A method to determine regional mechanical left ventricular dyssynchrony based on high temporal resolution short axis SSFP cine images

Left ventricular (LV) mechanical dyssynchrony has been proposed as a parameter to select patients for cardiac resynchronization therapy (CRT) [Bax et al JACC 2005].Several recent studies have shown that placing the LV pacing lead in the most delayed regions yields a better response to CRT [Ansalone et al JACC 2002]. However, most imaging-based methods assess global LV dyssynchrony providing a single value for the entire LV. Regional maps of LV dyssynchrony are required for planning LV lead placement. The objective of this study was to develop a method to create a map of regional left ventricular mechanical dyssynchrony based on short-axis SSFP cine images

Characterization of the size and location of dyssynchronous regions in patients undergoing CRT

The amount and location of left ventricular (LV) mechanical dyssynchrony affects an individual’s ability to respond positively to cardiac resynchronization therapy (CRT) [Bax et al JACC 2005]. By using high temporal resolution short-axis cines, it is possible to derive radial motion curves throughout the LV. These radial motion curves can be used to create maps showing dyssynchronous regions in patients enrolled for CRT. The objective of this study was to characterize the size and location of areas of mechanical dyssynchrony in patients scheduled for CRT by comparing their radial wall motion curves to radial motion curves from normal subjects

Telemetric Blood Pressure Assessment in Angiotensin II-Infused ApoE\u3csup\u3e-/-\u3c/sup\u3e Mice: 28 Day Natural History and Comparison to Tail-Cuff Measurements

Abdominal aortic aneurysm (AAA) is a disease of the aortic wall, which can progress to catastrophic rupture. Assessment of mechanical characteristics of AAA, such as aortic distensibility, may provide important insights to help identify at-risk patients and understand disease progression. While the majority of studies on this topic have focused on retrospective patient data, recent studies have used mouse models of AAA to prospectively evaluate the evolution of aortic mechanics. Quantification of aortic distensibility requires accurate measurement of arterial blood pressure, particularly pulse pressure, which is challenging to perform accurately in murine models. We hypothesized that volume/pressure tail-cuff measurements of arterial pulse pressure in anesthetized mice would have sufficient accuracy to enable calculations of aortic distensibility with minimal error. Telemetry devices and osmotic mini-pumps filled with saline or angiotensin-II were surgically implanted in male apolipoprotein-E deficient (ApoE-/-) mice. Blood pressure in the aortic arch was measured continuously via telemetry. In addition, simultaneous blood pressure measurements with a volume/pressure tail-cuff system were performed under anesthesia at specific intervals to assess agreement between techniques. Compared to controls, mice infused with angiotensin-II had an overall statistically significant increase in systolic pressure, with no overall difference in pulse pressure; however, pulse pressure did increase significantly with time. Systolic measurements agreed well between telemetry and tail-cuff (coefficient of variation = 10%), but agreement of pulse pressure was weak (20%). In fact, group-averaged pulse pressure from telemetry was a better predictor of a subject\u27s pulse pressure on a given day than a simultaneous tail-cuff measurement. Furthermore, these approximations introduced acceptable errors (15.1 ± 12.8%) into the calculation of aortic distensibility. Contrary to our hypothesis, we conclude that tail-cuff measures of arterial pulse pressure have limited accuracy. Future studies of aneurysm mechanics using the ApoE-/-/angiotensin-II model would be better in assuming pulse pressure profiles consistent with our telemetry findings instead of attempting to measure pulse pressure in individual mice

High Resolution Cine Displacement Encoding with Stimulated Echoes (DENSE) at 3T with Navigator Feedback for Quantification of Cardiac Mechanics

