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Biomedical subjects

A Jackson

Publications and source records attributed to A Jackson.

At least 145 records · Page 8Linked to original sources
PubMed1999

Use of single-slice thick slab phase-contrast angiography for the diagnosis of dural venous sinus thrombosis.

The aim of this study was to examine the reliability of single-slice phase-contrast angiography (SSPCA) as a rapid technique for the investigation of suspected dural venous sinus occlusion. Images were obtained on 25 normal volunteers to document the accuracy of SSPCA in the demonstration of slow flow states. Normal volunteers were imaged using sagittal and coronal SSPCA (slice thickness 13 cm, matrix 256 x 256, TR 14 ms, TE 7 ms, flip angle 20 degrees, peak velocity encoding rate 30 cm/s). Sinus patency and flow rate were confirmed by measurement of flow in the superior sagittal and transverse sinuses using quantified single-slice phase difference images. Imaging was performed in 50 patients undergoing routine brain scans in order to determine the optimal slice orientation for clinical use. Twenty-one patients with suspected dural venous sinus thrombosis were also investigated with SSPCA and the diagnosis confirmed by one or more alternative imaging techniques. Imaging time was 29 s per acquisition and image quality was good in all cases. Variations in dural sinus patency and flow in normal volunteers were accurately predicted by SSPCA (kappa = 0.92). Use of a single angulated slice (130 mm thick, para-sagittal image angled 30 degrees towards coronal and 30 degrees towards transverse) provided sufficient separation of right- and left-sided venous structures to allow use of a single projection. The presence and extent of sinus occlusions in 14 patients and the absence of thrombosis in 7 were accurately identified by SSPCA. Sensitivity and specificity in this limited study were both 100%. The SSPCA technique takes less than 30 s and provides a reliable and rapid technique for the diagnosis of dural venous sinus thrombosis.

Adult↗
PubMed1999

Relationship of components of an alcohol interoceptive stimulus to induction of desire for alcohol in social drinkers.

The ability of a low (0.2 g/kg) oral dose of ethanol to provide a drug discriminative stimulus was studied in young healthy human volunteers, who were social drinkers. Seventeen of 24 subjects acquired the discrimination following 10 trials in which they received aliquots of ethanol or of placebo drink (tonic water mixed with Tabasco sauce). In generalization studies, in which the dose of ethanol was varied, discrimination performance was dose dependent; doses greater than 0.05 g/kg gave rise to significant ethanol-appropriate responding. Concurrent estimates of the subjective effects of doses administered as discriminative stimuli revealed that two factors--taste and light-headedness--were associated with discrimination: at the training dose, 0.2 g/kg, although both the factors taste and light-headedness were significantly increased, only taste predicted discrimination performance. At lower doses, taste did not contribute to discrimination, but the subjective rating light-headedness correlated significantly with discrimination accuracy. Post hoc analyses of the influence of the amount of alcohol regularly drunk by the volunteers, on discrimination performance suggested light-headedness correlated with discriminative performance only in social drinkers drinking more than 20 units per week. In a second experiment, groups of "high" (mean 40 units per week) and "low" (mean 10 units per week) social drinkers were prospectively identified. Discrimination performance of 0.2 g/kg ethanol in orange juice vs. orange juice vehicle indicated that both groups were able to perform the discrimination following a single training trial, and that generalization curves over the range 0.05-0.2 g/kg were dose dependent, and not different between the groups. At the lowest dose, discrimination performance was predicted by taste, stimulation, and light-headedness in the "high" group, but not in the "low" group. The ability of these ethanol doses to induce feelings of craving for ethanol were assessed in parallel, using the Desire for Alcohol Questionnaire (DAQ). "High" drinkers showed higher desire for ethanol on all factors of the DAQ except the "positive negative reinforcement" factor, and sampling ethanol tended to increase desire in these measures. However, at each dose, the induction of feelings of desire for ethanol showed a negative correlation with discrimination performance. These findings are discussed in the context of the ability of animals and humans to use several components of drug-induced stimuli in the performance of drug discrimination, and the role of such discriminative stimuli in priming of ethanol drinking.

Alcohol Drinking↗
PubMed1999

Ikaros DNA-binding proteins direct formation of chromatin remodeling complexes in lymphocytes.

