Dynamic speckle reveals details of heart vasculature

27 Apr 2023

Paris-Saclay University technique could help identify organs suitable for transplantation.

Accurate identification of heart disease in living patients is critical for many reasons, but coronary health also affects the suitability of the organ for subsequent use in organ transplantation.

In the majority of cases, graft failure after heart transplantation is attributable to abnormalities like severe coronary artery disease, according to a project at Paris-Saclay University, and as donors become eligible for heart transplantation careful screening for congenital abnormalities should be carried out.

Heart disease and cholesterol deposits in the blood vessels can be identified using coronary angiography, but the invasive nature of the technique limits its applicability to fewer than one third of at-risk donors.

The Paris-Saclay project has developed a possible alternative, based on the imaging of dynamic speckle patterns from the beating heart after it has been removed from a donor and kept supplied with blood, an organ preservation procedure termed ex vivo perfusion. The work was published in Journal of Biomedical Optics.

"This optical technique allows high-resolution imaging of the entire peripheral vasculature of the heart in real time," said Elise Colin from Paris-Saclay University.

The project's imaging technique is based on the detection of spatially depolarized speckle fields generated from multiple scattering of light into red blood cells, termed laser speckle orthogonal contrast imaging (LSOCI). This modification to basic speckle imaging uses polarimetric filtering to preferentially detect photons that undergo multiple scattering under the surface, and suppress those coming from first-order surface scattering.

Previous trials on the skin of living subjects have shown that the LSOCI principle allowed imaging of red blood cells at depths of around 2 millimeters at a special resolution of 80 microns.

Identifying heart abnormalities

In trails of the ex vivo coronary application, the project used a 785-nanometer laser source and a camera mounted on an articulated arm fixed above the perfusion module containing the donor heart, to generate and analyze the rapidly varying speckle patterns.

For this application the project enhanced the quality of data being recorded by taking advantage of the periodic movement of the beating heart, through a postprocessing method termed multiperiod-enhanced signal-to-noise ratio (MPE-SNR). This involves taking a series of sequential images to depict the vasculature at similar heart positions as a reference cycle, and using the inherent redundant periods in a pulsed laser regime to filter out unwanted noise and visualize the authentic vasculature.

A sequence of such images enabled vasculatures in the heart as small as 100 microns to be imaged in a few seconds, according to the project team.

If the new technique enables precise visualization of blood circulation, it might in the future prove able to identify myocardial perfusion abnormalities that indicate underlying heart conditions, such as the coronary artery disease of concern for transplantation and for general health.

"The LSOCI method coupled with MPE-SNR allows imaging of the complete peripheral vasculature of a beating heart in a noninvasive way, with high spatial resolution and in only a few seconds," said the project in its paper. "Although clinical transfer will raise many difficulties, it could also be used for the observation of other phenomena in the human arterial system that present periodic excitation of blood flow."