Demand for kidney transplants—which can be lifesaving for patients with chronic kidney disease (CKD)—has greatly outstripped supply. And so critically ill patients may languish for years on waiting lists, undergoing dialysis, while physicians may sometimes have little choice but to accept donations of damaged kidneys in desperate attempts to save lives.
Now, however, a research team from Toronto has developed a new method for evaluating the quality of a donor kidney prior to implantation: They used photoacoustic (PA) imaging to visualize scarring, also known as fibrosis, an accumulation of excessive collagen that is a common form of damage in donor kidneys. Their results produced clear images of kidney scarring just hours before surgery. During this window of opportunity, an accurate assessment could mean the difference between implanting an organ with decades-long durability—or one that quickly fails, sending a patient right back to dialysis and the years-long waitlist.
PA combines laser and ultrasound—a sequence that PhD candidate Eno Hysi likens to thunder and lightning. “We shine light on kidney tissue, which creates a pressure wave that can be heard using an ultrasound probe.” The sound data is then run through a proprietary algorithm based on a technique called spectral unmixing, which reveals the amount of collagen in the kidney.
The imaging technology is faster, noninvasive, and more comprehensive method of assessing kidney damage than needle biopsy, the procedure currently used to assess the amount of kidney scarring in prospective donors. Not only is needle biopsy a painful procedure that poses the risk of bleeding, its is hampered by potentially inaccurate estimates based on a tissue sample size of only 1% of the kidney.
“It wasn’t at all obvious that it would work”
When Hysi first proposed using spectral unmixing to focus on collagen in kidney tissue, nothing in prior medical physics knowledge hinted that the application was even possible. “Typically, for the technique to work, you need to see large peaks and valleys in how components absorb light,” says Michael Kolios, PhD, of Ryerson University. “But collagen is flat, so it wasn’t at all obvious that it would work.”
Hysi persisted with the counterintuitive approach. With so many other biological substances exhibiting peaks and valleys once spectral unmixing is applied, collagen might stand out conspicuously by virtue of its own flatness. The findings validated his hypothesis, and the proprietary algorithms are now being patented.
In less than two minutes, PA can generate a 2D image with enough detail to quantify total scarring in a kidney. Within 15 minutes, 3D imaging allows visualization not only of overall scarring, but also its varied distribution throughout the kidney.
The research is now moving into clinical trials at St. Michael’s Hospital in Toronto, where the investigators will assess how closely their predictions on kidney quality mirror actual outcomes in patients.
Featured image: Photoacoustic maps of the degree of scarring within the kidney. The color intensity denotes the concentration of collagen, the core component of kidney scarring. Credit Eno Hysi.