Tagged Magnetic Resonance Imaging Research Articles

Tongue and Lateral Upper Airway Movement with Mandibular Advancement

To characterize tongue and lateral upper airway movement and to image tongue deformation during mandibular advancement. Dynamic imaging study of a wide range of apnea hypopnea index (AHI), body mass index (BMI) subjects. Not-for-profit research institute. 30 subjects (aged 31-69 y, AHI 0-75 events/h, BMI 17-39 kg/m(2)). Subjects were imaged using dynamic tagged magnetic resonance imaging during mandibular advancement. Tissue displacements were quantified with the harmonic phase technique. Mean mandibular advancement was 5.6 ± 1.8 mm (mean ± standard deviation). This produced movement through a connection from the ramus of the mandible to the pharyngeal lateral walls in all subjects. In the sagittal plane, 3 patterns of posterior tongue deformation were seen with mandibular advancement-(A) en bloc anterior movement, (B) anterior movement of the oropharyngeal region, and (C) minimal anterior movement. Subjects with lower AHI were more likely to have en bloc movement (P = 0.04) than minimal movement. Antero-posterior elongation of the tongue increased with AHI (R = 0.461, P = 0.01). Mean anterior displacements of the posterior nasopharyngeal and oropharyngeal regions of the tongue were 20% ± 13% and 31% ± 17% of mandibular advancement. The posterior tongue compressed 1.1 ± 2.2 mm supero-inferiorly. Mandibular advancement has two mechanisms of action which increase airway size. In subjects with low AHI, the entire tongue moves forward. Mandibular advancement also produces lateral airway expansion via a direct connection between the lateral walls and the ramus of the mandible. Brown EC; Cheng S; McKenzie DK; Butler JE; Gandevia SC; Bilston LE. Tongue and lateral upper airway movement with mandibular advancement. SLEEP 2013;36(3):397-404.

A Comparison of Hyperelastic Warping of PET Images with Tagged MRI for the Analysis of Cardiac Deformation.

The objectives of the following research were to evaluate the utility of a deformable image registration technique known as hyperelastic warping for the measurement of local strains in the left ventricle through the analysis of clinical, gated PET image datasets. Two normal human male subjects were sequentially imaged with PET and tagged MRI imaging. Strain predictions were made for systolic contraction using warping analyses of the PET images and HARP based strain analyses of the MRI images. Coefficient of determination R 2 values were computed for the comparison of circumferential and radial strain predictions produced by each methodology. There was good correspondence between the methodologies, with R 2 values of 0.78 for the radial strains of both hearts and from an R 2 = 0.81 and R 2 = 0.83 for the circumferential strains. The strain predictions were not statistically different (P ≤ 0.01). A series of sensitivity results indicated that the methodology was relatively insensitive to alterations in image intensity, random image noise, and alterations in fiber structure. This study demonstrated that warping was able to provide strain predictions of systolic contraction of the LV consistent with those provided by tagged MRI Warping.

Construction of a two-parameter empirical model of left ventricle wall motion using cardiac tagged magnetic resonance imaging data

BackgroundA one-parameter model was previously proposed to characterize the short axis motion of the LV wall at the mid-ventricle level. The single parameter of this model was associated with the radial contraction of myocardium, but more comprehensive model was needed to account for the rotation at the apex and base levels. The current study developed such model and demonstrated its merits and limitations with examples.Materials and methodsThe hearts of five healthy individuals were visualized using cardiac tagged magnetic resonance imaging (tMRI) covering the contraction and relaxation phases. Based on the characteristics of the overall dynamics of the LV wall, its motion was represented by a combination of two components - radial and rotational. Each component was represented by a transformation matrix with a time-dependent variable α or β.Image preprocessing step and model fitting algorithm were described and applied to estimate the temporal profiles of α and β within a cardiac cycle at the apex, mid-ventricle and base levels. During this process, the tagged lines of the acquired images served as landmark reference for comparing against the model prediction of the motion. Qualitative and quantitative analyses were performed for testing the performance of the model and thus its validation.ResultsThe α and β estimates exhibited similarities in values and temporal trends once they were scaled by the radius of the epicardium (repi)and plotted against the time scaled by the period of the cardiac cycle (Tcardiac) of each heart measured during the data acquisition. α/repi peaked at about Δt/Tcardiac=0.4 and with values 0.34, 0.4 and 0.3 for the apex, mid-ventricle and base level, respectively. β/repi similarly maximized in amplitude at about Δt/Tcardiac=0.4, but read 0.2 for the apex and - 0.08 for the base level. The difference indicated that the apex twisted more than the base.ConclusionIt is feasible to empirically model the spatial and temporal evolution of the LV wall motion using a two-parameter formulation in conjunction with tMRI-based visualization of the LV wall in the transverse planes of the apex, mid-ventricle and base. In healthy hearts, the analytical model will potentially allow deriving biomechanical entities, such as strain, strain rate or torsion, which are typically used as diagnostic, prognostic or predictive markers of cardiovascular diseases including diabetes.

