In a paper published in October 2019, researchers from different institutions came to MAX IV to study timing performance of scintillators, materials employed in applications such as cancer diagnosis. At FemtoMAX they achieved an instrumental time resolution of 38 picoseconds, something never recorder in literature before.
FemtoMAX, the ultrafast beamline at MAX IV, is now showing its real potential. An article published on the Nature Partner Journal 2D Materials and Applications, gives insights on a new approach in material R&D that can open the door to a new generation of scintillating materials. Researchers from CERN, Università degli Studi Milano-Bicocca, University of Tartu, Universitè de Lyon, and Ghent University, investigated the timing performance of CdSe-based nanoplatelets, a new type of ultrafast scintillator. The team performed part of their experiments at FemtoMAX, where they were able to probe their samples using an unprecedented fast time resolution of the X-ray source of 38 picoseconds (a 0.000 000 000 001 of a second).
“It’s an exceptional time resolution. 38ps – picoseconds– with multi-KeV energy excitation (close to real scintillation regime) is quite an achievement that has not been demonstrated anywhere else” says Rosana Martinez Turtos, first author of the article, at the time at CERN and now working at Aarhus University, Denmark. The result is so unusual that during the article acceptance process the team was asked to confirm that the reported excitation pulse had been obtained with an X-ray source and not with an optical/laser pulse, more commonly used for ultrafast emissions. At FemtoMAX the authors were able to perform experiments reproducing the 511KeV excitation source used in medical imaging. “An ultrafast and highly energetic excitation source as FemtoMAX is the perfect tool to probe the energy transfer processes and mechanisms between the organic host and inorganic emitting centers”.
One important application of scintillating materials is in time-of-flight positron emission tomography (TOF-PET), a crucial technique in fields such as cancer diagnosis. In a TOF-PET scanner, scintillator crystals detect the energy emitted by a radioactive probe inside the tissue and transforms it into visible light. The next step in the evolution of TOF-PET technology revolves around improving the time resolution of the scanner to achieve real-time molecular imaging. Having real-time information on how tumorous cells behave within the human body would revolutionize the way we diagnose, monitor, and treat cancer. “The timing performance of scintillators used nowadays in TOF-PET is one of the bottlenecks to reach real-time molecular imaging for cancer diagnosis”, explains Rosana.
One way to improve time resolution of TOF-PET scanners and get closer to real-time imaging is by implementing faster scintillators with better timing performance, such as the ultrafast CdSe-based nanoplatelets studied in this work. A TOF-PET scanner detects pairs of photons emitted in coincidence from the tissue in opposite directions. The difference in the time these two photons take to reach opposite scintillator crystals (t2 – t1) defines the time resolution of TOF-PET machines. The more accurate the measurement of the time resolution, the better the image we can obtain from a TOF-PET scan. “This paper contributes to advance the research associated to develop CdSe-based nanocomposites for future applications in the next generation of ultrafast TOF-PET scanners”.
And far more can be achieved at FemtoMAX. As Rosana explains: “this is only the first step towards sub-picosecond time resolution that the group from Tartu University and CERN plan to eventually achieve at FemtoMAX”. The journey towards real-time molecular imaging in PET scanners not only is advancing, it is getting faster thanks to cutting-edge technology such as the ultrafast FemtoMAX at MAX IV.
Header image: This is a transaxial slice of the brain of a 56 year old patient (male) taken with positron emission tomography (PET). Author: Jens Maus. Source: wikipedia.org
Turtos, R.M., Gundacker, S., Omelkov, S. et al.
On the use of CdSe scintillating nanoplatelets as time taggers for high-energy gamma detection.
npj 2D Mater Appl 3, 37 (2019)
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