Assessing donor hearts with laser speckle imaging

In the majority of cases, graft failure after heart transplantation is attributable to abnormalities like severe coronary artery disease. French researchers are now using a new, non-invasive technique to visualise microvasculature in donor hearts and detect abnormal blood flow.

As organ donors with advanced age and pre-existing heart conditions become eligible for heart transplantation, careful screening for congenital abnormalities has become crucial. Invasive coronary angiography is an essential screening tool that can detect coronary artery disease (CAD), a condition characterised by cholesterol deposits in the heart’s arteries. However, due to logistical challenges the technique is used for less than a third of donors who are at risk of developing CAD.

To overcome this limitation, a new heart preservation procedure called ex situ heart perfusion (ESHP) has been developed. By allowing the supply of oxygenated nutrients to the heart via blood vessels, ESHP allows doctors to monitor the performance of the heart and screen it for any defects outside the body. However, coronary angiography conducted during ESHP is known to damage the heart and result in primary graft failure. Alternative coronary imaging tools are, therefore, required to identify abnormal blood flows in donor hearts and to determine their eligibility for transplantation.

Researchers from Paris-Saclay University have now introduced a safe and non-invasive optical technique that allows imaging of coronary blood circulation in donor hearts during ESHP. The method utilises a recently developed speckle imaging technique, known as laser speckle orthogonal contrast imaging (LSOCI), that was developed to detect the multiple scattering of moving red blood cells. Their work has been reported in the Journal of Biomedical Optics (JBO).

In their study, the researchers improved the imaging capability of LSOCI to observe small blood vessels in the heart. The proposed method thus analyses blood flow in the heart using a specific polarimetric filtering process that allows suppression of surface scattering. Thus, the time varying speckle patterns used for the imaging process are mainly generated by multiple scattering on moving red blood cells inside peripheral vessels.

“The optical technique allows high-resolution imaging of the entire peripheral vasculature of the heart in real time,” said team leader Professor Elise Colin.

To test their method, the researchers developed a clinical model to study coronary circulation on donor hearts before transplantation. They then used a laser and a camera mounted on an articulated arm fixed above the perfusion module — which contained the donor heart — to generate and analyse rapidly varying speckle patterns.

To overcome the challenges in tracking vasculature due to the beating of the heart, the researchers further optimised the technique with a method called multi-period-enhanced signal-to-noise ratio (MPE-SNR). They took a series of images over time to build a set of frames that depicted the vasculature at similar heart positions. Each image in this sequence was then optimised using the other images to reduce noise and enhance details. The optimised image represented the vasculature at a different time point, and the researchers used a sequence of such images to visualise vasculatures as small as 100 µm in a few seconds.

The newly developed imaging technique thus enables precise visualisation of blood circulation, and could in the future be used to identify myocardial perfusion abnormalities that indicate underlying heart conditions such as coronary artery disease.

Image courtesy of the study authors under CC BY 4.0. DOI: 10.1117/1.JBO.28.4.046007