Image analysis – Image transformation or preprocessing – Measuring image properties
Reexamination Certificate
2000-04-17
2004-07-13
Patel, Jayanti K. (Department: 2724)
Image analysis
Image transformation or preprocessing
Measuring image properties
C250S371000
Reexamination Certificate
active
06763147
ABSTRACT:
TECHNICAL FIELD AND PRIOR ART
The invention relates to a process for the formation of an image obtained by a camera and comprising an array of detector pixels.
The invention more particularly applies to the field of medical imaging using gamma cameras integrating a detector in the form of an array of pixels based on CdZnTe or CdTe semiconductor material.
The array of detector pixels of a gamma camera is constituted by regularly spaced pixels, surmounted by a collimator, preferably having square holes.
The collimator is placed in front of the array of pixels in order to only retain the radiation having an incidence perpendicular to the surface of the pixels. The semiconductor detectors directly convert the energy of the gamma photons into charge carriers. The collection of the charge carriers takes place by means of contacts deposited on each pixel and to which is applied a high bias voltage. The amplification and shaping of the signal are then effected by an electronic circuit, whose digital output supplies the value allocated to the image pixel.
Therefore the response of a pixel of the array corresponds to the sum of the gamma events received at the surface of the pixel.
The image produced by a gamma camera detector constituted by CdZnTe or CdTe semiconductor material pixels has a very pronounced “mosaic” appearance. This “mosaic” appearance is very disadvantageous compared with the continuous appearance of the image produced by an Anger detector.
An Anger detector makes it possible to transform the incident gamma rays into light and then electric pulses, define the location of the gamma photons which have interacted and measure the deposited energy. An Anger detector is constituted by a collimator, a scintillator crystal, a light guide, photomultiplier tubes and locating electronics.
The holes of the collimator, perpendicular to the scintillator surface, only permit the passage of rays normal to the entrance plane of the detector. The scintillator-light guide assembly makes it possible to transform the incident gamma photons into light photons and distribute the light over several photomultipliers. The light photons are emitted isotropically, their number following Poisson's law. The photomultipliers transform these light photons into electrons, whose number is then multiplied by dynodes. The number of photoelectrons emitted also follows Poisson's law.
The locating electronics calculates a barycentre of contributions of photomultipliers, whose significances correspond to their geographical position on the crystal and the resulting image is therefore created by sampling these responses.
An object of the invention is to implement a process enabling the images from an array of gamma camera detector pixels to have a quality like that of images from an Anger camera.
The invention relates to a process for the formation of an image obtained from an array of detector pixels comprising at least one detector pixel, the image formed being constituted by at least one set of P image pixels for each detector pixel. The process comprises:
a stage making it possible to create N elementary pixels from one detector pixel, N being an integer equal to or lower than P and
a stage of randomly distributing events received by each detector pixel in the N image pixels corresponding thereto.
An advantage of the invention is that of eliminating the “mosaic” appearance of the image produced by a gamma camera.
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patent: 5491342 (1996-02-01), Lim et al.
patent: 5508524 (1996-04-01), Goldberg et al.
patent: 5576547 (1996-11-01), Ferreira et al.
patent: 5847398 (1998-12-01), Shahar et al.
patent: 6025875 (2000-02-01), Vu et al.
patent: 6091070 (2000-07-01), Lingren et al.
Dinten Jean-Marc
Gliere Alain
Koenig Anne
Mestais Corinne
Azarian Seyed
Commissariat a l'Energie Atomique
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Jayanti K.
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