Publications

2018
Choi S, Han SI, Jung D, Hwang HJ, Lim C, Bae S, Park OK, Tschabrunn CM, Lee M, Bae SY, Yu JW, Ryu JH, Lee S-W, Park K, Kang PM, Lee WB, Nezafat R, Hyeon T, Kim D-H. Highly conductive, stretchable and biocompatible Ag-Au core-sheath nanowire composite for wearable and implantable bioelectronics [Internet]. Nature Nanotechnology 2018; Publisher's VersionAbstract
Wearable and implantable devices require conductive, stretchable and biocompatible materials. However, obtaining composites that simultaneously fulfil these requirements is challenging due to a trade-off between conductivity and stretchability. Here, we report on Ag–Au nanocomposites composed of ultralong gold-coated silver nanowires in an elastomeric block-copolymer matrix. Owing to the high aspect ratio and percolation network of the Ag–Au nanowires, the nanocomposites exhibit an optimized conductivity of 41,850 S cm−1 (maximum of 72,600 S cm−1). Phase separation in the Ag–Au nanocomposite during the solvent-drying process generates a microstructure that yields an optimized stretchability of 266% (maximum of 840%). The thick gold sheath deposited on the silver nanowire surface prevents oxidation and silver ion leaching, making the composite biocompatible and highly conductive. Using the nanocomposite, we successfully fabricate wearable and implantable soft bioelectronic devices that can be conformally integrated with human skin and swine heart for continuous electrophysiological recording, and electrical and thermal stimulation.
Fahmy AS, Rausch J, Neisius U, Chan RH, Maron MS, Appelbaum E, Menze B, Nezafat R. Automated Cardiac MR Scar Quantification in Hypertrophic Cardiomyopathy Using Deep Convolutional Neural Networks. JACC: Cardiovascular Imaging 2018; [PDF]
Wang C, Jang J, Neisius U, Nezafat M, Fahmy A, Kang J, Rodriguez J, Goddu B, Pierce P, Berg S, Zhang J, Wang X, Nezafat R. Black blood myocardial T mapping. Magn Reson Med 2018;Abstract
PURPOSE: To develop a black blood heart-rate adaptive T -prepared balanced steady-state free-precession (BEATS) sequence for myocardial T mapping. METHODS: In BEATS, blood suppression is achieved by using a combination of preexcitation and double inversion recovery pulses. The timing and flip angles of the preexcitation pulse are auto-calculated in each patient based on heart rate. Numerical simulations, phantom studies, and in vivo studies were conducted to evaluate the performance of BEATS. BEATS T maps were acquired in 36 patients referred for clinical cardiac MRI and in 1 swine with recent myocardial infarction. Two readers assessed all images acquired in patients to identify the presence of artifacts associated with slow blood flow. RESULTS: Phantom experiments showed that the BEATS sequence provided accurate T values over a wide range of simulated heart rates. Black blood myocardial T maps were successfully obtained in all subjects. No significant difference was found between the average T measurements obtained from the BEATS and conventional bright-blood T ; however, there was a decrease in precision using the BEATS sequence. A suppression of the blood pool resulted in sharper definition of the blood-myocardium border and reduced partial voluming effect. The subjective assessment showed that 16% (18 out of 108) of short-axis slices have residual blood artifacts (12 in the apical slice, 4 in the midventricular slice, and 2 in the basal slice). CONCLUSION: The BEATS sequence yields dark blood myocardial T maps with better definition of the blood-myocardium border. Further studies are warranted to evaluate diagnostic accuracy of black blood T mapping.
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Nakamori S, Nezafat M, Ngo LH, Manning WJ, Nezafat R. Left Atrial Epicardial Fat Volume Is Associated With Atrial Fibrillation: A Prospective Cardiovascular Magnetic Resonance 3D Dixon Study. J Am Heart Assoc 2018;7(6)Abstract
