Noninvasive stereotactic assembly

A noninvasive stereotactic assembly for guiding an instrument to a target within a patient's head which includes a nasion and left and right temporal bones, the target having a coordinate determined by a three-dimensional coordinate system of image data of the patient's head, the instrument defining a lengthwise line which is initially oriented along a Z-axis toward an origin of the three-dimensional coordinate system, said stereotactic assembly comprising:

• a head frame subassembly including
• a pair of seat blocks which are spaced apart from each other in a left-and-right direction, each of said seat blocks having left and right surfaces and being formed with a guiding slot which extends through said left and right surfaces,
• a pair of adjustable pin members which are slidably and respectively mounted in said guiding slots of said seat blocks, and which have respectively left and right pointed ends that are adapted to be brought into rigid engagement with the left and right temporal bones, respectively, so as to cooperatively define an X-axis of the three-dimensional coordinate system,
• a nasion positioning member including
• a beam body which extends in the left-and-right direction to terminate at left and right actuated end segments, and
• a nasion pad which is mounted on a mid segment of said beam body between said left and right actuated end segments, and which has a mid area adapted to be brought into rigid engagement with the nasion of the patient, and an index protrusion opposite to and in line with said mid area in an anterior-and-posterior direction, such that when said mid area is in rigid engagement with the nasion of the patient, said index protrusion and said mid area cooperatively defines a Y-axis of the three-dimensional coordinate system, which intersects with the X-axis to define the origin,
• a pair of cantilever units each including
• a cantilever block secured to a corresponding one of said seat blocks, and
• a cantilever arm which extends from said cantilever block in the anterior-and-posterior direction, and which is configured to permit a corresponding one of said left and right actuated end segments to be adjustably moved along the anterior-and-posterior direction, and
• a pair of adjusting units each of which is coupled to a corresponding one of said adjustable pin members so as to permit said adjustable pin members to move toward or away from each other;
• and
• an instrument positioning subassembly including
• two ring members which are mounted rotatably on and outboard of said seat blocks about the X-axis, respectively, and which, according to the coordinate of the target, are simultaneously turned angularly by a first predetermined angle, such that the lengthwise line is offset from the Z-axis by a first offset angle which is equal to the first predetermined angle,
• a bridging rail member having an arc segment which extends in a circumferential direction about the origin, and two end segments which flank said arc segment, and which are secured to said two ring members, respectively, such that said arc segment and said two end segments cooperatively define a reference plane,
• a movable bracket mounted slidably on said arc segment, and defining a radially oriented index line, which is parallel to the lengthwise line of the instrument in an initial position, said movable bracket, according to the coordinate of the target, being slid relative to the origin by a second predetermined angle, such that the lengthwise line is further offset from the Z-axis by a second offset angle, which is equal to the second predetermined angle,
• a swivel member defining a central plane, and having a distal end and a proximate end which is swivel-mounted on said movable bracket about a swivel axis normal to said reference plane so as to permit said swivel member to swivel from a starting position, where said radially oriented index line is within said central plane, to an ending position, where said central plane intersects with said radially oriented index line by a first compensation angle to compensate for the second offset angle, and
• an instrument holder configured to hold the instrument, and having an outward end and an inward end which is opposite to said outward end along the lengthwise line, and which is hinged to said distal end of said swivel member about a hinge axis within said reference plane, such that said outward end of said instrument holder is turned about the hinge axis by a second compensation angle to compensate for the first offset angle so as to permit the instrument to be guided toward the target along the lengthwise line parallel to the Z-axis.