The era of Photon Counting CT !
Last week, I was talking about the exciting technology whose final product many engineering enthusiasts are eagerly waiting for, namely the photon counting CT and my colleagues suggested I put this up briefly in writing for a wider reach. The very first time I read about its 2nd prototype, was back in 2019 [1] but today with the exponential rise in big data and machine learning, CT algorithms have evolved boundlessly!
Current market detectors [EID] use the principle of Scintillation that converts x-ray interactions (read: energy) into visible light, which is confined within the detector realm via an anti-scatter grid or optical reflectors to be able to amass and convert them into electrical signals via photodiodes. These signals are then compared and measured with the help of many customisable Application SIC chips [Fig 1] . Simply put, this process involves a lot of hardware and software running in tandem.
Comes in the concept of Photon Counting: Instead of using the output from the accumulated x-ray energies of various keV, the photon counting [Cadmium Telluride/Silicon] detectors measures every single x-ray energy signal. How is this beneficial? Well the possibilities are umpteen!
With this, billions of measurements are recorded at a lightning speed and in turn, these captured and counted photons are thereafter translated into a picture that a doctor can understand. This makes the visualizations clearer than ever by detecting small lesions or abnormalities that could be missed by traditional CT scanners – all without having to compromise on dose, especially on obese patients!. In easier words, the information in every photon can be extracted, calculated and displayed without having to miss out on minute details [see the cover photo of the article] avoiding the case of its predecessors
Apart from other major healthcare vendors like Siemens [NAEOTOM Alpha?], Philips and Canon who are also leading members in the race, Prismatic sensors AB's breakthrough discovery helped GE's R&D team also lead with its deep silicon technology as early as 2021 [2 & 2.1] and is currently still being tested, awaiting FDA's clearance.
For the engineering geeks: ?It measures the pulse height of the incoming photon signal which is proportional to the x-ray energy. This way it can identify and further segregate every signal data corresponding with its energy to produce images at different kv’s
We can also eliminate unwanted noise [by discarding certain low threshold kev’s] thereby achieving a far greater spatial resolution. Also, The optical reflectors within the scintillating detectors are not required anymore since the HV bias between the cathode and anode converts the absorbed xrays into pairs [creating a hole in the valence band after the e- shifts to the conduction band] and converts it directly with the help of smaller pixelated anodes [3]
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Figure 2: (a)?Conventional energy-integrating detector; an incoming X?ray photon is converted to multiple visible photons, which are eventually detected by a?light sensor resulting in a?wide signal?(c). b?Direct conversion of incoming X?ray photons into measurable charge clouds. d?Photons reaching the detector can be almost simultaneously distinguished by a?photon-counting detector.
The benefits are way too many to enlist in one post but i'm always down to discuss more about Biomed tech. Excited to get to work on/with them very soon ??
[2] Of course while selecting the materials, a lot of considerations have to be made right from its sourcing, market availability, to the decay time each material offers.Additional read about this detector: https://www.scholarpedia.org/article/Silicon_detectors_in_High_Energy_Physics_experiments#:~:text=Silicon%20detectors%20are%20widely%20used,the%20experiments%20deduces%20many%20parameters.
Field Service Specialist at GE Healthcare
2 年Well done Omar Shah Congrats for this article ??