X-ray diagnostic device for mammography examinations

An X-ray diagnostics device for mammography examinations has an arm for an X-ray tube and a subject table as well as a compression plate arranged between the X-ray tube and the subject table, the compression plate being connected to the arm and being displaceable along it to compress a female breast. The arm is rotatable around a horizontal shaft, and the shaft is secured to a mount that is laterally displaceable. The mount is displaceably attached to a lifting arrangement connected to the stand that is height-adjustable. A control device accepts output signals from position sensors that indicate the height and lateral positions of the arm as well as from a synchro system that indicates the rotational angle of the arm, to control displacement arrangements the arm such that a rotation of the arm around an axis that can be arbitrarily selected along the longitudinal axis of the stand that is substantially aligned with the center axis of the compressed breast.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to an X-ray diagnostic device for mammography examinations having an arm for an X-ray tube and a subject table as well as a compression plate arranged between the X-ray tube and the subject table, the compression plate being connected to the arm and being displaceable along it, wherein the arm can be rotated around a horizontal shaft and is height-adjustable along an imaginary longitudinal axis of a stand.

2. Description of the Prior Art

An X-ray diagnostic device of this type is disclosed in European Application Patent 0 370 089. In this device, the rotational axis of the arm lies outside the center of gravity of the arm. In order for the arm with the X-ray tube, the compression plate and the subject table to be able to be rotated around the rotational axis, the free end of the rotational axis is provided with a gearwheel rigidly connected to this end that is driven by a comparatively strong and thus comparatively large, motor. A pneumatic spring device serves for additional weight compensation of the arm. The vertical displacement of the arm ensues with a motor and a toothed rack that are arranged separately from the rotational device of the arm.

In a routine examination of a breast of a patient, a first vertical exposure and subsequently a second exposure are made, with the arm being rotated by an angle between 45° and 60° between the two exposures. An exposure when the arm has been turned by approximately 90° also can be made in conjunction with a further examination. In order to avoid the patient having to step aside given rotation of the arm from the first exposure position into the second exposure position, the extension of the imaginary center axis of the rotational axis is arranged in the device disclosed in European Application 0 370 089 so that it lies immediately above the subject table. The distance between the subject table and the center axis is fixed, which means that most patients must undertake a certain lateral position correction when changing from a vertical exposure position into a lateral exposure position. Only a few patients have a breast size for which this device is suitable without such a correction, so that the imaginary center axis lies in axial alignment with the imaginary center axis of the compressed breast.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an X-ray diagnostic device for mammography examinations of the type initially described wherein the rotary motions of the arm can be implemented simply, so that the arm can be rotated around an isocenter adapted to the patient from one exposure position into another exposure position with the desired rotational angle, and such that the patient can remain in position regardless of the breast size.

This object is achieved in an X-ray diagnostic device of the type initially described wherein the arm is rotatable with a first displacement arrangement around the horizontal shaft, the shaft is secured to a mount that is laterally displaceable with a second displacement arrangement, as a result of which the arm is laterally displaceable. The arrangement mount is displaceably attached to a lifting arrangement connected to the stand, the lifting arrangement is height-adjustable with a third displacement arrangement. A control device is operable, using a control program that accepts output signals of position sensors that indicate the height and lateral positions of the arm as well as from a synchro system that indicates the rotational angle of the arm. The control device controls the second and third displacement arrangements for the displacement of the arm laterally and in height as well as the first displacement arrangement for the rotation of the arm such that a rotation of the arm around an axis that can be arbitrarily selected along the longitudinal axis of the stand is enabled. In particular, the first and second displacement arrangements preferably are low-power, inexpensive motors that can rotate the arm around the selective axis with the assistance of the control device. Due to the compact structure of the aforementioned arm arrangement, a weight compensation device is not needed for the rotary movements of the arm, since the rotary movements always ensue in the proximity of the center of gravity of the arm.

In an embodiment of the X-ray diagnostics device of the invention, the imaginary axis lies at a distance from the subject table is half the distance between the subject table and the compression plate when the compression plate is in a compression position. The choice of rotating the arm around the selected axis assures that the patient need not be repositioned when changing the exposure angle, regardless of the breast size.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1schematically shows an X-ray diagnostics device for mammography examinations, i.e. a mammography device, having a stand1that carries an arm arrangement2that shall be described later. The arm arrangement2is height-adjustable with the assistance of a motor3and a screw4having one end connected to a part5that is rigidly arranged at the arm mechanism.

