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Biomedical subjects

L D Hall

Publications and source records attributed to L D Hall.

At least 19 recordsLinked to original sources

Magnetic resonance imaging: a new window into industrial processing.

Although the most important use of nuclear magnetic resonance imaging (MRI) continues to be for diagnostic medicine, recognition is being gained for many nonmedical applications. Examples include the following areas: petrogeology, food, agriculture, polymers and polymer-composites, and pharmaceuticals. These areas all involve studies of species that have short spin-spin relaxation times, and consequently need far fast gradient switching. These technical details are discussed and typical applications given.

Industry

An investigation of the origins of contrast in NMR spin echo images of plant tissue.

The effects that the spatial distribution of water protons and their transverse relaxation times have on the image contrast of spin echo images of courgette was investigated. The T2-weighted image of courgette contains the most anatomical information. The image contrast was explained using a phenomenological theory based on the Bloch equations, which gave an insight into the morphology and microdynamics of water in the plant tissue. The perceived contrast in the spin echo images of courgette, glucose and Sephadex bead solutions can be dramatically altered by keeping all the imaging acquisition parameters constant, such as the recycle and echo time, but reducing the interpulse spacing by introducing a CPMG train of 180 degrees pulses into the middle of the sequence. These changes were interpreted by considering the microenvironment of the water. This work demonstrates that the origin of image contrast in T2-weighted images of plant tissue can be understood using the water proton transverse relaxation theory developed by Hills et al.

Dextrans

MELAS syndrome with mitochondrial tRNA(Leu)(UUR) mutation: correlation of clinical state, nerve conduction, and muscle 31P magnetic resonance spectroscopy during treatment with nicotinamide and riboflavin.

We report a patient with mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes treated with riboflavin and nicotinamide for 18 months, during which time previously frequent encephalopathic spells ceased. To confirm clinical benefit, we withdrew treatment and monitored response with muscle 31P magnetic resonance spectroscopy (MRS) and sural nerve conduction studies. Of three prospectively chosen MRS variables, two changed coincidentally with clinical end points; phosphocreatine (PCr)/adenosine triphosphate recovery rates fell in parallel with sural nerve sensory amplitudes, and a drop in muscle bioenergetic efficiency (relationship of inorganic phosphate/PCr to the accelerating force of contracting muscle) coincided with development of encephalopathy. Investigations revealed a deficiency of respiratory complex I and mutation of the mitochondrial tRNA(Leu)(UUR). We suggest that a defective cellular energy state in mitochondrial disease may be partially treatable and that changes seen in appropriate muscle spectroscopy studies may parallel improvement in brain and peripheral nerve function.

Adult

Accuracy of lower extremity arterial duplex mapping.

We performed lower extremity arterial duplex mapping from the aortic bifurcation to the ankle in 150 consecutive patients evaluated for aortic and lower extremity arterial reconstruction and compared lower extremity arterial duplex mapping in a blinded fashion to angiography. On the basis of history, physical examination, and four-cuff segmental Doppler pressures individual lower extremities were classified as normal, isolated aortoiliac disease, infrainguinal disease, and multilevel inflow and outflow disease. For vessels proximal to the tibial arteries, lower extremity arterial duplex mapping was analyzed for its ability to insonate individual arterial segments, detect a 50% or greater stenosis, and distinguish stenosis from occlusion. In the tibial arteries lower extremity arterial duplex mapping was evaluated for its ability to visualize tibial vessels and to predict interruption of tibial artery patency from origin to ankle. Lower extremity arterial duplex mapping visualized 99% of arterial segments proximal to the tibial vessels, with overall sensitivities for detecting a 50% or greater lesion ranging from 89% in the iliac vessels to 67% at the popliteal artery. Stenosis was successfully distinguished from occlusion in 98% of cases. In the tibial vessels lower extremity arterial duplex mapping was better at visualizing anterior tibial and posterior tibial artery segments (94% and 96%) than peroneal artery segments (83%), (p less than 0.001). Overall sensitivities for predicting interruption of tibial artery patency were 90% for the anterior tibial, 90% for the posterior tibial, and 82% for the peroneal. Clinical disease category did not influence in a major way the accuracy of lower extremity arterial duplex mapping in either above-knee or below-knee vessels.