Single syllable tongue motion analysis using tagged cine MRI

The complicated muscle activity of the human tongue and the resultant surface shapes can give us important clues about speech motor control and pathological tongue motion. This study uses tagged magnetic resonance imaging to provide a 2D surface deformation analysis of the tongue, as well as a 4D compression–expansion analysis, during utterances of four different syllables (/ba/, /ta/, /sha/ and /ga/). All speech tasks were performed several times to confirm the repeatability of the motion analysis. The results showed that the tongue has unique motion patterns for utterances of different syllables, and these differences, which may not be observed by a simple surface analysis, can be examined thoroughly by a 4D motion model-based analysis of the tongue muscles.

Assessment of the liver strain among cirrhotic and normal livers using tagged MRI

To use magnetization tagged magnetic resonance imaging (MRI) (tag-MRI) to quantify cardiac induced liver strain and compare strain of cirrhotic and normal livers. Tag-MRI was performed at 1.5T on eight subjects with no history of liver disease and 10 patients with liver cirrhosis. A breath-hold peripheral pulse-gated (PPG) conventional tag-MRI cine sequence was performed with planes to include the left lobe of the liver and the inferior wall of the heart. Commercially available software HARP (Diagnosoft, Palo Alto, CA) was used for image analysis and strain calculation. Three regions-of-interest (ROIs) were selected: segment II of the liver near the heart (A), right liver lobe far from the heart (B), and the left ventricular wall (C). The average and maximal (max) strain were measured in A, B, and C. The maximum strains were used to generate a cardiac-corrected strain gradient: (maxA-maxB)/maxC. Results were compared with Student's t-test (SPSS, Chicago, IL). In subjects with no history of liver disease vs. cirrhotic patients, the average strain was 22% ± 7% vs. 4% ± 3% (P < 0.001), the max strain was 63% ± 15% vs. 17% ± 5% (P < 0.001), and the corrected strain gradient was 0.52 ± 0.16 vs. 0.11% ± 0.08%. There is a significant difference in liver strain measured with tag-MRI between subjects with no history of liver disease and patients with cirrhosis.

A B‐spline approach to phase unwrapping in tagged cardiac MRI for motion tracking

A novel B-Spline based approach to phase unwrapping in tagged magnetic resonance images is proposed for cardiac motion tracking. A bicubic B-spline surface is used to model the absolute phase. The phase unwrapping problem is formulated as a mixed integer optimization problem that minimizes the sum of the difference between the spatial gradients of absolute and wrapped phases, and the difference between the rewrapped and wrapped phases. In contrast to the existing techniques for motion tracking, the proposed approach can overcome the limitation of interframe half-tag displacement and increase the robustness of motion tracking. The article further presents a hybrid harmonic phase imaging-B-spline method to take the advantage of the harmonic phase imaging method for small motion and the efficiency of the B-Spline approach for large motion. The proposed approach has been successively applied to a full set of cardiac MRI scans in both long and short axis slices with superior performance when compared with the harmonic phase imaging and quality guided path-following methods.

