The goal of this project is to develop a robotic system to assist the physician in minimally invasive ultrasound
interventions. In current practice, the physician must manually hold the ultrasound probe in one hand and manipulate the
needle with the other hand, which can be challenging, particularly when trying to target small lesions. To assist the
physician, the robot should not only be capable of providing the spatial movement needed, but also be able to control the
contact force between the ultrasound probe and patient. To meet these requirements, we are developing a prototype
system based on a six degree of freedom parallel robot. The system will provide high bandwidth, precision motion, and
force control. In this paper we report on our progress to date, including the development of a PC-based control system
and the results of our initial experiments.
The development of image-guided interventions requires validation studies to evaluate
new protocols. So far, these validation studies have been limited to animal models and to
software and physical phantoms that simulate respiratory motion but cannot
accommodate needle punctures in a realistic manner. We have built a computer-controlled
pump that drives an anthropomorphic respiratory phantom for simulating
natural breathing patterns. This pump consists of a power supply, a motion controller
with servo amplifier, linear actuator, and custom fabricated pump assembly. By
generating several sample waveforms, we were able to simulate typical breathing
patterns. Using this pump, we were able to produce chest wall movements similar to
typical chest wall movements observed in humans. This system has potential applications
for evaluating new respiratory compensation algorithms and may facilitate improved
testing of image-guided protocols under realistic interventional conditions.
An effective treatment method for organs that move with respiration (such as the lungs, pancreas, and liver) is a major goal of radiation medicine. In order to treat such tumors, we need (1) real-time knowledge of the current location of the tumor, and (2) the ability to adapt the radiation delivery system to follow this constantly changing location. In this study, we used electromagnetic tracking in a swine model to address the first challenge, and to determine if movement of a marker attached to the skin could accurately predict movement of an internal marker embedded in an organ. Under approved animal research protocols, an electromagnetically tracked needle was inserted into a swine liver and an electromagnetically tracked guidewire was taped to the abdominal skin of the animal. The Aurora (Northern Digital Inc., Waterloo, Canada) electromagnetic tracking system was then used to monitor the position of both of these sensors every 40 msec. Position readouts from the sensors were then tested to see if any of the movements showed correlation. The strongest correlations were observed between external anterior-posterior motion and internal inferior-superior motion, with many other axes exhibiting only weak correlation. We also used these data to build a predictive model of internal motion by taking segments from the data and using them to derive a general functional relationship between the internal needle and the external guidewire. For the axis with the strongest correlation, this model enabled us to predict internal organ motion to within 1 mm.
In this study, we collected respiratory motion data of external skin markers and internal liver fiducials from several swine. The POLARIS infrared tracking system was used for recording reflective markers placed on the swine’s abdomen. The AURORA electromagnetic tracking system was used for recording 2 tracked needles implanted into the liver. This data will be used to develop correlation models between external skin movement and internal organ movement, which is the first step towards the ability to compensate for respiratory movement of the lesion. We are also developing a motion simulator for validation of our model and dose verification of mobile lesions in the CYBERKNIFE Suite. We believe that this research could provide significant information towards the development of precise radiation treatment of mobile target volumes.
This paper describes a computer program to utilize electromagnetic tracking guidance during insertion of peripherally inserted central catheters. Placement of a Peripherally Inserted Central Catheter (PICC) line is a relatively simple, routine procedure in which a catheter is inserted into the veins of the lower arm and threaded up the arm to the vena cava to sit just above the heart. However, the procedure requires x-ray verification of the catheter position and is usually done under continuous fluoroscopic guidance. The computer program is designed to replace fluoroscopic guidance in this procedure and make PICC line placement a bedside procedure. This would greatly reduce the time and resources dedicated to this procedure. The physician first goes through a quick registration procedure to register the patient space with the computer screen coordinates. Once registration is completed, the program provides a continuous, real-time display of the position of the catheter tip overlaid on an x-ray image of the patient on an adjacent computer screen. Both the position and orientation of the catheter tip is shown. The display is very similar to that shown when using fluoroscopy.
This paper describes a computer program for volumetric treatment planning and image guidance during radiofrequency (RF) ablation of hepatic tumors. The procedure is performed by inserting an RF probe into the tumor under image guidance and generating heat to 'cook' a spherical region. If the tumor is too large to be ablated in a single burn, then multiple overlapping spherical burns are needed to encompass the entire target area. The computer program is designed to assist the physician in planning the sphere placement, as well as provide guidance in placing the probe using a magnetic tracking device. A pre-operative CT scan is routinely obtained before the procedure. On a slice by slice basis, the tumor, along with a 1 cm margin, is traced by the physician using the computer mouse. Once all of the images are traced, the program provides a three-dimensional rendering of the tumor. The minimum number of spheres necessary to cover the target lesion and the 1 cm margin are then computed by the program and displayed on the screen.
The purpose of this study was to quantify skin motion over the liver when patients are repositioned during image-guided interventions. Four human subjects with different body habitus lay supine on the interventional radiology table. The subjects held their arms up over their heads and down at their sides for 13 repositioning trials. Precise 3-D locations of the four skin fiducials permitted deformable skin motion to be quantified. For the first two occasions, the average skin motion was 1.00±0.82 mm in the arms-up position and 0.94±0.56 mm in the arms-down position, a small, but not statistically significant difference. Three out of the four subjects exhibited increased skin motion in the arms-up position, suggesting that patient-positioning technique during CT imaging may have an effect on the skin-motion component of registration error in image-guided interventions. The average skin motion was 0.65±0.39 mm for Subject 1 and 1.32±0.78 mm for Subject 2, a significant difference. Subjects 3 and 4 demonstrated a similar amount of skin motion. The subject with the largest body habitus demonstrated significantly less skin motion, an observation that is difficult to explain. The skin fiducial on the xiphoid process exhibited significantly less skin motion than the other fiducials, suggesting that certain anatomic locations could influence motion of the fiducial, and subsequently, the introduced error.