Biomedical subjects

R L Galloway

Publications and source records attributed to R L Galloway.

At least 19 recordsLinked to original sources

PubMed2001

Beam calibration without a phantom for creating a 3-D freehand ultrasound system.

To create a freehand three-dimensional (3-D) ultrasound (US) system for image-guided surgical procedures, an US beam calibration process must be performed. The calibration method presented in this work does not use a phantom to define in 3-D space the pixel locations in the beam. Rather, the described method is based on the spatial relationship between an optically tracked pointer and a similarly tracked US transducer. The pointer tip was placed into the US beam, and US images, physical coordinates of the pointer and the transducer location were simultaneously recorded. US image coordinates of the pointer were mapped to the physical points using two different registration methods. Two sensitivity studies were performed to determine the location and number of points needed to calibrate the beam accurately. Results showed that the beam is most efficiently calibrated with approximately 20 points collected from throughout the beam. This method of beam calibration proved to be highly accurate, yielding registration errors of approximately 0.4 mm.

Calibration↗

PubMed2001

The process and development of image-guided procedures.

Medical imaging has been used primarily for diagnosis. In the past 15 years there has been an emergence of the use of images for the guidance of therapy. This process requires three-dimensional localization devices, the ability to register medical images to physical space, and the ability to display position and trajectory on those images. This paper examines the development and state of the art in those processes.

Biomedical Engineering↗

PubMed2000

Surface registration for use in interactive, image-guided liver surgery.

OBJECTIVE: Liver surgery is difficult because of limited external landmarks, significant vascularity, and inexact definition of intra-hepatic anatomy. Intra-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 intrinsic 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 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 the "gold standard" for error measurement. RESULTS: Errors for surface registration were 2.9 mm for the entire surface and 2.8 mm for embedded targets. CONCLUSION: 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.

Computer Simulation↗

PubMed2000

Technical advances toward interactive image-guided laparoscopic surgery.

BACKGROUND: Laparoscopic surgery uses real-time video to display the operative field. Interactive image-guided surgery (IIGS) is the real-time display of surgical instrument location on corresponding computed tomography (CT) scans or magnetic resonance images (MRI). We hypothesize that laparoscopic IIGS technologies can be combined to offer guidance for general surgery and, in particular, hepatic procedures. Tumor information determined from CT imaging can be overlayed onto laparoscopic video imaging to allow more precise resection or ablation. METHODS: We mapped three-dimensional (3D) physical space to 2D laparoscopic video space using a common mathematical formula. Inherent distortions present in the video images were quantified and then corrected to determine their effect on this 3D to 2D mapping. RESULTS: Errors in mapping 3D physical space to 2D video image space ranged from 0.65 to 2.75 mm. CONCLUSIONS: Laparoscopic IIGS allows accurate (<3.0 mm) confirmation of 3D physical space points on video images. This in combination with accurately tracked instruments and an appropriate display may facilitate enhanced image guidance during laparoscopy.

Equipment Design↗

PubMed2000

Registration of physical space to laparoscopic image space for use in minimally invasive hepatic surgery.

While laparoscopes are used for numerous minimally invasive (MI) procedures, MI liver resection and ablative surgery is infrequently performed. The paucity of cases is due to the restriction of the field of view by the laparoscope and the difficulty in determining tumor location and margins under video guidance. By merging MI surgery with interactive, image-guided surgery (IIGS), we hope to overcome localization difficulties present in laparoscopic liver procedures. One key component of any IIGS system is the development of accurate registration techniques to map image space to physical or patient space. This manuscript focuses on the accuracy and analysis of the direct linear transformation (DLT) method to register physical space with laparoscopic image space on both distorted and distortion-corrected video images. Experiments were conducted on a liver-sized plastic phantom affixed with 20 markers at various depths. After localizing the points in both physical and laparoscopic image space, registration accuracy was assessed for different combinations and numbers of control points (n) to determine the quantity necessary to develop a robust registration matrix. For n = 11, average target registration error (TRE) was 0.70 +/- 0.20 mm. We also studied the effects of distortion correction on registration accuracy. For the particular distortion correction method and laparoscope used in our experiments, there was no statistical significance between physical to image registration error for distorted and corrected images. In cases where a minimum number of control points (n = 6) are acquired, the DLT is often not stable and the mathematical process can lead to high TRE values. Mathematical filters developed through the analysis of the DLT were used to prospectively eliminate outlier cases where the TRE was high. For n = 6, prefilter average TRE was 17.4 +/- 153 mm for all trials; when the filters were applied, average TRE decreased to 1.64 +/- 1.10 mm for the remaining trials.

