Influence of the distribution of stiffness in the human left ventricular myocardium on shape change in diastole

The finite-element method of stress analysis was applied, in its 3-dimensional form, to models of the left ventricular wall of two patients. The basic geometry and pressure changes were available from biplane angiographic and catheter data. A parametric study of the influence of the distribution of assumed wall stiffness was carried out on the computer models. By comparison with the experimental data the significance of the various changes could be assessed. For example, stiffness of the annulus fibrosus appears to exert a major influence on the deformation and volume change of the ventricle whereas that of the apex does not. The presence of infarcts in the region of the base are more significant than those near the apex. The spiral structure of the myocardium, and the ratio of longitudinal/circumferential stiffness are major determinants of diastolic wall position. These results appear to have appreciable clinical significance.     

Feasibility of quantitative analysis of regional left ventricular function in the post-infarct mouse by magnetic resonance imaging with retrospective gating

We aimed testing feasibility of identification of regional left ventricular (LV) endocardial motion abnormalities in mice undergoing coronary ligation (MI), using cine magnetic resonance with retrospective gating and computation of regional fractional area change (RFAC), by comparison with histological “gold standard” evaluation. ROC analysis determined the optimal RFAC cut-off values for detecting regional ischemic injury. This approach was tested on 18 MI and 10 sham mice. Automated regional LV motion interpretation and bull's eye display allowed non-invasive localization of the induced infarction. Possible applications to future studies assessing the effectiveness of pharmacological treatments or regenerative medicine are expected.     

An approach to evaluation of the point-spread function for 23Na magnetic resonance imaging

Despite the technical challenges that require lengthy acquisitions to overcome poor signal-to-noise ratio (SNR), sodium (²³Na) magnetic resonance imaging (MRI) is an intriguing area of research due to its essential role in human metabolism. Low SNR images can impact the measurement of the point-spread function (PSF) by adding uncertainty into the resulting quantities. Here, we present methods to calculate the PSF by using the modulation transfer function (MTF), and a 3D-printed line-pair phantom in the context of ²³Na MRI. A simulation study investigated the effect of noise on the resulting MTF curves, which were derived by direct modulation (DM) and a method utilizing Fourier harmonics (FHs). Experimental data utilized a line-pair phantom with nine spatial frequencies, filled with different concentrations (15, 30, and 60 mM) of sodium in 3% agar. MTF curves were calculated using both methods from data acquired from density-adapted 3D radial projections (DA-3DRP) and Fermat looped orthogonally encoded trajectories (FLORET). Simulations indicated that the DM method increased variability in the MTF curves at all tested noise levels over the FH method. For the experimental data, the FH method resulted in PSFs with a narrower full width half maximum with reduced variability, although the improvement in variability was not as pronounced as predicted by simulations. The DA-3DRP data indicated an improvement in the PSF over FLORET. It was concluded that a 3D-printed line-pair phantom represents a convenient method to measure the PSF experimentally. The MTFs from the noisy images in ²³Na MRI have reduced variability from a FH method over DM.     

Quantification of left ventricular modification in weightlessness conditions from the spatio-temporal analysis of 2D echocardiographic images

Two-dimensional echocardiography (2DE) performed during flights with a parabolic trajectory to simulate weightlessness provides a unique means to study left ventricular (LV) modifications to prevent post-flight orthostatic intolerance in astronauts. However, conventional analysis of 2DE is based on manual tracings and depends on experience. Accordingly, the aim was objectively to quantify, from 2DE images, the LV modifications related to different gravity levels, by applying a semi-automated level-set border detection technique. The algorithm validation was performed by the comparison of manual tracing results, obtained by two independent observers with 20 images, with the semi-automated measurements. To quantify LV modifications, three consecutive cardiac cycles were analysed for each gravity phase (1 Gz, 1.8 Gz, 0 Gz). The level-set procedure was applied frame-by-frame to detect the LV endocardial contours and obtain LV area against time curves, from which end-diastolic (EDA) and end-systolic (ESA) areas were computed and averaged to compensate for respiratory variations. Linear regression (y=0.91x+1.47, r=0.99, SEE:0.80 cm²) and Bland-Altman analysis (bias=−0.58 cm², 95% limits of agreement=±2.14 cm²) showed excellent correlation between the semi-automatic and manually traced values. Inter-observer variability was 5.4%, and the inter-technique variability was 4.1%. Modifications in LV dimensions during the parabola were found: compared with 1 Gz values, EDA and ESA were significantly reduced at 1.8 Gz by 8.8±5.5% and 12.1±10.1%, respectively, whereas, during 0 Gz, EDA and ESA increased by 13.3±7.3% and 11.6±5.1%, respectively, owing to abrupt changes in venous return. The proposed method resulted in fast and reliable estimations of LV dimensions, whose changes caused by different gravity conditions were objectively quantified.     

