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Biomedical subjects

J M Hutchison

Publications and source records attributed to J M Hutchison.

At least 19 recordsLinked to original sources
PubMed1992

Immunodeficiency syndrome associated with wasting and opportunistic infection in juvenile llamas: 12 cases (1988-1990).

Immunodeficiency was diagnosed as the cause of severe debilitating disease characterized by weight loss, failure to grow, and persistent infections that failed to respond to treatment in 12 young llamas. The llamas were affected after maternal-acquired immunity had decreased; failure of passive transfer of immunoglobulins thus was not suspected. Areas of lymph nodes containing T lymphocytes were hypocellular, suggesting T-cell involvement. High serum immunoglobulin concentrations were not found, despite the existence of infectious disease, suggesting at least secondary B-cell involvement. Results of lymphocyte blastogenesis assays were suggestive of B- and T-cell involvement. It was not possible to determine whether the condition was inherited or acquired.

Animals↗
PubMed1991

AURA: a new respiratory monitor and apnoea alarm for spontaneously breathing patients.

Previous attempts to introduce non-invasive monitoring of ventilation of spontaneously breathing patients into routine practice have been unsuccessful. The Aberdeen University Respiratory Alarm (AURA) allows such monitoring by utilizing the pyroelectric property of polarized polyvinylidine fluoride sensors to detect temperature changes that occur during breathing into an oxygen delivery face mask. A quartz crystal oscillator generates pulses that allow measurement of interexpiratory time and ventilatory frequency. The system incorporates LED digital displays, a bargraph and audiovisual alarms. An analog output permits display and analysis of the sensed signals. AURA performed satisfactorily in both volunteer studies and six patients in the clinical setting. AURA may be an appropriate respiratory transducer in those patients requiring oxygen therapy.

Adult↗
PubMed1990

Impedance imaging in upper arm fractures.

We used the Aberdeen impedance imaging system to drive a constant current of 1 mA on a 10 kHz sine wave into the upper arm encircled by an elastic belt of 16 equi-spaced strip electrodes. The system was used to examine a normal upper arm, an upper arm with a recent humeral fracture and an upper arm with a clinically united fracture. We approximated the human upper arm to a circular cylinder and assumed bilateral symmetry of normal human limbs. We measured transverse limb resistivity ratios and reconstructed static two-dimensional images of the spatial distribution of log(resistivity) by the equipotential back projection technique using a homogeneous muscle equivalent saline reference. Our results indicate that impedance osteography provides unique information about the changing electrical characteristics at the fracture site. This information could prove a useful adjunct to clinical and radiological tests for fracture union.

Calibration↗
PubMed1990

AURA: a new respiratory monitor.

The Aberdeen University Respiratory Alarm (AURA) is designed to monitor the respiratory rate and the inter- expiratory period (respiratory gap) in the spontaneously breathing patient using polarised polyvinylidene fluoride sensors incorporated in the Oxygen delivery mask. The monitor is composed of three modules--the sensor module includes a pair of polyvinylidene film strips mounted on the inner surface of the Oxygen mask. The difference in temperature between the ambient Oxygen enriched air and the warmer expired air allows the pyroelectric property of the sensors to be harnessed. The sensor arrangement allows a differential signal to develop between them which is amplified, filtered and rectified prior to triggering a counter. The timing module is based on a 32,768 Hz crystal oscillator that generates pulses allowing the period between expirations to be measured and compared to the maximum allowable period set by the user. The respiratory rate is also measured and compared to the minimum set by the user using EPROMS and comparators. The display module consists of a bar-graph display of the level of the sensed signal with each breath with a soft audible click. Eight segment LEDs are used to provide a digital display of the respiratory rate and the respiratory gap. Audiovisual alarms are triggered when the rate falls short of the set rate and/or when the gap exceeds the set gap. The need for continuous respiratory monitoring of the spontaneously breathing adult in hospital practice led us to develop this prototype with sensors whose design and configuration can be considerably improved.

Adult↗
PubMed1989

The Aberdeen Impedance Imaging System.

