Reza Nezafat

Recurrence of Atrial Fibrillation Correlates With the Extent of Post-Procedural Late Gadolinium Enhancement : A Pilot Study

OBJECTIVES We sought to evaluate radiofrequency (RF) ablation lesions in atrial fibrillation (AF) patients using cardiac magnetic resonance (CMR), and to correlate the ablation patterns with treatment success. BACKGROUND RF ablation procedures for treatment of AF result in localized scar that is detected by late gadolinium enhancement (LGE) CMR. We hypothesized that the extent of scar in the left atrium and pulmonary veins (PV) would correlate with moderate-term procedural success. METHODS Thirty-five patients with AF, undergoing their first RF ablation procedure, were studied. The RF ablation procedure was performed to achieve bidirectional conduction block around each PV ostium. AF recurrence was documented using a 7-day event monitor at multiple intervals during the first year. High spatial resolution 3-dimensional LGE CMR was performed 46 +/- 28 days after RF ablation. The extent of scarring around the ostia of each PV was quantitatively (volume of scar) and qualitatively (1: minimal, 3: extensive and circumferential) assessed. RESULTS Thirteen (37%) patients had recurrent AF during the 6.7 +/- 3.6-month observation period. Paroxysmal AF was a strong predictor of nonrecurrent AF (15% with recurrence vs. 68% without, p = 0.002). Qualitatively, patients without recurrence had more completely circumferentially scarred veins (55% vs. 35% of veins, p = NS). Patients without recurrence more frequently had scar in the inferior portion of the right inferior pulmonary vein (RIPV) (82% vs. 31%, p = 0.025, Bonferroni corrected). The volume of scar in the RIPV was quantitatively greater in patients without AF recurrence (p < or = 0.05) and was a univariate predictor of recurrence using Cox regression (p = 0.049, Bonferroni corrected). CONCLUSIONS Among patients undergoing PV isolation, AF recurrence during the first year is associated with a lesser degree of PV and left atrial scarring on 3-dimensional LGE CMR. This finding was significant for RIPV scar and may have implications for the procedural technique used in PV isolation.

Accuracy, Precision, and Reproducibility of Four T1 Mapping Sequences: A Head-to-Head Comparison of MOLLI, ShMOLLI, SASHA, and SAPPHIRE

PURPOSE To compare accuracy, precision, and reproducibility of four commonly used myocardial T1 mapping sequences: modified Look-Locker inversion recovery (MOLLI), shortened MOLLI (ShMOLLI), saturation recovery single-shot acquisition (SASHA), and saturation pulse prepared heart rate independent inversion recovery (SAPPHIRE). MATERIALS AND METHODS This HIPAA-compliant study was approved by the institutional review board. All subjects provided written informed consent. Accuracy, precision, and reproducibility of the four T1 mapping sequences were first compared in phantom experiments. In vivo analysis was performed in seven healthy subjects (mean age ± standard deviation, 38 years ± 19; four men, three women) who were imaged twice on two separate days. In vivo reproducibility of native T1 mapping and extracellular volume (ECV) were measured. Differences between the sequences were assessed by using Kruskal-Wallis and Wilcoxon rank sum tests (phantom data) and mixed-effect models (in vivo data). RESULTS T1 mapping accuracy in phantoms was lower with ShMOLLI (62 msec) and MOLLI (44 msec) than with SASHA (13 msec; P < .05) and SAPPHIRE (12 msec; P < .05). MOLLI had similar precision to ShMOLLI (4.0 msec vs 5.6 msec; P = .07) but higher precision than SAPPHIRE (6.8 msec; P = .002) and SASHA (8.7 msec; P < .001). All sequences had similar reproducibility in phantoms (P = .1). The four sequences had similar in vivo reproducibility for native T1 mapping (∼25-50 msec; P > .05) and ECV quantification (∼0.01-0.02; P > .05). CONCLUSION SASHA and SAPPHIRE yield higher accuracy, lower precision, and similar reproducibility compared with MOLLI and ShMOLLI for T1 measurement. Different sequences yield different ECV values; however, all sequences have similar reproducibility for ECV quantification.

