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Biomedical subjects

D A Turner

Publications and source records attributed to D A Turner.

At least 91 records · Page 5Linked to original sources
PubMed1991

Truncation artifact: a potential pitfall in MR imaging of the menisci of the knee.

Because truncation artifacts on magnetic resonance (MR) images may be confused with meniscal tears, measures to suppress them were investigated in a human cadaver knee and prospective and retrospective studies of patients. The artifacts were most prominent when the acquisition matrix was 128 x 256 and the 128-pixel (phase-encoded) axis was in a superoinferior (SI) orientation. An anteroposterior (AP) orientation of the 128-pixel axis or use of a 256 x 256 acquisition matrix reduced the prominence of or nearly eliminated the artifacts. A review of reports of MR imaging and arthroscopic examinations of 83 knees yielded eight menisci that were falsely interpreted at MR imaging as having tears. Retrospective review of the images suggested that the errors were due to truncation artifacts in two cases. Truncation artifacts will cause relatively little difficulty if diagnostic observers are aware of their characteristics and simple steps are taken to minimize their prominence, including acquiring images in 192 x 256 or 256 x 256 matrices or AP rather than SI orientation of the phase-encoded (128-pixel) axis of 128 x 256 matrices.

Autopsy↗
PubMed1991

Lesioning of the striatum reverses motor asymmetry in the 6-hydroxydopamine rodent model of parkinsonism.

In the rat several paradigms of grafting of adrenal medulla into the striatum were studied following the induction of a parkinsonian model, using a unilateral 6-hydroxydopamine (6-OHDA) lesion of the substantia nigra. Direct autologous grafting of adrenal medulla into the caudate-putamen complex, a radiofrequency lesion of the striatum alone, and a radiofrequency lesion followed by delayed grafting of adrenal medulla were compared by analyzing rotational behavior. Direct grafting of adrenal medulla produced an overall reduction in apomorphine induced turning behavior by 43.5% when compared with controls. Radiofrequency lesioning of the striatum without graft showed the best improvement over control animals with a 92% reduction in the total number of rotations induced by apomorphine. Delayed grafting into the caudate lesion cavity also produced a dramatic reduction in motor asymmetry but did not improve the behavioral outcome over that of the lesion alone. Animals receiving only radiofrequency lesions exhibited a band of increased tyrosine hydroxylase like immunoreactivity bordering the lesion cavity. Graft survival was limited in the non-lesioned animals but appeared enhanced in the animals whose striatum was previously lesioned. Lesion location within the striatum influenced the behavioral outcome. Large reductions in apomorphine-induced rotations could result from small lesions of the dorso-lateral striatum. These findings indicate that selective destruction of the caudate-putamen complex without tissue transplantation produces a dramatic reduction in the motor asymmetry of 6-OHDA treated rats. Suggested explanations for the decrease in induced rotational behavior with radiofrequency lesions include a decrease in the number of striatal dopamine receptors following cell destruction and lesion-induced recovery of host dopaminergic afferents. Striatal damage in critical areas can reverse some of the motor behavior associated with the 6-OHDA model and needs to be considered when evaluating the effects of neural grafting in this model.

Adrenal Medulla↗
PubMed1991

Excitatory synaptic potentials in kainic acid-denervated rat CA1 pyramidal neurons.

Intracellular recordings were performed in the CA1 region of the rat hippocampus following an ipsilateral intraventricular injection of kainic acid. Seven days postlesion, graded bursts of up to four action potentials could be evoked by stimulation of the stratum radiatum. The evoked EPSPs underlying these bursts showed a prolonged 10-90% rise time and half-width compared to control EPSPs, an absence of a significant inhibitory phase, and an increase in magnitude and duration at depolarized resting levels. The evoked EPSPs also exhibited a significant decrease in amplitude and time course in response to D-APV (D-2-amino-5-phosphonovaleric acid; 1-20 microM), though this effect was variable from cell to cell. The prolonged time course, voltage sensitivity, and response to a selective NMDA antagonist confirmed that the major component of the EPSP in neurons from lesioned slices was mediated by NMDA receptors. The partial denervation of the CA1 area induced by the kainic acid led to both an enhanced NMDA-mediated excitatory phase and a decrease in postsynaptic inhibition, resulting in the pronounced hyperexcitability noted in the lesioned slices.