BACKGROUND: Recent studies demonstrated a strong association between atrial fibrillation (AF) and epicardial fat around the left atrium (LA). We sought to assess whether epicardial fat volume around the LA is associated with AF, and to determine the additive value of LA-epicardial fat measurements to LA structural remodeling for identifying patients with AF using 3-dimensional multi-echo Dixon fat-water separated cardiovascular magnetic resonance. METHODS AND RESULTS: A total of 105 subjects were studied: 53 patients with a history of AF and 52 age-matched patients with other cardiovascular diseases but no history of AF. The 3-dimensional multi-echo Dixon fat-water separated sequence was performed for LA-epicardial fat measurements. AF patients had significantly greater LA-epicardial fat (28.9±12.3 and 14.2±7.3 mL for AF and non-AF, respectively; <0.001) and LA volume (110.8±38.2 and 89.7±30.3 mL for AF and non-AF, respectively; =0.002). LA-epicardial fat adjusted for LA volume was still higher in patients with AF compared with those without AF (<0.001). LA-epicardial fat and hypertension were independently associated with the risk of AF (odds ratio, 1.17; 95% confidence interval, 1.10%-1.25%, <0.001, and odds ratio, 3.29; 95% confidence interval, 1.17%-9.27%, =0.03, respectively). In multivariable logistic regression analysis adjusted for body surface area, LA-epicardial fat remained significant and an increase per mL was associated with a 42% increase in the odds of AF presence (odds ratio, 1.42; 95% confidence interval, 1.23%-1.62%, <0.001). Combined assessment of LA-epicardial fat and LA volume provided greater discriminatory performance for detecting AF than LA volume alone (c-statistic=0.88 and 0.74, respectively, DeLong test; <0.001). CONCLUSIONS: Cardiovascular magnetic resonance 3-dimensional Dixon-based LA-epicardial fat volume is significantly increased in AF patients. LA-epicardial fat measured by 3-dimensional Dixon provides greater performance for detecting AF beyond LA structural remodeling.
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Hosny A, Keating SJ, Dilley JD, Ripley B, Kelil T, Pieper S, Kolb D, Bader C, Pobloth A-M, Griffin M, Nezafat R, Duda G, Chiocca EA, Stone JR, Michaelson JS, Dean MN, Oxman N, Weaver JC. From Improved Diagnostics to Presurgical Planning: High-Resolution Functionally Graded Multimaterial 3D Printing of Biomedical Tomographic Data Sets [Internet]. 3D Printing and Additive Manufacturing 2018;5(2) Publisher's VersionAbstract
Three-dimensional (3D) printing technologies are increasingly used to convert medical imaging studies into tangible (physical) models of individual patient anatomy, allowing physicians, scientists, and patients an unprecedented level of interaction with medical data. To date, virtually all 3D-printable medical data sets are created using traditional image thresholding, subsequent isosurface extraction, and the generation of .stl surface mesh file formats. These existing methods, however, are highly prone to segmentation artifacts that either over or underexaggerate the features of interest, thus resulting in anatomically inaccurate 3D prints. In addition, they often omit finer detailed structures and require time- and labor-intensive processes to visually verify their accuracy. To circumvent these problems, we present a bitmap-based multimaterial 3D printing workflow for the rapid and highly accurate generation of physical models directly from volumetric data stacks. This workflow employs a thresholding-free approach that bypasses both isosurface creation and traditional mesh slicing algorithms, hence significantly improving speed and accuracy of model creation. In addition, using preprocessed binary bitmap slices as input to multimaterial 3D printers allows for the physical rendering of functional gradients native to volumetric data sets, such as stiffness and opacity, opening the door for the production of biomechanically accurate models.
Fahmy AS, Neisius U, Tsao C, Berg S, Goddu E, Pierce P, Basha T, Ngo L, Manning WJ, Nezafat R. Gray blood late gadolinium enhancement cardiovascular magnetic resonance for improved detection of myocardial scar. J Cardiovasc Magn Reson 2018;Abstract

