US20060011853A1 - High energy, real time capable, direct radiation conversion X-ray imaging system for Cd-Te and Cd-Zn-Te based cameras - Google Patents

High energy, real time capable, direct radiation conversion X-ray imaging system for Cd-Te and Cd-Zn-Te based cameras Download PDF

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US20060011853A1
US20060011853A1 US11/017,629 US1762904A US2006011853A1 US 20060011853 A1 US20060011853 A1 US 20060011853A1 US 1762904 A US1762904 A US 1762904A US 2006011853 A1 US2006011853 A1 US 2006011853A1
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pixel
image
high energy
imaging system
module
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Konstantinos Spartiotis
Tuomas Pantsar
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Direct Conversion Ltd Oy
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Ajat Ltd Oy
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Priority to US11/017,629 priority Critical patent/US20060011853A1/en
Priority to EP05780149A priority patent/EP1763685B1/en
Priority to KR1020087029856A priority patent/KR100989666B1/ko
Priority to EP07104046A priority patent/EP1795918B1/en
Priority to EP10152915A priority patent/EP2192422B1/en
Priority to AT05780149T priority patent/ATE457467T1/de
Priority to PCT/IB2005/001896 priority patent/WO2006003487A1/en
Priority to KR1020077001623A priority patent/KR100962002B1/ko
Priority to JP2007519900A priority patent/JP2008524874A/ja
Priority to DE602005019297T priority patent/DE602005019297D1/de
Priority to KR1020087029854A priority patent/KR100987404B1/ko
Priority to US11/226,877 priority patent/US8530850B2/en
Publication of US20060011853A1 publication Critical patent/US20060011853A1/en
Assigned to OY AJAT LTD reassignment OY AJAT LTD ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: PANTSAR, TUOMAS, SPARTIOTIS, KONTANTINOS
Priority to US13/935,663 priority patent/US20130334433A1/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/24—Measuring radiation intensity with semiconductor detectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14634—Assemblies, i.e. Hybrid structures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/0296—Inorganic materials including, apart from doping material or other impurities, only AIIBVI compounds, e.g. CdS, ZnS, HgCdTe
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
    • H04N25/67—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response
    • H04N25/671—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
    • H04N25/67—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response
    • H04N25/671—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction
    • H04N25/673—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to fixed-pattern noise, e.g. non-uniformity of response for non-uniformity detection or correction by using reference sources
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
    • H04N25/68—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to defects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/30—Transforming light or analogous information into electric information
    • H04N5/32—Transforming X-rays
    • H04N5/321—Transforming X-rays with video transmission of fluoroscopic images
    • H04N5/325—Image enhancement, e.g. by subtraction techniques using polyenergetic X-rays

Definitions

  • the present invention is in the field of semiconductor imaging systems for imaging x-ray and gamma ray radiant energy. More specifically, the invention relates to a high energy charge-integrating imaging devices utilizing Cd—Te or Cd—Zn—Te based detector substrates in combination with CMOS readout substrates. Additionally, the invention relates to a process for calibrating such high energy radiation imaging systems.
  • the detecting or recording means is a photosensitive film or an analog device such as an Image Intensifier.
  • Digital radiation imaging is performed by converting radiation impinging on the imaging device (or camera) to an electronic signal and subsequently digitizing the electronic signal to produce a digital image.
  • Digital imaging systems for producing x-ray radiation images currently exist.
  • the impinging or incident radiation is converted locally, within the semiconductor material of the detector, into electrical charge which is then collected at collection contacts/pixels, and then communicated as electronic signals to signal processing circuits.
  • the signal circuits perform various functions, such as analog charge storing, amplification, discrimination and digitization of the electronic signal for use to produce an digital image representation of the impinging radiation's field strength at the imaging device or camera.
  • These types of imaging systems are referred to as “direct radiation detection” devices.
  • the impinging radiation is first converted into light in the optical or near optical part of the visible light spectrum.
