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Biomedical subjects

C R Crawford

Publications and source records attributed to C R Crawford.

18 recordsLinked to original sources
PubMed1992

Minimum scan speeds for suppression of motion artifacts in CT.

Cardiac and ventilatory motions cause artifacts at chest computed tomography (CT). To determine how short the scan times on third-generation units must be to avoid such artifacts, motion was measured with fast and ultrafast CT scans. Minimum detectable motion was then determined. The longest scan time that avoided a barely perceptible artifact was calculated by dividing the minimum detectable motion by the peak physiologic velocity. The posterior left ventricular wall moved at a maximum velocity of 52.5 mm/sec, necessitating a scan time of 19.1 msec or less to avoid artifact. Lung vessels near the heart moved at 40.5 mm/sec for a scan time of 24.7 msec or less. During quiet breathing, pulmonary vessels moved at 10.7 mm/sec for a scan time of 93.5 msec or less. The authors conclude that the shortest scan time on third-generation units (0.6 second) cannot prevent all artifacts arising from motion in the chest. Even ultrafast scan times (50 msec) are not short enough to eliminate artifacts on these units. Thus, reduction of motion artifacts will require techniques other than fast scanning.

Artifacts↗
PubMed1991

Sodium-dependent, concentrative nucleoside transport in Walker 256 rat carcinosarcoma cells.

Nucleoside transport in Walker 256 cells was reexamined using formycin B, a nonmetabolized analog of inosine. In the presence of dipyridamole to inhibit the equilibrative (facilitated diffusion) transporter previously described in these cells, the initial rate of uptake of 1 microM formycin B was 10-fold greater in Na(+)-containing medium than in Na(+)-free medium. In the presence of Na+ and dipyridamole the intracellular concentration of formycin B exceeded that in the medium within one min and was 6-fold greater than that of the medium by 5 min. Na(+)-dependent transport of formycin B was inhibited by low concentrations of inosine, but not thymidine. Furthermore, Na(+)-dependent transport of uridine, but not thymidine, was apparent in the presence of dipyridamole. These data indicate that Walker 256 cells have, in addition to the previously described equilibrative transporter, a concentrative nucleoside transporter. The specificity of this transporter appears to correspond to one of the two Na(+)-dependent transporters previously described in mouse intestinal epithelial cells.

Animals↗
PubMed1991

Survival of an upper lip aesthetic complex using arterial reanastomosis only.

Venous congestion after microvascular replantation remains a formidable problem even under ideal circumstances. The patient reported is a young woman with a traumatically avulsed upper lip aesthetic complex. Blood flow was reestablished using microanastomosis of the labial artery, however, no veins of adequate size could be recovered. With systemic administration of heparin, allowing the flap to bleed freely in addition to the use of medicinal leeches, we were able to salvage an avulsed upper lip aesthetic complex with the use of a single arterial microanastomosis. This patient report exemplifies alternative methods used in dealing with venous inadequacy in a composite replant.

Adult↗
PubMed1990

Isolation and characterization of an L1210 cell line retaining the sodium-dependent carrier cif as its sole nucleoside transport activity.

Nucleoside permeation across mammalian cell membranes is complex with at least four distinct transporters known. Two of these (es and ei) are equilibrative (facilitated diffusion) carriers that have been studied is considerable detail. The other two (cif and cit) are concentrative, Na(+)-dependent carriers. A major obstacle to the characterization of the latter two mechanisms has been the lack of suitable model systems expressing only a single nucleoside transport activity. The present study describes the isolation of a cell line that has cif as its sole nucleoside transporter. L1210/MC5-1 cells, which have es and cif transport activity, were mutagenized and plated in soft agar containing two cytotoxic nucleosides (tubercidin (7-deazaadenosine) and cytosine arabinoside) that are substrates for es but not cif. A clonal line (L1210/MA-27.1) was isolated which retained the capacity for Na(+)-dependent [3H]formycin B transport but was unable to transport [3H]thymidine, a substrate for es but not cif. Failure of the mutant to transport thymidine was also demonstrated by the inability of thymidine (with adenine as a purine source) to rescue these cells from methotrexate toxicity. Furthermore, the mutant lacked nitrobenzylthioinosine (NBMPR) binding activity (an integral part of the es transporter) as demonstrated by reversible NBMPR binding and photoaffinity labeling with [3H]NBMPR. Loss of es transport activity was also demonstrated by the failure of NBMPR to affect the toxicity of 2-chlorodeoxyadenosine (IC50 approximately 30 nM) in L1210/MA27.1 cells. In contrast, NBMPR decreased the IC50 for 2-chlorodeoxyadenosine from 100 to 30 nM in the parental L1210/MC5-1 cell line. These results are consistent with the mechanism of NBMPR potentiation of 2-chlorodeoxyadenosine toxicity in L1210 cells being a blockade of efflux via es while the nucleoside is pumped into the cells by the concentrative cif carrier.

