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Biomedical subjects

M D Harpen

Publications and source records attributed to M D Harpen.

At least 55 records · Page 3Linked to original sources
PubMed1983

Ultrasonographic determination of renal mass and renal volume.

Volumes and surface areas of 45 kidneys were determined ultrasonographically in vivo before autopsy and in a water bath phantom after autopsy by means of both the ellipsoid and the stepped section methods. Comparison of results revealed that renal volume may be determined by the simplest method, the ellipsoid method, with sufficient accuracy for clinical use. Results also revealed that renal mass expressed in grams may be directly obtained from renal volume expressed in milliliters, but mass in grams was found to correlate better with renal surface area than with renal volume. A formula relating renal mass to both volume and surface area was developed from regression analysis of the data and was found to provide a more precise estimate of renal mass than does mass computed from either volume or surface area alone.

Humans↗
PubMed1983

Determination of left-ventricular volume from first-pass kinetics of labeled red cells.

A mathematical model is presented for the dynamics of a bolus of technetium-99m-labeled red blood cells through the left ventricle. It is used to correct for attenuation the count rate observed over the left ventricle during a conventional gated blood-pool study. The left-ventricular volumes are calculated from the corrected count rates and expressed as a percentage of total blood volume, or in absolute terms if a blood sample is obtained. The procedure is applied to a number of patients with nonvalvular cardiac disease. Cardiac volumes determined by the method are found to correlate well (r = 0.98) with those determined by contrast left ventriculography. The method is simple, requires no special equipment, and can be applied with existing computer software.

Adult↗
PubMed1982

In vivo evaluation in intrathyroidal iodide metabolism.

A new coincidence counting method is used to measure absolute thyroid 125I activity with accurate correction of extrathyroidal neck activity. Data collected are analyzed according to a three-compartment model, giving parameters both dependent and independent of plasma iodide concentration. Iodide is postulated to form a complex with the iodide trap before it is transported and organified. The initial carrier-iodide complex, the intrathyroidal free iodide, and the thyroidal organic iodide pool can be determined as percentages of the injected activity. The trapping rate, the leakage rate, and the organification rate for iodide are determined as fractional turnover rates of the compartments independent of the plasma iodide concentration. The analysis is applied to the study of intrathyroidal iodide metabolism in a group of goitrous patients and a group of treated hyperthyroid patients. In the euthyroid goitrous patients, the trapping rate is slow, ranging from 0.051-0.085 min-1, and the intrathyroidal iodide pool is characteristically small, being 0.017-0.118%. The organification rate is 0.628-1.19 min-1. The leakage of iodide is virtually zero. In the treated hyperthyroid group, organification is not detectable, due to suppressive treatment by thionamides. The trapping rate is elevated (0.199-0.592 min-1), and the leakage rate is estimated to be in the range of 0.057-0.157 min-1. Because of the organification block, the intrathyroidal iodide pool is larger than that of our euthyroid group, being 1.50-7.59%. The compartment sizes and fractional turnover rates are in good agreement with previously reported values.

Adolescent↗
PubMed1981

Simultaneous determination of free thyroxine and capacity of thyroxine-binding globulin.

A simple method is described for the simultaneous determination of capacity thyroxine-binding of globulin (TBG) and free thyroxine concentration (FT4). The ratio of bound to free T4 (B/F) is first determined for two total-T4 concentrations using a Sephadex G-25 competitive-binding technique. TBG capacity and FT4 can both the calculated assuming a known value of affinity constant of TBG. The method is linear over a twenty-fold serum dilution. FT4 calculated is identical to that calculated using the method of Irvine. TBG capacity is shown to be linearly correlated to TBG concentration as determined by radioimmunoassay and is consistent with a molecular weight of 69,000 Daltons and one T4 binding site per molecule. FT4 is found to correlate with the free thyroxine index in a complicated way, depending on the degree of TBG saturation.

Binding, Competitive↗
PubMedDate not supplied

A functional estimate of overlap between adjacent coronary circulations in the dog.

We measured the functional overlap between the left arterior descending (LAD) and the rest of the coronary arteries in the dog heart. The measurements were performed by loading only the field of the LAD with 133Xe gas via a close-arterial injection during normal perfusion. The LAD perfusion was then interrupted and blood was allowed to flow retrograde from the distal LAD segment. This caused a condition of extremely low flow in the tissue perfused by the LAD. Examination of the washout kinetics revealed two distinct compartments. The slow compartment accounted for 97% of the injected Xenon and was assumed to represent the central ischemic field of the LAD. The fast component accounted for only 3% of the injected tracer and was assumed to include all regions of admixture between the LAD and other coronary vessels at the lateral borders. Thus, less than 3% of the LAD's field functionally communicates with the rest of the coronary circulation.

Animals↗
PubMedDate not supplied

Magnetic resonance and CT imaging correlated with clinical status in SSPE.

