James D. Stefansic

Functional Organization of Visual Cortex in the Owl Monkey

In this study, we compared the organization of orientation preference in visual areas V1, V2, and V3. Within these visual areas, we also quantified the relationship between orientation preference and cytochrome oxidase (CO) staining patterns. V1 maps of orientation preference contained both pinwheels and linear zones. The location of CO blobs did not relate in a systematic way to maps of orientation; although, as in other primates, there were approximately twice as many pinwheels as CO blobs. V2 contained bands of high and low orientation selectivity. The bands of high orientation selectivity were organized into pinwheels and linear zones, but iso-orientation domains were twice as large as those in V1. Quantitative comparisons between bands containing high or low orientation selectivity and CO dark and light bands suggested that at least four functional compartments exist in V2, CO dense bands with either high or low orientation selectivity, and CO light bands with either high or low selectivity. We also demonstrated that two functional compartments exist in V3, with zones of high orientation selectivity corresponding to CO dense areas and zones of low orientation selectivity corresponding to CO pale areas. Together with previous findings, these results suggest that the modular organization of V1 is similar across primates and indeed across most mammals. V2 organization in owl monkeys also appears similar to that of other simians but different from that of prosimians and other mammals. Finally, V3 of owl monkeys shows a compartmental organization for orientation selectivity that remains to be demonstrated in other primates.

Liver Planning Software Accurately Predicts Postoperative Liver Volume and Measures Early Regeneration

BACKGROUND Postoperative or remnant liver volume (RLV) after hepatic resection is a critical predictor of perioperative outcomes. This study investigates whether the accuracy of liver surgical planning software for predicting postoperative RLV and assessing early regeneration. STUDY DESIGN Patients eligible for hepatic resection were approached for participation in the study from June 2008 to 2010. All patients underwent cross-sectional imaging (CT or MRI) before and early after resection. Planned remnant liver volume (pRLV) (based on the planned resection on the preoperative scan) and postoperative actual remnant liver volume (aRLV) (determined from early postoperative scan) were measured using Scout Liver software (Pathfinder Therapeutics Inc.). Differences between pRLV and aRLV were analyzed, controlling for timing of postoperative imaging. Measured total liver volume (TLV) was compared with standard equations for calculating volume. RESULTS Sixty-six patients were enrolled in the study from June 2008 to June 2010 at 3 treatment centers. Correlation was found between pRLV and aRLV (r = 0.941; p < 0.001), which improved when timing of postoperative imaging was considered (r = 0.953; p < 0.001). Relative volume deviation from pRLV to aRLV stratified cases according to timing of postoperative imaging showed evidence of measurable regeneration beginning 5 days after surgery, with stabilization at 8 days (p < 0.01). For patients at the upper and lower extremes of liver volumes, TLV was poorly estimated using standard equations (up to 50% in some cases). CONCLUSIONS Preoperative virtual planning of future liver remnant accurately predicts postoperative volume after hepatic resection. Early postoperative liver regeneration is measureable on imaging beginning at 5 days after surgery. Measuring TLV directly from CT scans rather than calculating based on equations accounts for extremes in TLV.

Optical imaging reveals retinotopic organization of dorsal V3 in New World owl monkeys

Optical imaging of intrinsic responses to visual stimuli in extrastriate cortex of owl monkeys provided evidence for the dorsal half of the third visual area, V3. Visual stimuli were used to selectively activate locations in dorsolateral V2 and the rostrally adjoining presumptive V3. Consistent with the proposed retinotopies of dorsal V2 and dorsal V3, small bars of drifting gratings along the horizontal meridian of the contralateral hemifield activated cortex along the V2/V3 border, whereas such stimuli along the vertical meridian activated cortex along the rostral border of V3. Stimuli in limited locations in the lower visual quadrant revealed mirror reversals of retinotopy in dorsal V2 and V3, whereas stimuli in the upper visual quadrant failed to activate either region. Brain sections processed for cytochrome oxidase from the same cases provided architectonic borders of V2 that matched those indicated by the optical imaging. The results support the concept that a narrow dorsal V3 exists in monkeys. V3d borders dorsal V2 and contains a smaller, mirror-image representation of the lower visual quadrant.

