To reduce X-ray exposure while improving image quality, an area of interest is selected in the image. The image of the selected area is updated frequently, comparable to a rate of updates used today for the whole image. The rest of the image is updated at a significantly lower rate. Since the area of interest normally is a small part of the overall area, the total exposure is reduced significantly. A fast X-ray shutter, placed near the X-ray source, blocks the radiation from areas outside the area of interest. The shutter automatically retracts when the complete image is updated. The area of interest can be selected by the user or automatically selected based on activity in the image. Since most of the exposures are taken at a reduced collimation angle, limited by the area of interest, the area of interest is imaged at reduced scatter and better quality.
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; and
exposing 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.