  • the light is subsequently converted to an electronic signal using photo detector diodes or the like, and the resultant electronic signal is then digitized and used to produce a digital image representation of the impinging radiation's field strength at the imaging device or camera.
  • This type of imaging system is referred to as an “indirect radiation detection” device.
  • a flat panel imaging device/camera typically involves collecting and integrating a pixel's charge over a period of time and outputting the resultant analog signal which is then digitized.
  • Present charge integration times are typically from 100 msec to several seconds.
  • Devices presently available in the field are suitable for single exposure digital x/gamma-ray images, or for slow multi-frame operation at rates of up to 10 fps (frames per second).
  • the digitization accuracy typically is only about 10 bits, but can be 14 to 16 bits if the charge integration time is sufficiently long.
  • the high end of digitization accuracy currently is accomplished in imaging systems wherein the typical charge integration times range from several hundred milliseconds up to a few seconds.
  • Designing and manufacturing a sensitive, high energy radiation-imaging device is a very complex task. All the device's structural modules and performance features must be carefully designed, validated, assembled and tested before a fully functioning camera can be constructed. Although great progress has been made in the research and development of semiconductor radiation imaging devices, a large number of old performance issues remain and certain new performance issues have developed. Some of the new performance issues result from solving other even more severe performance problems, while some are intrinsic to the operating principle of such devices.
  • High energy “direct radiation detector” type x-ray imaging systems typically utilize semiconductor detector substrate composed of Cd—Te or Cd—Zn—Te compositions.
  • the Cd—Te or the Cd——Zn—Te detector substrate is typically bump-bonded to a CMOS readout (signal processing) substrate. It can also be electronically connected to the CMOS readout with the use of conductive adhesives (see US Patent Publication No. 2003/0215056 to Vuorela).
  • CMOS readout substrate integrates the charge generated from the absorption the impinging x/gamma rays in the thickness of material of the detector substrate.
  • Cd—Te or Cd—Zn—Te/CMOS based charge-integration devices can be divided into two major areas: electrical performance problems and materials/manufacturing defects.
  • Electrical performance problems can be further subdivided into six different though partially overlapping problems: leakage current, polarization or charge trapping, temporal variation, temperature dependency, X-ray field non-uniformity, and spectrum dependency.
  • Materials/manufacturing defects problems can also be further subdivided into: Cd—Te or Cd——Zn—Te detector material issues, CMOS-ASIC production issues, and overall device manufacturing issues.
  • EP0904655 describes an algorithm for correcting pixel values of a Cd—Te or Cd—Zn—Te imaging device.
  • EP0904655 simply provides a correction algorithm for correcting pixel values from a single exposure and consequently displaying such pixel values.
  • the present invention is a high energy, direct radiation conversion, real time X-ray imaging system. More specifically, the present real time X-ray imaging system is in tended for use with Cd—Te and Cd—Zn—Te based cameras. The present invention is particularly useful in X-ray imaging systems requiring high image frame acquisitions rates in the presence of non linear pixel performance.
  • the present invention is “high energy” in that it is intended for use with X-ray and gamma ray radiation imaging systems having a field strength of 1 Kev and greater.
  • the high energy capability of the present X-ray imaging system is derived from its utilization of detector substrate compositions comprising Cadmium and Telluride (e.g., Cd—Te and Cd——Zn—Te based radiation detector substrates) in the imaging camera.
  • Cd—Te and Cd——Zn—Te based detector substrates define the present invention as being a direct radiation conversion type detector, because the impinging radiation is directly converted to electrical charge in the detector material itself.
  • the detector substrate is a monolith and has a readout face or surface which is highly pixelized, i.e., it has a high density pattern of pixel charge collectors/electrodes on it.
  • the pattern is high density in that the pitch (distance from center-to-center) of the pixel charge collectors is 0.5 mm or less.
  • Each pixel's collector/electrode is in electrical communication (e.g., via electrical contacts such as bump-bonds or conductive adhesives) to the input of a pixel readout ASIC on the readout/signal processing substrate.
  • the detector substrate provides for directly converting incident x-rays or gamma radiation to an electrical charge and for communicating the electrical charge signals via the pixel electrical contact to the readout ASIC.
