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Biomedical subjects

R A Robb

Publications and source records attributed to R A Robb.

At least 19 recordsLinked to original sources
PubMed1998

Prostate cancer microvessels: a novel method for three-dimensional reconstruction and analysis.

BACKGROUND: Studies of prostate cancer microvessels to date have relied on routine two-dimensional images from histologic tissue sections, and there have been no previous reports of three-dimensional (3D) reconstruction and analysis of prostatic microvessels in benign or malignant specimens. Knowledge about the 3D architecture of microvessels would be useful for determining the utility and limitations of two-dimensional (2D) measures, as well as for determining the usefulness of 3D measures to predict pathologic stage and patient outcome in prostate cancer. However, the ability to study microvessels in 3D must first be demonstrated. METHODS: We developed a novel method to visualize and analyze prostate microvessels in three dimensions from serially-sectioned prostate specimens, including tissue preparation, reconstruction of serial histologic sections into 3D volumes, extraction of vessels from this data set, and calculation of geometric characteristics. Eleven regions of benign and cancer tissue were studied and compared in an effort to validate our methodology. RESULTS: Microvessels and glandular elements from benign and malignant tissue were visualized together in three dimensions. In the 3D visualizations, microvessels associated with cancer were seen to have more arbitrary pathways, increased tortuosity, and a more casual relationship with glandular elements than microvessels associated with benign tissue. A quantitative measure, the volume length density, discriminated between benign tissue and cancer better than simple microvessel density in this exploratory study. CONCLUSIONS: Microvessels in prostate cancer have a more homogeneous distribution and greater tortuosity than those in benign tissue. Volume length density of microvessels shows promise as a 3D marker in prostate cancer.

Adenocarcinoma↗
PubMed1998

Scalp-recorded EEG localization in MRI volume data.

Scalp-recorded EEG is a noninvasive and widely available tool for studying normal and dysfunctional human neurophysiology with unsurpassed temporal resolution. However, scalp-recorded EEG data is difficult to correlate with anatomy, and most current display and neural source estimation algorithms are based on unrealistic spherical or elliptical models of the head. It is possible to measure the positions of electrodes on the patient's scalp, and to register those electrode positions into the space of a high-resolution MRI volume, and to then use the patient-specific anatomy as the basis for display and estimation of neural sources. We use a surface matching algorithm to register digitized electrode and scalp surface coordinates to a three-dimensional MRI volume. This study uses fiducial markers in phantom and volunteer studies to quantitatively estimate the accuracy of the electrode registration method. Our electrode registration procedure is accurate to 2.21 mm for a realistic head phantom and accurate to 4.16 mm on average for five volunteers. This level of accuracy is considered within acceptable limits for clinical applications.

Algorithms↗
PubMed1998

Optimized homomorphic unsharp masking for MR grayscale inhomogeneity correction.

Grayscale inhomogeneities in magnetic resonance (MR) images confound quantitative analysis of these images. Homomorphic unsharp masking and its variations have been commonly used as a post-processing method to remove inhomogeneities in MR images. However, little data is available in the literature assessing the relative effectiveness of these algorithms to remove inhomogeneities, or describing how these algorithms can affect image data. In this study, we address these questions quantitatively using simulated images with artificially constructed and empirically measured bias fields. Our results show that mean-based filtering is consistently more effective than median-based algorithms for removing inhomogeneities in MR images, and that artifacts are frequently introduced into images at the most commonly used window sizes. Our results demonstrate dramatic improvement in the effectiveness of the algorithms with significantly larger windows than are commonly used.

Algorithms↗
PubMed1997

Three-dimensional reconstruction of aqueous channels in human trabecular meshwork using light microscopy and confocal microscopy.

Conventional two-dimensional imaging of the trabecular meshwork (TM) provides limited information about the size, shape, and interconnection of the aqueous channels within the meshwork. Understanding the three-dimensional (3-D) relationships of the channels within this tissue may give insight into its normal function and possible changes present in the eye disease glaucoma. The purpose of our study was to compare laser scanning confocal microscopy with standard 1 micron Araldite-embedded histologic sections for 3-D analysis of the trabecular meshwork. In addition, the study was done to determine whether computerized 3-D reconstruction could isolate the fluid spaces of the trabecular meshwork and determine the size of interconnections between the fluid spaces. Confocal microscopy appears comparable to 1 micron Araldite-embedded tissue sections and has the advantage of inherent registration of the serial tissue sections. Three-dimensional reconstruction allowed the isolation of the fluid spaces within the trabecular meshwork and revealed the presence of numerous interconnections between larger fluid spaces. The distribution of these interconnections was randomly arranged, with no predilection for specific regions within the trabecular meshwork. This distribution of constrictions and "expansion chambers" may provide a clue to the mechanism by which subtle histologic changes are associated with increased ocular pressure in glaucoma.

Aqueous Humor↗
PubMed1997

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.

Algorithms↗
PubMed1997

Evaluating virtual endoscopy for clinical use.

