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N J Dudley

Publications and source records attributed to N J Dudley.

At least 19 recordsLinked to original sources
PubMed2005

A systematic review of the ultrasound estimation of fetal weight.

OBJECTIVES: The range and use of ultrasound fetal measurements have gradually been extended. Measurements have been combined to estimate fetal weight by mathematically based non-linear regression analysis or physically based volumetric methods. Fetal weight estimation is inaccurate, with poor sensitivity for prediction of fetal compromise. Several authors have shown the unacceptable level of intra- and interobserver variability in fetal measurement and the impact of errors on growth assessment. The aims of this study were to review the available methods and possible sources of inaccuracy. METHODS: Four databases were searched for studies comparing ultrasound estimated fetal weight (EFW) with birth weight. Studies meeting the inclusion criteria evaluated 11 different methods. Errors were graphically summarized. RESULTS: No consistently superior method has emerged. Volumetric methods provide some theoretical advantages. Random errors are large and must be reduced if clinical errors are to be avoided. CONCLUSIONS: The accuracy of EFW is compromised by large intra- and interobserver variability. Efforts must be made to minimize this variability if EFW is to be clinically useful. This may be achieved through averaging of multiple measurements, improvements in image quality, uniform calibration of equipment, careful design and refinement of measurement methods, acknowledgment that there is a long learning curve, and regular audit of measurement quality. Further work to improve the universal validity and accuracy of fetal weight estimation formulae is also required.

Birth Weight↗
PubMed2003

Radioisotope for occult lesion localisation (ROLL) of the breast does not require extra radiation protection procedures.

AIM OF STUDY: Dosimetry data from patients and hospital personnel involved in the use of radioisotope for occult lesion localisation (ROLL) of the breast were collected to determine the need for extra radiation protection procedures. METHODS: Sixty-three patients have been enrolled to date into a randomised trial evaluating ROLL. Two megabecquerels of (99m)Tc- MAA in a syringe was mixed with X-ray contrast medium; this was injected directly into the lesion under image guidance. A gamma-detecting probe (Neo-Probe) was used to locate the area of radioactivity. Radiation doses to all staff groups were estimated using time and motion studies and dose rate measurements at a range of distances during each stage of ROLL. RESULTS: The finger dose [FD](+/-95% CI) was considered to be the critical variable for surgeons and radiologists. Surgeon FD=9.3+/-3.3 microSv, Radiologist FD=0.5+/-0.13 microSv. Whole body doses [WBD](+/-95% CI) were estimated for other staff groups. Nurse WBD=0.4+/-0.4 microSv, porter WBD: nil, contamination and waste: nil. CONCLUSIONS: In the case of a surgeon performing 100 procedures per annum, a FD dose of approximately 1 mSv is received, well within the annual dose limit of 150 mSv. Annual WBD to assisting staff may reach 0.04 mSv, compared to an annual limit of 6 mSv. These low doses and the lack of contamination of radioactive waste indicate that no additional radiation protection measures are required.

Breast Neoplasms↗
PubMed2003

Clinical agreement between automated and calculated ultrasound measurements of bladder volume.

Non-invasive urine volume measurement is an important tool in the management of dysfunctional and neuropathic bladders in children. Ultrasound imaging devices have been used for many years for this purpose. An automated scanner (Bladderscan) is now available and has been recommended by a number of authors, but there is conflicting evidence in the literature regarding the accuracy and appropriate clinical application of the device. We aimed to assess the level of clinical agreement between the two methods. 36 urine volume measurements were made on 11 children using both instruments. Although there was a good correlation between the methods (r=0.97), the clinical agreement was poor (limits of agreement +/-77 ml). 13 voided volumes were directly measured and compared with the difference between pre- and post-void ultrasound measurements. The systematic errors were small but the mean absolute errors were 54 ml and 23 ml, respectively, for the automated and ultrasound imaging methods. If used correctly, ultrasound imaging provides more accurate results and can compete with the cost, convenience and ease of use of the automated method. Low cost, highly portable ultrasound imaging devices are now available and should be used in preference to the Bladderscan.

Automation↗
PubMed2002

The importance of quality management in fetal measurement.

