Tagged Cine MRI Research Articles

Three dimensional MRI analyses of tongue muscle behavior

3D and 4D MRI provides unique, high dimensional data for use in clinical applications and scientific models. Our group is currently using diffusion tensor MRI (DTI) and tagged-cine MRI (tMRI) to explore the fiber direction of muscles in the tongue and the shortening patterns of those fibers during speech. tMRI uses “magnetic tags” to mark and track tissue points, so that when the tissue deforms, the tags reflect these deformations. Soft tissue motion patterns, such as those within the tongue during speech, provide a link between muscle activation and tongue surface shape. Tissue points also demark the endpoints and internal points of muscles, and can identify tongue muscle position and shortening during speech. Tracking tongue muscle motion is unique to tMRI because their interdigitated fibers make them fairly opaque to EMG. Disambiguating muscles and identifying their shortening pattern is a first step to relating muscle action to tongue deformation. The second tool, DTI, identifies the location and orie...

T-tubule disease: Relationship between t-tubule organization and regional contractile performance in human dilated cardiomyopathy

Evidence from animal models suggest that t-tubule changes may play an important role in the contractile deficit associated with heart failure. However samples are usually taken at random with no regard as to regional variability present in failing hearts which leads to uncertainty in the relationship between contractile performance and possible t-tubule derangement. Regional contraction in human hearts was measured by tagged cine MRI and model fitting. At transplant, failing hearts were biopsy sampled in identified regions and immunocytochemistry was used to label t-tubules and sarcomeric z-lines. Computer image analysis was used to assess 5 different unbiased measures of t-tubule structure/organization. In regions of failing hearts that showed good contractile performance, t-tubule organization was similar to that seen in normal hearts, with worsening structure correlating with the loss of regional contractile performance. Statistical analysis showed that t-tubule direction was most highly correlated with local contractile performance, followed by the amplitude of the sarcomeric peak in the Fourier transform of the t-tubule image. Other area based measures were less well correlated. We conclude that regional contractile performance in failing human hearts is strongly correlated with the local t-tubule organization. Cluster tree analysis with a functional definition of failing contraction strength allowed a pathological definition of ‘t-tubule disease’. The regional variability in contractile performance and cellular structure is a confounding issue for analysis of samples taken from failing human hearts, although this may be overcome with regional analysis by using tagged cMRI and biopsy mapping.

Abstract 95: Longitudinal In Vivo Quantification of Infarct Size and Cardiac Function in a Murine Model of Myocardial Infarction using Novel Compact High-Performance MRI

Intro: Delayed Enhancement Imaging (DEI) characterizes MI and predicts therapeutic efficacy following coronary revascularization, stem cell transplantation, or other procedures. Typically gadolinium-based (Gd) contrast agents are injected intravenously and accumulate in the lesion, differentiating between normal and diseased myocardium. Traditionally, DEI has been explored using superconducting high-field MRI. Using a novel compact MRI at 1 Tesla, there is increased sensitivity to Gd-based contrast agents compared with higher-field MRI systems. Hypothesis: In this study, DEI on a compact MRI system was employed with spatial intensity analysis to measure infarct size. Tagged cine MRI assessed myocardial strain using the HARP method. Post-mortem histology of Masson Trichrome staining estimated infarct size. Correlation analysis determined relationships between infarct size measured via DEI and histology. Methods: C57BL/6 MI mice had ligation of the left anterior descending artery. Four sham control and five MI mice we imaged using compact MRI (ICON compact MRI, Billerica, MA) and monitored longitudinally over 21 days for infarct progression and cardiac function in vivo. DE imaging was performed 10-20 minutes post injection of 2 μL Gd contrast agent (ProHance, 0.5 mmol/ml). Images were acquired in short axis, 1 mm superior to the apex. Post-processing analysis (pcVirtue, Diagnosoft, Morrisville, NC) measured cardiac function and infarct size. Results and Conclusions: Analyses of DEI data indicate an average infarct size of 24.85 +/- 15.09 % in the left ventricle. One week after MI induction, a much lower EF was observed in MI mice with respect to control (35.3 +/- 7.567% vs. 67.3 +/- 1.6 %), with a slight recovery of cardiac function in MI mice by week 3 (EF = 45.5 +/- 3.1%). Strain analysis also indicated significantly lower average peak strain in MI vs control mice (6.9 +/- 4.3 vs. 21.5 +/- 0.4 %). Preliminary results demonstrate successful monitoring of cardiac function while performing DEI to visualize and quantify MI at 1 Tesla and leverage the benefits of the increased sensitivity of Gd-based contrast imaging with novel compact MRI. Such imaging and analysis techniques could be used to test efficacy of multiple therapeutic interventions.

