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1.  IDENTIFICATION OF MYOCARDIAL INFARCTION USING THREE-DIMENSIONAL STRAIN TENSOR FRACTIONAL ANISOTROPY 
Accurate localization of myocardial viability is important in diagnosis of infarction. Regional strain function provides excessive information for clinical decision making but comparison of strain tensor profiles across differing tissue types is usually difficult due to multivariate nature of tensors. It is desirable to describe tensors with simplified scalar indices which are more mathematically and statistically intuitive. In this work, anisotropy of tensors in healthy and experimental infarct regions in a large animal model is assessed and compared to directional components of strain tensors which are currently the most popular indices in active use. Myocardial strain tensors are computed using zHARP, a magnetic resonance (MR) tagging technique that provides quantification of cardiac function with direct computation of three-dimensional tensors from two-dimensional short axis MR images. Fractional anisotropy of strain tensors shows high correlation with late gadolinium enhanced images and is capable of discrimination between healthy and infarcted regions.
doi:10.1109/ISBI.2010.5490309
PMCID: PMC3892898  PMID: 24443666
Strain tensor; HARP; zHARP; Fractional Anisotropy; Infarction
2.  Regional Coronary Endothelial Function is Closely Related to Local Early Coronary Atherosclerosis in Patients with Mild Coronary Artery Disease: A Pilot Study 
Background
Coronary endothelial function (endoFx) is abnormal in patients with established coronary artery disease (CAD) and was recently shown by MRI to relate to the severity of luminal stenosis. Recent advances in MRI now allow the non-invasive assessment of both anatomic and functional (endoFx) changes that previously required invasive studies. We tested the hypothesis that abnormal coronary endoFx is related to measures of early atherosclerosis such as increased coronary wall thickness (CWT).
Methods and Results
Seventeen arteries in fourteen healthy adults and seventeen arteries in fourteen patients with non-obstructive CAD were studied. To measure endoFx, coronary MRI was performed before and during isometric handgrip exercise, an endothelial-dependent stressor and changes in coronary cross-sectional area (CSA) and flow were measured. Black blood imaging was performed to quantify CWT and other indices of arterial remodeling. The mean stress-induced change in CSA was significantly higher in healthy adults (13.5%±12.8%, mean±SD, n=17) than in those with mildly diseased arteries (-2.2±6.8%, p<0.0001, n=17). Mean CWT was lower in healthy subjects (0.9±0.2mm) than in CAD patients (1.4±0.3mm, p<0.0001). In contrast to healthy subjects, stress-induced changes in CSA, a measure of coronary endoFx, correlated inversely with CWT in CAD patients (r= -0.73, p=0.0008).
Conclusions
There is an inverse relationship between coronary endothelial function and local CWT in CAD patients but not in healthy adults. These findings demonstrate that local endothelial-dependent functional changes are related to the extent of early anatomic atherosclerosis in mildly diseased arteries. This combined MRI approach enables the anatomic and functional investigation of early coronary disease.
doi:10.1161/CIRCIMAGING.111.969691
PMCID: PMC3665274  PMID: 22492483
coronary disease; endothelium; magnetic resonance imaging
3.  Three-dimensional regional strain analysis in porcine myocardial infarction: a 3T magnetic resonance tagging study 
Background
Previous studies of mechanical strain anomalies in myocardial infarction (MI) have been largely limited to analysis of one-dimensional (1D) and two-dimensional (2D) strain parameters. Advances in cardiovascular magnetic resonance (CMR) methods now permit a complete three-dimensional (3D) interrogation of myocardial regional strain. The aim of this study was to investigate the incremental value of CMR-based 3D strain and to test the hypothesis that 3D strain is superior to 1D or 2D strain analysis in the assessment of viability using a porcine model of infarction.