OBJECTIVES: The aims of this study were to evaluate factors contributing to inaccuracy in fetal measurements and to assess the clinical importance of measurement quality. METHODS: One hundred images of biparietal diameter (BPD), head circumference (HC) and abdominal circumference (AC) measurements were collected from six centers (1800 measurements); the proportion meeting quality criteria was assessed. Four hundred images of AC were collected from one center, each image measured by ellipse fitting and tracing methods; clinical agreement between the methods was assessed. Fetal weight estimation (EFW) errors were compared between quality controlled and non-quality controlled studies. Images of three ACs on each of 400 fetuses were collected; where one measurement failed to meet quality criteria, it was compared with an optimal measurement on the same fetus. RESULTS: Eighty-nine percent, 87% and 60% of BPD, HC and AC, respectively, met all quality criteria. Limits of agreement between ellipse and traced AC were -4.7 mm to 12.5 mm; 22% of sections were non-elliptical. EFW errors were significantly different but were confounded by differences in time to delivery. Limits of agreement between optimal and suboptimal AC measurements were -15.1 mm to 7.7 mm. CONCLUSIONS: AC quality criteria are less easily recognized and obtained than those for head measurements; training, adherence to protocols and audit are important. Differences between ellipse and traced AC may not justify the use of separate charts; the number of non-elliptical sections suggests that ellipse fitting is not appropriate. Comparison between EFW errors is not a suitable tool for audit. Failure to meet quality criteria results in clinically significant errors.

Abdomen↗
PubMed2001

A computerised quality control testing system for B-mode ultrasound.

Current methods of ultrasound (US) imaging quality control involve an observer taking a series of measurements on test object images. This process is very labour-intensive, rapidly becoming more so as the complexity of US scanners increases. Also, many of the measurements are based on the subjective judgement of the operator and are, therefore, prone to an undesirable level of intraobserver and interobserver variation. We have developed a suite of programs to analyse captured US images to estimate a number of performance parameters, including resolution, high- and low-contrast penetration depths and high- and low-contrast sensitivity. In this system, images of the ATS Laboratories Multipurpose Phantom Model 539 are acquired on a PC with a video capture card, and analysed using the software developed. Automated tests have been developed for resolution, low- and high-contrast penetration and low- and high-contrast sensitivity. A preliminary validation of the system was carried out using images from two curvilinear probes and a linear-array probe operating at 5 MHz, 7.5 MHz and 10 MHz, respectively. The 95% confidence intervals ranged from +/- 17% to +/- 21% for resolution measurements and from 0% to +/- 1.5% for low-contrast penetration. The system provides an index of visibility for high- and low-contrast targets, as compared to the coarse visual assessment of a human observer, with 95% confidence intervals ranging from +/- 6% to +/- 13% for low-contrast sensitivity and from +/- 3% to +/- 25% for high-contrast sensitivity. Advantages of the system over the human observer include improved reproducibility and increased information regarding visibility of targets. A more detailed multicentre validation is currently being undertaken.

Automation↗
PubMed2001

A review of two alternative ultrasound quality assurance programmes.

OBJECTIVE: This study reviewed the results of B-mode Quality Assurance (QA) performance tests on 17 real-time ultrasound scanners, performed over a period of 3 years, in order to assess their value. Following this review we revised and simplified our testing schedules to include two tests for noise and sensitivity. The value of the new schedules was assessed. METHODS: Initially, testing schedules were similar to those recommended by two professional bodies. Results were reviewed to determine whether the tests predicted or confirmed faults. We then introduced a simplified testing programme using alternative measurements, attempting to demonstrate or predict noise related faults that affect the image, but were not demonstrated by current tests. These new tests have been performed on 24 ultrasound machines for up to 18 months. RESULTS: A review of results has shown that measurements occasionally fall outside tolerance due to chance, and that faults that significantly affect the image, e.g. probe faults and noise, are reported by the users without predictive or concomitant changes in test results using our original schedules. Faults occur that do not immediately affect image quality and are not reported by the users. Inappropriate settings, e.g. monitors, are frequently reset at QA, particularly where there are potentially untrained users. The additional tests showed consistent changes in noise (four) or sensitivity (one) on five machines. CONCLUSION: Our earlier tests were inadequate in demonstrating deterioration in the clinical performance of ultrasound imaging equipment. Introduction of a revised testing schedule has resulted in changes in equipment performance being detected and rectified.

Equipment Failure Analysis↗
PubMed1996

The importance of rigorous testing of circumference measuring callipers.

On-screen circumference measurements are frequently made in obstetric ultrasound and are also made in other ultrasound specialties. The accuracy of electronic callipers is traditionally checked by linear measurement in a test object; this does not adequately test callipers used for nonlinear measurement. This technical note describes a simple test object designed for both linear and nonlinear calliper checks. Results show one machine to generate consistently large overmeasurements (15%). The clinical consequences of such overmeasurement may be serious. Appropriate quality control is essential.

Algorithms↗
PubMed1996

External radiation protection audit in National Health Service hospitals. Radiation protecgtion advisors (RPA) of the Nottingham City Hospital NHS Trust and the Oxford Radcliffe Hospital NHS Trust.

