The cardiac activity causes tissue deformations in the lungs, due to the mechanical action of the heart on the lobes and to the pulsatility of blood vessels. The role of the cardiac activity on the ventilation in normal and injured lung is still not completely understood.
Temporally resolved X-Ray CT can be used to study the deformation of the tissues at different phases of periodic motions, but the existing techniques are limited in spatial or temporal resolution. We developed therefore a high-resolution temporally-resolved tomographic technique to acquire, during a single scan, different phases of the cardiac induced lung motion in rabbits.
This technique was developed at the ESRF, at the biomedical beamline, using propagation-based phase-contrast imaging and a fast PCO camera coupled with an optics giving a spatial resolution of 20 µm. A respiratory pause was induced in a mechanical ventilated rabbit to suppress the motion of the ventilation. Projections were acquired continuously at a constant rate of 130 Hz during a single complete rotation. During the 5 minutes required for the acquisition, apnoeic oxygenation allowed to extend the apnea, without strong modifications in the cardiac activity, assuring a stable and periodic motion. The ECG signal was recorded and analysed using a wavelet transform, to identify the phase of the motion associated to each projection. 15 different frames were reconstructed along the 350ms of the cardiac cycle.
Deformation maps between the frames were computed to study, at high resolution, the effects of the cardiac motion on the lungs. Possible applications include the study of the elasticity of lung tissues and effect of the heart in the ventilation in both healthy and injured lungs.