Surgery – Instruments – Stereotaxic device
Reexamination Certificate
1999-09-14
2001-03-27
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Stereotaxic device
Reexamination Certificate
active
06206891
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to devices for stereotactic localization of an object in space, especially, but not limited to, such devices for use in localizing an instrument during a medical procedure.
BACKGROUND OF THE INVENTION
Stereotactic localization refers to the localization of an object in a three-dimensional workspace by means of two or more two-dimensional sensors viewing the object along different sight lines. A three-dimensional coordinate system is established in the workspace and the three-dimensional coordinates of the object are calculated from the two-dimensional views obtained by the sensors. Stereotactic localization is important, for example, during invasive surgery when it is necessary to locate in the operating space, with a high degree of accuracy, part of a surgical instrument. For example, the location of the exposed handle of a probe in the operating space may be determined, from which the location of the tip of the probe inside the patient's body may be calculated. In such cases, the location of the tip may be registered in a displayed computerized image of the patient, such as an X-ray, sonogram, or CAT scan.
The sensors used in stereotactic localization may be cameras that sense light emitted by objects to be detected in the workspace. Devices utilizing video cameras as sensors are described in L. Adams, et al., IEEE Computer Graphics and Application Vol. 10 (1990), No. 3, pp. 43-51; M. P. Helibrun, et al., Stereotactic and Functional Neurosurgery 1992, No. 58, pp. 94-98; N. Meitland et al., Proceedings of the 5
th
British Machine Vision Conference, York, BMVA Press, 1994 pp. 609-618 and in U.S. Pat. Nos. 5,603,318 and 5,792,147. Alternatively, the objects of interest may be modified to emit another form of energy detected by the sensors. The type of energy used may be radio-frequency radiation (as disclosed in U.S. Pat. No. 5,251,635), sound waves (U.S. Pat. No. 4,012,588), or pulsed DC magnetic fields (U.S. Pat. No. 5,558,091). Devices based on the detection of pulsed infrared light radiation by video cameras are disclosed in U.S. Pat. Nos. 5,622,170, 5,197,476 and 5,792,147.
An array of two-dimensional sensors to be used in stereotactic localizing systems must be calibrated prior to use in order to establish the relative orientation of the sensors in the array and other parameters necessary for locating objects in space. In one calibration procedure, a plurality of target objects are placed in the workspace at points of known three-dimensional coordinates, and stereotactic views of the targets are obtained by the sensors. The resulting calibration data are then used to generate a localization function determining the three-dimensional coordinates of an object in the workspace from the two-dimensional stereotactic views of it obtained by the sensors. Computation of a localization function is described, for example, in Jain, R. et al.,
Machine Vision,
McGraw-Hill, New York 1995. The localization function involves 14 parameters that are calculated from the calibration data. Six of these parameters characterize sensor positions and orientation, two characterize the sensor projections of the focal plane, four characterize optical distortion of the lens, and two characterize scaling factors and aspect ratio. The accuracy of the calculated camera parameters, and hence of the localization function, is limited by the number of target points used for obtaining the calibration data. For the localization function to be accurate in the entire workspace, calibration data must be obtained over a set of target points spanning as large a volume in the workspace as possible and being as dense as possible in that volume.
U.S. Pat. No. 5,603,318 discloses a device consisting of a small number of targets attached to the patient that serve for calibration of sensors in a medical stereotactic procedure. Since the number of targets used for the calibration is small, and is necessarily located outside the patient's body, the calibration data yielded are accurate only near the targets. The accuracy rapidly diminishes to intolerable levels at locations away from the targets including locations of medical interest (e.g. inside a patient's body). This calibration method necessitates that it be performed in the workspace and that the calibration device be present in the workspace during the medical procedure.
Alternative methods in the art use a fixed planar or box-type three-dimensional calibrating target that provides at least three surfaces as calibrating targets. These devices also do not have a sufficiently high target density to provide accurate calibration data for high accuracy localization during a medical procedure.
SUMMARY OF THE INVENTION
The present invention provides a device and method for obtaining calibration data in a fixed coordinate system for calibrating an array of two-dimensional sensors to be used in stereotactic localization. The calibration system produces calibration data on a dense array of target points (typically several thousand) spanning the entire workspace and is not physically present in the workspace when subsequent localization determinations are performed. The calibration data yielded by the invention allow accurate calculation of the sensor array parameters and this, in turn, allows localization of objects in the workspace with a high degree of accuracy.
The invention permits subsequent localization of objects without the calibration device being present in the workspace and without having to carry out the calibration process in the same workspace as the localization is to take place.
In accordance with the invention an array of one or more targets is mounted on a positioner that sequentially positions the target array at a large number of locations in the workspace. At each location, accurate positional information of the center of each target in the array is obtained. At each location, two-dimensional sensor views of the target are also obtained.
The invention may further comprise means for calibrating the sensors, or means for calculating a localization function, from the calibration data. Since all sensors are calibrated simultaneously and a large number (several thousand) of target points are used in calibration, accurate values of the camera parameters are obtained. The invention may be used in localizing part of a surgical instrument during a medical procedure. In this case, the invention may comprise means for registering a localized part in a displayed computerized image of the patient such as an x-ray image, magnetic resonant image, or a computerized tomographic image.
The invention thus provides a device for use in obtaining one or more calibration parameters of an array of two-dimensional sensors used in stereotactic localization of objects in a workspace, the device comprising:
(a) a target array comprising one or more targets; and
(b) a positioner capable of positioning the target array at a desired location in the workspace.
The invention further provides a method for obtaining one or more calibration parameters of an array of two-dimensional sensors used in stereotactic localization of objects in a workspace, each sensor in the sensor array viewing the workspace along a fixed sight line and producing a signal characteristic of its view of the workspace, the method comprising:
(a) positioning a target array at one or more desired locations in the workspace;
(b) for each of the one or more desired locations, processing the signals produced by one or more sensors in the sensor array; and
(c) calculating the one or more calibration parameters of the sensor array.
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Amir Avner
Studnitzki Alexander
Kinberg Robert
MedEye Medical Technology Ltd.
Philogene Pedro
Venable
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