Information
-
Patent Grant
-
6502985
-
Patent Number
6,502,985
-
Date Filed
Friday, May 5, 200024 years ago
-
Date Issued
Tuesday, January 7, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Fitzpatrick, Cella, Harper & Scinto
-
CPC
-
US Classifications
Field of Search
US
- 378 207
- 378 147
- 378 150
- 378 151
- 378 145
-
International Classifications
-
Abstract
A system and method for automatically collimating X-rays. A digital X-ray system (100) includes a generator (108), a sensor unit (110), a control station (112), and a preview monitor (114). The generator (108) generates X-ray radiation that is captured by the sensor unit (110) as a digital image and transmitted to the control station (112). The captured image is displayed on the preview monitor (114). The generator (108) includes a collimator (212) that collimates the generated radiation into a primary beam of X-rays. The size and shape of the primary beam can be adjusted by modifying collimation parameters. A short duration beam of X-rays is generated by the generator (108) and captured (414) by the sensor unit (110). This step is repeated as necessary or desired. The resulting digital images are analyzed (418) by the control station (112) to calculate a calibration coefficient. Another short duration beam of X-rays is generated and a reference image is captured (514). The control station (112) analyzes the reference image and uses the calibration coefficient to collimate the collimator (212) to achieve a desired goal, such as radiating all or only part of an object being radiated. Once the collimator (212) is adjusted, the X-ray image of the subject is exposed.
Description
BACKGROUND
1. Field of the Invention
This invention pertains in general to X-ray systems and in particular to a method and system for collimating the X-rays in such systems.
2. Background of the Invention
Since the discovery of X-rays in 1895 by Wilhelm Roentgen, the predominant method for capturing an X-ray image has been by exposing a photographic film. A disadvantage of using photographic film is that chemical processing must be performed on it to convert the latent X-ray image into a viewable image. Because of this chemical processing, there is a delay between when the film is exposed and when the image is viewable. For medical X-ray images taken in the emergency room, for example, this delay in viewing the image can be critical. Chemical processing of the film, moreover, requires special handling and disposal of the chemicals in order to avoid environmental contamination.
In recent years, computed radiography (CR) has provided a means to take X-ray images without using photographic film or chemical processing. When using CR, the X-ray image is captured with a photostimulable luminescent plate. The plate is then placed in a special scanner to convert the captured image into a digital form for subsequent viewing at a computer workstation. Though this technique eliminates the use of photo processing chemicals, there is still a significant delay introduced before the X-ray image is viewable.
More recently, a technique known as digital radiography (DR) has been developed that eliminates both the need for chemical processing and the significant delay in producing a viewable image. In DR, a sensor unit, typically an array of amorphous silicon, is used to capture the X-ray image and produce a digital representation of the image. The sensor unit is coupled to a control station with a cable or other communications link. The cable provides power to the sensor unit and transmits digital communication signals between the sensor unit and the control station. Accordingly, the control station receives substantially real-time data describing the X-rays detected by the sensor plate.
In all of the above X-ray systems, there is a need to aim the X-ray generator and collimate the X-rays before capturing the image. Typically, the generated X-rays pass through an adjustable collimator having an aperture that restricts the size and shape of the primary beam of X-ray radiation. Collimation serves to: 1) reduce scatter from X-rays not required for imaging, thereby improving image quality; and 2) reduce unnecessary X-ray exposure to the patient. Before exposing the X-ray image, an X-ray technologist manually adjusts the collimator by shining a light located at or near the X-ray generator onto the X-ray sensor or the patient's anatomical region of interest. The technologist observes the light reflecting off the sensor plate or patient and manually adjusts the aperture in the collimator. Once the light is properly collimated, the X-ray image is exposed.
In a fast-paced medical environment, such as a hospital emergency room or a busy clinic, the technologist wastes valuable time and resources when visually collimating the X-ray generator. Moreover, locating the collimating light near the generator adds an extra level of complexity to the generator design. Therefore, there is a need for an X-ray system that simplifies the collimation process. Preferably, the system would reduce the time and effort expended by the X-ray technologist to collimate the X-rays and would not need a visible light to perform collimation.
