Injecting radioactive materials into your body might sound crazy, but it’s a useful tool for gaining snapshots of our physiology. Positron emission tomography (PET) uses radioactive particles to track the footprints of diseases like cancer and neurodegeneration. Now, researchers are working to build the world’s first full-body PET scanner, which they claim will increase our power to understand what’s going on in our bodies through more vivid PET images and the opportunity to examine how the whole body responds to drugs and toxins.
The team published their first paper on early details of the project last month in Physics in Medicine and Biology and outline their ambitions for the scanner this week in Science Translational Medicine. Science checked in with Simon Cherry and Ramsey Badawi, two bioengineers at the University of California, Davis, leading the charge to build the scanner. They have dubbed their future machine “EXPLORER,” (EXtreme Performance LOng REsearch scanneR) and hope to run their first human subject by late 2018.
This interview has been edited for clarity and length.
Q: What advantages does full-body PET have over traditional PET?
R.B.: Pretty much every PET scan that's ever been done in humans has been limited by the fact that there's not a huge amount of signal collected. This is because radiation is emitted in all directions, so it muddles the image.
S.C.: With the total-body scanner, we are surrounding the body with detectors, which stop that radiation and turn it into a signal. It gives us this huge boost. Now for the same radiation dose that we currently give, we collect a lot more signal. This also allows us to reduce the radiation dose. If we're happy with the signal that we currently have, we can instead reduce the dose by a factor of 40 and still get the same signal we would get on today’s scanners.
Q: How much radiation are we talking about?
R.B.: In the latest calculations we did, we can get the dose down to the equivalent of flying from Los Angeles [California] to London and back.
Q: What else can we look at with a full-body scanner that we can’t look at with a smaller one?
S.C.: Obviously when developing new treatments, pharmaceutical companies have a target of interest. But the problem when you get into human clinical trials is toxic side effects in other parts of the body. And so one thing that EXPLORER does that I think will be very exciting for drug development is that we can radioactively label that drug and watch where it goes in the body over time. We can see its concentration in every single tissue and organ in the body. Drug companies are very excited about that prospect, because it will allow them not just to ask, “Is my drug reaching a tumor?" but “How much is in the liver?” for example. So it can help us identify the best drug candidates, and we can hopefully have fewer failures in clinical trials.
R.B.: Another area that we’re quite interested in is toxicology. For example, there are lots and lots of nanoparticles in our environments. You get them in lipstick, sunscreen, and all sorts of other sources. And their fate in the body is not totally clear. You could label some of these nanoparticles with [a long-lasting tracer] and we think with the increased sensitivity of EXPLORER, you’d be able to image those nanoparticles throughout the body for maybe up to a month. That has never been done before.
S.C.: You could also do a similar thing with cell-based therapies, where you label a subset of immune cells or stem cells and then follow them for several weeks with PET to see what happens to them throughout the body.
Q: What are the remaining hurdles for getting this technology up and running?
S.C.: The first human [research] scans, we hope, will take place in late 2018. Clinical scans are another matter because you have to get FDA [Food and Drug Administration] approval for the device, and so it’s a little unknown how much longer that process will take. Another piece that we're working on right now is data handling and how we move massive amounts of data through the detectors and the electronics and off onto hard drives, how we then process that data into images, and how we store that data.
Q: How will the cost compare to one of today’s scanners for patients and doctors?
S.C.: That’s a very difficult question to answer. The prototype we are building, this 2-meter-long device, is going to be, I would say, three to five times the price of a regular PET scanner. But that’s very comparable to today’s high-end MRI scanners.
R.B.: And you’ve always got to put cost in the context of benefit. If we get the extra-rich information that we think we're going to get, it may well be that we’re looking at a completely different way of doing PET scans, and then we’re talking about a very different business model.