Virtual endoscopy is a term used to describe computer simulated endoscopy procedures derived from high resolution images of patient anatomy. By simulating the endoscopic examination, the patient is spared the discomfort and possible complications of an actual examination. The physician also has more flexibility in a virtual endoscopic examination of 3D patient data in comparison to a real endoscopic examination. Virtual endoscopy removes the physical and physiologic constraints of real endoscopy and can create views that are not possible in an actual endoscopic examination. This may enhance the performance of actual endoscopic examinations. Virtual endoscopy may also be used to perform "numerical biopsies"; anatomic measurements such as size, distance, shape, and density. Virtual endoscopy allows the physician to comprehensively explore the patient anatomy using an intuitive and interactive interface. There are currently two technical approaches to performing virtual endoscopy: perspective volume rendering and surface rendering of polygonal models. Perspective volume rendering uses traditional volumetric rendering algorithms to create visualizations directly from the volumetric dataset. Polygonal models require a preprocessing step to convert the segmented volume information into a polygonal surface that may be displayed at real time frame rates. Both paradigms have inherent strengths and weaknesses. We illustrate and compare the methods on actual patient data, including simulated endoscopic examinations of the airways, colon and esophagus. Preliminary results in virtual endoscopy show promise and will continue to be an area of active research leading to useful clinical applications.

Algorithms↗
PubMed1997

Resection of a large temporooccipital parenchymal arteriovenous fistula by using deep hypothermic circulatory bypass. Case report.

The authors believe this to be the first published case in which a deep hypothermic cardiopulmonary bypass was used to facilitate resection of a large parenchymal arteriovenous fistula. The use of this procedure facilitated resection of the lesion by allowing compression and manipulation of large venous varices that were overlying the deeper arterial feeding vessels. The surgical rationale, technique, and intra- and postoperative management are discussed.

Adult↗
PubMed1996

Otocephalus: histopathology and three-dimensional reconstruction.

Otocephaly is a lethal malformation of the first and second branchial arches, which consists of ventromedial displacement of the external ear structures (synotia), mandibular aplasia (agnathia), absence of the tongue (aglossia), and microstomia. We present the first complete description of the temporal bone findings in a case of otocephalus. A three-dimensional computer-assisted reconstruction of the right temporal bone was performed, allowing a unique graphic analysis. An extremely low-lying middle fossa tegmen was noted with malrotation of the middle ear structures. Severe ossicular malformations were also found. An anomalous course of the internal carotid artery was noted with indentation of the basal turn of the cochlea. All three layers of the otic capsule were incompletely developed. Cochlear bony dehiscences were noted. These findings are consistent with early arrest of fetal development and malrotation caused by lack of growth pressure from the mandibular arch. Implications of these findings in the embryologic development of the ear are discussed.

Abnormalities, Multiple↗
PubMed1994

Three-dimensional volumetric ultrasound imaging of arterial pathology from two-dimensional intravascular ultrasound: an in vitro study.

The objectives of this study were to evaluate: (1) the feasibility of generating three-dimensional (3-D) ultrasound (US) volumetric images of arterial segments from intravascular (IV) US images by retaining full range of gray levels; (2) the feasibility of volumetric quantitation of various arterial wall pathology from the 3-D volume US images of arterial segments. IVUS provides morphologic details of arterial wall diseases. This is seen as variation in gray levels. However, when a 3-D US image is generated currently, the full range of gray levels is not utilized. This limits optimal assessment of arterial wall pathology. Sequential cross-sectional IVUS images from 11 arterial segments consisting of various pathology were obtained in vitro by calibrated withdrawal of an IVUS catheter. These images were digitized by an 8 bit digitizer to retain full 256 gray levels of brightness. 3-D volume generation was carried out using "ANALYZE" software. After the IVUS imaging, arterial segments were sectioned transversely in a 0.3-0.4 mm cross section and stained with hematoxylin, eosin and elastin. Geometrical measurements and gross morphological changes of the arterial segments were noted and correlated with the corresponding section of the image from the three-dimensional volume. Arterial wall pathology, its extent and its effect on lumen geometry were easily appreciated in multiple tomographic sections of a 3-D volume image. Similarly, arterial wall pathology was easily quantitated from 3-D volume. The above assessments were only feasible by retaining full range of gray levels in the 3-D volume image. This study indicates that (1) it is feasible to generate a 3-D US volume image by retaining full range of gray levels from IVUS images, (2) retaining full range of gray levels allows optimal assessment of arterial wall pathology and its extent in 3-D volume, and (3) IVUS allows quantitation of arterial wall pathology, and thereby one can assess the effect of intervention.

Arteries↗
PubMed1991

Brain surface cortical sulcal lengths: quantification with three-dimensional MR imaging.

