CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of U.S. patent application Ser. No. 16/190,679, entitled “PASSIVE THERMAL CONTROL OF X-RAY TUBES”, filed Nov. 14, 2018, which is herein incorporated by reference in its entirety for all purposes.

BACKGROUND

The subject matter disclosed herein relates to X-ray tubes used in medical imaging and, in particular, to the thermal control of X-ray tubes.

In non-invasive imaging systems, X-ray tubes are used in fluoroscopy, projection X-ray, tomosynthesis, and computer tomography (CT) systems as a source of X-ray radiation. Typically, the X-ray tube includes a cathode and a target. A thermionic filament within the cathode emits a stream of electrons towards the target in response to heat resulting from an applied electrical current, with the electrons eventually impacting the target. Once the target is bombarded with the stream of electrons, it produces X-ray radiation and heat.

The X-ray radiation traverses a subject of interest, such as a human patient, and a portion of the radiation impacts a detector or photographic plate where the image data is collected. Generally, tissues that differentially absorb or attenuate the flow of X-ray photons through the subject of interest produce contrast in a resulting image. In some X-ray systems, the photographic plate is then developed to produce an image which may be used by a radiologist or attending physician for diagnostic purposes. In digital X-ray systems, a digital detector produces signals representative of the received X-ray radiation that impacts discrete pixel regions of a detector surface. The signals may then be processed to generate an image that may be displayed for review. In CT systems, a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is displaced around a patient.

The X-ray tube has a useful life over a large number of examination sequences, and must generally be available for examination sequences upon demand in a medical care facility, as examination sequences may or may not be scheduled, for example due to emergency situations. When the X-ray tube is not in use, the X-ray tube may cool between imaging sequences, as no electrons are being emitted by the thermionic element (i.e., substantially no heat is being generated). This cooling may result in the target material dropping below its ductile to brittle transition temperature, which can result in fracture of the target or reduced operating life. Existing techniques to warm X-ray tubes are often unreliable and inefficient, as typical thermal transition processes may take up to one hour and can over or undershoot a desired target temperature, resulting in instability of the target material. In such cases, image sequences may be delayed or, in cases where imaging sequences are performed before the target is properly warmed, the target may rupture. Accordingly, a need exists for improved thermal control in X-ray tubes.

BRIEF DESCRIPTION

Certain embodiments commensurate in scope with the originally claimed subject matter are summarized below. These embodiments are not intended to limit the scope of the claimed subject matter, but rather these embodiments are intended only to provide a brief summary of possible forms of the subject matter. Indeed, the subject matter may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

In one embodiment, a system for passive thermal control of an X-ray tube is provided. The system includes an X-ray tube having an electron beam target and including a rotary bearing assembly supporting the electron beam target in rotation. The rotary bearing assembly includes a stationary shaft and a bearing sleeve configured to rotate with respect to the stationary shaft during operation of the X-ray tube. The rotary bearing assembly also includes a first coolant flow path extending through a center of the stationary shaft and a second coolant flow path disposed through a radially inward portion of the stationary shaft disposed about the center of the stationary shaft. The rotary bearing assembly further includes a flow control valve configured to passively regulate flow of coolant through the second coolant flow path based on a pressure of the coolant.

In another embodiment, an imaging system is provided. The imaging system includes an X-ray tube having an electron beam target and including a rotary bearing assembly supporting the electron beam target in rotation. The rotary bearing assembly includes a stationary shaft and a bearing sleeve configured to rotate with respect to the stationary shaft during operation of the X-ray tube. The rotary bearing assembly also includes a first coolant flow path extending through a center of the stationary shaft and a second coolant flow path disposed through a radially inward portion of the stationary shaft disposed about the center of the stationary shaft. The rotary bearing assembly further includes a flow control valve configured to passively regulate flow of coolant through the second coolant flow path based on a pressure of the coolant. The imaging system also includes a digital detector configured to receive radiation from the X-ray tube transmitted through a subject of interest. The imaging system further includes an image acquisition circuit configured to control acquisition of image data from the detector.

In a further embodiment, a system for passive thermal control of an X-ray tube is provided. The system includes an X-ray tube having an electron beam target and including a rotary bearing assembly supporting the electron beam target in rotation. The rotary bearing assembly includes a stationary shaft and a bearing sleeve configured to rotate with respect to the stationary shaft during operation of the X-ray tube. The rotary bearing assembly also includes a first coolant flow path extending through a center of the stationary shaft. The stationary shaft includes a first end having an inlet for the first coolant flow path and a second end disposed opposite the first end having an outlet for the first coolant flow path. The rotary bearing assembly further includes a second coolant flow path disposed through a radially inward portion of the stationary shaft disposed about the center of the stationary shaft. The rotary bearing assembly even further includes a flow control valve configured to passively regulate flow of coolant through the second coolant flow path based on a pressure of the coolant. The flow control valve includes a spring disposed adjacent the first end or the second end of the stationary shaft. The flow control valve is configured when closed to block the coolant from entering the second coolant flow path, and the flow control valve is configured when open to allow the coolant to flow into the second coolant flow path.

