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Biomedical subjects

E McVeigh

Publications and source records attributed to E McVeigh.

11 recordsLinked to original sources
PubMed2000

Induction of ovulation in women undergoing assisted reproductive techniques: recombinant human FSH (follitropin alpha) versus highly purified urinary FSH (urofollitropin HP).

This multicentre, open, randomized, study compared the efficacy and safety of recombinant follicle stimulating hormone (rFSH; follitropin alpha) with highly purified urinary human FSH (uFSH; urofollitropin HP) in women undergoing ovulation induction for assisted reproductive techniques. Following long down-regulation with buserelin, patients received two ampoules of 75 IU (150 IU) s.c. rFSH or highly purified uFSH for 6 days, after which the dose could be increased until they fulfilled the criteria for human chorionic gonadotrophin (HCG) administration. Of 168 patients recruited, 155 received at least one dose of FSH, and 137 received HCG [68: rFSH (85%); 69: uFSH (92%)]. Following oocyte retrieval and fertilization, up to three embryos were replaced/patient and luteal support was given. The mean number of oocytes retrieved/patient was 10.2 +/- 6.0 for rFSH patients compared with 10.8 +/- 6.1 in the uFSH group (not significant). There was a trend towards fewer ampoules used (22.3 +/- 6.5 versus 24.3 +/- 6.5), higher pregnancy (44.3 versus 41.4%) and live birth rates (33.8 versus 26.7%), as well as a lower miscarriage rate (0.0 versus 16.7%) in favour of rFSH. However, no significant differences in efficacy parameters were recorded. Ovarian hyperstimulation syndrome occurred in 8.6% and 7.9% of rFSH and uFSH patients respectively. In conclusion, this protocol was effective in inducing multiple follicular development and high numbers of oocytes were retrieved with both drugs.

Adolescent↗
PubMed1998

Model studies of the role of mechano-sensitive currents in the generation of cardiac arrhythmias.

Mechano-electrical feedback is studied by incorporating linear, instantaneously activating mechano-sensitive conductances into single cardiac cell models, as well as one- and two-dimensional cardiac network models. The models qualitatively reproduce effects of maintained mechanical stretch on experimentally measured action potential characteristics such as amplitude, maximum diastolic potential, peak upstroke velocity, and conduction velocity. Models are also used to simulate stretch-induced depolarizations, action potentials, and arrhythmias produced by pulsatile volume changes in left ventricle of dog. The mechano-sensitive conductance threshold for a stretch-induced action potential is closely related to the magnitude of the time-independent K+ current, IK1, which offsets inward mechano-sensitive current. Activation of mechano-sensitive conductances in small, spatially localized region of cells can evoke graded depolarizations, propagating ectopic beats, and if timed appropriately, spiral reentrant waves. Mechano-sensitive conductance changes required to evoke these responses are well within the physiologically plausible range. Results therefore indicate that many mechano-electrical feedback effects can be modeled using linear, instantaneously activating mechano-sensitive conductances. As an example of how stretch can occur in real human hearts, magnetic resonance images with saturation tagging are used to reconstruct the three-dimensional left ventricular wall motion. In patients with infarcts or recent ischemic events, "paradoxical deformation" is observed in that regions of myocardium are stretched rather than contracted during systole. In contrast, normal hearts contract uniformly with no stretch during systole. Paradoxical deformations in ischemic hearts may therefore present one possible substrate for the mechanically induced arrhythmias modeled above.

Action Potentials↗
PubMed1998

Regional myocardial function.

Methods for noninvasive tissue tracking and quantification of myocardial shortening with magnetic resonance imaging have been developed using presaturation tagging and velocity encoded phase maps. The concurrent development of rapid scanning techniques, such that a complete cine loop of a slice can be obtained in a breath-hold, has made the measurement of myocardial wall motion in patients a simple and reproducible examination. These methods make it possible to quantify the severity and extent of regional heart wall motion abnormalities both at rest and during stress.

