User:Gfischer

From CISSTwiki

Gregory S Fischer

• Company: JHU
• Department: NSF ERC CISST
• Office phone: 1-410-516-3417
• E-Mail:
• Web page: http://www.cisst.org/~gfischer

Field of research / Projects

MRI Compatible Robotics

Pneumatically Operated Robot for Transperineal Prostate Diagnosis and Treatment

Magnetic Resonance Imaging (MRI) has potential to be a superior medical imaging modality for guiding and monitoring prostatic interventions. MRI can provide high-quality 3D visualization of prostate and surrounding tissue. However, the benefits can not be readily harnessed for interventional procedures due to difficulties that surround the use of highfield (1.5T or greater). The strong magnetic field prevents the use of conventional mechatronics and the confined physical space makes it extremely challenging to access the patient. We have designed a robotic assistant system that overcomes these difficulties and promises safe and reliable intra-prostatic needle placement inside closed high-field MRI scanners.

Augmented Reality Procedural Guidance

MR Image Overlay for Joint Arthrography

Magnetic Resonance Imaging (MRI) provides great potential for planning, guiding, monitoring and controlling interventions. MR arthrography (MRAr) is the imaging gold standard to assess small ligament and fibrocartilage injury in joints. In contemporary practice, MRAr consists of two consecutive sessions: 1) an interventional session where a needle is driven to the joint space and MR contrast is injected under fluoroscopy or CT guidance, and 2) A diagnostic MRI imaging session to visualize the distribution of contrast inside the joint space and evaluate the condition of the joint. Our approach to MRAr is to eliminate the separate radiologically guided needle insertion and contrast injection procedure by performing those tasks on conventional high-field closed MRI scanners. We propose a 2D augmented reality image overlay device to guide needle insertion procedures. This approach makes diagnostic high-field magnets available for interventions without a complex and expensive engineering entourage. In preclinical trials, needle insertions have been performed in the joints of porcine and human cadavers using MR image overlay guidance; insertions successfully reached the joint space on the first attempt in all cases.

Electromagnetic Tracker Navigation

Developing electromagnetically (EM) tracked tools can be very time consuming. Tool design traditionally takes many iterations, each of which requires construction of a physical tool and performing lengthy experiments. We propose a simulator that allows tools to be virtually designed and tested before ever being physically built. Both tool rigid body (RB) configurations and reference RB configurations are configured; the reference RB can be located anywhere in the field, and the tool is virtually moved around the reference in user-specified pattern. Sensor measurements of both RBs are artificially distorted according to a previously acquired error field mapping, and the 6-DOF frames of the Tool and Reference are refit to the distorted sensors. It is possible to predict the tool tip registration error for a particular tool and coordinate reference frame (CRF) in a particular scenario before ever even building the tools.

Sensing Surgical Instruments

Gaining access to a surgical site via retracting neighboring tissue can result in complications due to occlusion of the tissue blood supply resulting in ischemic damage. By incorporating oxygenation sensors on the working surfaces of surgical retractors and graspers, it is possible to measure the local tissue oxygen saturation and look for trends in real-time. Further, by measuring tissue interaction forces simultaneously, we can further augment the information available to the surgeon. The sensors provide a means for sensory substitution to help compensate for the decreased sensation present in minimally invasive laparoscopic and robotic procedures that are gaining significant popularity. Sensing surgical instruments will allow for safer and more effective surgeries while not interfering with the normal workflow of a procedure.

Robotic Ultrasound and Liver Ablation

There has been increased interest in minimally invasive ablative treatments that typically require precise placement of the ablator tool to meet the predefined planning, and lead to efficient tumor destruction. Standard ablative procedures involve free hand transcutaneous ultrasonography (TCUS) in conjunction with manual tool positioning. Unfortunately, existing TCUS systems suffer from many limitations and results in failure to identify nearly half of all treatable liver lesions. Freehand manipulation of the ultrasound (US) probe and ablator tool critically lacks the level of control, accuracy, stability, and guaranteed performance required for these procedures. Freehand US results in undefined gap distribution, anatomic deformation due to variable pressure from the sonographer’s hand, and severe difficulty in maintaining optimal scanning position. In response to these limitations, we developed a dual robotic arm system that manages both ultrasound manipulation and needle guidance. We have performed a comparative performance study between robotic vs. freehand systems for both US scanning and needle placement in mechanical and animal tissue phantoms.

Robotic Neurosurgery

Steady Hand Guided Aneurysm Clip Applier

Steady hand guidance provides high accuracy motion while keeping the surgeon in contact with the surgical instrument. Force sensors are applied between the instrument and the robot, and as the surgeon applies forces to the instrument, the robot move accordingly. Tremor reduction, force scaling, andvirtual fixtures can be applied to enhance control. This application uses steady hand guidance to precisely place brain aneurysm clips. The system was demonstrated and received good feedback at the CNS Conference in Denver, CO.

CT Guided Intra Cranial Hemorrhage(ICH) Evacuation

We developed a robotic system for rapid removal blood from the brain after a bleeding event resulting in blood in the ventricles or brain parenchyma. The procedure is performed inside a CT scanner. A hematome evacuator is aligned with the target “out-of-plane”, with the use of a couch-mounted 2-DOF remote center of motion (RCM) robot. The robot is calibrated to CT image space with pure image based out-of-plane stereotactic registration. The system is frameless and the patient is secured in treatment position in a non-invasive manner. We achieved excellent out-of-plane tool placement accuracy in mechanical phantoms (1.0 mm) and demonstrated the workflow on human cadaver.

Publications / Posters

Please see my publication list on my web page:
http://www.cisst.org/~gfischer

Press Coverage

Description of the MRI Image Overlay on the NSF ERC Achievements Showcase
MRI-Guided Needle Placement with Augmented Reality Guidance

Demonstration of the Image Overlay system to High School students
The Washington Post Magazine featured the program in its November 9, 2003 edition
University Introduces High School Students to Computer-Assisted Surgery