  • the readout/signal processing ASIC provides for processing the electrical signal from its associated pixel as necessary (e.g., digitizing, counting and/or storing the signal) before sending it on for further conditioning and display.
  • the capability of the present invention to be read out at high frame rates enables the real time imaging feature.
  • Real time imaging refers to the capability of the system to generate image frames for display in sufficiently rapid succession to provide a moving picture record in which movement appears to occur substantially real time to the human eye.
  • the imaging device or camera is “readout” at a high frame rate.
  • a high frame rate as used herein means that the accumulation and distribution of electrical charge developed in the detector semiconductor substrate is utilized (“readout”) to produce a digital image frame at a rate greater than about 10 individual image frames per second up to 50 and greater individual image frames per second.
  • An individual image frame is a digital representation of the active area (pixel pattern) of the camera's detector substrate. An image frame is generated each time the ASIC substrate is readout.
  • the digital representation can be described as a matrix of digitized individual pixel signal values. That is, each pixel value of each pixel in the image frame is a digitized representation of the intensity of the electronic signal level readout for the corresponding specific pixel on the detector substrate.
  • each pixel value in the image frame includes an individual calibration correction specific to that pixel value, and therefore in fact is a corrected digital pixel value.
  • the specific calibration correction for each image pixel is derived from the present pixel value correction calibration process.
  • the individual corrected digital pixel values of the same specific image pixel from different image frames is processed according to an algorithm of the calibration process over at least some of the collected image frames to provide the pixel value to be displayed in the final image. Therefore, it is a further object of the present invention to provide a calibration (or correction) method to enable the current invention to be implemented.
  • the calibration method is applicable on each pixel of the imaging system and takes into account the offset and gain corrections as well as temporal (time) corrections as this is applied on a frame by frame basis. There maybe no need to have different correction for each pixel and each frame but in accordance with the current invention at least some of the frames have different temporal correction for corresponding pixels.
  • FIG. 1 is a block diagram generally illustrating the interconnect relationship of components of the present high energy, direct radiation conversion, real time X-ray imaging system
  • FIG. 2 is a schematic representation of an imaging device useful in the camera module of the present invention.
  • FIG. 3 is a graphic representation of the output over time of a single pixel circuit of a Cd—Te based direct conversion camera using detector bias voltage switching. The figure illustrates that the output signal from a typical pixel circuit drifts over time as circuit recovers from a bias voltage switching event (pulse).
  • FIG. 4 is a graph illustrating the temporal variation in the raw intensity value of the same single image pixel of FIG. 3 overlaid with a series of image frame capture points generated over time after a bias voltage switching event.
  • FIG. 5 is a graph illustrating normalization of the intensity value of an image pixel by the application of a specific time dependent correction coefficient to the raw intensity value of the particular image pixel's output in each image frame.
  • FIG. 6 is a graph illustrating an asymmetric data sampling feature of the calibration procedure of the present imaging system for ameliorating the problem of excessive data collection and processing load.
  • FIG. 7 is a block flow chart illustrating a general overview of the present calibration procedure.
  • FIG. 8 is a block flow diagram illustrating a data collection strategy from a single pixel circuit at a specific reference X-ray field intensity.
  • FIG. 9 is a block flow diagram illustrating a strategy for calculating correction coefficients for each image pixel in a pixel frame.
  • FIG. 10 is a block flow diagram illustrating a strategy for detecting and compensating for bad or uncorrectable pixels.
  • FIG. 11 is a block flow diagram illustrating the application of the present calibration process to provide a normalize image frame.
  • FIG. 12A is a graph illustrating the typical prior uniform sampling method wherein an integration by uniform parts type calculation is used to determine correction coefficient for normalizing pixel intensity values at specific times or intensities to fit a curve.
  • FIG. 12B is a graph illustrating an asymmetric sampling method wherein an integration by increasing parts type calculation is used to determine correction coefficients for normalizing pixel intensity values at specific times.