SUMMARY OF THE INVENTION
The above needs are met by a digital X-ray system (
100
) having a generator (
108
) and a sensor unit (
110
) in communication with the control station (
112
). In addition to the sensor unit (
110
) and control station (
112
), the digital X-ray system (
100
) preferably includes a preview monitor and operation panel (
114
) for controlling the X-ray system (
100
), an image archiver (
116
) for storing images captured by the sensor unit (
110
), a viewing workstation (
118
) for viewing and manipulating the images stored in the archiver (
116
), and a hard copy output device (
120
) for printing the images. In a preferred embodiment of the present invention, the sensor unit (
110
) captures the digital X-ray images and transmits the images to the control station (
112
). Then, the images can be manipulated by the other components of the X-ray system (
100
).
The generator (
108
) preferably includes a radiation source such as an X-ray tube (
210
) and a collimator (
212
). The collimator (
212
) includes a portion blocking the radiation, an adjustable aperture (
226
) through which a primary beam of radiation passes, and an actuator (
230
) for adjusting the aperture. By adjusting collimation parameters which affect the size and shape of the aperture (
226
), the size and shape of the primary beam can be adjusted.
The sensor unit (
110
) is surrounded by a protective cover (
310
). Within the cover (
310
) are preferably a scintillator (
312
), a sensor plate (
314
), and sensor electronics (
316
). When the sensor unit (
110
) is exposed to X-rays, the scintillator (
312
) converts the X-rays into visible light. The position and intensity of the light is detected by the sensor plate (
314
) and stored as a digital image. The digital image is then transmitted to the control station (
112
).
In use, the aperture (
226
) is constricted (
410
) and a relatively short duration beam is directed (
412
) at the sensor unit (
110
). The resulting digital image is transmitted (
416
) to the control station (
112
). This process is repeated one or more times with a displaced aperture (
226
) and the control station (
112
) calculates (
428
) a calibration coefficient from the captured digital images. This coefficient is preferably stored (
430
) in the control station (
112
).
To capture an X-ray image of a subject, a reference image is captured (
514
) from a short-duration beam and transmitted (
516
) to the control station (
112
). The control station (
112
) analyzes (
518
) the reference image and uses the calibration coefficient to adjust the aperture (
226
) to achieve a desired goal. In one embodiment, the aperture (
226
) is adjusted to cover the entire field of the sensor plate (
314
). In another embodiment, the aperture (
226
) is adjusted to restrict the X-ray beam and eliminate unwanted exposure beyond the periphery of the X-ray subject. In yet another embodiment, the technologist views the digital image and defines an area of exposure. The control station (
112
) automatically calculates aperture (
226
) parameters to restrict the beam to precisely the defined area. Once the aperture (
226
) is adjusted, the image of the X-ray subject is captured (
526
).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a block diagram of a digital X-ray system
100
according to an embodiment of the present invention;
FIG. 2
is a high-level cutaway view of an embodiment of the generator
108
of the digital X-ray system
100
, including an X-ray tube
210
and a collimator
212
;
FIG. 3
is a cutaway perspective illustration of the sensor unit
110
of the digital X-ray system
100
according to an embodiment of the present invention;
FIG. 4
is a flow diagram illustrating the interactions between the generator
108
, the sensor unit
110
, and the control station
112
when calculating the calibration coefficient; and
FIG. 5
is a flow diagram illustrating the interactions between the generator
108
, the sensor unit
110
, and the control station
112
when adjusting the aperture
226
to achieve a desired goal while capturing an image.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1
is a block diagram of a digital X-ray system
100
according to an embodiment of the present invention. A sensor unit
110
is in communication with a control station
112
. The control station
112
, in turn, is preferably coupled to a preview monitor/operation panel
114
, an image archiver
116
, a viewing workstation
118
, and a hard copy output device
120
.
In one embodiment, an X-ray generator
108
generates X-rays that are captured as digital data by the sensor unit
110
. The digital data are transmitted from the sensor unit
110
to the control station
112
via a communications link
122
, which in one embodiment is the wireless link described in U.S. application Ser. No. 09/251,755, entitled WIRELESS X-RAY SYSTEM, filed on Feb. 18, 1999, assigned to the same assignee as the present invention and hereby incorporated by reference herein. The control station
112
preferably stores the digital data as a digital image in a temporary storage. In addition, the control station
112
transmits the digital image to the operation panel
114
which preferably displays the image on a preview monitor
114
. An X-ray technologist preferably uses the image displayed on the preview monitor
114
to evaluate the quality of the image, input patient and exposure information, if necessary, and direct the image to be stored in the image archiver
116
.