Left ventricular torsion and longitudinal shortening: two fundamental components of myocardial mechanics assessed by tagged cine-MRI in normal subjects

Cardiac magnetic resonance imaging (Cardiac MRI) has become a gold standard diagnostic technique for the assessment of cardiac mechanics, allowing the non-invasive calculation of left ventricular long axis longitudinal shortening (LVLS) and absolute myocardial torsion (AMT) between basal and apical left ventricular slices, a movement directly related to the helicoidal anatomic disposition of the myocardial fibers. The aim of this study is to determine AMT and LVLS behaviour and normal values from a group of healthy subjects. A group of 21 healthy volunteers (15 males) (age: 23-55 y.o., mean: 30.7 ± 7.5) were prospectively included in an observational study by cardiac MRI. Left ventricular rotation (degrees) was calculated by custom-made software (Harmonic Phase Flow) in consecutive LV short axis planes tagged cine-MRI sequences. AMT was determined from the difference between basal and apical planes LV rotations. LVLS (%) was determined from the LV longitudinal and horizontal axis cine-MRI images. All the 21 cases studied were interpretable, although in three cases the value of the LV apical rotation could not be determined. The mean rotation of the basal and apical planes at end-systole were -3.71° ± 0.84° and 6.73° ± 1.69° (n:18) respectively, resulting in a LV mean AMT of 10.48° ± 1.63° (n:18). End-systolic mean LVLS was 19.07 ± 2.71%. Cardiac MRI allows for the calculation of AMT and LVLS, fundamental functional components of the ventricular twist mechanics conditioned, in turn, by the anatomical helical layout of the myocardial fibers. These values provide complementary information about systolic ventricular function in relation to the traditional parameters used in daily practice.

Myocardial deformation recovery from cine MRI using a nearly incompressible biventricular model

This paper presents a method for biventricular myocardial deformation recovery from cine MRI. The method is based on a deformable model that is nearly incompressible, a desirable property since the myocardium has been shown to be nearly incompressible. The model uses a matrix-valued radial basis function to represent divergence-free displacement fields, which is a first order approximation of incompressibility. This representation allows for deformation modeling of an arbitrary topologies with a relatively small number of parameters, which is suitable for representing the motion of the multi-chamber structure of the heart. The myocardium needs to be segmented in an initial frame after which the method automatically determines the tissue deformation everywhere in the myocardium throughout the cardiac cycle. Two studies were carried out to validate the method. In the first study the myocardial deformation was recovered from a 3D anatomical cine MRI sequence of a healthy volunteer and then validated against the manual segmentation of the biventricular wall and against the corresponding 3D tagged cine MRI sequence. The average volume agreement between the model and the manual segmentation had a false positive rate of 3.2%, false negative rate of 2.8% and true positive rate of 91.4%. The average distance between the model and manually determined intersections of perpendicular tag planes was 1.7mm (1.2 pixel). The same procedures was repeated on another set of 3D anatomical and tagged MRI scans of the same volunteer taken four months later. The recovered deformation was very similar to the one obtained from the first set of scans. In the second study the method was applied to 3D anatomical cine MRI scans of three patients with ventricular dyssynchrony and three age-matched healthy volunteers. The recovered strains of the normal subjects were clearly stronger than the recovered strains of the patients and they were similar to those reported by other researchers. The recovered deformation of all six subjects was validated against manual segmentation of the biventricular wall and against corresponding tagged MRI scans. The agreement was similar to that of the first study.

Using tagged cine-MRI and finite-element method to lower bound the number of independently controllable motor units in the tongue

The biomechanical structure of the tongue is unusual in that there is no rigid structure, such as a bone, for the muscles to act against. In order to understand these biomechanics and their control, a mathematical model has been created. This model has the form of a nonlinear controllable incompressible elastic structure that undergoes large deformations. The model was used to solve a simplified two-dimensional inverse problem. For a simple speech motion (/i-u/), the trajectories of specific points within the tongue were tracked by means of tagged cine MRI. These points correspond to finite element nodes and were used as input to the simplified model. The remaining unknowns in the model are the set of muscle activations that produce the observed motion. Because there is no such set of activations, the set that best approximates the observed motion in a least squares sense was chosen. The results indicate that there must be independently controllable compartments in SL and GG in order to produce this movement. Three methods were used to improve the representation of the tongue and the resolution of the model: refinement of the number of elements, refinement of the number of muscle activations, and the inclusion of dynamics.

An ultrasound and tagged cine MRI study of German vowels

German vowels contrast along the tense–lax as well as the rounding dimension, rendering a relatively complex (front) vowel system. The difference between tense and lax vowels is often described in terms of more extreme articulator movement and greater muscular tension for tense vowels, manifest especially in tongue root displacement and tongue height. These factors are assumed to correlate in the Germanic languages. This study uses ultrasound data to investigate global tongue shape and in particular tongue root differences for German monophthongs in stressed position. Preliminary results for one speaker indicate that some vowel pairs are nearly identical in tongue height, but differ in tongue root displacement. Rounded front vowels are more retracted and lower than their unrounded counterparts. The /a: a/ pair, which has been described as contrasting in duration only, exhibits a clear qualitative difference as well. In addition, tagged cine MRI data were collected for a subset of high and mid vowels. This technique allows inferring expansion and contraction of the tongue musculature and thus can inform about differences in muscular tension between tense and lax vowels. [Supported by NIH Grant RO1-DC01758.]