  • FIG. 12C is a graph illustrating an alternative sampling method wherein an asymmetric linear polynomic calculation is used to determine correction coefficients for normalizing pixel intensity values at specific times.
  • the present invention is a high energy, real-time capable, direct radiation conversion X-ray imaging system 10 . More specifically, the present invention relates to such X-ray imaging systems 10 utilizing a Cd—Te or Cd——Zn—Te based camera.
  • the present real-time capable X-ray imaging system 10 like imaging systems generally, comprises a camera module, an image processor 14 , and a display means 16 .
  • the camera module 12 includes an X-ray imaging device 28 having a Cd—Te or Cd——Zn—Te based radiation detector substrate 30 in electrical communication with an Application Specific Integrated Circuit (ASIC) readout substrate 32 .
  • ASIC Application Specific Integrated Circuit
  • FIG. 2 is a schematic representation of an imaging device 28 useful in the camera module 12 of the present imaging system 10 .
  • the detector semiconductor substrate 30 has electrical connections 35 to an readout ASIC substrate 32 (e.g., bump-bonds in the preferred embodiment illustrated).
  • the detector material 34 a Cadmium-Telluride based composition in the present invention, of the semiconductor substrate 30 absorbs incoming radiation, and in response to the absorption the radiation energy is directly converted to electrical charges within the thickness of the detector material 34 .
  • the electrical charges are collected at the detector pixel's collection electrode (pixel contact) 38 of each active or functioning pixel 36 , and electrically communicated through the electrical connections 35 to the pixel circuit contacts 33 on the pixel circuit 31 of the readout ASIC substrate 32 .
  • the electric charge signals are stored and/or processed at a detector pixel's corresponding pixel circuit 31 on the readout ASIC 32 . Thereafter, the ASIC pixel circuits 31 are usually multiplexed and an analog output is sequenced and digitized either on chip or off-chip.
  • the camera module 12 and the high speed frame processor module 18 are in communication via a cable link 60 .
  • the camera module 12 provides processed and organized pixel data, representing the individual raw pixel circuit output of each pixel cell 29 , to the frame processor module 18 .
  • the high speed frame processor module 18 includes a frame grabber circuit typical of the field, which captures the pixel circuit data from the camera module 12 further processes the pixel circuit data to provide a raw time-stamped image frame representing the raw pixel circuit output of each pixel cell 29 .
  • the frame processor 18 then communicates the raw time-stamped image frame data via a frame data link 66 to the calibration module 20 if the system is in the calibration mode, or otherwise to the normalization module 24 .
  • the calibration module 20 controls the calibration process.
  • the calibration process analyzes the raw time-stamped image frame data and other calibration parameters, such as reference field radiation intensity, and generates the data necessary to load the look-up table of the calibration data structure module 22 .
  • the calibration module 20 writes to the data structure via a database link 68 . Without proper calibration data loaded into the look-up table, any image output from the normalization module 24 to the display module will be inaccurate. Therefore, the calibration process must be run prior to normal imaging operation of the present system.
  • the frame processor 18 communicates the time-stamped image frame data to the normalization module 24 .
  • the normalization module 24 operates on each image pixel of the raw time-stamped image frame with the image pixel's corresponding correction requirement derived from the look-up table via a second database link 70 .
  • the normalization module 24 then provides a normalized image frame to the display module 16 via a display data link 74 . Every image pixel of the normalized image frame represents its corresponding raw image pixel intensity value corrected by its corresponding correction coefficient from the look-up table.
  • Cadmium-Telluride based detector substrates 30 there is a continuous leakage current (aka: dark current) that must be compensated for.
  • Certain Cd—Te or Cd——Zn—Te detector materials 34 are manufactured having a blocking contact (not shown) to control the level of leakage current.
  • Other manufactures have various amounts of Zn or other dopants in the detector material 34 to suppress leakage current.
  • the leakage current creates noise and also fills up the charge collection gates 33 on each pixel circuit 31 .