Heart↗
PubMed1997

Measurement of ovarian volume by transvaginal sonography before ovulation induction with human menopausal gonadotrophin for in-vitro fertilization can predict poor response.

The study tests the hypothesis that small ovaries measured on transvaginal sonography (TVS) are associated with a poor response to ovulation induction by human menopausal gonadotrophin (HMG) for in-vitro fertilization (IVF). A total of 140 infertile patients with morphologically normal ovaries undergoing IVF was studied. The mean ovarian volume of each patient was measured on TVS before starting HMG. Subsequent routine IVF management was conducted without knowledge of the results of TVS. The mean ovarian volume was 6.3 cm3 (range 0.5-18.9, SD= 3.1). Patients (n = 17; group A) with small ovaries of < 3 cm3 (i.e. overall mean volume - 1 SD) were compared to patients (n = 123; group B) with ovaries > or = 3 cm3. Both groups were of similar age (mean 35.8 versus 34.4 years). Early basal FSH concentrations were increased in group A (9.5 versus 7.0 mIU/ml, P = 0.025). The cycle was abandoned before planned oocyte recovery in nine patients (52.8%) from group A and in 11 patients (8.9%) from group B because of poor response to ovulation induction (P < 0.001). Increased age and ovarian volume were associated independently with cancellation of the cycles. The remaining eight patients from group A who had oocytes retrieved required higher doses of HMG (87.5 versus 53.8 ampoules, P < 0.01), yielded fewer follicles (10.3 versus 14.5, P < 0.05) and fewer oocytes were recovered from them (6.8 versus 11.0, P < 0.05) compared with group B. There was no difference in the fertilization or pregnancy rates or the number of embryos available for transfer in either group. Our results indicate a strong association between ovarian volume and ovarian reserve. Small ovaries are associated with poor response to HMG and a very high cancellation rate during IVF. Assessment of ovarian size should be an integral part of infertility evaluation.

Adult↗
PubMed1994

Left ventricular wall thickness and regional systolic function in patients with hypertrophic cardiomyopathy. A three-dimensional tagged magnetic resonance imaging study.

BACKGROUND: Regional performance of the hypertrophied left ventricle (LV) in hypertrophic cardiomyopathy (HCM) is still incompletely characterized with studies variably reporting that the hypertrophied myocardium is hypokinetic, akinetic, or has normal function. Different imaging modalities (M-mode or two-dimensional echocardiography) and methods of analysis (fixed or floating frame of reference for wall motion analysis) yield different results. We assessed regional function in terms of systolic wall thickening and shortening and related these parameters to end-diastolic thickness using tagged magnetic resonance imaging and the three-dimensional volume-element approach. METHODS AND RESULTS: In 17 patients with HCM and 6 healthy volunteers, four parallel short-axis images with 12 radial tags and two mutually orthogonal long-axis images with four parallel tags were obtained at end diastole and end systole. After the LV endocardial and epicardial borders were traced, three-dimensional volume elements were constructed by connecting two matched planar segments in two adjacent short-axis image planes, accounting for translation, twist, and long-axis shortening. A total of 72 such volume elements encompassed the entire LV. From each of these elements, end-diastolic thickness and systolic function (fractional thickening and circumferential shortening) were calculated. The average end-diastolic thickness was 15.8 +/- 4.2 mm in patients with HCM, which was significantly greater than that in healthy subjects (8.6 +/- 2.1 mm, P < .001). Fractional thickening was significantly less in patients with HCM than in healthy subjects (0.31 +/- 0.22 versus 0.56 +/- 0.23, P < .001). There was a highly significant inverse correlation between fractional thickening and end-diastolic thickness that was independent of the type of hypertrophy or age group. Similar inverse relations were observed between circumferential shortening and end-diastolic wall thickness. CONCLUSIONS: The myocardium in patients with HCM is heterogeneously thickened and the fractional thickening and circumferential shortening of the abnormally thickened myocardium are reduced compared with healthy subjects. The decrease in fractional thickening and shortening is inversely related to the local thickness.

