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Biomedical subjects

H Azhari

Publications and source records attributed to H Azhari.

28 records · Page 2Linked to original sources
PubMed1995

A noninvasive comparative study of myocardial strains in ischemic canine hearts using tagged MRI in 3-D.

Regional reduction in myocardial function has long been utilized for noninvasive detection and localization of ischemic regions in the left ventricle. In this study, we compared the ability of 13 different myocardial strain indexes to discriminate between ischemic and nonischemic tissue. Using magnetic resonance imaging with tagging and three-dimensional reconstruction, we noninvasively tracked the deformation of 24 myocardial cuboids in each of nine canine hearts with acute ischemia induced by coronary artery ligation. Monastral blue staining was used for postmortem assessment of ischemia. The ability of each index to discriminate between normal and ischemic zones was evaluated using the "t" statistic. The best discrimination was obtained by the endocardial area strain [t = 7.5 +/- 3.0 (SD)], a local measure of systolic shrinkage on the endocardial surface, and by the magnitude of the endocardial principal strain (t = 7.0 +/- 1.9). Transmural wall thickening (t = 6.1 +/- 2.3) was the third best functional index. The same three indexes correlated most closely with perfusion, as assessed by monastral blue staining. These findings imply that these are the preferable functional indexes for mapping of ischemic myocardial regions.

Animals↗
PubMed1993

Noninvasive quantification of principal strains in normal canine hearts using tagged MRI images in 3-D.

Previous studies of myocardial strains have been largely limited to invasive procedures in isolated regions. Utilizing images from tagged magnetic resonance imaging (MRI) in three dimensions (3-D), we noninvasively quantified in vivo endocardial (endo) and epicardial (epi) principal strains (PS) throughout the left ventricle (LV) and tested their uniformity. Seven normal hearts in paced reclosed-chest dogs were studied. Combining long- and short-axis images, 24 myocardial cuboids were tagged at end diastole (ED), imaged at end systole and ED, and reconstructed in 3-D. The cuboids were circumferentially arranged in three parallel approximately 1-cm-thick short-axis slices (8 cuboids/slice). By application of finite strain analysis to each cuboid, the major PS (i.e., magnitude and angle with respect to the circumferential direction of maximal shortening) was calculated for each face. when strains are averaged globally (i.e., using all regions), the average magnitude of endo PS exceeded epi PS approximately twofold: -0.24 +/- 0.07 (SD) vs. -0.11 +/- 0.05 (P < 0.05). On the other hand, the PS angle with respect to the circumferential direction at epi exceeded the angle at endo (P < 0.05) by 33 +/- 36 degrees. Average PS direction at epi, 59 +/- 32 degrees, aligned with the expected fiber direction but was perpendicular to it at endo, 26 +/- 30 degrees. However, significant regional variations were observed from wall to wall and from apex to base. When variations in location were accounted for, the pooled SD for the PS magnitudes dropped to 0.032 and for the direction to only 15 degrees. Furthermore, it was found that the anterior-posterior pair of walls contracted differently (P < 0.05) from the septal-lateral pair of walls. These observations indicate that regional myocardial function is heterogeneous and is location dependent.

Animals↗
PubMed1992

A conical model to describe the nonuniformity of the left ventricular twisting motion.

The systolic contraction and fiber shortening in the left ventricle (LV) produces torsional moments in the myocardium, resulting in a gradient of angular displacements about the long axis. This is manifested as a counterclockwise rotation of the apex relative to the base, when viewed from the apex. Recent studies with magnetic resonance imaging (MRI), using noninvasive magnetic tags, have revealed three important properties of the LV twist: (a) The angle of twist (i.e., the angular rotation of a slice relative to the basal slice) is consistently higher at the endocardium as compared to the epicardium; (b) The twist increases towards the apex; and (c) Straight MRI-tagged radial lines at end-diastole (ED) are slightly curved at end-systole (ES), implying a nonlinear transmural variation of the twist. The present study suggests that the geometry of the LV at ES can be represented by a thick-walled hollow cone, and that the transmural twist patterns from ED to ES can be described using the continuum mechanics approach and a small strain analysis of an isotropic cone subjected to external torque. The predicted results are compared with the noninvasive MRI measurements of transmural twist in eight human volunteers. Given the epicardial angles of twist of each slice, the predicted endocardial angles of twist are in good correlation with the experimental findings (r = 0.86, slope = 1.09, SEE = 4.1 degrees). In addition, the model reliably describes the changes in the twist magnitude from apex to base (no significant difference from experimental values, P = 0.2), and predicts the curvilinear pattern at ES of the originally straight ED radial lines. Thus, the conical model with uniform properties of the LV, reliably predicts the nonuniformity of the twist patterns, implying that the LV twist is strongly affected by LV geometry.