Extracting tongue muscle contraction patterns from tagged cine MRI

This study presents mechanically modeled 3-D volumetric strains for the tongue during speech for the syllable ‘‘sha.’’ Multiplanar tagged cine MRI (tMRI) provided input data for a B-spline, geometry-independent, cardiac tag tracking method, devised for the heart, which has been adapted for the tongue. Three sets of tMRI images with orthogonal tag planes were collected in 10 axial and 5 sagittal slices for 24 consecutive time phases. The sagittal slices were recorded twice, once each with a series of horizontal and vertical tag planes. The axial slices were recorded once with lengthwise (anterior-to-posterior) tag planes. These tag planes reflect deformations in the SI, AP, and RL directions, respectively. Within the tongue we tracked 3-D motion, calculated 3-D strains in each image plane, and reconstructed 3-D deformation for the entire volume. From the model muscle contraction patterns are inferred for genioglossus anterior, verticalis, and transverse. To infer muscle contraction we determined the lines of action for each muscle, and tracked their linear strains in the appropriate planes for all 24 time phases. Results showed that muscle compressions are consistent with expected muscle contractions, and we were able to distinguish between transverse and verticalis activity. [Work supported by NIH/NIDCD Grant No. DC01758.]

Delineation of normal human left ventricular twist throughout systole by tagged cine magnetic resonance imaging.

Myofibril shortening and the oblique fiber orientation of the left ventricular myocardium results in a twisting motion of the left ventricle. Advances in cardiac magnetic resonance imaging (MRI) have made it possible to label the myocardium noninvasively and track this motion (twist) through the cardiac cycle, but little data exist on its complete systolic time course. The purpose of this study was to delineate the normal human systolic time course of ventricular twist using tagged cine-MRI. Tagged cine-MRI was performed in 10 healthy subjects. The mean systolic twist angle relative to the short axis centroid for the 10 volunteers was calculated. Interstudy and intra- and interobserver variability were assessed. During isovolumic contraction, all ventricular twist was counterclockwise. Later in systole, the basal segments changed direction and rotated in a clockwise direction, whereas the apical segments continued counterclockwise rotation. The midpoint for rotation was 45+/-8% of ventricular length. The mean short axis net ventricular twist (apex-base) at 80% systole was 12.6+/-1.5 degrees. The four wall segments showed heterogeneity in twist (lateral wall, 20.6+/-1.7 degrees; anterior wall, 17.5+/-5.1 degrees; inferior wall, 8.8+/-4.9 degrees; septum, 3.5+/-2.4 degrees). The anterior and lateral walls demonstrated significantly higher twist than the other walls (p < 0.01). Torsion increased steadily throughout systole after isovolumic contraction, whereas twist displayed rate changes. The mean interstudy and intra- and interobserver differences were less than 2.1 degrees. The close similarity in twist between subjects and the low interstudy and inter/intraobserver variation indicates that twist is a robust parameter of myocardial function. Torsion varies smoothly during systole, which may play a role in minimizing oxygen consumption. These data can serve as a baseline from which to compare alterations in regional myocardial function in disease.

Two kinematic models of the human tongue from MRI data

Two models of tongue motion were developed and applied to tagged cine MRI data of the human tongue during movement from the consonants /k/ and /s/ to the vowels /i/, /a/, and /u/, in three sagittal slices (L, M, R). The first model, a global kinematic model, utilized surface edges of the tongue perimeter observed within the images. The model focused on decomposing tongue surface movements into the following mechanical deformations: rigid-body motions (translation and rotation) and homogeneous stretch and shear. The global model indicated that coarticulatory effects occurred in both vowels and consonants. Deformation was greatest from /k/ to /a/, and was composed primarily of horizontal expansion, vertical compression, and vertical lowering. Asymmetries were observed in the deformation patterns. The second model, a local kinematic model based on the motion of approximately 40 tag intersection points within the tongue, utilized the same low-order polynomial basis functions that are applied in finite-element analysis, within a finite number of small discreet regions. Specifically, the local model quantified the principal strains within discrete regions inside the tongue during consonant–vowel deformations. The local model was able to illuminate detail of local muscle activity within an individual syllable.

Cardiac tagging with breath-hold cine MRI.

A method is presented for measuring myocardial deformation in a breath-hold with tagged cine MRI. Tagged cine images of human hearts are obtained in arbitrary oblique planes on a standard imager with as few as four heartbeats. The scan time has been reduced 16- to 64-fold from previous techniques.