at a particular point in its cycle can then be picked out and superimposed on each other to produce a clearer picture. The device itself consists of coils of optical fibre that are attached to the patient's chest and abdomen using a dressing strip. When optical fibres are bent into a curve, part of any light travelling down them ends up being lost out of the side of the fibre as it tries to make it round the bend. The tighter the bend, the more light is lost. In this system, light is shone into the cables from one end, and the amount coming out of the other end is recorded, and displayed on a computer.
Breathing causes the patients chest to contract and relax.
This movement makes the coils in the optical fibre tighter or looser which in turn affects the amount of light escaping from the optical fibre. The difference in the amount of light coming out of the end of the fibre thus gives a measure of respiration. The heart pounding in the chest also alters the shape of the coils, but to a much lesser degree than the breathing process. Although other systems exist that can monitor heart rates and breathing inside MRI scanners, they are based on much more complex technology, and are a lot more expensive than this method. Early results obtained from laboratory volunteers look encouraging, and the researchers plan to test the system inside an MRI scanner in the next few months.