Analysis of the relationship between left ventricular pressure and motor current for evaluation of native cardiac function during left ventricular support with a centrifugal blood pump

Control of the ventricular assist device (VAD) for native heart preservation should be attempted, and the VAD could be one strategy for dealing with the shortage of donors in the future. In the application of nonpulsatile blood pumps for ventricular assistance from the ventricular apex to the aorta, bypass flow and hence the motor current of the pumps change in response to the ventricular pressure change. Utilizing these intrinsic characteristics of the continuous-flow pumps, in this study we investigated whether motor current could be used as an index for continuous monitoring of native cardiac function. In study 1, a centrifugal blood pump (CFP) VAD was installed between the apex and descending aorta of a mock circulatory loop. In this model, a baseline with a preload of 10 mmHg, afterload of 40 mmHg, and LV systolic pressure of 40 mmHg was used. The pump speed was fixed at 1300, 1500, and 1700 rpm, and LV systolic pressure was increased up to 140 mmHg by steps of 20 mmHg while the changes in LV pressure, motor current, pump flow, and aortic pressure were observed. In study 2, an in vivo experiment was performed using three sheep. A left heart bypass model was created using a centrifugal pump from the ventricular apex to the descending aorta. The LVP was varied through administration of dopamine while the changes in LV pressure, pump flow, and motor current at 1500 and 1700 rpm were observed. An excellent correlation was observed in both in vitro and in vivo studies in the relationship between motor current and LV pressure. In study 1, the correlation coefficients were 0.77, 0.92, and 0.99 for 1300, 1500, and 1700 rpm, respectively. In study 2, they were 0.88 (animal no. 1), 0.83 (animal no. 2), and 0.88 (animal no. 3) for 1500 rpm, and 0.95 (animal no. 2) and 0.93 (animal no. 3) for 1700 rpm. These results suggest that motor current amplitude monitoring could be useful as an index for the control of VAD for native heart preservation.     

Kinetic magnetic resonance imaging analysis of swallowing: a new approach to pharyngeal function

The emergence of turbo-FLASH MR sequences allows us to acquire five 10-mm sections each second and thus to catch images of the soft tissues during function. One can trace the pathway of a liquid between the tongue, the soft palate, the epiglottis and the pharyngeal apparatus and analysis the role of the anatomic structures during swallowing. Restricted to the sagittal plane for the purpose of this preliminary study, this technique can be extended to the other planes to provide a three-dimensional analysis of oropharyngeal function or dysfunction.     

Left ventricular function in the post-infarct failing mouse heart by magnetic resonance imaging and conductance catheter: a comparative analysis

Aim: Murine myocardial infarction (MI) models are increasingly used in heart failure studies. Magnetic resonance imaging (MRI) and pressure–volume loops by conductance catheter (CC) enable physiological phenotyping. We performed a comparative analysis of MRI vs. CC to assess left ventricular (LV) function in the failing mouse heart. Methods: MI was created by LAD ligation. MRI (day 14) and CC (day 15) were used to determine LV end‐diastolic volume (EDV), end‐systolic volume (ESV) and ejection fraction (EF). Results: Pooled data yielded moderate‐to‐strong linear correlations: EDV: R = 0.61; ESV: R = 0.72; EF: R = 0.81. We analysed three groups, no MI (sham, n = 10), small MI (<30% of LV, n = 14) and large MI (>30%, n = 20). Volumes and EF were consistently lower by CC than by MRI, but group differences were evident for both techniques. Receiver‐operating characteristic analysis indicated good sensitivity and specificity for both techniques, with superior results for MRI. Conclusions: CC and MRI are highly valuable for evaluation of LV volume and function. MRI is recommended for longitudinal studies, accurate absolute volumes and anatomical information. Unique features of CC are its online signal with high temporal resolution, and advanced analysis of LV function and energetics.     