Background

Low scar-to-blood contrast in late gadolinium enhanced (LGE) MRI limits the visualization of scars adjacent to the blood pool. Nulling the blood signal improves scar detection but results in lack of contrast between myocardium and blood, which makes clinical evaluation of LGE images more difficult.

Methods

GB-LGE contrast is achieved through partial suppression of the blood signal using T2magnetization preparation between the inversion pulse and acquisition. The timing parameters of GB-LGE sequence are determined by optimizing a cost-function representing the desired tissue contrast. The proposed 3D GB-LGE sequence was evaluated using phantoms, human subjects (n = 45) and a swine model of myocardial infarction (n = 5). Two independent readers subjectively evaluated the image quality and ability to identify and localize scarring in GB-LGE compared to black-blood LGE (BB-LGE) (i.e., with complete blood nulling) and conventional (bright-blood) LGE.

Results

GB-LGE contrast was successfully generated in phantoms and all in-vivo scans. The scar-to-blood contrast was improved in GB-LGE compared to conventional LGE in humans (1.1 ± 0.5 vs. 0.6 ± 0.4, P < 0.001) and in animals (1.5 ± 0.2 vs. -0.03 ± 0.2). In patients, GB-LGE detected more tissue scarring compared to BB-LGE and conventional LGE. The subjective scores of the GB-LGE ability for localizing LV scar and detecting papillary scar were improved as compared with both BB-LGE (P < 0.024) and conventional LGE (P < 0.001). In the swine infarction model, GB-LGE scores for the ability to localize LV scar scores were consistently higher than those of both BB-LGE and conventional-LGE.

Conclusion

GB-LGE imaging improves the ability to identify and localize myocardial scarring compared to both BB-LGE and conventional LGE. Further studies are warranted to histologically validate GB-LGE.

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Whitaker J, Tschabrunn CM, Jang J, Eran L, O'Neill M, Manning WJ, Anter E, Reza N. Cardiac MR Characterization of left ventricular remodeling in a swine model of infarct followed by reperfusion. J Magn Reson Imaging 2018;Abstract

BACKGROUND:

Myocardial infarction (MI) survivors are at risk of complications including heart failure and malignant arrhythmias.

PURPOSE:

We undertook serial imaging of swine following MI with the aim of characterizing the longitudinal left ventricular (LV) remodeling in a translational model of ischemia-reperfusion-mediated MI.

ANIMAL MODEL:

Eight Yorkshire swine underwent mid left anterior descending coronary artery balloon occlusion to create an ischemia-reperfusion experimental model of MI.

FIELD STRENGTH/SEQUENCES:

1.5T Philips Achieva scanner. Serial cardiac MRI was performed at 16, 33, and 62 days post-MI, including cine imaging, native and postcontrast T1 , T2 and dark-blood late gadolinium enhanced (DB-LGE) scar imaging.

ASSESSMENT:

Regions of interest were selected on the parametric maps to assess native T1 and T2 in the infarct and in remote tissue. Volume of enhanced tissue, nonenhanced tissue, and gray zone were assessed from DB-LGE imaging. Volumes, cardiac function, and strain were calculated from cine imaging.

STATISTICAL TESTS:

Parameters estimated at more than two timepoints were compared with a one-way repeated measures analysis of variance. Parametric mapping data were analyzed using a generalized linear mixed model corrected for multiple observations. A result was considered statistically significant at P < 0.05.

RESULTS:

All animals developed anteroseptal akinesia and hyperenhancement on DB-LGE with a central core of nonenhancing tissue. Mean hyperenhancement volume did not change during the observation period, while the central core contracted from 2.2 ± 1.8 ml at 16 days to 0.08 ± 0.19 ml at 62 days (P = 0.008). Native T1 of ischemic myocardium increased from 1173 ± 93 msec at 16 days to 1309 ± 97 msec at 62 days (P < 0.001). Mean radial and circumferential strain rate magnitude in remote myocardium increased with time from the infarct (P < 0.05).

DATE CONCLUSION:

In this swine model of MI, serial quantitative cardiac MR exams allow characterization of LV remodeling and scar formation.

LEVEL OF EVIDENCE:

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.

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El-Rewaidy H, Nezafat M, Jang J, Nakamori S, Fahmy A, Nezafat R. Nonrigid Active Shape Model-Based Registration Framework for Motion Correction of Cardiac T1 Mapping. Magn Reson Med 2018;Abstract

ASM Reg T1

PURPOSE: Accurate reconstruction of myocardial T1 maps from a series of T1-weighted images consists of cardiac motions induced from breathing and diaphragmatic drifts. We propose and evaluate a new framework based on active shape models to correct for motion in myocardial T1 maps.
METHODS: Multiple appearance models were built at different inversion time intervals to model the blood-myocardium contrast and brightness changes during the longitudinal relaxation. Myocardial inner and outer borders were automatically segmented using the built models, and the extracted contours were used to register the T1-weighted images. Data acquired from 210 patients using a free-breathing acquisition protocol were used to train and evaluate the proposed framework. Two independent readers evaluated the quality of the T1 maps before and after correction using a four-point score. The mean absolute distance and Dice index were used to validate the registration process.
RESULTS: The testing data set from 180 patients at 5 short axial slices showed a significant decrease of mean absolute distance (from 3.3 ± 1.6 to 2.3 ± 0.8 mm, P < 0.001) and increase of Dice (from 0.89 ± 0.08 to 0.94 ± 0.4%, P < 0.001) before and after correction, respectively. The T1 map quality improved in 70 ± 0.3% of the motion-affected maps after correction. Motion-corrupted segments of the myocardium reduced from 21.8 to 8.5% (P < 0.001) after correction.
CONCLUSION: The proposed method for nonrigid registration of T1-weighted images allows T1 measurements in more myocardial segments by reducing motion-induced T1 estimation errors in myocardial segments. Magn Reson Med, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

