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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 r = 0.953; p 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.

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.

Objective: Liver surgery is diflicult because of limited external landmarks, significant vascularity, and inexact definition of intra-hepatic anatomy. htra-operative ultrasound (IOUS) has been widely used in an attempt to overcome these difficulties, but is limited by its two-dimensional nature, inter-user variability, and image obliteration with ablative or resectional techniques. Because the anatomy of the liver and intra-operative removal of hepatic ligaments make inuinsic or extrinsic point-based registration impractical, we have implemented a surface registration technique to map physical space into CT image space, and have tested the accuracy of this method on an anatomical liver phantom with embedded tumor targets.Materials and Methods: Liver phantoms were created from anatomically correct molds with “tumors” embedded within the substance of the liver. Helical CT scans were performed with 3-mm slices. Using an optically active position sensor, the surface of the liver was digitized according to ana...

Blood flow and magnetic field inhomogeneities lead to distortions in MR angiography (MRA) images that present added risk for stereotactic neurosurgical applications. These effects are demonstrated in an MRA image of a model of cerebrovasculature. Analysis of the effects of velocity, acceleration, jerk, and field inhomogeneities on vessel position is presented; results are used to predict vessel shifts for several cerebral blood vessels. The actual encoded position for flowing spins is shown to be a moment-weighted average position. Maximum shift of 3.11 mm was reduced to 0.05 mm when velocity compensation was added. Velocity compensation applied specifically in the phase-encoding direction reduces flow-dependent shifts to the point that they can be safely ignored even if acceleration and jerk are present. Those prescribing and using MRA images for stereotactic applications must be aware of whether compensation is actually applied along the phase-encoding axis when a flow-compensated sequence is used.

Indications for liver surgery to treat primary and secondary hepatic malignancies are broadening. Utilizing data from B-mode or 2-dimensional intraoperative ultrasound, it is often challenging to replicate the findings from preoperative CT or MRI scans. Additional data from more recently developed image-guidance technology, which registers preoperative axial imaging to a 3-dimensional real-time model, may be used to improve operative planning, locate difficult to find hepatic tumors, and guide ablations. Laparoscopic liver procedures are often more challenging than their open counterparts. Image-guidance technology can assist in overcoming some of the obstacles to minimally invasive liver procedures by enhancing ultrasound findings and ablation guidance. This manuscript describes a protocol that evaluated an open image-guidance system, and a subsequent protocol that directly compared, for validation, a laparoscopic with an open image-guidance system. Both protocols were limited to ablations within the liver. The laparoscopic image-guidance system successfully creates a 3-D model at both 7 and 14 mm Hg that is similar to the open 3-D model. Ultimately, improving intraoperative image guidance can help expand the ability to perform both laparoscopic and open liver surgeries.

BackgroundUltrasound (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.MethodsAn 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.ResultsOver 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

Preoperative planning combined with image-guidance has shown promise towards increasing the accuracy of liver resection procedures. The purpose of this study was to validate one such preoperative planning tool for four patients undergoing hepatic resection. Preoperative computed tomography (CT) images acquired before surgery were used to identify tumor margins and to plan the surgical approach for resection of these tumors. Surgery was then performed with intraoperative digitization data acquire by an FDA approved image-guided liver surgery system (Pathfinder Therapeutics, Inc., Nashville, TN). Within 5-7 days after surgery, post-operative CT image volumes were acquired. Registration of data within a common coordinate reference was achieved and preoperative plans were compared to the postoperative volumes. Semi-quantitative comparisons are presented in this work and preliminary results indicate that significant liver regeneration/hypertrophy in the postoperative CT images may be present post-operatively. This could challenge pre/post operative CT volume change comparisons as a means to evaluate the accuracy of preoperative surgical plans.

Interactive image-guided liver surgery (Linasys device, Pathfinder Therapeutics, Inc., Nashville, TN) requires a user-oriented, easy-to-use, fast segmentation preoperative surgical planning system. This system needs to build liver models displaying the liver surface, tumors, and the vascular system of the liver. A robust and efficient tool for this purpose was developed and evaluated. For the liver surface or other bulk shape organ segmentation, the delineation was conducted on multiple slices of a CT image volume with a region growing algorithm. This algorithm incorporates both spatial and temporal information of a propagating front to advance the segmenting contour. The user can reduce the number of delineation slices during the processing by using interpolation. When comparing our liver segmentation results to those from MeVis (Breman, Germany), the average overlap percentage was 94.6%. For portal and hepatic vein segmentation, three-dimensional region growing based on image intensity was used. All second generation branches can be identified without time-consuming image filtering and manual editing. The two veins are separated by using mutually exclusive region growing. The tool can be used to conduct segmentation and modeling of the liver, veins, and other organs and can prepare image data for export to Linasys within one hour.

