Picker International, Inc.

Koninklijke Philips Corporation N.V.

Hung Y Wong

Donald E Negrelli

David Nicolay

Robert J Vagi

Zhongmin Steve Lin

Mark W Magalotti

An adaptive median filter ( ) provides dynamic detection and correction of digital image defects which are caused by defective or malfunctioning elements of a radiation detector array ( ). The adaptive median filter receives ( ) lines of pixel values of a digital image that may have defects and a user-defined defect threshold. The lines of pixel values are scanned on a pixel-by-pixel basis using a kernel of n&times;n pixels, where the kernel contains the candidate pixel being examined ( ). Each kernel is numerically reordered ( ) and a median value is calculated ( ). A defect threshold value is calculated by multiplying the user-defined defect threshold criteria and the candidate pixel value ( ). A reference value is calculated by subtracting the candidate pixel value and the median value ( ). The reference value is compared to the defect threshold value ( ). The candidate pixel value is replaced by the median value ( ) if it differs from the median value by more than the predefined defect threshold, e.g., 20%. The adaptive median filter is particularly effective in detecting and correcting double line and double column defects in digital images. In addition, the filter minimizes image blurring and maintains image resolution by filtering only defective pixels.

Method and apparatus for digital image defect correction and noise filtering

A gantry (18) that carries an x-ray source (14) and an x-ray detector (16) rotates around a test phantom (10) in a forward direction. A plurality of forward projection images are generated and stored in a forward image memory (42). The angle at which each forward direction projection image is generated is stored in a position memory (56). The gantry is then rotated in a reverse direction and a reverse direction image is generated at generally the same angular positions as in the forward rotation direction. The forward and reverse direction projection images of the phantom are analyzed to determine an offset or error between each corresponding forward and reverse angular image position. The offsets are stored in an angular position look-up table (80) and a pixel reregistration look-up table (82). In subsequent reverse scans, the angular position at which the reverse direction projection images are taken are altered in accordance with the angular offset for the corresponding angular position. The forward sweep images are video pixel position shifted in accordance with the video pixel offset for the corresponding angular position to bring the forward and reverse direction projection images into registration.

Rotational digital subtraction angiography phantom

A patient is positioned on a patient support (12) and a gantry (16) carrying an x-ray source (10) and a radiation detector assembly (14) are rotated around the subject. The detector assembly includes a video camera (28) which is run in a synchronous mode to generate a first plurality of images at regular temporal intervals T.sub.blanking. Because each image requires a finite time for generation, it is acquired over an interval of arc between a starting angular orientation (A.sub.S .degree., B.sub.S .degree.) and a terminal angular orientation (A.sub.T .degree., B.sub.T .degree.). A position encoder (40) monitors the terminal positions of each of the first series of images. The patient is then injected with a radiographic dye and the gantry is rotated in a reverse direction. A comparator compares the stored terminal angular positions of each forward direction image and the current angular position of the gantry. A trigger circuit (54) triggers an asynchronous mode x-ray exposure controller (50) such that a video image is commenced at each terminal angular orientation. Images generated over substantially the same arc segment are subtracted (66) to form a difference image for storage in a difference image memory (68) and display on a monitor (72).

Rotational angiography dye and mask image acquisition and synchronization

A video processing system includes a plurality of identical video switch modules (A). Each of the video switch modules has matching inputs and outputs such that received signals can be passed through unchanged, enabling the modules to be connected in a daisy chain or series relationship. Each of the modules further includes inputs and outputs for receiving video signals from and sending video signals to procedure rooms (B). Preferably, each of the procedure rooms includes medical diagnostic apparatus (10-18) which produce one or more unprocessed video signals, a first video monitor (22) for displaying first processed video signals, a second monitor (24) for displaying second processed video signals, and a VCR (20) for recording and playing back second processed video signals. The daisy chain of video switch modules is interconnected at one end with a shared digital image processing system (C). Unprocessed video signals from a selected one of the procedure rooms are connected by its corresponding video switch module and the other daisy chained modules to the digital image processing system. The digital image processing system processes the received video signals and images from memory (34) to provide at least first and second processed video signals that are sent back through the daisy chained switch modules to the selected module.

Daisy chain video switches

A multi-mode acquisition x-ray imaging system (A) provides a unified apparatus and method to acquire valid x-ray video images including the last image of a run, and to display these images flicker-free on an image monitor (50). A beam blanking signal (54) synchronizes operation of a TV camera (48) and TV camera controller (56), so all image data or frames acquired in any acquisition mode including one having a pulse exposure rate or an asynchronous pulse exposure rate is acquired and processed by a digital imaging system (40). The image data is stored in a dual buffered storage (76) which alternatingly connects a first buffer (80a) and a second buffer (80b) to the image monitor (50). When the exposure rate is changed, transition logic (84) determines whether images, exposed during the transition to another exposure rate are under or overexposed.

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Solon, OH, United States of America

Hung Y Wong