Jihye Jang

Innovative interference mitigation approaches: Analytical analysis, implementation and validation

This paper focuses the attention on the problem of Radio Frequency Interference (RFI) mitigation in the framework of GNSS. The paper concentrates on interference mitigation algorithms to be applied within the digital part of a GNSS receiver. The first part of the paper focuses on the mitigation of RFI based on Wavelets. The theoretical fundamentals of the approach are presented, introducing the continuous and the discrete wavelet transformations, and its application to the mitigation of pulsed interferences is demonstrated. The mitigation of strong pulses as well as of low power Distance Measurement Equipment (DME) pulses is discussed and the results obtained for both the cases are presented. In the second part of the paper the mitigation of Continuous Wave Interference (CWI) by means of Notch Filtering is studied, presenting the fundamental steps of this method and presenting its benefits by means of simulation results.

Native myocardial T1 as a biomarker of cardiac structure in non-ischemic cardiomyopathy

Diffuse myocardial fibrosis is involved in the pathology of nonischemic cardiomyopathy (NIC). Recently, the application of native (noncontrast) myocardial T1 measurement has been proposed as a method for characterizing diffuse interstitial fibrosis. To determine the association of native T1 with myocardial structure and function, we prospectively studied 39 patients with NIC (defined as left ventricular ejection fraction (LVEF) ≤ 50% without cardiac magnetic resonance (CMR) evidence of previous infarction) and 27 subjects with normal LVEF without known overt cardiovascular disease. T1, T2, and extracellular volume fraction (ECV) were determined over 16 segments across the base, mid, and apical left ventricular (LV). NIC participants (57 ± 15 years) were predominantly men (74%), with a mean LVEF 34 ± 10%. Subjects with NIC had a greater native T1 (1,131 ± 51 vs 1,069 ± 29 ms; p <0.0001), a greater ECV (0.28 ± 0.04 vs 0.25 ± 0.02, p = 0.002), and a longer myocardial T2 (52 ± 8 vs 47 ± 5 ms; p = 0.02). After multivariate adjustment, a lower global native T1 time in NIC was associated with a greater LVEF (β = -0.59, p = 0.0003), greater right ventricular ejection fraction (β = -0.47, p = 0.006), and smaller left atrial volume index (β = 0.51, p = 0.001). The regional distribution of native myocardial T1 was similar in patients with and without NIC. In NIC, native myocardial T1 is elevated in all myocardial segments, suggesting a global (not regional) abnormality of myocardial tissue composition. In conclusion, native T1 may represent a rapid, noncontrast alternative to ECV for delineating myocardial tissue remodeling in NIC.

Increased myocardial native T1 relaxation time in patients with nonischemic dilated cardiomyopathy with complex ventricular arrhythmia

To study the relationship between diffuse myocardial fibrosis and complex ventricular arrhythmias (ComVA) in patients with nonischemic dilated cardiomyopathy (NICM). We hypothesized that NICM patients with ComVA would have a higher native myocardial T1 time, suggesting more extensive myocardial diffuse fibrosis.

Comparison of spoiled gradient echo and steady-state free-precession imaging for native myocardial T1 mapping using the slice-interleaved T1 mapping (STONE) sequence.

Cardiac T1 mapping allows non‐invasive imaging of interstitial diffuse fibrosis. Myocardial T1 is commonly calculated by voxel‐wise fitting of the images acquired using balanced steady‐state free precession (SSFP) after an inversion pulse. However, SSFP imaging is sensitive to B1 and B0 imperfection, which may result in additional artifacts. A gradient echo (GRE) imaging sequence has been used for myocardial T1 mapping; however, its use has been limited to higher magnetic field to compensate for the lower signal‐to‐noise ratio (SNR) of GRE versus SSFP imaging. A slice‐interleaved T1 mapping (STONE) sequence with SSFP readout (STONE–SSFP) has been recently proposed for native myocardial T1 mapping, which allows longer recovery of magnetization (>8 R–R) after each inversion pulse. In this study, we hypothesize that a longer recovery allows higher SNR and enables native myocardial T1 mapping using STONE with GRE imaging readout (STONE–GRE) at 1.5T. Numerical simulations and phantom and in vivo imaging were performed to compare the performance of STONE–GRE and STONE–SSFP for native myocardial T1 mapping at 1.5T. In numerical simulations, STONE–SSFP shows sensitivity to both T2 and off resonance. Despite the insensitivity of GRE imaging to T2, STONE–GRE remains sensitive to T2 due to the dependence of the inversion pulse performance on T2. In the phantom study, STONE–GRE had inferior accuracy and precision and similar repeatability as compared with STONE–SSFP. In in vivo studies, STONE–GRE and STONE–SSFP had similar myocardial native T1 times, precisions, repeatabilities and subjective T1 map qualities. Despite the lower SNR of the GRE imaging readout compared with SSFP, STONE–GRE provides similar native myocardial T1 measurements, precision, repeatability, and subjective image quality when compared with STONE–SSFP at 1.5T.