Point-based registration for image-guided neurosurgery has become the industry standard. While the use of intrinsic points is appealing because of its retrospective nature, affixing extrinsic objects to the head prior to scanning has been demonstrated to provide much more accurate registrations. Points of reference between image space and physical space are called fiducials. The extrinsic objects which generate those points are fiducial markers. The markers can be broken down into two classifications: skin-mounted and bone-implanted. Each has distinct advantages and disadvantages. Skin-mounted fiducials require simply sticking them on the patient in locations suggested by the manufacturer, however, they can move with tractions placed on the skin, fall off and perhaps the most dangerous problem, they can be replaced by the patient. Bone implanted markers being rigidly affixed to the skull do not present such problems. However, a minor surgical intervention (analogous to dental work) must be performed to implant the markers prior to surgery. Therefore marker type and use has become a decision point for image-guided surgery. We have performed a series of experiments in an attempt to better quantify aspects of the two types of markers so that better informed decisions can be made. We have created a phantom composed of a full-size plastic skull [Wards Scientific Supply] with a 500 ml bag of saline placed in the brain cavity. The skull was then sealed. A skin mimicking material, DragonSkinTM [SmoothOn Company] was painted onto the surface and allowed to dry. Skin mounted fiducials [Medtronic-SNT] and bone-implanted markers [Z-Kat]were placed on the phantom. In addition, three additional bone-implanted markers were placed (two on the base of the skull and one in the eye socket for use as targets). The markers were imaged in CT and 4 MRI sequences (T1-weighted, T2 weighted, SPGR, and a functional series.) The markers were also located in physical space using an Optotrak 3020 [Northern Digital Inc]. Registrations between image space and physical space were performed and fiducial and target registration errors were determined. Finally the 5 bone-implanted makers which penetrated the skin were removed and a traction equivalent to 25% of the weight of the average human head was applied to the “skin” surface. Target and fiducial registrations were again performed.

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

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.

In interactive, image-guided surgery, current physical space position in the operating room is displayed on various sets ofmedical images used for surgical navigation. One useful image display format for image-guided hepatic surgery is liversurface renderings. Deep-seated tumors within the liver can be projected onto the surface of these renderings and providepertinent information concerning the location and size of metastatic liver tumors. Techniques have been developed by ourgroup to create hepatic surface renderings. An independently implemented variation ofthe marching cubes algorithm is usedon segmented livers to create a triangulated surface, which is displayed using OpenGL, a 3-D graphics and modelingsoftware library. Tumors are segmented separately from the liver so that their colors differ from that of the liver surface.The liver is then rendered slightly transparent so that tumors can be seen within liver and aid surgeons in preoperativeplanning. The graphical software is also bundled into a dynamic linked library (DLL) and slaved with ORION, our WindowsNT based image-guided surgical system. We have tested our graphics DLL on a liver phantom embedded with "tumors". Asurface-based registration algorithm was used to map current surgical position onto a transparent phantom rendering thatindicates tumor location. The rendering view is updated as surgical position is changed. For minimally invasive procedures,we will use the direct linear transformation and the same surface-based registration technique to map rendered tumorsdirectly onto an endoscopic image. This will be especially useful in localizing deep-seated tumors for ablation and resectionprocedures.Keywords: surface renderings, image-guided surgery, OpenGL, liver surgery

