Medical imaging systems

Details Medical imaging systems Medical imaging systems

1999-06-21

2001-07-31

Kim, Robert H. (Department: 2882)

X-ray or gamma ray systems or devices

Accessory

Alignment

C250S462100

Reexamination Certificate

active

06267503

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to medical imaging systems and in particular to a method and apparatus for aligning an imaging device relative to a patient's body. The invention is particularly, but not exclusively, applicable to the positioning of x-ray apparatus.
BACKGROUND OF THE INVENTION
When taking an x-ray of a patient, it is important to correctly position the x-ray source relative to the patient's body. Typically, the x-ray film is placed beneath a table on which the patient lies, with an ionization chamber positioned between the patient and the film. In order to ensure that the image formed on the film is in focus, the vertical distance of the x-ray source above the patient is set by the operator. Similarly, in order to ensure that the x-ray beam is incident upon the appropriate region of the patient's body, the x-ray source can also be moved by the operator in a horizontal plane.
Given the known dangers of x-ray exposure, it is important to confine the x-ray beam to that region of the body which is of particular interest. However, by utilising a smaller beam area the risk of missing the anatomical region of interest is increased. Failure to correctly capture an image of the area of interest will result in the need to take a further x-ray image, in addition to the wastage of x-ray film. Misalignment of the x-ray source in the vertical direction may also result in an out of focus image requiring that the x-ray procedure be repeated.
A known system for enabling accurate positioning of the x-ray source in the horizontal plane involves the projection of a beam of light from a light source onto a patient's body. The light source is positioned adjacent to the x-ray source and is fixed relative thereto. Typically, a x-ray radiation translucent mirror is used to direct the light beam onto the patient's body along the path taken by the x-ray beam. Prior to taking the x-ray, the operator positions the x-ray source using the light beam as a guide. Whilst in theory this system improves x-ray source alignment, in practice, regular checks must be carried out on the x-ray apparatus to ensure that the light source does not become misaligned relative to the x-ray source. Misalignment is common due to the strain placed upon the x-ray apparatus by constant movement. In addition, positioning systems of this type rely upon the expert knowledge and perception of a human operator to correctly position the light beam. X-ray images can be required for any part of the body and the operator may find difficulty in exactly centering the x-ray source to obtain a focused exposure.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate or mitigate at least one of the disadvantages of the existing system.
According to a first aspect of the present invention there is provided apparatus for aligning an imaging device relative to a human or animal body to enable an image of an operator selected anatomical region to be obtained, the apparatus comprising:
a plurality of light reflective markers for attachment to respective anatomical landmarks of the body, which landmarks mark out said anatomical region;
an image sensor arranged in use to view at least a portion of the body including attached reflective markers;
a light source arranged in use to illuminate attached reflective markers; and
an image processing computer for receiving image data from the image sensor, the computer being arranged:
a) to store or access a database of standard patient records including, for each of a plurality of anatomical regions, a locating position for the imaging device relative to the positions of said anatomical landmarks;
b) to select an appropriate record from the database using operator input data for the patient to be imaged;
c) to select from the selected record a relative locating position for the imaging device using operator input data identifying the anatomical region to be imaged;
d) to determine from said image data the position of the reflective markers relative to the imaging device, and
e) to determine using the selected relative locating position and the determined positions, the actual position at which the imaging device should be located in order to obtain the desired image.
The number of reflective markers required depends upon the particular area to be imaged. Typically however, a relatively small number of markers are used, e.g. between two and five.
Preferably, the image sensor comprises at least one CCD camera. Alternatively, the image sensor comprises a pair of CCD cameras which are spaced apart so as to enable a three dimensional image of a patient's body to be obtained. The resulting three dimensional image can be used in order to provide position information in three dimensions. The computer may be arranged to store focus information defining a preferred focal distance for each anatomical region. The three dimensional position information may be used to manually, or automatically set the distance of the imaging device from the patient's body. Preferably, three dimensional rendering techniques can be applied to allow a 3-D visual image of the patient to be presented to an operator, maximising the information available to the operator.
Preferably said image sensor is positioned adjacent to said light source and the light reflective markers are retro-reflective markers which tend to reflect light in the direction of the light source and the image sensor.
Preferably, the image sensor is arranged to generate image data in which areas without reflective markers are identified as black with the reflective markers being identified as light spots. This may be achieved by appropriately setting the aperture of the image sensor or by shuttering the image sensor at an appropriately high speed. Alternatively, or in addition, image data generated by the image sensor may be applied to a variable gain amplifier.
Preferably, the light source comprises a flash lamp which may be operated in synchronisation with an image sensor shutter.
Preferably, the imaging device which is aligned by the present invention is a x-ray imaging system.
Preferably, the image sensor is rigidly secured to the x-ray generating apparatus so that alignment of the image sensor relative to the x-ray tube can be accurately maintained.
In one embodiment of the invention, the image processing computer comprises a video display unit. The computer may be arranged to superimpose the determined positions of the light reflective markers on the display. The locating position of the imaging device may also be displayed.
The apparatus of the above first aspect of the present invention may comprise positioning means, coupled to said computer, for automatically positioning the imaging means The image processing computer may also be arranged to locate the imaging device at the correct focal distance, e.g. using said three-dimensional position information and using a calibration frame containing permanent markers positioned strategically on the x-ray table.
According to a second aspect of the present invention there is provided a method of aligning an imaging device relative to a human or animal body to enable an image of a selected anatomical region to be obtained, the method comprises the steps of:
attaching a plurality of light reflective markers to anatomical landmarks of the body;
illuminating the body and the reflective markers with light;
detecting light reflected from the reflective markers with an image sensor;
selecting from a database of standard patient records, a record appropriate to the patient or animal to be imaged, each record including, for each of a plurality of anatomical regions, a locating position for the imaging device relative to the positions of said anatomical landmarks;
selecting from the selected record a set of relative positions using operator input data identifying the anatomical region to be imaged;
using the selected relative position data and the determined positions of the reflective markers to determine the actual position at which the imag

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