B1-insensitive T2 preparation for improved coronary magnetic resonance angiography at 3 T

At 3 T, the effective wavelength of the RF field is comparable to the dimension of the human body, resulting in B1 standing wave effects and extra variations in phase. This effect is accompanied by an increase in B0 field inhomogeneity compared to 1.5 T. This combination results in nonuniform magnetization preparation by the composite MLEV weighted T2 preparation (T2 Prep) sequence used for coronary magnetic resonance angiography (MRA). A new adiabatic refocusing T2 Prep sequence is presented in which the magnetization is tipped into the transverse plane with a hard RF pulse and refocused using a pair of adiabatic fast‐passage RF pulses. The isochromats are subsequently returned to the longitudinal axis using a hard RF pulse. Numerical simulations predict an excellent suppression of artifacts originating from B1 inhomogeneity while achieving good contrast enhancement between coronary arteries and surrounding tissue. This was confirmed by an in vivo study, in which coronary MR angiograms were obtained without a T2 Prep, with an MLEV weighted T2 Prep and the proposed adiabatic T2 Prep. Improved quantitative and qualitative coronary MRA image measurement was achieved using the adiabatic T2 Prep at 3 T. Magn Reson Med, 2006. Published 2006 Wiley‐Liss, Inc.

Cardiovascular magnetic resonance characterization of mitral valve prolapse.

OBJECTIVES This study sought to develop cardiovascular magnetic resonance (CMR) diagnostic criteria for mitral valve prolapse (MVP) using echocardiography as the gold standard and to characterize MVP using cine CMR and late gadolinium enhancement (LGE)-CMR. BACKGROUND Mitral valve prolapse is a common valvular heart disease with significant complications. Cardiovascular magnetic resonance is a valuable imaging tool for assessing ventricular function, quantifying regurgitant lesions, and identifying fibrosis, but its potential role in evaluating MVP has not been defined. METHODS To develop CMR diagnostic criteria for MVP, characterize mitral valve morphology, we analyzed transthoracic echocardiography and cine CMR images from 25 MVP patients and 25 control subjects. Leaflet thickness, length, mitral annular diameters, and prolapsed distance were measured. Two- and three-dimensional LGE-CMR images were obtained in 16 MVP and 10 control patients to identify myocardial regions of fibrosis in MVP. RESULTS We found that a 2-mm threshold for leaflet excursion into the left atrium in the left ventricular outflow tract long-axis view yielded 100% sensitivity and 100% specificity for CMR using transthoracic echocardiography as the clinical gold standard. Compared with control subjects, CMR identified MVP patients as having thicker (3.2 +/- 0.1 mm vs. 2.3 +/- 0.1 mm) and longer (10.5 +/- 0.5 mm/m(2) vs. 7.1 +/- 0.3 mm/m(2)) indexed posterior leaflets and larger indexed mitral annular diameters (27.8 +/- 0.7 mm/m(2) vs. 21.5 +/- 0.5 mm/m(2) for long axis and 22.9 +/-0.7 mm/m(2) vs. 17.8 +/- 0.6 mm/m(2) for short axis). In addition, we identified focal regions of LGE in the papillary muscles suggestive of fibrosis in 10 (63%) of 16 MVP patients and in 0 of 10 control subjects. Papillary muscle LGE was associated with the presence of complex ventricular arrhythmias in MVP patients. CONCLUSIONS Cardiovascular magnetic resonance image can identify MVP by the same echocardiographic criteria and can identify myocardial fibrosis involving the papillary muscle in MVP patients. Hyperenhancement of papillary muscles on LGE is often present in a subgroup of patients with complex ventricular arrhythmias.

