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Biomedical subjects

P Doyle

Publications and source records attributed to P Doyle.

At least 19 recordsLinked to original sources
PubMed2006

Calibrating automatic exposure control devices for digital radiography.

The energy responses of digital radiography detectors differ from those of screen-film systems. To provide a consistent level of image quality at different tube potentials automatic exposure control (AEC) devices must be calibrated to suit the energy response of the image receptor with which they are intended for use. AEC calibration for digital radiography systems requires an alternative parameter to optical density, ideally one related to the quality of a digital image. Energy responses of computed radiography (CR) and indirect digital radiography (IDR) image receptors have been calculated, and compared with those for screen-film systems. Practical assessments of the relative sensitivities of a CR detector made using the detector dose indicator (DDI), pixel value and signal-to-noise ratio showed similar variations with tube potential. The DDI has been used to determine the correct kV compensation curve required to calibrate the AECs for the loss in detector sensitivity with tube potential. AECs are set up relative to a predetermined air kerma incident on the detector at 80 kV for CR and IDR systems using this curve and the method used is described. Factors influencing the calibration of AECs for digital radiography including techniques, types of phantom and contributions from scatter are reviewed, and practical methods recommended for use.

Aluminum↗
PubMed2006

Application of contrast-to-noise ratio in optimizing beam quality for digital chest radiography: comparison of experimental measurements and theoretical simulations.

The contrast-to-noise ratio (CNR) has been employed in optimizing beam quality for imaging a chest phantom using digital radiography. The relationship between CNR and tube potential has been studied for regions of different attenuations representing the lung, heart and abdomen, and a figure of merit (FOM) incorporating effective dose has been calculated to enable dose performance to be included. Direct measurements of imaging performance have been compared with simulations based on a model representing object attenuations. The study has shown reasonable agreement between measurements of CNR and calculated values. The CNR values in the lung and heart regions are higher at 60-80 kV, while those for the abdomen are higher at 90-110 kV. Incorporating a 0.2 mm copper filter has minimal effect on image quality and the FOM is higher because of the reduction in dose. For imaging the heart and abdomen, performance was improved through use of a technique to remove scatter, with an air-gap technique giving a higher FOM because of the lower dose. The CNR and FOM can provide useful quantities for evaluating imaging performance to optimize beam quality for different imaging tasks.

Abdomen↗
PubMed2006

Performance evaluation and testing of digital intra-oral radiographic systems.

Four digital intra-oral radiographic systems were tested and evaluated; three charge-coupled device (CCD) based systems from RVG, Visualix and Sidexis and a photostimulable phosphor (PSP) system from DenOptix. Image quality was assessed using three purpose-built phantoms to measure uniformity, low contrast detail detectability and signal-to-noise ratio (SNR). Limiting resolution was measured using a 20 lp mm(-1) bar pattern. Radiation output inaccuracies caused difficulties in achieving optimum doses for CCD systems. However, the accuracy was improved by using K-edge filters. SNR measurements proved to be a useful tool in assessing system performance. Each system has specific attributes: resolution was highest for the RVG system, the Visualix system measured the highest SNR and the lowest exposure settings were on the Sidexis system. Test methods and phantoms developed are suitable for acceptance testing and commissioning digital dental X-ray systems and for programming each system to produce an optimum level of image quality.

Equipment Design↗
PubMed2006

Predicting the impact of in vitro fertilisation and other forms of assisted conception on perinatal and infant mortality in England and Wales: examining the role of multiplicity.

The increased risk of perinatal and infant mortality observed among in vitro fertilisation (IVF) births and other assisted conception births is thought to be largely attributable to multiplicity. Using mortality statistics and estimates of the proportion of births following infertility treatment, we predicted the excess stillbirths and infant deaths associated with twins and higher order births resulting from assisted conception in England and Wales. According to our results, approximately 73 deaths could have been avoided in 2001 if all IVF infants had been born as singletons or as naturally occurring monozygotic twins, equating to a population attributable risk fraction of around 1% for perinatal and infant deaths. If we include all types of assisted conception, this figure was estimated to be around 4% of deaths-more than 220 perinatal and infant deaths in 2001. We confirm the public health importance of multiple births associated with assisted conception.

England↗
PubMed2006

Techniques for measurement of dose width product in panoramic dental radiography.

Dose width product (DWP) is the quantity recommended for assessment of patient dose for panoramic dental radiography. It is the product of the absorbed dose in air in the X-ray beam integrated over an exposure cycle and the width of the beam, both measured at the receiving slit. A robust method for measuring the DWP is required in order to facilitate optimization of practices and enable comparison of dose levels at different centres. In this study, three techniques for measuring the DWP have been evaluated through comparison of results from 20 orthopantomographic units. These used a small in-beam semiconductor detector and X-ray film, a pencil ionization chamber and an array of thermoluminescent dosemeters (TLDs). The mean results obtained with the three techniques agreed within +/-6%. The technique employing a pencil ionization chamber of the type used for dose assessment of CT scanners is the simplest and most reliable method. The in-beam detector and film method has larger errors both from positioning the radiation detector and from measurement of X-ray beam width, which should be the full width at half maximum obtained from a scan of the film optical density. The TLD array method was accurate, but more time consuming to carry out. The mean DWP for the units studied was 65 mGy mm and the mean dose-area product was 89 mGy cm2. The DWP for 30% of the units tested exceeded the diagnostic reference dose of 65 mGy mm, recommended by the National Radiological Protection Board.