Accurate two-dimensional cardiac strain calculation using adaptive windowed Fourier transform and Gabor wavelet transform

Cardiac strain calculated from tagged magnetic resonance (MR) images provides clinicians information about abnormalities of heart-wall motion in patients. It is important to develop an accurate method to determine the cardiac strain efficiently. An adaptive windowed harmonic phase (AWHARP) method is proposed for cardiac strain calculation. AWHARP is based on adaptive windowed Fourier transform (AWFT) and 2D Gabor wavelet transform (2D-GWT). The AWFT provides a spatially varying representation of the signal spectra, which allows the harmonic phase (HARP) image to be extracted with high accuracy. Instantaneous spatial frequencies are calculated using 2D-GWT, and the widths of the adaptive windows are then determined according to the instantaneous spatial frequencies for multi-resolution analysis of phase extraction. The proposed method was studied using simulated images and patients' MR images. Both single tagged images (SPAMM) and subtracted tagged images (CSPAMM) were generated using our simulation method, and their results calculated using AWHARP and HARP methods were compared. Normal and pathological tagged MR images were also processed to evaluate the performance of our method. Our experimental results show that the accuracies of phase and strain images calculated using the AWHARP method are higher than that calculated using the HARP method especially for large tag line deformation. The improvement in accuracies can be up to 3.2 strain (E1) and 17.3 calculation from MR images reveals that the cardiac strain in the end-systolic state is significantly reduced for patients with hypertrophic cardiomyopathy (HCM) compared to that of healthy subjects. The proposed AWHARP is an accurate and efficient method for cardiac strain estimation from MR images. This new algorithm can help clinicians to detect left ventricle dysfunctions and myocardial diseases with accurate cardiac strain analysis.

Changes in myofilament lattice spacing accounts for differences in systolic strains in Vinculin deficient mouse hearts

Vinculin has been previously shown to play a significant role in mechanotransduction and may affect myocardial mechanical function in a directionally‐dependent manner. Cardiac MRI tagging in a vinculin knockout (VclKO) mouse model revealed significant decreases in systolic sheet‐normal shear strain (P&lt;0.05) and systolic sheet strain (P&lt;0.05) in KO mice compared with littermate wildtype (WT) controls. We hypothesized that an increase in transverse systolic stress development may explain these observations, and changes in myofilament lattice spacing in the VclKO could alter systolic stress in the myocytes. Actin‐myosin lattice spacing was then measured and normalized to sarcomere length in barium‐contracted WT and VclKO hearts with values of 19.1±1.51 nm and 21.8±1.39 nm, respectively. These results were used as inputs in a structural model of crossbridge geometry similar to that of Schoenberg (1980), which showed a significant increase in the radial component of sacromere force in the VclKO compared with WT. The calculated distribution of forces was then used in a three‐dimensional finite element model in which end systolic sheet strains were predicted. The results matched the trends seen experimentally between the WT and VclKO mice. These results suggest that the change in systolic strains seen experimentally in the VclKO mice can be explained by the increase in lattice spacing seen in the knockout mice.

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Role of Vinculin in Ventricular Wall Function

Vinculin (Vcl) is a ubiquitously expressed cytoskeletal protein that localizes at cell adhesion sites in cardiomyocytes. It is a key component in the costamere, which anchors the sarcomeric cytoskeleton to the extracellular matrix via integrins. It has been previously shown that it plays a significant role in mechanotransduction and may affect myocardial mechanical function in a directional-dependent manner. To determine the role of Vcl in regional wall mechanics, cardiac MRI tagging was performed in a cardiac-myocyte-specific vinculin knockout (VclKO) mouse model revealing significant decreases in systolic sheet-normal shear strain (P<0.05) and systolic sheet strain (P<0.05) in KO mice compared with littermate wildtype (WT) controls. In addition, measurements in isolated papillary muscles in heterozygous global vinculin knockout mice showed no difference in isometric fiber tension development consistent with no change in systolic fiber strain in vivo. A finite element model of ventricular mechanics suggested an increase in transverse systolic stress development may explain these observations. We hypothesized that this may be due to an increase in myofilament lattice spacing in the VclKO. Lattice spacing and sarcomere length were measured from optical diffraction patterns generated from FFTs of electron micrographs of VclKO and control hearts. The center-to-center spacing between myosin filaments was 37.6±2.55 nm in barium-contracted VclKO hearts (n=3) compared with 32.9±2.37 nm in WT controls (n=3). In hearts fixed at zero load, this spacing averaged 33.5±1.35 nm in VclKO (n=3) vs. 30.8±0.68 nm in WT (n=3). These results along with sarcomere length measurements suggest Vcl can mediate myofilament architecture and hence directional-dependent systolic force generation. We hypothesize that increasing lattice spacing alters the crossbridge binding angle of myosin heads, increasing the transverse force that they generate. The resulting increase in transverse myofiber stiffness during systole decreases systolic sheet strains.