Stroke normalized pressure: a useful parameter for the analysis of left ventricular outflow obstruction

A new method of presenting the in vivo left ventricular pressure-flow data is developed in the present study. This separates left ventricle ejection into unrestricted, progressively restricted and severely restricted cases. This method uses ejection volume and time to define a normalizing ‘stroke’ pressure, which is successful in collapsing the large variability of in vivo data to a few curves with characteristic shapes, depending on the degree of obstruction. Hypertrophic cardiomyopathy is shown to fall into both unrestricted and progressively restricted categories. Normal hearts form the unrestricted case, while a severe aortic valvular stenosis is characteristic of the severely restricted case.     

Comparison of computerized tomography with magnetic resonance imaging (MRI) in the evaluation of encephalic ventricular volume

Summary The volume of the encephalic ventricles was determined from computerized tomographic (CT) and magnetic resonance imaging (MRI) scans of seven subjects without apparent pathology and three subjects with enlarged ventricles. Since there are many conditions in which the encephalic ventricles become enlarged such as Alzheimer's disease and hydrocephalus, accurate measurement of these structures provides (1) a valuable and safe means of aiding in the diagnosis of such conditions and (2) important follow-up information on affected patients. This paper presents the data obtained from the second phase of a three phase study. The first phase demonstrated the possibility of measuring fluid filled spaces by MRI in three phantom preparations (small, medium, and large ventricles). The results were compared with those obtained from the computerized tomography (CT) scans of the same preparations. This phase of the study compares the volumes obtained from CT scans with those obtained from MRI scans of the same individuals. The volumetric calculations were done with the aid of a Calcomp 9000 digital analyser programmed to compensate for the scale factor and slice thickness of the images. The results obtained from the MRI scans correlated closely with those obtained from the CT scans of the same subjects. The third and final phase of the project is the development of an MRI volumetric data base for the encephalic ventricles using a larger number of subjects.

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Etude comparée en TDM et en IRM de l'évaluation du volume des ventricules cérébraux

Résumé Le volume des ventricules cérébraux a été déterminé d'après des données tomodensitométriques et de résonance magnétique chez 7 sujets sans pathologie apparente et chez 3 malades présentant des ventricules élargis. De nombreuses conditions pathologiques sont susceptibles d'entraîner un tel élargissement ventriculaire, telles la maladie d'Alzheimer et l'hydrocéphalie; aussi la mesure précise de ces structures permet: une aide valable et sûre pour l'établissement du diagnostic de ces maladies et une information importante lors du follow-up de ces patients. Ce travail présente les résultats obtenus au cours de la deuxième phase d'une étude à 3 étapes. La première phase avait démontré la possibilité de mesurer des espaces liquidiens par résonance magnétique, à l'aide de 3 préparations fantômes («ventricules» petits, moyens et larges). Les résultats furent comparés avec ceux obtenus par examen tomodensitométrique des mêmes préparations [4]. La phase actuelle de cette étude compare les volumes obtenus par TDM avec ceux obtenus par IRM chez les mêmes individus. Les calculs volumétriques ont été réalisés à l'aide d'un ordinateur Calcomp 9000 programmé pour compenser les facteurs d'agrandissement et d'épaisseur de coupe des images. Les résultats obtenus d'après les données de l'IRM peuvent être corrélés étroitement avec ceux obtenus par TDM avec ces mêmes patients. La troisième et dernière étape du projet est le développement des données volumétriques obtenues par IRM concernant les ventricules cérébraux chez un plus grand nombre de sujets.

