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Biomedical subjects

R Turner

Publications and source records attributed to R Turner.

At least 55 records · Page 3Linked to original sources
PubMed2001

High incidence of lichen sclerosus in patients with squamous cell carcinoma of the penis.

BACKGROUND: There is a well-documented association between lichen sclerosus (LS) and vulval carcinoma in women; however, until recently, there have only been anecdotal reports of penile squamous cell carcinoma (SCC) occurring in men with LS. OBJECTIVE: The incidence of penile carcinoma occurring on a background of LS remains uncertain, and we wished to examine this possible association further. METHOD: To address this, all the cases (n = 20) of penile SCC held on our pathology database (4 years) were examined. Histology was reviewed, blind to the clinical picture, for evidence of LS, applying strict histological criteria. Subsequently, clinical notes were reviewed for history of LS before the SCC presented, and history of previous circumcision, treatments, node involvement, metastases and death. RESULTS: In eight cases, evidence of LS was found in the excision specimen. Seven of these had well-differentiated SCC. In the 12 cases with no evidence of LS, only three were well differentiated. With case note review, seven had a history of LS (four with histological LS), sometimes preceding the SCC by 10 years. These all had well-differentiated SCC. Ten of the 20 patients are dead, seven from metastatic disease. Four deaths occurred in the 'well-differentiated LS' group, but only one from penile SCC metastatic disease. CONCLUSIONS: There appears to be a definite association between SCC of the penis and the presence of LS, similar to that reported between LS and vulval SCC in women. Of the 20 patients with penile SCC studied, 11 had a clinical history and/or histological evidence of LS. However, clinical presentation of the LS or need for circumcision may precede the SCC by many years. As follow-up is impractical, counselling at the time of diagnosis is very important, and it is essential that medical practitioners are aware of this association so that the subsequent risk from SCC is reduced.

Adult↗
PubMed2001

Brain areas sensitive to coherent visual motion.

Detection of coherent motion versus noise is widely used as a measure of global visual-motion processing. To localise the human brain mechanisms involved in this performance, functional magnetic resonance imaging (fMRI) was used to compare brain activation during viewing of coherently moving random dots with that during viewing spatially and temporally comparable dynamic noise. Rates of reversal of coherent motion and coherent-motion velocities (5 versus 20 deg s-1) were also compared. Differences in local activation between conditions were analysed by statistical parametric mapping. Greater activation by coherent motion compared to noise was found in V5 and putative V3A, but not in V1. In addition there were foci of activation on the occipital ventral surface, the intraparietal sulcus, and superior temporal sulcus. Thus, coherent-motion information has distinctive effects in a number of extrastriate visual brain areas. The rate of motion reversal showed only weak effects in motion-sensitive areas. V1 was better activated by noise than by coherent motion, possibly reflecting activation of neurons with a wider range of motion selectivities. This activation was at a more anterior location in the comparison of noise with the faster velocity, suggesting that 20 deg s-1 is beyond the velocity range of the V1 representation of central visual field. These results support the use of motion-coherence tests for extrastriate as opposed to V1 function. However, sensitivity to motion coherence is not confined to V5, and may extend beyond the classically defined dorsal stream.

Brain↗
PubMed2001

Magnetic resonance angiography in facial and other pain: neurovascular mechanisms of trigeminal sensation.

For much of the twentieth century migraine and cluster headache have been considered as vascular headaches whose pathophysiology was determined by changes in cranial vascular diameter. To examine nociceptive neural influences on the cranial circulation, the authors studied healthy volunteers' responses to injection of the pain-producing compound capsaicin in terms of the caliber of the internal carotid artery. The study was conducted using magnetic resonance angiographic techniques. Injection of capsaicin into the skin innervated by the ophthalmic (first) division of the trigeminal nerve elicited 40% +/- 27% (mean +/- SD) increase in vascular cross-sectional area in the right (ipsilateral) internal carotid artery when compared with the mean baseline ( P < 0.001). Injection of capsaicin into the skin of the chin to stimulate the mandibular (third) division of the trigeminal nerve and into the leg led to a similar pain perception and failed to produce any significant change in vessel caliber. The data suggest that there is a highly functionally organized, somatotopically congruent trigeminal innervation of the cranial vessels, with a potent vasodilator effect of the ophthalmic division on the large intracranial vessels. The data are consistent with the notion that pain drives changes in vessel caliber in migraine and cluster headache, not vice versa. These conditions therefore should be regarded as primary neurovascular headaches not as vascular headaches.

