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Biomedical subjects

M W Groch

Publications and source records attributed to M W Groch.

30 records · Page 2Linked to original sources
PubMed1985

Dual-isotope motion correction technique for gated exercise scintigraphy.

In exercise multigated blood-pool imaging, significant degradation of image quality occurs as a result of patient movement under the gamma camera. Motion correction devices using centroid tracking of x-y events emanating from the organ of interest cannot be applied to blood-pool studies, because cardiac contraction and rotation masks the correctable patient motion component. We have developed a dual-isotope motion correction technique (DIMC) which utilizes a second point source of dissimilar energy (241Am) to monitor movement. Positional centroids from events incident in the 241Am window are used to develop correction coordinates which are applied to the 99mTc blood-pool events. The ability of DIMC to reduce blur due to motion has been evaluated qualitatively with phantoms and quantitatively by using spatial resolution measurements obtained from stationary line sources and from sources moving at varying rates. Based on these criteria, we have found the device to be capable of reducing over 90% of the image blur of objects moving at 5.1 cm per sec. In preliminary gated exercise studies, subjective perception of image quality was shown to be significantly improved in the DIMC corrected image, when compared to images obtained without DIMC. Improvement in image quality for exercise gated studies is of particular importance because of the low count density obtained during these procedures.

Americium↗
PubMed1983

Coronary artery disease: detection by phase analysis of rest/exercise radionuclide angiocardiograms.

Thirty-six patients with chest pain but no myocardial infarction or conduction defects and 4 volunteers (3 normals and 1 with asymptomatic aortic insufficiency) underwent radionuclide angiocardiography. Phase analysis was performed and the standard deviation (SD) ("spread") and skewness ("asymmetry") of the left ventricular (LV) phase histogram determined at rest and during maximum exercise. The SD of the LV phase histogram was of no value; however, when -0.1 was taken as the upper limit of normal skewness at maximum exercise, skewness was equally as sensitive as conventional criteria for coronary artery disease (CAD) and also more specific. The authors conclude that LV histogram skewness during maximum exercise may be superior to conventional criteria for detection of CAD with rest/exercise radionuclide angiocardiograms.

Adult↗
PubMed1982

Noninvasive identification of initial site of abnormal ventricular activation by least-square phase analysis of radionuclide cineangiograms.

Least-square phase analysis (LSPA) of radionuclide cineangiograms demonstrates the sequence of onset of inward ventricular movement noninvasively. To validate the method and explore its ability to identify abnormal initial sites of ventricular activation, LSPA was applied to 14 patients with pacemakers (one with electrodes in two locations) (group 1) and three patients with recurrent ventricular tachycardia (VT) (group 2) who had undergone electrophysiologic endocardial mapping. The segment in which the site of initial ventricular activation was located was correctly identified in 13 of 15 paced studies and in two of three group 2 patients during VT. Pacing increased the duration of spread of onset of inward ventricular movement, and the duration of spread of onset correlated well with the duration of the QRS (r = 0.80). The sequence of onset of inward ventricular movement during VT was similar to the sequence of depolarization in all three group 2 patients. These preliminary results suggest that the sequence of onset of ventricular contraction as depicted by LSPA is a valid representation of the actual contraction sequence and that LSPA or radionuclide cineangiography correctly identifies abnormal sites of initial ventricular activation.

Arrhythmias, Cardiac↗
PubMed1982

Sequence and timing of ventricular wall motion in patients with bundle branch block. Assessment by radionuclide cineangiography.

We determined the sequence and timing of inward ventricular wall motion by least-square phase analysis of radionuclide cineangiograms in 10 patients with left bundle branch block (LBBB), five patients with right bundle branch block (RBBB) and 11 patients with normal conduction. All LBBB and RBBB patients had normal coronary arteries and no segmental wall motion abnormalities. The left ventricle (LV) was divided into eight segments and the right ventricle (RV) into three; sequence and timing were scored by three observers. In normal subjects, wall motion begins in either or both ventricles and ends in the LV or both ventricles. In patients with LBBB it begins in the RV and ends in the LV; in patients with RBBB is begins in the LV and ends in the RV or both ventricles. The intraventricular wall motion is also altered in the ventricle ipsilateral to a bundle branch block. In LBBB, the mean time of onset of LV wall motion is delayed 1.9 frames (38 msec), whereas RV wall motion is normal. In RBBB, the onset of RV wall motion is delayed 1.3 frames (26 msec), whereas LV wall motion is not delayed.

Adult↗
PubMed1978

Radionuclide kymography for the assessment of regional myocardial wall motion.

Regional myocardial wall motion is usually evaluated qualitatively from ECG-gated end-systolic and end-diastolic blood-pool images. Radionuclide kymography, which displays a one-dimensional scintigraphic image in time, synchronized with the electrocardiogram, provides a method to quantitate this motion. The technique is analogous to M-mode ultrasound in that one dimension is displayed as a function of time, but the activity distribution is displayed in place of acoustic interfaces. The motion of regional myocardial segments can be measured from multiple kymographic projections across the cardiac blood pool, after equilibration of a radioactive tracer. Radionuclide kymography is potentially better quantitatively than gated blood-pool imaging and is not hindered by viewing windows as are single- and multiple-transducer ultrasonography. Regional wall motion determined from radionuclide kymography correlated well with that determined from contrast left ventriculography in a series of patients. Since the kymographic sweep is initiated by the R wave of the ECG and proceeds continuously throughout the cardiac cycle, the temporal sequence of regional myocardial contraction can be directly assessed and related to corresponding portions of the ECG.