FIG. 2shows the arm arrangement2, composed of an arm6, an X-ray tube7arranged at the arm6and a subject table8as well as a compression plate9arranged between the X-ray tube7and the subject table8, the compression plate9is connected to the arm6and is displaceable along it.FIG. 2also shows that the arm6of the arm arrangements is rotatable around a horizontal shaft10with the assistance of a motor11. The shaft10is secured to a lateral carriage12, i.e. a carriage that is laterally displaceable with the assistance of a motor13. As a result, the arm6is also laterally displaceable. The carriage12is displaceably arranged at a lifting element14that is connected via the aforementioned part5to the screw4for displacing the lifting element14and, thus, for displacing the arm arrangement2in height.FIG. 2also shows the end face15of the mammography device. This end face15is provided with a slot16in which the part5proceeds and along which the arm mechanism2is therefore height-displaceable.

Before an examination of a breast of a patient (not shown), the arm arrangement2is shifted along a longitudinal axis24of the stand1into a position wherein the subject table8assumes a position suitable for the patient. (The longitudinal axis24is definable within the stand1, but is not a separate physical components). The longitudinal axis24preferably proceeds parallel to the slot16. With the compression plate9, the breast is now pressed against the subject table8until an optimum compression of the breast has been obtained for an exposure, whereupon a vertical exposure of the breast is implemented. The compression plate9is provided with a distance-measuring unit17that measures the distance from the subject table8in this position. The distance-measuring unit17, which preferably is attached to that end of the compression plate9that is directed toward the arm6, shall be described below. The patient is released from the compressed position after a first vertical exposure of the breast, and the arm6is rotated from the described, vertical exposure position into a second exposure position having an angle of 45° through 60° from the first exposure position. Such a second exposure position is shown inFIG. 3. The arm6is then rotated around an axis18that lies at a distance from the subject table8that corresponds to half the distance between the subject table8and the compression plate9when the compression plate9is in its above-described compression position. Like the axis24, the axis18is definable but is not a separate physical component.

The position of the axis18is determined with the assistance of the distance-measuring unit17and a control device19, which shall be described below.

The rotation of the arm6around the axis18ensues by a simultaneous combination of all motion possibilities of the arm mechanism2, i.e. partly by rotating the arm6around the shaft10, partly by a height displacement of the arm6and partly by a lateral displacement of the arm6.

FIG. 4shows a control device19for the arm arrangement2in the form of a schematic block circuit diagram. The control device19is composed of a position sensor20, which indicates the height position of the arm6, of a position sensor21that indicates the lateral position of the arm, and a synchro system22that indicates the rotational angle of the arm6. The sensors20,21and the synchro system22are not shown in other figures, however, they can be placed at strategic locations at the mammography device. The control device19is also includes the distance measuring unit17described in conjunction withFIG. 2. The control device19also has a control program23that—when the arm6is rotated—is continuously supplied with signals from the sensors20,21and from the synchro system22that respectively correspond to the momentary height, lateral and rotary positions of the arm6. The control program23also stores input signals from the distance-measuring unit17that correspond to the distance between the subject table8and the compression plate9. The control program23divides the value of the input signal by two and thus calculates the position of the horizontal axis18around which the arm6is to be turned. The horizontal axis18always lies in axial alignment with the center axis of the breast when it is in a compression position. The control program23processes the supplied information. The result of the processed information is then supplied to the motor11for rotating the arm6, to the motor13for the lateral displacement of the carriage12as well as to the motor3for the vertical displacement of the arm6. A control device19of this type is disclosed in U.S. Pat. No. 4,109,059 and therefore need not be described in greater detail. The distance-measuring unit17described herein is not disclosed in conjunction with the control device according to this United States patent.

Because the control device19can individually calculate an optimum axis18around which the arm6can be rotated for each patient in the described way, a repositioning of the patient from a vertical exposure position into a desired, lateral exposure position is not necessary, regardless of the size of the beast. The axis18is always applied along the longitudinal axis24of the stand1that proceeds parallel to the slot16.