Radiation protection advisers are accustomed to carrying out internal audit in organizations for which they provide services but, traditionally, external audit has not been a part of the radiation protection adviser function. To provide an external audit function, two teams of radiation protection advisers undertook external radiation protection audits of their respective organizations, including the radiation protection adviser function itself. These audits were more representative of audits or inspections carried out by government agencies, for example the Health and Safety Executive and the former Inspectorate of Pollution, now the Environment Agency. Subsequently, reports, including recommendations for remedial action, were prepared for each management by the external auditors. The process of setting up and carrying out the external audits is described. Guidelines are suggested for those seeking to carry out an external audit.

England↗
PubMed1995

The estimation of administered activity of krypton-81m for lung ventilation studies.

Measurement or estimation of the activity of krypton-81m administered to a patient during lung ventilation imaging is difficult, due to the short half-life and continuous delivery via pipework, and no satisfactory method exists. Calculations based on generator activity have the disadvantages that this activity may not be accurately known and that not all activity eluted is inhaled by the patient. The aim of this study was to develop a simple method for estimating the administered activity from the number of counts in each patient image. A formula based on the ratio of counts in 81mKr and technetium-99m lung ventilation and perfusion images was developed and reduced so that administered activity could be directly calculated from the total 81mKr counts, the 99mTc count rate, the administered activity of 99mTc and a constant representing the ratio of counts expected from equal activities of each radioisotope. The formula allows a direct calculation from the image acquisition data following an initial set of experimental work to establish the constant for a particular gamma camera and collimator system.

Administration, Inhalation↗
PubMed1995

Selection of appropriate ultrasound methods for the estimation of fetal weight.

Many methods for fetal weight estimation have been proposed. Earlier formulae were derived solely by regression analysis but more recently formulae based on physical models have been developed. Some of these formulae are lengthy and difficult to use. The main purpose of this study was to evaluate a concise area based formula developed several years ago against popular and recently published formulae. Data from 388 patients over a 5 year period were collected from clinically required ultrasound scans performed within 10 days of delivery. Four of the seven formulae evaluated proved to be equally accurate over a broad range of birthweights (mean absolute deviations 245-249 g), including the area based formula and a circumference based formula derived from it. On the grounds of the number of terms, the precision of coefficients, the physical meaning and the greater accuracy of individual area measurements compared with those derived from circumference, the area based formula should be the method of choice.

Algorithms↗
PubMed1994

Presentation of colour flow maps of the peripheral circulation.

The use of continuous wave Doppler ultrasound for lower limb arterial assessment is a well established technique in most district hospitals. Patients found to have disturbances in blood flow attributable to arterial plaques are often referred for arteriographic visualization of the disease with its inherent risks and complications. The availability of colour flow mapping on modern ultrasound scanners provides a non-invasive way of detecting the size and extent of these plaques and, in some institutions, is replacing arteriography. One possible disadvantage of the use of colour flow mapping is that it does not provide a permanent record showing the relationship of the plaques to the patient's gross anatomy in the same way as arteriography. This may limit the acceptability of this technique. At Lincoln work was undertaken to develop a system for presenting images of a whole segment of a limb simultaneously along with the associated blood velocity spectrum. This was performed first by hand and then a suite of computer software was developed to automate the process. Comparisons were made between the ultrasound based images and arteriography, showing the techniques to be of similar diagnostic value. The technique provides composite images showing anatomical detail, blood flow and velocity spectra for ease of interpretation. Further studies will be undertaken in order to define patient groups where diagnostic arteriography can be avoided.

Color↗
PubMed1993

Wheelchair safety.

Explore the source record for details and available documents.

Accident Prevention↗
PubMed1993

Quality assurance in obstetric ultrasound.

Ultrasound examination is a routine element of antenatal care, and an accurate and reliable ultrasound service is essential for confident patient management. Qualitative findings, e.g. fetal normality and placental site, may be confirmed at delivery, but this form of audit is not suitable for fetal measurements owing to the variation in gestation at delivery and the complexity of neonatal assessment. Our aim was to develop a simple audit method applied a short time after the ultrasound scan. The method was based on assessment of measured images against measurement criteria which are clearly defined in the literature, results for each criterion being recorded in a spreadsheet. Two main forms of report were generated, the first showing overall achievement of satisfactory measurements for each sonographer, the second providing graphical information to show which criteria required greater attention by individual sonographers. Over several phases of audit problems of quality recognition and technical skill were isolated, graphical reports were used to guide tuition and the levels of performance were improved. The method itself and the results satisfy managers at all levels that standards are in place and are being maintained.

Embryonic and Fetal Development↗