     

Evaluation of encephalic ventricular volume from the magnetic resonance imaging scans of thirty-eight human subjects

Summary Accurate volume determination of the encephalic ventricles is of importance in several clinical conditions, including Alzheimer's presenile dementia, schizophrenia, and benign intracranial hypertension. Previous studies have investigated the accuracy with which magnetic resonance imaging (MRI) can be used in clinical practice to evaluate the encephalic ventricles. However, adequate evaluation of pathological conditions depends on a sufficient amount of morphometric data from normal subjects. To begin establishing this data base for normal subjects, we evaluated the MRI scans of 38 subjects found to have no apparent pathology and calculated the ventricular volume in each case by using methods previously developed in our laboratory. The results were then compared with published volumes determined from studies that used either ventricular casts or computerized tomographic scans. The average total ventricular volume for all 38 subjects was 17.4 cm³, while that for males was 16.3 cm³ and that for females was 18.0 cm³. A small but significant correlation was found between age of subject and ventricular volume, with ventricular size increasing with age.

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Evaluation du volume des ventricules cérébraux à partir des images obtenues en résonance magnétique nucléaire chez 38 sujets humains

Résumé La détermination exacte du volume des ventricules cérébraux est importante en clinique comme par exemple dans la démence présénile d'Alzheimer, la schizophrénie et l'hypertension intracrânienne bénigne. Des études antérieures ont étudié la fiabilité de la résonance magnétique nucléaire en pratique clinique pour évaluer le volume des ventricules cérébraux. Toutefois une évaluation correcte dans les conditions pathologiques implique une bonne connaissance des données morphométriques du sujet normal. Pour établir ces données sur « le sujet normal », nous avons étudié les coupes obtenues en IRM chez 38 sujets apparemment indemnes de toute pathologie; nous avons calculé le volume ventriculaire dans chaque cas en utilisant des méthodes mises au point auparavant dans notre laboratoire. Les résultats ont été ensuite comparés avec ceux obtenus par d'autres études utilisant soit des moules ventriculaires, soit des coupes tomographiques computérisées. Le volume ventriculaire total moyen chez 38 sujets est de 17,4 cm³, mais il est chez les sujets masculins de 16,3 cm³ et chez les sujets de sexe féminin de 18 cm³. Une corrélation faible mais significative a été trouvée entre l'âge du sujet et le volume ventriculaire, étant entendu que la taille du ventricule augmente avec l'âge.

     

应用二尖瓣环运动速度和时间指标评价冠心病患者左室整体舒张功能

目的：应用脉冲多普勒组织成像（DTI）定量分析并比较心绞痛与心肌梗死（心梗）患者二尖瓣环长轴方向上舒张运动速度和时间变化，探讨其评价左室整体舒张功能异常的价值。方法：冠心病心绞痛组16例、心梗组34例、对照组16例。记录二尖瓣环侧壁、间隔、前壁和下壁的运动频谱。测量舒张早、晚期峰值运动速度及其比值，舒张早期波开始时间、达峰时间和局部等容舒张时间，并计算4个位点的均值，分别以Em、Am、Em/Am、QEm、TEm和IVRTm表示。结果：心绞痛组和心梗组Em和Em/Am显著低于对照组（P<0.01），心梗组Em又低于心绞痛组（P<0.01）；心绞痛组和心梗组QEm、TEm及IVRTm显著长于对照组（P<0.01或P<0.05），心梗组IVRTm又长于心绞痛组（P<0.01）；IVRTm与Em呈显著负相关（r=-0.64, P<0.01）。结论：脉冲DTI所测Em、Em/Am、QEm、TEm及IVRTm均可反映冠心病患者左室整体舒张功能异常，Em和IVRTm尚可反映心肌缺血损害的严重程度。     

Head surface digitization and registration: A method for mapping positions on the head onto magnetic resonance images