Methods
Infarction was induced surgically in 20 farm pigs. Cine, late gadolinium enhancement, and CMR tagging images were acquired at 11 days before (baseline), and 11 days (early) and 1 month (late) after induction of infarct. Harmonic phase analysis was performed to measure circumferential, longitudinal, and radial strains in myocardial segments, which were defined based on the transmurality of delayed enhancement. Univariate, bivariate, and multivariate logistic regression models of strain parameters were created and analyzed to compare the overall diagnostic accuracy of 3D strain analysis with 1D and 2D analyses in identifying the infarct and its adjacent regions from healthy myocardium.
Results
3D strain differed significantly in infarct, adjacent, and remote segments (p < 0.05) at early and late post-MI. In univariate, bivariate, and multivariate analyses, circumferential, longitudinal, and radial strains were significant factors (p < 0.001) in differentiation of infarct and adjacent segments from baseline values. In identification of adjacent segments, receiver operating characteristic analysis using the 3D strain multivariate model demonstrated a significant improvement (p < 0.01) in overall diagnostic accuracy in comparison with 2D (circumferential and radial) and 1D (circumferential) models (3D: 96%, 2D: 81%, and 1D: 71%). A similar trend was observed in identification of infarct segments.
Conclusions
Cumulative 3D strain information accurately identifies infarcts and their neighboring regions from healthy myocardium. The 3D interrogation of myocardial contractility provides incremental diagnostic accuracy in delineating the dysfunctional and nonviable myocardium in comparison with 1D or 2D quantification of strain. The infarct neighboring regions are the major beneficiaries of the 3D assessment of regional strain.
doi:10.1186/1532-429X-14-85
PMCID: PMC3534020  PMID: 23237210
Magnetic resonance tagging; Harmonic phase analysis; Three-dimensional regional strain; Myocardial infarction; Diagnostic accuracy
4.  Total Removal of Unwanted Harmonic Peaks (TruHARP) MRI for Single Breath-Hold High-Resolution Myocardial Motion and Strain Quantification 
Current MRI methods for myocardial motion and strain quantification have limited resolution because of Fourier space spectral peak interference. Methods have been proposed to remove this interference in order to improve resolution; however, these methods are clinically impractical due to the prolonged imaging times. In this paper, we propose total removal of unwanted harmonic peaks (TruHARP); a myocardial motion and strain quantification methodology that uses a novel single breath-hold MR image acquisition protocol. In post-processing, TruHARP separates the spectral peaks in the acquired images, enabling high-resolution motion and strain quantification. The impact of high resolution on calculated circumferential and radial strains is studied using realistic Monte Carlo simulations, and the improvement in strain maps is demonstrated in six human subjects.
doi:10.1002/mrm.22403
PMCID: PMC3417065  PMID: 20665800
MRI; HARP; tagging; cardiac motion; strain quantification
5.  Practical Signal-to-Noise Ratio Quantification for Sensitivity Encoding: Application to Coronary MRA 
Purpose
To develop and evaluate a practical method for the quantification of signal-to-noise ratio (SNR) on coronary magnetic resonance angiograms (MRA) acquired with parallel imaging.
Materials and Methods
To quantify the spatially varying noise due to parallel imaging reconstruction, a new method has been implemented incorporating image data acquisition followed by a fast noise scan during which radiofrequency pulses, cardiac triggering and navigator gating are disabled. The performance of this method was evaluated in a phantom study where SNR measurements were compared to those of a reference standard (multiple repetitions). Subsequently, SNR of myocardium and posterior skeletal muscle was determined on in vivo human coronary MRA.
Results
In a phantom, the SNR measured using the proposed method deviated less than 10.1% from the reference method for small geometry factors (<=2). In-vivo, the noise scan for a 10 minutes coronary MRA acquisition was acquired in 30s. Higher signal and lower SNR, due to spatially varying noise, were found in myocardium compared to posterior skeletal muscle.
Conclusion
SNR quantification based on a fast noise scan is a validated and easy-to-use method when applied to 3D coronary MRA obtained with parallel imaging as long as the geometry factor remains low.
doi:10.1002/jmri.22571
PMCID: PMC3098458  PMID: 21591001
SNR measurement; parallel imaging; coronary MRA; phased array coils; image noise
6.  Assessment of distribution and evolution of Mechanical dyssynchrony in a porcine model of myocardial infarction by cardiovascular magnetic resonance 
Background
We sought to investigate the relationship between infarct and dyssynchrony post- myocardial infarct (MI), in a porcine model. Mechanical dyssynchrony post-MI is associated with left ventricular (LV) remodeling and increased mortality.