Cardiac MR Characterization of left ventricular remodeling in a swine model of infarct followed by reperfusion: LV Remodeling in a Swine Infarct Model

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

Reproducibility of free-breathing multi-slice native myocardial T1 mapping using the slice-interleaved T1 (STONE) sequence

Background Quantitative myocardial T1 mapping is a promising technique for assessment of interstitial diffuse fibrosis. Recently, a novel T1 mapping sequence for free-breathing, multi-slice, myocardial T1 mapping using the sliceinterleaved T1 (STONE) has been developed [1], which was shown to provide superior accuracy compared to MOLLI [2]. However, in-vivo reproducibility and precision of this sequence was not studied. In this study, we sought to investigate the reproducibility and precision of the STONE sequence for in-vivo native myocardial T1 measurement.

Three-dimensional holographic visualization of high-resolution myocardial scar on HoloLens

Visualization of the complex 3D architecture of myocardial scar could improve guidance of radio-frequency ablation in the treatment of ventricular tachycardia (VT). In this study, we sought to develop a framework for 3D holographic visualization of myocardial scar, imaged using late gadolinium enhancement (LGE), on the augmented reality HoloLens. 3D holographic LGE model was built using the high-resolution 3D LGE image. Smooth endo/epicardial surface meshes were generated using Poisson surface reconstruction. For voxel-wise 3D scar model, every scarred voxel was rendered into a cube which carries the actual resolution of the LGE sequence. For surface scar model, scar information was projected on the endocardial surface mesh. Rendered layers were blended with different transparency and color, and visualized on HoloLens. A pilot animal study was performed where 3D holographic visualization of the scar was performed in 5 swines who underwent controlled infarction and electroanatomic mapping to identify VT substrate. 3D holographic visualization enabled assessment of the complex 3D scar architecture with touchless interaction in a sterile environment. Endoscopic view allowed visualization of scar from the ventricular chambers. Upon completion of the animal study, operator and mapping specialist independently completed the perceived usefulness questionnaire in the six-item usefulness scale. Operator and mapping specialist found it useful (usefulness rating: operator, 5.8; mapping specialist, 5.5; 1–7 scale) to have scar information during the intervention. HoloLens 3D LGE provides a true 3D perception of the complex scar architecture with immersive experience to visualize scar in an interactive and interpretable 3D approach, which may facilitate MR-guided VT ablation.

Black blood myocardial T2 mapping

To develop a black blood heart‐rate adaptive T2‐prepared balanced steady‐state free‐precession (BEATS) sequence for myocardial T2 mapping.

Nonrigid active shape model-based registration framework for motion correction of cardiac T1 mapping: ASM-Based Registration for Cardiac T1 Mapping

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.

Papillary muscle native T1 time is associated with severity of functional mitral regurgitation in patients with non-ischemic dilated cardiomyopathy

Methods Forty DCM patients (55 ± 13 years) and 20 healthy adult control subjects (54 ± 13 years) were enrolled. Slice interleaved T1 mapping sequence (STONE) was employed for the native T1 mapping, which enables acquisition of 5 slices in the short-axis plane within a 90 sec free-breathing scan. For calculating papillary muscle native T1 time, both anterior and posterior papillary muscles were manually traced on custom software (MediaCare, Boston, MA, USA). We measured papillary muscle diameter, length and shortening on cine MRI. Phase contrast images were acquired perpendicular to the proximal ascending aorta to quantify blood flow. Mitral regurgitation volume was calculated as the difference between the LV stroke volume and ascending aorta forward flow. DCM patients were allocated into 2 groups based on the presence or absence of functional mitral regurgitation.