Background: Measures of cardiac mechanics such as myocardial wall strain are better predictors of outcomes in patients with heart disease compared to traditional clinical measures and ejection fraction. Cine displacement encoding with stimulated echoes (DENSE) is an ideal method for quantifying cardiac motion which encodes tissue displacement in the phase of the MR signal and provides pixel-level resolution for quantifying cardiac mechanics. To date, DENSE has been implemented with resolution limited to 2-3 pixels across the myocardium. While this resolution is higher than most other techniques for quantifying cardiac mechanics, it may limit the ability of DENSE to quantify finer details such as transmural strains (subendocardial, midmyocardial and subepicardial) and right ventricular mechanics. We hypothesized that it is possible to efficiently increase the resolution of DENSE by a factor of 4 utilizing a navigator feedback system. Methods: 10 subjects (age 27 ± 3) with normal ECG and no history of cardiovascular disease were consented. A 3.0T Siemens Tim Trio with a 6-element chest and 24-element spine coil was configured with a navigator feedback system. The feedback system projected the navigator image of the diaphragm to the subject in real time to optimize breathold position. Standard resolution 2D cine DENSE was acquired with: 6 spiral interleaves, FOV = 340 mm, matrix = 96 × 96, thickness = 8 mm, TE/TR = 1.08/17, flip angle = 20, averages = 1, navigator acceptance window = ± 3 mm. High resolution 2D cine DENSE images were acquired by quadrupling the number of spirals to 24, increasing the matrix to 256 × 256, and increasing the averages to 3. Three short- and two long-axis images were acquired with each technique. Left ventricular strains and torsion were compared between the techniques using Bland-Altman. Results: The high resolution images took 11 times longer to acquire but the navigator feedback system provided good efficiency (69 ± 9%) for a total acquisition time of roughly 5 minutes per slice. The high resolution images had excellent quality with a noticeable improvement over standard resolution. There was a systematic but negligible difference between standard and high resolution data for circumferential and longitudinal strains. Radial strains showed the largest differences consistent with a systematic under-estimation of radial strain from standard resolution DENSE. Torsion was not significantly different between the two methods. Conclusions: High resolution cine DENSE MRI with navigator feedback is feasible at 3T and produces high quality images with 4 times the resolution of standard DENSE. Left ventricular circumferential strains, longitudinal strains, and torsion showed negligible differences between high and low resolution DENSE. Radial strains were significantly different, potentially due to better accuracy with high resolution DENSE due to the increased number of pixels within the thickness of the myocardial wall

Assessment of intra- and inter-ventricular cardiac dyssynchrony in patients with repaired Tetralogy of Fallot: a cardiac magnetic resonance study

Using radiative magnetohydrodynamic simulations of the magnetized solar photosphere and detailed spectro-polarimetric diagnostics with the Fe I 6301.5 Å and 6302.5 Å photospheric lines in the local thermodynamic equilibrium approximation, we model active solar granulation as if it was observed at the solar limb. We analyze general properties of the radiation across the solar limb, such as the continuum and the line core limb darkening and the granulation contrast. We demonstrate the presence of profiles with both emission and absorption features at the simulated solar limb, and pure emission profiles above the limb. These profiles are associated with the regions of strong linear polarization of the emergent radiation, indicating the influence of the intergranular magnetic fields on the line formation. We analyze physical origins of the emission wings in the Stokes profiles at the limb, and demonstrate that these features are produced by localized heating and torsional motions in the intergranular magnetic flux concentrations

Quantification of Right Ventricular Function from Short-Axis Displacement-Encoded Images

Background Right ventricular (RV) function is important in many disease states, but is difficult to quantify from routine MR imaging. Previous work has shown that long-axis deformation/strain is the most critical contributor to global RV function; however, short-axis datasets allow for better coverage of the RV. Thus it would be ideal to be able to quantify RV long-axis function using short-axis slice orientations. We hypothesized that a stack of three-dimensional (3D) displacement encoded (DENSE) images could reliably quantify longitudinal deformation of the RV to overcome the need for acquiring additional long-axis views of the RV. Methods A contiguous stack of cine short-axis DENSE images encompassing the entire RV was acquired with 3D encoding in eight healthy volunteers (Age: 27 ± 3 years) using a 3T Siemens Tim Trio scanner. Endo- and epicardial boundaries were manually drawn on each image to generate a 3D reconstruction of the RV myocardium. The measured displacement field was used to deform the mesh and longitudinal strains were computed at every point throughout the volume. For comparison to the short-axis stack with 3D encoding, a standard four-chamber DENSE image with two-dimensional in-plane displacement encoding was acquired. Similar to the 3D analysis, a mesh was deformed using the measured displacements and was subsequently used to determine longitudinal RV strain values. For comparison with the four-chamber data, only short-axis points lying within the four-chamber imaging slices were used to compute peak longitudinal strain. All strains were compared using a two-tailed paired t-test. Results Right ventricular longitudinal strains derived from short-axis 3D DENSE images (-20 ± 4%) were comparable to values obtained from four-chamber images (-16 ± 2%) (p = 0.14). In addition to obtaining information solely at the four-chamber/short-axis intersection, we computed a global RV longitudinal strain of -17 ± 2% from 3D DENSE data (p = 0.64 relative to four-chamber only). Bland Altman analysis yielded a non-significant bias of 3 ± 11% between four-chamber and short-axis longitudinal strain estimates. Conclusions We have demonstrated that short-axis 3D DENSE imaging allows for accurate characterization of right ventricular longitudinal strain compared to a standard long-axis four-chamber acquisition which is typically used to look at RV function. In addition, 3D DENSE acquired in a short-axis orientation allows for more complete coverage of the RV compared to acquisitions based on long-axis image planes. It is likely that the more complete assessment of RV function provided by 3D DENSE could potentially improve upon the accuracy, reproducibility and prognostic ability of common echocardiographic techniques such as the tricuspid annular plane systolic excursion (TAPSE), but future work will need to investigate this