Each Timepix tile consists of an edgeless silicon sensor. The edgeless sensor technology allows all of the tiles to be tightly packed together from all sides. Thus the whole imaging area of the camera is fully sensitive to the radiation – there are no gaps between the tiles in the image.
The minimum detectable energy is typically 5 keV in the case of X-ray photons. The intrinsic spatial resolution of the camera is defined by pixel size, which is 55 µm. The pixels situated on the borders of the tiles are 2.5 times larger in one direction. The corner pixels of tiles are 2.5 times larger in both directions.
The camera is connected to the controlling computer via a USB 2.0 cable with a readout time of 0.65 seconds per frame. The thermal stabilisation of the camera is provided by an active water cooling system with chiller. The power consumption is 25 W.
Key Features of WidePIX 5×5 Curved:
Sensor Material: Silicon
Sensor Thickness: 300 μm and 500 μm
Sensitive Area: 71 mm x 57 mm
Number of Pixels: 1280 x 1280
Pixel Pitch: 55 μm
Resolution: 9 lp/mm
Readout Speed: 10 frames/s
Photon Counting Speed: up to 3 x 106 photons/s/pixel
Energy Resolution: 0.8 keV (THL) and 2 keV (ToT)
Threshold Step Resolution: 0.1 keV
Min Detectable Energy: 5 keV for X-rays
Readout Chip: Timepix
Pixel Mode of Operation: Counting, Time-over-Threshold, Time-of -Arrival
Connectivity: USB 2.0
Weight: 1.5 kg
Dimensions: 233 mm x 120 mm x 40 mm (L x W x H)
Software: Pixet PRO
Small Animal Spectral Imaging
Cancer research, bio-mechanics, and drug testing are just a few examples of where X-ray imaging contributes to research in biology and medicine. New photon counting detectors represent a serious advancement for these applications, compared to previously used synchrotrons. The energy sensitivity of modern cameras opens better possibilities to identify individual types of tissue. That has important consequences in various industries, for example cancer research, where the tumour tissue can be better distinguished from the healthy one.Find out more about this application here.
The leading detector technology, which Advacam uses for its products and solutions is based on Medipix hybrid pixel detectors. These devices were developed within international collaboration of universities and research laboratories lead by team at CERN during past 20 years. Advacam team’s members have been part of the Medipix Collaboration from it inception and have been contributing to the technology.
Photon Counting Technology
Advacam’s imaging cameras are direct conversion single photon counting pixel detectors that represent the cutting edge of current radiation imaging technology. The term “single photon counting” means that every single photon of X-ray radiation detected in individual pixel is processed and counted. The technology brings two major advantages in comparison to the conventional X-ray imaging – high contrast together with sharp images and spectral information of X-rays that allows material specific information to be displayed in colors.
In the direct conversion cameras each pixel of the semiconductor crystal is directly connected to the complex CMOS circuit using a conductive solder bump. In the indirect conversion cameras a scintillation layer is attached on top of a photodiode. The photodiodes manufactured on a simple CMOS circuit that enables fine pixel sizes.
Illustrative comparison of a single pixel of a direct conversion and indirect conversion cameras.
The term direct conversion refers to immediate conversion of the X-rays into electric charge within the semiconductor crystal. The principle is contrary to the conventional indirect conversion where the X-rays are first converted into visible light in the scintillation layer that subsequently is converted into electric charge in the photodiodes.
Illustration of the operation principles in a single pixel between the direct and indirect conversion cameras.
The photon counting principle of detection eliminates all other sources of noise that are present in CCD or flat-panel based cameras. This leads to considerably better signal-to-noise ratio and therefore detectability of more details in images. The images sharpness or the actual spatial resolution of the captured image is defined by the electric charge in the CMOS readout. Even thought the pixel size of of the direct converting cameras is larger than that of the conventional indirect conversion cameras, the signal of the detected X-rays is better focused into the pixels. The typical size of a direct conversion pixel ranges from few millimeters to tens of micro meters where Advacam represents the highest pixel density of the current industrial X-ray cameras with 55 um pixel size. The video below describes the differences between conventional indirect conversion, direct conversion charge integrating and photon counting cameras. It summarises the major differences in the captured image quality in terms of spatial resolution, image noise and material discrimination.
The energy sensitivity is as important advancement of the imaging technology as was the colour photography and film. Contrary to regular X-ray imaging cameras, the photon counting cameras can discriminate or even directly measure energy (wavelength) of incoming photons. Since each element of the sample has different X-ray attenuating properties, it is possible to estimate material composition of the sample if the energy of the photons is measured. The spectral sensitivity offers major improvement over the conventional X-ray imaging cameras.