An event-driven distributed processing architecture for image-guided cardiac ablation therapy.

Medical imaging data is becoming increasing valuable in interventional medicine, not only for preoperative planning, but also for real-time guidance during clinical procedures. Three key components necessary for image-guided intervention are real-time tracking of the surgical instrument, aligning the real-world patient space with image-space, and creating a meaningful display that integrates the tracked instrument and patient data. Issues to consider when developing image-guided intervention systems include the communication scheme, the ability to distribute CPU intensive tasks, and flexibility to allow for new technologies. In this work, we have designed a communication architecture for use in image-guided catheter ablation therapy. Communication between the system components is through a database which contains an event queue and auxiliary data tables. The communication scheme is unique in that each system component is responsible for querying and responding to relevant events from the centralized database queue. An advantage of the architecture is the flexibility to add new system components without affecting existing software code. In addition, the architecture is intrinsically distributed, in that components can run on different CPU boxes, and even different operating systems. We refer to this Framework for Image-Guided Navigation using a Distributed Event-Driven Database in Real-Time as the FINDER architecture. This architecture has been implemented for the specific application of image-guided cardiac ablation therapy. We describe our prototype image-guidance system and demonstrate its functionality by emulating a cardiac ablation procedure with a patient-specific phantom. The proposed architecture, designed to be modular, flexible, and intuitive, is a key step towards our goal of developing a complete system for visualization and targeting in image-guided cardiac ablation procedures.

Patient specific physical anatomy models.

The advent of small footprint stereo-lithographic printers and the ready availability of segmentation and surface modeling software provide a unique opportunity to create patient-specific physical models of anatomy, validation of image guided intervention applications against phantoms that exhibit naturally occurring anatomic variation. Because these models can incorporate all structures relevant to a procedure, this allows validation to occur under realistic conditions using the same or similar techniques as would be used in a clinical application. This in turn reduces the number of trials and time spent performing in-vivo validation experiments. In this paper, we describe our general approach for the creation of both non-tissue and tissue-mimicking patient-specific models as part of a general-purpose patient emulation system used to validate image guided intervention applications.

An integrated system for real-time image guided cardiac catheter ablation.

Minimally invasive cardiac catheter ablation procedures require effective visualization of the relevant heart anatomy and electrophysiology (EP). In a typical ablation procedure, the visualization tools available to the cardiologist include bi-plane fluoroscopy, real-time ultrasound, and a coarse 3D model which gives a rough representation of cardiac anatomy and electrical activity. Recently, there has been increased interest in incorporating detailed, patient specific anatomical data into the cardiac ablation procedure. We are currently developing a prototype system which both integrates a patient specific, preoperative data model into the procedure as well as fuses the various visualization modalities (i.e. fluoroscopy, ultrasound, EP) into a single display. In this paper, we focus on two aspects of the prototype system. First, we describe the framework for integrating the various system components, including an efficient communication protocol. Second, using a simple two-chamber phantom of the heart, we demonstrate the ability to integrate preoperative data into the ablation procedure. This involves the registration and visualization of tracked catheter points within the cardiac chambers of the preoperative model.

Patient specific dynamic geometric models from sequential volumetric time series image data.

Generating patient specific dynamic models is complicated by the complexity of the motion intrinsic and extrinsic to the anatomic structures being modeled. Using a physics-based sequentially deforming algorithm, an anatomically accurate dynamic four-dimensional model can be created from a sequence of 3-D volumetric time series data sets. While such algorithms may accurately track the cyclic non-linear motion of the heart, they generally fail to accurately track extrinsic structural and non-cyclic motion. To accurately model these motions, we have modified a physics-based deformation algorithm to use a meta-surface defining the temporal and spatial maxima of the anatomic structure as the base reference surface. A mass-spring physics-based deformable model, which can expand or shrink with the local intrinsic motion, is applied to the metasurface, deforming this base reference surface to the volumetric data at each time point. As the meta-surface encompasses the temporal maxima of the structure, any extrinsic motion is inherently encoded into the base reference surface and allows the computation of the time point surfaces to be performed in parallel. The resultant 4-D model can be interactively transformed and viewed from different angles, showing the spatial and temporal motion of the anatomic structure. Using texture maps and per-vertex coloring, additional data such as physiological and/or biomechanical variables (e.g., mapping electrical activation sequences onto contracting myocardial surfaces) can be associated with the dynamic model, producing a 5-D model. For acquisition systems that may capture only limited time series data (e.g., only images at end-diastole/end-systole or inhalation/exhalation), this algorithm can provide useful interpolated surfaces between the time points. Such models help minimize the number of time points required to usefully depict the motion of anatomic structures for quantitative assessment of regional dynamics.