The repeatability and accuracy of brain surface cortical sulcal length measurements obtained with three-dimensional (3D) reconstructions of volumetric, gradient-echo magnetic resonance (MR) images were tested. The brains of eight healthy adult volunteers and one cadaver were imaged in both the coronal and sagittal planes to yield a set of 128 1.5-2.0-mm-thick contiguous sections. 3D reconstructions of the brain cerebral cortical surfaces were obtained with computer software. Location and distance measurements of surface sulci were repeated on each reconstructed image. The same structures in the cadaver brain were independently measured with a 3D electromagnetic digitizer to validate the results of the 3D MR imaging method. All measurements from reconstructed images had high repeatability, and there were no statistically significant differences between measurement trials. The accuracy of measurements with 3D MR imaging was also good; the mean difference between digitizer and 3D MR measurements for sulcal lengths was 0.81 cm (average, 5.45-12.9 cm).

Adult↗
PubMed1991

Multiplanar quantitative computed tomography for bone mineral analysis in dogs.

The purpose of this study was to determine the precision and accuracy of quantitative computed tomography bone mineral analysis in dogs in coronally reconstructed images. Nonhomogeneous tissues, such as bones with fractures or deformities, may be better analyzed if multiplanar reconstruction of the transaxial data could be performed without degradation of information. Our analysis demonstrated that coronal reconstruction of quantitative-computed tomography data was precise (1.2 to 4.7%) and accurate (1.3 to 7.5%) in vitro. The technique displays high-quality images, which can be analyzed at any location within the volume scanned. Quantitative computed tomography of canine osteotomy healing in vivo accurately determined bone mineral density of selected regions of interest. Bone mineral density correlated highly with calcium content of the tissue (R2 = 0.76, P less than 0.0001).

Animals↗
PubMed1991

A software system for interactive and quantitative visualization of multidimensional biomedical images.

A comprehensive software system called ANALYZE has been developed which permits detailed investigation and evaluation of 3-D biomedical images. The software can be used with any 2-D or 3-D imaging modality, including x-ray computed tomography, radionuclide emission tomography, ultrasound tomography, magnetic resonance imaging and both light and electron microscopy. The package is unique in its synergistic integration of fully interactive modules for direct display, manipulation and measurement of multidimensional image data. Several original algorithms are included which improve image display efficiency and quality. One of the most versatile and powerful algorithms is interactive volume rendering, which is optimized to be fast without compromising image quality. An important advantage of this technique is to display 3-D images directly from the original data and to provide on-the-fly combinations of selected image transformations and/or volume set operations (union, intersection, difference, etc.). The inclusion of a variety of interactive editing and quantitative mensuration tools significantly extends the usefulness of the software. Any curvilinear path or region-of-interest can be manually specified and/or automatically segmented for numerical determination and statistical analyses of distances, areas, volumes, shapes, densities and textures. ANALYZE is written entirely in "C" and runs on several standard UNIX workstations. It is being used in a variety of applications by over 40 institutions around the world, and has been licensed by Mayo to several imaging companies. The software architecture permits systematic enhancements and upgrades which has fostered development of a readily expandable package. ANALYZE comprises a powerful "visualization workshop" for rapid prototyping of specific application packages, including applications to interactive surgery simulation and radiation treatment planning. ANALYZE offers the potential to accurately and reproducibly examine, from images, the structure and function of any cell, tissue, limb, organ or organ system of the body, much like a surgeon or pathologist might do in real life, but entirely non-invasively, without pain or destruction of tissue. These capabilities promise exciting new insights into the basic processes of life, and major advances in health care delivery through improved diagnosis and treatment of disease.

Computer Graphics↗
PubMed1990

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.

Computer Simulation↗
PubMed1990

EEG scalp electrode projection onto three-dimensional surface rendered images of the brain.

A technique is described for generating magnetic resonance-based, surface rendered images of the brain with electroencephalographic (EEG) scalp electrode positions projected onto the cortical surface. This technique (EEG electrode projection) was used in 10 patients who subsequently underwent surgery for medically intractable frontal lobe epilepsy. In most cases of intractable epilepsy, successful surgery entails the resection of electrophysiologically abnormal cortical tissue rather than an identifiable mass lesion. EEG electrode projection is a unique and useful surgical tool because it provides images that spatially correlate the surface anatomy of the brain and the electrophysiologic abnormality recorded at the scalp. Excellent correlation was found between cortical topography delineated by the surface rendered images and cortical anatomy at surgery. Agreement between EEG electrode projection and electrocorticography as to the location of the electrophysiologic abnormality increases confidence that appropriate cortical areas have been identified for resection. The technique provides new and unique insight into important anatomic-electrophysiologic relationships and aids in formulation of surgical strategy.

Adult↗
PubMed1990

Three-dimensional reconstruction of the temporal bone.

Study of the complex anatomy and pathology of the temporal bone has traditionally used microscopy which permits analysis in only two dimensions. Recent advances in bioimaging technology have permitted visualization and reconstruction of computed tomography images in three dimensions. We have developed a technique that applies this technology in the imaging and reconstruction of human temporal bones. Data taken from serial histologic sections of the temporal bone are entered into a computer. The sections are edited and, through the use of specially developed software, a realistic three-dimensional reconstruction is produced. The reconstructed image can be rotated along any of three axes, and structures within the temporal bone can be isolated for more detailed analysis. Applications for the study of pathologic conditions of the temporal bone will be discussed.

Adult↗