Humans↗

PubMed2000

Depth-buffer targeting for spatially accurate 3-D visualization of medical images.

During interactive image-guided surgery (IIGS), a surgeon uses data from medical images to help guide the surgical procedure. At Vanderbilt University, an IIGS software system called Orion has been developed which is capable of displaying up to four 512 x 512 images and the current surgical position using an active optical tracking system. Orion is capable of displaying data from any tomographic image volume and from any NTSC video image. An additional display module has been implemented to display three-dimensional information as well as the tomographic slices. This provides the surgeon with valuable anatomical information that is not readily obtained from the tomographic slices alone. Before the surgery, a set of rendered images is created, each with a different angular view of the tomographic volume in order to surround the site of surgical interest. The major objectives of the display module are to display the appropriate rendered image from the set, identify the current probe position on the selected image, and provide an indication of distance between the probe and the physical point of the anatomy indicated on the image. This can provide the surgeon with vital information such as distance to blood vessels, tumors, or other critical structures.

Humans↗

PubMed1999

Image-guided surgery: preliminary feasibility studies of frameless stereotactic 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-m3 (3 X 3 X 3-m) space. CONCLUSION: Interactive image-guided surgery appears to be feasible for open and laparoscopic hepatic procedures and may enhance future operative localization.

Animals↗

PubMed1998

Sublabial, transseptal, transsphenoidal approach to the pituitary region guided by the ACUSTAR I system.

OBJECTIVE: Advances in imaging resolution have resulted in superior visualization of intracranial anatomy. Because of the inherent complexity of the surgical exposure of these lesions, intraoperative localizing techniques are required. Currently, C-arm fluoroscopy provides only two-dimensional localization for these anatomic structures. The recently described ACUSTAR I system, developed in conjunction with Codman and Shurtleff, Inc. (Randolph, Mass.), is an interactive, image-guided device that allows three-dimensional localization with a degree of accuracy previously unattainable. We assessed the clinical utility of the ACUSTAR I system for intraoperative spatial confirmation during transsphenoidal approaches to pituitary lesions. METHODS: Eight patients underwent transsphenoidal approaches to pituitary lesions with the assistance of the ACUSTAR I system. The spatial relationships were clinically judged intraoperatively by the surgeon and by use of traditional C-arm fluoroscopy and then were compared with the ACUSTAR I system results. RESULTS: In all eight patients, the ACUSTAR I system correctly displayed the surgical orientation and provided localization to within less than 1 mm. In two patients, this facilitated the redirection of an errant approach. No complications were associated with the use of this image-guided device. CONCLUSIONS: The ACUSTAR I system is useful in displaying accurate, three-dimensional anatomic relationships during transsphenoidal approaches to pituitary lesions. This system provides critical information intraoperatively to redirect errant approaches and prevent significant morbidity.

Adenoma↗

PubMed1998

An ultrasonic approach to localization of fiducial markers for interactive, image-guided neurosurgery--Part I: Principles.

Fiducial markers are reference points used in the registration of image space(s) with physical (patient) space. As applied to interactive, image-guided surgery, the registration of image space with physical space allows the current location of a surgical tool to be indicated on a computer display of patient-specific preoperative images. This intrasurgical guidance information is particularly valuable in surgery within the brain, where visual feedback is limited. The accuracy of the mapping between physical and image space depends upon the accuracy with which the fiducial markers were located in each coordinate system. To effect accurate space registration for interactive, image-guided neurosurgery, the use of permanent fiducial markers implanted into the surface of the skull is proposed in this paper. These small cylindrical markers are composed of materials that make them visible in the image sets. The challenge lies in locating the subcutaneous markers in physical space. This paper presents an ultrasonic technique for transcutaneously detecting the location of these markers. The technique incorporates an algorithm based on detection of characteristic properties of the reflected A-mode ultrasonic waveform. The results demonstrate that ultrasound is an appropriate technique for accurate transcutaneous marker localization. The companion paper to this article describes an automatic, enhanced implementation of the marker-localization theory described in this article.

Adipose Tissue↗

PubMed1998

An ultrasonic approach to localization of fiducial markers for interactive, image-guided neurosurgery--Part II: Implementation and automation.

