Patent Application
20060259267
This invention relates generally to tilt calibration systems, and more particularly, to a tilt angle calibration system for a positioner.
Typically, a positioner in a medical imaging apparatus includes mechanisms for longitudinal and lateral tilt for a patient bed, and pivot rotation for a vascular gantry. The positioner provides convenient positioning of a patient for medical imaging. One example of a positioner is a vascular gantry comprising a C-arm and a pivot axis. Examples of medical imaging apparatus include an X-ray apparatus and a vascular imaging apparatus.
Drive mechanisms for tilting the positioner require calibration for setting of a zero degree position for accurate positioning of the patient for examination. The zero degree position is often referred to the “home” position.
Generally, systems for calibrating tilt angle of the positioner e.g. a vascular positioner in a medical imaging apparatus include various procedures for determining the relative difference between the zero degree position of an axis (e.g. lateral tilt axis, longitudinal tilt axis) of the vascular positioner and a position sensor's reading corresponding to the zero degree position. The relative difference is often referred to as home offset or datum shift.
Known systems for tilt calibration of a vascular positioner e.g. patient bed include manual procedures that are followed at the time of manufacture of the table.
However, manual calibration procedures are generally cumbersome and involve multiple steps for appropriate execution by a skilled field engineer.
Furthermore, re-calibration of the tilt angle becomes necessary at the time of servicing and/or installation of the table, particularly for example, during software updates or drive chain replacement.
Thus, conventional systems do not (i) provide for an automated calibration procedure that significantly reduces manufacturing time, equipment installation and servicing time (ii) improve patient safety by providing redundant angle information and avoiding single point failure (iii) provide uniform manual panning effort between subsequent installations and (iv) significantly simplify the configuration and reduce the number of components by eliminating limit switches and accessories for calibration.
The above-mentioned shortcomings, disadvantages and problems are addressed herein, which will be understood by reading and studying the following specification.
In some embodiments, a tilt calibration system for a positioner in a medical imaging apparatus is provided, wherein the system comprises at least one first sensor configured to determine the position of at least one vascular positioner axis relative to the ground surface, at least one second sensor configured to determine the position of the at least one vascular positioner axis relative to a home position, and a processor configured to determine a home offset (datum shift) in response to the position of the positioner axis relative to the ground and the position of the positioner axis relative to the home position.
In some embodiments, a patient support table is provided, wherein the table comprises at least one tilt drive coupled to a patient support surface, a tilt position feedback device connected to the tilt drive, an accelerometer coupled to the patient bed, and a processor connected to the accelerometer and the tilt position feedback device.
In some embodiments, a patient support table comprises a first unit for determining the position of at least one tilting member relative to the ground, a second unit for determining the position of the at least one tilting member relative to a home position, and a processor for determining a home offset in response to the output of the first unit and the second unit.
Apparatus, systems and methods of varying scope are described herein. In addition to the aspects and advantages described here, further aspects and advantages will become apparent by reference to the drawings and reading the detailed description that follows.
In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that embodiments may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the embodiments. The following detailed description is, therefore not to be taken in a limiting sense.
Various embodiments provide a tilt calibration system for a positioner having a positioner axis 44 such as, a vascular positioner, e.g. a vascular gantry 42, a patient bed, in a medical imaging apparatus such as, for example, in an X-ray apparatus, vascular imaging apparatus, etc. Various specific embodiments include a patient support table in a medical imaging apparatus.
However, the embodiments are not so limited, and may be implemented in connection with other systems such as, for example, a camera, aircraft flight control systems, pallet indexing in machining center, automobile security systems, special switches, etc.
The vascular positioner includes at least one of a patient bed and a vascular gantry 42.
For example, the vascular positioner axis 44 may include at least one of a lateral tilt axis and a longitudinal tilt axis.
In an embodiment, the first sensor 110 includes at least one of an accelerometer 60 and an inclinometer 36, wherein the accelerometer 60 has a Micro Electromechanical Systems (MEMS) configuration.
