Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/58—Testing, adjusting or calibrating thereof
  • A61B6/582—Calibration
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
  • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
  • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
  • G01N23/046—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material using tomography, e.g. computed tomography [CT]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T7/00—Details of radiation-measuring instruments
  • G01T7/005—Details of radiation-measuring instruments calibration techniques
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T5/00—Image enhancement or restoration
  • G06T5/40—Image enhancement or restoration using histogram techniques
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T5/00—Image enhancement or restoration
  • G06T5/77—Retouching; Inpainting; Scratch removal
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T7/00—Image analysis
  • G06T7/0002—Inspection of images, e.g. flaw detection
  • G06T7/0012—Biomedical image inspection
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T7/00—Image analysis
  • G06T7/80—Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
  • H04N23/30—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from X-rays
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/40—Arrangements for generating radiation specially adapted for radiation diagnosis
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/10—Image acquisition modality
  • G06T2207/10116—X-ray image
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/30—Subject of image; Context of image processing
  • G06T2207/30004—Biomedical image processing
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/30—Subject of image; Context of image processing
  • G06T2207/30168—Image quality inspection
• • 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

Definitions

• the present invention relates to direct and computed
• the invention more particularly relates to a method for preventing a sub-optimal gain map quality by detecting avoidable disturbances present in the x-ray beam-path during system
• System calibration is extremely important for digital and computed projection radiography where flat-panel detectors and x-ray storage media in combination with digitizers are used to acquire digital images for clinical, veterinary or industrial use.
• image acquisition devices are rather complex hybrid (analog and digital) systems which are composed of a variety of highly interacting mechanical, electro-optical, physico-chemical, electronics, software and image-processing components and processes each having its typical tolerances and physical properties.
• the overall image quality performance of a radiographic system can also depend on the ambient temperature, the humidity, the atmospheric pressure as well as on the x-ray exposure history linked to the degree of system usage and the system's actual age.
• the image-acquisition system needs to be cleaned and recalibrated on a regular basis.
• the system calibration process not only delivers a better adjusted and cleaner state of the radiographic equipment but also generates one or multiple image-wide maps at pixel resolution for the reconstruction of unstable and or defective pixels, rows and columns in addition to one or more gain maps for the software- or hardware-based, pixel-wise sensitivity-correction of raw diagnostic images.
• a gain map of a detector system is an image-wide
• the gain map which is determined as one of the outputs of the ( re ) calibration process, is often calculated from a set of non-x-ray exposed, raw dark-images in combination with a set of dedicated, homogeneously exposed raw flat field images.
• the flat- panel-detector is geometrically positioned these dedicated image sets, required for the gain map determination during calibration, can easily be acquired sequentially from the operator's control cabinet without the need for further manual interventions to the system itself.
• Disturbing objects can have various dimensions from very big (e.g. a screw-driver, a pull-over) to very small (e.g. a screw, a washer, a lost staple).
• very big e.g. a screw-driver, a pull-over
• very small e.g. a screw, a washer, a lost staple
• Some objects with a mixed material composition can locally introduce strongly fluctuating x-ray attenuation (e.g. a dosimeter) whereas others have hardly noticeable, fuzzy and noisy object- borders (e.g. a cleaning-cloth) . Even an unexpected visit of an insect accidentally interfering with the x-ray beam path during system recalibration can't be totally excluded.
• non-corrected raw flat-panel detector images also in scope for this inspection, can exhibit a significant level of streakiness and strip-wise signal-variation due to the multiple ASICs-based electronic circuits used for the parallel image read-out of the detector array.
• sub-optimal gain maps for the correction of many thousands of future raw diagnostic images can potentially be generated without notice. Best case such a sub-optimal gain map will generate a corrected verification flat field image, often acquired as a final step in the calibration procedure, which is showing a sufficient level of image disturbance to be regarded as a system calibration problem by the operator who is performing the (re) calibration activities.
• An automatic method relying on the statistical analysis of a multitude of adjacent or partially overlapping, potentially object- disturbed regions-of-interest , can act on the raw (non-corrected) , dedicated flat field images, acquired for the purpose of gain map calculation to optimize the overall image quality performance of direct and computed radiography image-acquisition systems.