Adult↗
PubMed1993

Accurate systolic wall thickening by nuclear magnetic resonance imaging with tissue tagging: correlation with sonomicrometers in normal and ischemic myocardium.

OBJECTIVES: This study examined whether the correlation of systolic wall thickening (%WT) by nuclear magnetic resonance (NMR) imaging with wall thickening by sonomicrometry (SM) is improved by using a three-dimensional volume element model of the left ventricular wall. BACKGROUND: Left ventricular wall obliquity with respect to the imaging plane causes overestimation of wall thickness by planar imaging techniques. Wall thickness perpendicular to the endocardial surface can be accurately calculated by three-dimensional reconstruction of left ventricular wall segments. METHODS: Sonomicrometers were placed transmurally in 11 dogs (left anterior descending artery territory) with an imaging marker, visible on NMR imaging, sewn to the epicardial crystal. Two adjacent NMR short-axis image planes were radially segmented by four perpendicular spin-saturated planes (tags), dividing the myocardium into eight volume elements, one of which contained the sonomicrometer crystal pair. Left ventricular thickness and thickening were calculated by four methods: 1) linear = distance between epicardium and endocardium at midpoint in the segment with the sonomicrometer; 2) planar = area of that segment divided by the mean of the endocardial and epicardial arc lengths; 3) biplanar = average of wall thicknesses calculated by the planar method from the segment with sonomicrometers and the corresponding segment located in the adjacent short-axis imaging plane; and 4) three-dimensional = volume of the element with the sonomicrometers divided by the mean of the endocardial and epicardial surface areas. RESULTS: Regressions for all methods using pooled data from control periods and during ischemia: Linear %WT = 0.59 + 1.31 SM%WT (r = 0.71, SEE = 0.28, p < 0.0002) Planar %WT = 1.43 + 1.62 SM%WT (r = 0.87, SEE = 0.19, p < 0.0001) Biplanar %WT = 2.09 + 1.46 SM%WT (r = 0.90, SEE = 0.15, p < 0.0001) Three-dimensional %WT = 0.19 + 1.49 SM%WT (r = 0.95, SEE = 0.10, p < 0.0001) CONCLUSIONS: Nuclear magnetic resonance imaging with tissue tagging allows accurate noninvasive assessment of systolic wall thickening. The three-dimensional volume element approach, by accounting for obliquity between the image plane and the left ventricular wall, provides the strongest correlation between NMR imaging and percent systolic wall thickening by sonomicrometer crystals.

Animals↗
PubMed1992

Measurement of radiotracer concentration in brain gray matter using positron emission tomography: MRI-based correction for partial volume effects.

Accuracy in in vivo quantitation of brain function with positron emission tomography (PET) has often been limited by partial volume effects. This limitation becomes prominent in studies of aging and degenerative brain diseases where partial volume effects vary with different degrees of atrophy. The present study describes how the actual gray matter (GM) tracer concentration can be estimated using an algorithm that relates the regional fraction of GM to partial volume effects. The regional fraction of GM was determined by magnetic resonance imaging (MRI). The procedure is designated as GM PET. In computer simulations and phantom studies, the GM PET algorithm permitted a 100% recovery of the actual tracer concentration in neocortical GM and hippocampus, irrespective of the GM volume. GM PET was applied in a test case of temporal lobe epilepsy revealing an increase in radiotracer activity in GM that was undetected in the PET image before correction for partial volume effects. In computer simulations, errors in the segmentation of GM and errors in registration of PET and MRI images resulted in less than 15% inaccuracy in the GM PET image. In conclusion, GM PET permits accurate determination of the actual radiotracer concentration in human brain GM in vivo. The method differentiates whether a change in the apparent radiotracer concentration reflects solely an alteration in GM volume or rather a change in radiotracer concentration per unit volume of GM.

