Tagged Magnetic Resonance Imaging Research Articles

89-05: Validation of NOGA-derived assessment of left ventricular function against MRI

Purpose: Measurements of left ventricular (LV) systolic function, in particular strain, are gaining popularity as predictor of CRT effectiveness. Also, spatially accurate strain mapping, may help guiding intramyocardial biological therapy delivery and assessment. We recently developed a method for the simultaneous assessment of the LV electrical and mechanical activity. We sought to compare volume and strain measurements derived from electromechanical anatomical mapping (EMAM) with the gold standard technique, MRI. Methods: In 22 patients, EMAM maps (NOGA XP, BDS) and MRI images (3.0 T Magnetom Skyra, Siemens) were obtained within 1 month. MRI images were analyzed to obtain end-systolic (ESV), end-diastolic volumes (EDV) and ejection fractions (EF) from cine images and circumferential strain (CS) from MRI tagging images. EMAM was analyzed using custom software: volumes were calculated as the volume enclosed by the convex surface fitting the catheter tip positions, while CS was derived from the motion field of the catheter tip at the different locations. Regional peak CS values were averaged over points belonging to the same cardiac sector (6 sectors for the basal, mid and apical levels). Inter-technique agreement was tested through correlation and Bland-Altman analysis. Conclusion: This is the first study demonstrating the feasibility of assessing ventricular systolic function based on EMAM, and validating it against the current reference technique. The proposed approach allows the combined assessment of the electrical and mechanical activities without the need of error-prone separate strain and electrical imaging. EMAM-based strain analysis may be extended to the entire cardiac cycle, overcoming the limitations associated with the fading MRI tags.

Assessment of left ventricular mechanical dyssynchrony in left bundle branch block canine model: Comparison between cine and tagged MRI.

To compare cine and tagged magnetic resonance imaging (MRI) for left ventricular dyssynchrony assessment in left bundle branch block (LBBB), using the time-to-peak contraction timing, and a novel approach based on cross-correlation. We evaluated a canine model dataset (n = 10) before (pre-LBBB) and after induction of isolated LBBB (post-LBBB). Multislice short-axis tagged and cine MRI images were acquired using a 1.5 T scanner. We computed contraction time maps by cross-correlation, based on the timing of radial wall motion and of circumferential strain. Finally, we estimated dyssynchrony as the standard deviation of the contraction time over the different regions of the myocardium. Induction of LBBB resulted in a significant increase in dyssynchrony (cine: 13.0 ± 3.9 msec for pre-LBBB, and 26.4 ± 5.0 msec for post-LBBB, P = 0.005; tagged: 17.1 ± 5.0 msec at for pre-LBBB, and 27.9 ± 9.8 msec for post-LBBB, P = 0.007). Dyssynchrony assessed by cine and tagged MRI were in agreement (r = 0.73, P = 0.0003); differences were in the order of time difference between successive frames of 20 msec (bias: -2.9 msec; limit of agreement: 10.1 msec). Contraction time maps were derived; agreement was found in the contraction patterns derived from cine and tagged MRI (mean difference in contraction time per segment: 3.6 ± 13.7 msec). This study shows that the proposed method is able to quantify dyssynchrony after induced LBBB in an animal model. Cine-assessed dyssynchrony agreed with tagged-derived dyssynchrony, in terms of magnitude and spatial direction. J. MAGN. RESON. IMAGING 2016;44:956-963.

Diagnosing Cardiac Deformations using 3d Optical Flow

This paper explores the viability of applying 3D optical flow techniques on 3D heart sequences to diagnose cardiac abnormalities and disease. Tagged magnetic resonance imaging (TMRI) is a non-invasive method to visualize in vivo myocardium motion during a cardiac cycle. By tracking the 3D trajectories of tagged material points it is possible to construct a volumetric model of the heart. Specifically, we use generated meshless deformable models (MDM) which describe an object as a point cloud inside the object boundary. We extend the 2D least squares and regularization approaches of Lucas and Kanade to 3D in order capture the flow, specifically the contraction and expansion of various parts of the heart motion. Features are extracted from this flow and a rudimentary SVM is used to classify unhealthy hearts.

3D harmonic phase tracking with anatomical regularization.

