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J Ehrhardt

Publications and source records attributed to J Ehrhardt.

28 records · Page 2Linked to original sources
PubMed1992

Segmentation techniques for the classification of brain tissue using magnetic resonance imaging.

A technique is described for classifying brain tissue into three components: gray matter, white matter, and cerebrospinal fluid. This technique uses simultaneously registered proton density and T2-weighted images. Samples of each of the three types of tissue are identified on both image sets and used as "training classes"; these tissue samples are then used to generate a linear discriminant function, which is used to classify the remaining pixels in the image data set. Effects of varying the location and number of training classes have been explored; six pairs of training classes have been found to yield a suitable classification. Interrater and test-retest reliability have been examined and found to be good. Intrascanner and interscanner reproducibility has also been evaluated; classification rates are reproducible within the same individual when the same scanner is used, but in this study poor reproducibility occurs when the same individual is scanned on two different scanners. The validity of the technique has been tested by examining correlations between traced and segmented regions of interest, evaluating correlations with age, and conducting phantom studies, in addition to using visual inspection of the classified images as an indication of face validity. From all four perspectives, the method has been found to have good validity. Additional applications, strengths, and limitations are discussed.

Age Factors↗
PubMed1987

Magnetic resonance imaging of children with Duchenne muscular dystrophy.

Eight children representing a spectrum of clinical states of biopsy-proven Duchenne muscular dystrophy (DMD) underwent magnetic resonance (MR) scans to assess the degree of muscular involvement and disease progression. Five muscle groups (neck, shoulder girdle, pelvic girdle, thigh and calf) were evaluated. In each case, involved muscles were clearly demarcated. Image estimates of disease severity by degree of muscle involvement correlated well with clinical staging. In our experience MR is useful for assessment of disease stage, selection of appropriate muscles for biopsy and planning for courses of physical and rehabilitation therapy.

Adipose Tissue↗
PubMed1976

Effects of time on volume and distribution of coronary collateral flow.

Changes in the volume and distribution of collateral blood flow were studied during the 1st h after coronary occlusion in nine open-chest dogs. Labeled microspheres (7-10 mum) were injected into the left atrium prior to and 20 s, 5 min, and 60 min after acute occlusion of the midcircumflex coronary artery so that myocardial perfusion to small segments of the entire left ventricle could be measured. The segmental perfusions were classified as normally perfused, severely hypoperfused, moderately hypoperfused, and borderline hypoperfused. Standard hemodynamic measurements were obtained and relative coronary vascular resistance to the normally perfused and hypoperfused zones was calculated. The principal conclusions of the study are as follows: 1) during the 1st h after coronary occlusion the collateral flow to the hypoperfused myocardium increases substantially; 2) the increase in collateral flow is distributed fairly evenly to various hypoperfused zones and is associated with a marked decrease in coronary vascular resistance; and 3) as a result of this influx in collateral flow the size of the hypoperfused area decreases and the relative proportion of severely hypoperfused segments within the hypoperfused area decreases.

Animals↗
PubMed1976

Effect of intra-aortic balloon counterpulsation on the motion and perfusion of acutely ischemic myocardium. An experimental echocardiographic study.

The effect of intra-aortic balloon counterpulsation (IABC) on the motion and perfusion of ischemic left ventricular posterior myocardium was studied in 30 open-chest dogs, using ultrasound to register motion and 7-10 mu radioactive microspheres to determine perfusion. Circumflex coronary artery ligation produced acute aneurysmal bulging during isovolumetric contraction and diminished ischemic wall velocity during systolic ejection. Myocardial perfusion was determined in five dogs; perfusion of the area supplied by the ligated coronary artery fell from a control value of 72.9 +/- 13.8 (SE) to 30.0 +/- 2.3 cc/100 g/min (P less than 0.05) at 5 minutes after coronary occlusion. IABC was then administered for one hour, with a fall in aortic systolic pressure (112 +/- 6 to 105 +/- 7 mm Hg, P less than 0.05) and rise in peak aortic diastolic pressure (94 +/- 6 to 102 +/- 7 mm Hg, P less than 0.05). Despite this the ischemic area showed no change in perfusion (measured at the same time): 30.0 +/- 2.3 to 28.0 +/- 2.4 cc/100 g/min. Little change in wall motion occurred: aneurysmal bulging decreased modestly (4.5 +/- 0.3 to 3.6 +/- 0.3 mm, P less than 0.05), but ischemic wall velocity did not increase. After cessation of counterpulsation and one hour of coronary reperfusion aneurysmal bulging disappeared and wall velocity improved. The addition of norepinephrine (eight dogs) or nitroprusside (seven dogs) to intraaortic balloon counterpulsation did not cause a significant further improvement in the response of the dyskinesis during the period of ischemia. We conclude that IABC has little effect on ischemic dyskinesis, probably due to its failure to improve perfusion of the acutely ischemic myocardium.

Acute Disease↗
PubMed1976

Effects of acute coronary occlusion on the motion and perfusion of the normal and ischemic interventricular septum.

