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Biomedical subjects

R L Galloway

Publications and source records attributed to R L Galloway.

27 records · Page 2Linked to original sources
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↗
PubMed1989

The optical measurement of 1,2-propanediol for the determination of lung capillary permeability surface area.

A technique has been developed which allows for the optical measurement of the concentration-time relationship for a diffusion-limited material in indicator dilution studies. The material, 1-2 propanediol, is used as a probe of the permeability of capillaries in the lung. Comparisons between standard radioisotope measurements and the optical measurements are provided and show excellent agreement. The optical method represents an improvement over the standard radioisotope method in that it provides the same data at lower cost, lower risk, and without the delay required by the radiographic methods.

Animals↗
PubMed1989

Magnetic resonance and computed tomographic image-directed stereotaxy for animal research.

Current stereotactic frames for animal experimentation presume normal intracranial anatomy for atlas-directed probe placement. This is an invalid assumption for animal brain tumor models, where distortions of cerebral anatomy make image-directed stereotaxy necessary. To address this need, an accurate and reproducible magnetic resonance and computed tomographic compatible image-directed stereotactic apparatus for animal experimentation is presented.

Animals↗
PubMedDate not supplied

Sulfhemoglobinated erythrocytes as an optical intravascular tracer in the lung.

Sulfhemoglobinated erythrocytes (SHb-RBC's) were examined for utility as an optical multiple indicator dilution tracer in lung studies. A device was developed to measure this tracer optically in flowing blood. Arterial blood was sampled from cannulated, anesthetized dogs and pumped through the device that measured the optical density (OD) of blood at 620 nm. This system was calibrated for increasing SHb-RBC concentrations using an unsteady-state indicator dilution procedure. Areas under optical density (delta OD) profiles were well correlated with injected SHb-RBC volumes using linear regression (r2 > 0.9). This linearity was independent of blood oxygenation, hematocrit, or pH. In vivo lung indicator dilution studies in the intact dog were performed and compared to radioisotope indicator studies using 51Cr labeled erythrocytes. Coefficient of variation (CV) between the two curves was 0.065 under baseline conditions, 0.085 for studies performed during hypoxia, and 0.073 after pH was lowered. We conclude that this device linearly measured SHb-RBC content in whole blood and that SHb-RBC is as accurate a lung indicator dilution tracer as 51Cr-erythrocytes.

Animals↗
PubMedDate not supplied

Factors affecting perceived tumor volumes in magnetic resonance imaging.

Irregularly structured brain tumors, such as glioblastomas, challenge attempts to visualize and quantify their three dimensional structure. Magnetic resonance imaging (MRI) represents one tool for attempting to noninvasively track tumor size. MR images demonstrate widely varying perceived tumor margins. In addition, adjunct therapies, such as the administration of steroids, greatly affect the volumes perceived in images formed by certain pulse sequences. In this study tumors were grown in 15 dogs and the tumor size tracked for a period of time. The dogs were placed on dexamethasone for a week and another series of scans was obtained. No other therapies were provided. The data for visualized tumor size are provided for T1, T2, and proton density. Weighted images are provided and the relationships between the scans are discussed.

Animals↗
PubMedDate not supplied

Growth factors in the tumorigenicity of a brain tumor cell line.

We studied a virally induced canine gliosarcoma brain tumor cell line capable of producing brain tumors in vivo following intracerebral inoculation of the cells into the brains of adult mongrel dogs. Cloned populations from this cell line differed in their ability to produce brain tumors in vivo. In vitro transforming growth factor-beta secretion by each clone correlated with in vivo tumorigenicity. Mitogenic activity like that produced with platelet-derived growth factor was also secreted by each clone and correlated with in vivo tumorigenicity. Epidermal growth factor and transforming growth factor-alpha production was not detected in any of the clones of canine gliosarcoma cells. Although only some of the brain tumor cell clones were able to produce tumors in immunologically normal dogs, brain tumors were produced in all dogs pretreated with cyclosporin and in all "nude" mice, suggesting that tumor immunology plays an important role in this brain tumor model. In vitro cloning efficiency of each brain tumor cell clone also correlated with in vivo tumorigenicity. We postulate that transforming growth factor-beta may both stimulate brain tumor cell growth and inhibit host antitumor immune surveillance.

Animals↗
PubMedDate not supplied

Comparison of projection algorithms used for the construction of maximum intensity projection images.

OBJECTIVE: Four methods of producing maximum intensity projection (MIP) images were studied and compared. MATERIALS AND METHODS: Three of the projection methods differ in the interpolation kernel used for ray tracing. The interpolation kernels include nearest neighbor interpolation, linear interpolation, and cubic convolution interpolation. The fourth projection method is a voxel projection method that is not explicitly a ray-tracing technique. The four algorithms' performance was evaluated using a computer-generated model of a vessel and using real MR angiography data. The evaluation centered around how well an algorithm transferred an object's width to the projection plane. RESULTS: The voxel projection algorithm does not suffer from artifacts associated with the nearest neighbor algorithm. Also, a speed-up in the calculation of the projection is seen with the voxel projection method. Linear interpolation dramatically improves the transfer of width information from the 3D MRA data set over both nearest neighbor and voxel projection methods. Even though the cubic convolution interpolation kernel is theoretically superior to the linear kernel, it did not project widths more accurately than linear interpolation. A possible advantage to the nearest neighbor interpolation is that the size of small vessels tends to be exaggerated in the projection plane, thereby increasing their visibility. CONCLUSION: The results confirm that the way in which an MIP image is constructed has a dramatic effect on information contained in the projection. The construction method must be chosen with the knowledge that the clinical information in the 2D projections in general will be different from that contained in the original 3D data volume.

Algorithms↗
PubMedDate not supplied

Laser system for measuring small changes in plasma tracer concentrations.

The authors developed a laser-diode system that can be used for on-line optical concentration measurements in physiologic systems. Previous optical systems applied to whole blood have been hampered by artifacts introduced by red blood cells (RBCs). The system introduced here uses a commercially available filter cartridge to separate RBCs from plasma before plasma concentration measurements are made at a single wavelength. The filtering characteristics of the Cellco filter cartridge (#4007-10, German-town, MD) were adequate for use in the on-line measurement system. The response time of the filter cartridge was less than 40 seconds, and the sieving characteristics of the filter for macromolecules were excellent, with filtrate-to-plasma albumin ratios of 0.98 +/- 0.11 for studies in sheep and 0.94 +/- 0.15 for studies in dogs. The 635-nm laser diode system developed was shown to be more sensitive than the spectrophotometer used in previous studies (Klaesner et al., Annals of Biomedical Engineering, 1994; 22, 660-73). The new system was used to measure the product of filtration coefficient (Kfc) and reflection coefficient for albumin (delta f) in an isolated canine lung preparation. The delta fKfc values [mL/(cmH2O.min.100 g dry lung weight)] measured with the laser diode system (0.33 +/- 0.22) compared favorably with the delta fKfc obtained using a spectrophotometer (0.27 +/- 0.20) and with the Kfc obtained using the blood-corrected gravimetric method (0.32 +/- 0.23). Thus, this new optical system was shown to accurately measure plasma concentration changes in whole blood for physiologic levels of Kfc. The same system can be used with different optical tracers and different source wavelengths to make optical plasma concentration measurements for other physiologic applications.

Analysis of Variance↗