In another embodiment, the control station
112
transmits a list of patient names and other information to the sensor unit
110
before the X-ray images are captured. The sensor unit
110
stores the names in a memory and displays the names on an alphanumeric display. The X-ray technologist matches a displayed name with the patient before taking the X-ray image. When the image is captured, the name of the patient is preferably encoded with the image according to the Digital Imaging and Communications in Medicine (DICOM) standard. The X-ray image is transferred to the control station
112
.
The image archiver
116
preferably stores hundreds or thousands of digital images. An X-ray technologist can use the viewing workstation
118
to retrieve an image from the. archiver
116
, display the image on a display coupled to the viewing workstation
118
, and perform assorted image manipulations, as described, for example, in U.S. patent application Ser. No. 09/057,083 now U.S. Pat. No. 6,208,762, entitled OPTIMIZED ENHANCEMENT OF DIGITAL IMAGES, filed on Apr. 8, 1998, assigned to the same assignee as the present application, and hereby incorporated by reference herein. The hard copy output device
120
prints copies of images stored in the image archiver
116
.
FIG. 2
is a high-level cutaway view of an embodiment of the generator
108
, including an X-ray tube
210
and a collimator
212
. The illustrated generator
108
demonstrates the functionality of a typical generator and is not necessarily representative of an actual X-ray generator. An X-ray system
100
according to the present invention may use any source of X-ray radiation and should not be limited to the generator
108
of FIG.
2
.
The X-ray tube
210
is surrounded by a sealed glass envelope
214
. Within the envelope are an anode
216
and a cathode
218
. The cathode emits electrons
220
, which strike a target
222
on the anode
216
. The interaction of the electrons
220
with the electrons and positively charged nuclei of the target
222
generates X-ray radiation
224
. The energy of the X-ray emission is controlled by the voltage applied to the tube
210
. The X-rays
224
radiate from the target
222
and a portion of the X-rays encounter the collimator
212
.
The collimator
212
contains a sheet of lead or other material that blocks the X-ray radiation. An adjustable aperture
226
in the collimator
212
allows a “primary beam”
228
of X-ray radiation to pass through the collimator
212
. The size and shape of the primary beam
228
is controlled by adjusting the size and shape of the aperture
226
. In one embodiment, an actuator
230
controls the aperture
226
. The actuator
230
is preferably either a servo motor or a stepper motor and is operated by a control signal from the control station
112
.
FIG. 3
is a cutaway perspective illustration of the sensor unit
110
according to an embodiment of the present invention.
FIG. 3
illustrates the top
302
of the sensor unit
110
, defined as the side receiving the primary beam
328
from the X-ray generator
108
, and the various lower layers of the sensor unit
110
. The sensor unit
110
is surrounded by a protective cover
310
. Within the cover
310
are a scintillator
312
and a sensor plate
314
. As is well known in the art of X-ray detection, the scintillator
312
preferably converts X-ray energy into visible light. The visible light from the scintillator
312
is detected by the sensor plate
314
, which digitally records the location and intensity of each light flash. In one embodiment of the present invention, the sensor unit
110
produces digital X-ray images having 2688×2688 12-bit (4096 gray scale) pixels.
FIG. 4
is a flow diagram illustrating the interactions between the generator
108
, the sensor unit
110
, and the control station
112
when calculating a calibration coefficient. In the flow diagram, time flows from the top of the diagram to the bottom and horizontal lines represent communications between the various entities.
FIG. 4
illustrates only major interactions between the entities and does not represent every interaction.
Initially, the X-ray technologist positions
410
the X-ray generator
108
and the sensor unit
110
in the desired positions. In one embodiment of the present invention, the sensor unit
110
is stationary and only the generator
108
can be positioned. In another embodiment, both the generator
108
and the sensor unit
110
are freely positionable.
The X-ray system
100
uses a calibration coefficient to calculate the collimation parameters. There is a linear relationship between movement of the aperture
226
and movement of the exposure boundary on the sensor unit
110
. This relationship is defined by the calibration coefficient as follows:
(aperture displacement)×(calibration coefficient)=exposure boundary displacement
The calibration coefficient varies with the distance between the generator
108
and the sensor unit
110
. In a preferred embodiment of the present invention, and most X-ray systems, however, this distance is fixed. Therefore, once the calibration coefficient is determined and stored in the control station
112
, there is no need for re-calibration unless the source-sensor distance is changed to a distance for which there is no stored coefficient.