Adult↗
PubMed2000

Form and motion coherence activate independent, but not dorsal/ventral segregated, networks in the human brain.

There is much evidence in primates' visual processing for distinct mechanisms involved in object recognition and encoding object position and motion, which have been identified with 'ventral' and 'dorsal' streams, respectively, of the extra-striate visual areas [1] [2] [3]. This distinction may yield insights into normal human perception, its development and pathology. Motion coherence sensitivity has been taken as a test of global processing in the dorsal stream [4] [5]. We have proposed an analogous 'form coherence' measure of global processing in the ventral stream [6]. In a functional magnetic resonance imaging (fMRI) experiment, we found that the cortical regions activated by form coherence did not overlap with those activated by motion coherence in the same individuals. Areas differentially activated by form coherence included regions in the middle occipital gyrus, the ventral occipital surface, the intraparietal sulcus, and the temporal lobe. Motion coherence activated areas consistent with those previously identified as V5 and V3a, the ventral occipital surface, the intraparietal sulcus, and temporal structures. Neither form nor motion coherence activated area V1 differentially. Form and motion foci in occipital, parietal, and temporal areas were nearby but showed almost no overlap. These results support the idea that form and motion coherence test distinct functional brain systems, but that these do not necessarily correspond to a gross anatomical separation of dorsal and ventral processing streams.

Brain↗
PubMed2000

Progress toward ignition with noncryogenic double-shell capsules

Inertial confinement fusion implosions using capsules with two concentric shells separated by a low density region (double shells) are reported which closely follow one dimensional (1D) radiatively driven hydrodynamics simulations. Capsule designs which mitigate Au M-band radiation asymmetries appear to correspond more closely to 1D simulations than targets lacking mitigation of hohlraum drive M-band nonuniformities. One capsule design achieves over 50% of the unperturbed 1D calculated yield at a convergence ratio of 25.5, comparable to that of a double-shell design for an ignition capsule at the National Ignition Facility.

Journal Article↗
PubMed2000

Cost effectiveness of an intensive blood glucose control policy in patients with type 2 diabetes: economic analysis alongside randomised controlled trial (UKPDS 41). United Kingdom Prospective Diabetes Study Group.

OBJECTIVE: To estimate the cost effectiveness of conventional versus intensive blood glucose control in patients with type 2 diabetes. DESIGN: Incremental cost effectiveness analysis alongside randomised controlled trial. SETTING: 23 UK hospital clinic based study centres. PARTICIPANTS: 3867 patients with newly diagnosed type 2 diabetes (mean age 53 years). INTERVENTIONS: Conventional (primarily diet) glucose control policy versus intensive control policy with a sulphonylurea or insulin. MAIN OUTCOME MEASURES: Incremental cost per event-free year gained within the trial period. RESULTS: Intensive glucose control increased trial treatment costs by pound 695 (95% confidence interval pound 555 to pound 836) per patient but reduced the cost of complications by pound 957 (pound 233 to pound 1681) compared with conventional management. If standard practice visit patterns were assumed rather than trial conditions, the incremental cost of intensive management was pound 478 (-pound 275 to pound 1232) per patient. The within trial event-free time gained in the intensive group was 0.60 (0.12 to 1.10) years and the lifetime gain 1.14 (0.69 to 1.61) years. The incremental cost per event-free year gained was pound 1166 (costs and effects discounted at 6% a year) and pound 563 (costs discounted at 6% a year and effects not discounted). CONCLUSIONS: Intensive blood glucose control in patients with type 2 diabetes significantly increased treatment costs but substantially reduced the cost of complications and increased the time free of complications.

Adult↗
PubMed2000

Characterization and correction of interpolation effects in the realignment of fMRI time series.

Subject motion in functional magnetic resonance imaging (fMRI) studies can be accurately estimated using realignment algorithms. However, residual changes in signal intensity arising from motion have been identified in the data even after realignment of the image time series. The nature of these artifacts is characterized using simulated displacements of an fMRI image and is attributed to interpolation errors introduced by the resampling inherent within realignment. A correction scheme that uses a periodic function of the estimated displacements to remove interpolation errors from the image time series on a voxel-by-voxel basis is proposed. The artifacts are investigated using a brain phantom to avoid physiological confounds. Small- and large-scale systematic displacements show that the artifacts have the same form as revealed by the simulated displacements. A randomly displaced phantom and a human subject are used to demonstrate that interpolation errors are minimized using the correction.

Algorithms↗
PubMed2000

A method for removing imaging artifact from continuous EEG recorded during functional MRI.

