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Biomedical subjects

R J Knowles

Publications and source records attributed to R J Knowles.

At least 19 recordsLinked to original sources
PubMed1989

The influence of Calicophoron microbothrium on the susceptibility of Bulinus tropicus to Schistosoma bovis.

A total of 480 snails were collected from 3 habitats on the Mau Escarpment, Kenya, and were identified as Bulinus tropicus. Of the 351 snails examined alive in London, 75 were infected with Calicophoron microbothrium, 39 with C. microbothrium and Schistosoma bovis, 1 with S. bovis, 24 with other species of trematodes and 212 were uninfected. Examination of digestive glands of B. tropicus either uninfected or infected with both C. microbothrium and S. bovis demonstrated that it is possible to differentiate between parasite and host enzyme activity using glucose phosphate isomerase. However, malate dehydrogenase enables a much clearer differentiation between the enzyme activity of the schistosome and that of the amphistome. Laboratory snail infection experiments demonstrated that it is possible successfully to infect B. tropicus with S. bovis if the snails have previously been exposed to miracidia of C. microbothrium.

Animals↗
PubMed1988

MR imaging of portal venous thrombosis: correlation with CT and sonography.

Fourteen patients with portal venous thrombosis (PVT) diagnosed by CT and/or sonography were studied with MR. Three of the 14 had portal hypertension. The MR findings were compared with those of eight patients with portal hypertension, but without CT or sonographic evidence of PVT. MR imaging showed portal venous thrombosis in all 14 PVT cases. Intraluminal thrombi of less than 5 weeks duration appeared markedly hyperintense relative to liver and muscle on both T1- and T2-weighted images. Older thrombi appeared hyperintense relative to liver and muscle in eight of 11 cases, but only on T2-weighted images. MR showed thrombi in 11% more portal vessels than did CT (MR = 30, CT = 27) and in 28% more vessels than did sonography (MR = 32, sonography = 25). MR also showed 24% more collateral vessels than did CT (MR = 31, CT = 25) and 50% more vessels than did sonography (MR = 33, sonography = 22). Third-echo images (echo time = 96 msec, repetition time = 1500-2150 msec) verified the presence of venous thrombi in 28 (93%) of 30 PVT vessels, and they differentiated flow-related intravascular signal from true thrombi in six (17%) of 36 portal hypertension vessels. We conclude that MR is a valuable tool for imaging portal vein thrombosis. MR is a good substitute for CT and can be more informative than sonography.

Female↗
PubMed1987

Segmental patterns of avascular necrosis of the femoral heads: early detection with MR imaging.

Thirty-two patients (64 hips) in whom avascular necrosis (AVN) of the femoral heads was highly suspected clinically were studied by magnetic resonance (MR) imaging, radionuclide bone scintigraphy, and conventional radiography. MR studies were positive for AVN in 37 hips, compared with 30 positive scintigraphic studies. In all cases in which scintigraphy and radiography were positive, MR imaging demonstrated decreased signal from the affected femoral heads, indicative of bone marrow disease. Imaging results were confirmed by biopsy or subsequent imaging appearances. In patients with negative initial scintigraphic and radiographic studies, the MR imaging criterion for a positive study was a moderately decreased bone marrow signal displaying segmental patterns within an otherwise normal-appearing femoral head on relatively T1-weighted images. In this series of high-risk patients, radionuclide scintigraphy had a sensitivity of 81%, compared with 100% for MR imaging. MR imaging should be the imaging modality of choice for early evaluation of bone marrow changes indicative of AVN.

Femur Head Necrosis↗
PubMed1986

Effect of magnetic resonance imaging on DDD pacemakers.