2-Chloroadenosine↗
PubMed1990

Nucleoside transport in L1210 murine leukemia cells. Evidence for three transporters.

L1210 murine leukemia cells have two nucleoside transport activities that differ in their sensitivity to nitrobenzylmercaptopurine riboside (NBMPR). This study re-examines NBMPR-insensitive nucleoside transport in these cells and finds that it is mediated by two components, one Na(+)-dependent and the other Na(+)-independent. A mutant selected previously for loss of NBMPR-insensitive transport lacks only the Na(+)-independent activity. When NBMPR is used to block efflux via the NBMPR-sensitive transporter, uptake of formycin B (a nonmetabolized analog of inosine) is concentrative in both the parental and mutant cells, but the intracellular concentration of the nucleoside is 5-fold lower in the parental cells. Decreased accumulation of formycin B in the parental cells is due to efflux of the nucleoside via the NBMPR-insensitive, Na(+)-independent transporter that the mutant lacks. The Na(+)-dependent transporter appears to accept most purine, but not pyrimidine, nucleosides as substrates. Two exceptions are uridine, a good substrate, and 7-deazaadenosine, a poor substrate. In contrast, all of the nucleosides tested are substrates for the Na(+)-independent transporter. We conclude that L1210 cells have three distinct nucleoside transporters and that the specificity of the Na(+)-dependent transporter is similar to that of one of the two Na(+)-dependent nucleoside transporters seen in mouse intestinal epithelial cells.

Affinity Labels↗
PubMed1990

Identification and reconstitution of the nucleoside transporter of CEM human leukemia cells.

The major nucleoside transporter of the human T leukemia cell line CEM has been identified by photoaffinity labeling with the transport inhibitor nitrobenzylmercaptopurine riboside (NBMPR). The photolabeled protein migrates on SDS-PAGE gels as a broad band with a mean apparent molecular weight (75,000 +/- 3000) significantly higher than that reported for the nucleoside transporter in human erythrocytes (55,000) (Young et al. (1983) J. Biol. Chem. 258, 2202-2208). However, after treatment with endoglycosidase F to remove carbohydrate, the NBMPR-binding protein in CEM cells migrates as a sharp peak with an apparent molecular weight (47,000 +/- 3000) identical to that reported for the deglycosylated protein in human erythrocytes (Kwong et al. (1986) Biochem. J. 240, 349-356). It therefore appears that the difference in the apparent molecular weight of the NBMPR-sensitive nucleoside transporter between the CEM cell line and human erythrocytes is a result of differences in glycosylation. The NBMPR-binding protein from CEM cells has been solubilized with 1% octyl glucoside and reconstituted into phospholipid vesicles by a freeze-thaw sonication technique. Optimal reconstitution of uridine transport activity was achieved using a sonication interval of 5 to 10 s and lipid to protein ratios of 60:1 or greater. Under these conditions transport activity in the reconstituted vesicles was proportional to the protein concentration and was inhibited by NBMPR. Omission of lipid or protein, or substitution of a protein extract prepared from a nucleoside transport deficient mutant of the CEM cell line resulted in vesicles with no uridine transport activity. The initial rate of uridine transport, in the vesicles prepared with CEM protein, was saturable with a Km of 103 +/- 11 microM and was inhibited by adenosine, thymidine and cytidine. The Km for uridine and the potency of the other nucleosides as inhibitors of uridine transport (adenosine greater than thymidine greater than cytidine) were similar to intact cells. Thus, although the nucleoside transporter of CEM cells has a higher molecular weight than the human erythrocyte transporter, it exhibits typical NBMPR-sensitive nucleoside transport activity both in the intact cell and when reconstituted into phospholipid vesicles.

