Patent Application
20080060133
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments that 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 other 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 as limiting the scope of the invention.
In an embodiment, a dual-stage positioning system is disclosed. The positioning system is provided with a coarse positioning subsystem for providing a reference and a fine positioning subsystem for providing high precision alignment.
In various embodiments a positioning system using a dual-stage drive assembly for an imaging device is disclosed. The embodiments, however, are not so limited, and may be implemented in connection with other systems such as industrial imaging system, tracking systems, various positioning systems etc. In an embodiment, the positioning system imparts very high precision for the required range and coarse precision for the remaining displacement range. In another embodiment, the movement of the object being scanned is programmed as per the cross sectional volume of the part. A velocity profile, a mapping between the velocity of the patient support over a cross section of area or volume of the object being scanned is calculated. The velocity of the patient support is directly proportional to the volume of the object. In an embodiment, the movement of the patient support is programmed based on the velocity profile. Various parts require different types of velocity profiles, which can be preprogrammed and easily executed whenever required.
In an embodiment, the imaging device 100 comprises an imaging gantry 105. The imaging gantry 105 includes a tunnel 125 for receiving a patient 110 and a radiation source 130 for providing radiations. A patient support 115 having a patient support surface is provided for engaging and supporting the patient 110. A positioning system 120 is provided for moving and aligning the patient support 115, which is received in the tunnel 125 of the imaging device 100. For better quality images and desired results the patient support needs to be positioned with fine precision. In an embodiment, the fine precision is in the range of micrometer precision. In an embodiment, the positioning system is designed to align or position the patient support along an X-axis with a precision of one micrometer for a range of 0-300 millimeters. The positioning system will be explained in detail with reference to
The positioning system 220 comprises a fine positioning subsystem 221 and a coarse positioning subsystem 226. The patient support 215 is a patient table. The patient support 215 is coupled to the fine positioning subsystem 221 through a fine feed 222. The fine feed 222 may be any mechanism, which can connect the fine positioning subsystem 221 to the patient support 215. This may include a clamp, or a bracket or any other holding means. The fine positioning subsystem 221 is capable of aligning or positioning the patient support 215 with a precision of a micrometer. In an embodiment, the fine positioning subsystem 221 aligns the patient support 215 with a precision of one micrometer for a range of 0-300 millimeters along the X-axis of the imaging device. However, it will be understood that the fine positioning system 221 may position the patient support 215 with other fine precisions. The fine positioning subsystem 221 is further coupled with the coarse positioning subsystem 226. In an embodiment the fine positioning subsystem 221 is a precision screw mechanism. The precision screw mechanism includes a screw arrangement 223 and an electric motor 225 coupled to the screw arrangement. The electric motor 225 is connected to the screw arrangement 223 by means of a timer belt 224. The fine positioning subsystem will be explained in detail in
The coarse positioning system 226 is configured to be prime mover. In an embodiment the coarse positioning subsystem 226 includes one or more double-end shaft motors (not shown) comprising shafts that extend outwardly in opposite directions. One or more timer pulleys 227 can be mounted on each end of the double-end shaft motor. One or more belts 228 can extend over the timer pulleys 227. The belts can be coupled to the double-end shaft motor through a coupling device (not shown). The belt 228 can also be coupled to fine positioning subsystem 221 through a coarse feed 229. As the fine positioning subsystem 221 is coupled with the patient supporting 215, the coarse positioning subsystem 226 will be able to move the patient support 215 laterally. The coarse positioning subsystem 226 is configured to align the patient support with a precision of one millimeter for a range of 0-2000 millimeters. However the various ranges of precisions may be achieved using the same concept but with different design as per the requirements of the particular application. By using the coarse positioning subsystem 226 a reference position is achieved, and using the fine positioning subsystem 221 the patient support 215 is aligned or positioned with micrometer precision. The coarse positioning subsystem using double-end shaft motors will be explained in detail in
In an embodiment the coarse positioning subsystem is configured to be a prime mover operating in a closed loop. However the coarse positioning system may be configured to be a coarse screw drives mechanism, a hydraulic drive mechanism and friction drive mechanism.
