Precision placement of instruments for minimally invasive procedures using a "needle driver" robot.

Medical practice continues to move toward less invasive procedures. Many of these procedures require the precision placement of a needle in the anatomy. Over the past several years, our research team has been investigating the use of a robotic needle driver to assist the physician in this task. This paper summarizes our work in this area. The robotic system is briefly described, followed by a description of a clinical trial in spinal nerve blockade. The robot was used under joystick control to place a 22 gauge needle in the spines of 10 patients using fluoroscopic imaging. The results were equivalent to the current manual procedure. We next describe our follow-up clinical application in lung biopsy for lung cancer screening under CT fluoroscopy. The system concept is discussed and the results of a phantom study are presented. A start-up company named ImageGuide has recently been formed to commercialize the robot. Their revised robot design is presented, along with plans to install a ceiling-mounted version of the robot in the CT fluoroscopy suite at Georgetown University.

Feasibility of percutaneous transabdominal portosystemic shunt creation.

Evaluation of the anatomic feasibility of the percutaneous transabdominal puncture of selected portal and hepatic veins in patients with cirrhosis was performed. This approach would become the framework for an image-guided robot-assisted needle drive mechanism for use in transjugular intrahepatic portosystemic shunt (TIPS) creation. Retrospective analysis of 10 CT and 14 MRI axial abdominal studies was carried out to determine whether single simultaneous transabdominal puncture of portal and hepatic veins was possible. A necessary modification of the TIPS procedure was tested in an ex vivo porcine model under fluoroscopy. Eighteen of 24 patients (75%) had intrahepatic vascular anatomy amenable to a single transabdominal puncture. Successful catheterization of portal and hepatic veins using a modified approach for TIPS was accomplished in two ex vivo porcine livers. A suitable anatomic approach for modified TIPS is present in a majority of patients with cirrhosis. Feasibility of the technique using this anatomic approach was confirmed in two ex vivo porcine models. This study serves as an initial step in a novel technical approach to TIPS using a new anatomic approach for this procedure.

Image-guided robotic delivery system for precise placement of therapeutic agents.

The effectiveness of conventional solid tumor treatment is limited by the systemic toxicity and lack of specificity of chemotherapeutic agents. Present treatment modalities are frequently insufficient to eliminate competent cancer cells without exceeding the limits of toxicity to normal tissue. The coming generation of cancer therapeutics depends on the precise targeting and sustained release of antitumor agents to overcome these limitations. We are developing an image-guided, robotic system for precise intratumoral placement of anticancer drugs and sustained release devices to advance this new treatment paradigm. The robotic system will use intraoperatively obtained computed tomographic (CT) images from a mobile CT scanner for guidance. The concept is to track patient anatomy and localize instruments using currently available optical tracking technology. Tracking will also be used to register patient anatomy with the images. The physician can then use the registered image to select an appropriate tumor target and entry location and to plan the instrument path. This path will then be transmitted to the robot, which orients and drives the instrument to the desired target under physician control. Achievement of the target is confirmed via intraoperative CT. This system will provide instrument guidance that is precise, direct, and controllable. Error due to poor target visualization and hand unsteadiness should be reduced greatly. The basic components of the system (robot, mobile CT, tracking) have been demonstrated in our laboratory, and the integration of the components is in progress. In future work, we plan to fuse preoperative PET imaging with intraoperative CT to allow functional as well as anatomic image guidance.

Software development for registration of digital subtraction angiography (DSA) images in uterine fibroid embolization.

The ISIS Center at Georgetown University Medical Center has developed a comprehensive program for image-guided procedures in the spine. As part of this program, ISIS has developed a software application known as I-SPINE (ISIS's Spine Procedure Imaging Navigation Engine). I-SPINE is a Windows NT application, which is based on the Analyze/AVM libraries. The software architecture follows the Microsoft Foundation Classes (MFC) single document, multiple view paradigm. This has allowed the developers to add new visualization modules to I-SPINE that aid physicians in procedures outside the spine. One such procedure I-SPINE has been expanded for is uterine fibroid embolization. The idea is that by registering and subtracting post-embolization angiographic images from pre-treatment images the resulting image can be used to quantify the embolization effect on the fibroid circulation and predict the treatment response. The I-SPINE digital subtraction angiography (DSA) module allows the interventional radiologist to open a series of pre and post-embolization DSA images that shows the vascular structures of the uterus and the fibroid or fibroids. From these images, the radiologist selects an appropriate image from each series. The selected images are then hand registered using pixel shifting. Once the images are registered, the pixels are subtracted resulting in an image that shows the embolized arteries that were supplying the fibroids.

Paired comparison of vascular wall reactions to Palmaz stents, Strecker tantalum stents, and Wallstents in canine iliac and femoral arteries.