To calculate the calibration coefficient, the aperture
226
in the collimator
212
is moved
412
to a constricted position. Then, the generator
108
generates
412
a relatively short duration beam of X-ray radiation towards the sensor unit
110
. In one embodiment, the short duration beam lasts for approximately 20 milliseconds. Preferably, the beam is generated in response to the technologist entering a command on the control station
112
. The beam is captured
414
by the sensor unit
110
and converted into a digital image or other digital format. This image is transmitted
416
to the control station
112
via the communications link
122
. The control station
112
analyzes
428
and stores the image.
After the first image is analyzed, the aperture
226
is opened by a displacement d
1
and the process is repeated. The aperture
226
is preferably opened automatically by the actuator
230
in response to control signals received
420
from the control station
112
. The control station
112
analyzes the two images and determines the resultant exposure boundary displacement d
2
corresponding to the aperture displacement d
1
. The control station
112
calculates
428
and stores the calibration coefficient as d
2
/d
1
and associates it with the source-sensor distance. These calibration steps can be repeated as many times as are necessary or desired to establish one or more calibration coefficients.
Once the calibration coefficient is established, the X-ray system
100
is calibrated for the particular use.
FIG. 5
is a flow diagram illustrating the interactions between the generator
108
, the sensor
110
, and the control station
112
when adjusting the aperture
226
to achieve a desired goal while capturing an image. The X-ray subject can optionally be present while the technologist calibrates the X-ray system
100
for the particular use.
To calibrate the X-ray system
100
for a particular use, the technologist first positions
510
the generator
108
and sensor
110
and uses
512
a short duration X-ray beam to capture
514
a reference image. This reference image is transmitted
516
to the control station
112
and the control station analyzes
518
the image and uses the calibration coefficient to generate collimation parameters. These parameters are transmitted
520
to the generator and cause the actuator
230
to adjust
522
the aperture
226
. These steps can be repeated as many times as are necessary or desired to achieve a desired collimation.
In one embodiment, the control station
112
constricts the aperture
226
and uses the reference image(s) and calibration coefficient to calculate collimation parameters for widening the beam to cover the entire field of the sensor unit
110
. In another embodiment, the control station
112
uses the reference images to determine where on the sensor unit
110
a maximum (unattenuated) signal was received. The control station
112
uses the calibration coefficient to determine precisely by how much the beam should be constricted to eliminate unwanted exposure beyond the periphery of the X-ray subject or other object being X-rayed. This constriction minimizes the area of the sensor unit
110
receiving X-rays not passing through the X-ray subject and thereby reduces unwanted X-ray scatter. In a third embodiment, the technologist views the reference image captured from the short duration exposure and defines the desired area of exposure. For example, the technologist can use a keyboard, mouse, or other input device to define the borders of the desired area of exposure. The control station
112
uses the calibration coefficient to determine by how much the beam should be constricted or expanded to cover only the defined region.
Once the collimator
212
is properly adjusted, the technologist preferably positions the subject to be X-rayed between the generator
108
and the sensor unit
110
(if the subject is not already so positioned) and causes the generator
108
to generate
524
a full duration beam. In one embodiment, the fill duration is approximately 200 milliseconds. The X-ray image is captured
526
by the sensor unit
110
and transmitted
528
to the control station
112
for subsequent processing.
The above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. The scope of the invention is to be limited only by the following claims. From the above discussion, many variations will be apparent to one skilled in the relevant art that would yet be encompassed by the spirit and scope of the invention.
Claims
- 1. A method for collimating radiation, comprising the steps of:analyzing a plurality of collimation images captured by a sensor unit for capturing an x-ray image based on x-ray radiation from a generator, wherein in capturing the plurality of collimation images the x-ray radiation is collimated to a plurality of different positions by a collimator for collimating x-ray radiation and wherein in analysis of the plurality of collimation images, a calibration coefficient is calculated for calibration of the collimator, the calibration coefficient at least being responsive to a relationship, in the plurality of collimation images, between movement of an aperture in the collimator and movement of an exposure boundary on the sensor unit; and generating a collimation parameter for collimation of the collimator at least in accordance with the calibration coefficient, a reference image from the sensor unit, and an area defined on the reference image.
- 2. A method according to claim 1, wherein the analyzing step is for analyzing two collimation images from the sensor unit responsive to two exposures of x-ray radiation collimated to two different positions by the collimator, and wherein the calibration coefficient is calculated responsive to a linear relationship between movement of the aperture in the collimator and movement of an exposure boundary on the sensor unit.