  • the use of blocking contacts introduces the problem of polarization or charge trapping which becomes evident after few seconds of operation, for example, after 5 sec, 10 sec or 60 sec etc., depending on the device.
  • Cadmium-Telluride based compositions i.e., Cd—Te and Cd——Zn—Te
  • Cd—Te and Cd——Zn—Te Cadmium-Telluride based compositions
  • Even in the absence of a blocking contact the issue of the leakage current and crystal defects do not allow long exposures in excess of 100 msec without increasing the size of the charge storage capacitor on each pixel circuit 31 of the ASIC readout substrate 32 .
  • the present invention has been successfully practiced using a capacitance of the order 50 fF as charge storage capacitance on each ASIC pixel circuit receiving charge.
  • capacitance of the order 50 fF as charge storage capacitance on each ASIC pixel circuit receiving charge.
  • the practical maximum exposure time given the Cd—Te or Cd——Zn—Te leakage current and other defects would be 100 msec or less.
  • a very useful mechanism for preventing excessive polarization (charge trapping) from forming in a direct conversion (charge coupled) radiation detector device is to briefly cycle the high voltage bias off and on, a technique called detector bias voltage switching.
  • the detector substrate bias voltage is switched off for a brief period (less than 100 milliseconds) at the end of a data collection cycle.
  • the duration of a data collection cycle is selectable, e.g., from every three to twenty or more seconds.
  • Bias voltage switching prevents polarization or charge trapping from developing in the detector substrate 30 .
  • the bias voltage switching technique is new in the field of X-ray imaging systems, and does have certain aspects that can impact image quality if the are not addressed.
  • Dead-time is the period in a data collection cycle when the detector bias voltage is off and no detector charges can be collected.
  • Pixel response drift is a the result of switching the detector bias voltage back on, and is the initial period that the data collection cycle that the that the pixel's response to a static radiation field has not yet stabilized. Both of these limitations are illustrated in FIG. 3 .
  • the data collection cycle time Ct was the time between the initiation of detector bias voltage off/on pulses 50 .
  • the dead-time Dt consists of the actual high voltage down-time Vo plus some stabilization time after the high voltage has been switched back on.
  • the effect of dead-time Dt cannot be less than Vo, and hence cannot be completely eliminated in a switched detector bias voltage imaging system.
  • it can be minimized in part by reducing the off-time of the bias voltage to as short a period as is appropriate to allow any polarization (trapped charge) to bleed off and/or to keep the dead-time to a negligibly small portion of the data collection cycle.
  • the other potentially limiting aspect of a bias voltage switched detector is pixel response drift Rd, which relates to the non-linear aspect of a pixel circuit's output signal over time 40 in response to a static radiation field exposure level. See FIG. 3 .
  • This non-linearity is most pronounced immediately following the voltage-on step of the voltage off-on pulse 50 . Uncorrected, this non-linearity causes pumping of the image's overall brightness level in a real time image display.
  • the pixel cell non-linear response in a switched bias voltage imaging device is an excellent case for applying the post-image frame generation calibration method of the present imaging system to eliminate this intensity distortion of a real time X-ray image display.
  • the present calibration method 10 is especially useful for practice in digital imaging systems utilizing detector bias voltage switching.
  • the camera module 12 of a digital imaging system utilizing detector bias voltage switching typically comprises a detector/CMOS assembly 28 having thousands of pixel cells 29 , each comprising a detector pixel 36 and an associated pixel circuit 31 .
  • Each pixel circuit 31 includes associated circuitry and a pixel circuit signal output (not shown) producing a digitized pixel signal for that pixel circuit 31 .
  • a pixel circuit output signal indicates the intensity of the X-ray/Gamma ray radiation energy impinging on the associated detector pixel 36 . See FIG. 2 .
  • the collected digitized pixel signal outputs are communicated via a camera link 60 to a high speed frame processor module 18 of the image processor 14 .
  • the frame processor module 18 includes a frame grabber circuit which receives the individual pixel circuit output signals from each pixel circuit 31 .