An axial skeleton based surface deformation algorithm for patient specific anatomic modeling.

Traditionally, finite element analysis or mass-spring systems are used to calculate deformations of geometric surfaces. Patient-specific geometric models can be comprised of tens of thousands, even hundreds of thousands of polygons, making finite element analysis and mass-spring systems computationally demanding. Simulations using deformable patient specific models at real time rates are prohibitive under such a computational burden. This paper presents a method for simulating deformable surfaces by deforming a skeletal representation of the surface, rather than the surface itself, yielding an efficient method for interactive simulation with models.

A prospective study of serum pseudocholinesterase levels in patients with chronic spinal pain: a preliminary study.

STUDY DESIGN: One-dimensional polyacrylamide gel electrophoresis was used to study serum esterase enzymatic activity in three groups of patients and one group of normal volunteers. OBJECTIVES: To determine whether there is a statistically significant correlation between variations of serum pseudocholinesterase and the perception of pain in patients with chronic spinal pain. SUMMARY OF BACKGROUND DATA: Changes in levels of cholinesterase in the extracellular space of the brain and in the cerebral spinal fluid have been found to be associated in animal pain experimentation. METHODS: Ninety-three surgical patients with chronic spinal pain, six surgical control subjects operated for conditions not associated with pain, 21 normal control volunteers, and nine disabled patients receiving monetary benefits were studied. The patients were analyzed for a period of time by rating the perception of their pain with a visual assessment score at the time venous blood was drawn. Serum samples were prepared, serum pseudocholinesterase was monitored, separated, and quantified according to Allen et al.5 Paired sample t tests were used to statistically evaluate the data. RESULTS: A trend of correlation was noted between preoperative serum pseudocholinesterase levels and visual assessment score: serum pseudocholinesterase levels increased as visual assessment score increased. The mean preoperative serum pseudocholinesterase level of chronic spinal pain patients (1313; SE = 26), which was significantly higher than the mean levels of the normal control volunteers (941; SE = 24; P<0.001) and that of surgical control subjects (1018; SE = 63; P <0.01), decreased significantly with anesthesia (P<0.005). The mean preoperative serum pseudocholinesterase level of the surgical controls, however, remained unchanged with anesthesia. A correlation demonstrated between visual assessment score and serum pseudocholinesterase in chronic spinal pain patients was not observed in six of nine patients receiving disability payments for more than a year. CONCLUSIONS: Measurements of quantitative alterations of serum pseudocholinesterase levels may be useful in the treatment of patients with chronic spinal pain.

Patient-specific anatomic models from three dimensional medical image data for clinical applications in surgery and endoscopy.

Virtual surgery and endoscopy use computer-generated volume renderings and/or models created from 3D medical image scans (CT or MRI) of individual patients. The patient's anatomy, including organs and other internal structures of interest, are then traversed in a virtual "fly-through," giving nearly the same visual impression as if the corresponding real organ was being examined intraoperatively, or as if an actual video or fiberoptic endoscopic procedure was being performed. Such virtual examinations may provide capabilities and information not possible or available in physical examinations. The potential is to provide a noninvasive computer-aided treatment plan or diagnostic screening procedure to augment or replace conventional invasive procedures. With sophisticated image processing and computational analysis, it is possible to perform realistic and useful simulations of surgical and endoscopic procedures, including "virtual dissection and resection" and "virtual biopsy." Surgical margins can be accurately assessed and differential tissue diagnoses made based upon spectral or other information contained in the patient-specific images and models.

Patient-specific anatomic models. Geometric surface generation from three-dimensional medical images using a specified polygonal budget.