Aged

Magnetic resonance imaging of the head and spine: effective for the clinician or the patient?

OBJECTIVES: To test how the results of magnetic resonance imaging influence clinicians' diagnoses and management plans for patients with cranial and spinal problems and to assess changes in the quality of life of these patients. DESIGN: Survey of patients undergoing cranial and spinal magnetic resonance imaging with questionnaires about diagnoses and intended management plans before and after imaging and quality of life questionnaires at the time of imaging and again four months later. SETTING: Regional magnetic resonance imaging and spectroscopy unit. SUBJECTS: 100 consecutive patients referred for cranial imaging in early 1989; 100 similar patients referred for spinal imaging. MAIN OUTCOME MEASURES: Changes in clinicians' leading diagnoses after magnetic resonance imaging and their confidence in these diagnoses; changes in intended management plans; assessment of the contribution to the future management of the patient; changes in patients' quality of life. RESULTS: Magnetic resonance imaging altered the clinicians' leading diagnoses in 35 of 169 (21%) cases. The clinicians became more confident about their leading diagnoses in 90 of 167 (54%). There was a change in management plan in 113 of 182 (62%). The clinicians considered that magnetic resonance imaging made an important contribution to management in 119 of 162 (73%) patients. Overall, the patients' quality of life was unchanged at the four month assessment. CONCLUSIONS: Magnetic resonance imaging of patients with cranial and spinal problems influences clinicians' diagnoses and management plans, but the quality of life of these patients remains unchanged.

Adolescent

A general formalism for the manipulation of multiple-echo data sets, and application to chemical shift editing.

A general data processing formalism is presented which can be applied to the signal intensities of successive echoes of a multiple-echo data set in order to null those species for which the signal decay function is exponential. If asymmetric echo times are introduced into the multiple-echo sequence then chemical shift images akin to those obtained from the magnitude Dixon method can be obtained in half the data acquisition time.

Animals

Localized in vivo proton spectroscopy of the human kidney.

In vivo 1H spectroscopy using the STEAM sequence for localization has been applied to the human kidney in normal volunteers and subjects with successful renal transplants. We show that, within the resolution of our measurements, trimethylamines are present in the spectra from some of the subjects and absent from others. The prominent peak seen at 5.8 ppm in the spectrum is identified as that from urea and not lipid, as previously suggested.

Humans

Cardiac tagging in the rat using a DANTE sequence.

We demonstrate the application of a DANTE tagging sequence to in vivo imaging of the rat heart. This sequence generates narrow parallel tag lines in a short space of time and is combined with cardiac gating to image the heart wall at eight points throughout the cycle.

Animals

Magnetic resonance imaging in a model of atherosclerosis: use of a collar around the rabbit carotid artery.

Transverse cardiac-cycle gated high resolution magnetic resonance images have been obtained from the neck of the New Zealand white rabbit both in normal animals and from those in which a collar had been earlier positioned around one carotid artery. The study included animals fed on normal and on high cholesterol diets with the surgical modification having been demonstrated previously to cause a rapid and reproducible lesion resembling early atherosclerosis. The aim of the work was to investigate the attainable spatial resolution and sensitivity at a field strength of 2 T using a large radiofrequency transmitter system and a surface coil receiver with which spin-echo images have been obtained. Visualization was enhanced using a three-dimensional interpolation technique. An image resolution of 200 microns was readily obtained but was shown to be insufficient for delineating pathological features within the artery wall such as intimal layer thickening. The results have been compared with histopathological findings which confirmed that any morphological changes were within the pixel resolution of the image. Extensions to the methodology are proposed which should be able to detect atherosclerotic changes with a resolution of 50 microns within a feasible imaging time. In addition, the MRI study of how the surgical intervention alters the artery shape and curvature was carried out and the MRI demonstrated that collar implantation in general does not occlude the artery and causes only a slight and gradual degree of curvature to the vessel.

Animals

Magnetic resonance imaging: when is one sequence sufficient?