Resveratrol Improves Myocardial Perfusion in a Swine Model of Hypercholesterolemia and Chronic Myocardial Ischemia

Background— Resveratrol may provide protection against coronary artery disease. We hypothesized that supplemental resveratrol will improve cardiac perfusion in the ischemic territory of swine with hypercholesterolemia and chronic myocardial ischemia. Methods and Results— Yorkshire swine were fed either a normal diet (control, n=7), a hypercholesterolemic diet (HCC, n=7), or a hypercholesterolemic diet with supplemental resveratrol (100 mg/kg/d orally, HCRV, n=7). Four weeks later, an ameroid constrictor was placed on the left circumflex artery. Animals underwent cardiac MRI and coronary angiography 7 weeks later before euthanasia and tissue harvest. Total cholesterol was lowered about 30% in HCRV animals (P<0.001). Regional wall motion analysis demonstrated a significant decrease in inferolateral function from baseline to 7 weeks in HCC swine (P=0.04). There was no significant change in regional function in HCRV swine from baseline to 7 weeks (P=0.32). Tissue blood flow during stress was 2.8-fold greater in HCRV swine when compared with HCC swine (P=0.04). Endothelium-dependent microvascular relaxation response to Substance P was diminished in HCC swine, which was rescued by resveratrol treatment (P=0.004). Capillary density (PECAM-1 staining) demonstrated fewer capillaries in both HCC and HCRV swine versus control swine (P=0.02). Immunoblot analysis demonstrated significantly greater expression in HCRV versus HCC swine of the following markers of angiogenesis: VEGF (P=0.002), peNOS (ser1177) (P=0.04), NFkB (P=0.004), and pAkt (thr308) (P=0.001). Conclusions— Supplemental resveratrol attenuates regional wall motion abnormalities, improves myocardial perfusion in the collateral dependent region, preserves endothelium-dependent coronary vessel function, and upregulates markers of angiogenesis associated with the VEGF signaling pathway.

Combined saturation/inversion recovery sequences for improved evaluation of scar and diffuse fibrosis in patients with arrhythmia or heart rate variability.

To develop arrhythmia‐insensitive inversion recovery sequences for improved visualization of myocardial scar and quantification of diffuse fibrosis.

Low-dimensional-structure self-learning and thresholding: regularization beyond compressed sensing for MRI reconstruction.

An improved image reconstruction method from undersampled k‐space data, low‐dimensional‐structure self‐learning and thresholding (LOST), which utilizes the structure from the underlying image is presented. A low‐resolution image from the fully sampled k‐space center is reconstructed to learn image patches of similar anatomical characteristics. These patches are arranged into “similarity clusters,” which are subsequently processed for dealiasing and artifact removal, using underlying low‐dimensional properties. The efficacy of the proposed method in scan time reduction was assessed in a pilot coronary MRI study. Initially, in a retrospective study on 10 healthy adult subjects, we evaluated retrospective undersampling and reconstruction using LOST, wavelet‐based l1‐norm minimization, and total variation compressed sensing. Quantitative measures of vessel sharpness and mean square error, and qualitative image scores were used to compare reconstruction for rates of 2, 3, and 4. Subsequently, in a prospective study, coronary MRI data were acquired using these rates, and LOST‐reconstructed images were compared with an accelerated data acquisition using uniform undersampling and sensitivity encoding reconstruction. Subjective image quality and sharpness data indicate that LOST outperforms the alternative techniques for all rates. The prospective LOST yields images with superior quality compared with sensitivity encoding or l1‐minimization compressed sensing. The proposed LOST technique greatly improves image reconstruction for accelerated coronary MRI acquisitions. Magn Reson Med, 2011.

