KEYWORDS: Visualization, Magnetic resonance imaging, Magnetism, Image processing, Fourier transforms, Algorithm development, Data acquisition, Data processing, Scanners, C++
The FastHARP magnetic resonance pulse sequence can acquire taggged cardiac images at a rate of 45 ms per frame, enabling 7-20 harmonic phase (HARP) images per heartbeat per tag orientation. By switching the tag orientation every heartbeat, data from just two heartbeats can be used to compute in-plane quantities describing myocardial deformation, such as circumferential and radial strain. Standard HARP software, however, requries about one second to compute each strain image, which is not fast enough to keep up with the FastHARP pulse sequence. In this work, we have developed real-time algorithms for HARP processing of tagged MR images. The code was implemented along wiht a visualization tool that runs in conjunction with the FastHARP pulse sequence. HARP strain computations and display can now be carried out in real-time after a one heartbeat delay. The software is also fast enough to track and plot the time profile of strain of one or more points in the myocardium in real-time. Our software has now been integrated into a research testbed for magnetic resonance cardiac stress testing, contributing to the emerging suite of clinical cardiac MRI protocols.
This paper presents a new method for measuring longitudinal strain of the heart using harmonic phase magnetic resonance imaging (HARP-MRI). The heart is tagged using 1-1 SPAMM at end-diastole with tagging surfaces parallel to the imaging plane. Two image sequences are acquired for a short-axis slice with two different encodings in the direction orthogonal to the imaging plane. A method to compute a sequence of longitudinal strain estimates from this data is described.
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