Incompressible deformation estimation algorithm (IDEA) from tagged MR images.

Measuring the 3D motion of muscular tissues, e.g., the heart or the tongue, using magnetic resonance (MR) tagging is typically carried out by interpolating the 2D motion information measured on orthogonal stacks of images. The incompressibility of muscle tissue is an important constraint on the reconstructed motion field and can significantly help to counter the sparsity and incompleteness of the available motion information. Previous methods utilizing this fact produced incompressible motions with limited accuracy. In this paper, we present an incompressible deformation estimation algorithm (IDEA) that reconstructs a dense representation of the 3D displacement field from tagged MR images and the estimated motion field is incompressible to high precision. At each imaged time frame, the tagged images are first processed to determine components of the displacement vector at each pixel relative to the reference time. IDEA then applies a smoothing, divergence-free, vector spline to interpolate velocity fields at intermediate discrete times such that the collection of velocity fields integrate over time to match the observed displacement components. Through this process, IDEA yields a dense estimate of a 3D displacement field that matches our observations and also corresponds to an incompressible motion. The method was validated with both numerical simulation and in vivo human experiments on the heart and the tongue.

Reversible jump MCMC methods for fully automatic motion analysis in tagged MRI

Tagged magnetic resonance imaging (tMRI) is a well-known noninvasive method for studying regional heart dynamics. It offers great potential for quantitative analysis of a variety of kine(ma)tic parameters, but its clinical use has so far been limited, in part due to the lack of robustness and accuracy of existing tag tracking algorithms in dealing with low (and intrinsically time-varying) image quality. In this paper, we evaluate the performance of four frequently used concepts found in the literature (optical flow, harmonic phase (HARP) magnetic resonance imaging, active contour fitting, and non-rigid image registration) for cardiac motion analysis in 2D tMRI image sequences, using both synthetic image data (with ground truth) and real data from preclinical (small animal) and clinical (human) studies. In addition we propose a new probabilistic method for tag tracking that serves as a complementary step to existing methods. The new method is based on a Bayesian estimation framework, implemented by means of reversible jump Markov chain Monte Carlo (MCMC) methods, and combines information about the heart dynamics, the imaging process, and tag appearance. The experimental results demonstrate that the new method improves the performance of even the best of the four previous methods. Yielding higher consistency, accuracy, and intrinsic tag reliability assessment, the proposed method allows for improved analysis of cardiac motion.

Impact of Physiological Ventricular Deformation on the Morphology of the T-Wave: A Hybrid, Static-Dynamic Approach

Ventricular wall deformation is widely assumed to have an impact on the morphology of the T-wave that can be measured on the body surface. This study aims at quantifying these effects based on an in silico approach. To this end, we used a hybrid, static-dynamic approach: action potential propagation and repolarization were simulated on an electrophysiologically detailed but static 3-D heart model while the forward calculation accounted for ventricular deformation and the associated movement of the electrical sources (thus, it was dynamic). The displacement vectors that describe the ventricular motion were extracted from cinematographic and tagged MRI data using an elastic registration procedure. To probe to what extent the T-wave changes depend on the synchrony/asynchrony of mechanical relaxation and electrical repolarization, we created three electrophysiological configurations, each with a unique QT time: a setup with physiological QT time, a setup with pathologically short QT time (SQT), and pathologically long QT time (LQT), respectively. For all three electrophysiological configurations, a reduction of the T-wave amplitude was observed when the dynamic model was used for the forward calculations. The largest amplitude changes and the lowest correlation coefficients between the static and dynamic model were observed for the SQT setup, followed by the physiological QT and LQT setups.

