RSNA2023 Leading Through Change
Daily Bulletin

How Persistence, Collaboration and Lucky Breaks Brought Total-Body PET to Clinical Practice

Friday, Dec. 01, 2023

By Evonne Acevedo

At the RSNA/AAPM Symposium, presenters shared the journey toward development—and the revolutionary potential—of the first clinical medical device that images the entire human body at once.

(Left to right) Chen, Cherry, Nardo and Badawi

"Total-body PET is not just an advancement; it's a transformation in medical imaging," said moderator Guang-Hong Chen, PhD, the Charles A. Mistretta Professor of Medical Physics and Radiology at the University of Wisconsin in Madison. "This innovative technology is a game-changer, especially in oncology, cardiology and neurology, offering new possibilities in detecting, staging and treating diseases."

Other scanners can build up a picture of the whole body by scanning in multiple parts and then "pasting" images together, explained Simon R. Cherry, PhD, distinguished professor emeritus of biomedical engineering and radiology at UC Davis Health. This new total-body technology needs only a single scan.

"It also represents a step change in performance of PET scanners, with an effective sensitivity gain of a factor of about 40, which allows much higher image quality, or imaging much faster, or at a much lower radiation dose," Dr. Cherry explained.

Assembling the Team

The total-body scanner has involved more than 15 years in the making. Ramsey Badawi, PhD, vice-chair for research in the Department of Radiology and chair of nuclear medicine at UC Davis, took the audience on a humorous journey through his team's multiple rejections from various funding sources before they landed a grant from the NIH Center for Strategic Scientific Initiatives' Provocative Questions program. Grant in hand, they assembled a consortium of determined individuals from the physics, medicine and industry arenas, and finally partnered with United Imaging in Shanghai to bring the first scanner to life.

Dubbed EXPLORER, the scanner features 564,480 scintillation crystals and 53,760 photodetectors, and it weighs about 1,000 kilograms (more than 2,200 pounds).

The team tasked Lorenzo Nardo, MD, PhD, the director of nuclear medicine and theranostics at UC Davis, with establishing the clinical implementation of EXPLORER and building a molecular imaging center around the system. Dr. Nardo directs multiple research projects and clinical trials utilizing EXPLORER.

"Once EXPLORER was installed at UC Davis," Dr. Nardo said, "We had a difficult choice to make about how to use the scanner amongst the many different possible ways this technology would allow. So we had to develop protocols."

Imaging Immune Response to COVID

This year, the UC Davis team provided the first images of the human body's immune response after COVID-19 infection. Through a series of stunningly illustrative images and animations, the researchers demonstrated how total-body PET can depict T-cell distributions across the body—yielding higher spatial resolution and less noise for the image quality necessary for detailed modeling, while requiring a lower dose of radioactive tracers, minimizing patient exposure to radiation.

Dr. Cherry demonstrated the real-time uptake of radiotracers throughout different body systems as seen on the scanner, emphasizing its utility for dynamic imaging, in which positioning of the patient starts before radiotracer injection, and a series of images are sequenced with tracer kinetic modeling. "We have the opportunity to do what radiologists have been doing with the brain for a long time, mapping connections in the brain."

"If we can do this at a total body level with PET, we can look at functional, metabolic and molecular connectivity across the whole body," Dr. Cherry said. "This offers huge opportunities in systems medicine, when we combine it with our rich range of radiotracers across many different physiological, metabolic and molecular targets."

The RSNA/AAPM Symposium represents an ongoing partnership between RSNA and the American Association of Physicists in Medicine, which was founded by attendees of the RSNA Annual Meeting in 1958. Since then, the two societies have continued to emphasize collaboration to bring new developments to real-world clinical practice.

Access the RSNA/AAPM Symposium (R4-PL07) on demand at