The Aberdeen Impedance Imaging System is designed to reconstruct 2 dimensional images of the average distribution of the amplitude and phase of the complex impedance within a 3 dimensional region. The system uses the four electrode technique in a 16 electrode split-array. The system hardware consists of task-orientated electronic modules for: driving a constant current, multiplexing the current drive, demultiplexing peripheral voltages, differential amplification, phase sensitive detection and low-pass filtration, digitisation with a 14 bit analog to digital converter (ADC), and -control logic for the ADC and multiplexors. A BBC microprocessor (Master series), initiates a controlled sequence for the collection of a number of data sets which are averaged and stored on disk. Image reconstruction is by a process of convolution-backprojection similar to the fan-beam reconstruction of computerised tomography and is also known as Equipotential Backprojection. In imaging impedance changes associated with fracture healing the changes may be large enough to allow retrieval of both the amplitude and phase of the complex impedance. Sequential imaging of these changes would necessitate monitoring electronic and electrode drift by imaging an equivalent region of the contralateral limb. Differential images could be retrieved when the image of the normal limb is the image template. Better characterisation of tissues would necessitate a cleaner retrieval of the quadrature signal.

Adult↗
PubMed1989

Impedance osteography: a technique to study the electrical characteristics of fracture healing.

The occurrence of a fracture in a limb is accompanied by large changes in the electrical characteristics of the region. Resistivity of bone is more than a hundred times that of bone. The relative permittivities of the two are also different. The fracture site is also known to be electronegative. Electrical Impedance Imaging is capable of reconstructing a two dimensional (2D) representation of the average distribution of amplitude and phase in a three dimensional (3D) region. The spatial resolution in impedance imaging is low, yet the technique is sensitive to properties that are rapidly changing in growing tissues. Though the reconstructed image is an average of a thick slice, this may be of some advantage in impedance osteography precluding the need for imaging multiple planes to cover the extent of the fracture. We used the Aberdeen Impedance Imaging System which uses the 4 electrode technique in a split array, and a current of 1 milliampere on a carrier of 10 kHz to collect a number of data sets. The averaged data sets were used to reconstruct images by the Equipotential backprojection method. In this pilot study we concentrated on the real part of the complex impedance to produce images of log resistivity. The a-priori assumption of bilateral symmetry of human limbs allowed us to reconstruct equivalent regions of the normal and fractured limbs by inverting the electrode array. We obtained static images of the distribution of log resistivity when we used a homogeneous distribution as a reference, and a differential image comparing the fractured to the normal limb. The three patients in our study were at different clinical stages of fracture healing as confirmed by radiography. Our results show the feasibility of using the technique to study and monitor fractures during the healing process.

Bone and Bones↗
PubMed1988

Projective Fourier angiography.

The Fourier imaging of flow is discussed, and the limitations of imaging time, spatial and velocity resolution, imposed on this technique when applied in conjunction with ECG synchronization are examined. It is argued that this method is best used in projective format, and in vivo examples are presented. The relative velocity spectrum obtained is largely system independent, and quantification of velocity is implicit in the Fourier technique.

Angiography↗
PubMed1988

Magnetic resonance image synthesis from an interleaved saturation recovery/inversion recovery sequence.

An interleaved saturation recovery/inversion recovery (SR/IR) pulse sequence allows the sign of the IR signal to be retained even if images are formed from the magnitude of the two-dimensional complex Fourier transforms of the raw data. Synthesis of images by a linear combination of SR and signed IR pixel values has proved a valuable method of relaxation time (T1) contrast manipulation without the need to re-image the slice. Linear combination has also allowed IR images with a wide range of time-to-inversion (TI) values to be synthesized from an SR/IR pair obtained with TI = 200 ms and time-to-recovery (TR) = 1000 ms, thus avoiding the need for computationally intensive calculations based on complicated relaxation equations.

Computer Simulation↗
PubMed1986

The indirectly obtained fetal heart rate: comparison of first- and second-generation electronic fetal monitors.