A previous study suggested the safety of exposing patients with certain pacemakers models to magnetic resonance imaging (MRI). However, the function of a variety of more advanced DDD pacemakers and the effect of higher magnetic and radio-frequency (rf) field strengths has not been reported. In the present study 4 different DDD pacemakers (Cordis 233F, Intermedic 283-01, Medtronic 7000A, and Pacesetter 283) were tested in a saline phantom under several conditions and with various imaging sequences. Pacemaker output was monitored using electrocardiographic telemetry. All units paced normally in the static magnetic field. However, during imaging, all units malfunctioned, with total inhibition of atrial and ventricular output in 3 of the pacemakers. In the fourth pacemaker, ventricular backup pacing was activated at high rf pulse repetition rates. However, the MRI scanner could trigger atrial output in this pacemaker at rates of up to 800/minute. All malfunctions were a result of rf interference, whereas gradient and static magnetic fields had no effect. Thus, despite magnetic fields had no effect. Thus, despite magnetic field strengths adequate to close pacemaker reed switches, rf interference during MRI may cause total inhibition of atrial and ventricular output in DDD pacemakers, and can also cause dangerous atrial pacing at high rates. MRI should be avoided in patients with these DDD pacemakers.

Electrocardiography↗
PubMed1985

Bulinus tropicus from Central Kenya acting as a host for Schistosoma bovis.

One hundred and twelve snails were collected from two habitats on the Mau Escarpment, Kenya and were provisionally identified as Bulinus tropicus from the characteristics of their shell and soft parts, chromosome number (n = 18), electrophoresis of egg protein on cellulose acetate strip and isoelectric focusing of AcP, GPI, HBDH, MDH and PGM digestive gland enzymes. Of the 55 specimens examined alive in London, 10 were infected with amphistome and schistosome larvae, 9 with amphistome larvae and the remainder were uninfected. The GPI and MDH separations of known infected snails showed two distinct areas of activity: host and parasite. Individual hamsters were exposed to schistosome cercariae emanating from each snail with a double infection (apart from one which died prematurely) and examination of the resulting adult worms showed that all were monomorphic for AcP with a band of enzyme activity at pH 6.45, characteristic of Schistosoma bovis. Examination of eggs found in two infections proved to be S. bovis in shape and size. Exposure of laboratory-bred snails of B. tropicus from the Mau Escarpment and other populations of B. tropicus proved negative. Thus, it is suggested that the presence of the amphistome infection may have a suppressive effect on the immune system of the snail, thereby allowing S. bovis to develop.

Animals↗
PubMed1985

Bulinus tropicus, a natural intermediate host for Schistosoma margrebowiei in Lochinvar National Park, Zambia.

Snails, provisionally identified as Bulinus tropicus, on the basis of chromosome number, egg protein profile, AcP and HBDH enzymes of the digestive gland, and radular morphology, from Lochinvar National Park, Zambia have been demonstrated to transmit Schistosoma margrebowiei naturally. The identification of the unpaired male schistosomes was confirmed by PGM and AcP analyses. The observations confirm earlier epidemiological predictions, and add another species of mollusc to the two, B. forskalii and B. scalaris, known to be natural intermediate hosts of S. margrebowiei.

Animals↗
PubMed1985

Multi-section multi-echo pulse magnetic resonance techniques: optimization in a clinical setting.

The user-selectable magnetic resonance imaging parameters involved in a multi-section multi-echo pulse sequence are described and their interrelationships explained. These parameters include repetition time (TR), echo delay time (TE), the number of sections (S), the number of echoes (E'), the time from the center of the last echo to the end of data acquisition (15 msec on the authors' system), and the time for T1 recovery. A simple mathematical relationship among these quantities, permitting easy calculation of the remaining parameters once a sufficient number have been specified, is given. In addition, a nomogram that permits rapid visual estimation of these parameters is presented. The effects of these choices and others is explained with respect to imaging time, region covered, and image contrast. Finally, the inherent trade-offs are illustrated in a clinical example involving the pelvis.

Humans↗
PubMed1984

Observations on Schistosoma intercalatum in south-east Gabon.