Background Liver surgery can be difficult because there are few external landmarks defining hepatic anatomy and because the liver has significant vascularity. Although preoperative tomographic imaging (computed tomography or magnetic resonance imaging) provides essential anatomical information for operative planning, at present it cannot be used actively for precise localization during surgery. Interactive image-guided surgery involves the simultaneous real-time display of intraoperative instrument location on preoperative images (computed or positron-emission tomography or magnetic resonance imaging). Interactive image-guided surgery has been described for tumor localization in the brain (frameless stereotactic surgery) and allows for interactive use of preoperative images during resections or biopsies. Hypothesis The application of interactive image-guided surgery (IIGS) is feasible for hepatic procedures from a biomedical engineering standpoint. Methods We developed an interactive image-guided surgery system for liver surgery and tested a porcine liver model for tracking liver motion during insufflation; liver motion during respiration in open procedures in patients undergoing hepatic resection; and tracking accuracy of general surgical instruments, including a laparoscope and an ultrasound probe. Results Liver motion due to insufflation can be quantified; average motion was 2.5 ± 1.4 mm. Average total liver motion secondary to respiration in patients was 10.8 ± 2.5 mm. Instruments of varying lengths, including a laparoscope, can be tracked to accuracies ranging from 1.4 to 2.1 mm within a 27-m 3 (3 × 3 × 3-m) space. Conclusion Interactive image-guided surgery appears to be feasible for open and laparoscopic hepatic procedures and may enhance future operative localization.

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.

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.

Liver surgery is difficult because of limited external landmarks, significant vascularity and inexact definition of intrahepatic anatomy. Intraoperative ultrasound (IOUS) has been widely used in an attempt to overcome these difficulties, but is limited by its two-dimensional nature, interuser variability and image obliteration with ablative or resectional techniques. Because the anatomy of the liver and intra-operative removal of hepatic ligaments make intrinsic or extrinsic point-based registration impractical, we have implemented a surface registration technique to localize physical points for liver phantoms and anatomically placed targets within the liver on CT images. Liver phantoms were created from anatomically correct molds with “tumors” imbedded within the substance of the liver. Helical CT scans were performed with 3 mm slices. Using an optically active position sensor, the surface of the liver was digitized according to anatomical segments. A surface registration was performed and RMS errors of the locations of internal tumors are presented as verification. An initial point based marker registration was performed and considered as the standard for error measurement. Errors for surface-registration were 2.9 mm for the entire surface and 2.8 mm for embedded targets. This is an initial study considering the use of surface registration for the purpose of physical to image registration in the area of liver 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.

Incorporation of Vascular Information into Interactive, Image-Guided SurgeryRobert L. Galloway, W. Andrew Bass, James D. Stefansic, Robert J. MaciunasVanderbilt University, Department of Biomedical EngineeringNashville, TN 37235ABSTRACTIn interactive, image-guided surgery (JIGS) we use stacked slice tomographic image sets as three dimensionalmaps of the patient's anatomy. Such sets can provide exquisite information on bony anatomy (Computed Tomography),soft tissue structure and lesion definition (Magnetic Resonance) or function (Positron Emission Tomography). However,none of these tomographic sets clearly show the location and extent of vascular structures, which may be of criticalimportance to the surgical process.Vascular information can be obtained from conventional x-ray angiography (XRA), a form of projection imaging,or from tomographic scans sensitive to flow such as Magnetic Resonance Angiography (MRA) or Computed TomographyAngiography (CTA). Projection images show the extent and intersection of vessels at high resolution but lose the three-dimensional relationship of the vessels during image formation. The high resolution available from conventionalangiograms makes them attractive for the localization of small aneurysms and other vascular anomalies, but the projectionnature of the image makes displaying surgical position difficult.We have developed techniques for interactively displaying surgical position on both tomographically derivedvascular sets such as CTA and MRA and on projection sets such as XRA. In the XRA images, homologous points aredetermined on the film and on the patient. Since we use extrinsic, bone-implanted fiducial markers for our surgicalguidance system, these markers can serve as most, if not all, of our homologous points and can be localized very preciselyon the film and in 3-space. A homogeneous transform matrix (HTM) is constructed to provide a best "first-guess" ofposition. The HTM is decomposed into nine spatial parameters which represent the XRA process and those parametersare optimized using Powell's Conjugate Direction Method.In the tomographic vascular images, the issue is not one of registration but one of display. We presently trackprobe position on tomographic slices but the information inherent in vascular tomograms is masked by a raster-slicedisplay; the vessel's path and extent are difficult to discern. Vascular path and extent are best displayed as a rotoscope ofprojection images created from the raster-slice set. By "rotating" a series of projection images the three-dimensionalgeometry is discerned by motion parallax.Keywords: Image-Guided Surgery, Registration, Angiography