Session S72.3

Non-Rigid Motion Compensation in Free-Breathing Myocardial Perfusion MRI

G Wollny*, MJ Ledesma-Carbayo, P Kellman, A Santos

Universidad Politécnica de Madrid
Madrid, Spain

Acquisition protocols of first-pass gadolinium enhanced, myocardial perfusion Magnetic Resonance Imaging (MRI) are too long for the average patient to hold their breath. Therefore, breathing movements are normally present in the image series that need to be compensated for in order to enable an automatic analysis of the myocardial perfusion.
In this work, we propose to allow the patient to breath normally and exploit the periodic breathing movement in the analysis procedure. The method consist of three main steps. First, we identify a subset of the series that corresponds to the same phase of the breathing movement by measuring a similarity criterion that is based on normalised gradient fields (NGF). Secondly, the images of this already partially aligned subset are then registered non-rigidly to one image picked from the middle of the series by minimising the NGF based similarity measure using a B-Spline based transformation and a Laplacian regularizer. Finally, for each of the remaining images of the series an individual reference image is created by linearly combining the two closest registered images of the above, phase-aligned subset, that will exhibit a similar intensity distribution as the image to be registered. Hence, registration is done by minimising the sum of squared differences, and applying the transformation and regularizer as described above.
The proposed method has been applied to four data sets and the registered images exhibit a very good alignment over the whole acquisition time course, making a further automatic analysis of the blood flow possible and visual inspection easier.
The proposed registration procedure minimises the influence of the contrast-agent induced intensity change on the registration as a whole. In addition, normal free breathing typically results in smaller, more predictable and more readily compensated respiratory motion than breath holding in situations when the patient can no longer hold their breath and take a large gasp. Free-breathing studies are also easier for the patient.

(Abstract Control Number: 206)