2-Amino-5-phosphonovalerate↗
PubMed1991

Multigated blood-pool imaging using heart sounds.

A method to trigger multigated blood-pool (MGBP) acquisition using both the first and second heart sound has been developed. The heart sound gating (HSG) circuitry identifies, individually, both the first (S1) and second (S2) heart sounds from their timing relationship alone, and provides two trigger points during the cardiac cycle. First heart sound gating may be performed to assess the systolic ejection portion of the cardiac cycle, with S2 gating utilized for reproduction of the diastolic filling portion of the cycle. Heart sound gating has been applied to twenty patients who underwent analysis of left ventricular function, and compared to conventional ECG-gated MGBP. Left ventricular ejection fractions calculated from MGBP studies using a first and a second heart sound trigger correlated well with conventional ECG gated acquisitions in patients adequately gated by HSG and ECG. Heart sound gating may be utilized in patients with rapidly changing heart rates, as S1 and S2 precisely define end-diastole and end-systole, respectively, and in situations when the ECG is inadequate for gating purposes.

Electrocardiography↗
PubMed1990

A patient with simultaneous absence of "classical" natural killer cells (CD3-, CD16+, and NKH1+) and expansion of CD3+, CD4-, CD8-, NKH1+ subset.

The clinical manifestations of putative natural killer (NK) cell deficiency are not well-known but theoretically should include recurrent tumors and systemic viral infections. In this article, we discuss a patient with recurrent condylomata, vulvar and cervical carcinoma in situ, pulmonary infiltrates of unknown significance, and a hypercoagulable state. This patient has a dramatic persistent deficiency in her circulating "classic" NK cells (CD3-, CD16+, NKH1+) and a simultaneous persistent expansion of a normally minor lymphocyte cell subset (CD3+, CD4-, CD8-, NKH1+) that does not express the alpha beta heterodimer of the T cell receptor. T-lymphocyte function, as measured by mitogen and alloantigen responsiveness in vitro, was normal. The coexistence of this particular clinical complex with this unusual set of laboratory abnormalities tends to emphasize our meager understanding of the biologic role of NK cells. At the very least, these findings suggest that the clinical manifestations of NK cell deficiency need not be dominated by disseminated systemic viral infections and that perhaps there should be a higher index of suspicion for the scrutinization of NK cell function.

Adult↗
PubMed1990

Data acquisition and analysis system for intracellular neuronal signals.

A comprehensive system for the acquisition and analysis of neurophysiological data is described, with a focus on intracellular data. The software comprising the system will evaluate a number of neuronal signals, including intracellular as well as extracellular recordings from neurons, evoked potentials and computer simulation data. Significant enhancements enable sampling at high resolution (50 kHz throughput to disk; +/- 15 bit or 96 db), concurrent with extensive on-line analysis capabilities and display. Modifications of existing software and development of new types of input and output devices and analysis can be incorporated as needed, using a binary digital database as the primary storage for the experimental signals and device-independent graphics.

Cell Communication↗
PubMed1990

Feed-forward inhibitory potentials and excitatory interactions in guinea-pig hippocampal pyramidal cells.