Humans↗
PubMed2005

Dose-image quality optimisation in digital chest radiography.

A range of techniques has been developed in conventional radiography for the chest, because of technical difficulties in imaging the wide variation of tissue densities. These techniques can differ significantly in tube potential selection, for scatter reduction and in application of manual or automatic exposure control. In this study a geometric chest phantom designed to simulate a chest image, has been used to study image quality on an indirect digital radiography (DR) system. Relative values for the signal-to-noise ratio (SNR), have been derived from analysis of contrast detail objects within the lung, heart and subdiaphragm regions of the phantom. Results showing the variation in SNR and detail perception with tube potential are presented for three radiographic techniques: using a grid, an air gap and no scatter reduction. SNR measurements provided a useful objective measure for assessment of image quality for optimising DR systems.

Artifacts↗
PubMed2005

Optimising automatic exposure control in computed radiography and the impact on patient dose.

Automatic exposure controls (AECs) used with computed radiography (CR) equipment need to be set for a constant signal level in the resultant images. The response varies with the energy of the X-ray beam in a different way from conventional film screen combinations. Dose to the imaging receptor has been employed in adjustment of the AECs for varying exposure conditions for CR systems installed in hospitals in the west of Scotland. However, other parameters could potentially be applied. In this study, three quantities have been investigated for use in setting the AEC function: the exposure indicator defined by the CR manufacturer, dose to the image receptor and image noise. Experiences gained in setting up the systems are described and results of a patient dose survey are reported.

Dose-Response Relationship, Radiation↗
PubMed2005

Why is there a modifying effect of gestational age on risk factors for cerebral palsy?

OBJECTIVE: To investigate risk factors for cerebral palsy in relation to gestational age. DESIGN: Three case-control studies within a geographically defined cohort. SETTING: The former Oxfordshire Health Authority. PARTICIPANTS: A total of 235 singleton children with cerebral palsy not of postnatal origin, born between 1984 and 1993, identified from the Oxford Register of Early Childhood Impairment; 646 controls matched for gestation in three bands: or=37 weeks. RESULTS: Markers of intrapartum hypoxia and infection were associated with an increased risk of cerebral palsy in term and preterm infants. The odds ratio (OR) for hypoxia was 12.2 (95% confidence interval 1.2 to 119) at or=37 weeks. Corresponding ORs for neonatal sepsis were 3.1 (1.8 to 5.4) and 10.6 (2.1 to 51.9). In contrast, pre-eclampsia carried an increased risk of cerebral palsy at >or=37 weeks (OR 5.1 (2.2 to 12.0)) but a decreased risk at <or=32 weeks (OR 0.4 (0.2 to 1.0)). However, all infants <or=32 weeks with maternal pre-eclampsia were delivered electively, and their risk of cerebral palsy was no lower than that of other electively delivered <or=32 week infants (OR 0.9 (0.3 to 2.7)). Nearly 60% of <or=32 week controls were delivered after spontaneous preterm labour, itself an abnormal event. CONCLUSION: Inflammatory processes, including pre-eclampsia, are important in the aetiology of cerebral palsy. The apparent reduced risk of cerebral palsy associated with pre-eclampsia in very preterm infants is driven by the characteristics of the gestation matched control group. Use of the term "protective" in this context should be abandoned.

Biomarkers↗
PubMed2004

Learning difficulties in children born to male UK nuclear industry employees; analysis from the nuclear industry family study.

There has been much debate about paternal pre-conceptual exposure to low level ionising radiation and possible increased risk of ill health among the children subsequently conceived. The prevalence of reported learning difficulties was examined in over 16000 children born to UK nuclear industry workers, using fathers' information on exposure from the workers' individual employment and dosimetry records. There was no evidence that paternal exposure to low level ionising radiation at work influences the prevalence of learning difficulties in otherwise healthy children conceived after exposure.

Adolescent↗
PubMed2001

Vision. Realignment of cones after cataract removal.

Through unique observations of an adult case of bilateral congenital cataract removal, we have found evidence that retinal photoreceptors will swiftly realign towards the brightest regions in the pupils of the eye. Cones may be phototropic, actively orientating themselves towards light like sunflowers in a field.

Adult↗
PubMed2001

Sex ratio of nuclear industry employees' children.