Registration of image space and physical space lies at the heart of any interactive, image-guided neurosurgery system. This paper, in conjunction with the previous companion paper [1], describes a localization technique that enables bone-implanted fiducial markers to be used for the registration of these spaces. The nature of these subcutaneous markers allows for their long-term use for registration which is desirable for surgical follow-up, monitoring of therapy efficacy, and performing fractionated stereotactic radiosurgery. The major challenge to using implanted markers is determining the location of the markers in physical space after implantation. The A-mode ultrasonic technique described here is capable of determining the three-dimensional (3-D) location of small implanted cylindrical markers. Accuracy tests were conducted on a phantom representing a human head. The accuracy of the system was characterized by comparing the location of a marker analogue as determined with an optically tracked pointer and the location as determined with the ultrasonic localization. Analyzing the phantom in several orientations revealed a mean system accuracy of 0.5 mm with a +/- 0.1-mm 95% confidence interval. These tests indicate that transcutaneous localization of implanted fiducial markers is possible with a high degree of accuracy.

Algorithms↗

PubMed1998

Surface-based registration of CT images to physical space for image-guided surgery of the spine: a sensitivity study.

This paper presents a method designed to register preoperative computed tomography (CT) images to vertebral surface points acquired intraoperatively from ultrasound (US) images or via a tracked probe. It also presents a comparison of the registration accuracy achievable with surface points acquired from the entire posterior surface of the vertebra to the accuracy achievable with points acquired only from the spinous process and central laminar regions. Using a marker-based method as a reference, this work shows that submillimetric registration accuracy can be obtained even when a small portion of the posterior vertebral surface is used for registration. It also shows that when selected surface patches are used, CT slice thickness is not a critical parameter in the registration process. Furthermore, the paper includes qualitative results of registering vertebral surface points in US images to multiple CT slices. The method has been tested with US points and physical points on a plastic spine phantom and with simulated data on a patient CT scan.

Humans↗

PubMed1997

Registration of head volume images using implantable fiducial markers.

In this paper, we describe an extrinsic-point-based, interactive image-guided neurosurgical system designed at Vanderbilt University, Nashville, TN, as part of a collaborative effort among the Departments of Neurological Surgery, Computer Science, and Biomedical Engineering. Multimodal image-to-image (II) and image-to-physical (IP) registration is accomplished using implantable markers. Physical space tracking is accomplished with optical triangulation. We investigate the theoretical accuracy of point-based registration using numerical simulations, the experimental accuracy of our system using data obtained with a phantom, and the clinical accuracy of our system using data acquired in a prospective clinical trial by six neurosurgeons at four medical centers from 158 patients undergoing craniotomies to resect cerebral lesions. We can determine the position of our markers with an error of approximately 0.4 mm in X-ray computed tomography (CT) and magnetic resonance (MR) images and 0.3 mm in physical space. The theoretical registration error using four such markers distributed around the head in a configuration that is clinically practical is approximately 0.5-0.6 mm. The mean CT-physical registration error for the phantom experiments is 0.5 mm and for the clinical data obtained with rigid head fixation during scanning is 0.7 mm. The mean CT-MR registration error for the clinical data obtained without rigid head fixation during scanning is 1.4 mm, which is the highest mean error that we observed. These theoretical and experimental findings indicate that this system is an accurate navigational aid that can provide real-time feedback to the surgeon about anatomical structures encountered in the surgical field.

Brain Diseases↗

PubMed1994

The application accuracy of stereotactic frames.

The purpose of incorporating stereotactic methodology into neurosurgical operations is to achieve a consistently high degree of accuracy in localizing intracranial targets. Therefore, the limits of resolution for the operation are a function of the accuracy of the particular stereotactic frame system. The total clinically relevant error (application accuracy) comprises errors associated with each procedural step, including imaging, target selection, vector calculations, and the mechanical errors of stereotactic frames. To evaluate these parameters, a systematic error analysis was carried out with four commonly used stereotactic devices: the Brown-Roberts-Wells, the Cosman-Roberts-Wells, the Kelly-Goerss COMPASS (modified Todd-Wells), and the Leksell frames. Over 21,500 independent accuracy test measurements were made with 11,000 computed tomograms. The results suggest a potentially significant degree of error in the application accuracy of all stereotactic instruments, which is accentuated by but not entirely due to imaging-associated errors. Clinically encountered levels of weightbearing by stereotactic frames may have a pronounced effect on their mechanical accuracy. Both the reapplication of aiming arc assemblies and the use of phantom base units introduce independent sources of mechanical inaccuracy into stereotactic procedures. The scope of individual error values and their determining factors must be considered with every clinical use of stereotactic frame systems.

