Bioelectric and biomagnetic measurements are differentially sensitive to spiral currents

Observations indicate that different information is contained in electrocardiograms and magnetocardiograms in both patients and healthy volunteers. Closed loop currents could explain this phenomenon. We hypothesized that open loops, such as the spirally shaped currents in the heart, also contribute to these differences. We modeled two types of open spiral-shaped loops, based on the heart geometry, using 12 artificial current dipoles in a physical torso phantom. The electric potentials and magnetic fields were measured simultaneously with increasing numbers of active dipoles in the spiral source geometries. We found a continuous increase in the measured amplitudes of the magnetic fields, up to a plateau value when 10 active dipoles were enabled. For the electric potentials, we found that the amplitudes increased when up to six or eight active dipoles had been enabled, and then decreased thereafter. We conclude that open loop currents also contribute to the experimentally observed differences in magnetocardiograms and electrocardiograms in both patients and healthy volunteers. Combined bioelectric and biomagnetic measurements should provide greater insight into heart activity than do single modality measurements

Quantitative diffusion tensor MR imaging of the brain: field strength related variance of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) scalars

The objectives were to study the "impact” of the magnetic field strength on diffusion tensor imaging (DTI) metrics and also to determine whether magnetic-field-related differences in T2-relaxation times of brain tissue influence DTI measurements. DTI was performed on 12 healthy volunteers at 1.5 and 3.0 Tesla (within 2 h) using identical DTI scan parameters. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured at multiple gray and white matter locations. ADC and FA values were compared and analyzed for statistically significant differences. In addition, DTI measurements were performed at different echo times (TE) for both field strengths. ADC values for gray and white matter were statistically significantly lower at 3.0 Tesla compared with 1.5 Tesla (% change between −1.94% and −9.79%). FA values were statistically significantly higher at 3.0 Tesla compared with 1.5 Tesla (% change between +4.04 and 11.15%). ADC and FA values are not significantly different for TE=91ms and TE=125ms. Thus, ADC and FA values vary with the used field strength. Comparative clinical studies using ADC or FA values should consequently compare ADC or FA results with normative ADC or FA values that have been determined for the field strength use

Measurement and Display of Instantaneous Regional Motion of the Myocardium

Quantitative assessment of regional heart motion has significant potential for more accurate diagnosis of heart disease and / or cardiac irregularities. Local heart motion may be studied from medical imaging sequences. Using functional parametric mapping, regional myocardial motion during a cardiac cycle can be color mapped onto a deformable heart model to obtain better understanding of the structure-to-function relationships in the myocardium. In this study, 3D reconstructions were obtained from the Dynamic Spatial Reconstructor 1-3 (DSR) at 15 time points throughout one cardiac cycle. Deformable models were created from the 3-D images for each time point of the cardiac cycle. From these polygonal models, regional excursions and velocities of each vertex representing a unit of myocardium were calculated for successive time intervals. The calculated results were visualized through model animations and / or specially formatted static images. The time point of regional maximum velocity and excursion of myocardium through the cardiac cycle was displayed using color mapping. The absolute value of regional maximum velocity and maximum excursion were displayed in a similar manner. Using animations, the local myocardial velocity changes were visualized as color changes on the cardiac surface during the cardiac cycle. Moreover, the magnitude and direction of motion for individual segments of myocardium could be displayed. These results suggest that the ability to encode quantitative functional information on dynamic cardiac anatomy enhances the diagnostic value of 4D images of the heart. Myocardial mechanics quantified this way adds a new dimension to the analysis of cardiac functional disease, including diastolic filling deficits and / or disturbances in regional electrophysiology and contraction patterns

Quantitative Analysis and Parametric Display of Regional Myocardial Mechanics

Quantitative assessment of regional heart motion has significant potential for more accurate diagnosis of heart disease and / or cardiac irregularities. Local heart motion may be studied from medical imaging sequences. Using functional parametric mapping, regional myocardial motion during a cardiac cycle can be color mapped onto a deformable heart model to obtain better understanding of the structure-to-function relationships in the myocardium, including regional patterns of akinesis or diskinesis associated with ischemia or infarction. In this study, 3D reconstructions were obtained from the Dynamic Spatial Reconstructor 1,2 (DSR) at 15 time points throughout one cardiac cycle of pre-infarct and post-infarct hearts. Deformable models were created from the 3-D images for each time point of the cardiac cycles. From these polygonal models, regional excursions and velocities of each vertex representing a unit of myocardium were calculated for successive time intervals. The calculated results were visualized through model animations and / or specially formatted static images. The time point of regional maximum velocity and excursion of myocardium through the cardiac cycle was displayed using color mapping. The absolute value of regional maximum velocity and maximum excursion were displayed in a similar manner. Using animations, the local myocardial velocity changes were visualized as color changes on the cardiac surface during the cardiac cycle. Moreover, the magnitude and direction of motion for individual segments of myocardium could be displayed. Comparisons of these dynamic parametric displays suggest that the ability to encode quantitative functional information on dynami