Affinity Labels↗
PubMed1990

The role of intraarterial vasodilators in the treatment of inadvertent intraarterial injection injuries.

Inadvertent arterial injections, both in cases of drug addiction and in iatrogenic situations, often result in significant loss of tissue and, eventually, loss of function distal to the injection site. Previous experimental studies regarding the effectiveness of agents to reverse vasospasm have been inconclusive. A recent clinical report, however, suggested that intraarterial injection of reserpine was affective in limiting tissue necrosis. This experiment was designed to study the affect of intraarterially injected reserpine and tolazoline hydrochloride in a rabbit ear model of necrosis following intraarterial injection of pentothal. Six groups of 5 rabbits each were studied. Animals in Group 1 received intraarterial saline injections. Animals in Group 2 received intraarterial pentothal. Animals in Group 3 received intraarterially injected pentothal plus intraarterial reserpine 30 minutes later. Animals in Group 4 received intraarterially injected pentothal plus intraarterial tolazoline 30 minutes later. Animals in Group 5 received intraarterially injected pentothal plus intraarterially injected reserpine and intraarterially injected tolazoline both administered immediately. Animals in Group 6 received intraarterially injected pentothal plus intraarterially injected reserpine and intraarterially injected tolazoline, both administered 30 minutes later. Results showed no significant difference in the amount of tissue necrosis between treated and untreated animals. We conclude that the use of intraarterial spasmolytic agents has no effect on the course of tissue necrosis after inadvertent intraarterial injections.

Animals↗
PubMed1985

Antigen stripping from the nematode epicuticle using the cationic detergent cetyltrimethylammonium bromide (CTAB).

The cuticular antigens of adult Nematospiroides dubius were selectively removed using the cationic detergent cetyltrimethylammonium bromide (CTAB). Nonionic, zwitterionic or anionic detergents were ineffective in comparison. The biochemical profile of the antigens removed by detergent was identical to that of surface antigens removed by homogenization, with the added advantage that detergent-stripped antigens lacked many of the background antigens (excretory/secretory--ES and somatic) seen in homogenates. In addition, the detergent was shown to act in a non-invasive manner as electron micrographs failed to reveal any gross damage to the nematode outer cuticle. The observed selective release of significant quantities of relatively clean nematode surface antigen by CTAB in a non-invasive or destructive manner provides the impetus for definitive studies on the relevance of surface antigens (in the absence of ES or somatic antigens) to the overall immunogenicity of this and other parasites.

Animals↗
PubMed1984

Use of zwitterionic detergent for the preparation of an influenza virus vaccine. 1: Preparation and characterization of disrupted virions.

The zwitterionic, Empigen BB an alkylbetaine based on a C12-C14 alcohol was shown to disrupt influenza A and B viruses in such a way as to retain the biological activity of the surface haemagglutinin (HA) and neuraminidase (NA) antigens. The optimal conditions required to obtain the maximum recovery of HA and NA activity from purified influenza X47 (H3N2) virus concentrate after treatment with Empigen, and the nature and the morphological appearance of the Empigen-treated preparations both before and following a sucrose density gradient purification step, are described. Matrix (M) protein was readily removed during purification, but nucleoprotein (NP) could not be separated from the surface protein activity.

Centrifugation, Density Gradient↗
PubMed1984

Use of a zwitterionic detergent for the preparation of an influenza virus vaccine: 2. Immunogenicity of Empigen-treated virus in animals.

The immunogenicity of zwitterionic detergent-disrupted influenza virus vaccine preparations, intact virus vaccine and vaccine preparations obtained by treatment of the intact virus with Triton-X 100 or cetyl trimethyl ammonium bromide (CTAB) was studied in hamsters and mice. In all experiments the intact, inactivated virus vaccine induced greater serum haemagglutination-inhibiting (HI) and neuraminidase-inhibiting (NI) antibody titres than the detergent-disrupted preparations. The serum HI antibody responses induced in hamsters and mice by Empigen-, Triton-, or CTAB-disrupted vaccines were similar, although more highly purified Empigen-disrupted preparations elicited marginally lower immune responses. In both animal species, all vaccine preparations afforded a similar degree of protection against homologous virus challenge.