1. The patterns of inhibition in the CA1 region of the rat hippocampus were evaluated by focal proximal and distal stratum radiatum stimulation, during intracellular recording. The characteristics of isolated inhibitory responses and the interactions of excitatory and inhibitory potentials were analysed. 2. The amplitude of minimal inhibitory postsynaptic potentials (IPSPs) evoked by both proximal and distal stimulation averaged -0.51 +/- 0.24 mV (mean +/- S.D.; n = 32). These responses demonstrated little variability from trial to trial and showed no net trends in amplitude at a stimulation rate of 1 Hz. 3. Minimal IPSPs demonstrated a short latency to onset (2.90 +/- 1.58 ms for proximal and 3.64 +/- 1.39 ms for distal) at stimulation levels which were insufficient to evoke an extracellular field potential. Thus, minimal IPSPs were recruited through feed-forward circuitry, based on the rapid onset and the lack of activation of recurrent collaterals. 4. The minimal IPSPs showed a similar 10-90% rise time for proximal and distal responses. However, the half-width and decay time constant (from the peak) were more prolonged for the distal stimulation, indicating that a late IPSP component was evoked primarily by the distal stimulation. This late component was not observed in isolation at low stimulation intensities. 5. The conductance transient underlying the IPSPs was calculated using a neurone cable model. The proximal IPSP responses were simulated by an alpha input function (at the soma) with a peak conductance in the range of 2.5-45 nS (alpha = 1.75; reversal potential -1.0 to -10 mV). The distal IPSP shape was only partially reproduced by a longer single transient (alpha = 1.25), suggesting the presence of a second, slower component. However, insufficient data on this slower component precluded a more exact simulation of the distal IPSP response. 6. Analysis of interactions between minimal excitatory postsynaptic potentials (EPSPs) and IPSPs showed that often the rising as well as the falling phase of the EPSP could be affected by the IPSP. At small stimulation levels, minimal EPSPs and IPSPs were closely overlapping, but the IPSPs were of significantly longer duration than EPSP responses. 7. The composite EPSP waveform shape became progressively truncated with increasing afferent stimulation. Feed-forward inhibition limited the time course of excitation to a narrow window, approximately 3-5 ms wide. Feed-forward postsynaptic inhibition significantly limited both the duration and the overall efficacy of small EPSPs in CA1 pyramidal neurones.

Action Potentials↗
PubMed1990

Risk of late stroke and survival following carotid endarterectomy procedures for symptomatic patients.

The long-term outcome following carotid endarterectomy for neurological symptoms was analyzed using a retrospective life-table approach in 212 patients who had undergone 243 endarterectomy procedures. The postoperative follow-up period averaged 38.9 +/- 2.1 months (mean +/- standard error of the mean). The endpoints of stroke and death were evaluated in these patients. Patient groups with the preoperative symptoms of amaurosis fugax, transient ischemic attack, and prior recovered stroke were similar in terms of life-table outcome over the follow-up period. Sixty-two percent of symptomatic patients were alive and free of stroke at 5 years. The late risk of stroke (after 30 days postoperatively) averaged 1.7% per year based on a linear approximation to the hazard at each life-table interval (1.3% per year for ipsilateral stroke). The trend of late stroke risk was clearly downward, however, and could be fitted more accurately by an exponential decay function with a half-life of 33 months. Thus, the risk of stroke following carotid endarterectomy for neurological symptoms was highest in the perioperative period, slowly declined with time, and occurred predominantly ipsilateral to the procedure. The definition of a prospective medical control group remains crucial for a critical analysis of treatment modalities following the onset of premonitory neurological symptoms. In the absence of an adequate control group for this series, the calculated perioperative and postoperative stroke risk from this study was compared to data obtained from the literature on stroke risk in medically treated symptomatic patients. This uncontrolled comparison of treatment modalities suggests the combined perioperative and postoperative stroke risk associated with carotid endarterectomy to be modestly improved over medical treatment alone.

Carotid Artery Diseases↗
PubMed1989

Magnetic resonance imaging of adrenal cortical carcinoma.

Five cases of adrenal cortical carcinoma examined with magnetic resonance (MR) are presented. Clinical histories, computed tomographic (CT) scans, and final pathologic findings were reviewed in each case. All masses were hypointense compared to the liver on T1-weighted images and became hyperintense compared to the liver on T2-weighted images. Signal intensity of adrenal masses, fat, and liver were measured. Adrenal/liver and adrenal/fat signal intensity ratios were then calculated. All the masses were readily identified with MR. The MR also demonstrated displacement or invasion of adjacent organs, as well as liver metastases. The inferior vena cava was also identified in each case. Even though there were no consistent MR findings to diagnose adrenal cortical carcinomas accurately, superior blood vessel identification and multiplanar capabilities may make MR the imaging modality of choice in evaluating the extent of disease and in planning surgical excision.

Adrenal Cortex↗
PubMed1989

Peripartum cardiomyopathy. A rare cause of pulmonary oedema in late pregnancy.