This paper presents a novel algorithm that extends HARP to handle 3D tagged MRI images. HARP results were regularized by an original regularization framework defined in an anatomical space of coordinates. In the meantime, myocardium incompressibility was integrated in order to correct the radial strain which is reported to be more challenging to recover. Both the tracking and regularization of LV displacements were done on a volumetric mesh to be computationally efficient. Also, a window-weighted regression method was extended to cardiac motion tracking which helps maintain a low complexity even at finer scales. On healthy volunteers, the tracking accuracy was found to be as accurate as the best candidates of a recent benchmark. Strain accuracy was evaluated on synthetic data, showing low bias and strain errors under 5% (excluding outliers) for longitudinal and circumferential strains, while the second and third quartiles of the radial strain errors are in the (-5%,5%) range. In clinical data, strain dispersion was shown to correlate with the extent of transmural fibrosis. Also, reduced deformation values were found inside infarcted segments.

Analytic signal phase-based myocardial motion estimation in tagged MRI sequences by a bilinear model and motion compensation.

Different mathematical tools, such as multidimensional analytic signals, allow for the calculation of 2D spatial phases of real-value images. The motion estimation method proposed in this paper is based on two spatial phases of the 2D analytic signal applied to cardiac sequences. By combining the information of these phases issued from analytic signals of two successive frames, we propose an analytical estimator for 2D local displacements. To improve the accuracy of the motion estimation, a local bilinear deformation model is used within an iterative estimation scheme. The main advantages of our method are: (1) The phase-based method allows the displacement to be estimated with subpixel accuracy and is robust to image intensity variation in time; (2) Preliminary filtering is not required due to the bilinear model. The proposed algorithm, integrating phase-based optical flow motion estimation and the combination of global motion compensation with local bilinear transform, allows spatio-temporal cardiac motion analysis, e.g. strain and dense trajectory estimation over the cardiac cycle. Results from 7 realistic simulated tagged magnetic resonance imaging (MRI) sequences show that our method is more accurate compared with state-of-the-art method for cardiac motion analysis and with another differential approach from the literature. The motion estimation errors (end point error) of the proposed method are reduced by about 33% compared with that of the two methods. In our work, the frame-to-frame displacements are further accumulated in time, to allow for the calculation of myocardial Lagrangian cardiac strains and point trajectories. Indeed, from the estimated trajectories in time on 11 in vivo data sets (9 patients and 2 healthy volunteers), the shape of myocardial point trajectories belonging to pathological regions are clearly reduced in magnitude compared with the ones from normal regions. Myocardial point trajectories, estimated from our phase-based analytic signal approach, seem therefore a good indicator of the local cardiac dynamics. Moreover, they are shown to be coherent with the estimated deformation of the myocardium.

Abstracts fromThe 33rd AnnualNational Neurotrauma SymposiumJune 28–July 1, 2015Santa Fe, New Mexico

Abstracts fromThe 33^rd AnnualNational Neurotrauma SymposiumJune 28–July 1, 2015Santa Fe, New Mexico

TH-CD-204-09: Physiological Modeling of Lung Motion Based On Hyperpolarized Gas Tagging MRI

Purpose: To model the respiratory motion of lung based on the physiological ground truth measured with hyperpolarized (HP) gas tagging magnetic resonance imaging (MRI). Methods: A novel 4D model was established to investigate the respiratory motion of lung based on the 3D HP gas tagging MRI (t-MRI) and 3D proton MRI (p-MRI). Images were acquired on one healthy volunteer in breath-hold at the inhalation and the exhalation phases, respectively. We obtained the displacement vector field (DVF) of each tagged grid (t-DVF) in the t-MRI images by directly measuring the spatial difference of the centroid of the grid, which therefore represented the physiological ground truth. The DVF of each voxel (p-DVF) in the p-MRI images were generated with deformable image registration. Regional ventilation, a metric used to evaluate of lung function, was calculated using the Jacobian determinant of DVF.The respiratory motion of lung was estimated by optimizing the p-DVF to minimize the differences between p-DVF and t-DVF, while preserving the ground truth of ventilation. The optimization was performed by considering the correction of t-DVF as a perturbation to the existing p-DVF. In order to evaluate the resultant model, the motion and the ventilation were compared to those of t-MRI and p-MRI, respectively. Results: Our 4D model represents a more realistic lung motion with the average deviation from the ground truth t-DVF reduced from 6.4 mm to 5.2 mm (p<0.05, student t-test) compared to the p-DVF. Furthermore, the accuracy of regional ventilation was also improved with larger cross correlation (0.98 v.s. 0.37) and mutual information values (5.84 v.s. 0.45). Conclusion: We have successfully created a novel 4D motion model of lung based on the physiological ground truth measured from HP gas tagging MRI. With this model, an accurate prediction of lung motion and deformation during respiration in 4D becomes possible.