Design and implementation of a PC-based image-guided surgical system

In interactive, image-guided surgery, current physical space position in the operating room is displayed on various sets of medical images used for surgical navigation. We have developed a PC-based surgical guidance system (ORION) which synchronously displays surgical position on up to four image sets and updates them in real time. There are three essential components which must be developed for this system: (1) accurately tracked instruments; (2) accurate registration techniques to map physical space to image space; and (3) methods to display and update the image sets on a computer monitor. For each of these components, we have developed a set of dynamic link libraries in MS Visual C++ 6.0 supporting various hardware tools and software techniques. Surgical instruments are tracked in physical space using an active optical tracking system. Several of the different registration algorithms were developed with a library of robust math kernel functions, and the accuracy of all registration techniques was thoroughly investigated. Our display was developed using the Win32 API for windows management and tomographic visualization, a frame grabber for live video capture, and OpenGL for visualization of surface renderings. We have begun to use this current implementation of our system for several surgical procedures, including open and minimally invasive liver surgery.

Experimental model for functional magnetic resonance imaging of somatic sensory cortex in the unanesthetized rat.

Functional magnetic resonance imaging (fMRI) has evolved into a method widely used to map neural activation in the human brain. fMRI is a method for recording blood oxygen level-dependent (BOLD) signals. These signals change with local cerebral blood flow coupled to neural activity. However, the relationship between BOLD signals and neural function is poorly understood and requires the development of animal models. Here we use an unanesthetized rat preparation to study BOLD responses to whisker stimulation in somatic sensory barrel cortex. Five rats were trained to tolerate restraint in a holder and fMRI noise with positive reinforcement. For maximal immobilization, the head was fastened to the holder with nuts screwed on threaded bolts attached to the head. On scanning day, residual stress was alleviated with injections of diazepam, and the rats were restrained in the holder and transferred into the scanner. After >75 min to allow the tranquilization to abate, structural images were acquired from three coronal brain slices. Subsequently, functional images were taken utilizing 4-min epochs without stimulation alternated with equivalent epochs during which the right caudal whiskers were stimulated with three air puffs/s. After 4 weeks, fMRI could be repeated in four rats. In seven of the nine functional runs, head motion was minimal and whisker stimulation resulted in a statistically significant (P </= 0.05) increase in BOLD signal in barrel cortex predominantly on the contralateral side. The results provide encouragement that long-term fMRI studies on cerebral function in unanesthetized rats may be feasible with our procedure.

Image-guided liver surgery: intraoperative projection of computed tomography images utilizing tracked ultrasound

BACKGROUND Ultrasound (US) is the most commonly used form of image guidance during liver surgery. However, the use of navigation systems that incorporate instrument tracking and three-dimensional visualization of preoperative tomography is increasing. This report describes an initial experience using an image-guidance system with navigated US. METHODS An image-guidance system was used in a total of 50 open liver procedures to aid in localization and targeting of liver lesions. An optical tracking system was employed to localize surgical instruments. Customized hardware and calibration of the US transducer were required. The results of three procedures are highlighted in order to illustrate specific navigation techniques that proved useful in the broader patient cohort. RESULTS Over a 7-month span, the navigation system assisted in completing 21 (42%) of the procedures, and tracked US alone provided additional information required to perform resection or ablation in six procedures (12%). Average registration time during the three illustrative procedures was <1 min. Average set-up time was approximately 5 min per procedure. CONCLUSIONS The Explorer™ Liver guidance system represents novel technology that continues to evolve. This initial experience indicates that image guidance is valuable in certain procedures, specifically in cases in which difficult anatomy or tumour location or echogenicity limit the usefulness of traditional guidance methods.