Methods
Cine, gadolinium-contrast, and tagged cardiovascular magnetic resonance (CMR) were performed pre-MI, 9 ± 2 days (early post-MI), and 33 ± 10 days (late post-MI) post-MI in 6 pigs to characterize cardiac morphology, location and extent of MI, and regional mechanics. LV mechanics were assessed by circumferential strain (eC). Electro-anatomic mapping (EAM) was performed within 24 hrs of CMR and prior to sacrifice.
Results
Mean infarct size was 21 ± 4% of LV volume with evidence of post-MI remodeling. Global eC significantly decreased post MI (-27 ± 1.6% vs. -18 ± 2.5% (early) and -17 ± 2.7% (late), p < 0.0001) with no significant change in peri-MI and MI segments between early and late time-points. Time to peak strain (TTP) was significantly longer in MI, compared to normal and peri-MI segments, both early (440 ± 40 ms vs. 329 ± 40 ms and 332 ± 36 ms, respectively; p = 0.0002) and late post-MI (442 ± 63 ms vs. 321 ± 40 ms and 355 ± 61 ms, respectively; p = 0.012). The standard deviation of TTP in 16 segments (SD16) significantly increased post-MI: 28 ± 7 ms to 50 ± 10 ms (early, p = 0.012) to 54 ± 19 ms (late, p = 0.004), with no change between early and late post-MI time-points (p = 0.56). TTP was not related to reduction of segmental contractility. EAM revealed late electrical activation and greatly diminished conduction velocity in the infarct (5.7 ± 2.4 cm/s), when compared to peri-infarct (18.7 ± 10.3 cm/s) and remote myocardium (39 ± 20.5 cm/s).
Conclusions
Mechanical dyssynchrony occurs early after MI and is the result of delayed electrical and mechanical activation in the infarct.
doi:10.1186/1532-429X-14-1
PMCID: PMC3268109  PMID: 22226320
7.  TRUHARP: SINGLE BREATH-HOLD MRI FOR HIGH RESOLUTION CARDIAC MOTION AND STRAIN QUANTIFICATION 
MRI techniques for tissue motion and strain quantifications have limited resolution because of interference from the conjugate echo or spectral peak in Fourier space. Methods have been proposed to remove this interference in order to improve resolution; however, these methods are clinically impractical due to long image acquisition time. In this paper, we propose TruHARP, an MRI motion and strain quantification methodology that involves a novel single breath-hold imaging protocol. In post-processing, TruHARP separates the spectral peaks in the acquired datasets, enabling high resolution motion and strain quantification. The impact of high resolution on circumferential and radial strain is studied using a realistic simulation and the improvement in strain maps is demonstrated in an in-vivo human study.
doi:10.1109/ISBI.2009.5193083
PMCID: PMC2886723  PMID: 20559463
MRI; HARP; tagging; motion and strain estimation
8.  FUZZY C-MEANS WITH VARIABLE COMPACTNESS 
Fuzzy c-means (FCM) clustering has been extensively studied and widely applied in the tissue classification of biomedical images. Previous enhancements to FCM have accounted for intensity shading, membership smoothness, and variable cluster sizes. In this paper, we introduce a new parameter called “compactness” which captures additional information of the underlying clusters. We then propose a new classification algorithm, FCM with variable compactness (FCMVC), to classify three major tissues in brain MRIs by incorporating the compactness terms into a previously reported improvement to FCM. Experiments on both simulated phantoms and real magnetic resonance brain images show that the new method improves the repeatability of the tissue classification for the same subject with different acquisition protocols.
doi:10.1109/ISBI.2008.4541030
PMCID: PMC2814437  PMID: 20126427
Biomedical image processing; fuzzy sets; image segmentation; magnetic resonance imaging

Results 1-8 (8)