- 3. A method according to claim 1, wherein the collimation parameter is generated such that radiation from the generator covers an entire field of the sensor unit.
- 4. A method according to claim 1, further comprising the steps of:displaying the reference image; and defining an area on the displayed reference image; wherein the generating step is for generating a collimation parameter for radiating the defined area.
- 5. A method according to claim 1, wherein the generating step comprises the steps of:analyzing the reference image to determined if radiation extends beyond an object to be radiated; and calculating the collimation parameter for reducing radiation extending beyond the object to be radiated, responsive to a positive determination that radiation extends beyond the object to be radiated.
- 6. A method according to claim 1, wherein the area defined on the reference image is defined with an input device by a user.
- 7. An x-ray system comprising:a sensor unit for capturing an x-ray image based on x-ray radiation from a generator; and a control unit coupled to the sensor unit and a collimator for collimating x-ray radiation from the generator; wherein the control unit comprises: a calibration unit for analyzing a plurality of collimation images captured by a sensor unit for capturing an x-ray image based on x-ray radiation from a generator, wherein in capturing the plurality of collimation images the generator is collimated to a plurality of different positions by a collimator for collimating x-ray radiation and wherein in analysis of the plurality of collimation images, a calibration coefficient is calculated for calibration of the collimator, the calibration coefficient at least being responsive to a relationship, in the plurality of collimation images, between movement of an aperture in the collimator and movement of an exposure boundary on the sensor unit; and a parameter generation unit for generating a collimation parameter for collimation of the collimator at least in accordance with the calibration coefficient, a reference image from the sensor unit, and an area defined on the reference image.
- 8. An x-ray system according to claim 7, wherein the calibration unit analyzes two collimation images from the sensor unit responsive to two exposures of x-ray radiation collimated to two different positions by the collimator, and calculates the calibration coefficient responsive to a linear relationship between movement of the aperture in the collimator and movement of an exposure boundary on the sensor unit.
- 9. An x-ray system according to claim 7, wherein the area defined on the reference image is defined with an input device by a user.
- 10. An x-ray system according to claim 7, wherein the area defined on the reference image corresponds to an entire field of the sensor unit.
- 11. An x-ray system according to claim 7, wherein the area defined on the reference image is defined to reduce radiation extending beyond an object to be radiated.
- 12. A computer-readable medium storing a computer-executable program, the computer program comprising instructions for:analyzing a plurality of collimation images captured by a sensor unit for capturing an x-ray image based on x-ray radiation from a generator, wherein in capturing the plurality of collimation images the generator is collimated to a plurality of different positions by a collimator for collimating x-ray radiation and wherein in analysis of the plurality of collimation images, a calibration coefficient is calculated for calibration of the collimator, the calibration coefficient at least being responsive to a relationship, in the plurality of collimation images, between movement of an aperture in the collimator and movement of an exposure boundary on the sensor unit; and generating a collimation parameter for collimation of the collimator at least in accordance with the calibration coefficient, a reference image from the sensor unit, and an area defined on the reference image.
- 13. A computer-readable medium according to claim 12, wherein the analyzing instruction is for analyzing two collimation images from the sensor unit responsive to two exposures of x-ray radiation collimated to two different positions by the collimator, and the calibration coefficient is calculated responsive to a linear relationship between movement of the aperture in the collimator and movement of an exposure boundary on the sensor unit.
- 14. A computer-readable medium according to claim 12, wherein the collimation parameter is generated for radiation to cover an entire field of the sensor unit.
- 15. A computer-readable medium according to claim 12, wherein the generating instruction comprises instructions for:analyzing the reference image to determine if radiation extends beyond an object to be radiated; and calculating the collimation parameter for reducing radiation extending beyond the object to be radiated, responsive to determination that radiation extends beyond the object to be radiated.
- 16. A computer-readable medium according to claim 12, wherein the area defined on the reference image is defined with an input device by a user.
US Referenced Citations (4)
Number |
Name |
Date |
Kind |
5844962 |
Kunert |
Dec 1998 |
A |
6208762 |
Garland et al. |
Mar 2001 |
B1 |
6215853 |
Kump et al. |
Apr 2001 |
B1 |
6259767 |
Neumann et al. |
Jul 2001 |
B1 |