The Ikaros gene family encodes zinc finger DNA-binding proteins essential for lineage determination and control of proliferation in the lymphoid system. Here, we report that, in the nucleus of a T cell, a major fraction of Ikaros and Aiolos proteins associate with the DNA-dependent ATPase Mi-2 and histone deacetylases, in a 2 MD complex. This Ikaros-NURD complex is active in chromatin remodeling and histone deacetylation. Upon T cell activation, Ikaros recruits Mi-2/HDAC to regions of heterochromatin. These studies reveal that Ikaros proteins are capable of targeting chromatin remodeling and deacetylation complexes in vivo. We propose that the restructuring of chromatin is a key aspect of Ikaros function in lymphocyte differentiation.

Adenosine Triphosphatases↗
PubMed1999

Characterization of the ABA-deficient tomato mutant notabilis and its relationship with maize Vp14.

The notabilis (not) mutant of tomato has a wilty phenotype due to a deficiency in the levels of the plant hormone abscisic acid (ABA). The mutant appears to have a defect in a key control step in ABA biosynthesis--the oxidative cleavage of a 9-cis xanthophyll precursor to form the C15 intermediate, xanthoxin. A maize mutant, viviparous 14 (vp14) was recently obtained by transposon mutagenesis. This maize genetic lesion also affects the oxidative cleavage step in ABA synthesis. Degenerate primers for PCR, based on the VP14 predicted amino acid sequence, have been used to provide probes for screening a wilt-related tomato cDNA library. A full-length cDNA clone was identified which is specific to the not gene locus. The ORFs of the tomato cDNA and maize Vp14 are very similar, apart from parts of their N-terminal sequences. The not mutation has been characterized at the DNA level. A specific A/T base pair deletion of the coding sequence has resulted in a frameshift mutation, indicating that not is a null mutant. This observation is discussed in connection with the relatively mild phenotype exhibited by not mutant homozygotes.

Abscisic Acid↗
PubMed1999

The effects of motion on parametric fMRI analysis techniques.

Subject motion during the time course of functional activation studies has been shown to cause spurious signals which can mimic 'true' activation. Therefore, the importance of motion correction has been widely recognized. Correction with post-processing using image registration software is common practice in functional imaging and analysis. Many image registration algorithms, developed for analysis requirements other than fMRI, assume rigid body motion. Although these techniques are now routinely used by a number of groups, rigid body coregistration has not yet been shown to reduce the effects of motion to an acceptable level in fMRI analysis, i.e. the effects on resulting correlation analysis directly. In this paper we have used volume data to assess rigid body co-registration in terms of motion artefacts for the different correlation approaches used in fMRI. We have developed a new way of visualizing motion effects in correlation analysis based on generating a scatter plot of correlation score against local image gradient. This technique has been tested on fMRI data sets from a functional paradigm suffering from motion correlated artefacts, with and without rigid body motion correction. Although we do not attempt to estimate the actual residual motion, this technique can be used to verify the results of analysis and select regions of relatively unambiguous activation. This paper assesses directly the rigid body assumption and proves the need for, and effectiveness of, co-registration for all correlation based analysis techniques. The specific differences between the popular correlation forms used are investigated and explained. We show that for certain forms of correlation analysis the effects of motion, while not removed altogether, are effectively statistically eliminated.

Adult↗
PubMed1999

Erythrocyte glutathione deficiency in symptom-free HIV infection is associated with decreased synthesis rate.

Although several studies have documented intra- and extracellular glutathione (GSH) deficiency in asymptomatic human immunodeficiency virus (HIV) infection, the mechanisms responsible for the altered GSH homeostasis remain unknown. To determine whether decreased synthesis contributes to this alteration of GSH homeostasis, a primed-constant infusion of [2H2]glycine was used to measure the fractional and absolute rates of synthesis of GSH in five healthy and five symptom-free HIV-infected subjects before and after supplementation for 1 wk with N-acetylcysteine. The erythrocyte GSH concentration of the HIV-infected group was lower (P < 0.01) than that of the control group (1.4 +/- 0.16 vs. 2.4 +/- 0.08 mmol/l). The smaller erythrocyte GSH pool of the HIV-infected group was associated with a significantly slower (P < 0.01) absolute synthesis rate of GSH (1.15 +/- 0.14 vs. 1.71 +/- 0.15 mmol. l-1. day-1) compared with controls. Cysteine supplementation elicited significant increases in both the absolute rate of synthesis and the concentration of erythrocyte GSH. These results suggest that the GSH deficiency of HIV infection is due in part to a reduced synthesis rate secondary to a shortage in cysteine availability.