Observations were made in the field and laboratory to determine the strain characteristics of Schistosoma intercalatum in south-east Gabon. For an isolate from Franceville, data are given for egg shape, behaviour of cercariae, seven enzyme systems separated by isoelectric focusing, and intermediate host specificity. Isolates from Cameroun (Edea) and Zaire (Kisangani) were included in a comparative study of the enzymes; Franceville and Edea isolates resembled each other but differed from the Zaire isolate in hexokinase and phosphoglucomutase. The Franceville isolate was polymorphic in phosphoglucomutase and glucosephosphate isomerase. The sum of characters indicates that S. intercalatum as known from south-east Gabon belongs to the strain found in Cameroun and western Gabon, rather than to the strain known from Zaire. More information is needed on strain distribution, particularly for an area including western Zaire and the Republic of the Congo, which appears to separate the two known strains.

Acid Phosphatase↗
PubMed1984

A new headholder for PET, CT, and NMR imaging.

A new headholder was developed for patient restraint and repositioning during positron emission tomography (PET), CT, and nuclear magnetic resonance (NMR) imaging procedures. A customized form was produced for each patient by pouring polyurethane resin and catalyst between an injection-molded polystyrene shell and a protective latex sheet and placing the patient's head in the form while the resin set. Excellent head restraint and repositioning was achieved when the headholder was used with a crossed-laser system. Repositioning accuracy was demonstrated by comparing transmission scans of the same patient obtained on different days and by comparing PET transmission scans with coplanar CT scans. No artifacts due to the headholder were apparent in CT, PET, and NMR images.

Evaluation Studies as Topic↗
PubMed1984

Magnetic resonance imaging systems: optimization in clinical use.

Magnetic resonance (MR) imaging confronts the user with a large number of options that can critically affect image quality. Among the most important parameters over which the user may exercise control are receiver frequency, tip angles, imaging and compensatory gradient strengths, the number of signals averaged, the number of phase encoding gradient steps, and the repetition times. All of these parameters were systematically varied and optimal values determined for a 0.5T Teslacon system, a task which employed both phantoms and normal volunteers. Under the normal conditions of tuning, the z-compensatory gradient presents the most critical adjustment. The compromise between image quality and time of study was also carefully examined, with the following determined as best: 192 gradient steps plus two signal averages for the head coil, or 192 gradient steps plus four signal averages for the body coil.

Humans↗
PubMed1979

Radioxenon ventilation studies with disposable apparatus: technique and application.

Modification of commercially supplied disposable apparatus for radioxenon ventilation imaging solved several problems: occasional poor inhalation of the initial bolus of gas, awkward initiation of the wash-out phase, and building up of pressure against which the patient must exhale in the wash-out phase. Two cases illustrate results of ventilation and perfusion imaging in chronic obstructive pulmonary disease and pulmonary embolism. A third case illustrates results before and after bullectomy, including quantitative data analysis of the wash-out phase. Although long-range economy is possible with permanent equipment, the use of the modified disposable apparatus may be preferable in certain circumstances.

Adult↗
PubMed1977

On Schistosoma margrebowiei Le Roux, 1933: the morphology of the egg, miracidium and cercaria, the compatibility with species of Bulinus, and development in Mesocricetus auratus.

The morphology of the egg, miracidium, and cercaria of Schistosoma margrebowiei are described. The compatibility of S. margrebowiei with species of Bulinus has been examined. The parasite develops well in the diploid, tetraploid and octoploid snails of the truncatus/tropicus complex with overall infection rates of 38.1%, 30.1% and 29.1% respectively, and in reticulatus group snails (Bulinus wrighti) with an infection rate of 45.8% of those snails surviving the prepatent period. Only two species of the forskali complex (Bulinus bavayi, Aldabra; Bulinus beccarii, South Arabia) are slightly compatible, and snails of the africanus group are incompatible. The overall worm return from 24 hamsters exposed individually to 100 cercariae was 39.8%; 82.1% of the worms were paired, the remainder unpaired. The growth of the paired worms was recorded from 28-60 days. The prepatent period in hamsters in 33 days, in sheep 38 days. The mean egg production was 837 eggs/day in infections ranging from 33 to 60 days. Most eggs (80.9%) were deposited in the intestine, and only 18.2% were deposited in the liver. The parasite is pathogenic in hamsters, and peak death rate occurred in the 50-60 day group infections which coincided with the period of peak egg production.

Animals↗