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Biomedical subjects

R W Barber

Publications and source records attributed to R W Barber.

At least 37 records · Page 2Linked to original sources
PubMed1988

An experimental study of the relationship between image quality and spatial resolution for the gamma camera.

Many centres make regular measures of gamma camera performance as part of routine quality assurance programmes. Such measures may detect gradual deterioration in the camera but provide no basis on which to decide when corrective action should be taken. It is necessary to know when changes in camera performance are significant in terms of perceived image quality. In this work, one index of performance, the full width half maximum (FWHM) of the line spread function, was degraded in a controlled manner and the ability of observers to detect this change in the images produced was examined. Both simple and complex objects were investigated. A suitable decision criterion was suggested which indicated that changes of about 0.3 mm in the FWHM of the camera could be detected in the image. This figure was essentially independent of the complexity of the image, the initial FWHM of the camera and, above 300 k, the number of counts in the image. The way in which this type of experiment can help to establish a rational basis for gamma camera quality assurance programmes is discussed.

Bone and Bones↗
PubMed1987

Effect of total starvation and very low calorie diets on intestinal permeability in man.

1. The effect of total starvation for 4-5 days on the intestinal uptake and urinary excretion of markers from an orally administered mixture of mannitol (5g), [14C]mannitol (0.5 microCi), lactulose (10 g) and 51Cr-labelled ethylenediaminetetra-acetate (51Cr-EDTA) (30 microCi), was assessed in five lean (group 1) and four obese (group 2) subjects. The effect of a very low calorie diet for 1 week and of a subsequent 5 day period of total starvation on intestinal permeability was assessed in a similar way in another group of obese subjects (group 3). Transit time from mouth to caecum of the fastest component of the oral mixture was assessed by the appearance of hydrogen in breath (all subjects), and the configuration of the transit spectrum through various segments of the gastrointestinal tract, was assessed by a radionuclide scan method (group 2 subjects only). The effect of starvation on plasma/renal clearance of these markers in subjects of group 2 was assessed with the use of a bolus intravenous injection of a mixture of mannitol (2 g). [14C]mannitol (10 microCi), lactulose (0.1 g) and 51Cr-EDTA (5 microCi). 2. The uptake and urinary excretion of orally administered mannitol was decreased by total starvation. The mean decrease was 47% in the lean subjects (P less than 0.025), 33% in group 2 obese subjects (P less than 0.05) and 41% in group 3 obese subjects P greater than 0.05). In contrast, starvation produced no significant change in either the excretion of 51Cr-EDTA or lactulose.(ABSTRACT TRUNCATED AT 250 WORDS)

Creatinine↗
PubMed1987

Radionuclide assessment of diastolic function in aortic regurgitation: a critical study of its measurement.

Systolic and diastolic ventricular function was assessed in patients with aortic regurgitation as the peak ejection and filling rates. The measured rate of change of volume was related to the ejection fraction when expressed in end diastolic volumes per second (EDV.s-1) but not when expressed as stroke volumes per second (STV.s-1) suggesting that an apparent variation in left ventricular volume change when expressed as EDV.s-1 may occur as a result of an increase in end diastolic volume rather than any absolute alteration in filling rate. There was a significantly greater increase in peak filling than peak ejection rate with increasing heart rate in patients with aortic regurgitation, and this relation was exaggerated compared with that in controls. No definite difference in these indices of left ventricular function was found in patients with aortic regurgitation of severity varying from mild to severe. Isolated measurements of left ventricular filling rate may not accurately reflect left ventricular compliance since other factors, particularly heart rate, must be considered.

Adult↗
PubMed1987

Radionuclide evaluation of aortic regurgitation: assessment of ventricular function by Fourier phase analysis.

Forty patients with chronic isolated aortic regurgitation were studied by phase analysis of equilibrium radionuclide ventriculography to see whether this technique could detect changes in left ventricular (LV) function before the onset of symptoms. This technique was compared to the radionuclide ejection fraction and echocardiography. The severity of LV volume overload was assessed using the radionuclide regurgitant index. Patients with clinically severe aortic regurgitation had severe volume overload (high regurgitation index), increased echocardiographic left ventricular dimensions and significantly increased phase spread (loss of synchrony of wall motion) compared to mild and moderate groups. All but one had well maintained global left ventricular function assessed by the ejection fraction. All seven patients with definite symptoms had a marked increase in phase spread and severe volume overload.

Adult↗
PubMed1987

The rapid reversibility of effects of changing lung volume on the clearance rate of inhaled 99Tcm-DTPA in man.