WE-AB-BRA-11: Development of Physiological-Based Virtual Thorax Phantoms for Evaluation of Deformable Image Registration

Purpose: To develop a methodology of constructing physiological-based virtual thorax phantom based on hyperpolarized (HP) gas tagging MRI for evaluating deformable image registration (DIR). Methods: Three healthy subjects were imaged at both the end-of-inhalation (EOI) and the end-of-exhalation (EOE) phases using a high-resolution (2.5mm isovoxel) 3D proton MRI, as well as a hybrid MRI which combines HP gas tagging MRI and a low-resolution (4.5mm isovoxel) proton MRI. A sparse tagging displacement vector field (tDVF) was derived from the HP gas tagging MRI by tracking the displacement of tagging grids between EOI and EOE. Using the tDVF and the high-resolution MR images, we determined the motion model of the entire thorax in the following two steps: 1) the DVF inside of lungs was estimated based on the sparse tDVF using a novel multi-step natural neighbor interpolation method; 2) the DVF outside of lungs was estimated from the DIR between the EOI and EOE images (Velocity AI). The derived motion model was then applied to the high-resolution EOI image to create a deformed EOE image, forming the virtual phantom where the motion model provides the ground truth of deformation. Five DIR methods were evaluated using the developed virtual phantom. Errors in DVF magnitude (Em) and angle (Ea) were determined and compared for each DIR method. Results: Among the five DIR methods, free form deformation produced DVF results that are most closely resembling the ground truth (Em=1.04mm, Ea=6.63°). The two DIR methods based on B-spline produced comparable results (Em=2.04mm, Ea=13.66°; and Em =2.62mm, Ea=17.67°), and the two optical-flow methods produced least accurate results (Em=7.8mm; Ea=53.04°; Em=4.45mm, Ea=31.02°). Conclusion: A methodology for constructing physiological-based virtual thorax phantom based on HP gas tagging MRI has been developed. Initial evaluation demonstrated its potential as an effective tool for robust evaluation of DIR in the lung.

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.

Regional assessment of LV wall in infarcted heart using tagged MRI and cardiac modelling

A segmental two-parameter empirical deformable model is proposed for evaluating regional motion abnormality of the left ventricle. Short-axis tagged MRI scans were acquired from 10 healthy subjects and 10 postinfarct patients. Two motion parameters, contraction and rotation, were quantified for each cardiac segment by fitting the proposed model using a non-rigid registration algorithm. The accuracy in motion estimation was compared to a global model approach. Motion parameters extracted from patients were correlated to infarct transmurality assessed with delayed-contrast-enhanced MRI. The proposed segmental model allows markedly improved accuracy in regional motion analysis as compared to the global model for both subject groups (1.22–1.40 mm versus 2.31–2.55 mm error). By end-systole, all healthy segments experienced radial displacement by ~25–35% of the epicardial radius, whereas the 3 short-axis planes rotated differently (basal: 3.3°; mid: −1° and apical: −4.6°) to create a twisting motion. While systolic contraction showed clear correspondence to infarct transmurality, rotation was nonspecific to either infarct location or transmurality but could indicate the presence of functional abnormality. Regional contraction and rotation derived using this model could potentially aid in the assessment of severity of regional dysfunction of infarcted myocardium.

Relating Speech Production to Tongue Muscle Compressions Using Tagged and High-resolution Magnetic Resonance Imaging.

The human tongue is composed of multiple internal muscles that work collaboratively during the production of speech. Assessment of muscle mechanics can help understand the creation of tongue motion, interpret clinical observations, and predict surgical outcomes. Although various methods have been proposed for computing the tongue's motion, associating motion with muscle activity in an interdigitated fiber framework has not been studied. In this work, we aim to develop a method that reveals different tongue muscles' activities in different time phases during speech. We use four-dimensional tagged magnetic resonance (MR) images and static high-resolution MR images to obtain tongue motion and muscle anatomy, respectively. Then we compute strain tensors and local tissue compression along the muscle fiber directions in order to reveal their shortening pattern. This process relies on the support from multiple image analysis methods, including super-resolution volume reconstruction from MR image slices, segmentation of internal muscles, tracking the incompressible motion of tissue points using tagged images, propagation of muscle fiber directions over time, and calculation of strain in the line of action, etc. We evaluated the method on a control subject and two post-glossectomy patients in a controlled speech task. The normal subject's tongue muscle activity shows high correspondence with the production of speech in different time instants, while both patients' muscle activities show different patterns from the control due to their resected tongues. This method shows potential for relating overall tongue motion to particular muscle activity, which may provide novel information for future clinical and scientific studies.

