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Biomedical subjects

H Griffiths

Publications and source records attributed to H Griffiths.

At least 127 records · Page 7Linked to original sources
PubMed1987

A dual-frequency applied potential tomography technique: computer simulations.

Applied potential tomography has been discussed in relation to both static and dynamic imaging. We have investigated the feasibility of obtaining static images by measuring profiles at two frequencies of drive current to exploit the differing gradients of electrical conductivity with frequency for different tissues. This method has the advantages that no profile for the homogeneous medium is then needed, and the electrodes can be coupled directly to the skin. To demonstrate the principle, computer simulations have been carried out using published electrical parameters for mammalian tissues at frequencies of 100 and 150 kHz. The distribution of complex electric potentials was calculated by the successive over-relaxation method in two dimensions for an abdominal cross-section with 16 electrodes equally spaced around the surface. From the computed electrode potentials, images were reconstructed using a back-projection method (neglecting phase information). Liver and kidney appeared most distinctly on the image because of their comparatively large conductivity gradients. The perturbations in the electrode potential differences between the two frequencies had a mean value of 5%, requiring accurate measurement in a practical system, compared with 150% when the 100 kHz values were related to a simulation of homogeneous saline equal in conductivity to muscle. The perturbations could be increased by widening the separation of the frequencies. Static imaging using a dual-frequency technique appears to be feasible, but a more detailed consideration of the electrical properties of tissues is needed to determine the optimum choice of frequencies.

Computer Simulation↗
PubMed1987

Applied potential tomography for non-invasive temperature mapping in hyperthermia.

In the field of hyperthermia for cancer treatment, much effort is being put into the development of non-invasive temperature monitoring so that the trauma of implanting thermocouple or thermistor probes in the patient can be avoided. Preliminary studies investigating the use of applied potential tomography (APT) for this purpose have been reported. APT has the advantages over other tomographic methods that the instrumentation is inexpensive, transportable, and could easily be accommodated in a hyperthermia treatment environment. Moreover, the temperature coefficient of electrical conductivity is large (2% degrees C-1) compared, for example, with the corresponding quantity in CT, the x-ray attenuation coefficient, which changes by only 0.04% degrees C-1. In our experimental system, 16 electrodes were fixed around a cylindrical block of agar simulating a human thigh. The system was driven with 5 mA at 50 kHz. The agar was heated using the 13.56 MHz capacitive system currently in clinical use in this hospital. By relating data sets recorded at different times during heating to a set recorded before heating, images of the temperature change in the agar with time were computed and are presented. The experiment was then repeated in vivo on the thigh of a volunteer.

Agar↗
PubMed1986

Specific absorption rate and tissue temperature in local hyperthermia.

Specific absorption rate (SAR) and tissue temperature were measured for a total of 83 treatments in 33 patients who received local hyperthermia treatment for cancer. The patients were grouped into three categories according to tumor size. Hyperthermia was induced by 13.56 MHz electromagnetic energy applied using capacitive coupling. A method is described for evaluating SAR from the tissue temperature traces at any time in the treatment when a step change is made in applied power. The method is possible only if the temperature traces are free from interference and the total power delivered to the patient is monitored. Mean values of SAR ranged from 4.6 to 89 W kg-1 depending on the treatment site. Satisfactory heating was achieved for superficial tumors, with temperatures greater than 42 degrees C being recorded in 69% of treatments. For axillary nodes only 4% of treatments exceeded 42 degrees C. For cervix tumors an idealized tumor model was used to estimate tumor temperature from the temperature and SAR measured in the adjacent normal tissue. From the model it appears necessary either to raise the systemic temperature to 40 degrees C or to increase the SAR by at least a factor of 4 to obtain a temperature of 42 degrees C in a typical tumor. Measurements of SAR and temperature are essential for feedback control of computer models which, in principle, could provide a complete distribution of temperature during a hyperthermia treatment. Furthermore, measured SAR provides a direct comparison of the power deposition from different treatment machines in a clinical environment. The data presented form a basis for comparison with the clinical use of other heating systems.

Absorption↗
PubMed1985

Solitary rib lesions.

Solitary rib lesions are not uncommon. They are frequently asymptomatic and usually benign. Virtually all of the malignant tumors are associated with an obvious soft tissue mass which merits further investigation. However, should any of the benign appearing lesions either become symptomatic, change appearance or start growing then they too should be biopsied.

Adolescent↗
PubMed1984

The inhibition by etomidate of the 11 beta-hydroxylation of cortisol.

The effect of a sleep-dose of etomidate on the plasma concentrations of cortisol, 11-deoxycortisol and 17 alpha OH-progesterone was investigated in eight patients; two other patients received thiopentone. Blood samples were collected at 0, 15 and 30 min after etomidate or thiopentone when an injection of tetracosactrin was given and a final sample was collected at 60 min. The plasma cortisol response to tetracosactrin was depressed below normal in patients given etomidate, and the 11-deoxycortisol response was very high, ranging from 36.4 to 184.7 nmol/l. The two patients that received thiopentone had a normal response to all steroids. The identity of the plasma 11-deoxycortisol in two patients was confirmed by high-performance liquid chromatographic separation and quantification by both spectrophotometric and radioimmunoassay measurements. These results suggest that a single dose of etomidate inhibits 11 beta-hydroxylation of cortisol.

17-Hydroxycorticosteroids↗
PubMed1981

Tibiotalar tilt--a new slant.

Classically tibiotalar tilt (TTT) is associated with four conditions: Fairbanks disease, hemophilia, sickle-cell anemia and juvenile rheumatoid arthritis. We have found it to be present in at least 20 other conditions including other dysplasias, developmental conditions such as fibrous dysplasia and a variety of other acquired disorders including various metabolic diseases and following previous trauma. The pathogenesis is controversial, but the most probable cause is related to stress and the blood supply of the distal tibial epiphysis. The differentiation of TTT from pseudotibiotalar tilt is also discussed.

Adolescent↗
PubMed1979

Is appendicitis familial?

A family history of appendicectomy was sought in two groups of children admitted to Llandough Hospital over sixteen months. The study group consisted of 29 children with histologically confirmed acute appendicitis, while the control group consisted of 29 children admitted for reasons unrelated to abdominal pain. A history of appendicectomy was elicited in first-degree relatives--that is, siblings and parents of 20 of the children in the study group and of four of the controls--a statistically significant difference. The results obtained from this study suggest that a familial predisposition to appendicitis exists.

Acute Disease↗
PubMed1979

Dicarboxylic aciduria: the response to fasting.

The urine of a child who presented with an episode of a disease resembling Reye's syndrome was found to contain large quantities of the dicarboxylic acids adipic and suberic acids, as well as the glycine conjugate of suberic acid, suberyl glycine. A variety of other dicarboxylic acids, both saturated and unsaturated, were also found in the urine at the time of the attack. It was found that the excretion of these unusual metabolites could be markedly increased by fasting for periods of greater than 10 h. These results indicate that the patient may have a defect in fatty acid oxidation which becomes clinically significant during periods of prolonged fasting.

Adipates↗