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Waseda Frontline Research Vol. 13: Visualizing the invisible! The future of radiation imaging (Part 2 of 3)

High-Energy Astrophysics Researcher
Professor Jun Kataoka
Department of Applied Physics, School of Advanced Science and Engineering, Faculty of Science and Engineering

Applying the technology developed for space science to the medical field

kataokasennsei2-1This time, the Center for Research Strategy asked Professor Kataoka about applying the technology developed in his research and discoveries in space to the medical field.

(Interview date: December 21, 2016)

From space to developing the next-generation PET

The attempt to apply the technology developed for space science to the medical field started from the Japan Science and Technology Agency (JST) advanced measurement and equipment development project. Firstly, the Positron Emission Tomography (PET), equipment used for early cancer detection, had problems with its very large size and expensive implementation cost. From there, the idea of arranging and using large numbers of very small, optical semiconductor amplification detector APDs (Avalanche Photodiodes) that were developed for the Astro-H satellite came about. We made a unit called a PET unit (3cm x 3cm x 8cm), which roughly fits in the palm of your hand. Though it is a small device, the resolution is about 1mm. In comparison to the PET equipment used now (resolution of 5mm), our team successfully increased the resolution quality. Moreover, we have also been working on various devices incorporating the next-generation PET technology by using a more sensitive optical sensor MPPC (Multi-Pixel Photon Counter).

However, there was the problem that in principle, gamma rays other than pair-annihilation gamma rays (511 keV) cannot be used with PET. In addition, PET requires specific tracers which can only be produced with large-scale equipment such as a cyclotron, which is also costly. Therefore, we are currently developing the world’s first multicolor 3D molecular imaging system, a palm-sized, small gamma-ray camera (Compton camera) with high accuracy.

 

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Figure: PET gantry for small animals using semiconductor optical sensor MPPC. With a high-resolution scintillator arrayed and combined with an MPPC, it is possible to realize a small and high-resolution next-generation device. Experiments using a mouse achieved a resolution of about 1 mm. In addition, focusing on the feature that semiconductor elements are strong against magnetic fields, we also developed the next generation PET device that can coexist with MRI (Source: Kataoka Laboratory)

 

Realizing gamma-ray imaging of 3D moving images in color

The Compton camera weighs just 580g. It is 4.9 cm × 5.6 cm × 10.6 cm in size, which is ultra-compact, but it can visualize 1MBq gamma-ray source (662 kilo-electron-volt) 40mm away in near real time, achieving a resolution of about 3 mm. Furthermore, by multi-angle pointing, three-dimensional image reconstruction is possible. In other words, 3D video in color could be obtained. This makes it possible, for example, to see three-color gamma-ray images in 3D animation when three different radionuclides that respectively accumulate in the thyroid, spine, and liver are administered to mice.

 

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Photo: Compton camera developed at the Kataoka Laboratory. It only weighs 580g and fits in Professor Kataoka’s hand.

 

As an successful example of 3D color radiation imaging in a living body with this palm-sized Compton camera, three radiopharmaceuticals131I (364 kilo-electron volts: 4MBq),85Sr (514 kilo-electron volts: 1MBq), and 65Zn (1116 kilo-electron volts: 1MBq) were administered to living mice (8 weeks old) and were measured in 30° steps from 12 different angles. Each measurement took 10 minutes per angle. You can see how 131I (iodine) is accumulated in the thyroid, 85Sr (strontium) in the bone, and 65Zn (zinc) in the liver. In the future, it will be possible to photograph 5 colors or even 6 colors by changing the energy of gamma rays. (For details, see the news on November 1, 2016 “Compton camera for 3D multi-color molecular imaging, in the palm of your hands“)

 

Photos, Figure: Imaging in which three types of radiopharmaceuticals were administered to living mice (Source: Kataoka Laboratory)

Photos, Figure: Imaging in which three types of radiopharmaceuticals were administered to living mice (Source: Kataoka Laboratory)

 

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Photo, Figure: 3D-imaging image of a living mouse (Source: Kataoka Laboratory)

 

Developing the ideal interdisciplinary loop

Besides early cancer detection, this technique can also be applied to check whether a transplantation site is established after a transplant surgery or to treat Alzheimer’s disease by changing the drug and making observations. Ultimately, my dream is to put an extremely miniaturized camera on a small satellite of about 30 kilograms and serve its original purpose to make gamma-ray observations of the universe. I would like to gradually improve this technology cultivated for space by polishing it in other fields and returning the results back to space science.

