Method and apparatus for analysing images

Abstract

A method is described for determining brain shift, such as the brain shift that occurs following a neurosurgical intervention. The method comprises taking a first image of the brain ( 4 ) of a subject, the first image showing the position of blood vessels ( 20 ) in the brain relative to a reference position ( 30 ). A second image of the brain ( 4 ), that has been acquired following an intervention on the subject is also taken. This second image has been acquired using computed tomography (CT) imaging apparatus, The second image shows the position of blood vessels ( 20 ′) in the brain relative to the reference position ( 30 ). Brain shift is then determined from the shift in position of the blood vessels in at least one region of interest ( 32 ) of the brain, with respect to the reference position ( 30 ), between the first and second images. Corresponding apparatus is also described.

1 . A system for performing surgery, comprising:
 a surgical robot for performing surgery on a patient, the surgical robot comprising:
 an articulated arm having a known position in a robot coordinate system, and 
 a fiducial marker unit that is attached or configured to be attached to the articulated arm, the fiducial marker unit having a reference structure that has a known position in the robot coordinate system when it is attached to the articulated arm; and 
   a medical imaging apparatus for acquiring intra-operative images of the patient, positions in the acquired intra-operative images being defined in an imaging coordinate system,   wherein, when the fiducial marker unit is attached to the articulated arm, the reference structure is configured to be positioned so that the reference structure is visible in images acquired by the medical imaging apparatus so that a positional relationship can be established between the robot coordinate system and the imaging coordinate system.   
     
     
         2 . The system according to  claim 1 , further comprising a table that is physically linked to the surgical robot and supports a part of the patient. 
     
     
         3 . The system according to  claim 1 , wherein the fiducial marker unit is configured to be attached to the articulated arm in a repeatable position. 
     
     
         4 . The system according to  claim 3 , wherein the articulated arm comprises a mount and the fiducial marker unit is configured to be attached to the mount. 
     
     
         5 . The system according to  claim 4 , wherein the fiducial marker unit has a known position relative to the mount when the fiducial marker unit is attached to the mount. 
     
     
         6 . The system according to  claim 5 , wherein the fiducial marker unit and the mount provide a kinematic attachment mechanism for releasably attaching the mount to the articulated arm in the known position. 
     
     
         7 . The system according to  claim 1 , wherein:
 a tool holder is provided at a distal end of the articulated arm, and   the tool holder is configured to hold the fiducial marker unit so that the fiducial marker unit is attached to the articulated arm when it is held by the tool holder.   
     
     
         8 . The system according to  claim 7 , wherein the tool holder is further configured to hold at least one surgical tool, the at least one surgical tool being separate from the fiducial marker unit. 
     
     
         9 . The system according to  claim 1 , wherein the medical imaging apparatus comprises a computerised tomography (CT) scanner and the reference structure comprises a plurality of computerised tomography (CT) visible markers. 
     
     
         10 . The system according to  claim 1 , wherein the surgical robot comprises a computer to control motion of the articulated arm. 
     
     
         11 . A fiducial marker unit for a surgical robot, comprising:
 a reference structure comprising one or more computerised tomography (CT) visible markers; and   an attachment portion configured to enable the fiducial marker unit to be releasably attached to the articulated arm of a surgical robot such that the reference structure has a known position in a robot coordinate system of the surgical robot.   
     
     
         12 . The fiducial marker unit of  claim 11 , wherein the attachment portion is configured to enable the fiducial marker unit to be releasably attached to the articulated arm in a repeatable position. 
     
     
         13 . The fiducial marker unit of  claim 11 , wherein the attachment portion is configured to enable the fiducial marker unit to be releasably attached to the articulated arm in the known position using a kinematic attachment mechanism. 
     
     
         14 . A method for registering a robot with a medical imaging apparatus, wherein:
 the medical imaging apparatus is configured to acquire images from an imaging volume and one or more positions in the acquired images are known in an imaging coordinate system, and   the robot comprises an articulated arm carrying a fiducial marker unit having a reference structure that is visible in images acquired by the medical imaging apparatus,   the method comprising the steps of:
 (i) placing the reference structure at a position within the imaging volume of the of the medical imaging apparatus, the position of the reference structure being known in a robot coordinate system of the robot; 
 (ii) acquiring an image of the reference structure using the medical imaging apparatus; 
 (iii) determining a position of the reference structure in the imaging coordinate system from the image acquired in step (ii); and 
 (iv) determining a difference between the position of the reference structure in the robot coordinate system and the position of the reference structure in the imaging coordinate system. 
   
     
     
         15 . The method according to  claim 14 , further comprising the step of calculating a coordinate transformation between the imaging coordinate system and the robot coordinate system based on the difference between the position of the reference structure in the robot coordinate system and the position of the reference structure in the imaging coordinate system. 
     
     
         16 . The method according to  claim 15 , further comprising the step of converting positions measured in the imaging coordinate system into positions in the robot coordinate system using the calculated coordinate transformation. 
     
     
         17 . The method according to  claim 15 , further comprising the steps of:
 acquiring at least one further image using the medical imaging apparatus, and   converting positions identified in the at least one further image into positions in the robot coordinate system using the calculated coordinate transformation.   
     
     
         18 . The method according to  claim 17 , wherein the at least one further image comprises an image of at least a part of a patient. 
     
     
         19 . The method according to  claim 14 , wherein at least a part of a patient is also located within the imaging volume in step (i) such that the image acquired in step (ii) includes both the reference structure and said at least a part of the patient. 
     
     
         20 . The method according to  claim 14 , comprising a step of attaching the fiducial marker unit to the articulating arm of the robot. 
     
     
         21 . The method according to  claim 14 , wherein the medical imaging apparatus comprises a CT scanner and the reference structure comprises a plurality of CT visible markers. 
     
     
         22 . The method according to  claim 15 , comprising the further step of performing a surgical procedure on a patient using the robot. 
     
     
         23 . The method according to  claim 22 , comprising a step of detaching the fiducial marker unit from the articulated arm of the robot prior to the step of performing the surgical procedure on the patient. 
     
     
         24 . The method according to  claim 22 , wherein the surgical procedure performed using the robot comprises a neurosurgical procedure that includes inserting an electrode or catheter along a trajectory to a target position within the brain of the patient, wherein calculation of at least one of the target position and the trajectory is based on the calculated coordinate transformation. 
     
     
         25 . An apparatus for performing surgery, comprising:
 a robot for performing surgery on a patient, the robot comprising:
 an articulated arm having a known position in a robot coordinate system, and 
 a fiducial marker unit that is attached or configured to be attached to the robot, the fiducial marker unit having a reference structure that the reference structure has a known position in the robot coordinate system when it is attached to the robot, 
   wherein, when the fiducial marker unit is attached to the robot, the fiducial marker unit is configured to be positioned so that the reference structure is visible in images acquired by an imaging apparatus.