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Biomedical subjects

D Dey

Publications and source records attributed to D Dey.

At least 19 recordsLinked to original sources
PubMed2000

3-D image guidance for minimally invasive robotic coronary artery bypass.

BACKGROUND: The introduction of a robot-assisted microsurgical system has made endoscopic coronary artery bypass grafting (ECABG) possible. Despite the success of this approach, surgeons still require better visualization tools for pre-surgical planning and intra-operative image guidance. Such visualization tools could, for example, assist in the placement of thoracic ports to acquire optimum access to the target vessels. In this paper we discuss the essential steps toward image-guided completely endoscopic coronary bypass surgery with robot assistance, and we present our preliminary efforts toward the development of a three-dimensional (3-D) virtual cardiac surgical planning platform (VCSP) for ECABG. METHODS: Preoperative 3-D images of the thorax acquired with computed tomography and electrocardiogram-gated magnetic resonance imaging are imported into VCSP. Using VCSP, a user may interactively visualize and manipulate the simulated thoracic ports in 3-D within the reconstructed thoracic region. We have also implemented a virtual endoscope to simulate the endoscopic view observed by the surgeon during the operation. Once the port placements for optimal access to the target vessels are determined, the positions of the simulated tools can be recorded and marked on the patient to specify the positions for port incisions. RESULTS: A static thorax phantom was used to verify the port placements obtained from VCSP simulations. The angles and the distances between the ports, the endoscope and the markers that were placed on the surface of the phantom were measured, and the results were compared with those obtained from simulation. The physical measured distances and angles agreed with the simulated results with average errors of 4 mm and 2 degrees, respectively. CONCLUSIONS: The VCSP image-guided surgical system allows a surgeon to visualize a patient's thorax in a 3-D interactive environment for planning surgical procedures, and to determine the optimum port placement based on preoperative 3-D images. However, during an operation, the positions and orientation of the heart and the coronary arteries are changed from their corresponding locations in the preoperative images due to carbon-dioxide insufflation, lung deflation, and dynamic motions of the beating heart. One of our future goals of this project is the use of mathematical models that correct for these changes so that our system could be applied to intra-operative image guidance.

Adult↗
PubMed1999

Problems in predicting cell damage from bubble bursting.

The question is addressed as to whether observed parameter(s) characterizing single bubble burst (bubble jet height and speed) can be used to predict cell damage in sparged animal cell cultures. Bubble burst profiles are examined in the presence of realistic concentrations of fetal calf serum (FCS) or Pluronic F-68 using a high-speed video technique. The damage to TBC3 hybridoma cells from bubble sparging, characterized as a first-order decline, is reduced by even very small concentrations of both FCS and Pluronic F-68, but neither single bubble burst parameters nor surface properties give usable correlations with death rate constants. &copy 1999 John Wiley & Sons, Inc.

Bioreactors↗
PubMed1999

Automatic three-dimensional multimodality registration using radionuclide transmission CT attenuation maps: a phantom study.

UNLABELLED: Coregistration of images from a single subject, acquired by different modalities, is important in clinical diagnosis, surgery and therapy planning. The purpose of this study was to evaluate, using a physical torso phantom, a novel, fully automated method for three-dimensional image registration of CT and SPECT, using radionuclide transmission (RNT) attenuation maps. METHODS: We obtained CT scans and SPECT scans paired with RNT maps of an anthropomorphic cardiac phantom. RNT attenuation maps were acquired using an uncollimated 99mTc-filled flood source. RNT and SPECT scans were acquired in the same spatial orientation (usual clinical practice in nonuniform attenuation correction). In addition, CT attenuation maps (CTMAPs) for 99mTc SPECT were generated from CT by linear energy scaling. RNT maps were registered to CT and CTMAPs by iterative simplex minimization of count difference and uniformity index (sum of RNT map intensity variances corresponding to each intensity level in the CT volume). In each iteration, three shifts and three angles were adjusted. To register SPECT to CT, we applied the RNT transformation parameters to SPECT. RESULTS: RNT maps could be registered to CT and CTMAP images using both criteria. The average three-dimensional distance between landmark and automated registration was 2.5 +/- 1.2 mm for count difference and 3.3 +/- 1.3 mm for uniformity index. The three-dimensional reproducibility errors were 1.2 +/- 0.7 mm for count difference, 2.1 +/- 0.5 mm for uniformity index and 2.3 +/- 1.0 mm for manual marker registration. The minimization of uniformity index was robust when up to 50% CT or RNT slices were missing and was not affected significantly (<2 mm) by realistic variation in CT values (+/- 12 Hounsfield units). CONCLUSION: In addition to typical use in nonuniform attenuation correction, RNT maps can be used for fully automated three-dimensional registration of SPECT to CT. Such registration is not affected by features and quality of SPECT images and avoids difficulties associated with fiducial markers. Our method can be applied to SPECT-CT registration of various organs, such as brain, heart, lungs, breasts and abdomen, including oncological scans.