Computers↗
PubMed1976

Thallium-201: scintillation camera imaging considerations.

Modulation transfer functions, line spread functions, and energy spectra were obtained for an Anger scintillation camera using three different collimators and commercially produced 201Tl. Images of a thyroid phantom were obtained using these collimators. For each of the three collimators, line spread functions and modulation transfer functions were obtained for both the 75-keV x-ray and 167-keV gamma photon of 201Tl. Although the intrinsic resolution of the scintillation camera is superior when imaging with the 167-keV gamma photon, system performance was superior when the 75-keV x-ray was imaged. Contamination form 202Tl, which emits abundant 439-keV gamma photons, degraded images taken at 167 keV because of septum penetration. At 75 and 167 keV the converging collimator yielded the best system performance. Imaging time was significantly shorter using the 75-keV x-rays.

Radioisotopes↗
PubMed1976

A new dual-probe system for the rapid bedside assessment of left ventricular function.

A mobile dual-probe system has been developed for the rapid bedside measurement of left ventricular ejection fraction (LVEF) from the beat-to-beat count rate variations that occur during the transit of a single radionuclide bolus through the left ventricle (LV). Cardiac output, pulmonary blood volume, and left ventricular end-diastolic volume can also be calculated. The dual-probe system incorporates a central collimated probe for monitoring activity in the LV surrounded by an annular detector collimated in such a manner as to provide simultaneous real-time monitoring of the LV background activity. The LVEFs obtained from this system correlated well with LVEFs derived from conventional single-plane contrast angiography (r=0.90) in a series of 33 patients with coronary artery disease. Positioning the dual probe over the midpoint of the LV is accomplished with standard M-mode ultrasound. Since the method is noninvasive and sensitive to volume changes in the LV, the dual probe is particularly useful for monitoring seriously ill patients as well as those with segmental wall-motion abnormalities.

Coronary Disease↗
PubMedDate not supplied

Respiratory gating in magnetic resonance imaging: improved image quality over non-gated images for equal scan time.

Magnetic resonance image quality is adversely affected by respiratory (RESP) motion during the scan. Respiratory gating improves magnetic resonance image (MRI) quality and removes artifacts, but has not been widely used, as RESP gating increases scan time. Our RESP-gating device was used to study scan time versus improvement in image quality using various gating modes; with and without combined electrocardiographic (ECG) gating. When RESP scans were acquired for the same time as non-gated scans, by using a wide RESP-gating window bracketing end expiration and a reduced number of pulse sequence repetitions, substantial improvement in image quality (over non-gated scans) resulted, despite the inferior statistical content of the acquisition.

Abdomen↗
PubMedDate not supplied

Quantitative gated blood pool SPECT for the assessment of coronary artery disease at rest.

BACKGROUND: Planar gated blood pool imaging (GBPI) has long proven to be useful for the noninvasive assessment of ventricular function. From a practical viewpoint, gated blood pool single photon emission computed tomography (GBPS) acquisition can be accomplished in the same time as a three-view planar series, with the benefit of a tomographic perspective that avoids chamber overlap. METHODS AND RESULTS: Quantitative gated blood pool SPECT was applied to 10 patients who underwent coronary arteriography, contrast ventriculography, and planar gated blood pool imaging. For each patient, the mid-short axis oblique slice was divided into 4 discrete segments using 4 different reference models and 2 forms of segmentation. A center of mass (counts) fixed in the end-diastolic frame and segmentation that bisected the ventricular septum proved to have the highest sensitivity and specificity for determining regional wall motion abnormalities at rest in myocardium supplied by severely diseased coronary arteries (>75 %). GBPS correctly identified 19 of 21 abnormal segments (90%), with good specificity (95%), whereas ventriculography identified 12 (57%) and planar GBPI identified 9 (43%) of the segments supplied by diseased coronaries. CONCLUSION: Quantitative GBPS appears to be a sensitive method for assessing coronary artery disease at rest in myocardium perfused by severely diseased coronary arteries.

Aged↗
PubMedDate not supplied

Radioactive decay.

When a parent radionuclide decays to its daughter radionuclide by means of alpha, beta, or isomeric transition, the decay follows an exponential form, which is characterized by the decay constant lambda. The decay constant represents the probability per unit time that a single radioatom will decay. The decay equation can be used to provide a useful expression for radionuclide decay, the half-life, the time when 50% of the radioatoms present will have decayed. Radiotracer half-life has direct implications in nuclear imaging, radiation therapy, and radiation safety because radionuclide half-life affects the ability to evaluate tracer kinetics and create appropriate nuclear images and also affects organ, tumor, and whole-body radiation dose. The number of radioatoms present in a sample is equal to the activity, defined as the number of transitions per unit time, divided by the decay constant; the mass of radioatoms present in a sample can be calculated to determine the specific activity (activity per unit mass). The dynamic relationship between the number of parent and daughter atoms present over time may lead to radioactive equilibrium, which takes two forms--secular and transient--and has direct relevance to generator-produced radionuclides.

Half-Life↗