Kim Manwaring

Implementation, calibration and accuracy testing of an image-enhanced endoscopy system

This paper presents a new method for image-guided surgery called image-enhanced endoscopy. Registered real and virtual endoscopic images (perspective volume renderings generated from the same view as the endoscope camera using a preoperative image) are displayed simultaneously; when combined with the ability to vary tissue transparency in the virtual images, this provides surgeons with the ability to see beyond visible surfaces and, thus, provides additional exposure during surgery. A mount with four photoreflective spheres is rigidly attached to the endoscope and its position and orientation is tracked using an optical position sensor. Generation of virtual images that are accurately registered to the real endoscopic images requires calibration of the tracked endoscope. The calibration process determines intrinsic parameters (that represent the projection of three-dimensional points onto the two-dimensional endoscope camera imaging plane) and extrinsic parameters (that represent the transformation from the coordinate system of the tracker mount attached to the endoscope to the coordinate system of the endoscope camera), and determines radial lens distortion. The calibration routine is fast, automatic, accurate and reliable, and is insensitive to rotational orientation of the endoscope. The routine automatically detects, localizes, and identifies dots in a video image snapshot of the calibration target grid and determines the calibration parameters from the sets of known physical coordinates and localized image coordinates of the target grid dots. Using nonlinear lens-distortion correction, which can be performed at real-time rates (30 frames per second), the mean projection error is less than 0.5 mm at distances up to 25 mm from the endoscope tip, and less than 1.0 mm up to 45 mm. Experimental measurements and point-based registration error theory show that the tracking error is about 0.5-0.7 mm at the tip of the endoscope and less than 0.9 mm for all points in the field of view of the endoscope camera at a distance of up to 65 mm from the tip. It is probable that much of the projection error is due to endoscope tracking error rather than calibration error. Two examples of clinical applications are presented to illustrate the usefulness of image-enhanced endoscopy. This method is a useful addition to conventional image-guidance systems, which generally show only the position of the tip (and sometimes the orientation) of a surgical instrument or probe on reformatted image slices.

Treatment of positional plagiocephaly with dynamic orthotic cranioplasty

Dynamic orthotic cranioplasty (DOC) was developed to treat asymmetrical head shape of a nonsynostotic origin, which is defined by the term positional plagiocephaly. These positional deformations have been found to correlate with a number of environmental factors. Infants with positional plagiocephal

Treatment of craniofacial asymmetry with dynamic orthotic cranioplasty

Dynamic Orthotic Cranioplasty (DOC) was developed to treat craniofacial deformities associated with positional plagiocephaly. This investigation describes the treatment of more than 750 patients with the DOC Band since 1988. All patients undergoing DOC treatment were fit with a custom fabricated orthosis made from a plaster impression taken from the infants head. When the orthosis was applied, the corrective pressure was directed to hold growth at the calvarial prominences and redirect symmetrical growth. A detailed medical history was obtained and anthropometric measurements were taken at start, exit, 12, 18, and 24 months follow-up. This information was recorded in a database created in Microsoft Excel. Mean length of treatment was 4.3 months with an average entrance age of 6.9 months. Analysis of anthropometric data showed significant reduction in mean cranial vault, skull base, and facial asymmetries. Correction of the more difficult skull base was documented with computed tomography. Our anthropometric and clinical observations document complete or near complete correction of asymmetry for a wide variety of head shapes. Based on the results of this investigation, we are able to support the earlier claims of our pilot study, which concluded that DOC is effective in the treatment of positional plagiocephaly.

Cranial Growth Unrestricted during Treatment of Deformational Plagiocephaly

Objectives: The Dynamic Orthotic Cranioplasty (DOC) BandTM is a cranial orthosis used to treat deformational plagiocephaly. The ability of this device to redirect growth and thus, improve craniofacial asymmetry has raised concerns regarding the potential restriction of cranial growth. The purpose of this study was to evaluate the growth of the head during correction of plagiocephaly. Methods: The study sample consisted of 190 children: 81 females (42.6%) and 109 males (57.4%) All patients had been diagnosed with nonsynostotic plagiocephaly, did not have other significant medical conditions, were compliant with DOC protocol, and had complete anthropometric measurements at entrance and exit from treatment. Growth of the head was evaluated using head circumference, maximum cranial width and maximum cranial length. Correction of plagiocephaly was evaluated by documenting the reduction of craniofacial asymmetry of the cranial vault, skull base and face. Paired t tests were used to assess the significance of changes in these anthropometric measurements. Differences were considered significant if p < 0.05. Results: Average entrance age was 6.5 months with a mean treatment time of 4.1 months. Statistical analysis demonstrated highly significant reductions in asymmetry in all three regions (p < 0.001). More importantly, these corrections were achieved with synchronous growth of the skull as demonstrated by highly significant increases (p < 0.001) in head circumference, maximum cranial width and maximum cranial length. Conclusions: These findings document statistically significant increases in cranial growth in association with concomitant reductions of the cranial asymmetries associated with deformational plagiocephaly.