Acetylcysteine↗
PubMed1999

The acute-phase protein response to human immunodeficiency virus infection in human subjects.

Although several studies have shown that asymptomatic human immunodeficiency virus infection elicits an increase in whole body protein turnover, it is not known whether this increased protein turnover includes changes in the kinetics of acute-phase proteins (APPs). To answer this question, we measured 1) the plasma concentrations of four positive (C-reactive protein, alpha1-antitrypsin, haptoglobin, and fibrinogen) and four negative APPs [albumin, high-density lipoprotein (HDL)-apolipoprotein (apo) A1, transthyretin, and retinol-binding protein] and 2) the fractional (FSR) and absolute (ASRs) synthesis rates of three positive and three negative APPs using a constant intravenous infusion of [2H5]phenylalanine in five subjects with symptom-free acquired immunodeficiency syndrome (AIDS) and five noninfected control subjects. Compared with the values of the controls, the plasma concentrations, FSRs, and ASRs of most positive APPs were higher in the AIDS group. The negative APPs had faster FSRs in the AIDS group, there was no difference between the ASRs of the two groups, and only HDL-apoA1 had a lower plasma concentration. These results suggest that symptom-free AIDS elicits an APP response that is different from bacterial infections, as the higher concentrations and faster rates of synthesis of the positive APPs are not accompanied by lower concentrations and slower rates of synthesis of most of the negative APPs.

Acute-Phase Proteins↗
PubMed1999

Moles and melanomas--who's at risk, who knows, and who cares? A strategy to inform those at high risk.

BACKGROUND: Malignant melanoma is uncommon but potentially fatal. Knowledge and attitudes play an important part in the early detection of this skin cancer. AIM: To assess knowledge, risk perception, and intended behaviour related to melanoma compared with actual risk status. To suggest measures to improve the primary and secondary prevention of melanoma in general practice for a high-risk group. METHOD: A prospective questionnaire survey was carried out on consecutive adults attending in 16 randomly selected group practices. Applying MacKie's personal risk factor chart for melanoma, the study assessed self-reported risk, knowledge of skin cancer--especially malignant melanoma--and self-reported preventive activity. RESULTS: A total of 3105 (69%) attenders completed the questionnaire. The responders showed greater concern for minor rather than major clinical signs in pre-existing moles. Young people and the professional classes were the least knowledgeable about skin cancer and exhibited the most risky behaviour in terms of sun exposure, failure to check their skin, and to seek medical advice about new or changing moles. The majority of an 8.7% high-risk group showed lack of awareness of their increased risk, and women in this group reported the highest desire for a suntan and the use of sunbeds. In addition to showing less concern than their low risk counterparts about moles growing in size, they were also reluctant to seek medical advice about new moles. CONCLUSION: Consideration should be given to targeting primary prevention and selective screening in general practice towards a high-risk group for malignant melanoma. Young people and the professional social class should receive particular attention.

Adolescent↗
PubMed1999

Comparison of three-dimensional visualization techniques for depicting the scala vestibuli and scala tympani of the cochlea by using high-resolution MR imaging.

BACKGROUND AND PURPOSE: Cochlear implantation requires introduction of a stimulating electrode array into the scala vestibuli or scala tympani. Although these structures can be separately identified on many high-resolution scans, it is often difficult to ascertain whether these channels are patent throughout their length. The aim of this study was to determine whether an optimized combination of an imaging protocol and a visualization technique allows routine 3D rendering of the scala vestibuli and scala tympani. METHODS: A submillimeter T2 fast spin-echo imaging sequence was designed to optimize the performance of 3D visualization methods. The spatial resolution was determined experimentally using primary images and 3D surface and volume renderings from eight healthy subjects. These data were used to develop the imaging sequence and to compare the quality and signal-to-noise dependency of four data visualization algorithms: maximum intensity projection, ray casting with transparent voxels, ray casting with opaque voxels, and isosurface rendering. The ability of these methods to produce 3D renderings of the scala tympani and scala vestibuli was also examined. The imaging technique was used in five patients with sensorineural deafness. RESULTS: Visualization techniques produced optimal results in combination with an isotropic volume imaging sequence. Clinicians preferred the isosurface-rendered images to other 3D visualizations. Both isosurface and ray casting displayed the scala vestibuli and scala tympani throughout their length. Abnormalities were shown in three patients, and in one of these, a focal occlusion of the scala tympani was confirmed at surgery. CONCLUSION: Three-dimensional images of the scala vestibuli and scala tympani can be routinely produced. The combination of an MR sequence optimized for use with isosurface rendering or ray-casting algorithms can produce 3D images with greater spatial resolution and anatomic detail than has been possible previously.