Cerebral perfusion differences in women currently with and recovered from anorexia nervosa

Anorexia nervosa is a serious psychiatric disorder characterized by restricted eating, a pursuit of thinness, and altered perceptions of body shape and size. Neuroimaging in anorexia nervosa has revealed morphological and functional alterations in the brain. A better understanding of physiological changes in anorexia nervosa could provide a brain-specific health marker relevant to treatment and outcomes. In this study, we applied several advanced magnetic resonance imaging (MRI) techniques to quantify regional and global cerebral blood flow (CBF) in 25 healthy women (HC), 23 patients currently with anorexia (AN-C) and 19 patients in long-term weight recovery following anorexia (AN-WR). Specifically, CBF was measured with pseudo-continuous arterial spin labeling (pCASL) MRI and then verified by a different technique, phase contrast (PC) MRI. Venous T2 values were determined by T2 relaxation under spin tagging (TRUST) MRI, and were used to corroborate the CBF results. These novel techniques were implemented on a standard 3T MRI scanner without any exogenous tracers, and the total scan duration was less than 10min. Voxel-wise comparison revealed that the AN-WR group showed lower CBF in bilateral temporal and frontal lobes than the AN-C group. Compared with the HC group, the AN-C group also showed higher CBF in the right temporal lobe. Whole-brain-averaged CBF was significantly decreased in the AN-WR group compared with the AN-C group, consistent with the PC-MRI results. Venous T2 values were lower in the AN-WR group than in the AN-C group, consistent with the CBF results. A review of prior work examining CBF in anorexia nervosa is included in the discussion. This study identifies several differences in the cerebral physiological alterations in anorexia nervosa, and finds specific differences relevant to the current state of the disorder.

The effect of free-breathing on left ventricular rotational mechanics in normal subjects and patients with duchenne muscular dystrophy

Reyhan et al. Journal of Cardiovascular Magnetic Resonance 2015, 17(Suppl 1):Q22 http://www.jcmr-online.com/content/17/S1/Q22 WALKING POSTER PRESENTATION Open Access The effect of free-breathing on left ventricular rotational mechanics in normal subjects and patients with duchenne muscular dystrophy Meral Reyhan 2,3 , Zhe Wang 2,1* , Hyun J Kim 2 , Nancy Halnon 4 , Paul J Finn 2 , Daniel B Ennis 2,1 From 18th Annual SCMR Scientific Sessions Nice, France. 4-7 February 2015 Background Patients with Duchenne Muscular Dystrophy (DMD) develop respiratory impairment and signs and symptoms of cardiac involvement at an early age. Quantitative mea- sures of cardiac function from MRI tagging can be used to stage disease progression and monitor the response to therapy. Traditional cardiac MRI exams, however, require repeated breath holding, which places a notable burden on patients with DMD and can impart intrathoracic pressure changes that alter cardiac function. The effect of free- breathing on quantitative measure of left ventricular (LV) rotational mechanics for DMD patients is incompletely understood. Objective: To evaluate differences in LV rota- tional mechanics acquired during breath holding (BH), free-breathing with averaging (AVG), and free-breathing with respiratory bellows gating (BEL). Methods 16 healthy volunteers (1 female, 27.8±3.9 years) and 5 DMD patients (all male, 11.3±3.7 years) were scanned on a 3.0T Siemens Scanner with BH, AVG and BEL. ORI-SPAMM (Reyhan. M et. al. JMRI 2014;39(2):339- 345) was used to acquire short-axis images at the base and apex of the heart. 280-330x280-330mm field-of- view, 6mm slice thickness, 192x192 acquisition matrix, 395 Hz/pixel receiver bandwidth, TE/TR =2.33-2.39/ 4.71-4.83 ms, 8 phase encode lines per segment, 12° imaging flip angle, 8 mm tag spacing, GRAPPA 2. LV Figure 1 Mean LV twist of (A) healthy volunteers and (B) patients with DMD for breath-held (BH, solid), free-breathing with averaging (AVG, dashed), and bellows gated (BEL, dash-dotted) methods. BH LV twist is generally higher compared to AVG or BEL, especially at its peak. Radiological Sciences, University of California Los Angeles, Los Angeles, CA, USA © 2015 Reyhan et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Quantitative left ventricular rotational mechanics in Duchenne and Becker muscular dystrophy patients