Chronic Tonsillar Herniation and Crouzon’s Syndrome

Patients born with craniofacial syndromes such as Crouzons syndrome will often develop hydrocephalus after their initial craniofacial reconstructive procedures. We have treated 10 patients with Crouzons syndrome; 5 patients required a shunting procedure after cranial remodeling. Each of these 5 shunted patients later demonstrated chronic tonsillar herniation on magnetic resonance imaging studies. One of these patients exhibited signs of pseudotumor cerebri and 1 had a spastic quadriparesis. Of the 5 patients who did not require a shunt, none displayed chronic tonsillar herniation. Our evidence suggests that jugular foramen stenosis produces an increased cerebral venous turgor that leads to a cerebrospinal fluid absorption defect and hydrocephalus. After the hydrocephalus is treated the increased venous turgor remains and provides the driving force for the development of chronic tonsillar herniation.

Use of Positron Emission Tomography for Presurgical Localization of Eloquent Brain Areas in Children with Seizures

Successful surgical management of a neoplastic or nonneoplastic seizure focus in close proximity to or within eloquent brain areas relies on precise delineation of the relationship between the lesion and functional brain areas. The aim of this series was to validate the usefulness and test the efficacy of noninvasive presurgical PET mapping of eloquent brain areas to predict surgical morbidity and outcome in children with seizures. To identify eloquent brain areas in 15 children (6 female and 9 male; mean age 11 years) with epileptogenic lesions PET images of regional cerebral blood flow were performed following the administration of [(15)O]water during motor, visual, articulation, and receptive language tasks. These images with coregistered magnetic resonance (MR) images were then used to delineate the anatomic relationship of a seizure focus to eloquent brain areas. Additional PET images using [18F]fluoro-2-deoxy-D-glucose (FDG) and [11C]methionine (CMET) were acquired to help localize the seizure focus, as well as characterize the lesion. Patient surgical management decisions were based on PET mapping in combination with coregistered MR images, PET-FDG findings, and the anatomic characteristics of the lesion. At follow-up 1-26 months after surgery, all patients that underwent temporal lobectomy (9 patients) and extratemporal resection (4 patients) for a neoplastic or nonneoplastic seizure focus are seizure-free with minimal postoperative morbidity. Of prime importance, no child sustained a postoperative speech or language deficit. PET imaging was also well tolerated without procedural complications. Based on PET mapping, a nonoperative approach was used for 2 children and a biopsy only was used in one child. When cortical injury involved prenatally determined eloquent cortex, PET demonstrated reorganization of language areas to new adjacent areas or even to the contralateral hemisphere. Integration of anatomical and functional data enhanced the surgical safety, defined optimal surgical approach, delineated the seizure focus from eloquent brain areas, facilitated maximum resection and optimized the timing of surgery, thereby minimizing surgical morbidity while maximizing surgical goals. PET measurements of FDG and CMET uptake were also helpful in localizing the seizure focus and grading the tumors. PET used for brain mapping in children provides the surgeon with strategic preoperative information not readily attainable with traditional invasive Wada testing or intraoperative cortical stimulation. PET mapping may also improve the outcome of extratemporal resections by allowing aggressive seizure focus resection. In addition, serial brain maps may optimize timing for surgical intervention by demonstrating reorganization of eloquent cortex often seen in younger children after cortical injury. Our results suggest that noninvasive presurgical brain mapping has the potential to reduce risk and improve neurologic outcome.

