Apparatus for automatically positioning a patient for treatment/diagnoses

• US 5,823,192 A
• Filed: 07/31/1996
• Issued: 10/20/1998
• Est. Priority Date: 07/31/1996
• Status: Expired due to Term

• Current Assignee: University of Pittsburgh of The Commonwealth System of Higher Education
• Original Assignee: University of Pittsburgh of The Commonwealth System of Higher Education
• Inventors: Kanade, Takeo, Greenberger, Joel, Athanassiou, Charalambos N., Shimoga, Karun B., Kalend, Andre M.
• Primary Examiner(s): Brown, Michael A.
• Application Number:
  US08/690,521
• Time in Patent Office: 811 Days
• Field of Search: 128/845, 128/846, 347/255, 347/260
• US Class Current: 128/845
• CPC Class Codes: A61B 6/04 Positioning of patients; Tiltable beds or the like operating tables A61G13/00; operating chairs A61G15/00
• CPC Class Codes: A61B 6/08 Auxiliary means for directing the radiation beam to a particular spot, e.g. using light beams
• CPC Class Codes: A61N 2005/105 using a laser alignment system
• CPC Class Codes: A61N 2005/1059 using cameras imaging the patient
• CPC Class Codes: A61N 5/1049 for verifying the position of the patient with respect to the radiation beam
• CPC Class Codes: A61N 5/1069 Target adjustment, e.g. moving the patient support

Abstract

A patient is automatically accurately positioned relative to a fixed refece of a treatment/diagnostic device by an optical system which operates a patient positioning assembly to bring fiducials or skin markers on the patient into coincidence with impingement points of laser beams projected in a fixed pattern relative to the device. Cameras record images of the fiducials and laser impingement points from which alignment error and velocity error in pixel space are determined. The velocity error in pixel space is converted to a velocity error in room space by the inverse of an Image Jacobian. The Image Jacobian is initially derived using rough values for system parameters and is continuously updated and refined using the calculated errors in pixel space derived from the camera images and errors in room space derived from position encoders on the treatment/diagnostic device.

Claims

1. Apparatus for automatically, accurately positioning a patient reclining on a moveable patient positioning assembly to a fixed base position relative to a fixed reference of a treatment/diagnostic device, said apparatus comprising:

a plurality of spaced apart fiducials arranged on said patient;

laser beam generator means for generating a plurality of laser beams projected in different directions relative to said fixed reference to impinge on the patient at impingement points which coincide with said fiducials when said patient is at said fixed base position;

camera means for generating images of said fiducials and said impingement points; and

means generating control signals from said images for driving said moveable patient positioning assembly to bring said fiducials into coincidence with said impingement points, thereby positioning said patient at said fixed base position.

2. The apparatus of claim 1 wherein said plurality of fiducials comprise three fiducials arranged on said patient in a common first plane and wherein said laser beam generator means comprises means generating three laser beams projected in different directions in a common reference plane.

3. The apparatus of claim 2 wherein said treatment/diagnosis device has a treatment plane and wherein said common reference plane is coincident with said treatment plane.

4. The apparatus of claim 1 wherein said means generating control signals from said images control signals comprises means generating signals in pixel space of said camera means including position signals representative of positions of said fiducials and said laser impingement points in pixel space and means generating control signals in room space from said signals in pixel space including means applying conversion means converting signals in pixel space to signals in room space.

5. The apparatus of claim 4 wherein said means applying conversion means comprises means continuously refining said conversion means.

6. The apparatus of claim 5 wherein said means continuously refining said conversion means comprises means establishing a last conversion means, means setting said patient positioning assembly in motion, means repetitively determining present position error of said fiducials relative to said laser impingement points in pixel space at specified sample times, means repetitively determining a present position error between said fiducials and said laser impingement points in room space at said sample times, and means updating said conversion means from said present position error in pixel space and said present position error in room space.

7. The apparatus of claim 5 wherein said means generating control signals from said images includes means repetitively generating a velocity error signal in pixel space from said position signals in pixel space, and wherein said conversion means comprises velocity conversion means converting said velocity error signal in pixel space to a velocity error signal in room space for controlling driving said patient positioning assembly to bring said fiducials into coincidence with said impingement points.

8. The apparatus of claim 5 adapted for use with a treatment/diagnostic device having a patient positioning assembly with multiple degrees of freedom and position encoder means generating outputs indicating position of said patient positioning assembly in said multiple degrees of freedom in room space, wherein said means continuously refining said conversion means comprises means establishing a rough initial value for said conversion means and means for repetitively determining a present position error of said fiducials relative to said laser impingement points in pixel space from said images of said fiducials and said impingement points, means repetitively determining a present position error between said fiducials and said laser impingement points in room space from said outputs of said position encoders, and means updating said conversion means from said present position error in pixel space and said present position error in room space.

9. The apparatus of claim 4 wherein said means generating signals in pixel space comprises means generating a position error signal representing error between positions of said fiducials and said laser impingement points in pixel space, means generating a velocity error signal in pixel space from said position error signal in pixel space, and wherein said conversion means comprises velocity conversion means converting said velocity error signal in pixel space to a velocity error signal in room space.

10. The apparatus of claim 5 wherein said means generating signals in pixels space comprises means generating said position signals repetitively at sampling intervals, said means generating control signals in room space comprises means generating a velocity error signal in pixel space from said position signals, repetitively at said sampling intervals, said means applying said conversion means comprises means applying an inverse of an Image Jacobian G to said velocity error signal in pixel space to generate a velocity error signal in room space for driving said movable patient positioning assembly, and said means continuously refining said conversion means comprises means repetitively at said sampling intervals updating said Image Jacobian according to the relationship:

##EQU4## wherein G(t) is an updated Image Jacobian at a present sampling interval, G(t-Δ

t) is the Image Jacobian from a most recent sampling period, ε

(t) is a present acceleration error in pixel space determined from said position error signals in pixel space, δ

(t) is a present velocity error in room space, δ

(t) is a present acceleration error in room space, δ

^T is a transform, W is a weighing matrix and ρ

is a forgetting factor.

11. The apparatus of claim 4 wherein said means applying conversion means comprises means requiring no detailed calibration of said cameras.

12. The apparatus of claim 11 wherein said means requiring no detailed calibration of said cameras comprises means establishing a rough initial value for said conversion means, and means for continuously refining said conversion means.