• Fig. 1 illustrates the decision making logic based on the set of local shoulder significance and unbalance results analyzed in the image as compared to a set of predetermined threshold levels
• Fig. 2 represents a local region-of-interest as cropped from an object-disturbed image-tile and its statistical translation into spatially distributed shoulder-pixel patterns
• Fig. 3 represents the valid pixel histogram of the object- disturbed local region-of-interest as analyzed and split
• Fig. 4 represents both local shoulder fractions and their shoulder ratio relative to their significance and unbalance
• radiography system where individual x-ray images, acquired to compose the set of homogeneously exposed images are individually subjected to a fast, automatic, disturbing object inspection method prior to being accepted as a valid input image for the calculation of an updated gain map.
• Fig. 1 explains a specific embodiment of the method of this invention by means of a process flow-chart acting on an individual image, acquired for the purpose of gain map determination, which might contain a disturbed, local region-of-interest .
• the avoidable, disturbed x-ray beam path condition is in this exemplary embodiment caused by an elastic band which was left behind by accident on the detector-surface before starting with
• a disturbed image-tile represented with high contrast- magnification for improved visibility of this low x-ray absorption object, shows how this 'forgotten to remove' object partially intersects with an arbitrarily chosen region-of-interest ROIij and how it locally influences the normally expected smooth background noise pattern which is typical for a homogeneously exposed detector image .
• the process of automatic detection of disturbing objects in homogeneously exposed flat field images starts by dividing the image, subjected to this inspection, in a plurality of much smaller, local regions-of-interest .
• the beam path inspection concept described in this embodiment uses 64x64 pixels ( 8 mm square ) inspection-ROIs with a l/4 th ROI- size overlap in both image directions.
• defect map which flags the detector-array's unreliable pixels, rows and colums may be available for the purpose of image-reconstruction using neighbouring, reliable pixel data.
• the inspection-ROI ' s valid pixels subset is derived from which either the local median (in a preferred embodiment) or the average or modus signal value is calculated .
• That value represents the central signal value y 'C'' for the further operations performed on the histogram of valid pixel values as depicted in Fig. 3. Since all the image-pixels are valid in digitizer- / media- based computed radiography (CR) a defect map is neither available nor required for the detection of beam-path disturbing objects during the inspection of the homogeneously exposed images made for the calculation of the CR-cassette ' s gain-image.
• CR computed radiography
• a lower and a higher signal shoulder can be defined inside the local histogram as the collections of the lower and the higher valid pixel shoulder fractions composed of the spatially distributed pixels having signal-values below C-delta or above C+delta .
• the histogram-gap, determined by the signal delta, that separates the low and the high shoulders from the central value can be predetermined as either a fraction of the central value itself or as a predetermined factor times the standard deviation of the smooth background noise, calculated as the median noise deviation estimate from a limited set of spatially distributed image ROIs.
• the shoulder ratio is calculated by dividing the biggest of both shoulder fractions by the smallest. Undisturbed image noise will typically return a near equity shoulder ratio.
• the shoulder ratio will increase.
• each of them is compared to its predetermined threshold level .
• the threshold for the shoulder fraction determines if the measured value is sufficiently significant to be flagged as one of the prerequisites for object detection.
• the threshold for the shoulder ratio determines if the measured value is sufficiently unbalanced to be flagged as one of the prerequisites for object detection.
• the decision logic for the detection of a ROI-disturbance is such that a local ROI is regarded as object-disturbed if a
• the result of that local ROI decision can be stored in an image-wide disturbance memory for further decision making regarding the image-disturbance at a higher level.
• An image-wide criterion could be that a very limited amount of solitary disturbed ROIs can still be accepted if these isolated disturbances all occur in ROI's adjacent to the image borders.
• the beam path is regarded as object disturbed. In that case additional inspection, cleaning and or a correction (e.g. the removal of the disturbing object ) of the x-ray beam path might be necessary before an image- retake can be performed.

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• 2012
  • 2012-06-11 EP EP12171474.5A patent/EP2675151A1/en not_active Withdrawn
• 2013
  • 2013-06-05 US US14/402,363 patent/US9741102B2/en not_active Expired - Fee Related
  • 2013-06-05 WO PCT/EP2013/061591 patent/WO2013186099A1/en not_active Ceased
  • 2013-06-05 BR BR112014030423A patent/BR112014030423A2/pt not_active IP Right Cessation
  • 2013-06-05 CN CN201380030642.XA patent/CN104350738B/zh not_active Expired - Fee Related
• 2014
  • 2014-11-17 IN IN9699DEN2014 patent/IN2014DN09699A/en unknown

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