To establish the effect of local and remote myocardial ischemia on interventricular septal motion, 27 open-chest dogs were studied using ultrasound and radioactive microspheres. In 14 dogs the left anterior descending coronary artery was ligated. If the ultrasound beam traversed ischemic septum (proximal LAD occlusion), significant (P less than 0.05) declines in systolic septal velocity (26.4 +/- 2.9 to 6.4 +/- 1.8 mm/sec), and excursion (2.6 +/- 0.3 to 0.7 +/- 0.2 mm) occurred, and systolic thickening was reduced. Similar significant changes were seen when the ultrasound beam traversed nonischemic septum adjacent to the ischemic area (distal LAD occlusion). In 13 additional dogs, circumflex coronary ligation produced posterior ischemia. The mean septal velocity for this group increased significantly (21.8 +/- 2.6 to 26.5 +/- 3.3 mm/sec), as did the septal excursion (2.5 +/- 0.2 to 3.1 +/- 0.4 mm). We conclude that acute LAD occlusion causes a reduction in systolic velocity, excursion, and thickening of both the involved ischemic and the adjacent nonischemic septum. When myocardial ischemia was produced in a part of the ventricle remote from the septum, septal velocity and excursion increased.

Animals↗
PubMed1975

Three dimensional geometry of acutely ischemic myocardium.

The distribution of coronary flow to small segments of the entire left ventricle (96 per dog; average weight = 0.78 g) was studied in 28 open-chested dogs utilizing 7-10 mu labeled microspheres. Although the flow to large areas of the ventricle was nearly evenly distributed, there was considerable heterogeneity of flow to small adjacent segments of myocardium (average standard deviation of the flow distributions was 17.3 +/- 3.2% of mean lfow). Approximately one-half of the measured heterogeneity of flow could be attributed to various extraneous factors, and one-half appears to be due to inherent heterogeneity of flow in the left ventricular myocardium. In ten of 28 dogs, the mid-circumglex coronary was suddenly occluded, and five minutes thereafter the distribution of left ventricular flow was determined with microspheres labeled with a different isotope. The ischemic regments were separated into three groups: severely ischemic, moderately ischemic, and borderline ischemic. The three dimmensional geometry of the acutely ischemic myocardium was analyzed, and four general conclusions were reached. 1) The percent distribution of severely ischemic segments, moderately ischemic segments, and borderline ischemic segments within an ischemic region varies from animal to animal. 2) Subendocardial segments were more frequently and more severely affected than neighboring mid-wall or epicardial segments. 3) No evidence of an "hyperperfused zone" of myocardium surrounding the ischemic area was found. 4) The flows to segments immediately adjacent to the severely ischemic segments were heterogeneous. Therefore, the concept of a geometrically defined "buffer zone" of moderately ischemic myocardium surrounding and separating severely ischemic from normally perfused myocardium no longer seems realistic.

Animals↗
PubMed1975

Correlation between echocardiographically demonstrated segmental dyskinesis and regional myocardial perfusion.

In order to evaluate the relationship between regional myocardial perfusion and segmental dyskinesis, 22 open chest dogs were studied using ultrasound to register cardiac wall motion and radioactive labeled microspheres to determine myocardial perfusion. In six dogs, motion and perfusion were correlated at two levels of partial circumflex coronary artery occlusion followed by complete occlusion. A good correlation between declining myocardial perfusion of all the ischemic segments and development of aneurysmal bulging (during isometric contraction) was seen: r = minus 0.80. A similar correlation between myocardial perfusion and endocardial wall velocity (during systolic ejection) was observed: r = 0.92. In nine dogs, the effect of 45 minutes of complete coronary occlusion followed by 30 minutes of reperfusion was evaluated with respect to perfusion and motion. After coronary reperfusion myocardial perfusion of the ischemic area returned to control levels (from 32.6 +/- 3.5 to 130.3 +/- 13.3 ml/100 g/min), but aneurysmal bulging during isometric contraction persisted. Endocardial wall velocity during systolic ejection showed a variable response to reperfusion, achieving values ranging from 32% to 162% of the preocclusion levels. In seven dogs the ultrasound beam was reflected off nonischemic myocardium adjacent to areas of ischemia resulting from coronary occlusion. Despite preservation of normal myocardial perfusion in these nonischemic areas wall motion abnormalities were evident: endocardial wall velocity declined from 25.8 +/- 5.8 to 14.0 +/- 4.9 mm/sec (P less than 0.01), and aneurysmal bulging in three animals. These changes may be due to transient undetected ischemia in the segments struck by the ultrasound beam, or to passive alteration of the motion of the normally perfused areas by the severe dyskinesis of the adjacent ischemic myocardium.

Animals↗
PubMedDate not supplied

Magnetic resonance imaging of human intracortical structure in vivo.

Current neuroimaging methodologies have lacked the resolution needed to visualize cortical organization at the microscopic level. As a consequence, when neurological diseases disrupt the internal structure of the cerebral cortex, the changes can only be visualized postmortem, by histological examination. This imposes severe limitations in the in vivo diagnosis and investigation of those conditions. Here, we report on a magnetic resonance technique that permitted the visualization of some features of cerebral cortex in 14 living human subjects and in 2 fixed brains. The key finding was a periodic pattern of low- and high-signal slabs, oriented perpendicularly to the pial surface, that seem to correspond, respectively, to columnar modules and myelin septa. The key parameters of the new protocol included modifications in pulse sequence, field of view, number of repetitions, and plane of sectioning.

Cerebral Cortex↗