It’s Alive! Kind of…A story of a unique liver model for ultrasound research

What does it mean to be alive? Is it just the circulation of essential nutrients and oxygenated blood? For your organs, I would argue that is most certainly the case, or at least for the first few hours outside of your body.

These questions are the core of organ transplantation – that if you extract the organ from a donor and take care to preserve it, you will have a few hours to safely transport and distribute the organ. Another element of this process is usually a rerouting system which helps keep the patient or organ alive. For heart operations a patient will go on bypass, a machine that acts like your heart by pumping all of your blood. For kidneys, a dialysis machine can be used to aid in the filtering of toxins that the organ normally performs.

So why is all of this important to an ultrasound researcher? One of the best organs to image with ultrasound is your liver as it is quite large (easier to find), close to your skin (no need to penetrate through lots of tissue), and relatively unobstructed by reflective objects such as your bones. This accessibility has led a large part of ultrasound research to focus on the liver, treating various liver diseases or cancers, as well as using it as a model for new therapies and treatments. However, livers don’t grow on trees, and researchers are limited to animal studies or clinical trials, all of which introduce new complications. Things like diseased or injured organs, resistance to treatment, or even allergies can disrupt the results of any experiment. Ideally, these researchers would have a liver that is still alive that they can then bring to the lab and perform their experiments on.

Within the past decade, this desire for a controlled environment liver model led some research groups to adapt the idea of organ transplantation to livers. What if instead of working with an animal model such as a pig, you were able to harvest its liver like an organ transplant, bring it back to your lab, and then attach said liver to a rerouting system to help keep it alive? Thus was born the machine perfused pig liver (MPL) model, a liver harvested from a pig, preserved and brought back to the lab, and then attached to a perfusion system which pumps essential nutrients and oxygenated blood at the same rate the pig’s heart normally would. Using this system, the liver does all of its normal functions for several hours even though it is sitting on a benchtop.

Using the MPL model has afforded ultrasound researchers many unique opportunities to investigate therapies on living tissue. Experiments have ranged from improving ultrasound images with contrast agents, to destroying cancers by heating the tissue with energy from ultrasound. The control over the two major circulatory pathways into the liver, the hepatic artery and the portal vein, allows researchers to understand the biological effects of each pathway and investigate how blood clots might affect the health of the liver. While some may compare the MPL to a Frankenstein’s monster level of science, it is no different from any other organ transplant, and the boon of scientific research from this one model will be tremendously valuable for the years to come.

Lance De Koninck is a second-year bioengineering PhD student studying how to better deliver drugs using ultrasound. His research explorers how ultrasound can increase the temperature inside of cells, weakening them and assisting drugs to better penetrate these cells.