BACKGROUND: Palmaz stents, Strecker stents, and Wallstents, all used clinically, differ substantially in their physical characteristics, yet how differently the vascular wall reacts to them has not been demonstrated conclusively. We therefore undertook a side-by-side comparison. METHODS AND RESULTS: One stent was implanted into each canine external iliac and/or the flexing portion of the proximal femoral artery. In 9 dogs, Palmaz stents were placed vis-à-vis Strecker stents, with follow-up of 2 and 4 months. In 7 dogs, Palmaz stents were placed vis-à-vis Wallstents, with 4 months of follow-up. Angiographic midstent luminal diameters immediately after placement and at follow-up as well as midstent cross-sectional areas of neointima were compared for significant differences. In addition, neointimal maturation, medial atrophy, and stent-related trauma were assessed. Angiographically, all arteries remained open. The degree of luminal narrowing by recoil and neointima never reached 50% and was modest for Palmaz stents and Wallstents (P = .33) but significantly higher for Strecker stents (P < .0001 compared with Palmaz stents). This corresponded histologically to a significantly thicker neointima (P = .003) over Strecker than over Palmaz stents but not between Palmaz stents and Wallstents (P = .18). Neointimal buildup was generally more pronounced in the femoral artery segments than in the iliac segments. Maturation of the neointima over Palmaz stents was much further advanced than over Strecker stents and slightly more advanced than over Wallstents. Pressure-related atrophy of the tunica media was least for Strecker stents and more pronounced but similar for Wallstents and Palmaz stents. Wallstent wire ends caused some wall trauma; several femoral Palmaz stent struts protruded through the media. CONCLUSIONS: The lower-hoop-strength, higher-profile tantalum Strecker stent is affected by vascular wall recoil and evokes a greater degree of neointima formation than the lower-profile, higher-hoop-strength Palmaz stent and Wallstent. Medial atrophy is pronounced outside the latter two stents. The rigid Palmaz stent can penetrate through the vascular wall in flexing arteries.

Injection characteristics and downstream contrast material distribution of flush aortography catheters: in vitro study.

Performance of 11 commercially available 4- and 5-F aortic flush catheters was evaluated with respect to the extent of upstream injection, catheter motion, and downstream homogeneity of a 10-, 15-, and 20-mL/sec bolus of 76% meglumine sodium diatrizoate at room temperature. Tests were made in a pulsatile aortic flow model containing circulating fluid isoviscous to blood. The injection process was recorded on videotape. Homogeneity of the contrast material bolus was determined spectrophotometrically from samples collected from the center and each of the four quadrants of the vessel lumen. Upstream contrast material injection between 1.5 and 7 cm in length emerged from all catheters; it was lowest with one of the "tennis racket" designs from one and a new spiral end-loop design (Halo) from another manufacturer. All catheters, except the most rigid and largest-caliber catheter (5.8 F) showed considerable shaft motion at the higher injection rates. Downstream contrast material mixing homogeneity was always best at the highest injection rate but altogether was better for the Halo catheter than for any other catheter tested. It is concluded that all tested 4- and 5-F aortic flush catheters show some undesirable features, but certain design modifications improve performance and comparative testing is helpful to distinguish such features.

Flexible tantalum stents implanted in aortas and iliac arteries: effects in normal canines.

Vascular endoprostheses made of knitted tantalum wire and expanded over angioplasty balloons were placed into aortas or iliac arteries of 14 normal dogs. Twelve stents were placed into the infrarenal abdominal aorta and two stents in the left common iliac arteries by the left carotid artery approach. To firmly expand the stent against the vascular wall, nominal stent sizes 0.5-1.0 mm larger than the measured arterial diameter were required. Arteriography performed at specified follow-up intervals showed no evidence of thrombi or emboli; all side branches (lumbar arteries) covered by the stents remained patent. Vascular diameter decreased minimally at 8 and 26 weeks, associated with histopathologic evidence of neointimal buildup. This buildup was highest at 8 weeks (mean, 313 microns) and was slightly less at 26 weeks (mean, 223 microns). Almost complete coverage by endothelium was seen as early as 3 weeks. It is concluded that the flexible tantalum wire stents are well tolerated by the arterial wall and become quickly endothelialized. No excessive neointimal buildup was observed during the 6-month study.

Quantitative digital subtraction arteriography with a calibration catheter.

Quantitative intraarterial digital subtraction arteriography (DSA) was performed using a calibration catheter with three distal metallic ring markers. The two outer markers were 50 mm apart, and the third marker was in the middle. Measurements of 54 vessel diameters of the abdominal aorta, renal, lumbar, and iliac arteries were performed in a comparison study with direct film arteriograms in 10 aortofemoral runoff studies. Diameter measurements were made by both the observer on hard copy DSA images and by a computer using modified semiquantitative software. Against measurements on film, which were used as the standard, deviation in measurement on digital images varied from 8 to 13% for arterial diameters less than 5 mm and from 2 to 6% for diameters greater than or equal to 5 mm. Projectional artifacts caused 3% or less error. Knowing these variations in measurement is important in order to determine error tolerances for clinical applications. The calibration catheter serves as a convenient internal marker for DSA.