X-ray or gamma ray systems or devices – Source – Electron tube
Reexamination Certificate
2000-12-21
2002-10-29
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Source
Electron tube
C378S109000, C378S065000, C378S111000
Reexamination Certificate
active
06473491
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method for exposing a treatment area in a passage inside a patient to x-ray radiation. In particular, the invention relates to a method and apparatus for x-ray treatment using an adaptable voltage source to an x-ray emitter.
The x-ray catheter of this application and various delivery systems for positioning such a catheter in a passage inside the body of a patient are described in co-pending patent application Ser. No. 08/701,764, “X-RAY CATHETER”, the contents of which are incorporated herein by reference.
From an electrical standpoint the x-ray emitter is a high voltage vacuum diode with a cold cathode. Typically, hot cathodes are used in standard x-ray tubes. A hot cathode has a third electrode which provides a low voltage current for heating the cathode and allows the anode current to be controlled by changing the temperature of the cathode.
In many x-ray devices, a field emission cathode, or a cold cathode, is preferred to a hot cathode. Space limitations in a very small device may eliminate the possibility of a third electrode. The desire to avoid heat generation at the x-ray emitter may also preclude the use of a hot cathode.
A disadvantage of a cold cathode diode system is that at any given stabilized voltage on the anode-cathode gap, the current is unstable in time, due to some inherent instabilities of the emission characteristics. The current can therefore run too high or too low compared with a desired current for the particular application. Too low a current will make the treatment time unacceptably long and too high a current can cause overheating of the emitter, possibly resulting in a high voltage discharge and destruction of the emitter. In addition, an unstable current makes it difficult to provide a precise accumulated dose, since the delivered dose is proportional to the current through the emitter.
A power source for an x-ray device is needed that compensates for inherent instabilities of the current over time. This type of power source is especially needed in x-ray devices having a cold cathode.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus and a method for exposing a treatment area in a passage inside a patient to x-ray radiation.
The method includes positioning an x-ray emitter at a treatment area, where the x-ray emitter is connected to a cable, setting a voltage source at a source voltage, and measuring a current through the x-ray emitter.
The method may include comparing a current with a high limit and a low limit. The method further includes increasing the source voltage if the current is lower than the low limit. The method further includes decreasing the source voltage if the current is higher than the high limit. The method includes determining the high limit and the low limit based on the source voltage and the desired radiation.
An apparatus of the invention includes an x-ray emitter, positionable in the passage, a cable connected to the x-ray emitter, a voltage source connected to the cable, and a current sensor for measuring the current.
The apparatus may include a current comparison device for comparing the measured current with a high limit and a low limit, and further include a voltage source control device operatively connected to the current comparison device. The embodiment may include a current integrator for integrating a current measured at the x-ray emitter.
These and various other features of novelty which characterize the invention are pointed out with particularity in the application. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the accompanying drawings, claims and descriptive matter, which form a part hereof.
REFERENCES:
patent: 5090043 (1992-02-01), Parker et al.
patent: 5621780 (1997-04-01), Smith et al.
patent: 5729583 (1998-03-01), Tang et al.
patent: 5748699 (1998-05-01), Smith
patent: 6069938 (2000-05-01), Chornenky et al.
patent: 6108402 (2000-08-01), Chornenky et al.
patent: 6148061 (2000-11-01), Shefer et al.
Chornenky Victor I.
Kerslick Graham S.
Meyer Steven T.
Satteson Michael R.
Dunn Drew A.
Maresh Catherine C.
Medtronic AVE Inc.
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