Combined EEG/fMRI recording has been used to localize the generators of EEG events and to identify subject state in cognitive studies and is of increasing interest. However, the large EEG artifacts induced during fMRI have precluded simultaneous EEG and fMRI recording, restricting study design. Removing this artifact is difficult, as it normally exceeds EEG significantly and contains components in the EEG frequency range. We have developed a recording system and an artifact reduction method that reduce this artifact effectively. The recording system has large dynamic range to capture both low-amplitude EEG and large imaging artifact without distortion (resolution 2 microV, range 33.3 mV), 5-kHz sampling, and low-pass filtering prior to the main gain stage. Imaging artifact is reduced by subtracting an averaged artifact waveform, followed by adaptive noise cancellation to reduce any residual artifact. This method was validated in recordings from five subjects using periodic and continuous fMRI sequences. Spectral analysis revealed differences of only 10 to 18% between EEG recorded in the scanner without fMRI and the corrected EEG. Ninety-nine percent of spike waves (median 74 microV) added to the recordings were identified in the corrected EEG compared to 12% in the uncorrected EEG. The median noise after artifact reduction was 8 microV. All these measures indicate that most of the artifact was removed, with minimal EEG distortion. Using this recording system and artifact reduction method, we have demonstrated that simultaneous EEG/fMRI studies are for the first time possible, extending the scope of EEG/fMRI studies considerably.

Adult↗
PubMed2000

Optimization of 3-D MP-RAGE sequences for structural brain imaging.

An optimized MR sequence for structural three-dimensional brain scans is presented, giving good T(1) contrast and excellent white matter/gray matter segmentation. Modification of the usual linear phase encoding order to centric phase encoding restores the contrast loss, which usually occurs after magnetization preparation during the acquisition process when large volumes are imaged. The deleterious effects on the point-spread function are compensated by means of an appropriate k-space filter. RF coil inhomogeneities are corrected by means of shaped excitation pulses. High contrast-to-noise images of the entire brain with 1 mm isotropic resolution can be obtained in 12 min. The contrast-to-noise-ratio is about 100% higher than for sequences based on linear phase encoding.

Anatomy, Cross-Sectional↗
PubMed2000

Nonlinear responses in fMRI: the Balloon model, Volterra kernels, and other hemodynamics.

There is a growing appreciation of the importance of nonlinearities in evoked responses in fMRI, particularly with the advent of event-related fMRI. These nonlinearities are commonly expressed as interactions among stimuli that can lead to the suppression and increased latency of responses to a stimulus that are incurred by a preceding stimulus. We have presented previously a model-free characterization of these effects using generic techniques from nonlinear system identification, namely a Volterra series formulation. At the same time Buxton et al. (1998) described a plausible and compelling dynamical model of hemodynamic signal transduction in fMRI. Subsequent work by Mandeville et al. (1999) provided important theoretical and empirical constraints on the form of the dynamic relationship between blood flow and volume that underpins the evolution of the fMRI signal. In this paper we combine these system identification and model-based approaches and ask whether the Balloon model is sufficient to account for the nonlinear behaviors observed in real time series. We conclude that it can, and furthermore the model parameters that ensue are biologically plausible. This conclusion is based on the observation that the Balloon model can produce Volterra kernels that emulate empirical kernels. To enable this evaluation we had to embed the Balloon model in a hemodynamic input-state-output model that included the dynamics of perfusion changes that are contingent on underlying synaptic activation. This paper presents (i) the full hemodynamic model (ii), how its associated Volterra kernels can be derived, and (iii) addresses the model's validity in relation to empirical nonlinear characterizations of evoked responses in fMRI and other neurophysiological constraints.

Brain↗
PubMed2000

Laparoscopic ultrasound of the liver.

OBJECTIVE: Despite recent advances in medical imaging, pre-operative evaluation of liver tumors, whether benign or malignant, is often lacking in accuracy and precision. With the development of surgical laparoscopy, the benefits of diagnostic laparoscopy have been combined with those of operative ultrasound. This article aims to describe the technique of laparoscopic ultrasound of the liver, and to define its applications and the role of its association with diagnostic laparoscopy in the localization and assessment for resectability of liver tumors. METHODS: After an initial visual inspection with the laparoscope, laparoscopic ultrasound is utilized to further examine the liver. This relies largely on recognition of branches of the portal vein and tributaries of the hepatic veins. During this procedure, the hepatic parenchyma is also examined. Minimal displacement of the transducer, using clockwise and anti-clockwise rotatory movements, allows a full exploration of the liver. RESULTS: The combination of visual with sonographic laparoscopy allows accurate localization of benign and malignant hepatic tumors, as well as ultrasound-guided biopsies of these. Laparoscopic ultrasound can detect small lesions previously unseen by pre-operative imaging techniques. The relationship of tumors to adjacent blood vessels can be defined. Portal vein thrombosis can be diagnosed. CONCLUSION: Curability and liver tumor resectability can be determined and the appropriate surgical treatment thus planned.

