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Biomedical subjects

J C Gore

Publications and source records attributed to J C Gore.

At least 181 records · Page 10Linked to original sources
PubMed1984

Studies of factors affecting the design of NMR contrast agents: manganese in blood as a model system.

Some factors affecting the performance of paramagnetic ions as contrast agents for proton NMR imaging have been studied. It is demonstrated that the relaxation rate of an aqueous solution of the ion is not reliably predicted by its magnetic moment, but that significant relaxation enhancement may result when the ion is complexed with large molecules, which increases the dominant correlation time. This enhancement in turn can be altered by factors such as pH and competition for binding. Chelation of the paramagnetic ion, which may be implemented to lower its toxicity, can considerably reduce its efficacy by not only limiting its access to water but also by preventing the enhancement from associations and macromolecules. For manganese the ratio T1/T2 is a useful parameter which is sensitive to the degree of metal binding. These features of paramagnetic relaxation enhancement in tissue are demonstrated in a series of experiments on systems consisting of blood components and manganese.

Contrast Media↗
PubMed1984

Relaxation enhancement using liposomes carrying paramagnetic species.

Studies were performed to investigate the effects upon the relaxation times of mouse organs of intravenously administered Mn-DTPA entrapped in multilamellar liposomes, Mn-DTPA, 0.9% NaCl entrapped in liposomes, 0.9% NaCl. Manganese concentrations in injectates and tissues were assessed with 54Mn and atomic absorption. T1 and T2 of freshly excised tissues were measured in an NMR spectrometer at 20 MHz and 37% C with IR and CPMG sequences. Entrapment of Mn-DTPA in liposomes increased 54Mn accumulation in liver by 207% and in spleen 1208% and reduced 54Mn in heart by 20% and in kidney by 24% relative to free Mn-DTPA. Statistically significant increases in relaxation rates were produced. However, the increase in relaxation rate per unit concentration of Mn in tissue is reduced by 31% in liver and 62% in spleen when Mn is delivered inside liposomes. These observations have implications for the design of NMR contrast agents.

Animals↗
PubMed1984

Preliminary observations on magnetic resonance imaging in refractory epilepsy.

We are studying the use of magnetic resonance (MR) imaging in localization of epileptogenic foci in patients with medically refractory partial epilepsy. Imaging is performed using a prototype resistive unit operating at 0.15 T. All studies include 7 mm axial sections obtained with a partial saturation sequence (TR = 200 msec) in which signals are recovered with a spin echo (TE = 11 msec) and images reconstructed using a modified 2D Fourier transform technique. Since the temporal lobe and limbic system are the commonest site of seizure foci in this group of patients, examinations were performed with the plane of section parallel to the temporal horns of the lateral ventricles. Consensus interpretations by a radiologist, neurologist and neurosurgeon have recognized findings considered possibly abnormal in six of 11 epilepsy patients and none of six normal volunteers. These preliminary results indicate that further study is warranted in this group of patients. Critical evaluation of such findings must be carried out in a larger group including normals and patients with a variety of neurologic disorders.

Adolescent↗
PubMed1984

Measurement of radiation dose distributions by nuclear magnetic resonance (NMR) imaging.

A method is described for determining the spatial distribution of radiation dose in a tissue-equivalent phantom using nuclear magnetic resonance imaging. The conversion of ferrous ions to ferric by ionising radiation alters the magnetic moment and electron spin relaxation times of the metal ion. The spin relaxation times (T1 and T2) of the hydrogen nuclei in an aqueous solution of a ferrous salt are consequently reduced substantially. These changes in T1 and T2 can be measured using standard NMR techniques. The same conversion is used in conventional Fricke dosimetry, which can be used to calibrate the technique.

Humans↗
PubMed1981

Imaging of the brain by nuclear magnetic resonance.

A nuclear magnetic resonance (NMR) machine constructed by Thorn-EMI Ltd was used to produce tomographic images of the brain in eight volunteers and fourteen patients. The use of an inversion recovery technique designed to emphasise variations in the spin-lattice time constant (T1) resulted in remarkable differentiation between grey and white matter in all subjects examined. White matter was seen both centrally and peripherally to subcortical level and the basal ganglia were clearly demarcated by the surrounding white matter and ventricular system. The posterior fossa was visualised with substantially less artefact than with X-ray computed tomography (CT) and both the brainstem and middle cerebellar peduncle were clearly shown. Pathological appearances in patients with glioblastoma multiforme, cerebral infarction, and cerebral aneurysm were demonstrated and compared with those seen with CT. The technique will require thorough clinical evaluation but appears to have considerable potential in the diagnosis of neurological disease.

Brain↗
PubMed1981

A method of measuring the radio-opacity of catheters.

Two methods for measuring the radio-opacity of catheters are described. An analysis of the physical quantities that are important for the satisfactory detection of a catheter inside a patient shows that an intrinsic index of radio-opacity can be defined and measured using a radiograph of a step wedge. Quantitative comparisons between catheters of different compositions may then be made, and results are presented of measurements made on several commercially available devices. It is suggested that the methods described are more satisfactory than previous techniques used to define standards, and that they highlight some anomalies in current catheter design and usage.

Catheterization↗
PubMed1980

Some sources of artefact in computed tomography.

A number of sources of error and artefact that may arise in X-ray computed tomography are considered. The importance of temporal and spatial non-uniformities in X-ray tube output and detector sensitivity, of changes in voltage supply, of an incomplete field of view, and of scattered radiation, are analysed by calculating their effect on the reconstructed image, and by estimating the noise power that they introduce. Computer simulation is used whenever the error is dependent on the object. The particular relevance of these errors in CT scanners employing arrays of detectors, such as an image intensifier, is emphasised.

Mathematics↗
PubMed1980

The reconstruction of objects from incomplete projections.

The effect of an imcomplete field of view on the reconstruction of objects from their projections is considered. An exact analytical method is used to calculate the reconstruction of an impulse and an annulus which lie out the field of view of an imaging device. A general impression of the effects of truncating the projections of any object may be obtained from these calculations of elemental objects.

Mathematics↗
PubMed1979

Transfer functions for describing ultrasound system performance.

A practical method of assessing ultrasonic A-scan pulse-echo scanner performance is described, which relies upon the identification and quantitation of an overall system transfer function. The mapping of reflecting elements into an image is then described by this transfer function, and indices of system performance, and particularly resolution and range accuracy, are developed in terms of the shape of the transfer function. Some advantages of this method compared to more conventional methods of assessing scanner performance are discussed.

Mathematics↗
PubMed1979

Image formation by back-projection: a reappraisal.

The theory of image formation by simple summation of an object's projections, without further processing, is considered. Calculations are presented of the resultant image from a point, a rectangle, an annulus, and three rotationally symmetric objects. The general features of these images are discussed and it is postulated that for many objects of interest a limited compensation for edge unsharpening would suffice to produce recognition of the objects.

Tomography↗
PubMed1977

Ultrasonic backscattering from human tissue: a realistic model.

The propagation of ultrasound pulses in inhomogeneous media is described, and it is shown that they are scattered by fluctuations in density and compressibility. It is proposed that some of the echoes recorded by diagnostic pulse echo equipment are produced in this way. The precise form of the acoustic field backscattered from tissues is calculated using realistic approximations about the nature of tissue inhomogeneitics and the form of the pulses used. It is shown that only limited information about tissue structure is contained in these signals, and the restrictions imposed by the use of typical pulses are indicated. The implications of this analysis for methods of tissue characterization and clinical imaging are discussed.

Humans↗