A case of peripartum cardiomyopathy that occurred together with pre-eclampsia is described. This gave rise to pulmonary oedema at 36 weeks' gestation. Intensive care management and the need for invasive monitoring, especially pulmonary artery wedge pressure, of patients who develop pulmonary oedema in the peripartum period is discussed.

Cardiomyopathies↗
PubMed1989

Femoral capital osteonecrosis: MR finding of diffuse marrow abnormalities without focal lesions.

Six painful hips in five patients were examined with magnetic resonance (MR) imaging and were found to have diffuse signal abnormalities in the marrow of the femoral head and neck, which extended into the intertrochanteric area in five cases. The abnormal regions were low in signal intensity on images obtained with a short repetition time (TR) and a short echo time (TE) and were isointense or hyperintense on long TR/TE images--findings that have been attributed by others to bone marrow edema. Edema was also seen in marrow just above the acetabulum in two cases. No focal abnormalities characteristic of osteonecrosis were seen. Osteonecrosis was subsequently shown to be present in all six femoral heads at core biopsy (three cases) or by subsequent development of focal MR abnormalities reported to be highly specific for osteonecrosis (three cases). The affected hips had been radiographically normal or subtly osteopenic and had shown intense radionuclide uptake in the femoral head at scintigraphy, with lesser abnormality in the neck and intertrochanteric region. Follow-up MR examinations of five of the six femoral heads showed the diffuse abnormalities to have been transient. Although diffuse MR abnormalities in the proximal femur are not specific, they may indicate the presence of osteonecrosis of the femoral head.

Adult↗
PubMed1989

Imaging of abdominal aortic aneurysms.

There is no single correct approach to evaluate aortic aneurysm. Variations in individual cases, equipment availability, technical expertise, and surgeons' preference frequently dictate the workup. Sonography is optimal for screening and follow-up in uncomplicated cases. CT is excellent in preoperative and postoperative evaluation of aneurysms and their potential complications. Angiography is used to determine visceral-branch involvement and define variations in vascular anatomy, although its routine preoperative use is controversial. MR imaging has emerged as a powerful tool to visualize and stage aneurysms.

Aorta, Abdominal↗
PubMed1989

The prognostic significance of peritoneal cytology for stage I endometrial cancer.

A retrospective study of 567 patients treated for surgical stage I endometrial cancer was undertaken to resolve the controversy over the significance of malignant peritoneal cytology findings in early-stage disease. Twenty-eight women (4.9%) had peritoneal cytology positive for malignant cells. Comparisons were made between the groups with positive and negative cytology. Subgroups used in analysis included stage according to the International Federation of Gynecology and Obstetrics, treatment regimen, histology, grade, depth of myometrial invasion, and cervical Papanicolaou smear results. Cervical smear status was the only subgroup in which a statistically significant difference was found, with the positive peritoneal cytology patients having a higher incidence of positive Papanicolaou smears (P = .01). Forty-nine women (8.6%) developed recurrent tumor, 7% of the negative-cytology group and 32% of the positive-cytology group (P = .0002). The progression-free survival rate was lowered significantly by positive peritoneal cytology (P less than .0001); patients with negative peritoneal cytology had a significantly better 5-year survival rate, 96 versus 84% (P = .0001). When multivariate analysis was performed on the 477 cases that had no missing values, peritoneal cytology remained significant for both survival rate (P = .01) and progression-free interval (P = .002). Positive peritoneal cytology is a poor prognostic factor for patients with surgical stage I endometrial cancer.

Adenocarcinoma↗
PubMed1988

Detection and localization of nonmetallic intraocular foreign bodies by magnetic resonance imaging.

Computed tomography (CT) is useful in detecting metallic intraocular foreign bodies. Magnetic resonance imaging (MRI) is a technique that might allow the detection and localization of nonmetallic intraocular foreign bodies. We performed CT and MRI scans on ten freshly enucleated sheep eyes, eight of which contained nonmetallic intraocular foreign bodies of wood, glass, plastic, or rock. Computed tomography correctly detected seven of eight foreign bodies, while MRI detected all eight of the foreign bodies. Computed tomography is necessary to determine the presence of a metallic foreign body, but when the CT scan is negative, MRI may still detect small nonmetallic foreign bodies.