Adult↗
PubMed1991

Regional three-dimensional geometry and function of left ventricles with fibrous aneurysms. A cine-computed tomography study.

BACKGROUND: To assess the extent and nature of the dysfunction surrounding aneurysms of the left ventricle (LV), we examined the parameters of local and global three-dimensional shape, size, and function of LVs of eight patients with histologically confirmed anterior fibrous aneurysms. METHODS AND RESULTS: Three-dimensional reconstructions of each LV were made from 10-12 short-axis fast cine-angiographic computed tomography (cine-CT) slices encompassing the entire heart at end diastole and end systole. Regional three-dimensional wall thickness, thickening, motion, curvature, and stress index were calculated for 84 elements encompassing the entire LV. The aneurysmal border was defined by a sharp decrease in end-diastolic wall thickness and separated the LV into an aneurysmal zone and a normal zone that was further divided into adjacent normal (AN) and remote normal (RN) zones. As expected, thickening was negligible in both the aneurysmal and the border zones. Although both the AN and the RN zones had normal wall thickness (1.05 +/- 0.20 and 1.09 +/- 0.20 cm, respectively), thickening was depressed in the AN (0.22 +/- 0.08 cm) but not the RN (0.44 +/- 0.19 cm) zones. The size of the dysfunction zone (defined as less than 2 mm thickening) was found to be considerably greater than the anatomic size of the aneurysm (60.9 +/- 13.7% versus 33.6 +/- 7.6% of the left ventricular endocardial area, respectively; p less than 0.001). In addition, the AN zone had a smaller curvature and a higher stress index than the RN zone. CONCLUSIONS: LVs with fibrous aneurysms are characterized by a relatively large region of nonfunction that encompasses the thin aneurysmal area and its transitional border zone, a normally functioning remote zone, and an intermediate region of normal wall thickness but with reduced function, which may be attributed to its low curvature and high stress index.

Algorithms↗
PubMed1990

Three-dimensional mapping of acute ischemic regions using MRI: wall thickening versus motion analysis.

Three-dimensional (3D) endocardial wall motion and thickening were compared as quantitative methods for distinguishing ischemic from non-ischemic myocardium and for their potential to map regional left ventricular (LV) function. Data were obtained by gated magnetic resonance (MR) images in seven open-chest dogs with acute ischemia. The LVs were reconstructed in 3D at end diastole (ED) and end systole (ES) with a helical coordinate system that wraps the endocardium and epicardium. Thickness and percent wall thickening were calculated by a 3D volume element method. Wall motion was calculated by the 3D displacement of the endocardium perpendicular to the wall using both fixed and floating centroids. Monastral blue nonstaining identified the ischemic regions from five anatomical slices of the LV, which corresponded to the in vivo image planes. Thickening and motion were compared at the centers of the ischemic and the remote normal zones, in addition to comparing the functional maps of the entire LV to the postmortem anatomical maps. All methods distinguished between the center of the ischemic zone and the remote normal zone; however, thickening discriminated most strongly between zones. Comparison of the 3D in vivo maps with the 3D postmortem maps showed that the sensitivity, specificity, and overall accuracy of the thickening algorithm exceeded those obtained by the wall motion algorithms with fixed or floating centroids. Thus wall thickening utilizing the 3D volume element approach is superior to 3D wall motion algorithms in distinguishing ischemic from nonischemic zones and in mapping regional function in the entire LV.

Acute Disease↗
PubMed1989

Quantitative characterization and sorting of three-dimensional geometries: application to left ventricles in vivo.

A procedure for automatic sorting of three-dimensional (3-D) shapes is proposed. The procedure is applied to sort into normal and abnormal categories, human left ventricles (LV) using in vivo data from 19 subjects (ten normal and nine abnormal LV's) studied by ultrafast tomography (Cine-CT). The procedure starts by utilizing a vector in a helical coordinate system to describe the spatial geometry of each individual LV cavity. This individual vector is then anatomically aligned and normalized to eliminate effects due to size, yielding a dimensionless vector, denoted as "geometrical cardiogram" (GCG). The GCG characterizes the instantaneous 3-D geometrical information of the individual LV. For the group of healthy subjects, the Karhunen-Loeve Transform (KLT) is then applied to compress the geometric information contained in their individuals' GCG vectors, at end diastole (ED) and end systole (ES), and yield a unique set of basis vectors. The "normal shape domain" is next defined as a truncated set of the KLT basis vectors from which a normal GCG can be reconstructed with a mean squared error (MSE) smaller than a defined threshold. The calculated MSE of any individual GCG reconstructed in this domain is then used as a criterion for sorting the 3-D shapes. Hearts which yield MSE greater than the threshold are considered abnormal. When applied to the study group of 19 subjects a significant difference (p less than 0.0001) between the MSE values obtained for the normal LV's, and those obtained for the abnormal LV's was detected, thus leading to a successful sorting of all the studied LV's. Finally, the KLT is applied to yield a compact representation of the 3-D geometry of any LV (normal or abnormal).