Regional Left Ventricular Myocardial Contractility and Stress in a Finite Element Model of Posterobasal Myocardial Infarction

Recently, a noninvasive method for determining regional myocardial contractility, using an animal-specific finite element (FE) model-based optimization, was developed to study a sheep with anteroapical infarction (Sun et al., 2009, "A Computationally Efficient Formal Optimization of Regional Myocardial Contractility in a Sheep With Left Ventricular Aneurysm," ASME J. Biomech. Eng., 131(11), p. 111001). Using the methodology developed in the previous study (Sun et al., 2009, "A Computationally Efficient Formal Optimization of Regional Myocardial Contractility in a Sheep With Left Ventricular Aneurysm," ASME J. Biomech. Eng., 131(11), p. 111001), which incorporates tagged magnetic resonance images, three-dimensional myocardial strains, left ventricular (LV) volumes, and LV cardiac catheterization pressures, the regional myocardial contractility and stress distribution of a sheep with posterobasal infarction were investigated. Active material parameters in the noninfarcted border zone (BZ) myocardium adjacent to the infarct (T(max_B)), in the myocardium remote from the infarct (T(max_R)), and in the infarct (T(max_I)) were estimated by minimizing the errors between FE model-predicted and experimentally measured systolic strains and LV volumes using the previously developed optimization scheme. The optimized T(max_B) was found to be significantly depressed relative to T(max_R), while T(max_I) was found to be zero. The myofiber stress in the BZ was found to be elevated, relative to the remote region. This could cause further damage to the contracting myocytes, leading to heart failure.

Validation of SPAMM tagged MRI based measurement of 3D soft tissue deformation

This study presents and validates a novel (non-ECG-triggered) MRI sequence based on spatial modulation of the magnetization (SPAMM) to noninvasively measure 3D (quasistatic) soft tissue deformations using only six acquisitions (three static and three indentations). In the current SPAMM tagged MRI approaches, data are typically constructed from many repeated motion cycles. This has so far restricted its application to the measurement of highly repeatable and periodic movements (e.g., cardiac deformation). In biomechanical applications where soft tissue deformation is artificially induced, often by indentation, significant repeatability constraints exist, and for clinical applications, discomfort and health issues generally preclude a large number of repetitions. A novel (non-ECG-triggered) SPAMM tagged MRI sequence is presented, whereby a single 1-1 (first order) SPAMM set is acquired following a 3D transient field echo acquisition. Full 3D deformation measurement is achieved through the combination of only six acquisitions (three static and three motion cycles). The 3D deformation measurements were validated using quasistatic indentation tests and marker tracking in a silicone gel soft tissue phantom. In addition, the technique's ability to measure 3D soft tissue deformation in vivo was evaluated using indentation of the biceps region of the upper arm in a volunteer. Following comparison to marker tracking in the silicone gel phantom, the SPAMM tagged MRI based displacement measurement demonstrated subvoxel accuracy with a mean displacement difference of 72 microm and a standard deviation of 289 microm. In addition, precision of displacement magnitude was evaluated for both the phantom and the volunteer data. The standard deviations of the displacement magnitude with respect to the average displacement magnitude were 75 and 169 microm for the phantom and volunteer data, respectively. The subvoxel accuracy and precision demonstrated in the phantom in combination with the precision comparison between the phantom and the volunteer data provide confidence in the methods presented for measurement of soft tissue deformation in vivo. To the author's knowledge, since only six acquisitions are required, the presented methodology is the fastest SPAMM tagged MRI method currently available for the noninvasive measurement of quasistatic 3D soft tissue deformation.