Fetal heart rate variability has become an essential component in evaluation of the fetus during continuous electronic fetal monitoring. Because of technical deficiencies of monitoring equipment, fetal heart rate variability may not always be available, such as during indirect monitoring of the fetus. In lieu of integration, a mathematical procedure called autocorrelation has, with the use of microprocessors, been incorporated into the fetal monitor, creating the "second generation" of electronic fetal monitoring. This study examined the accuracy of the first- and second-generation monitors by comparing simultaneously obtained indirect and direct real-time fetal heart rate data. The second-generation monitor produced an indirectly obtained fetal heart rate that was more accurate when compared with the directly obtained data than that with the first-generation fetal monitor. In addition, the variation in data from the first-generation monitor was substantially higher than that with the second-generation monitor. It is concluded that the fetal heart rate tracing from the second-generation monitor is more accurate when compared with the fetal electrocardiogram and may facilitate a truer interpretation of fetal heart rate variability than that obtained with the first-generation monitor.

Electrocardiography↗
PubMed1985

Particulate oral NMR contrast agents.

Insoluble paramagnetic compounds in suspension can be used to achieve visualization of the gastrointestinal system on magnetic resonance imaging (NMR). Particulate preparations of these agents decrease the T1 and T2 of solutions to which they are added. Gadolinium oxalate, a prototype of these particulate agents, was evaluated in vitro and in vivo (in rabbits) by NMR imaging. The effect of this compound upon T1 and T2 in vitro was also quantitated by NMR spectroscopy. Opacification of the upper gastrointestinal tract was achieved with gadolinium oxalate following oral administration. The colon was visualized following rectal administration.

Administration, Oral↗
PubMed1985

Nuclear magnetic resonance (NMR): I. Imaging biochemical change.

Nuclear magnetic resonance (NMR) imaging of hydrogen in body water and fat is proving valuable in clinical investigation of the brain. An introduction to the technique and to the biological significance of the images is presented here. The 'multi-parameter' nature of these images is stressed, and the individual parameters described. NMR imaging may well be of value in investigating the pathology of organic and functional psychoses.

Brain↗
PubMed1984

Nuclear magnetic resonance pulse sequence and discrimination of high- and low-fat tissues.

Signal size compared to independently measured T1 is described for various pulse sequences on the Aberdeen Mk II nuclear magnetic resonance imager. The ability of these sequences to discriminate between certain tissue types, and in particular between adipose tissue and muscle, is discussed. Inversion recovery, with a t interval of 200 ms, gives the best discrimination for this purpose, with a contrast ratio of 6 between fat and muscle. Other image types, and especially T1, give better contrast for low-lipid soft tissue such as liver and spleen.

Adipose Tissue↗
PubMed1984

NMR imaging in human pregnancy: a preliminary study.

In an effort to demonstrate the potential of nuclear magnetic resonance imaging (NMR) in the management of pregnancy, 15 patients in the first trimester and one in the third trimester of pregnancy have been investigated in the Aberdeen University NMR imager. Simple measurements of biparietal diameter and crown-rump length were made from both the NMR images and the ultrasound images on the same day, with good correlation between the two. The NMR data was displayed as inversion recovery, calculated T1, proton density and S1-S2 images. The proton density and S1-S2 images were found to be the most useful for the demonstration of the fetus and for discriminating between placenta and uterus. The calculated T1 data provided accurate quantification of the proton-spin lattice relaxation times of the different tissues, indicating that this measurement may be of use in the study of fetal brain development and placental function. The inversion recovery images showed poor tissue discrimination and were found to be of limited value. The unique information available using NMR and the non-invasive nature of the technique indicated that it should provide a useful method for the investigation of both fetal development and placental function in addition to making basic measurements of fetal size.

Cephalometry↗
PubMed1984

Estimating patient dielectric losses in NMR imagers.

Dielectric losses in the patient may impair radiofrequency receiver coil sensitivity, and transmitter coil efficiency, in nuclear magnetic resonance (NMR) imagers. The frequency dependence of this loss mechanism is derived. Patient losses in a solenoidal head coil used for imaging heads were simulated by a cylindrical saline phantom. The frequency dependence of the loss introduced by the phantom can indicate whether dielectric losses in the patient will be significant compared to eddy current losses. The detuning caused by the phantom is used to calculate an upper limit for the distributed stray capacitance between coil and patient. Given the approximate conductivity of the patient, an upper limit for the dielectric loss can be estimated. Some methods of reducing patient dielectric losses are suggested.

Electric Conductivity↗