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W J MacIntyre

Publications and source records attributed to W J MacIntyre.

At least 55 records · Page 3Linked to original sources
PubMed1986

Verification of Fourier phase and amplitude values from simulated heart motion using a hydrodynamic cardiac model.

Using pusher-plate-type artificial hearts, changes in the degree of synchrony and stroke volume were compared to phase and amplitude calculations from the first Fourier component of individual-pixel time-activity curves generated from gated radionuclide images (RNA) of these hearts. In addition, the ability of Fourier analysis to quantify paradoxical volume shifts was tested using a ventricular aneurysm model by which the Fourier amplitude was correlated to known increments of paradoxical volume. Predetermined phase-angle differences (incremental increases in asynchrony) and the mean phase-angle difference calculated from RNAs showed an agreement of -7 degrees +/- 4.4 degrees (mean +/- SD). A strong correlation was noted between stroke volume and Fourier amplitude (r = 0.98; P less than 0.0001) as well as between the paradoxical volume accepted by the 'aneurysm' and the Fourier amplitude (r = 0.97; P less than 0.0001). The degree of asynchrony and changes in stroke volume were accurately reflected by the Fourier phase and amplitude values, respectively. In the specific case of ventricular aneurysms, the data demonstrate that using this method, the paradoxically moving areas may be localized, and the expansile volume within these regions can be quantified.

Fourier Analysis↗
PubMed1985

Prediction of improvement in left ventricular function after ventricular aneurysmectomy using Fourier phase and amplitude analysis of radionuclide cardiac blood pool scans.

Postoperative improvement in left ventricular (LV) function is a common objective of LV aneurysmectomy, but is difficult to predict. The first Fourier component of time-activity curves of pre- and postoperative gated radionuclide angiographic studies was evaluated for this purpose in 20 patients who had undergone aneurysmectomy. LV aneurysms had portions that characteristically exhibited marked phase delay with varying degrees of amplitude. Total aneurysmal amplitude was obtained preoperatively by summing the amplitude component of all pixels that exhibited phase delay, suggesting paradoxical motion. LV ejection fraction (EF) before and after aneurysmectomy and the absolute postoperative increase in LVEF were calculated. Nine of 20 patients had an absolute increase of EF less than 10% despite resection of large aneurysms. A strong correlation was found between the absolute increase in EF after aneurysmectomy and the total amplitude within paradoxically moving areas (r = 0.93, p less than 0.0001). Thus, preoperative measurement of the total paradoxical amplitude predicts absolute change in EF and may be important in selecting patients for aneurysmectomy. The data also suggest that the total aneurysmal amplitude reflects the stroke volume ejected into an aneurysm in systole and that paradoxical expansion of an aneurysm contributes to LV dysfunction in some of these patients.

Adult↗
PubMed1985

Gated cardiac magnetic resonance structural imaging: optimization by electronic axial rotation.

Most magnetic resonance imaging has used body orthogonal axes with the Z axis placed along the length of the body and the X and Y axes at right angles to the body. This orientation is not optimum for the heart; visualization of sections along the short and long cardiac axes would best define cardiac structural detail and functional status. The new orientation was accomplished by selection of electronic angulation of the magnetic fields for each subject rather than by attempting to approximate the cardiac axes by altering the position of the patient. This technique improved visualization of comparative wall segments, valvular structures, and the true four-chamber view of the heart, and also gave the best visualization of the pericardium. In addition, more accurate estimates of chamber size and myocardial mass can be made from the short-axis orientation, since the sections are orthogonal to the myocardium.

Cardiomegaly↗
PubMed1985

Videodensitometric ejection fractions from intravenous digital subtraction left ventriculograms: correlation with conventional direct contrast and radionuclide ventriculography.