Magnetic resonance imaging of post-systolic shortening in a closed-chest rat model of coronary occlusion using myocardial tagging

The aim of the study was to evaluate the reliability and sensitivity of tagged cardiac magnetic resonance imaging (cMRI) in assessment of regional cardiac dysfunction induced by short ischemia. For clinical low dose dobutamine tests, quantitative strain analyses derived from tagged cMRI have been shown to be able to detect viable myocardium. However these preliminary data were obtained in patients with high grade coronary stenosis, likely to have a large ischemic territory. So it is not known whether MRI tagging could detect coronary occlusion i) of short duration and ii) in small ischemic areas. A model of closed-chest coronary artery occlusion was developed in Sprague-Dawley rats. 10 rats underwent a 3 minutes coronary occlusion followed by 30 minutes of reperfusion, directly in a 1.5 Tesla clinical MRI scanner. Efficiency and reversibility of the coronary occlusion was assessed by modifications of the ECG recording. Tagged images were acquired every 2.5 minutes using C-SPAMM with segmented cine fast field echo sequence. Strain analysis was performed with the Extrema Temporal Chaining algorithm in six sectors of the short axis slice, classified in 2 groups: anterolateral and inferolateral sectors were considered as ischemic whereas inferior, inferoseptal and anteroseptal sectors were remote. Contraction (maximum strain) and contractility (strain rate) derived from the myocardial strain curves were analysed using a linear model. Eight rats underwent hemodynamic measurements by intraventricular catheterism to evaluate global cardiac function along a similar protocol of ischemia-reperfusion. During the occlusion, contraction was reduced and delayed in the ischemic sectors compared to remote group (p<0.001). The contraction remained delayed during the first minutes of reperfusion (p<0.005) in the ischemic group, demonstrating post-systolic shortening. Contractility was decreased both during the occlusion and the first minutes of reperfusion. Hemodynamic measurements dit not show any abnormality of the systolic or diastolic function after the first minutes of reperfusion. We showed for the first time in a rat model that MRI tagging of a short coronary occlusion is feasible, on a 1.5 Tesla clinical scanner. We demonstrated in the ischemic sectors a transient contractile dysfunction which was not demonstrated by hemodynamic measurements. Besides the interest of such a method for non-invasive study of cardiac function in rodent, our data also suggest that tagged MRI could bring an important improvement in evaluation of the human cardiac function during stress imaging.

Correction of left ventricular wall thickening from short‐axis cine MRI for basal‐descent through‐plane motion

To solve the problem of the basal descent movement in quantification of the regional left ventricular (LV) myocardial wall thickness (WTh) and wall thickening (%WT) in short-axis (SA) cine MRI for effectively assessing the regional wall motion of LV myocardium. LV long-axis tagged MRI and SA cine MRI were performed to calculate the longitudinal translation and circumferential WTh of LV myocardium in eight normal volunteers. The new SA end-systolic thickness (EST) data were reconstructed from the original EST data, based on the quantified longitudinal translation of LV myocardium. The mean %WT of six segments in the basal section after correction was significantly different from that before correction in both intra- and inter-operator experiments. The polar map also showed the significant improvement of the variability of regional %WT and lack of quantification of %WT in the most basal SA slices after correction. The proposed technique demonstrated an important advantage to calculate the %WT in the most basal SA myocardial tissue, which was considered difficult to be achieved using cine MRI.

Myocardial Delayed Enhancement in Pulmonary Hypertension: Pulmonary Hemodynamics, Right Ventricular Function, and Remodeling