Animals↗
PubMedDate not supplied

Reprojection using a parallel backprojector.

Reprojection is the process by which projections are produced from an image, such that if these projections are filtered and backprojected, they yield the original image. In computed tomography, applications of reprojection include its use in algorithms for iterative beam hardening correction, metal artifact removal, and streak suppression. However, because of the computational expense of reprojection, algorithms that employ this process have never been widely used. A method will be presented that enables an unmodified backprojector to be used as a reprojector. Because backprojectors are designed to exploit the parallelism in the backprojection algorithm, the time required to obtain reprojections is significantly reduced.

Humans↗
PubMedDate not supplied

Reconstruction for fan beam with an angular-dependent displaced center-of-rotation.

A convolutional backprojection algorithm is derived for a fan beam geometry that has an angular-dependent displacement in its center-of-rotation from the midline of the fan beam. In both x-ray computed tomography and single photon emission computed tomography, misalignment can occur when the mechanical center-of-rotation is not colinear with midline of the fan beam. In some cases the shift in the center-of-rotation is constant for every angle, whereas, in other cases it varies with angular position. Standard reconstruction algorithms, which directly filter and backproject the fan beam data without rebinning into parallel beam geometry, have been derived for a geometry having its center-of-rotation at the midline of the fan beam. However, in the case of any misalignment of the center-of-rotation, if these conventional reconstruction algorithms are used to reconstruct the fan beam projections, structured artifacts and a loss of resolution will result. Simulations are performed that illustrate these artifacts and demonstrate how the new algorithm corrects for this misalignment. A method for estimating the parameters of the fan beam geometry, including the angular-dependent shift in the center-of-rotation, is also described.

Algorithms↗
PubMedDate not supplied

Two algorithms for the three-dimensional reconstruction of tomograms.

Three-dimensional (3-D) surface reconstructions provide a method to view complex anatomy contained in a set of computed tomography (CT), magnetic resonance imaging (MRI), or single photon emission computed tomography tomograms. Existing methods of 3-D display generate images based on the distance from an imaginary observation point to a patch on the surface and on the surface normal of the patch. We believe that the normalized gradient of the original values in the CT or MRI tomograms provides a better estimate for the surface normal and hence results in higher quality 3-D images. Then two algorithms that generate 3-D surface models are presented. The new methods use polygon and point primitives to interface with computer-aided design equipment. Finally, several 3-D images of both bony and soft tissue show the skull, spine, internal air cavities of the head and abdomen, and the abdominal aorta in detail.

Algorithms↗
PubMedDate not supplied

Computed tomography scanning with simultaneous patient translation.

This paper deals with methods of reducing the total time required to acquire the projection data for a set of contiguous computed tomography (CT) images. Normally during the acquisition of a set of slices, the patient is held stationary during data collection and translated to the next axial location during an interscan delay. We demonstrate using computer simulations and scans of volunteers on a modified scanner how acceptable image quality is achieved if the patient translation time is overlapped with data acquisition. If the concurrent patient translation is ignored, structured artifacts significantly degrade resulting reconstructions. We present a number of weighting schemes for use with the conventional convolution/backprojection algorithm to reduce the structured artifacts through the use of projection modulation using the data from individual and multiple slices. We compare the methods with respect to structured artifacts, noise, resolution and to patient motion. Review of preliminary results by a panel of radiologists indicates that the residual image degradation is tolerable for selected applications when it is critical to acquire more slices in a patient breathing cycle than is possible with conventional scanning.

Algorithms↗
PubMedDate not supplied

Estimation of geometrical parameters and collimator evaluation for cone beam tomography.

A method is presented for estimating the geometrical parameters for a cone beam detector geometry from the coordinates of the centroid of a projected point source sampled over 360 degrees. Nonlinear expressions are derived for the coordinates of the centroids in terms of the geometrical parameters which include: the two-dimensional coordinates of the projection of the center of rotation onto the detector image plane; the focal length; the distance from the focal point to the center of rotation; and the spatial coordinates of the point source itself. Experimental data were obtained using a rotating gamma camera with a symmetrically converging collimator. The Marquardt algorithm was used to estimate the parameters for this particular cone beam geometry. The method was able to estimate the geometrical parameters and evaluate the accuracy of the collimator construction.

Evaluation Studies as Topic↗