Forty-three patients who had undergone direct-contrast ventriculography were submitted to intravenous digital subtraction ventriculography and first-pass radionuclide ventriculography to compare the left ventricular ejection fractions obtained by each method. Ejection fractions were calculated by the area-length method from the direct contrast ventriculograms, by both area-length and videodensitometric methods from the digital subtraction ventriculograms, and by count densitometry from the radionuclide ventriculograms. Satisfactory correlations were found between values obtained by the late mask resubtracted videodensitometric method and the radionuclide method (r = 0.85) and by the digital ventriculographic area length method and direct-contrast method (r = 0.88). Videodensitometric methods may be an alternative way to estimate left ventricular ejection fractions accurately without reliance on geometric assumptions about the shape of the left ventricular cavity.

Analog-Digital Conversion↗
PubMed1985

Comparison of gated cardiac MRI and 2D echocardiography of intracardiac neoplasms.

The gross diagnostic factors of intracardiac tumor in four patients imaged by two-dimensional echocardiography (2D echo) and magnetic resonance imaging (MRI) were compared. Three cases had left and one had a right atrial tumor, all histologically identified as myxoma. Gated cardiac MRI depicted the size, shape, and surface characteristics of the tumors more clearly than 2D echo, because MRI provides better spatial and contrast resolution. Depiction of tumor attachment was poor to good with both techniques. Both techniques were highly accurate in localizing the tumor and displaying whether it was fixed or mobile. The global field of view provided by MRI allows better definition of tumor prolapse, secondary valvular obstruction, and cardiac chamber size. This study shows that despite its early stage of development, gated cardiac MRI provides superior image quality and is complementary to 2D echo for characterization and diagnosis of intracardiac tumor.

Adult↗
PubMed1985

Clinical evaluation of 360 degrees and 180 degrees data sampling techniques for transaxial SPECT thallium-201 myocardial perfusion imaging.

The most serious controversy regarding the application of transaxial SPECT technology to 201Tl myocardial perfusion imaging is the choice between 360 degrees compared with 180 degrees data sampling techniques. The present study utilized the original 360 degrees sampled raw data of 25 patients who had both SPECT 201Tl myocardial perfusion imaging and coronary angio/ventriculography for back projection reprocessing to accomplish the 360 degrees/180 degrees comparison. The results show a high incidence, 36% (9/25), of false-positive segmental perfusion abnormality and a high incidence, 24% (6/25), of moderate to severe degree of image distortion with the 180 degrees data sampled reconstructed images. These were not observed in the 360 degrees data sampled reconstructed images. The above findings confirmed our previous preliminary conclusion that even though the 180 degrees data sampling technique has the advantage of providing improved image contrast and reduction in acquisition time it is not a reliable technique and should be abandoned. The 360 degrees data sampling is the technique of choice for transaxial SPECT 201Tl myocardial perfusion imaging.

Adult↗
PubMed1984

Volume and planar gated cardiac magnetic resonance imaging: a correlative study of normal anatomy with thallium-201 SPECT and cadaver sections.

Magnetic resonance (MR) gated cardiac imaging was performed in ten subjects using a prototype 0.15-T resistive magnet imaging system. Volume and planar imaging techniques utilizing saturation recovery, proton Tl-weighted relaxation time pulse sequences produced images of the heart and great vessels with exquisite anatomic detail that showed excellent correlation with cadaver sections of the heart. The left ventricular myocardial segments also showed excellent correlation with the thallium-201 cardiac single photon emission computed tomography images. Volume acquisition allowed postprocessing selection of tomographic sections in various orientations to optimize visualization of a particular structure of interest. The excellent spatial and contrast resolution afforded by MR volume imaging, which does not involve the use of ionizing radiation and iodinated contrast material, should assure it a significant role in the diagnostic assessment of the cardiovascular system.

Aorta↗
PubMed1984

Magnetic resonance signal intensity patterns obtained from continuous and pulsatile flow models.

The purpose of this investigation was to extend previous steady state flow studies with magnetic resonance (MR) to pulsatile flow measurements obtained with gated cardiac techniques in man with a pulsatile artificial heart device. Bovine blood and a solution of MnCl2 were studied. Correlation was made with complex and time-varying MR signals observed in the descending aorta on cardiac gated images obtained through the midthorax. MR signals from flowing fluids represent velocity distribution as shown in a velocity profile, and laminar flow is distinguished from nonlaminar. At very slow flow rates, signal intensity is lower than background. As the rate is increased, paradoxical enhancement occurs followed by loss of signal, which is complete at 7 liters per minute with fluid and 15 liters per minute with blood. These areas correspond to maximum fluid velocities of 41 and 88 cm/sec, respectively.