In an embodiment, the second sensor 120 includes at least one feedback device 30 such as, for example, an encoder.
For example, the encoder may include an infinite-turn type absolute position encoder or an incremental encoder.
In an embodiment, the patient bed 100 includes at least one of a patient support surface 10 for supporting a patient for examination, a longitudinal plate 11 rigidly coupled to the patient support surface 10 from the underside of the patient support surface 10, and a tilt plate 12 (see
In an embodiment, (see
In an embodiment, the tilt drive 20 includes a ball screw mechanism 22 coupled to at least one drive motor 21.
For example, the ball screw mechanism 22 includes a driving member (e.g. nut 25 and a driven member (e.g. lead screw 23), wherein the driving member 25 is coupled to the drive motor 21 and the driven member is coupled to the tilt plate 12. The drive motor 21 drives the driving member 25, which in turn drives the driven member resulting in tilting movement of the tilt plate 12 and in turn the patient bed 100.
It should be noted that the either the nut 25 or the lead screw 23 may be configured as the driving member 25.
The CPU 40 issues a stop command signal when the output of the feedback device 30 indicates a predetermined angular position of the tilt plate 12. For example, the motion control unit 50 stops the tilting movement of the tilt plate 12, on receiving the stop command signal from the CPU 40.
In one example, the encoder is an infinite-turn type absolute position encoder connected to the driving member 25 through a gear mechanism.
Other examples may include an incremental encoder connected to the driving member 25.
In an embodiment, (see
In other embodiments, the accelerometer 60 may also be connected to the motion control unit 50.
In an embodiment, the accelerometer 60 has a Micro Electro Mechanical Systems (MEMS) configuration.
In another embodiment, the accelerometer 60 is a two-axis accelerometer capable of sensing the lateral tilt and the longitudinal tilt of the patient bed 100.
However, in other embodiments, accelerometers 60 such as, three-axis accelerometers may also be implemented depending on the number of tilt axes and the requirement.
It should be noted that the accelerometer 60 is mounted to the longitudinal plate 11 for enabling easy assembly to the patient bed 100. Alternatively, the accelerometer 60 may also be mounted on e.g. the tilt plate 12 or the patient support surface 10, that are tiltably associated with the patient bed 100.
One embodiment is illustrated using the following example:
Table 1 illustrates various positions (tilt angle) of patient bed 100 and the corresponding reading indicated by the tilt accelerometer 60:
Thus, the formula for calculating the tilt angle is:
Tilt angle=(Accelerometer Reading−1)*15 (1)
For example, the tilt position of the patient bed 100 is determined using an infinite-turn type absolute position encoder with an output of 13 bit per revolution.
At the time of manufacture of the patient support table 1, the feedback device 30 for example, the encoder, the shaft is configured to rotate freely through any angle such that the encoder may not indicate zero reading when the patient bed 100 is at zero degree position (home position 34).
A “home offset” is required to calibrate the encoder shaft and hence the tilt angle of the patient bed 100.
For example, for an encoder rotation of 0 degree, the encoder reading is 1024. For 1 rotation of the encoder, the encoder reading is 8192.
Thus, the formula to calculate the home offset is given by:
Home offset=[(Tilt angle*8192/360)−Encoder reading] (2)
Thus, for zero degree (home position 34) of the encoder shaft (zero tilt of the patient bed), the home offset is given by:
Home offset=(0*8192/360)−1024
Home offset=−1024 encoder counts.
The CPU 40 calculates the “home offset” in response to the output of the encoder and the accelerometer 60. The “home offset” may be stored for later use.
Thus, various embodiments provide a tilt angle calibration system for a medical imaging apparatus. Further embodiments provide a patient support table for a medical imaging apparatus.
While embodiments are described in terms of various specific embodiments, those skilled in the art will recognize that embodiments can be practiced with modifications such as, for example, the patient support table may include an inclinometer 36 configured to indicate the position of the patient bed 100 relative to the ground surface 32. However all such modifications are deemed to have been covered within the spirit and scope of the claims.
