Patent Number: 
Section: claims

1. An X-ray imaging system for displaying an image on a monitor, said system comprising an X-ray source, a collimator, and a masking unit comprising an adjustable shutter located between the X-ray source and the collimator, wherein the masking unit is configured to control the shutter so that part of said image is created at a higher refresh rate using a narrower X-ray beam than the rest of said image, said narrower beam defined by the shutter. 2. A system as in claim 1 wherein said masking unit comprises a plurality of moving coil rotary actuators connected to operate X-ray blocking blades of the shutter. 3. A system as in claim 1 wherein said image part created at the higher refresh rates and the rest of said image created at a lower refresh rate are blended seamlessly by using an image overlap region. 4. A system as in claim 1 wherein the firing of the X-ray source is synchronized to the position of said shutter. 5. A method for improving the resolution of a sequence of X-ray images while reducing the radiation level used, said method comprising the steps of:selecting an area-of-interest in said images;exposing said area-of interest at first refresh rate using a cone of X-rays matched to a size of said area-of-interest; andexposing full images with an X-ray cone covering the full images at a second refresh rate slower than said first refresh rate. 6. A method as in claim 5 wherein the area-of-interest is automatically selected by the system based on rates of change in the images. 7. A method as in claim 5 wherein the area-of-interest is defined automatically based on the change from image to image. 8. A method as in claim 5 wherein the area-of-interest is defined automatically based on the change from image to image, said change excluding periodic change. 9. A method as in claim 5 wherein the area-of-interest is defined automatically based on image to image, said changes excluding periodic changes by synchronizing operation of an X-ray source used to generate said images to a signal derived from said periodic changes. 10. A method as in claim 5 wherein said full image and said area-of-interest are blended seamlessly by using an image overlap region between both images. 11. A method as in claim 5 wherein said full image and said area-of-interest are blended seamlessly by using an image overlap region between both images and the pixel values in the area of interest are affected by both images. 12. A method as in claim 5 wherein both the location and shape of the area-of-interest can be selected by the user. 13. A method as in claim 5 wherein both the location and shape of the area-of-interest are selected automatically. 14. A method as in claim 5 wherein both the location and shape of the area-of-interest can be selected automatically by recognizing features of an object of interest. 15. A method as in claim 5 wherein the refresh rate outside the area-of-interest is automatically selected based on the detected rate of change of the images. 16. A method as in claim 5 wherein the area-of-interest is one of a plurality of areas-of-interest and the method comprises exposing each of said areas-of-interest to a radiation level higher than a radiation level delivered within said images outside of said areas-of-interest. 17. A method according to claim 5 wherein exposing said area-of-interest comprises delivering pulses from a pulsed X-ray source. 18. A method according to claim 17 comprising slaving firing of the pulsed X-ray source to positions of masks that match the cone of X-rays to the size of said area-of-interest. 19. A method according to claim 18 comprising moving the masks continuously. 20. A method according to claim 19 wherein the masks comprise slotted rotary masks and the method comprises adjusting a position of the area-of-interest by advancing or retarding rotation of one of the masks relative to another one of the masks.