Virtual reality offers the promise of highly interactive, natural control of the visualization process, greatly enhancing the scientific value of the data produced by medical imaging systems. Due to the computational and real time update requirements of virtual reality interfaces, however, the complexity of polygonal surfaces which can be displayed is limited. In this paper, we present a novel method for the production of a polygonal surface containing a pre-specified number of polygons from volumetric data. To preserve surface detail, we extract a set of curvature weights from the volumetric data and use these weights as the input vectors to a 2-D Kohonen network. The adaptation of the network to the input vectors results in a display surface that preserves useful detail relative to the number of polygons used.

Electron-beam CT: use of a calibration phantom to reduce variability in calcium quantitation.

PURPOSE: To measure scanner and patient variation in computed tomographic (CT) numbers for electron-beam CT and to determine the ability of calibration phantoms to reduce variability in calcium quantitation. MATERIALS AND METHODS: Two calibration phantoms were imaged to ensure longitudinal homogeneity and to determine the short-term intrascanner variation in CT numbers. Each phantom set was imaged twice a day for 14 weeks to determine intra- and interscanner variation. Data from examinations of 167 patients that included the phantom were analyzed to determine the intra- and interpatient variation in CT numbers of objects with known calcium concentrations. RESULTS: The calibration reduced scanner variations by approximately 25%. The calcium concentration associated with a CT number of 130 HU varied from 77.1 to 136.4 mg/cm3 and was dependent on patient girth, sex, smoking history, and image level. CONCLUSION: Scanner and patient variations in CT numbers in electron-beam CT can be reduced with a calibration phantom. In vitro and in vivo estimates of calcium concentration had a precision of 2% and 7%, respectively.

Preliminary study of an increase of a plasma apolipoprotein E variant associated with peripheral nerve damage. A finding in patients with chronic spinal pain.

STUDY DESIGN: This two-dimensional gel electrophoretic study analyzed the plasma of six groups of patients to determine the association of an elevated apolipoprotein E variant with peripheral nerve damage (PND). OBJECTIVES: To find a statistically significant plasma protein alteration in patients with PND including chronic spinal pain. SUMMARY OF BACKGROUND DATA: A twofold to fivefold increase in human plasma apolipoprotein E may be a physiologic response to PND as a 250-fold local increase in apolipoprotein E was reported in experimental PND studies in mammals. METHODS: A total of 36 patients with chronic lumbar pain, 28 normal control subjects, and 33 patients with other conditions were studied. Venipuncture was performed and plasma was studied using the technique of two-dimensional gel electrophoresis. Chi-square analysis was used to evaluate results. RESULTS: A statistically significant (P < 0.005) elevation of the plasma apolipoprotein E variant was found in patients with chronic lumbar pain. It also was elevated in patients with chronic cervical pain, extraspinal pain with PND, and chronic inflammatory diseases; but not in extraspinal pain without PND, or asymptomatic biomechanically deficient lumbar spines. CONCLUSIONS: This quantitative protein alteration, although not specific for PND, may prove useful in the treatment of conditions with this disorder, including chronic spinal pain.

Increased apolipoprotein-E concentrations in individuals suffering chronic low back syndrome identified by two-dimensional gel electrophoresis.

Non-biased screening of plasma proteins by two-dimensional gel electrophoresis from individuals suffering low back syndrome revealed a polypeptide spot that was increased 2-5-fold over the concentration found in normal control individuals. The apparent molecular weight (34-36 kDa) and pI (5.7) of this spot suggested that it might be apolipoprotein-E. Immunoblot analysis showed that the polypeptide was reactive with anti-apolipoprotein-E antibodies. N-terminal amino acid microsequence confirmed the identify of this polypeptide as apolipoprotein-E. We have determined that elevated plasma levels of apolipoprotein-E is associated with inflammation and nerve damage.

A computer model for the evaluation of the effect of corneal topography on optical performance.

We developed a method that models the effect of irregular corneal surface topography on corneal optical performance. A computer program mimics the function of an optical bench. The method generates a variety of objects (single point, standard Snellen letters, low contrast Snellen letters, arbitrarily complex objects) in object space. The lens is the corneal surface evaluated by a corneal topography analysis system. The objects are refracted by the cornea by using raytracing analysis to produce an image, which is displayed on a video monitor. Optically degraded images are generated by raytracing analysis of selected irregular corneal surfaces, such as those from patients with keratoconus and those from patients having undergone epikeratophakia for aphakia.