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Biomedical subjects

R Gadd

Publications and source records attributed to R Gadd.

10 recordsLinked to original sources
PubMed1999

Effective dose to children and adolescents from radiopharmaceuticals.

Published values of tissue weighting factors for adolescents and children derived from the life-span study of the atomic bomb survivors have been used to calculate the effective dose to patients aged 1, 5, 10 and 15 years undergoing a common paediatric procedure requiring one of the following radiopharmaceuticals: 99Tcm-mercaptoacetyltriglycine (MAG3), 99Tcm-diethylenetriaminepentaacetic acid (DTPA), 99Tcm-dimercaptosuccinic acid (DMSA), 99Tcm-pertechnetate, 99Tcm-iminodiacetic acid (IDA) derivatives, 99Tcm-hexamethylpropyleneamineoxine (HMPAO), 99Tcm-labelled leukocytes, 99Tcm-labelled erythrocytes, 99Tcm-phosphates, 99Tcm-methyloxyisobutylisonitrile (MIBI), 201Tl-chloride, sodium 123I-iodide, 123I-metaiodobenzylguanidine (MIBG) and 67Ga-citrate. Administered activities for each age group were based on ARSAC maximum usual values for adult patients and scaling factors listed by the European Association of Nuclear Medicine for different body weights. These effective doses were compared to values derived from ICRP whole-population tissue weighting factors and found to differ by -33% to +71% of these values, and by less than +/- 20% for two-thirds of the procedures. Because these differences were considerably less than the uncertainties in the estimates of organ absorbed dose, we conclude that these published age-specific tissue weighting factors should not be used for the estimation of effective dose to children and adolescents following the administration of radiopharmaceuticals, and that whole-population factors should continue to be used for these estimations.

Adolescent↗
PubMed1996

Feasibility of neonatal lung imaging using electrical impedance tomography.

The feasibility of detecting the lungs in preterm babies using electrical impedance tomography (EIT) was investigated. A single frequency instrument using 16 electrodes to apply current and detect peripheral voltages was constructed. The instrument applied AC current of 1.5 mA peak-peak at a carrier frequency of 20 kHz. Images were reconstructed using a sensitivity-regions backprojection method. A 9-day-old preterm baby was tested and data were collected at a speed of 10 frames/s. A dynamic image showing the lungs at full inspiration referenced to expiration is illustrated in this paper. Impedance measurements taken across the chest during the first 2 s did not show a clear pattern thus demonstrating irregular breathing. Region of interest analysis were carried out on the reconstructed images and tracked with time. Fourier transforms were then performed on these signals and a fundamental frequency at 1 Hz, corresponding to normal breathing rate of 60 breaths/min, was detected. Harmonics of the signal caused distortion especially on the left lung where the effects of cardiac events were more dominant.

Electric Impedance↗
PubMed1996

Data recovery from reduced electrode connection in electrical impedance tomography.

In electrical impedance tomography, a single channel failure causes distortion to the overall image. Mathematical modelling and curve-fitting techniques were used to recover corrupted data. A single channel was disconnected in two experiments on a saline-filled dish with one and two objects, respectively. Voltage gradient data were then synthesized from the overall shape of the curve and reconstructed. The technique demonstrated a considerable improvement in the image quality. We conclude that the technique can be adapted in applications where channel failure can occur regularly such as neonatal monitoring.

Biomedical Engineering↗
PubMed1992

Multifrequency electrical impedance tomography.

Multifrequency tomography may be conveniently achieved by sequentially sweeping the probing drive current and measuring the resultant voltages at each frequency. If events change during measurement comparisons between frequencies cannot be made. Mixing several frequency components may decrease acquisition time but increase the complexity of the instrumentation. A third method is described using Fourier transformation that enables simultaneous multifrequency measurements without an increase in instrumentation. A signal is constructed from a number of sinusoidal components of known amplitude and phase. This group of components is transformed into a time series by the inverse Fourier transform and applied to the object via a voltage or current source. Transforming the detected voltage back into Fourier components will provide the frequency response of the object. Data are collected in this way for all projections and tomograms reconstructed for each frequency. This has the advantage that no special detector is required; both in-phase and quadrature components are available and systematic errors may be easily corrected by software. This technique is demonstrated using a resistor phantom with known frequency-dependent perturbations.

Electric Conductivity↗
PubMed1992

Electrical impedance tomography. A sensitivity region reconstruction algorithm using adjacent drive current injection strategy.

The 'sensitivity region' method of back projection is converted from polar drive to adjacent drive current injection strategy and individual sensitivity coefficients incorporated. For each projection sensitivity coefficients for each pixel were established and pixels were grouped together into the 'sensitivity regions'. These contain all pixels that have their largest sensitivity coefficients associated with a particular measurement pair. Back projection of measurement data was performed using these coefficients as the basis of the reconstruction and less sensitive measurement pairs were ignored. Formulae for the back projection are discussed and images from computer simulated data and raw data supplied by Sheffield as part of this concerted action are presented. Comparison with polar current injection strategy is discussed.

Algorithms↗
PubMed1991

Quantitative radio-isotope scanning in ankylosing spondylitis: a clinical, laboratory and computerised tomographic study.

Quantitative sacroiliac and lumbar spine radio-isotope (Tc-99m MDP) scans were performed in 42 patients with ankylosing spondylitis, and repeated 12 months later in 25. Clinical and laboratory assessments as well as computerised tomographic (CT) scans of the sacroiliac joints (SIJ) and lateral lumbar spine x-rays, were performed. Bone (using the L3/4 area of the lumbar spine, sacrum, SIJ's and knee) to soft tissue (ST) ratios all correlated strongly with each other. Patients with high SIJ:ST ratios had significantly greater low-back stiffness (p less than 0.05). Change in serum IgA levels correlated negatively with change in bone: ST ratios. There was no relationship between bone: ST ratios and any other clinical or laboratory variables. The change in SIJ:ST ratios correlated positively with change in CT erosion score (p less than 0.05) and negatively with change in CT ankylosis score (p less than 0.05).

Adult↗