Summary We have developed a method for mapping positions on the head, such as anatomical landmarks, electrode locations, and stimulation sites, onto magnetic resonance (MR) images of the head. This method is based on the registration of two representations of the head surface: a series of contours obtained from MR images and a set of points measured from the head. The three-dimensional coordinates of each head point were acquired with the use of a magnetic digitizer, whose source was removed from the equipment and mounted on top of the subject's head. This arrangement seemed less uncomfortable for the subject than head immobilization and allowed the acquisition of many points without compromising the precision of the measurements. The digitized head surface was registered to MR image head contours using a surface registration algorithm. The registration provided the rotation and translation parameters needed for mapping head positions onto MR images. The precision of this mapping method has been estimated to be in the range of 3 to 8 mm. This method has been used to map dipole sources in electroencephalography and magnetoencephalography and to impose maps of scalp sites used in transcranial magnetic stimulation onto MR and PET images of the brain.Dr. Wang was on leave from the State University of Campinas, Brazil, and was supported by the Brazilian Research Council (CNPq) and the Research Foundation of Sao Paulo (FAPESP). We are grateful to J. Trettau, W. Groves, R. Hill, and L. Johnson for technical assistance, to B.J. Hessie for skillful editing, and to Drs. S. Bookheimer, E.M. Wassermann, A. Pascual-Leone, J. Valls-Solé, R. Thatcher, C.N. Chen, R. Levin, and C.A. Pelizzari for their cooperation. Dr. B.J. Roth provided valuable criticisms. The support of Dr. M. Eden, Director of the Biomedical Engineering and Instrumentation Program, is appreciated.     

A new cephalic reference plane for use with magnetic resonance imaging: the chiasmato-commissural plane

Summary A cephalic reference plane is described through the chiasmatic notch and the posterior commissure, which is easily identified on mid-sagittal cuts using magnetic resonance imaging. The horizontal cuts so obtained are almost parallel to the lateral fissure and are perpendicular to the axis of the brain stem.This work was published in part in C R Acad Sci Paris, t. 311, série III, p. 115–121, 1990     

Converging functional magnetic resonance imaging evidence for a role of the left inferior frontal lobe in semantic retention during language comprehension

Increasing evidence supports dissociable short-term memory (STM) capacities for semantic and phonological representations. Cognitive neuropsychological data suggest that damage to the left inferior and middle frontal gyri are associated with deficits of semantic STM, while damage to inferior parietal areas is associated with deficits of phonological STM. Patients identified as having semantic STM deficits are also impaired on a number of language comprehension and production paradigms. We used one such comprehension task derived from cognitive neuropsychological data to test predictions with functional magnetic resonance imaging (fMRI) using healthy participants. Using a task that required participants to make semantic anomaly judgements, we found significantly greater activation in areas of the left inferior frontal and middle frontal gyri for phrases that required maintenance of multiple words for eventual integration with a subsequent noun or verb. These data are consistent with our previous patient studies (Hanten & Martin, 2000; R. C. Martin & He, 2004; R. C. Martin & Romani, 1994 Martin, R. C. and Romani, C. 1994. Verbal working memory and sentence comprehension: A multiple-components view. Neuropsychology, 8: 506–523. [Crossref] , [Google Scholar]) that suggest that semantic STM is associated with the left inferior and middle frontal gyri and that deficits of semantic STM have particular consequences for comprehension tasks that require maintenance of several word meanings in unintegrated form.     

A layer-specific three-dimensional model for the simulation of balloon angioplasty using magnetic resonance imaging and mechanical testing

A detailed understanding of the mechanical procedure of balloon angioplasty requires three-dimensional (3D) modeling and efficient numerical simulations. We have developed a 3D model for eight distinct arterial components associated with specific mechanical responses. The 3D geometrical model is based on in vitro magnetic resonance imaging of a human stenotic postmortem artery and is represented by nonuniform rational B-spline surfaces. Mechanical tests of the corresponding vascular tissues provide a fundamental basis for the formulation of large strain constitutive laws, which model the typical anisotropic, highly nonlinear, and inelastic mechanical characteristics under supraphysiological loadings. The 3D finite-element realization considers the balloon–artery interaction and accounts for vessel-specific axial in situ prestretches. 3D stress states of the investigated artery during balloon expansion and stent deployment were analyzed. Furthermore, we studied the changes of the 3D stress state due to model simplifications, which are characterized by neglecting axial in situ prestretch, assuming plane strain states, and isotropic material responses, as commonly utilized in previous works. Since these simplifications lead to maximum stress deviations of up to 600%—where even the stress character may interchange—the associated models are, in general, inappropriate. The proposed approach provides a tool that has the potential (i) to improve procedural protocols and the design of interventional instruments on a lesion-specific basis, and (ii) to determine postangioplasty mechanical environments, which may be correlated with restenosis responses. © 2002 Biomedical Engineering Society. PAC2002: 8719Rr, 8761Lh, 8710+e     

