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Biomedical subjects

M LeFree

Publications and source records attributed to M LeFree.

9 recordsLinked to original sources
PubMed2000

Simulating coronary arteries in x-ray angiograms.

Clinical validation of quantitative coronary angiography (QCA) algorithms is difficult due to the lack of a simple alternative method for accurately measuring in vivo vessel dimensions. We address this problem by embedding simulated coronary artery segments with known geometry in clinical angiograms. Our vessel model accounts for the profile of the vessel, x-ray attenuation in the original background, and noise in the imaging system. We have compared diameter measurements of our computer simulated arteries with measurements of an x-ray Telescopic-Shaped Phantom (XTSP) with the same diameters. The results show that for both uniform and anthropomorphic backgrounds there is good agreement in the measured diameters of XTSP compared to the simulated arteries (Pearson's correlation coefficient 0.99). In addition, the difference in accuracy and precision of the true diameter measures compared to the XTSP and simulated artery diameters was small (mean absolute error across all diameters was < or = 0.11 mm +/- 0.09 mm).

Algorithms↗
PubMed1978

A new method of multiplanar emission tomography using a seven pinhole collimator and an Anger scintillation camera.

A new method of multiplanar emission tomography is described; it uses a wide-field Anger scintillation camera (37.5 cm crystal diameter) and a seven-pinhole collimator. The pinholes (5.5 mm) acquire data simultaneously from the emissing source and project the data onto seven independent regions of the camera crystal. Multiple planes are reconstructed from the initial seven-view data acquisition through the use of a computerized addition-multiplication algorithm and variation of the superposition relationships among the projected views. These planes are then altered iteratively by a least-error criterion following ray-sum comparison with the original views. Planar resolution (full-width-half-maximum) is 1.0 cm and depth resolution is 1.5 cm. In 42 patients with angiographically demonstrated coronary-artery disease, studies of myocardial Tl-201 perfusion, under exercise, have shown improved detection sensitivity in comparison with scintigraphy using parallel-hole collimation.

Coronary Disease↗
PubMed1977

Effects of digitalis on resting and isometric exercise myocardial perfusion in patients with coronary artery disease and left ventricular dysfunction.

Digitalis has been shown to improve the impaired ventricular function associated with coronary artery disease as well as to increase myocardial oxygen consumption and produce coronary vasoconstriction. To elucidate the net result of these contrasting effects, six patients with coronary artery disease and left ventricular ejection fractions less than 0.50 had 1.0 mCi thallium-201 injected intravenously at rest and during three minutes of 33% of maximal handgrip, off and on 0.25 mg daily maintenance digoxin. Thallium-201 scintigram images were taken 30 minutes later and were computer processed with orthogonal linearly interpolated background subtraction and maximal count density equalization. Processed images were visually graded on a 0, 1, or 2 scale for 18 sectors--nine from the AP projections and nine from the 40 degrees left anterior oblique projections. A score resulting from the summation of the 18 sector grades was made for each study, the maximum score being 36. Off digitalis, patients performing handgrip exercise decreased their scintigram scores from 25.7 +/- 1.5 (mean +/- SEM) to 23.0 +/- 1.0, P less than 0.05. When patients were on maintenance digoxin, scores did not change significantly during handgrip exercise. Post exercise scores were significantly higher on digoxin than off (P less than 0.05), whereas, resting scores were unaffected by digoxin. These data suggest that myocardial perfusion, as measured by thallium-201 uptake, is improved in patients on digitalis who have coronary artery disease and left ventricular dysfunction.

Blood Pressure↗
PubMed1976

Measurement of left ventricular mean circumferential fiber shortening velocity and systolic ejection rate by computerized radionuclide angiocardiography.

Recently attention has focused on ejection phase indexes as clinically relevant measures of left ventricular contractility. Using an Anger camera interfaced to a dedicated computer with injection of radionuclide (technetium 99m) into a wedged pulmonary arterial catheter we have developed a method for measuring left ventricular mean circumferential fiber shortening velocity and mean systolic ejection rate. For determination of mean fiber shortening velocity an area of interest coincident with the left ventricular minor axis is constructed and a time-activity curve obtained. In 31 atients radionuclide-determined values for mean fiber shortening velocity and mean systolic ejection rate correlated (r = 0.90, P less than 0.001 and r =0.98, P less than 0.001, respectively) with values for these indexes obtained from left cineventriculography. Left ventricular ejection fraction correlated with mean fiber shortening velocity and systolic ejection rate (r = 0.60, P less than 0.001 and r = 0.92, P less 0.001, respectively). No patient with a normal mean fiber shortening velocity or systolic ejection rate had a dimished ejection fraction. Because these radionuclide measurements do not require left heart catheterization, they can be frequently repeated.

Adult↗
PubMed1976

Radionuclide angiocardiographic measurement of left ventricular volume and ejection fraction.

In recent years a number of different radionuclidic techniques have been developed to measure left ventricular volume and ejection fraction. Area-measurement concepts have been applied to static and electrocardiographically gated radionuclidic images which have resulted in accurate measurement of left ventricular end-diastolic volume (LVEDV) and ejection fraction (LVEF). Gated (end-diastolic and end-systolic) image analysis has also proven capable of detecting regional left ventricular wallmotion abnormalities in patients with coronary disease. Time-activity curves can be extracted from left ventricular images, and several dynamic techniques have been developed and have also resulted in accurate measurement of LVEDV and LVEF. Radionuclide methods are currently available which are accurate and atraumatic and consequently applicable to the serial study of patients with heart disease. In particular, several of these radionuclide methods are relatively inexpensive and should be able to be performed in most hospitals.

Angiocardiography↗
PubMed1976

Measurement of right and left ventricular ejection fractions by radionuclide angiocardiography in coronary artery disease.

Utilizing a dynamic radionuclide method, the right and left ventricular ejection fractions were measured in 96 men with arteriographically defined coronary arterial disease and in 14 normal subjects. The radionuclidically estimated right ventricular ejection fraction (RVEF) correlated with the RVEF measured with biplane cineventriculographic studies (r = 0.80; n = 43), and the left ventricular ejection fraction (LVEF) measured from radionuclide data have been shown to correlate with the LVEF from single-plane cineventriculographic studies (r = 0.89; n = 60). The mean normal RVEF was 0.57 +/- 0.01 (SE) (range, 0.51 to 0.64), and the mean normal LVEF was 0.66 +/- 0.01 (range, 0.57 to 0.74). The LVEF was decreased in the men with coronary arterial disease and isolated obstruction of the left anterior descending coronary artery, double-vessel disease, and triple-vessel disease, but was normal in those with isolated right coronary disease. The RVEF was normal in each of these groups, except those with triple-vessel disease. Myocardial infarction was associated with impairment of LVEF, although some patients without myocardial infarction had depressed LVEF. The RVEF was preserved in patients with infarction, except those with multiple myocardial infarctions. Thus, impaired LVEF in coronary arterial disease is associated with myocardial infarction, and RVEF is relatively preserved except in multiple-vessel disease and myocardial infarction and in association with impaired LVEF.

Adult↗