Image Processing, Computer-Assisted↗
PubMed1998

Cross-linking of selected residues in the N- and C-terminal domains of Escherichia coli protein L7/L12 to other ribosomal proteins and the effect of elongation factor Tu.

Five different variants of protein L7/L12, each with a single cysteine substitution at a selected site, were produced, modified with 125I-N-[4-(p-azidosalicylamido)-butyl]-3-(2'-pyridyldithio)propion amide, a radiolabeled, sulfhydryl-specific, heterobifunctional, cleavable photocross-linking reagent that transfers radiolabel to the target molecule upon reduction of the disulfide bond. The proteins were reconstituted with core particles depleted of wild type L7/L12 to yield 70 S ribosomes. Cross-linked molecules were identified and quantified by the radiolabel. No cross-linking of RNA was detected. Two sites in the dimeric N-terminal domain, Cys-12 and Cys-33, cross-linked strongly to L10 and in lower yield to L11 but to no other proteins. The three sites in the globular C-terminal domain all cross-linked strongly to L11 and, in lower yield, to L10. Weaker cross-linking to 50 S proteins L2 and L5 occurred from all three C-terminal domain locations. The 30 S ribosomal proteins S2, S3, S7, S14, S18 were also cross-linked from all three of these sites. Binding of the ternary complex [14C]Phe-tRNA-elongation factor Tu.guanyl-5'-yl imidodiphosphate) but not [14C]Phe-tRNA.elongation factor Tu.GDP.kirromycin increased labeling of L2, L5, and all of the 30 S proteins. These results imply the flexibility of L7/L12 and the transient proximity of three surfaces of the C-terminal domain with the base of the stalk, the peptidyl transferase domain, and the head of the 30 S subunit.

Amino Acid Substitution↗
PubMed1998

Comparison of ordered subsets expectation maximization and Chang's attenuation correction method in quantitative cardiac SPET: a phantom study.

Photon attenuation is one of the primary causes of artifacts in cardiac single photon emission tomography (SPET). Several attenuation correction algorithms have been proposed. The aim of this study was to compare the effect of using the ordered subsets expectation maximization (OSEM) reconstruction algorithm and Chang's non-uniform attenuation correction method on quantitative cardiac SPET. We performed SPET scans of an anthropomorphic phantom simulating normal and abnormal myocardial studies. Attenuation maps of the phantom were obtained from computed tomographic images. The SPET projection data were corrected for attenuation using OSEM reconstruction, as well as Chang's method. For each defect scan and attenuation correction method, we calculated three quantitative parameters: average radial maximum (ARM) ratio of the defect-to-normal area, maximum defect contrast (MDC) and defect volume, using automated three-dimensional quantitation. The differences between the two methods were less than 4% for defect-to-normal ARM ratio, 19% for MDC and 13% for defect volume. These differences are within the range of estimated statistical variation of SPET. The calculation times of the two methods were comparable. For all SPET studies, OSEM attenuation correction gave a more correct activity distribution, with respect to both the homogeneity of the radiotracer and the shape of the cardiac insert. The difference in uniformity between OSEM and Chang's method was quantified by segmental analysis and found to be less than 8% for the normal study. In conclusion, OSEM and Chang's attenuation correction are quantitatively equivalent, with comparable calculation times. OSEM reconstruction gives a more correct activity distribution and is therefore preferred.

Algorithms↗
PubMed1995

The hinge region of Escherichia coli ribosomal protein L7/L12 is required for factor binding and GTP hydrolysis.

