Abstract:
A method for improving the quality of a fluoroscopic image where the image out of an image sequence of images which satisfies a predetermined minimum motion criterion is stored and this stored image is continuously displayed. The images may be acquired using a pulsed cardiac fluoroscope.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to pulsed cardiac fluoroscopy and, more particularly, to improving the quality of a fluoroscopic image displayed continuously, that is to say, for example, when the operator takes his foot off the control pedal of the fluoroscopic image acquisition device. 
     Fluoroscopy consists in acquiring radiographic images (referred to below as fluoroscopic images) at a high rate, these being intended to be displayed a display screen. Fluoroscopy is, for display the path of probes injected directly on example, used into blood vessels. 
     There are several versions of fluoroscopy. In this regard, mention may be made of what is referred to as continuous fluoroscopy, characterized by continuous exposure of the patient to X-rays, and what is referred to as pulsed fluoroscopy, characterized by X-ray pulses which have a predetermined time width and are repeated at the frequency with which the pictures are taken. 
     Thus, in pulsed fluoroscopy, when the operator presses the control pedal of the device, X-ray pulses are emitted sequentially, each pulse making it possible to acquire one fluoroscopic image. 
     When the operator takes his foot off the pedal, a fluoroscopic image is then displayed continuously on the display screen, and this image needs to be as sharp as possible. However, the beating of the heart causes the patient&#39;s chest to move, which leads to blurring of the images displayed in cardiac fluoroscopy. 
    
    
     BRIEF SUMMARY OF THE INVENTION 
     An embodiment of the invention provides for continuous display of a fluoroscopic image with the best possible sharpness, while minimizing the stresses experienced by the X-ray tube so as not to shorten its life. 
     An embodiment of the invention therefore provides a method of improving the quality of a fluoroscopic image displayed continuously following an image acquisition sequence in which the images are acquired using pulsed cardiac fluoroscope, in which that image out of the sequence of images which satisfies a predetermined minimum motion criterion is stored and this stored image is continuously displayed. 
     BRIEF DESCRIPTION OF THE DRAWING 
     Other advantages and characteristics of the invention will become apparent on studying the detailed description of entirely non-limiting embodiments, and the appended drawing in which the single FIGURE very schematically represents a system for acquiring fluoroscopic images. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the single FIGURE reference  1  denotes a table supporting a patient P. An X-ray generator  2  emits X-ray pulses at regular time intervals when the acquisition pedal  7  of the device is depressed. When each pulse is emitted, an X-ray beam  3  passes through the patient and is received on a detector  4  connected to processing means  5  whose architecture is based on a microcomputer. The images which are acquired are displayed on a display screen  6 . 
     According to a first embodiment of the invention, when the operator presses the pedal  7 , X-ray pulses are successively emitted at predetermined time intervals with, for example, a pulse width of the order of 15 ms. The images which are acquired are displayed directly on the display screen  6  after having been processed by the processing means  5 . When the operator takes his foot off the pedal  7 , the processing means  5  supply the X-ray generator with a control signal whose effect is to reduce the length of the pulse emitted, from 15 ms to about 5 ms. Furthermore, since the X-ray dose per image must remain constant, the level of X-rays emitted on this last image is increased, which it possible to improve the sharpness of this image which is acquired and displayed continuously on the screen  6 . 
     The person skilled in the art will therefore note that the increased heating of the X-ray tube due to the shortening of the pulse occurs only on the last image, and this does not therefore shorten the life of the tube. 
     According to another embodiment of the invention, the processing means  5  carry out image processing on the images of the sequence, so as to store the one which satisfies a minimum blur criterion. More specifically, for example, image-to-image correlation processing may be carried out on small areas of the image. Maximum correlation between two successive images is representative of minimum movement between these two images. The image associated with maximum correlation is then stored in real time. 
     This image processing may be carried out image by image, or alternatively on all the images of the 10 last cardiac cycle, which are continually stored. 
     According to another variant of the invention, a sensor  8  may be used, for example a blood pressure sensor or alternatively a device for electrocardiogram, so as to detect a diastole termination time, that is to say a time when the heart moves the least. The sensor then emits control signal to the processing means  5  which then store the image acquired at this time in a memory so as to display it continuously at the end of the acquisition of the image sequence, that is to say when the operator takes his foot of the pedal  7 . 
     The image stored may be the last image of the sequence, that is to say the one acquired when the operator takes his foot off the control pedal of the device. In this alternative embodiment, the invention provides for increasing the level of X-rays emitted on this last image, then storing this image. 
     In this embodiment variant, increasing the level of the X-rays leads to a shorter pulse length for thus the last image. This increased stress which the tube experiences is thus limited at the time when the last image is acquired. This pulse length is for example reduced to 5 ms whereas it is kept at 15 ms throughout the rest of the acquisition sequence. 
     According to another variant of the invention, image processing is carried out on the images of the sequence so as to store the one which satisfies a minimum blur criterion. By way of indication, this image processing may consist in an image to image correlation over small regions. The maximum correlation between two successive images is then looked for. 
     According to another variant of the invention, a sensor, for example a blood pressure sensor or, alternatively, a device for recording an electrocardiogram, is used to detect a diastole to termination time corresponding to very little movement of the heart, and, in response to a control signal emitted by the sensor, the image acquired when this control signal is received is stored. 
     Various modifications in structure and/or function and/or steps may be made by one skilled in the art to the disclosed embodiment without departing from the scope and extent of the invention.