Brain Diseases↗

PubMed1992

Interactive image-guided neurosurgery.

Interactive image-guided (IIG) surgery involves the synchronal display of the tip of a surgical device on preoperative scans. This display allows the surgeon to locate the present surgical position relative to the final site of surgical interest. We have developed a technique for IIG surgery device based on a six-degree-of-freedom articulated arm. Design accuracy for the arm is less than 0.1 mm and the present implementation has a submillimetric accuracy. The display can show the surgical position on any tomographic image set with simultaneous display on up to three image sets. Laboratory results and clinical applications are discussed.

Brain↗

PubMed1992

An independent application accuracy evaluation of stereotactic frame systems.

The purpose of incorporating stereotactic methodology into neurosurgical procedures is to consistently achieve a high degree of accuracy and precision in localizing intracranial targets. Therefore, the limits of resolution for the therapeutic intervention itself are a function of the accuracy and precision inherent to the particular stereotactic frame system itself. The total clinically relevant error (application accuracy) comprises errors associated with each procedural step, including imaging, target selection, vector calculation and the mechanical errors of stereotactic frames. To evaluate these parameters, a systematic error analysis was carried out in the 4 most commonly used CT-compatible stereotactic devices: the Brown-Roberts-Wells, Cosman-Roberts-Wells, Kelly-Goerss Compass (modified Todd-Wells) and Leksell frames. Over 7,681 independent test measurements were made. The results suggest a potentially significant degree of error in application accuracy of all stereotactic instrumentation which is accentuated by imaging-associated error. These individual error values must be considered with every clinical use of stereotactic frames.

Humans↗

PubMed1992

A universal system for interactive image-directed neurosurgery.

Stereotactic methods confer great accuracy to intracranial target localization, but require strict adherence to a complex program of mechanical and computational maneuvers. A computerized, articulated, localizing 'arm' has been developed that frees the neurosurgeon of these constraints and provides a completely intuitive, 'user-friendly' interface. This universal system is independent of whatever localizing fiducial system is selected. The arm may be sterilized for intracranial use. A variety of intraoperative end effectors may be selected. The patient's CT/MR/PET scans are loaded into computer memory and a three-dimensional shaded surface wireframe diagram of the patient's head is displayed simultaneously with up to 3 independent sets of cross-referenced CT/MR/PET scan images on the intraoperative video screen. The arm's endpoint location and the directional vector are shown as cursors on the relevant scan slices, and change continuously as the surgeon moves the arm. Because the information is continuously updated, an unlimited number of targets and trajectories may be displayed throughout the operation. The arm has an ultimate design accuracy for end-point localization to within 0.1 mm throughout a target volume of 40 x 40 x 40 cm. The tested application accuracy of the first prototype model is 0.31 mm. In clinical use during 30 surgeries, its real-world application accuracy is 0.9 mm. This system provides stereotactic accuracy and universally compatible, intuitive, interactive operation.

Biopsy↗

PubMed1990

Volumetric measurement of canine gliomas using MRI.

The evaluation of tumor size by neurodiagnostic imaging is an important tool in determining disease progression or treatment efficacy. Apparent tumor size on any single slice image is sensitive to tumor shape and slice orientation. Volumetric measurements which use multiple, stacked images attenuate that sensitivity and can provide insights into tumor architecture. Volumetric measurements were made of induced canine gliomas using three common MR imaging protocols and with and without a contrast agent. Comparisons of the volumes described by each technique are made.

Animals↗

PubMed1990

Stereotactic neurosurgery.

Stereotactic neurosurgery is the technique for locating targets of surgical interest within the brain relative to an external frame of reference. Traditionally, that has meant temporarily attaching a mechanical frame to the patient's skull or scalp. Recent techniques are moving toward ways of reducing the trauma to the patient while retaining the information provided by the frame. Historically, the predominant use of the frames was for placement of electrodes. The advent of computed tomography led to a rebirth of stereotaxy for biopsy and as a guide for resection. Recent advances in computing are supplementing these techniques to allow improved surgical planning and intraoperative information. Finally, highly directed radiation therapy or stereotactic radiosurgery is discussed.

Brain↗