Does preconceptional exposure to ionising radiation before conception affect the health of offspring? Some studies have suggested that radiation exposure might influence the sex ratio at birth, potentially indicating genetic damage. We examined the sex ratio of over 46000 children born to UK nuclear industry workers, using information on exposure from the workers' individual employment and dosimetry records. We found no statistically significant alterations of the sex ratio, and no evidence that exposure to low-level ionising radiation at work influences the sex ratio of children conceived after exposure.

Air Pollution, Radioactive↗
PubMed2001

Efficacy of a behaviorally based voice therapy protocol for vocal nodules.

The aim of this study was to assess the effects on vocal function of voice therapy for vocal nodules. Perceptual and physiological progressive changes were examined during a strictly structured, behaviorally based voice therapy protocol in which 11 women with vocal nodules participated. Randomized audio recordings from pretherapy and from each of the therapy approaches (vocal hygiene, respiration, direct facilitation, carryover) were used for perceptual evaluations. Six speech-language pathologists rated ten voice quality parameters. Two evaluation procedures were performed and compared. Interlistener reliability was sufficiently high in both tests. Significant effects of therapy were found for decreased overall dysphonia, press, instability, gratings, roughness, vocal fry, and "scrape." Nonsignificant group effects were found for breathiness, aphonic instances, and lack of sonority. No significant parameter changes occurred between baseline assessment and the completion of the initial (vocal hygiene) phase of therapy. Significant changes were found following the direct facilitation and respiration phases of therapy. Videostroboscopic evaluations made by two laryngologists showed that in no case were the nodules completely resolved. However, the nodules had decreased in size and edema was reduced after therapy for all clients, but one. Combined results suggest: (1) Alterations in vocal function were reflected in perceptual parameters, and (2) the voice therapy had a positive effect on voice quality, vocal status, and vocal function for the majority of the vocal nodule clients.

Adult↗
PubMed2001

Stem cell engraftment strategies.

The donor stem cell phenotype and host microenvironment determine the outcome of a stem cell transplant. In a series of transplant studies in syngeneic male to female or congenic Ly5.1/Ly5.2 models in which hosts have received no or minimal irradiation (100 cGy), evidence overwhelmingly supports the concept that syngeneic engraftment is determined by stem cell competition. These approaches can be extended to H-2 mismatched allogeneic mouse combination when antigen pre-exposure and CD40-CD40 ligand antibody blockage are employed. A human trial in patients with resistant neoplasia infusing pheresed blood with 10(8) CD3 cells/kg showed that tumor responses and complete chimerism occur with very low levels of CD34+ cells/kg and that the extent of previous treatment is a critical factor in determining chimerism. A major feature of transplants is the phenotype of the donor stem cell. This phenotype shows dramatic reversible plasticity involving differentiation, adhesion protein expression, and engraftment with cytokine-induced cell-cycle transit. Homing is probably also plastic. Marked fluctuations in engraftment capacity are also seen at different points in marrow circadian rhythm.

Adolescent↗
PubMed2001

Primary infertility in nuclear industry employees: report from the nuclear industry family study.

OBJECTIVE: To determine whether men and women who are occupationally exposed to ionising radiation are at increased risk of primary infertility. METHODS: A cross sectional analysis of reproductive outcome was reported in an occupational cohort of nuclear industry workers from the Atomic Energy Authority, Atomic Weapons Establishment, and British Nuclear Fuels in the United Kingdom. Data on employment and radiation monitoring supplied by employers were linked to data obtained from self administered questionnaires sent to all current employees and a sample of past workers. A total of 5353 men and 603 women aged 40 years or more at the time of survey whose first pregnancy, or attempt at pregnancy, had occurred after first employment in the nuclear industry were recruited to the study. Primary infertility was defined as consultation with a doctor about the failure to achieve at least one viable (24 weeks gestational age or more) pregnancy. RESULTS: 2.6% Of men and 3.7% of women reported primary infertility. For men, this proportion did not differ by amount of radiation monitored or by dose received. The prevalence of infertility was higher among monitored women than non-monitored women, but not significantly so and the numbers were too small to draw any firm conclusions. CONCLUSIONS: No support was found for a hypothesis linking exposure to low level ionising radiation among men with primary infertility. There was weak evidence of an association in women, but the relatively few monitored women prevented detailed examination of these data.

Adult↗
PubMed2000

Fast kinetics of chromatin assembly revealed by single-molecule videomicroscopy and scanning force microscopy.

Fluorescence videomicroscopy and scanning force microscopy were used to follow, in real time, chromatin assembly on individual DNA molecules immersed in cell-free systems competent for physiological chromatin assembly. Within a few seconds, molecules are already compacted into a form exhibiting strong similarities to native chromatin fibers. In these extracts, the compaction rate is more than 100 times faster than expected from standard biochemical assays. Our data provide definite information on the forces involved (a few piconewtons) and on the reaction path. DNA compaction as a function of time revealed unique features of the assembly reaction in these extracts. They imply a sequential process with at least three steps, involving DNA wrapping as the final event. An absolute and quantitative measure of the kinetic parameters of the early steps in chromatin assembly under physiological conditions could thus be obtained.

Animals↗