Patent Number: 051951215
Section: summary

BACKGROUND OF THE INVENTION a) Field of the Invention The present invention broadly relates to an apparatus for modulating the intensity of an X-ray beam generated in a given direction by an X-ray tube. More specifically, the invention relates to an apparatus of the above mentioned type, hereinafter called "X-ray beam modulator", that is motorized, remotely controlled and easy to operate, thereby making it easy to use into the X-ray cone and tube assembly of a radiographic system, such as, for example, a system for lower limb angiography, in order to obtain better density and contrast and less radiation exposure of the patient's legs and feet. b) Brief Description of the Prior Art It is well known that the X-ray absorption of a body depends on the thickness and/or density of this body. Thus, in a human being, the X-ray absorption varies substantially according to both the portion of the anatomy to be radiographed, and the specific body feature of the patient who is radiographed, depending on the thickness of his or her bones and his or her weight. Accordingly, there is a need for an apparatus for modulating the intensity of the X-ray beam projected towards a patient, depending on the portion of his or her anatomy to be radiographed and his or her physical condition, in order to achieve proper density and contrast over the entire radiographic film without unduly overexposing some portion of the patient's body. So far, such a need has been fulfilled with filters of different absorption rates that must be selected and positioned to intersect the X-ray beam according to the radiographic need. Such filters are of course very efficient, but time consuming to install. SUMMARY OF THE INVENTION The object of the present invention is to provide an X-ray beam modulator which is simple in structure and very easy to use and remotely control and which can be very easily incorporated into an X-ray cone and tube assembly of conventional structure and used with all kinds of screens and films, in order to vary the intensity of irradiation on some parts of the patients' body such as his or her legs and feet in the case of lower limb angiography, and to generate different compensation curves according to the patient's anatomy. In accordance with the invention, this object is achieved with an apparatus comprising: a rotor having a rotation axis parallel to the direction of the X-ray beam, the rotor being positioned adjacent this X-ray beam; means to drive the rotor about its rotation axis at variable speeds; a set of at least three blades made of a material opaque to X-ray, each of the blades comprising a central hub and a pair of symmetrical wings extending away from the hub, the blades of the set having their hubs slidably mounted on a corresponding set of radially projecting shafts symmetrically fixed to and about the rotor; return spring means to urge each of the blades radially inwardly towards the rotor along their respective shafts; and guiding means on each pair of hub and shaft to cause the corresponding blade to pivot about the shaft on which it is mounted when the speed of the rotor increases and the blades are then moved in unison radially outwardly against the action of the return spring means as a result of the centrifugal force. The blades and their shafts are sized to cause the blades to intersect the X-ray beam when the rotor is driven, and then modulate the intensity of the X-ray beam as a function of the angular position of the blades about their shafts, which allow more or less radiation to pass therebetween. Advantageously, the apparatus may further comprises programmable control means operatively connected to the means to drive the rotor in order to allow preselection of at least one given speed of rotation of the rotor corresponding to a required compensation curve. The invention and its advantages will be better understood upon rading the following, non-restrictive description of a preferred embodiment thereof, given with reference to the accompanying drawings.