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2017
El-Rewaidy H, Nakamori S, Addae G, Manning W, Nezafat R. Active shape models based motion correction for myocardial T1 Mapping. Proceedings of the 25th Annual Meeting of ISMRM Hawaii USA 2017;
Fahmy AS, Basha TA, Nezafat R. Analytically-derived parameter scouting for dark-blood Late Gadolinium Enhancement (DB-LGE) imaging. Proceedings of the 25th Annual Meeting of ISMRM  Hawaii USA 2017;
Nakamori S, Alakbarli J, Addae G, Jang J, Berg S, Kissinger KV, Goddu B, Manning WJ, Nezafat R. Changes in myocardial native T1 and T2 after physical exercise: A feasibility study. 20th Annual Scientific Sessions Society for Cardiovascular Magnetic Resonance Washington DC USA 2017;
Whitaker J, Tschabrunn C, Jang J, Leshem E, O’Neill M, Kissinger KV, Manning WJ, Anter E, Nezafat R. Characterization of left ventricular injury and remodelling using serial CMR scans in a swine model of myocardial infarction with ventricular arrhythmia. 20th Annual Scientific Sessions Society for Cardiovascular Magnetic Resonance Washington DC USA 2017;
Kang J, Jang J, Tarokh V, Nezafat R. Dictionary-based reconstruction for free-breathing myocardial T1 mapping. 25th Annual Meeting of ISMRM Hawaii USA 2017;
Rausch J, Menze BH, Chang R, Jang J, Applebaum E, Nezafat R. Fully automated left ventricle scar quantification with deep learning. Proceedings of the 25th Annual Meeting of ISMRM Hawaii USA 2017;
Whitaker J, Tschabrunn C, Anter E, Manning WJ, Nezafat R. Identification of right ventricular infarction using dark-blood late gadolinium enhanced LGE-CMR in a swine ischemia-reperfusion model. 20th Annual Scientific Sessions Society for Cardiovascular Magnetic Resonance Washington DC USA 2017;
Nakamori S, Ismail H, Ngo LH, Buxton AE, Manning WJ, Nezafat R. Impact of left ventricular geometry in predicting ventricular tachyarrhythmia in Patients with Left Ventricular Dysfunction: A Comprehensive Cardiovascular Magnetic Resonance Study . 20th Annual Scientific Sessions Society for Cardiovascular Magnetic Resonance Washington DC USA 2017;
Jang J, Nakamori S, Nezafat R. Improving precision of myocardial T1 mapping with 3-parameter model using tissue characteristic-based denoising. Proceedings of the 25th Annual Meeting of ISMRM Hawaii USA 2017;
Nakamori S, Alakbarli J, Bellm S, Motiwala SR, Addae G, Manning WJ, Nezafat R. Native T1 value in the remote myocardium is independently associated with left ventricular dysfunction in patients with prior myocardial infarction. 20th Annual Scientific Sessions Society for Cardiovascular Magnetic Resonance Washington DC USA 2017;
Jang J, Whitaker J, Tschabrunn CM, Leshem E, Contreras-Valdes FM, Anter E, Nezafat R. Optimal cut-off for unipolar and bipolar voltages to predict scar in LGE-MRI in swine model of ventricular tachycardia with Prior Myocardial Infarction. Heart Rhythm 2017 Chicago Illinois 2017;
Jang J, Contreras-Valdes FM, Tschabrunn CM, Leshem E, Whitaker J, Buxton AE, Nezafat R, Anter E. Substrate mapping of VT using decremental pacing: A novel strategy to identify localized regions susceptible for reentry. Heart Rhythm 2017 Chicago Illinois 2017;

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