Wang et al. Journal of Cardiovascular Magnetic Resonance 2015, 17(Suppl 1):Q34 http://www.jcmr-online.com/content/17/S1/Q34 WALKING POSTER PRESENTATION Open Access Quantitative left ventricular rotational mechanics in Duchenne and Becker muscular dystrophy patients Zhe Wang 2,1* , Meral Reyhan 2,3 , Nancy Halnon 4 , Sarah N Khan 2 , Paul J Finn 2 , Pierangelo Renella 5 , Daniel B Ennis 2,1 From 18th Annual SCMR Scientific Sessions Nice, France. 4-7 February 2015 Background Duchenne/Becker muscular dystrophy (D/BMD) is asso- ciated with early onset cardiomyopathy, with cardiac fibro- sis amongst the earliest manifestations. Changes in conventional estimates of cardiac function (e.g. ejection fraction, EF) may occur late in Duchenne and Becker mus- cular dystrophy (DMD/BMD). Cardiac MRI tagging is a noninvasive imaging biomarker for quantifying ventricular dysfunction in DMD/BMD cardiomyopathy. In particular, estimates of ventricular rotational mechanics (e.g. peak twist or normalized untwisting rate) may provide insight to early ventricular dysfunction. Furthermore, myocardial fibrosis in DMD/BMD patients is frequently reported and could significantly impact LV rotational mechanics. How- ever, the functional consequences of myocardial fibrosis in these patients are incompletely understood. The objective of this study was to quantify LV rotational mechanics in pediatric DMD/BMD patients with normal EF (N-EF) or low EF (L-EF) and with (f+) or without (f-) fibrosis. Methods Seventeen (N=17) male pediatric subjects (13.7±4.5 years old) genetically diagnosed with DMD/BMD consented to participate in an IRB approved study. Each patient under- went a cardiac 3T MRI exam that included evaluation of functional status with cine MRI, cardiac tagging MRI, and ventricular scar evaluation. Ten (M=10) non-aged- matched (29±4.3 years old) healthy volunteers were also evaluated to provide context for interpreting the pediatric data. LV mass, LVESV, LVEDV, and LVEF were calcu- lated. The normal EF cut-off was >55.9% for 8-15 year- olds (Danielle et. al. JMRI 2009, 29: :552-559) and >53.2% for 16-20 year-olds (Sarikouch et. al. Circulation 2010 Jan;3(1):65-76). The presence or absence of myocardial fibrosis was determined by consensus agreement. Compar- isons were made using t-tests with Holm-Sidak correction. Results The volunteers had LV peak twist (LV-PT) of 12.2 ± 2.6° and lower LV normalized untwist rate (LV-NUR) -12.5 ± 2.1° s -1 . The table shows lower LV-PT and LV-NUR in the EF-n/f- group compared to controls. LV-PT and LV-NUR significantly decreased in the N-EF/f+ group. LV-PT and LV-NUR were further decreased in the L-EF/f+ and were lowest in the L-EF/f+ group. T-tests with Holm-Sidak cor- rection showed significant difference between L-EF/f- and L-EF/f+ in LV-PT. No significant difference was detected for LV-NUR. Conclusions LV-PT and LV-NUR are lower in patients with DMD/ BMD despite normal EF, compared to the healthy volun- teers. Both low EF and the presence of fibrosis are asso- ciated further decreased LV-PT and LV-NUR. Fibrosis alone has a significant effect on LV rotational mechanics and should be further evaluated. Table 1 Normal (EF-N) Fibrosis (-) LV-PT: 9.3± 2.2° Abnormal (EF-L) N=6 LV-NUR: -11.1± 3.2° s-1 Fibrosis (+) LV-PT: 7.8± 2.2° LV-NUR: -9.1± 2.2° s-1 LV-PT: 8.7± 1.4° N=2 LV-NUR: -10.5± 1.2° s-1 N=6 LV-PT: 5.3 ±0.5° N=3 LV-NUR: -8.3± 0.5° s-1 Radiological Sciences, University of California Los Angeles, Los Angeles, CA, USA Full list of author information is available at the end of the article © 2015 Wang et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Real-space imaging of macroscopic diffusion and slow flow by singlet tagging MRI

Magnetic resonance imaging can be used to study motional processes such as flow and diffusion, but the accessible timescales are limited by longitudinal relaxation. The spatially selective conversion from magnetization to long-lived singlet order in designer molecules makes it possible to tag a region of interest for an extended period of time, of the order of several minutes. Here we exploit this concept of “singlet tagging” to monitor diffusion over a macroscopic scale as well as very slow flow.