Transplanted Demineralized Bone Graft in Cranial Reconstructive Surgery

Surgical reconstruction of cranial deformities and synostosis is occasionally accompanied by incomplete bone growth to cover all areas of cranial vault that have been exposed in the correction. The restrictive nature of some forms of synostosis require more bone in the repair than is available using the childs natural skull for autogenous bone cranioplasty. Rib and iliac crest autografts have been used with success. These grafts must be harvested form a remote site with increased morbidity. A split-thickness skull autograft is the cranioplasty material of choice but children under the age of 6 years may lack the skull thickness needed to use this technique. Perforated demineralized bone matrix has been transplanted in 46 operations in 42 patients from 1990 to 1995 for repair of residual skull defects in children having previously undergone craniofacial repairs, for primary reconstruction of the cranial vault for patients with synostosis and for repair of skull defects resulting from trauma and skull tumor excisions. The vast majority of grafts have resulted in complete closure of the defect, providing a matrix for new bone formation. These patients are presented. Surgical techniques of cranial defect repair with perforated demineralized bone matrix are discussed.

Magnetic Field Guided Endoscopic Dissection through a Burr Hole May Avoid More Invasive Craniotomies A Preliminary Report

The neuroendoscope, coupled with radiofrequency or laser dissecting tools, can effectively resect obstructing membranes, biopsy and debulk tumor, and evacuate hematomas when the pathology is within the ventricular system. This less invasive approach through a burr hole usually avoids craniotomies. When the abnormal condition is within parenchyma or in the presence of opacifying bloody fluid, landmarks are not recognizable and the neurosurgeon quickly becomes disoriented. A more extensive craniotomy or a stereotaxic-guided procedure is then necessary. We describe our preliminary experience with a geographic intracranial navigation system using realtime measurement of electromagnetic field strength in multiple planes to precisely indicate the position of the tip of the endoscope. A transmitting antenna is positioned beneath the patients head. A 1.5 centimeter cubic antenna receiver is mounted upon a lenscope with instrument channel. The scope is guided into the surgical field after insertion through a burr hole. A square wave pulsed electromagnetic field measurement is made 140 times per second with correction for the earths magnetic field once per second. Intracranial position data for the dissecting tip in regard to X, Y, Z, pitch, roll and yaw are output to a digitized computer map of the patients MRI or CT scan. Also displayed on the computer screen is the video image from the endoscope. The neurosurgeon thus has simultaneous realtime geographic and near-field localization as he dissects. Electromagnetic field guided accuracy is within 2.0 mm inside the allowable 24 inch working sphere about the patients head. Coupled with near-field video precision, accuracy is within 1 mm of recognizable dissection planes.(ABSTRACT TRUNCATED AT 250 WORDS)

Positron Emission Tomography Using [18F] Fluorodeoxyglucose and [ 11C] L-Methionine to Metabolically Characterize Dysembryoplastic Neuroepithelial Tumors

Dysembryoplastic neuroepithelial tumors are unique and benign congenital tumors occurring frequently in children and adolescents. Differentiation from other low-grade tumors is important for management. Five patients with confirmed dysembryoplastic neuroepithelial tumors were studied with positron emission tomography using glucose and protein metabolic uptake in an attempt to categorize these tumors metabolically. Functional brain mapping also was obtained to aid in operative management. Results of the study conclude that dysembryoplastic neuroepithelial tumors, although having similar neuroimgaing characteristics to other low-grade tumors, are distinguished by a unique metabolic profile. They are inactive tumors with no significant glucose or protein metabolic activity. The combination of preoperative positron emission tomographic metabolic studies with functional brain mapping allowed for prediction of tumor type, defined eloquent areas of cortical function, and improved approach and resection of the tumors with minimal risk of neurologic impairment. (J Child Neurol 1999;14:673-677).

Comparison of skin necrosis in rats by using a new microneedle electrocautery, standard-size needle electrocautery, and the shaw hemostatic scalpel

“Microneedle” electrocautery was compared against the standard- size needle electrocautery and the Shaw hemostatic scalpel to determine the differences in tissue necrosis when used as a cutting instrument. Incisions were made on the dorsal skin of anesthetized white rats using each of the three devices with the no. 15 scalpel as control. The specimens were submitted for histological evaluation. The microneedle caused less necrosis than the standard-size needle electrocautery (0.18 vs 0.27 mm, p<0.01) and less necrosis than the Shaw hemostatic scalpel set at 220°F (0.18 vs 0.25 mm, p<0.05). The microneedle electrocautery was also found to be an instrument that causes very little tissue distortion during fine dissection and helps to minimize blood loss in craniofacial and neurosurgical operations.