Wavelet-Domain Medical Image Denoising Using Bivariate Laplacian Mixture Model

In this paper, we proposed novel noise reduction algorithms that can be used to enhance image quality in various medical imaging modalities such as magnetic resonance and multidetector computed tomography. The noisy captured 3-D data are first transformed by discrete complex wavelet transform. Using a nonlinear function, we model the data as the sum of the clean data plus additive Gaussian or Rayleigh noise. We use a mixture of bivariate Laplacian probability density functions for the clean data in the transformed domain. The MAP and minimum mean-squared error (MMSE) estimators allow us to efficiently reduce the noise. The employed prior distribution is mixture and bivariate, and thus accurately characterizes the heavy-tail distribution of clean images and exploits the interscale properties of wavelets coefficients. In addition, we estimate the parameters of the model using local information; as a result, the proposed denoising algorithms are spatially adaptive, i.e., the intrascale dependency of wavelets is also well exploited in the enhancement process. The proposed approach results in significant noise reduction while the introduced distortions are not noticeable as a result of accurate statistical modeling. The obtained shrinkage functions have closed form, are simple in implementation, and efficiently enhances data. Our experiments on CT images show that among our derived shrinkage functions usually BiLapGausMAP produces images with higher peak SNR. However, BiLapGausMMSE is preferred especially for CT images, which have high SNRs. Furthermore, BiLapRayMAP yields better noise reduction performance for low SNR MR datasets such as high-resolution whole heart imaging while BiLapGauMAP results in better performance in MR data with higher intrinsic SNR such as functional cine data.

Coronary magnetic resonance vein imaging: Imaging contrast, sequence, and timing

Recently, there has been increased interest in imaging the coronary vein anatomy to guide interventional cardiovascular procedures such as cardiac resynchronization therapy (CRT), a device therapy for congestive heart failure (CHF). With CRT the lateral wall of the left ventricle is electrically paced using a transvenous coronary sinus lead or surgically placed epicardial lead. Proper transvenous lead placement is facilitated by the knowledge of the coronary vein anatomy. Cardiovascular MR (CMR) has the potential to image the coronary veins. In this study we propose and test CMR techniques and protocols for imaging the coronary venous anatomy. Three aspects of design of imaging sequence were studied: magnetization preparation schemes (T2 preparation and magnetization transfer), imaging sequences (gradient‐echo (GRE) and steady‐state free precession (SSFP)), and imaging time during the cardiac cycle. Numerical and in vivo studies both in healthy and CHF subjects were performed to optimize and demonstrate the utility of CMR for coronary vein imaging. Magnetization transfer was superior to T2 preparation for contrast enhancement. Both GRE and SSFP were viable imaging sequences, although GRE provided more robust results with better contrast. Imaging during the end‐systolic quiescent period was preferable as it coincided with the maximum size of the coronary veins. Magn Reson Med, 2007.

Clinical recommendations for cardiovascular magnetic resonance mapping of T1, T2, T2* and extracellular volume: A consensus statement by the Society for Cardiovascular Magnetic Resonance (SCMR) endorsed by the European Association for Cardiovascular Imaging (EACVI)

Parametric mapping techniques provide a non-invasive tool for quantifying tissue alterations in myocardial disease in those eligible for cardiovascular magnetic resonance (CMR). Parametric mapping with CMR now permits the routine spatial visualization and quantification of changes in myocardial composition based on changes in T1, T2, and T2*(star) relaxation times and extracellular volume (ECV). These changes include specific disease pathways related to mainly intracellular disturbances of the cardiomyocyte (e.g., iron overload, or glycosphingolipid accumulation in Anderson-Fabry disease); extracellular disturbances in the myocardial interstitium (e.g., myocardial fibrosis or cardiac amyloidosis from accumulation of collagen or amyloid proteins, respectively); or both (myocardial edema with increased intracellular and/or extracellular water). Parametric mapping promises improvements in patient care through advances in quantitative diagnostics, inter- and intra-patient comparability, and relatedly improvements in treatment. There is a multitude of technical approaches and potential applications. This document provides a summary of the existing evidence for the clinical value of parametric mapping in the heart as of mid 2017, and gives recommendations for practical use in different clinical scenarios for scientists, clinicians, and CMR manufacturers.