The development and initial evaluation of a realistic simulated SPECT dataset with simultaneous respiratory and cardiac motion for gated myocardial perfusion SPECT

We developed a realistic simulation dataset for simultaneous respiratory and cardiac (R&C) gated SPECT/CT using the 4D NURBS-based Cardiac-Torso (NCAT) Phantom and Monte Carlo simulation methods, and evaluated it for a sample application study. The 4D NCAT phantom included realistic respiratory motion and beating heart motion based on respiratory gated CT and cardiac tagged MRI data of normal human subjects. To model the respiratory motion, a set of 24 separate 3D NCAT phantoms excluding the heart was generated over a respiratory cycle. The beating heart motion was modeled separately with 48 frames per cardiac cycle for each of the 24 respiratory phases. The resultant set of 24 × 48 3D NCAT phantoms provides a realistic model of a normal human subject at different phases of combined R&C motions. An almost noise-free SPECT projection dataset for each of the 1152 3D NCAT phantoms was generated using Monte Carlo simulation techniques and the radioactivity uptake distribution of 99mTc sestamibi in different organs. By grouping and summing the separate projection datasets, separate or simultaneous R&C gated acquired data with different gating schemes could be simulated. In the initial evaluation, we combined the projection datasets into ungated, 6 respiratory-gates only, 8 cardiac-gates only, and combined 6 respiratory-gates & 8 cardiac-gates projection datasets. Each dataset was reconstructed using 3D OS-EM without and with attenuation correction using the averaged and respiratory-gated attenuation maps, and the resulting reconstructed images were compared. These results were used to demonstrate the effects of R&C motions and the reduction of image artifact due to R&C motions by gating and attenuation corrections. We concluded that the realistic 4D NCAT phantom and Monte Carlo simulated SPECT projection datasets with R&C motions are powerful tools in the study of the effects of R&C motions, as well as in the development of R&C gating schemes and motion correction methods for improved SPECT/CT imaging.

Assessment of the Left Ventricle Wall Motion Using Tagged Magnetic Resonance Imaging Data (tMRI)

In this paper, the Radial Strain (RS) and Strain Rate (SR) was calculated using tagged MRI (tMRI) data. Using tagged magnetic resonance imaging (tMRI), the left ventricle short axis of five healthy adults (three men and two women) and four healthy male rats was imaged during diastolic and systolic phases on the mid-ventricle level. The RS and radial SR of the left ventricle were calculated at the mid-ventricular level of the cardiac cycle. The peak RS for rat and human heart was found to be 46.8 ± 0.68 and 40.7 ± 1.44, respectively, and it occurred at 40% of the cardiac cycle for both human and rat hearts. The peak systolic and diastolic radial SR for human heart was 1.10 ± 0.08 s- 1 and - 1.78 ± 0.02 s- 1, respectively, while it was 4.25 ± 0.02 s- 1 and - 5.16 ± 0.23 s- 1, respectively for rat heart. The results show that tMRI data can be used to characterize the cardiac function during systolic and diastolic phases of the cardiac cycle, and as a result, it can be used to evaluate the cardiac motion by calculating its RS and radial SR at different locations of the cardiac wall during both diastolic and systolic phases. This study also approves the validity of the tagged MRI data to accurately describe the radial cardiac motion.