A variant form of Escherichia coli ribosomal protein L7/L12 that lacked residues 42 to 52 (L7/L12: delta 42-52) in the hinge region was shown previously to be completely inactive in supporting polyphenylalanine synthesis although it bound to L7/L12 deficient core particles with the normal stoichiometry of four copies per particle (Oleinikov AV, Perroud B, Wang B, Traut RR (1993) J Biol Chem, 268, 917-922). The result suggested that the hinge confers flexibility that is required for activity because the resulting bent conformation allows the distal C-terminal domain to occupy a location on the body of the large ribosomal subunit proximal to the base of the L7/L12 stalk where elongation factors bind. Factor binding to the hinge-truncated variant was tested. As an alternative strategy to deleting residues from the hinge, seven amino acid residues within the putative hinge region were replaced by seven consecutive proline residues in an attempt to confer increased rigidity that might reduce or eliminate the bending of the molecule inferred to be functionally important. This variant, L7/L12:(Pro)7, remained fully active in protein synthesis. Whereas the binding of both factors in ribosomes containing L7/L12:delta 42-52 was decreased by about 50%, there was no loss of factor binding in ribosomes containing L7/L12:(Pro)7, as predicted from the retention of protein synthesis activity. The factor:ribosome complexes that contained L7/L12:delta 42-52 had the same low level of GTP hydrolysis as the core particles completely lacking L7/L12 and EF-G did not support translocation measured by the reaction of phe-tRNA bound in the A site with puromycin. It is concluded that the hinge region is required for the functionally productive binding of elongation factors, and the defect in protein synthesis reported previously is due to this defect. The variant produced by the introduction of the putative rigid Pro7 sequence retains sufficient flexibility for full activity.

Amino Acid Sequence↗
PubMed1994

Ultrastructural changes in HeLa cells associated with enteroadherent Escherichia coli isolated from infants with diarrhoea in Calcutta.

In the present study, we compared two enteroadherent Escherichia coli (EAEC) not belonging to the classical enteropathogenic O serotypes with respect to their attachment to and invasion of HeLa cells. Depending on the pattern of adherence to HeLa cells, one of the strains showed localized adherence (LA), and the other showed diffuse adherence (DA). Electronmicroscopic study showed that LA-EAEC produced the intimate attaching and effacing lesions and intracellular penetration in cultured HeLa cells. In contrast, DA-EAEC exhibited fimbrially-mediated adhesion to HeLa cells. Both LA and DA possessed morphologically distinct fimbriae. LA-EAEC expressed rod-like fimbriae, whereas fibrillar fimbriae were observed in DA strain. Ultrastructural study showed that the mechanisms of invasion by both the strains were different. LA-EAEC strains invaded the cells after pedestal formation and were enclosed in membrane-bound vacuoles. In contrast, DA-EAEC showed no membrane dissolution and pedestal formation during internalization of HeLa cells. A carefully controlled study will be necessary to establish the pathogenic role of DA-EAEC in diarrhoea.

Bacterial Adhesion↗
PubMed1990

[Waldenström's hyperglobulinemic purpura. Apropos of a case].

The authors report the case of a thirteen-year-old girl who developed clinical manifestations suggestive of Schönlein-Henoch purpura and in whom biologic tests outruled this condition and led to the diagnosis of Waldenström hyperglobulinemic purpura. Investigations illustrated the immunologic nature of this disease, outruled an underlying disease and established the diagnosis of primary hyperglobulinemic purpura.

Adolescent↗
PubMed1990

[Nesidioblastosis. Apropos of 12 new cases].

Two new cases of diffuse hyperplasia of the pancreas are reported. This infrequent condition is caused by intermittent and variable insulin hypersecretion. The hyperinsulinism is responsible for severe, lasting and intractable hypoglycemia that causes seizures and mental retardation. Onset usually occurs in the neonatal period. The diagnosis of hyperinsulinism rests on four criteria: the presence of increased insulin levels in the face of hypoglycemia, the low urinary excretion of ketone bodies during hypoglycemic episodes, the need for more than 15/mg/kg/min glucose to maintain the serum glucose level above 2 mmol/l, and a positive response to glucagon. The topographic diagnosis is often disappointing. Medical treatment of the hypoglycemia with diazoxide is a transient measure. Subtotal pancreatectomy is indispensable. Postoperative results are variable. Insulin deficiency diabetes mellitus is common and unusual in that insulin induces an exaggerated response. Recovery can be observed. If hypoglycemia recurs, diazoxide is often effective.

Female↗
PubMed1989

Precocious desynapsis of XY-bivalent in mouse germinal cells: influence of mitomycin C on tumour-bearing and normal mice.

A comparative study on the cytotoxic potential of anticancer-antibiotic mitomycin C has been made on tumour-bearing and normal mice considering precocious desynapsis of sex bivalent as parameter. The study indicates a strikingly differential effect of the drug on the phenomenon in two different types of mice. The administration of mitomycin C at therapeutic dose although enhances the frequency of precocious desynapsis of XY-bivalent in non-tumour (normal) mice to a significant extent (compared to control), the same drug at the same dose fails to produce a similar effect on tumour-bearing specimens. Discussions have been made on: (i) the probable cause for this differential effect, (ii) the mechanism of mitomycin action on precocious desynapsis of sex bivalent and, (iii) the possible significance of the findings in relation to cancer chemotherapy.

Animals↗