Adolescent↗
PubMedDate not supplied

Dynamic analysis of left-ventricular shape based on curvature function.

The local curvature function is defined as the change in curvature around the circumference of the LV silhouette. The local instantaneous curvature function is used here to quantify regional left-ventricular (LV) performance throughout the cardiac cycle. Left ventriculography images, taken in the right anterior oblique (RAO) view from nine patients with normal ventricular contraction, and eight patients with anterior hypokinesis (AHK) are used. The local curvature around the circumference of the LV is calculated for each heart throughout the ejection period. The dynamic increase in the curvature of the apex, defined as apical sharpening, is a typical feature of LV contraction. Apical sharpening from end-diastole to end-systole is closely related to the degree of hypokinesis. Normal hearts show larger apical sharpening (128 +/- 57%, SD) than do AHK hearts (46 +/- 13%, p = 0.002). The ratio between apical and anterior curvatures at ES has been found to be 7 +/- 3.5 for normal hearts and 2.3 +/- 0.6 for AHK hearts (p = 0.003). Linear regression between the ventricular volume and apical curvature yields a significant relationship for the normal hearts (r = 0.82 +/- 0.06, average p = 0.07), but not for the AHK hearts (r = 0.72 +/- 0.2, average p = 0.24). Thus, the information inherent in the local curvature of the LV and its dynamic change throughout the cardiac cycle may be used to distinguish between normal and anterior hypokinetic hearts.

Cardiomyopathies↗
PubMedDate not supplied

Evaluation of regional load in acute ischemia by three-dimensional curvatures analysis of the left ventricle.

Geometric remodeling of the left ventricule (LV) following myocardial infarction and ischemic insult is associated with myocardial load redistribution. Regional curvatures based on 3-D reconstructions of the LV are used to calculate the regional loads. The technique uses surface normals to derive local circumferential and meridional curvatures. Following the validation of the procedure on simple geometric shapes, the effect of acute ischemia on the regional load redistribution was studied in six open chest dogs. Short axis magnetic resonance imaging (MRI) scans were used to reconstruct end-diastolic (ED) and end-systolic (ES) LV images by applying our helical shape descriptor, before and after acute coronary occlusion. Regional curvatures as well as local wall thickness by the volume element method were calculated before and after acute ischemia, and were used to approximate regional loads, by a regional stress index (sigma/P). Postmortem evaluation using monastral blue staining was used to divide each LV to normal (NZ), ischemic (IZ), and border (BZ) zones in the ischemic case, and to the anatomically matched regions in the preischemic LVs. Ischemia affects the local curvatures and loads both at ED and ES. At ED, sigma/P rose significantly only in the IZ. Similarly, at ES, the highest increase in load was detected in the IZ, but increases in circumferential and meridional load were seen in all regions. Identifying the load redistribution following acute ischemia helps delineate the mechanisms affecting geometric LV remodeling following myocardial infarction.

Animals↗
PubMedDate not supplied

Regional three-dimensional geometry of the normal human left ventricle using cine computed tomography.

The aim of this study is to provide accurate three-dimensional measurements of left ventricular geometrical indices in relation to regional myocardial function. The analysis of the three-dimensional regional geometry and function of left ventricles of ten normal human volunteers is based on three-dimensional reconstructions of the left ventricle from cine computed tomography images, at end diastole and end systole, demonstrating normal left ventricular spatial, geometrical, and functional variability. Regional wall thickness, curvature and surface normals, as well as wall thickening and endocardial wall motion, are calculated and mapped for the entire left ventricle. The circumferential asymmetry of the left ventricle is reflected by the smaller circumferential and meridional curvatures at the septum. Thickening is highest at the anterior and lateral walls. Longitudinally, circumferential curvature increases toward the apex, whereas both wall thickness and wall thickening at end systole are largest at the midventricular level, decreasing toward the apex and base. This study describes the circumferential and apex-to-base variations in regional left ventricular geometric parameters of the normal human left ventricle, using three-dimensional imaging and analysis.

Adult↗