  • the frame processor module 18 organizes the individual digitized pixel signals into an image frame, with each image pixel of the image frame representing the pixel signal of a corresponding to the pixel circuit in the imaging device 28 of the camera module 12 .
  • the intensity of an image pixel in the image frame is representative of the strength of the pixel signal received from the corresponding pixel circuit 31 .
  • FIG. 7 is an overview of the steps of the calibration process of the present imaging system.
  • FIGS. 8 to 10 detail the calibration procedure.
  • FIG. 11 details the normalization procedure, wherein the raw image pixel data from the frame processor module is normalized.
  • the calibration process uses a software driven calibration module 20 to create and maintain a “look-up table” resident in a data structure module 22 .
  • the look-up table is a set of time dependent, image pixel specific correction coefficients 54 for each pixel of an image frame.
  • the pixel specific correction values 54 are referenced to a target uniform intensity value 52 (see FIG. 5 ), and are used to correct the raw value of the specific image pixel to a normalized value. Therefore, each image pixel represented in an image frame has a data set of time dependent correction coefficients in the look-up table of the data structure module 22 generated for each of a number of reference x-ray field intensities.
  • the time dependency of a set of correction coefficients/values derives from the application of a time-stamp to each image frame processed by the high speed frame module.
  • the time-stamp indicates the time elapsed since the start of the data collection cycle Ct that the image frame was generated.
  • the time stamped image frames 44 were captured (grabbed) from the camera module 12 at uniform frame intervals 46 in the data collection cycle Ct. Therefore, the time-stamped image frames 44 always had the same time difference relative to each other.
  • a separate calibration data set was calculated for each image pixel and included a correction value for that specific image pixel at each time-stamp in the data collection cycle Ct.
  • the calibration data can be thought of or organized as consisting of N different calibration data sets, one for each image frame of the data collection cycle Ct, each frame data set comprising a separate correction value/coefficient for each image pixel in the frame.
  • N should be selected as the highest number of different time stamps possible N max , or in other words, the highest frame rate possible.
  • N ⁇ N max has to be selected.
  • First step in the calibration method is to collect the relevant data, specifically, the response of the camera's imaging device 28 to different reference radiation field intensities.
  • the response of each pixel cell 29 of the device 28 is collected for all the time-stamps in the data collection cycle Ct. In the preferred embodiment illustrated, this step was repeated at least 20 times, to reduce the effect of incoming quantum noise. Collecting the relevant data this way corrects for any non-uniformities in the detector or ASIC components, but also intrinsically provides “flat-field” correction.
  • the calibration method tied the imaging device 28 of the camera module 12 to a specific geometric relationship with the radiation source. Which is to say, the calibration had to be redone whenever the radiation source or the geometry between the imaging device 28 and the radiation source changed. Also, calibration was repeated for each radiation spectrum used.
  • MAP Maximum A Posteriori
  • p(x) is the uninteresting scaling factor, evidence. If we assume normal distribution for noise and for function parameter prior p ( x
  • the final parameter values can be solved by differentiating the equation above with respect to all the function parameters a i and then setting the derivative equal to zero.
  • the motivation for using weighted least squares is that when using different X-ray intensities, the quantum noise for the highest intensity is much higher than, for example, the dark current. This allows more weight to be given to smaller values, which are probably more accurate.
  • the total data rate for 50 fps operation was 248 MB/second.
  • the previous image values were also read from the memory, which gave another 24.8 MB/second, and a total of 273 MB/second memory bandwidth. If the images are displayed on a screen, the 16-bit pixel values is read from the memory, a 32-bit color value is read from the lookup-table per pixel and the final 32-bit values is stored in the display memory giving additional 124 MB/second for a grand total of 397 MB/second. And the field is moving to even larger cameras.
  • FIGS. 12A to 12 C are a further illustration of this.
  • FIG. 12A shows the prior art method of error sampling. However, at 300 fps with a 30 sec data collection cycle and a 100,000 pixel camera, and 4 parameters at 4 bytes/parameter, 13 GB of data must be collected and processed. This is impractical.