Adult↗
PubMed1999

Can current models explain the lack of liver complications in Y-90 microsphere therapy?

Normal liver complications have not been observed in Y-90 microsphere therapy of hepatic tumors [selective internal radiation (SIR)], despite clinical studies reporting estimated absorbed doses to normal liver between 100 and 150 Gy. The purpose of the study was to see whether predictions of normal tissue complication probability (NTCP) models for liver based on clinical data from external beam therapy are consistent with clinical results of SIR. Liver NTCP was calculated using a parallel architecture model and normal liver dose-volume histograms that have been proposed for SIR. A parallel model including internal functional subunit structure is also proposed. Dose rate effects are incorporated. A criterion for comparing model calculations with clinical data is presented. For the parallel architecture model, the predicted NTCP is sensitive to the dose distribution in normal liver and to the model parameters, particularly the repair time. With reasonable assumptions about the microsphere distribution, the parallel model with parameters deduced from external beam therapy outcome analysis is consistent with the observed lack of liver complications. Inclusion of FSU structure widens the range of assumptions under which consistency is found. The parallel model can be consistent with the clinically observed lack of liver complications in SIR. More information about the activity distribution and the radiobiology of normal liver under conditions typical of microsphere therapy should be sought.

Humans↗
PubMed1999

The application of three-dimensional magnetic resonance imaging rendering of the inner ear in assessment for cochlear implantation.

OBJECTIVE: To study the use of three-dimensional (3D) rendering of T2-weighted magnetic resonance imaging (MRI) images into 3D models of the inner ear in the preoperative assessment for cochlear implantation. STUDY DESIGN: A retrospective case review of cochlear implant candidates undergoing preoperative imaging studies to determine their suitability for surgical implantation. SETTING: A tertiary referral center for the northwest area of England with an established 10-year-old program in cochlear implantation. PATIENTS: Selected adult and pediatric patients referred for cochlear implant assessment from 1996 to 1998, who underwent computerized tomography (CT) and MRI studies. INTERVENTION: Diagnostic imaging modality to assess the structure and patency of the inner ear. MAIN OUTCOME MEASURES: To see how detailed anatomic information provided by these 3D models influenced surgical decisions. RESULTS: Four case studies (with their 3D models) are presented to illustrate different points of interest. CONCLUSION: These 3D models provide the implanting surgeon with precise, detailed, and easily interpretable information about the cochlea, which help to guide surgical implantation, or in certain cases, to decide against attempting surgery in the presence of unfavorable anatomic factors.

Child↗
PubMed1999

Reducing AIDS risk among inner-city women: a review of the Collectivist Empowerment AIDS Prevention (CE-AP) Program.

We discuss the process underlying our HIV-prevention project for young inner-city women. Health interventions are almost uniformly based on individualistic models of health and behavior. In contrast, AIDS and AIDS prevention, by their very social nature, may require more collectivist principles of disease, health, and intervention. We conducted a behavioral intervention, the Collectivist Empowerment AIDS Prevention (CE-AP) Program, with young, inner-city women to deal with this critical health issue. Our primary intervention goal was to promote women's sense of owning and making healthy choices about their bodies. We attempted to accomplish this by emphasizing the concepts of empowerment, collectivism (as opposed to individualism), and culturally sensitive skill building. Collectivism is emphasized to encourage women to involve others in their behavioral health decisions and to gain power through social joining and coalition building. A woman's behavioral decisions affect many others in her life. Thus, involving others in decision making emphasizes the connection between an individual's actions and their impact on interpersonal relationships. CE-AP was found to be effective in changing safer-sex behavior and we review our findings and future directions.

Acquired Immunodeficiency Syndrome↗