X-ray or gamma ray systems or devices – Source support – Source cooling
Reexamination Certificate
1999-11-26
2002-03-26
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Source support
Source cooling
C378S201000
Reexamination Certificate
active
06361208
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to x-ray generating devices. More particularly, the present invention relates to an x-ray tube having an integral housing assembly that allows for improved performance, especially in x-ray mammography applications.
2. The Relevant Technology
X-ray devices are extremely valuable tools for use in a variety of medical applications. For example, such equipment is commonly used in areas such as diagnostic and therapeutic radiology; radiography is of particular use to diagnose breast cancers.
Regardless of the particular application involved, the basic operation of medical x-ray devices is similar. In general, x-rays, or x-ray radiation, are produced when electrons are produced and released, accelerated, and then stopped abruptly. Typically, this entire process takes place within a housing that defines an evacuated envelope; the housing is typically constructed of glass, metal, or a combination thereof. Three primary components are typically disposed within the evacuated envelope: a cathode, which produces the electrons; an anode, which is axially spaced apart from the cathode and oriented so as to receive electrons emitted by the cathode; and an electrical connection for allowing a voltage generation element to apply a voltage between the cathode and the anode to accelerate the emitted electrons.
In operation, a voltage potential is applied between the cathode and the anode. This causes the electrons that are emitted from the cathode filament to form a thin stream or beam, and accelerate to a very high velocity towards target surface positioned on the anode. This target surface (sometimes referred to as the focal track) is comprised of a refractory metal, so that when the electrons strike the target surface, at least a portion of the resulting kinetic energy is converted to electromagnetic waves of very high frequency, i.e., x-rays. The resulting x-rays emanate from the anode target surface, and are then collimated for penetration into an object, such as an area of a patient's body. As is well known, the x-rays that pass through the object can be detected and analyzed so as to be used in any one of a number of applications, such as a medical diagnostic examination.
In general, a very small part of the input energy results in the production of x-rays. A majority of the kinetic energy resulting from the electron collisions at the target surface is converted into heat of extremely high temperatures. The heat is absorbed by the anode and is conducted to other portions of the anode assembly, and to the other x-ray tube components that disposed within the evacuated envelope housing. Over time, this heat can damage the anode, the anode assembly, and/or other tube components, and can reduce the operating life of the x-ray tube and/or the performance and operating efficiency of the tube.
Several approaches have been used to help alleviate problems arising from the presence of these high operating temperatures. For example, in some x-ray devices the x-ray target, or focal track, is positioned on an annular portion of a rotatable anode disk. The anode disk (also referred to as the rotary target or the rotary anode) is then mounted on a supporting shaft and rotor assembly, that can then be rotated by some type of motor. During operation of the x-ray tube, the anode disk is rotated at high speeds, which causes the focal track to continuously rotate into and out of the path of the electron beam. In this way, the electron beam is in contact with any given point along the focal track for only short periods of time. This allows the remaining portion of the track to cool during the time that it takes to rotate back into the path of the electron beam, thereby reducing the amount of heat absorbed by the anode.
While the rotating nature of the anode reduces the amount of heat present at the focal spot on the focal track, a large amount of heat is still present within the anode, the anode drive assembly, and other components within the evacuated housing. This heat must be continuously removed to prevent damage to the tube (and any other adjacent electrical components) and to increase the x-ray tube's efficiency and overall service life.
One approach has been to place the housing that forms the evacuated envelope within a second outer metal housing, which is sometimes referred to as a “can.” This outer housing or can serves several functions. First, it acts as a radiation shield to prevent radiation leakage. As such, it must be at least partially constructed from some type of dense, x-ray absorbing metal, such as lead. Second, the outer housing serves as a container for a cooling medium, such as a dielectric oil, which is can be continuously circulated by a pump over the outer surface of the inner evacuated housing. As heat is emitted from the x-ray tube components (anode, anode drive assembly, etc.), it is radiated to the outer surface of the evacuated housing, and then at least partially absorbed by the coolant fluid. The heated coolant fluid is then passed to some form of heat exchange device, such as a radiative surface, and the heat is removed. The fluid is then re-circulated by the pump back through the outer housing and the process repeated.
The dielectric oil (or similar fluid) can be used to serve functions other than cooling. For example, the oil serves as an electrical insulator between the inner evacuated housing, which contains the cathode and anode assembly, and the outer housing, which is typically comprised of a conductive metal material.
While useful as a heat removal medium and/or as an electrical insulator, the use of oil and similar liquids can be problematic in several respects. For example, use of a fluid adds complexity to the construction and operation of the x-ray generating device in several areas. First, use of fluid requires that there be a second outer housing or can structure to retain the fluid. This outer housing is constructed of a material that is capable of blocking x-rays, and it must be large enough to be completely disposed about the inner evacuated housing and allow fluid to be disposed therein. This increases the cost and manufacturing complexity of the overall device. Also, the outer housing requires a large amount of physical space, resulting in the need for an overall larger x-ray generating device. Similarly, the space required for the outer housing reduces the amount of space that can be utilized by the inner evacuated housing, which in turn limits the amount of space that can be used by other components within the x-ray tube. For example, the size of the rotating anode is limited; a larger diameter anode is desirable because it is better able to dissipate heat as it rotates.
Moreover, construction of the outer housing adds expense and manufacturing complexity to the overall device in other respects. If the liquid is used as a coolant, the device may also be equipped with a pump and a radiator and the like, that in turn must be interconnected within a closed circulation system via a system of tubes and fluid conduits. Also, since the oil expands when it is heated, the closed system must provide a facility to expand, such as a diaphragm or similar structure. Again, these additional components add complexity and expense to the x-ray device's construction. Moreover, the tube is more subject to fluid leakage and related catastrophic failures attributable to the fluid system.
The presence of a liquid coolant/dielectric is also detrimental because it does not function as an efficient noise insulator. In fact, the presence of a liquid may tend to increase the mechanical vibration and resultant noise that is emitted by the operating x-ray tube. This noise can be distressing to the patient and/or the operator. The presence of liquid also limits the ability to utilize other, more efficient materials for dampening the noises emitted by the x-ray tube due to space restrictions and the need for effective electrical insulation.
Some prior art x-ray tubes have eliminated t
Artig Christopher F.
Coles Scott
Lange Mark
Quinn Karen
Takenaka Jeff
Church Craig E.
Varian Medical Systems
Workman & Nydegger & Seeley
LandOfFree
Mammography x-ray tube having an integral housing assembly does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mammography x-ray tube having an integral housing assembly, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mammography x-ray tube having an integral housing assembly will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2825877