Algorithms↗
PubMed1992

Evaluation of marrow perfusion in the femoral head by dynamic magnetic resonance imaging. Effect of venous occlusion in a dog model.

RATIONALE AND OBJECTIVES: There is a continuing need for a greater sensitivity of magnetic resonance imaging (MRI) in the diagnosis of avascular necrosis (AVN). Previously, it was demonstrated that a dynamic MRI method, with gadolinium-DTPA (Gd-DTPA) enhancement, can detect acute changes not seen on spin-echo images after arterial occlusion in a dog model. Because venous congestion appears to be a more directly relevant hemodynamic abnormality in a majority of clinical AVN cases, the authors extended the dynamic MRI technique to study changes in venous occlusion. METHODS: Dynamic MRI of the proximal femur was performed in five adult dogs before and after unilateral ligation of common iliac and lateral circumflex veins. Sixteen sequential gradient-recalled pulse sequence (GRASS) images (time resolution = 45 mseconds, echo time = 9 mseconds, flip angle = 65 degrees) were obtained immediately after a bolus intravenous injection of 0.2 mmol/kg of Gd-DTPA. Simultaneous measurements of regional blood flow were made using the radioactive microsphere method. RESULTS: After venous ligation, there was a 25% to 45% decrease in the degree of enhancement compared with preligation values on the ligated side. The decrease in cumulative enhancement (integrated over the entire time course) was statistically significant. The occlusion technique was verified by confirming a statistically significant decrease in blood flow determined by the microsphere method. CONCLUSIONS: Dynamic Gd-DTPA-enhanced fast MRI technique can detect acute changes in bone marrow perfusion due to venous occlusion. This technique may have applications in the early detection of nontraumatic AVN.

Animals↗
PubMed1991

Bone marrow perfusion evaluated with gadolinium-enhanced dynamic fast MR imaging in a dog model.

The authors studied, in a dog model, the feasibility of using gadolinium-enhanced dynamic magnetic resonance (MR) imaging to noninvasively monitor bone marrow perfusion of the proximal femur. With a gradient-recalled acquisition, sequential images of 10 hips in five healthy dogs were obtained for 14 minutes after an intravenous bolus injection of 0.2 mmol of gadopentetate dimeglumine per kilogram. The study was repeated after unilateral arterial embolization of major femoral vessels. Radiolabeled microspheres were injected before and after vessel occlusion. After unilateral embolization, statistically significant differences in enhancement were observed between embolized and control sides (eg, 31% vs 83% average peak enhancement in the femoral neck). There was a high correlation (r = .81 [average]) between the MR data and the microsphere blood flow measurements. The postembolization data indicate that contrast-enhanced fast MR imaging may allow early detection of abnormal bone marrow flow. This technique may be valuable in evaluating patients at risk for avascular necrosis of the femoral head, especially in posttraumatic cases.

Animals↗
PubMedDate not supplied

Rapid measurement of T1 with spatially selective pre-inversion pulses.

A method is described for rapidly obtaining a multipoint estimate of T1 from a sample that is homogeneous over a few millimeters. An image of the longitudinal recovery curve is produced through the application of successive "pre-inversion" slices that are perpendicular to the imaging slice. These pre-inversion pulses are analogous to pre-saturation pulses, but they are much thinner and the tip angle is 180 degrees. The baseline for the recovery is measured from sections of the sample that have not been perturbed by the slice selective pre-inversion pulses. The existence of the baseline value and the lack of slice profile effects allows a quick T1 estimate (QT1) to be made with a simple linear regression algorithm. The QT1 values are found to correlate very well with T1 values measured with the scanner in "spectrometer' mode, for volumes as small as 5 x 5 x 5 mm. Possible applications are T1 estimates in homogeneous samples and tissues, and scouting the T1 range of a tissue to be measured with higher resolution volume localization techniques.

Algorithms↗