Although the imaging technique is new, the technology behind it is not: Microcomputed tomography (micro-CT) scans have been in use for decades. Initially, micro-CT scanners could only image the human body’s harder tissues, such as bone and teeth, because those tissues better absorb the x-rays that give the technology its imaging power.
Imaging softer tissues has been more challenging, although many labs around the world have developed multiple techniques for doing so by injecting soft tissue with contrast agents that better absorb x-rays. That means those labs already have access to everything they need to make such 3D images of intact hearts. “I think we were successful because we knew how to handle and prepare the tissue very carefully,” says Jarvis, a muscle physiologist.
Still another challenge in this kind of research is obtaining access to normal, intact heart tissue, which is usually reserved for heart-transplant patients. With collaborators at the University of Minnesota’s Visible Heart Lab, the team gained access to human hearts that had been intended for use in transplantation, but which had not been transplanted for varying reasons. The team’s experimentation with actual human hearts was minimal, though, because they only needed to scale up from having perfected the imaging technique using the hearts of smaller mammals, including rats. “So you do have to modify your technique a little bit,” says Jarvis, such as by allowing a longer period of time for the contrast agent to diffuse into the human heart tissue. Theirs was an iodine-based agent, and that diffusion took two weeks.
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