The purpose of this study was to assess predictors of MRI-identified septal delayed enhancement mass at the right ventricular (RV) insertion sites in relation to RV remodeling, altered regional mechanics, and pulmonary hemodynamics in patients with suspected pulmonary hypertension (PH). Thirty-eight patients with suspected PH were evaluated with right heart catheterization and cardiac MRI. Ten age- and sex-matched healthy volunteers acted as controls for MRI comparison. Septal delayed enhancement mass was quantified at the RV insertions. Systolic septal eccentricity index, global RV function, and remodeling indexes were quantified with cine images. Peak systolic circumferential and longitudinal strain at the sites corresponding to delayed enhancement were measured with conventional tagging and fast strain-encoded MRI acquisition, respectively. PH was diagnosed in 32 patients. Delayed enhancement was found in 31 of 32 patients with PH and in one of six patients in whom PH was suspected but proved absent (p = 0.001). No delayed enhancement was found in controls. Delayed enhancement mass correlated with pulmonary hemodynamics, reduced RV function, increased RV remodeling indexes, and reduced eccentricity index. Multiple linear regression analysis showed RV mass index was an independent predictor of total delayed enhancement mass (p = 0.017). Regional analysis showed delayed enhancement mass was associated with reduced longitudinal strain at the basal anterior septal insertion (r = 0.6, p < 0.01). Regression analysis showed that basal longitudinal strain remained an independent predictor of delayed enhancement mass at the basal anterior septal insertion (p = 0.02). In PH, total delayed enhancement burden at the RV septal insertions is predicted by RV remodeling in response to increased afterload. Local fibrosis mass at the anterior septal insertion is associated with reduced regional longitudinal contractility at the base.

Evaluation of left ventricular rotation by two-dimensional speckle tracking method and real-time three-dimensional echocardiography: comparison with MRI tagging method.

Recently, it has become possible to evaluate left ventricular (LV) torsion by two-dimensional (2D) speckle tracking images. However, LV torsion is a three-dimensional (3D) performance, which per se cannot be assessed by the 2D speckle tracking method. The present study investigated the accuracy of the 2D speckle tracking method and real-time 3D echocardiography in measuring LV rotation, comparing with the MRI tagging method. We assessed LV apical rotation using the 2D speckle tracking method, real-time 3D echocardiography, and MRI tagging method in 26 normal subjects, and compared the results of these three methods. LV apical rotation was measured just before the level in which the posterior papillary muscle was absorbed into the free wall. The degree of LV apical rotation evaluated by the 2D speckle tracking method (Δθ 2D) was significantly smaller than that evaluated by 3D echocardiography (Δθ 3D) and the MRI tagging method (Δθ MRI) (Δθ 2D 7.3±2.8°; Δθ 3D 8.8±3.4°; Δθ MRI 9.0±3.4°; Δθ 2D vs. Δθ 3D, p=0.0001; Δθ 2D vs. Δθ MRI, p<0.0001). There were good correlations among Δθ 2D, Δθ 3D, and Δθ MRI, but agreement between Δθ 3D and Δθ MRI (mean difference 0.14±1.43°) was better than that between Δθ 2D and Δθ MRI (mean difference 1.68±1.89°). The degree of LV apical rotation was underestimated with the 2D speckle tracking method compared with the MRI tagging method, whereas it could be precisely measured by 3D echocardiography.

Harmonic phase interference for the detection of tag line crossings and beyond in homogeneous strain analysis of cardiac tagged MRI data

Homogenous strain analysis (HSA) was developed to evaluate regional cardiac function using tagged cine magnetic resonance images of heart. Current cardiac applications of HSA are however limited in accurately detecting tag intersections within the myocardial wall, producing consistent triangulation of tag cells throughout the image series and achieving optimal spatial resolution due to the large size of the triangles. To address these issues, this article introduces a harmonic phase (HARP) interference method. In principle, as in the standard HARP analysis, the method uses harmonic phases associated with the two of the four fundamental peaks in the spectrum of a tagged image. However, the phase associated with each peak is wrapped when estimated digitally. This article shows that special combination of wrapped phases results in an image with unique intensity pattern that can be exploited to automatically detect tag intersections and to produce reliable triangulation with regularly organized partitioning of the mesh for HSA. In addition, the method offers new opportunities and freedom for evaluating myocardial function when the power and angle of the complex filtered spectra are mathematically modified prior to computing the phase. For example, the triangular elements can be shifted spatially by changing the angle and/or their sizes can be reduced by changing the power. Interference patterns obtained under a variety of power and angle conditions were presented and specific features observed in the results were explained. Together, the advanced processing capabilities increase the power of HSA by making the analysis less prone to errors from human interactions. It also allows strain measurements at higher spatial resolution and multi-scale, thereby improving the display methods for better interpretation of the analysis results.