In an embodiment the fine positioning subsystem 321 is programmed to move the patient support 315, based on a velocity profile. The fine positioning subsystem 321 is provided with a programmer 326 for configuring the fine positioning subsystem 321 for moving or positioning the patient support 315 based on a velocity profile. The programmer 326 is coupled with the electric motor 325. The displacement of scanning part of the object being scanned can be programmed as per the cross sectional area or volume of the part. The velocity of patient moving along the X-axis through the scanning beam in an imaging device is directly proportional to the volume of the object being scanned. Thus in a particular area of cross section, if the volume is more, then scanning time will be more compared to parts with lesser area of cross section or volume. By programming the movement of the patient support surface the scanning time may be reduced. In effect, if a part with less volume of cross section is being scanned, it requires less time and hence the patient support may be moved quickly. This will reduce the time of scan. Various parts of the object will have different types of velocity profiles, which can be preprogrammed and easily executed whenever required.
For programming the displacement of the patient support the velocity profile of the object is obtained. The velocity profile includes mapping of velocity of the patient support in an imaging device over the cross sectional area/volume of the object being scanned.
The second drive 400 may further comprise multiple timer pulleys 427 rotatably placed beneath the patient support 415. Operation of the double-end shaft motor 425 causes rotation of the timer pulley 405. The timer pulleys 405 drive the belt 440 extending between the timer pulleys 405. The belt 440 in turn secures the first drive 212 through the coarse feed. The first drive 212 is coupled to the patient support through the fine feed. Therefore, the rotation of the timer pulleys 405 causes a linear movement of patient support 415.
Each timer pulley 405 can be directly coupled to a feedback device 435 at a first end. The feedback device 435 is a sensor assembly providing an indication of an absolute position of the patient support 415. The sensor assembly comprises a magnet secured to the carrier 450 and a magnetic absolute linear position sensor secured to one of the elongated rails 445 of the patient support 415. The relative position of the carrier 450 with respect to the magnetic absolute linear position sensor of the elongated rails 445 can be determined from the output signal provided by the magnetic absolute linear position sensor. The feedback device 435 can be configured to be an encoder. More particularly, the feedback device 435 can be configured to be an absolute encoder for greater positioning accuracy.
In an embodiment the output of the feedback device 435 may be provided to the programmer 326. This will allow the programmer 326 to select the desired velocity profile based on the position of the patient support.
The timer pulley 405 can also be coupled to a brake device 430 at a second end. The brake device can be a positive clamping device. The brake device ensures that the carrier position is not disturbed after the carrier is positioned at a predetermined position. This provides a reference position for the first drive. Further, the brake device 430 can configured to be an electro-mechanical brake for better safety.
In an embodiment the second drive is configured to be a coarse screw mechanism. This includes a screw arrangement capable of positioning the patient support coarsely. The coarse screw mechanism further includes an electric motor coupled to the screw arrangement through a belt.
In an embodiment the second drive is configured to be a set of hydraulic cylinders used to move the patient support along the X-axis. Few cylinders placed in a particular configuration would help to attain the required coarse position.
The fine positioning subsystem is actuated once an initial reference position is reached and the electro mechanical brakes actuated. These pair of brakes will rigidly hold the patient support in its initial reference position and this will act as a reference position to the fine positioning subsystem. This fine positioning subsystem has a very precise screw mechanism coupled with a stepper motor or servo motor in a close loop. The displacement least count can be of one micrometer as the stroke is limited to 300 mm only. The rigidity, accuracy, repeatability and control will be absolute. The errors will be reduced drastically because of the range control and least count.
The manufacturing and production of the positioning system is simplified when compared to the conventional positioning system using super drive systems like magnetic motors or linear motors to achieve similar accuracies and least count. The manufacturing cost is saved around 40%. The positioning system requires less assembly time and can be accommodated easily due to the flexibility of the tooth belt used. Therefore the manufacturing, assembling, transport and handling of the positioning system are simple, cheap and reliable.
Since the positioning of the patient support is programmed based on the velocity profile, the scanning time can be reduced. As dual stage positioning system is used, the patient support and the patient supported thereby may be placed with very high precision.
Thus various embodiments of positioning system are disclosed. However, it should be noted that the invention is not limited to this or any particular application or environment. Rather, the technique may be employed in a range of applications, including medical imaging systems, industrial imaging systems, tracking system or any other positioning technology, to mention a few. The invention also discloses a method of aligning a patient for exposing to radiations.
While the invention has been described with reference to preferred embodiments, those skilled in the art will appreciate that certain substitutions, alterations and omissions may be made to the embodiments without departing from the spirit of the invention. Accordingly, the foregoing description is meant to be exemplary only, and should not limit the scope of the invention as set forth in the following claims.