  • FIG. 12B shows a present non-uniform method of error sampling, which under camera operating perimeters similar to FIG. 12A only generated about 480 MB of data to be collected and processed.
  • FIG. 12C illustrates a preferred non-uniform error sampling method using linear interpolation. Under camera operating perimeters similar to FIG. 12A , this method only generated about 16 MB of data to be collected and processed. This is a reduction in storage and processing requirements by a factor of 30 over the prior art method of FIG. 12A .
  • a selection can be made to utilize an optimized subset image frames, which the present calibration does.
  • the changes in a pixel cell's circuit output signal over time 40 are more drastic.
  • the calibration data sets should include more relatively reference frames from this portion of the collection cycle Ct than towards the end of the collection cycle Ct where the output signal over time 40 can be relatively flatter.
  • an automatic method was used to allow the user to change exposure time (i.e. frame rate) and/or the off-time of the detector bias voltage 50 , but the settings can be accomplished manually as well.
  • the present calibration method calculates a local average value of a set of neighboring pixel cell output signals and then compares this value to individual pixel output signal values. This allows the calibration method to adapt to a non-stationary radiation field.
  • the relative positions on the ASIC hybrids are ideally close and uniform, which means that there are some inactive areas (dead space) between adjacent hybrids and that the relative distances can vary between different adjacent hybrid.
  • the solution to this problem is two-step. First, measurements were made of the distances between hybrids and possible rotation angles of hybrids based on a calibration image of a reference object. Then, the errors were corrected based on these measurements. The measurements were made by using the camera itself as a measuring device, and taking images with a calibrated reference object that has very accurate dimensions. Then after measuring the distances, the known and measured values were compared and the mismatches detected.

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US11/017,629 2004-07-06 2004-12-20 High energy, real time capable, direct radiation conversion X-ray imaging system for Cd-Te and Cd-Zn-Te based cameras Abandoned US20060011853A1 (en)

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US11/017,629 US20060011853A1 (en) 2004-07-06 2004-12-20 High energy, real time capable, direct radiation conversion X-ray imaging system for Cd-Te and Cd-Zn-Te based cameras
KR1020087029854A KR100987404B1 (ko) 2004-07-06 2005-07-01 카드뮴-텔루르계 및 카드뮴-아연-텔루르계 카메라용 고에너지 실시간 직접 방사선 변환 엑스선 이미징 시스템
PCT/IB2005/001896 WO2006003487A1 (en) 2004-07-06 2005-07-01 High energy, real time capable, direct radiation conversion x-ray imaging system for cd-te and cd-zn-te based cameras
JP2007519900A JP2008524874A (ja) 2004-12-20 2005-07-01 Ｃｄ−ＴｅおよびＣｄ−Ｚｎ−Ｔｅベースカメラ用の高エネルギーの実時間可能な直接放射線変換Ｘ線撮像システム
EP07104046A EP1795918B1 (en) 2004-07-06 2005-07-01 High energy, real time capable, direct radiation conversion x-ray imaging system for CD-TE and CD-ZN-TE based cameras
EP10152915A EP2192422B1 (en) 2004-07-06 2005-07-01 High energy, real time capable, direct radiation conversion X-ray imaging system for Cd-Te and Cd-Zn-Te based cameras
AT05780149T ATE457467T1 (de) 2004-07-06 2005-07-01 Echtzeitfähiges hochleistungs- röntgenbildgebungssystem mit direkter strahlungsumwandlung für kameras auf cd-te- und cd-zn-te-basis
EP05780149A EP1763685B1 (en) 2004-07-06 2005-07-01 High energy, real time capable, direct radiation conversion x-ray imaging system for cd-te and cd-zn-te based cameras