We have studied 100 patients undergoing magnetic resonance imaging (MRI) in eight well-defined clinical problems. The relative values of the clinical details and the initial imaging sequence in reaching the final MR diagnoses were assessed. For each patient, two radiologists independently predicted the likely radiological findings from the clinical details. They then assessed the radiological appearances shown by the initial imaging sequence (which was chosen according to the clinical problem). Lastly, they made a final interpretation using all the available information. Prediction of likely radiological abnormalities from the clinical details proved unreliable. However, the radiological assessment of the initial imaging sequence was reliable for clinical problems related to the pituitary fossa, posterior fossa, internal auditory meatus and for suspected multiple sclerosis. In these patient groups additional sequences might be reserved for those with equivocal findings. Conversely, assessment of the initial imaging sequence proved unreliable compared with the full radiological assessment for clinical problems in the lumbar spine, the axilla and the knee. This study has led us to reduce the number of sequences performed for some clinical problems, with a commensurate increase in the throughput of patients.

Clinical Competence

Magnetic resonance imaging of experimental allergic encephalomyelitis in primates.

The potential use of quantitative MRI to characterize early, as well as late, immune-mediated lesions of multiple sclerosis (MS) has been investigated. Experimental allergic encephalomyelitis (EAE) was induced in 4 male Macaca fascicularis monkeys, and the development of the disease followed using quantitative MRI at 0.15 Tesla. Serial scans were recorded daily, beginning at day 9 after inoculation. Lesions were detected before the onset of clinical signs, due to an elevation in the spin-lattice (T1) and spin-spin (T2) relaxation times. The T1 and T2 values from the lesions were shown to increase over time, indicative of progressive change at a molecular level. The appearance of any new lesions and any changes in existing ones were noted; this allowed dating of the lesions postmortem. Pathological correlation showed the long T1 and T2 values to be associated with the presence of inflammation, demyelination and haemorrhagic necrosis. Microscopically similar lesions had the same MRI characteristics. In addition, these studies showed the oldest lesions to be the most haemorrhagic; this is contrary to the belief that haemorrhage is a secondary event in EAE. The results show that quantitative MRI is sensitive to variable pathology, and has the potential for use in characterizing the pathological progression in MS.

Animals

Measurement of regional left ventricular function using labelled magnetic resonance imaging.

A technique for assessing regional left ventricular function using magnetic resonance imaging is described. Spatial modulation of magnetization (SPAMM) is effected immediately before images are obtained at various intervals during the cardiac cycle using a modified field echo even rephasing technique (FEER). By performing such modulation in two planes, a grid pattern of labelling can be produced across the image. On the resulting labelled short axis images of the left ventricle, the systolic increase in thickness (thickening) and decrease in length (shortening) of different regions of myocardium can then be measured. The findings in five normal volunteers are presented. Radial shortening was twice as great in the endocardium (mean 20.4%, standard deviation (SD) 5.7) than in the epicardium (mean 10.2%, SD 5.5) and appears to offer more promise as a marker of regional function than simple thickening (mean 9.8%, SD 13.6).

Adult

Duplex ultrasound criteria for diagnosis of splanchnic artery stenosis or occlusion.

Mesenteric artery duplex scanning appears promising for detection of splanchnic artery stenosis or occlusion or both in patients with symptoms suggestive of chronic intestinal ischemia. However, no specific duplex criteria have been developed for detection of mesenteric artery stenosis. We obtained mesenteric artery duplex scans and infradiaphragmatic lateral aortograms in 34 patients to determine duplex criteria for mesenteric stenosis. Seventy percent or greater angiographic stenosis was present in 10 superior mesenteric arteries and 16 celiac arteries. Duplex scans were reviewed to determine if celiac artery and superior mesenteric artery ratios of peak systolic velocities and end-diastolic velocities to peak aortic systolic velocity, as well as celiac artery and superior mesenteric artery peak systolic velocities and end-diastolic velocities alone, could predict a greater than or equal to 70% angiographic stenosis or occlusion or both. The results obtained by use of receiver operator curves indicated peak systolic velocity alone was an accurate predictor of splanchnic artery stenosis. Specifically, a peak systolic velocity greater than or equal to 275 cm/sec in the superior mesenteric artery and greater than or equal to 200 cm/sec in the celiac artery or no flow signal (superior mesenteric artery and celiac artery) predicted a 70% to 100% stenosis with sensitivity, specificity, and positive predictive values of 89%, 92%, and 80% for the superior mesenteric artery. Similar values for the celiac artery were 75%, 89%, and 85%, respectively. End-diastolic velocities or calculated velocity ratios conveyed no additional accuracy in predicting splanchnic artery stenosis.

