The problem of extrapolating cost-effective relevant information from distinctly finite or sparse data, while balancing the
competing goals between workflow and engineering design, and between application and accuracy is the 'sparse data
extrapolation problem'. Within the context of open abdominal image-guided liver surgery, one realization of this
problem is compensating for non-rigid organ deformations while maintaining workflow for the surgeon. More
specifically, rigid organ-based surface registration between CT-rendered liver surfaces and laser-range scanned
intraoperative partial surface counterparts resulted in an average closest-point residual 6.1 ± 4.5 mm with maximumsigned
distances ranging from -13.4 to 16.2 mm. Similar to the neurosurgical environment, there is a need to correct for
soft tissue deformation to translate image-guided interventions to the abdomen (e.g. liver, kidney, pancreas, etc.). While
intraoperative tomographic imaging is available, these approaches are less than optimal solutions to the sparse data
extrapolation problem. In this paper, we compare and contrast three sparse data extrapolation methods to that of datarich
interpolation for the correction of deformation within a liver phantom containing 43 subsurface targets. The
findings indicate that the subtleties in the initial alignment pose following rigid registration can affect correction up to 5-
10%. The best deformation compensation achieved was approximately 54.5% (target registration error of 2.0 ± 1.6 mm)
while the data-rich interpolative method was 77.8% (target registration error of 0.6 ± 0.5 mm).
The current protocol for image-guidance in liver surgeries involves rigid registration algorithm. Systematic studies
have shown that the liver can deform up to 2cms during surgeries thereby compromising the accuracy of the surgical
navigation systems. Compensating for intraoperative deformations using computational models has shown promising
results. In this work, we follow up the initial rigid registration with a computational approach. The proposed
computational approach relies on the closest point distances between the undeformed pre-operative surface and the
rigidly registered deformed intra-operative surface. We also introduce a spatial smoothing filter to generate a
realistic deformation field using the closest point distances. The proposed approach was validated in both phantom
experiments and clinical cases. Preliminary results are encouraging and suggest that computational models can be
used to improve the accuracy of image-guided liver surgeries.
Biomechanical models that describe soft-tissue deformations provide a relatively inexpensive way to correct registration
errors in image guided neurosurgical systems caused by non-rigid brain shifts. Quantifying the factors that cause this
deformation to sufficient precision is a challenging task. To circumvent this difficulty, atlas-based method have been
developed recently which allow for uncertainty yet still capture the first order effects associated with brain deformations.
More specifically, the technique involves building an atlas of solutions to account for the statistical uncertainty in factors
that control the direction and magnitude of brain shift. The inverse solution is driven by a sparse intraoperative surface
measurement. Since this subset of data only provides surface information, it could bias the reconstruction and affect the
subsurface accuracy of the model prediction. Studies in intraoperative MR have shown that the deformation in the
midline, tentorium, and contralateral hemisphere is relatively small. The falx cerebri and tentorium cerebelli, two of the
important dural septa, act as rigid membranes supporting the brain parenchyma and compartmentalizing the brain.
Accounting for these structures in models may be an important key to improving subsurface shift accuracy. The goals of
this paper are to describe a novel method developed to segment the tentorium cerebelli, develop the procedure for
modeling the dural septa and study the effect of those membranes on subsurface brain shift.
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.
KEYWORDS: Liver, Data modeling, Image registration, Computing systems, Surgery, Data processing, Image-guided intervention, Data acquisition, Process modeling, Data integration
Acquiring and incorporating intraoperative data into image-guided surgical systems has been shown to increase the
accuracy of these systems and the accuracy of image-guided surgical procedures. Even with the advent of powerful
computers and parallel clusters, the ability to integrate highly resolved computer model information in the planning and
execution of image-guided surgery is challenging. More often than not, the computational times required to process
preoperative models and incorporate intraoperative data for feedback are too cumbersome and do not meet the real time
constraints of surgery, for both planning and intraoperative guidance. To decrease the computational time for the
surgeon and minimize the resources in the operating room, we have developed a dual compute node framework for
image-guided surgical procedures: (i) a high-capability compute resource which acts as a server to facilitate preoperative
planning, and (ii) a low-capability compute resource which acts as a server node/compute node to process the
intraoperative data and rapidly integrate the model-based analysis for therapeutic/surgical feedback. In this framework,
the preoperative planning utilities and intraoperative guidance system act as client-nodes/graphics-nodes that are assisted
by the model-assistant. Processed data is transferred back to the graphics node for planning display or intraoperative
feedback depending on which resource is engaged. In order to efficiently manage the data and the computational
resources we also developed a novel software manager. This dual-capability resource compute node concept and the
software manager are reported in this work, and the low-capability resource compute node is investigated within the
context of image-guided liver surgery using data acquired during hepatic tumor resection therapies. Preliminary results
indicate that the dual node concept can significantly decrease the computational resources and time required for image-guided
surgical procedures.