Five normal non-smoking subjects inhaled an aerosol of 99Tcm-DTPA in saline with a mass median aerodynamic diameter of 0.6 micron. The rate of clearance (k) of the inhaled 99Tcm-DTPA from lung to blood was measured using a gamma scintillation camera with computer data acquisition. During a single clearance study the subjects voluntarily breathed close to total lung capacity (TLC) and close to residual volume (RV). They breathed at one volume for 5 min, then at the opposite volume for 5 min and finally reverted to the original volume for 5 min with a 1 min pause between each manoeuvre. The order in which each subject performed these breathing patterns was randomized. Tidal volume, respiratory frequency and end expired volume were measured with a water spirometer. When they breathed close to TLC the rate of clearance increased (k = 4.62 +/- 1.03%/min) compared with breathing close to RV (k = 1.96 +/- 0.5%/min). This effect of changing volume was immediately reversible after adopting each new lung volume. There were no significant changes in tidal volume or respiratory frequency between each 5 min period. There was no significant difference between the clearance increased (k = 4.62 +/- 1.03%/min) compared with breathing close to RV (k = 1.96 +/- 0.5%/min). This effect of changing volume was immediately reversible after adopting immediate and reversible.

Administration, Inhalation↗
PubMed1986

A comparison of radionuclide methods of evaluating aortic regurgitation with observations on the effect of exercise and symptoms.

The severity of aortic regurgitation, as assessed by the radionuclide regurgitant index and Fourier amplitude ratio, was compared in 29 patients. Both methods were highly reproducible and agreed in patients with mild-to-moderate regurgitation. The regurgitant index fell with exercise. This change showed a linear relationship with heart rate, allowing the regurgitant index to be corrected for heart rate. There was general agreement between the radionuclide method and echocardiography, but the regurgitant index was unable to select patients with symptoms. The regurgitant index provides an overall guide to the severity of aortic regurgitation, but may be unreliable in the presence of deteriorating ventricular function.

Aortic Valve Insufficiency↗
PubMed1986

The accuracy of functional parameters extracted from ventricular time-activity curves by Fourier curve fitting: a simulation study.

The accuracy of functional parameters derived from multiple harmonic Fourier curve fitting of left ventricular time-activity curves (TACs) was assessed in simulated curves of exactly known characteristics. Curves were generated to represent TACs of equilibrium gated radionuclide ventriculography (ERNV) sampling at 16 frames cycle-1. Curves of varying shape and noise characteristics were studied. The number of harmonics used in the fitting process was variable, the number being determined by an automated 'goodness of fit' test based on the chi-squared test. The accuracy of measured peak ejection rate (PER) and peak filling rate (PFR) was independent of the shape of the curve, but the accuracy of the time to these slopes (TPER, TPFR) was dependent on the steepness of the slope. The accuracy of the measured parameters improved as the influence of noise decreased allowing more harmonics to be added. The values of PER and PFR in control subjects varied between individuals, and with heart rate. There was less variation in the ratio (PER/PFR) of the slopes between individuals, and the accuracy of the ratio was better than that of the individual values of PER and PFR. Functional parameters of predictable accuracy may be determined by Fourier curve fitting at the statistical quality of global or regional ventricular TACs derived from ERNV sampling at 16 frames cycle-1.

Fourier Analysis↗
PubMed1986

The reliability of first harmonic Fourier phase analysis fitting to simulated time-activity curves.

The accuracy of the phase value and closeness of curve fitting from Fourier first harmonic analysis is assessed in a range of simulated time-activity curves, of varying amplitude and noise characteristics at three heart rates, over the full and reduced R-R intervals. The accuracy of the phase value is not impaired by reducing the period to that of optimal fitting, whereas the closeness of fitting is improved, particularly at resting heart rates. The reliability of first harmonic Fourier analysis may be improved by reducing the period to which fitting is undertaken to the dynamic part of the time-activity curve.

Fourier Analysis↗
PubMed1985

Improved selection of patients for aneurysmectomy by combined phase and amplitude analysis of gated cardiac scintigraphy.

Twelve patients undergoing left ventricular aneurysmectomy were studied by combined phase and amplitude analysis of gated blood pool scintigraphy before and after operation, to establish whether the presence of paradoxical systolic movement, as defined by this method, influenced the result of surgical treatment. There was a significant increase in the ejection fraction after operation in those patients with paradoxical systolic movement and no improvement in those with akinesis. The extent of the increase in ejection fraction was related to the size of paradoxical segment resected. It is argued that this improvement in left ventricular function reflects a reduction in the left ventricular and diastolic volume and improved efficiency of ejection of the stroke volume, resulting from resection of the scar. Combined phase and amplitude analysis may help in selecting patients most likely to benefit from aneurysmectomy.

Adult↗
PubMed1985

Quantification of intracardiac shunts by gold-195m, a new radionuclide with a short half life.

Gold-195m, a radionuclide with a short half life (30.5 s) was used to quantify left to right intracardiac shunts. The results of this method were compared with those obtained with technetium-99m, a method that was validated against oximetry. In five patients the pulmonary to systemic flow ratio (greater than 3:1) obtained by both radionuclides indicated that the level of shunting was too high to be measured accurately. In one patient fragmentation of the bolus meant that no satisfactory gamma fit could be obtained. In the remaining 16 patients there was no significant difference between two successive 195mAu studies. The agreement between 99mTc results and 195mAu results was excellent. Oxygen administration, straight leg raising exercise, and the use of oblique projections did not affect the values of the pulmonary to systemic flow ratio. The technique of quantification of intracardiac shunts by 195mAu gives reproducible and accurate results and the low radiation dose means that it is suitable for use in children with suspected left to right shunts.