Five patients afflicted with subacute sclerosing panencephalitis were studied with computed tomography and magnetic resonance imaging. Computed tomography documented changes of nonspecific cerebral atrophy and low attenuation in the subcortical white matter. Magnetic resonance imaging revealed bilateral, symmetric, and diffuse abnormal increased signal in the white matter of the cerebral hemispheres with normal posterior fossa structures in 4 of 5 patients. Magnetic resonance imaging was superior to computed tomography in demonstrating the total extent of abnormality and may be the imaging modality of choice for this childhood disease.

Adolescent↗
PubMedDate not supplied

A new method of calculating absolute thyroid activity in intravenous I-123 uptake tests.

A technique for determining the absolute activity of I-123 in early thyroidal uptake tests is presented. The method is independent of geometry, tissue attenuation, an extrathyroidal neck activity (ENA). It utilizes the efficiency factors (ExT and E gamma T) derivable for the thyroid gland using coincidence counting techniques, and a quantity, alpha, characteristics of the vascularity of the individual patient. Although ENA is not determined in absolute terms (e.g., percent of injected dose), count rates due to ENA are determined. After subtracting the ENA from the total count rates thyroidal uptake can be determined as absolute activity by means of the efficiency factors. The validity and usefulness of the technique have been demonstrated in phantom and patient studies. Thyroid uptakes of less than 0.1% of injected dose can be measured accurately in our patient studies.

Adolescent↗
PubMedDate not supplied

Nuclear magnetic resonance of convective dispersive flow.

Presented is a solution to a differential equation governing the transverse magnetization of a fluid whose flow is governed by the process of convective dispersion. The solution describes the case of flow parallel to an applied magnetic field gradient with boundary conditions and velocity profiles consistent with those likely to be encountered in nuclear magnetic resonance imaging of arterial or venous blood flow.

Animals↗
PubMedDate not supplied

Monte Carlo simulation of spectroscopic imaging data.

Presented is a quantitative analysis of fat and water spectroscopic imaging. Nuclear magnetic resonance (NMR) signal decay curves obtained from conventional and spectroscopic imaging of a variety of fat and water samples in a phantom and of bone marrow, adipose tissue, and muscle from a clinical scan are analyzed to determine the transverse relaxation times and percent contribution to total signal of the fat and water fractions. The variance-covariance structure of parameter estimations obtained by the spectroscopic imaging technique is compared with those obtained by the conventional in-phase imaging technique by means of a Monte Carlo simulation.

Adipose Tissue↗
PubMedDate not supplied

Sample noise with circular surface coils.

Presented is a straightforward derivation of the effective sample resistance presented to the input amplifier of a nuclear magnetic resonance imager when flat circular surface coils are used to image lossy media. The resistance may be used to determine sample noise following the method of Hoult and Lauterbur.

Magnetic Resonance Spectroscopy↗
PubMedDate not supplied

The density matrix formalism of nuclear relaxation: a review.

This is a review of the density matrix formalism of quantum statistical mechanics as it relates to nuclear relaxation. The single spin and coupled exchanging two spin systems are treated explicitly. We show the circumstances under which these models reduce to the more familiar expressions used to describe proton relaxation in tissue. The effect of radiofrequency (rf) pulses on the density matrix is presented as well as the density matrix description of the Carr-Purcell pulse technique and conditions under which even and odd echo trains will superpose or are independent of rf pulse rate.

Magnetic Resonance Spectroscopy↗
PubMedDate not supplied

Eddy current disruption: effect on nuclear magnetic resonance coil impedance and power loss.

We present a theoretical development and experimental verification of a description of power loss and sample resistance for a lossy sample in a nuclear magnetic resonance radio frequency coil for a sample geometry where the eddy current streamlines are disrupted from their usually assumed circular paths. Specifically treated is the case of a lossy hemisphere. The problem is solved for two orientations; with the induction parallel and perpendicular to the flat surface of the hemisphere. Results of this analysis as well as those for the full sphere as presented by Hoult and Lauterbur are compared with observation for a variety of sample conductivities and orientation.

Electric Conductivity↗
PubMedDate not supplied

Analysis of capacitive coupling and associated loss for a solenoidal magnetic resonance imaging radio-frequency coil.

Presented is an analysis of the capacitive coupling between a magnetic resonance imaging radio-frequency (rf) coil and a dielectric sample. Calculated is the coil self-capacitance and power loss in the medium. The capacitively coupled power loss is compared with the more familiar inductively coupled eddy current loss and the predicted dependence of self-capacitance on coil and sample size is studied experimentally in a series of single-turn slotted solenoids of various sizes.

Magnetic Resonance Imaging↗
PubMedDate not supplied

Harmonic structure of cylindrical imaging coils.

Presented is a derivation of an exact closed-form expression for the spectra of resonant frequencies for magnetic resonance imaging birdcage coils in the limit of long coils with many elements. Results of the analysis are compared with observation in a variety of birdcage coils where it is shown that for even relatively short coils the progression of resonant frequencies are of the form omega m = omega 1m +/- 1/2 + low pass; -high pass, with m integer and omega 1 the primary resonance.

Magnetic Resonance Imaging↗