Recently, research in this field has advanced, and we are now working on neutron imaging. For example, in cancer radiotherapy, a method applying particle beams to tumor locations in order to damage cancer cells has been adopted, but it is necessary to apply a considerable amount. At that time, many neutrons are generated, and unintended secondary radiation occurs. However, there is still quantitative observation that has not yet been done. If neutrons can be imaged, the exposure dose can be visualized and monitored. We are currently conducting research under such concept. Beyond X-rays and gamma rays, I want to image objects that have never been seen before.

 

Development of a highly precise, low-exposure multicolor CT system

Other efforts in the medical field include the development of low-exposure, multicolor X-ray CT (computer tomography) and proton beam CT systems. As you may know, conventional radiography and X-ray CT are basically two-dimensional still images and monochrome images without energy information. On the other hand, no cameras of visible light only shoot black and white these days, and you can take videos with ordinary digital cameras. If we can do the same thing with X-ray CT, it is clear that the amount of information obtained will increase dramatically. It will be possible to identify unknown substances in real time and to correct artifacts in black and white images.

Also, there is an issue of radiation exposure in X-ray CT. On average, you become exposed to approximately 10mSv in one CT scan. This is an equivalent to about five times the radiation exposure that an adult male receives in daily life in a year, so it is not something that should be taken a number of times in a short period of time. Yet, if this dose can be reduced, a CT scan can be taken more often, inevitably making the lesion areas easier to find.

Therefore, we are advancing the development of X-ray CT from two approaches: coloring and lowering radiation exposure. Currently, we are developing a CT system which can shoot multicolor images with a dose of about 1/100th of the conventional amount by combining an independently developed high-precision scintillator with a semiconductor optical amplifier element MPPC, which has been developed for space science. In addition, we are also starting the basic development of proton CT that obtains CT images themselves with a proton beam.

Figure: Trial of low-exposure multicolor X-ray CT using a MPPC light sensor. MPPC has an internal amplification factor as high as 1-million times, and it is possible to perform "coloring" for each X-ray pulse, which is usually impossible. As a result, CT imaging can be performed without being buried in noise even at a low dose of about 1/100th of the conventional level. It is also possible to take images with different energies. (Source: Kataoka Laboratory)

Figure: Trial of low-exposure multicolor X-ray CT using a MPPC light sensor. MPPC has an internal amplification factor as high as 1-million times, and it is possible to perform “coloring” for each X-ray pulse, which is usually impossible. As a result, CT imaging can be performed without being buried in noise even at a low dose of about 1/100th of the conventional level. It is also possible to take images with different energies. (Source: Kataoka Laboratory)

Leveraging the University’s strength for further studies

Compared to space science, the medical field is generally characterized by the short span it takes from research to application. For example, the next-generation PET development is pursued all over the world, and some have already been put to practical use. In particular, MRI-PET devices integrated with nuclear magnetic resonance imaging (MRI) have also been invented by making full use of the characteristics of semiconductor devices resistant to magnetic fields, and the next-generation devices from 10 years ago are becoming a reality now. Putting a multicolor X-ray CT into practical use will still take time, but conversely, our role is to engage in long-term research. I would like to take advantage of the strength, in a sense, as a university not demanding immediate results to pursue my studies.

In the final part, Professor Takaoka will discuss applying his research’s technology cultivated for space science to the environmental field.

☞Click here for Part 1
☞Click here for Part 3

 

Profile

kataokasennsei profileJun Kataoka

Professor Kataoka graduated from the University of Tokyo’s Faculty of Science in 1995 and its Graduate School of Science in 2000 (Doctor of Science). He became an assistant at Tokyo Institute of Technology’s Graduate School of Science and Engineering in 2001 and later appointed as assistant professor in 2007. From 2009, he served as associate professor in the Graduate School of Advanced Science and Engineering at Waseda Research Institute for Science and Engineering. He has held his current position as professor of physics and applied physics since 2014.

Website: Kataoka Laboratory

Major achievements

Publications

Awards and recognition:
2001 Cosmic-Ray Physics Achievement Award
2004 The Astronomical Society of Japan Young Astronomer Award
2009 NASA Group Achievement Award
2012 The Young Scientist’s Prize from the Minister of Education, Culture, Sports, Science and Technology
2013 Publications of the Astronomical Society of Japan Excellent Paper Award (Co-authored)
2014 Waseda Research Award (High-Impact Publication)
2016 Waseda University’s Core Researcher of the Next Generation

Recent news on research
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