Adult

Relative metabolic efficiency of concentric and eccentric exercise determined by 31P magnetic resonance spectroscopy.

To determine the relative metabolic efficiency (metabolic energy used per unit of mechanical energy output) of negative to positive muscular power, we used 31P magnetic resonance spectroscopy to monitor the cellular energy metabolism of limb muscles in eight healthy subjects during a nonfatiguing, mixed concentric-eccentric activity and during its concentric and eccentric components. We also studied isometric contractions. We found that in terms of the flow of metabolic energy through the muscle cells, the cost of concentric exercise at this intensity was proportional to the mechanical power generated, but the cost of eccentric and isometric exercise did not increase significantly as the apparent intensity of the exercise increased over the range studied. Although the pattern was similar in all subjects, the quantitative relationship between metabolic cost and mechanical output was different in subjects with different muscular strength. The qualitative results can be explained in the context of the known biochemistry and biophysics of the cellular contractile apparatus (sliding filament theory, with independent force generators).

Adult

Lipid characterization in an animal model of atherosclerosis using NMR spectroscopy and imaging.

High resolution 1H and 13C NMR spectroscopic measurements including 1H/13C 2D correlation and magnetic resonance imaging (MRI) studies, have been carried out on intact rabbit aortic tissues ex vivo using animals fed both normal and high cholesterol diets. The results show that 1H and 13C NMR spectroscopy can distinguish mobile lipids and can differentiate between normal triglyceride content and cholesterol-enriched lipids, in intact tissue, There were considerable differences in the level of deposition of cholesteryl esters in animals all fed on the same diet. Confirmation is presented of temperature-dependent differences in mobility and organization between the triglycerides found in control tissue and the cholesteryl esters found in aortas from high lipid diet animals. Water-suppressed MRI showed evidence of lipid accumulation in the aortas of high cholesterol diet rabbits. It is concluded that the hypercholesterolaemic rabbit model of atherosclerosis, coupled with such NMR methods, may offer a noninvasive method of monitoring disease development, allowing the evaluation of the effect of therapeutic agents on the progress of atherosclerosis.

Animals

Axillary fibrosis or recurrent tumour. An MRI study in breast cancer.

Magnetic resonance imaging was performed in 35 patients with breast carcinoma in an attempt to elucidate the cause for arm oedema or neurological symptoms. In each patient the clinician was asked to predict at the outset whether tumour recurrence or radiation fibrosis was more likely on clinical grounds. MRI demonstrated features compatible with fibrosis in 21 and tumour recurrence in 10; the MRI findings were equivocal in four patients. The range of these appearances is described and demonstrated. The MRI findings were at gross variance with the clinical opinion in 10 patients, upgrading eight patients to tumour recurrence and downgrading two to radiation fibrosis. Although histological confirmation is only available in three patients, corroborative evidence (that is repeat MRI, clinical follow up) is presented which suggests that the MRI interpretation was correct in the remaining patients. MRI can provide a working diagnosis in these patients; this allows a more rational approach to treatment than a diagnosis based on clinical examination alone.

Adult

Magnetic resonance imaging of the brain and brain-stem in elderly patients with dizziness.

Twenty elderly patients (mean age 82 years) with dizziness were examined by magnetic resonance imaging (MRI). The findings have been compared with those from nine healthy subjects of similar age who acted as a control group. The technique proved acceptable to all these patients, and in the majority (65%) the overall radiographic quality of the resulting images was adequate, good or excellent. Nineteen of the 20 patients showed evidence of abnormal high signal intensity within white matter, often close to the frontal horns but also more widely scattered within the cerebral hemispheres; similar lesions were seen in the brain-stem in eight of the patients. However these white matter changes were equally prevalent in the control group. No cause for dizziness has been shown by MRI.

Aged

Polymeric controlled release systems.

There are wide applications of great importance for the improved and efficient administration of many materials--particularly in the pharmaceutical area. The introduction of novel polymeric materials and related formulation technologies now provide a versatile means for the precisely controlled delivery of many physiologically active substances. A further advantage is a decrease in patient discomfort and compliance, and decreased side-effects.

Chemistry, Pharmaceutical