Animals↗
PubMed1984

Magnetic resonance of the chest: initial experience with imaging and in vivo T1 and T2 calculations.

Magnetic resonance (MR) imaging of the chest was performed in 33 patients; 28 patients had a variety of malignant tumors and five had benign processes involving the pleura, chest wall, mediastinum, hila , and pulmonary parenchyma. In addition, in vivo T1 and T2 calculations were performed on 17 malignancies and 2 benign processes. Of the 18 patients examined with both MR and computed tomography (CT), 15 MR examinations were considered to be as diagnostic as CT in demonstrating abnormalities. In two cases, CT was superior to MR. In one case without adequate vascular opacification on CT, MR was superior in differentiating a mass from pulmonary artery. It is concluded that, with current technology without respiratory or cardiac gating, MR offers little improvement in diagnosis over contrast-enhanced CT. Furthermore, it does not appear possible to predict tissue type based on T1 and T2 measurements because of a wide overlap in these values.

Carcinoma, Bronchogenic↗
PubMed1981

Imaging capability of an experimental digital subtraction angiography unit.

We evaluated an experimental digital subtraction unit in terms of field uniformity, linearity of signal response to x-radiation, response of the log amplifier, and imaging capability as measured with the Rose phantom. For comparison, conventional film subtraction phantom measurements were made. Our results indicate that this unit exhibits greater sensitivity to contrast media than conventional film subtraction units.

Angiography↗
PubMed1981

Recirculation subtraction for analysis of left-to-right-cardiac shunts: concise communication.

The object of this study is to improve the techniques for describing the lung dilution curve for shunt quantification by separating the effects of systemic recirculation on the curve form those of direct shunt return. The time of the systemic recirculation peak was estimated by determination of transit times from the right and left ventricles and lung. A gamma variate fit based on the distribution of points at that segment was applied to the recirculation curve and subtracted from the original lung dilution curve. Similar gamma variate fitting was performed for both primary and shunt curves. Rather than fitting the gamma variate of the shunt curve by the leading edge only, a larger portion could now be used since the trailing edge of the curve is clearer following recirculation subtraction. The algorithm is completely automatic, requiring no operator intervention or selection of curve-fitting regions. The correlation coefficient for comparison of the dilution-curve analysis with oximetry determinations was 0.92 in a series of 29 patients.

Adolescent↗
PubMed1981

Noninvasive measurement of cardiopulmonary blood volume. Evaluation of the centroid method.

Cardiopulmonary blood volume (CPV) and mean pulmonary transit time (MTT) determined by radionuclide measurements (Tc-99m HSA) were compared with values obtained from simultaneous dye-dilution (DD) studies (indocyanine green). The mean transit time was obtained from radionuclide curves by two methods: the "peak-to-peak" time and the interval between the two centroids determined from the right and left-ventricular time-concentration curves. Correlation of dye-dilution MTT and "peak-to-peak" time was significant (r = 0.79, p less than 0.001), but its correlation with centroid-derived values was better (r = 0.86, p less than 0.001). CPV values (using the centroid method for radionuclide technique) correlated significantly with values derived from dye-dilution curves (r = 0.74, p less than 0.001). Discrepancies between the two were greater the more rapid the circulation (r = 0.61, p less than 0.01), suggesting that minor inaccuracies of dye-dilution methods, due to positioning or delay of the system, can become magnified in hyperkinetic conditions. The radionuclide method is simple, repeatable, and noninvasive, and it provides simultaneous evaluation of pulmonary and systemic hemodynamics. Further, calculation of the ratio of cardiopulmonary to total blood volume can be used as an index of overall venous distensibility and relocation of intravascular blood volume.

Adolescent↗