Animals↗
PubMed1988

Waveform and amplitude characteristics of evoked responses to dendritic stimulation of CA1 guinea-pig pyramidal cells.

1. Dendritic synaptic responses were evoked in CA1 hippocampal pyramidal cells using a microstimulation protocol which included focal excitation of proximal and distal apical afferents. Ensembles of excitatory postsynaptic potentials (EPSPs) were analysed for magnitude, waveform parameters and fluctuation characteristics between responses. 2. The peak amplitude of the minimal detectable responses to dendritic stimulation ranged from 0.12 to 0.89 mV. Control experiments showed separation of the minimal EPSPs from extracellular field potentials and somatic inhibition. The EPSPs demonstrated no significant amplitude trends over ensembles of 150-300 responses, at a 2 Hz stimulation rate. 3. Both minimal (less than 1 mV) and large (1-5 mV) proximal and distal evoked EPSPs were clearly different in terms of all waveform parameters analysed. However, the large EPSPs exhibited substantially less proximal-distal separation than the minimal responses. 4. The separation of minimal proximal and distal responses was similar to that predicted by earlier dendritic model simulations, after revision of the model parameter determining shape of the synaptic input. The proximal and distal synapses are separated by approximately 0.6 dendritic length constants (lambda), within an average apical dendritic tree of 0.9 lambda. 5. The decrease in proximal-distal separation with increasing EPSP size may stem from recruitment of non-laminar dendritic afferents and the addition of feed-forward inhibitory potentials. These circuitry features of the CA1 region lead to an effective electrical shortening of the apical dendritic tree for large EPSPs and in particular to an enhanced efficacy of distal synapses.

Action Potentials↗
PubMed1988

Uterine leiomyomas in the infertile patient: preoperative localization with MR imaging versus US and hysterosalpingography.

Eleven women with a history of infertility and uterine leiomyomas underwent magnetic resonance (MR) imaging of the pelvis prior to myomectomy. Nine also underwent preoperative pelvic ultrasonography (US), and ten underwent hysterosalpingography. All studies were interpreted prospectively by independent observers. With each imaging modality, the location (one of 11 anatomic segments), size, and appearance of detected uterine leiomyomas were determined and compared with surgical and histologic findings. Among the nine patients who underwent both MR and US, the sensitivity (85%) and accuracy (94%) of MR imaging for abnormal segments was significantly better than that of US (sensitivity = 69%, P = .015; accuracy = 87%, P = .043). For the ten patients who underwent both MR and hysterosalpingography, the sensitivity (91%) and accuracy (96%) of MR imaging was better than that of hysterosalpingography (sensitivity = 18%, P = .0005; accuracy = 72%, P = .0005). The specificities of the three modalities did not significantly differ (100%, 97%, and 98% for MR, US, and hysterosalpingography, respectively). These data suggest that MR imaging is superior to US or hysterosalpingography for preoperatively locating uterine leiomyomas.

Adult↗
PubMed1988

Carcinoma of the breast: detection with MR imaging versus xeromammography.

Detectability of breast cancer with magnetic resonance (MR) imaging versus xeromammography was quantitatively compared. MR images were obtained of breasts of 120 women who underwent xeromammography. T1 values were determined for masses larger than 2 cm. Cancer was histologically confirmed in 39 breasts and was considered excluded from 81 due to results of biopsy, cyst aspiration, or sonography or absence of change in xeromammographic findings over time. Images were blindly interpreted by three observers, and results were expressed as receiver operating characteristic curves. Detectability of breast cancer was substantially better with xeromammography than with MR imaging for all observers (P less than .03, 10(-6), and .001). On MR images, spiculation of a mass, distorted architecture, skin thickening, and nipple or skin retraction were specific but relatively insensitive indicators of cancer. Masses with smooth, distinct margins and signal intensity greater than that of fat on T2-weighted images were always benign. Other findings and T1 values were not diagnostically useful. The authors conclude that xeromammography is superior to MR imaging in detection of breast cancer.

Breast Diseases↗