X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
2001-05-30
2003-01-14
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S098700
Reexamination Certificate
active
06507638
ABSTRACT:
BACKGROUND OF THE INVENTION
At least one preferred embodiment of the present invention generally relates to a medical x-ray imaging system employing an electronic video camera that operates upon visible light to control brightness. At least one preferred embodiment of the present invention relates to an electronic video camera that utilizes a neutral density filter having varying opacity across the filter and that is adjustable for light attenuation.
In the past, medical diagnostic imaging systems have been proposed for imaging regions of interest in patients through the use of x-ray sources and receptors positioned on opposite sides of a patient's region of interest. Typical x-ray imaging systems utilize an x-ray source and receptor that are movable to various positions relative to the patient's region of interest. The x-ray source is controlled to adjust the amount of x-rays transmitted therefrom, passed through the patient and impinged on the x-ray receptor. X-ray receptors generally include an image intensifier having an x-ray detection layer that detects x-rays passing through a patient. The image intensifier converts the x-rays to visible light which is, in turn, guided onto an object plane proximate a video camera. The video camera includes an optical lens system focusing light from the object plane onto an image plane proximate a light sensitive sensor. One example of a light sensitive sensor is a charge coupled device. The light sensitive sensor detects and converts the visible light at the image plane data that is processed and ultimately displayed to a user.
Various anatomical regions attenuate x-rays to different degrees depending upon thickness, density, structure and the like of the anatomic region. These different characteristics of patient anatomy attenuate x-rays to different degrees and may degrade x-ray images where an anatomy of interest is located proximate certain other types of anatomy.
Operators of x-ray imaging equipment attempt to improve image quality of x-ray images through a variety of manners. One such manner for improving x-ray image quality involves adjusting the x-ray intensity transmitted by the x-ray source. For instance, anatomical regions that highly attenuate x-rays are imaged better by increasing the number of x-rays transmitted from the source. By increasing the x-ray transmissions, the user similarly increases the photon statistics sensed at the receptor (e.g., the number of photons impingent upon the image intensifier). As the photon statistics increase, the image intensifier converts more and more x-rays to visible light, thereby increasing the brightness of the light incident on the object plane of the electronic video camera. The light brightness may rise to a level sufficient to saturate the light sensor, such as the CCD. As the sensed light becomes excessive, the resulting processed and displayed image degrades. Image degradation may appear in several forms, such as a washed out image, an image having poor contrast between adjacent anatomies, and the like.
In the past, x-ray systems have attempted to prevent the light brightness from overloading the sensor by adding an iris to the electronic video camera having an adjustable opening passing only a desired amount of light. The diameter of the opening can be varied to affect the desired average attenuation of the brightness of the light at the object plane. As the system reduces the iris opening to “stop down” or partially close the iris opening, feedback sensing will detect that the average brightness of the light at the object plane is reduced, and the system can automatically increase the amount of x-rays impinging upon the receptor.
In accordance with the foregoing, the quality of the ultimately displayed image is influenced by the amount of x-ray flux (intensity) that is incident upon the image intensifier. The amount of light that is allowed to pass through the optics of the electronic video camera typically controls the amount of x-ray flux. A higher quality image requires more x-ray flux and more x-ray flux is permitted by decreasing the iris aperture that passes light through the camera optics, thereby avoiding sensor saturation. Motor controlled irises precisely control the amount of light passed through the optics in order to ensure that the minimum x-ray flux necessary is used in view of patient concerns. The iris aperture diameter and thus the amount of x-ray flux may be varied during single patient imaging procedure. Hence, light intensity is typically controlled automatically by the x-ray imaging system in accordance with commands from a user entered to initiate an imaging operation.
It is preferable that the electronic video camera only focus light near the object plane onto the image plane. The compact nature of x-ray systems typically results in the object plane and image plane being in close proximity to opposite ends of the camera optics. Hence, structure within the camera optics, such as glass surfaces and the like through which the light passes are located proximate the object plane. The glass surface and other transparent structure near the object plane may be focused by the camera optics onto the image plane as the iris aperture is reduced. These transparent structures in or near the camera optics may contain blemishes, such as scratches, digs and the like and may accumulate foreign material such as dirt. The blemishes and/or dirt may be close enough to the object plane as to become at least partially focused onto the image plane when the iris aperture is stopped down. The camera optics may partially focus images of the blemishes or dirt onto the image plane sufficiently that the light sensor at the image plane detects the blemishes/dirt as data conveyed to the processor to be imaged. These projections of blemishes and dirt create unwanted artifacts at the image plane that result as artifacts appearing in the displayed image.
FIG. 8
illustrates an exemplary configuration for the camera optics as formed in accordance with conventional systems. The camera optics
75
include a glass or other transparent layer
77
located at the input side to the camera optics proximate the object plane
79
. The glass or other transparent layer
77
represents any kind of structure that could be part of the camera optics
75
such that this structure presents an opportunity for its surfaces to contain blemishes or dirt that may partially be in focus. For example, structure
77
could be part of the forward lens system
81
, or structure
77
could be leaded glass installed for the purpose of reducing x-ray radiation beyond the optics such as would otherwise irradiate the optical sensor. The image intensifier directs light rays representative of an x-ray image onto the object plane
79
. A forward lens system
81
is located proximate the glass layer
77
which directs light ray traces
83
and
86
, from the object plane
79
through optical components
87
onto a rear lens system
89
. The forward lens system also directs light ray traces
84
and
85
from blemishes/dirt in the glass layer
77
onto the rear lens system
89
. The forward lens system
81
collimates the light ray traces
83
-
86
, while the rear lens system
89
reconverges the light ray traces
83
-
86
. The forward and rear lens systems
81
and
89
cooperate such that light ray traces
83
and
86
projecting from the object plane are collimated at the forward lens system
81
into a parallel manner and converged at the rear lens system
89
onto an image plane
91
. When blemishes and dirt exist on the surface of the glass layer
77
, light ray traces
84
and
85
are focused by the forward and rear lens systems
81
and
89
at a point
97
An adjustable iris
93
is opened and closed based upon the desired x-ray flux to control the amount of light ray traces passed therethrough onto the rear lens system
89
. As the adjustable iris
93
reduces the opening therethrough, the shape and size of a focus region
95
proximate the image plane
91
expands. The focus region represents an area in w
Anderton R. Larry
Curtis Steven E.
Dellapenna Michael A.
GE Medical Systems Global Technology Company LLC
McAndrews Held & Malloy Ltd.
Porta David P.
Vogel Peter J.
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