KR1020077001623A KR100962002B1 (ko) 2004-07-06 2005-07-01 카드뮴-텔루르계 및 카드뮴-아연-텔루르계 카메라용고에너지 실시간 직접 방사선 변환 엑스선 이미징 시스템
KR1020087029856A KR100989666B1 (ko) 2004-07-06 2005-07-01 엑스선 이미징 시스템
DE602005019297T DE602005019297D1 (de) 2004-07-06 2005-07-01 Echtzeitfähiges hochleistungs-röntgenbildgebungssystem mit direkter strahlungsumwandlung für kameras auf cd-te- und cd-zn-te-basis
US11/226,877 US8530850B2 (en) 2004-07-06 2005-09-14 High energy, real time capable, direct radiation conversion X-ray imaging system for Cd-Te and Cd-Zn-Te based cameras
US13/935,663 US20130334433A1 (en) 2004-07-06 2013-07-05 High energy, real time capable, direct radiation conversion x-ray imaging system for cd-te and cd-zn-te based cameras

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US10426361B2 (en) 2013-06-14 2019-10-01 Novadaq Technologies ULC Quantification of absolute blood flow in tissue using fluorescence-mediated photoplethysmography
US10285603B2 (en) 2013-06-14 2019-05-14 Novadaq Technologies ULC Quantification of absolute blood flow in tissue using fluorescence mediated photoplethysmography
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US20170303800A1 (en) * 2014-10-09 2017-10-26 Novadaq Technologies Inc. Quantification of absolute blood flow in tissue using fluorescence-mediated photoplethysmography
US10631746B2 (en) * 2014-10-09 2020-04-28 Novadaq Technologies ULC Quantification of absolute blood flow in tissue using fluorescence-mediated photoplethysmography
US20160356162A1 (en) * 2015-06-03 2016-12-08 Rolls-Royce Plc Manufacture of component with cavity
US20190355116A1 (en) * 2015-09-23 2019-11-21 Novadaq Technologies ULC Methods and systems for assessing healing of tissue
US10636144B2 (en) * 2015-09-23 2020-04-28 Novadaq Technologies ULC Methods and systems for assessing healing of tissue
US10311567B2 (en) * 2015-09-23 2019-06-04 Novadaq Technologies ULC Methods and systems for assessing healing of tissue
US20170084024A1 (en) * 2015-09-23 2017-03-23 Novadaq Technologies Inc. Methods and systems for assessing healing of tissue
US10646128B2 (en) 2016-02-16 2020-05-12 Novadaq Technologies ULC Facilitating assessment of blood flow and tissue perfusion using fluorescence-mediated photoplethysmography
US11701016B2 (en) 2016-02-16 2023-07-18 Stryker European Operations Limited Facilitating assessment of blood flow and tissue perfusion using fluorescence-mediated photoplethysmography
US11140305B2 (en) 2017-02-10 2021-10-05 Stryker European Operations Limited Open-field handheld fluorescence imaging systems and methods
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US12028600B2 (en) 2017-02-10 2024-07-02 Stryker Corporation Open-field handheld fluorescence imaging systems and methods
CN107569249A (zh) * 2017-08-25 2018-01-12 沈阳东软医疗系统有限公司 一种晶体能量校正方法和装置
US11559267B2 (en) 2018-04-25 2023-01-24 Athlos Oy Ultra-fast scanning x-ray imaging device
US11647972B2 (en) 2018-04-25 2023-05-16 Athlos Oy Ultra-fast scanning x-ray imaging device
US11653886B2 (en) 2018-04-25 2023-05-23 Athlos Oy Ultra-fast scanning x-ray imaging device

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EP2192422B1 (en) 2013-03-06
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KR100987404B1 (ko) 2010-10-12
EP1763685A1 (en) 2007-03-21
KR20090006227A (ko) 2009-01-14
WO2006003487B1 (en) 2006-04-06
US20060071174A1 (en) 2006-04-06
KR100989666B1 (ko) 2010-10-28
WO2006003487A1 (en) 2006-01-12
US8530850B2 (en) 2013-09-10
EP1763685B1 (en) 2010-02-10
KR100962002B1 (ko) 2010-06-08
US20130334433A1 (en) 2013-12-19
ATE457467T1 (de) 2010-02-15
KR20070036780A (ko) 2007-04-03
DE602005019297D1 (de) 2010-03-25

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