Source NIH

Watch this brief video and you might guess you’re seeing an animated line drawing, gradually revealing a delicate take on a familiar system: the internal structures of the human body. But this movie doesn’t capture the work of a talented sketch artist. It was created using the first 3D, full-body imaging device using positron emission tomography (PET).

The device is called an EXPLORER (EXtreme Performance LOng axial REsearch scanneR) total-body PET scanner. By pairing this scanner with an advanced method for reconstructing images from vast quantities of data, the researchers can make movies.

For this movie in particular, the researchers injected small amounts of a short-lived radioactive tracer—an essential component of all PET scans—into the lower leg of a study volunteer. They then sat back as the scanner captured images of the tracer moving up the leg and into the body, where it enters the heart. The tracer moves through the heart’s right ventricle to the lungs, back through the left ventricle, and up to the brain. Keep watching, and, near the 30-second mark, you will see in closer focus a haunting capture of the beating heart.

This groundbreaking scanner was developed and tested by Jinyi Qi, Simon Cherry, Ramsey Badawi, and their colleagues at the University of California, Davis [1]. As the NIH-funded researchers reported recently in Proceedings of the National Academy of Sciences, their new scanner can capture dynamic changes in the body that take place in a tenth of a second [2]. That’s faster than the blink of an eye!

This movie is composed of frames captured at 0.1-second intervals. It highlights a feature that makes this scanner so unique: its ability to visualize the whole body at once. Other medical imaging methods, including MRI, CT, and traditional PET scans, can be used to capture beautiful images of the heart or the brain, for example. But they can’t show what’s happening in the heart and brain at the same time.

The ability to capture the dynamics of radioactive tracers in multiple organs at once opens a new window into human biology. For example, the EXPLORER system makes it possible to measure inflammation that occurs in many parts of the body after a heart attack, as well as to study interactions between the brain and gut in Parkinson’s disease and other disorders.

EXPLORER also offers other advantages. It’s extra sensitive, which enables it to capture images other scanners would miss—and with a lower dose of radiation. It’s also much faster than a regular PET scanner, making it especially useful for imaging wiggly kids. And it expands the realm of research possibilities for PET imaging studies. For instance, researchers might repeatedly image a person with arthritis over time to observe changes that may be related to treatments or exercise.

Currently, the UC Davis team is working with colleagues at the University of California, San Francisco to use EXPLORER to enhance our understanding of HIV infection. Their preliminary findings show that the scanner makes it easier to capture where the human immunodeficiency virus (HIV), the cause of AIDS, is lurking in the body by picking up on signals too weak to be seen on traditional PET scans.

While the research potential for this scanner is clearly vast, it also holds promise for clinical use. In fact, a commercial version of the scanner, called uEXPLORER, has been approved by the FDA and is in use at UC Davis [3]. The researchers have found that its improved sensitivity makes it much easier to detect cancers in patients who are obese and, therefore, harder to image well using traditional PET scanners.

As soon as the COVID-19 outbreak subsides enough to allow clinical research to resume, the researchers say they’ll begin recruiting patients with cancer into a clinical study designed to compare traditional PET and EXPLORER scans directly.

As these researchers, and other researchers around the world, begin to put this new scanner to use, we can look forward to seeing many more remarkable movies like this one. Imagine what they will reveal!

References:

[1] First human imaging studies with the EXPLORER total-body PET scanner. Badawi RD, Shi H, Hu P, Chen S, Xu T, Price PM, Ding Y, Spencer BA, Nardo L, Liu W, Bao J, Jones T, Li H, Cherry SR. J Nucl Med. 2019 Mar;60(3):299-303.

[2] Subsecond total-body imaging using ultrasensitive positron emission tomography. Zhang X, Cherry SR, Xie Z, Shi H, Badawi RD, Qi J. Proc Natl Acad Sci U S A. 2020 Feb 4;117(5):2265-2267.

[3] “United Imaging Healthcare uEXPLORER Total-body Scanner Cleared by FDA, Available in U.S. Early 2019 .” Cision PR Newswire. January 22, 2019.

Links:

Positron Emission Tomography (PET) (NIH Clinical Center)

EXPLORER Total-Body PET Scanner  (University of California, Davis)

Cherry Lab  (UC Davis)

Badawi Lab  (UC Davis Medical Center, Sacramento)

NIH Support: National Cancer Institute; National Institute of Biomedical Imaging and Bioengineering; Common Fund