Endoscopic tracking for use in interactive image-guided surgery

In minimally invasive surgery (MIS), endoscopes are used in real-time to enhance visualization and minimize invasion of healthy tissue. Unfortunately, the field of view provided by the scope is limited. In interactive image guided surgery (IIGS), the display of present surgical position on preoperative tomographic images enhances the surgeons field of view and provides knowledge of surgical anatomy. However, changes in the anatomy during surgery are not realized by the current IIGS techniques. This manuscript details the initial experiments conducted to merge the strengths of MIS with IIGS. This incudes: (1) developing a technique for accurately tracking an endoscope in physical space and (2) determining a transformation to map endoscopic image space into physical (patient) space.

Evaluation of a minimally invasive image-guided surgery system for hepatic ablation procedures.

Background. The Explorer Minimally Invasive Liver (MIL) system uses imaging to create a 3-dimensional model of the liver. Intraoperatively, the system displays the position of instruments relative to the virtual liver. A prospective clinical study compared it with intraoperative ultrasound (iUS) in laparoscopic liver ablations. Methods. Patients undergoing ablations were accrued from 2 clinical sites. During the procedures, probes were positioned in the standard fashion using iUS. The position was synchronously recorded using the Explorer system. The distances from the probe tip to the tumor boundary and center were measured on the ultrasound image and in the corresponding virtual image captured by the Explorer system. Results. Data were obtained on the placement of 47 ablation probes during 27 procedures. The absolute difference between iUS and the Explorer system for the probe tip to tumor boundary distance was 5.5 ± 5.6 mm, not a statistically significant difference. The absolute difference for probe tip to tumor center distance was 8.6 ± 7.0 mm, not statistically different from 5 mm. Discussion. The initial clinical experience with the Explorer MIL system shows a strong correlation with iUS for the positioning of ablation probes. The Explorer MIL system is a promising tool to provide supplemental guidance information during laparoscopic liver ablation procedures.

Registration of ultrasound images

In many surgical procedures, ultrasound is used for real- time visualization in order to minimize invasion of healthy tissue. Unfortunately, the exact location of soft tissues and the composition of tissues of interest may be difficult to determine using ultrasound. In interactive image guided surgery (IIGS), the display of present surgical position on preoperative tomographic imags enhances the surgeons locational awareness and provides knowledge of surgical anatomy. However, changes in the anatomy during surgery are not realized by the current IIGS techniques. This manuscript details initial experiments conducted to merge the strengths of intraoperative ultrasound imaging with IIGS. This includes: 1) developing a technique for accurately tracking an ultrasound probe in physical space and 2) determining a transformation to map ultrasound image space into physical space.

Interactive image-guided hepatic surgery

While laparoscopes are used for numerous minimally invasive procedures, minimally invasive liver resection and ablation occur infrequently. the paucity of cases is due to limited field of view and difficulty in determination of tumor location and margins under video guidance. By merging minimally invasive surgery with interactive, image-guided surgery, we hope to make laparoscopic liver procedures feasible. In previous work, we described methods for tracking an endoscope accurately in patient space and registration between endoscopic image space and physical space using the direct linear transformation (DLT). We have now developed a PC-based software system to display up to four 512 Χ 512 images indicating current surgical position using an active optical tracking system. We have used this system in several open liver cases and believe that a surface-based registration technique can be used to register physical space to tomographic space after liver mobilization. For preliminary phantom liver studies, our registration error is approximately 2.0mm. The surface-based registration technique will allow better localization of non-visible liver tumors, more accurate probe placement for ablation procedures, and more accurate margin determination for open surgical liver cases. The surface-based registration technique will allow better localization of non-visible liver tumors, more accurate probe placement for ablation procedures, and more accurate margin determination for open surgical liver cases. The surface-based/DLT registration methods, in combination with the video display and tracked endoscope, will hopefully make laparoscopic liver cryoablation and resection procedures feasible.