An Ultrasound-Driven Kinematic Model for Deformation of the Infarcted Mouse Left Ventricle Incorporating a Near-Incompressibility Constraint

Mathematical models of varying complexity have proved useful in fitting and interpreting regional cardiac displacements obtained from imaging methods such as ultrasound speckle tracking or MRI tagging. Simpler models, such as the classic thick-walled cylinder model of the left ventricle (LV), can be solved quickly and are easy to implement, but they ignore regional geometric variations and are difficult to adapt to the study of regional pathologies like myocardial infarctions. Complex, anatomically accurate finite-element models work well, but are computationally intensive and require specialized expertise to implement. We developed a kinematic model that offers a compromise between these two traditional approaches, assuming only that displacements in the left ventricle are polynomial functions of initial position and that the myocardium is nearly incompressible, while allowing myocardial motion to vary spatially as would be expected in an ischemic or dyssynchronous LV. Model parameters were determined using an objective function with adjustable weights to account for confidence in individual displacement components and desired strength of the incompressibility constraint. The model accurately represented the motion of both normal and infarcted mouse LVs during the cardiac cycle, with normalized root mean square errors in predicted deformed positions of 8.2 ± 2.3% and 7.4 ± 2.1% for normal and infarcted hearts, respectively.

A motion tracking method that applies a spread spectrum communication technique to tagging MR imaging.

We propose a new motion tracking method that encodes an object's position information using tagging magnetic resonance (MR) images as digital codes, and we assess the method's feasibility in stationary and moving phantoms. The encoding and decoding of tag patterns employ principles of spread spectrum communication. We used a segmented fast low angle shot cine sequence (FLASH) with spatial modulation of magnetization (SPAMM) preparation pulses to encode position information as 7-bit code words and used this spread code to decode the position information. To make 7-bit code words using tag images, we adjusted the flip angle and phase of the 4 composite radiofrequency (RF) pulses and the gradient magnetic field strength in the SPAMM pulse to generate 7 types of tag patterns. The proposed method required 7 acquisitions with 7 types of tag patterns. We compared results with images obtained by conventional tagging in stationary and moving phantom experiments. In a stationary phantom, the proposed method showed the same ability to identify pixel position as conventional tagging method using improved SNR images with the average of 7 acquisitions. In a moving phantom, pixel position was successfully decoded by the proposed method on a pixel-by-pixel basis. In this method, the motion of the phantom was detected by the simple calculation of the correlation coefficient of the code words. We introduced a spread spectrum communication technique to tagging MR imaging that regards tag patterns as digital codes, and we demonstrated the method's potential to detect pixel position in sub-pixel resolution.

60 * Greater mechanical dyssynchrony is demonstrated by cardiac magnetic resonance cine imaging amongst heart failure patients awaiting cardiac resynchronisation therapy with strict left bundle branch block

Introduction: The era of cardiac resynchronisation therapy (CRT) has led to improved understanding of left ventricular activation and stricter criteria have been proposed for left bundle branch block (LBBB). These criteria have shown a greater prediction for LV mechanical dyssynchrony with 2D strain echocardiography and cardiac MRI tagging. We have further tested this hypothesis using cardiac cine MRI endocardial tracking technology and also investigated the impact of this measure of mechanical dyssynchrony on CRT response rate. Methods: We investigated a total of 47 patients awaiting CRT with traditional LBBB with a cardiac MRI pre implant. Offline analysis of the cine imaging was undertaken in order to determine the endocardial volume change systolic dyssynchrony index (SDI) of 16 segments. Pre-implant ECGs were analyzed for strict LBBB (QRS ≥ 140ms for men, ≥130ms for women and mid QRS notching/slurring in ≥2 contiguous leads). Reverse remodeling was assessed at 6 months with echocardiography. Response was defined as ≥15% improvement in LV end systolic volume. Results: These patients were aged 66.1±11.7 years, 83% were male, and 45% had an ischaemic etiology. On ECG analysis 83% had strict LBBB. In the strict LBBB group the SDI was 12.3±5.2% where as in the traditional LBBB group it was 6.7±2.5% (p=0.005). Presence of an ischaemic aetiology had no impact on SDI (p=0.216). Linear regression of SDI vs. amount of remodeling (change in LVESV) generates a regression coefficient of 2.02 (p=0.01) and a correlation coefficient of R=0.49 (p=0.01). ROC analysis determines the optimum SDI cut-off for response as 10% with an area under the curve of 0.797, a sensitivity of 81% and a specificity of 79%. Conclusion: In patients with LBBB selected for CRT under current guidance the presence of strict LBBB predicts increased mechanical dyssynchrony demonstrated as SDI with cine MRI. Presence of mechanical dyssynchrony defined as an SDI ≥10% is a good predictor of volumetric response to CRT in this cohort. ![Graphic][1] [1]: /embed/inline-graphic-1.gif