Adolescent↗
PubMed1985

Radiation doses from technetium-99m DTPA administered as an aerosol.

A model is presented which enables radiation doses following the administration of technetium-99m diethylenetriaminepentaacetic acid ([99mTc]DTPA) aerosol to be calculated. The organ with potentially the highest radiation dose is shown to be the bladder wall. Radiation doses to the lungs, kidneys, and bladder wall and the effective whole-body dose are discussed in terms of the lung clearance rate of [99mTc]DTPA aerosol and the pattern of bladder voiding. The model indicated the influence of urine flow rate on bladder dose assuming a critical volume at which bladder voiding occurs. It is concluded that significant reductions in radiation doses may be achieved by encouraging patients or subjects undergoing investigations using [99mTc]DTPA aerosols to drink freely following the study.

Aerosols↗
PubMed1984

Measurement of regional lower limb blood flow in normal humans by inhalation of 133Xe.

A non-invasive method of measuring regional calf blood flow after inhalation of 133Xe has been investigated. The mean blood flow at rest was 3.3 ml X min-1 X 100 g tissue-1 by the 133Xe method and 3.5 ml X min-1 X 100 g tissue-1 by plethysmography. There was a significant correlation r = 0.88, P less than 0.001. During exercise the mean blood flow in the anterior tibial compartment increased from 3.4 to 10.9 ml X min-1 X 100 g tissue-1 in ten cases and in the posterior compartment from 3.3 to 7.1 ml X min-1 X 100 g tissue-1 in seven cases as measured by the 133Xe technique. The inhalation method seems to be an accurate, reliable and non-invasive method for measuring tissue blood flow in the human calf at rest and during exercise.

Adult↗
PubMed1984

Regional cerebral perfusion imaging in the elderly.

Tomographic emission scintigraphy of the brain using a stationary gamma-camera and rotating slant hole collimator, following intravenous injection of 123I-n-isopropyl p-iodoamphetamine, yields high quality images of regional cerebral blood flow. The technique has been used on 20 geriatric patients and is non-invasive, well-tolerated, and hitherto only associated with trivial adverse effects. It appears to be particularly useful in supporting a clinical diagnosis of multi-infarct disease but the demonstration of zones of underperfused but not necessarily infarcted cerebral tissue may well have wider research implications.

Aged↗
PubMed1984

Measurement of skin and total blood flow to the rabbit lower limb by washout of freely diffusible radioactive tracers introduced intra-arterially.

Good agreement was obtained when measuring total (capillary) blood flow in 9 rabbit thighs using two different techniques. The 133Xenon washout technique yielded a mean value of 8.0 cm3 X min-1 X 100 g tissue-1 whilst the microsphere technique gave a mean value of 7.8 cm3 X min-1 X 100 g tissue-1. There was a significant correlation (r = 0.83, p less than 0.006). In a further 14 rabbit thighs an attempt was made to measure skin blood flow by washout of 85Kr and to compare it with the microsphere technique. 133Xe promises to be a useful tracer for measuring lower limb flow when introduced intra-arterially. Because 85Kr tends to underestimate skin blood flow, and because of problems of diffusion of the tracer between compartments, which are discussed, this tracer is not satisfactory as a technique for measuring skin blood flow.

Animals↗
PubMed1983

Effects of coronary artery bypass grafting on left ventricular function assessed by multiple gated ventricular scintigraphy.

The effect of coronary artery bypass grafting on global left ventricular ejection fraction and regional contraction was studied in 56 consecutive patients with chronic stable angina pectoris by means of multiple gated ventricular scintigraphy at rest and during dynamic supine exercise before and six weeks after myocardial revascularisation. Before operation, exercise induced a significant fall in ejection fraction and regional wall motion score. Six weeks after operation 52 patients were symptomless. Resting ejection fraction and regional wall motion score were unchanged but during exercise ejection fraction increased significantly, and the previous exercise induced regional wall motion abnormalities were abolished. All four patients with persisting angina showed the same pattern as before operation, with a fall in left ventricular ejection fraction and regional wall motion score during exercise. Multiple gated ventricular scintigraphy affords a safe, objective, reproducible, and non-invasive means of assessing serial ventricular function at rest and during exercise in patients with ischaemic heart disease. The technique confirms that coronary bypass surgery abolishes exercise induced abnormalities of left ventricular function, but has no influence on resting function.

Angina Pectoris↗
PubMed1977

A unified model for scheduling elective admissions.

A model is presented that deals with two problems not previously solved: it handles the random arrival of requests for admission and permits continuous updating of scheduling decisions in a dynamic process, and it provides global long-term optimization of patient census rather than a series of suboptimal short-term solutions. The model can be used either for continuous dynamic scheduling or for periodic static scheduling. It is usable with many different system objectives and levels of computer resources, although an on-line computer is needed for its most effective use in the dynamic mode.

Appointments and Schedules↗