Biopsy↗
PubMed2000

Allogeneic stem cell transplantation. An economic comparison of bone marrow, peripheral blood, and cord blood technologies.

OBJECTIVES: To compare outcome attributes of three available technologies for stem cell transplantation--bone marrow transplantation (BM), peripheral blood cell transplantation (PB), and cord blood transplantation (CB). To compare the cost per recipient for the three technologies, incorporating all donor and antigen matching functions, as well as the transplantation procedures. METHODS: Review of relevant literature using the CancerLit and HealthSTAR databases (plus earlier searches of MEDLINE and Embase) to summarize outcome differences. Estimations of cost per transplant using models drawing on Canadian experience. RESULTS: The literature review indicated that PB may have a modest advantage over BM in terms of outcomes. The literature indicated that CB has longer engraftment times (although this may be due to inadequate controls). Our modeling exercise indicated that costs for PB and BM are similar. CB has a higher cost per recipient, due in large part to the higher testing costs for every donated unit. CONCLUSIONS: Current literature is inadequate to provide an outcomes comparison of CB, PB, and BM. Viewed from a system-wide perspective, CB is a higher cost technique. However, PB and CB are emerging as technologies, and so our results should be viewed alongside the notion that there may be a steep learning curve in these technologies.

Bone Marrow Transplantation↗
PubMed2000

Anti-infective measures and Entonox equipment: a survey.

We surveyed 102 maternity suites to investigate whether the guidelines of the Association of Anaesthetists of Great Britain and Ireland, for the use of anti-infective filters or fully disposable anaesthetic breathing systems for each patient, were being followed with regard to Entonox equipment on labour wards. Of 100 units giving information (98%), only seven used filters and only two replaced tubing between cases. Our survey shows that the recommended policy is not being applied to Entonox apparatus in delivery suites.

Anesthetics, Inhalation↗
PubMed2000

The spectrum of mitochondrial DNA deletions is a ubiquitous marker of ultraviolet radiation exposure in human skin.

We and colleagues have suggested that deletions of mitochondrial DNA may be useful as a biomarker of ultraviolet radiation exposure in skin. In this study using a southwestern approach involving monoclonal antibodies against thymine dimers we provide direct evidence for the presence of ultraviolet-induced damage in mitochondrial DNA purified from any nuclear DNA contamination. Previous studies have been limited, as they have focused on the frequency of a single mitochondrial DNA deletion. Therefore we have addressed the question of the spectrum of mitochondrial DNA deletions in skin and whether this can be used as an index of overall DNA damage. We have used a long polymerase chain reaction technique to determine the mitochondrial DNA deletion spectrum of almost the entire mitochondrial genome in 71 split skin samples in relation to sun exposure. There was a significant increase in the number of deletions with increasing ultraviolet exposure in the epidermis (Kruskal-Wallis test, p = 0.0015) but not the dermis (p = 0.6376). The findings in the epidermis are not confounded by any age-dependent increases in mitochondrial DNA deletions also detected by the long polymerase chain reaction technique. The large spectrum of deletions identified in our study highlights the ubiquitous nature and the high mutational load of mitochondrial DNA associated with ultraviolet exposure and chronologic aging. Compared with the detection of single deletions using competitive polymerase chain reaction, we show that long polymerase chain reaction is a sensitive technique and may therefore provide a more comprehensive, although not quantitative, index of overall mitochondrial DNA damage in skin.

Biomarkers↗
PubMed2000

Solar Particle Events from a risk management perspective.

Solar Particle Events pose a health risk to astronauts in space. Today, SPE forecasts are inadequate to provide advance warning with sufficient credibility to lead operators to initiate protective measures. However, research on SPEs and Coronal Mass Ejections suggests that the space weather community is on the verge of substantial improvements in understanding solar energetic particle acceleration and propagation. This paper describes the impact of SPEs, reviews the physics of SPEs, discusses current SPE forecast tools, and describes an approach to provide the comprehensive space weather data necessary to implement physics-based SPE risk management.

Algorithms↗