The first experimental cross-sectional medical image achieved without the use of tomography was recently demonstrated by a team of researchers from the US and Japan. The study, which was published in Nature Photonics in 2021, might enable cheaper, simpler, and more accurate medical imaging.
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New, ultrafast photon detectors made a significant achievement possible. Simon Cherry, a professor of both biomedical engineering and radiology at the University of California (UC) Davis, said:
We're literally imaging at the speed of light, which is something of a holy grail in our field.
The experiments were led by Sun Il Kwon and Ryosuke Ota. Kwon is also a member of the UC Davis Department of Biomedical Engineering. Ota is an engineer at Hamamatsu Photonics, Japan, the company that developed the advanced photon detector technology used to create medical images.
Tomography is a mathematical process used to recreate cross-sectional images from imaging data obtained by X-ray or gamma-ray devices. It is necessary for CT and PET scanning, but adds cost and complexity to medical imaging while limiting accuracy.
Why Were Ultrafast Photon Detectors Needed?
In PET scanning, molecules are tagged with a radioactive isotope (such as trace amounts of fluorine-18) and injected into the body. The body’s organs and tissues take the molecules up, but the isotope is unstable and emits positrons while it is decaying.
When one of these positrons meets an electron in the body, the two particles annihilate each other. This interaction gives off two annihilation photons, which generate Cherenkov photons when they hit the detector, producing a signal. PET scanning works by tracking the origin and directory of these annihilation photons to build an image of the tissues tagged with isotopes.
Until now, researchers could only build up this image with the help of tomographic reconstruction. This was because detectors were too slow to accurately sense the arrival times of the two photons and pinpoint their location based on the difference between the two times.
Using ultrafast photon detectors, the authors of the latest research detected Cherenkov photons with an average timing precision of just 32 picoseconds (32 trillionths of a second). This ultrafast detection enabled the team to determine where annihilation photons had arisen with a spatial precision of just 4.8 mm.
Because of the high level of speed and accuracy achieved, the researchers could create cross-section medical images of a radioactive isotope directly from the annihilation photons. No tomography math was required to reconstruct the image.
Next Steps for the Research
The new article includes details of various tests that scientists carried out to test the accuracy of the new ultrafast imaging method. They used test objects that mimic the human brain to demonstrate its applicability in medical imaging.
The team believes that the new procedure is ultimately scalable to the level required for clinical diagnostics. The technique could potentially create higher quality images with a lower radiation dose than traditional PET scanning is capable of.
The method is also potentially faster than PET scanning, and may even be used for real-time medical imaging due to the fact that no reconstruction is needed after data is acquired.
Currently, PET scans are expensive and relatively inaccessible. They are also a technically limited technology, as the complete information contained in the annihilation photons’ travel time is not captured by clinical scanners used today.
The new procedure only requires a compact equipment setup. It could lead to cheaper, easier, and more accurate scans of the human body in the future.
Making Medical Imaging More Accessible
Currently, more than 4 billion people around the world do not have access to medical imaging. Ultrasound machines cost hospitals upwards of $100,000, and many hospitals simply cannot afford the expense.
This new research will contribute to the development of more accessible medical imaging techniques in the future, and joins global philanthropic attention on the problem of inaccessible medical imaging.
The Gates Foundation is invested in Butterfly iQ, for example. The startup company was founded by Jonathan Rothberg, a genetics researcher from Yale University and an experienced business creator.
Butterfly iQ’s groundbreaking product is an inexpensive, handheld ultrasound device that costs only $2,000. The technology is built on a technique developed by Rothberg that puts ultrasound technology on a computer chip. The device is portable and handheld, and connects to an iPhone app.
The pocket-sized ultrasound device went on sale to medical professionals in 2020. Butterfly iQ plans to sell the device in 150 countries where the local economy will allow them to price it realistically. The Gates Foundation will then distribute it in a further 53 countries where medical professionals are less well resourced.
The point of devices such as these is to make medical imaging a routine part of life around the world. Thermometers were once only used in the doctor’s office, argues Rothberg, but now they are used by laypeople and professionals alike around the world.
The same may come true for medical imaging. Combined with the proliferation of eHealth products, wearables, virtual healthcare and treatment, and medical AI, easy-to-use, cheap, and compact techniques like Rothberg’s may bring about new democratization in health.
References and Further Reading
Deptula, C. (2021) Detector Advance Could Lead to Cheaper, Easier Medical Scans. [Online] UC Davis. Available at: https://www.ucdavis.edu/health/news/detector-advance-could-lead-cheaper-easier-medical-scans.
Kwon, S.I., et al. (2021) Ultrafast timing enables reconstruction-free positron emission imaging. Nature Photonics. https://doi.org/10.1038/s41566-021-00871-2.
12 Innovations That Will Change Health Care and Medicine in the 2020s. (2019) [Online] Time. Available at: https://time.com/5710295/top-health-innovations/.