Similar to the well documented brain shift experienced during neurosurgical procedures, intra-operative soft
tissue deformation in open hepatic resections is the primary source of error in current image-guided liver surgery
(IGLS) systems. The use of bio-mechanical models has shown promise in providing the link between the deformed,
intra-operative patient anatomy and the pre-operative image data. More specifically, the current protocol for deformation
compensation in IGLS involves the determination of displacements via registration of intra-operatively
acquired sparse data and subsequent use of the displacements to drive solution of a linear elastic model via the
finite element method (FEM). However, direct solution of the model during the surgical procedure has several
logistical limitations including computational time and the ability to accurately prescribe boundary conditions
and material properties. Recently, approaches utilizing an atlas of pre-operatively computed model solutions
based on a priori information concerning the surgical loading conditions have been proposed as a more realistic
avenue for intra-operative deformation compensation. Similar to previous work, we propose the use of a simple
linear inverse model to match the intra-operatively acquired data to the pre-operatively computed atlas. Additionally,
an iterative approach is implemented whereby point correspondence is updated during the matching
process, being that the correspondence between intra-operative data and the pre-operatively computed atlas is
not explicitly known in liver applications. Preliminary validation experiments of the proposed algorithm were
performed using both simulation and phantom data. The proposed method provided comparable results in the
phantom experiments with those obtained using the traditional incremental FEM approach.
Often within the clinical environment of a neurosurgical brain tumor procedure, the surgeon is faced with the difficulty
of orienting the patient's head to maximize the success of removing the pathology. Currently, these decisions are based
on the experience of the surgeon. The primary objective of this paper is to demonstrate how a mathematical model can
be used to evaluate the different patient positioning for tumor resection therapies. Specifically, therapies involving
gravity-induced shift are used to demonstrate how a series of candidate approaches to the tumor can result in
significantly different deformation behavior of brain tissue. To quantitatively assess the advantages and disadvantages of
potential approaches, three different midline tumor locations were used to evaluate for the extent of tumor exposure and
the magnitude of tensile stress at the brain-tumor interface, both of which are reliable indicators of the ease of resection.
Preliminary results indicate that the lateral decubitus position is best suited for midline tumors.
In this paper, preliminary results from an image-to-physical space registration platform are presented. The
current platform employs traditional and novel methods of registration which use a variety of data sources to
include: traditional synthetic skin-fiducial point-based registration, surface registration based on facial contours,
brain feature point-based registration, brain vessel-to-vessel registration, and a more comprehensive cortical
surface registration method that utilizes both geometric and intensity information from both the image volume
and physical patient. The intraoperative face and cortical surfaces were digitized using a laser range scanner
(LRS) capable of producing highly resolved textured point clouds. In two in vivo cases, a series of registrations
were performed using these techniques and compared within the context of a true target error. One of the
advantages of using a textured point cloud data stream is that true targets among the physical cortical surface
and the preoperative image volume can be identified and used to assess image-to-physical registration methods.
The results suggest that iterative closest point (ICP) method for intraoperative face surface registration is
equivalent to point-based registration (PBR) method of skin fiducial markers. With regard to the initial image
and physical space registration, for patient 1, mean target registration error (TRE) were 3.1±0.4 mm and 3.6
±0.9 mm for face ICP and skin fiducial PBR, respectively. For patient 2, the mean TRE were 5.7 ±1.3 mm, and
6.6 ±0.9 mm for face ICP and skin fiducial PBR, respectively. With regard to intraoperative cortical surface
registration, SurfaceMI outperformed feature based PBR and vessel ICP with 1.7±1.8 mm for patient 1. For
patient 2, the best result was achieved by using vessel ICP with 1.9±0.5 mm.
Compensating for intraoperative brain shift using computational models has shown promising results. Since computational time is an important factor during neurosurgery, a priori knowledge of the possible sources of deformation can increase the accuracy of model-updated image-guided systems (MUIGS). In this paper, we use sparse intraoperative data acquired with the help of a laser-range scanner and introduce a strategy for integrating this information with the computational model. The model solutions are computed preoperatively and are combined with the help of a statistical model to predict the intraoperative brain shift. Validation of this approach is performed with measured intraoperative data. The results indicate our ability to predict intraoperative brain shift to an accuracy of 1.3mm ± 0.7mm. This method appears to be a promising technique for increasing the speed and accuracy of MUIGS.
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