MR tomograph comprising a positioning system for the exact determination of the position of a manually guided manipulator

A method for determining the exact position of a tip of a biopsy needle relative to a measuring object, in particular the head, mamma or extremities of a patient, investigated by means of a magnetic resonance (MR) imaging measurement and located in an investigation volume of a MR tomograph, the MR tomograph having a magnet system for the generation of a homogenous magnetic field within the investigation volume and a gradient system for generating magnetic gradient fields which vary linearly in the investigation volume, wherein the magnet system and the gradient system permit access to the investigation volume along at least two axes which intersect at an essentially right angle, the MR tomograph having a radio-frequency (RF) transmitting and receiving system for irradiating RF pulses onto the measuring object and for receiving MR signals from the measuring object as well as an evaluation and display means for generating and displaying an MR image from inside the measuring object, the method comprising the steps of:

• a) disposing a first frame component on and without relative motion with respect to the measuring object, said first frame component having a marking member disposed on said first frame component within the investigation volume in which the magnetic field is homogenous and the gradient fields are linear, said marking member comprising an MR substance in which measurable MR signals can be excited;
• b) moving the biopsy needle relative to said first frame component using a second frame component to which the biopsy needle is mounted, said second frame component being movable relative to said first frame component;
• c) determining a spatial position of the biopsy needle relative to said first frame component without using any MR signal;
• d) determining an absolute position of said first frame component using imaging MR measurements simultaneously during actuation of the biopsy needle and using measuring signals from said marking member;
• and
• e) displaying said spatial position of the biopsy needle in the image.

A method for guiding a tip of a biopsy needle to a predetermined point inside a measuring object, wherein the biopsy needle is guided on two circular arcs outside of the measuring object in a defined manner and can be displaced along an axis located essentially perpendicular to the circular arcs, the method comprising the steps of:

• a) disposing a first frame component on and without relative motion with respect to the measuring object, said first frame component having a marking member disposed on said first frame component within the investigation volume in which the magnetic field is homogenous and the gradient fields are linear, said marking member comprising an MR substance in which measurable MR signals can be excited;
• b) locating the biopsy needle outside of the measuring object;
• c) displaying an MR image of the measuring object;
• d) marking a desired position on said MR image;
• e) determining, using evaluation and display means, optimum coordinates along the circular arcs and the axis;
• f) fading permanently updated deviations from said optimum coordinates into the MR image;
• g) manually minimizing said deviations through movement of said biopsy needle along the circular arc;
• and
• h) manually inserting said biopsy needle into the measuring object along the axis taking into consideration said permanently updated deviation until a tip of the biopsy needle is located at said desired position.

A positioning system for the exact determination of the position of a manually guided manipulator, in particular a tip of a biopsy needle, relative to a measuring object, in particular the head, mamma or extremities of a patient, investigated by means of a magnetic resonance (MR) imaging measurement and located in an investigation volume of an MR tomograph, the MR tomograph having a magnet system for the generation of a homogenous magnet field within the investigation volume and a gradient system for generating magnetic gradient fields which vary linearly in the investigation volume, wherein the magnet system and the gradient system permit access to the investigation volume along at least two axes which intersect at an essentially right angle, the MR tomograph having a radio frequency (RF) transmitting and receiving system for irradiating RF pulses onto the measuring object and for receiving MR signals from the measuring object as well as an evaluation and display means for generating and displaying an MR image from inside the measuring object, the positioning system comprising:

• a first frame component disposed on and without relative motion with respect to the measuring object;
• a marking member disposed on said first frame component within the investigation volume in which the magnetic field is homogenous and the gradient fields are linear, said marking member comprising an MR substance in which measureable MR signals can be excited to define a position of said first frame component in the MR image via an imaging MR measurement;
• a second frame component to which the manipulator is mounted, said second frame component movable relative to said first frame component;
• movable mechanics disposed on said second frame component for moving the manipulator relative to said first frame component;
• measuring means for determining a spatial position of the manipulator relative to said first frame component without using any MR signal;
• means for displaying said spatial position in the MR image, wherein said movable mechanics comprises an angle member for mechanically guiding the manipulator within a range of solid angle and wherein said measuring means comprise means for determining an angular position of the manipulator, wherein said angle member comprises a ball joint.