  Micro-vascular flow in the myocardium is of significant importance clinically
but remains poorly understood. Up to 25% of patients with symptoms of coronary
heart diseases have no obstructive coronary arteries and have suspected
microvascular diseases. However, such microvasculature is difficult to image in
vivo with existing modalities due to the lack of resolution and sensitivity.
Here, we demonstrate the feasibility of transthoracic super-resolution
ultrasound localisation microscopy (SRUS/ULM) of myocardial microvasculature
and hemodynamics in a large animal model and in patients, using a cardiac
phased array probe with a customised data acquisition and processing pipeline.
A multi-level motion correction strategy was proposed. A tracking framework
incorporating multiple features and automatic parameter initialisations was
developed to reconstruct microcirculation. In two patients with impaired
myocardial function, we have generated SRUS images of myocardial vascular
structure and flow with a resolution that is beyond the wave-diffraction limit
(half a wavelength), using data acquired within a breath hold. Myocardial
SRUS/ULM has potential to improve the understanding of myocardial
microcirculation and the management of patients with cardiac microvascular
diseases.