Supervised pattern recognition for the prediction of contrast-enhancement appearance in brain tumors from multivariate magnetic resonance imaging and spectroscopy

OBJECTIVE: The purpose of this study was to develop a pattern classification algorithm for use in predicting the location of new contrast-enhancement in brain tumor patients using data obtained via multivariate magnetic resonance (MR) imaging from a prior scan. We also explore the use of feature selection or weighting in improving the accuracy of the pattern classifier. METHODS AND MATERIALS: Contrast-enhanced MR images, perfusion images, diffusion images, and proton spectroscopic imaging data were obtained from 26 patients with glioblastoma multiforme brain tumors, divided into a design set and an unseen test set for verification of results. A k-NN algorithm was implemented to classify unknown data based on a set of training data with ground truth derived from post-treatment contrast-enhanced images; the quality of the k-NN results was evaluated using a leave-one-out cross-validation method. A genetic algorithm was implemented to select optimal features and feature weights for the k-NN algorithm. The binary representation of the weights was varied from 1 to 4 bits. Each individual parameter was thresholded as a simple classification technique, and the results compared with the k-NN. RESULTS: The feature selection k-NN was able to achieve a sensitivity of 0.78+/-0.18 and specificity of 0.79+/-0.06 on the holdout test data using only 7 of the 38 original features. Similar results were obtained with non-binary weights, but using a larger number of features. Overfitting was also observed in the higher bit representations. The best single-variable classifier, based on a choline-to-NAA abnormality index computed from spectroscopic data, achieved a sensitivity of 0.79+/-0.20 and specificity of 0.71+/-0.11. The k-NN results had lower variation across patients than the single-variable classifiers. CONCLUSIONS: We have demonstrated that the optimized k-NN rule could be used for quantitative analysis of multivariate images, and be applied to a specific clinical research question. Selecting features was found to be useful in improving the accuracy of feature weighting algorithms and improving the comprehensibility of the results. We believe that in addition to lending insight into parameter relevance, such algorithms may be useful in aiding radiological interpretation of complex multimodality datasets.     

A novel method for measuring bowel motility and velocity with dynamic magnetic resonance imaging in two and three dimensions

Increasingly, dynamic magnetic resonance imaging (MRI) has potential as a noninvasive and accessible tool for diagnosing and monitoring gastrointestinal motility in healthy and diseased bowel. However, current MRI methods of measuring bowel motility have limitations: requiring bowel preparation or long acquisition times; providing mainly surrogate measures of motion; and estimating bowel-wall movement in just two dimensions. In this proof-of-concept study we apply a method that provides a quantitative measure of motion within the bowel, in both two and three dimensions, using existing, vendor-implemented MRI pulse sequences with minimal bowel preparation. This method uses a minimised cost function to fit linear vectors in the spatial and temporal domains. It is sensitised to the spatial scale of the bowel and aims to address issues relating to the low signal-to-noise in high-temporal resolution dynamic MRI scans, previously compensated for by performing thick-slice (10-mm) two-dimensional (2D) coronal scans. We applied both 2D and three-dimensional (3D) scanning protocols in two healthy volunteers. For 2D scanning, analysis yielded bi-modal velocity peaks, with a mean antegrade motion of 5.5 mm/s and an additional peak at ~9 mm/s corresponding to longitudinal peristalsis, as supported by intraoperative data from the literature. Furthermore, 3D scans indicated a mean forward motion of 4.7 mm/s, and degrees of antegrade and retrograde motion were also established. These measures show promise for the noninvasive assessment of bowel motility, and have the potential to be tuned to particular regions of interest and behaviours within the bowel.     

A novel 3D approach for determination of frontal and coronal plane tibial slopes from MR imaging

Background

The proximal tibia is geometrically complex, asymmetrical, and variable, is heavily implicated in arthrokinematics of the knee joint, and thus a contributor to knee pathologies such as non-contact anterior cruciate ligament injury. Medial, lateral, and coronal tibial slopes are anatomic parameters that may increase predisposition to knee injuries, but the extent to which each contributes has yet to be fully realized. Previously, two-dimensional methods have quantified tibial slopes, but more reliable 3D methods may prove advantageous.