Shelley H Zhang

3DQRS: A method to obtain reliable QRS complex detection within high field MRI using 12-lead electrocardiogram traces

To develop a technique that accurately detects the QRS complex in 1.5 Tesla (T), 3T, and 7T MRI scanners.

Gradient-induced voltages on 12-lead ECGs during high duty-cycle MRI sequences and a method for their removal considering linear and concomitant gradient terms.

To restore 12‐lead electrocardiographic (ECG) signal fidelity inside MRI by removing magnetic field gradient‐induced voltages during high gradient duty cycle sequences.

FPGA-based acceleration of MRI registration: an enabling technique for improving MRI-guided cardiac therapy

Background Quantification of edema and scar maps with cardiac MR images (cMRIs) enables effective Radiofrequency Ablation (RFA) of arrhythmias during the Electrophysiology (EP) procedure [1]. This demonstrates the paramount advantage over the EP catheterization under X-ray and ultrasound guidance. High-contrast and resolution cMRIs can be obtained preoperatively as a EP roadmap for surgical planning of RFA, whilst real-time MRI (rtMRI) can be used to guide catheterization and update the cMRI model [2] to provide intraoperative visualization of a 3D vascular map. A fast and efficient technique of non-rigid image co-registration is required. Although feature-based registration methods can be rapidly processed by computing sparse features, the outcome is sensitive to blurred images with artifacts that happens regularly in low-resolution rt-MRI, causing significant errors in feature detections. With the use of Field-programmable Gate Array (FPGA), we hypothesized that novel data structure and architecture of memory access can allow robust registration based on comparison of image intensity patterns, thus fulfilling the real-time requirements for clinical practice.

Left-ventricular mechanical activation and aortic-arch orientation recovered from magneto-hydrodynamic voltages observed in 12-lead ECGs obtained inside MRIs: a feasibility study.

To explore use of the Magnetohydrodynamic Voltage (VMHD), observed in intra-MRI 12-lead electrocardiograms (ECG), to indicate the timing of the onset of left-ventricular mechanical activation (LVMA) and the orientation of the aortic-arch (AAO). Blood flow through the aortic arch during systole, in the presence of the MRI magnetic field (B0), generates VMHD. Since the magnitude and direction of VMHD are determined by the timing and directionality of blood flow relative to B0, we hypothesized that clinically useful measures, LVMA and AAO, could be extracted from temporal and vectorial VMHD characteristics. VMHD signals were extracted from 12-lead ECG traces by comparing traces obtained inside and outside the MRI scanner. VMHD was converted into the Vectorcardiogram frame of reference. LVMA was quantified in 1 subject at 1.5T and 3 subjects at 3T, and the result compared to CINE MRI. AAO was inferred for 4 subjects at 3T and compared to anatomical imaging of the aortic arch orientation in the transverse plane. Axa0<xa010% error was observed in LVMA measurements, while axa0<xa03° error was observed in aortic arch orientation measurements. The temporal and vectorial nature of VMHD is useful in estimating these clinically relevant parameters.

Rapid quantification of stroke volume using magnetohydrodynamic voltages in 3T MRI: a feasibility study

Background The Electrocardiogram (ECG) is a standard clinical tool for cardiac physiological monitoring, required for cardiac synchronization during cardiac MRI, despite signal artifacts resulting from Magnetohydrodynamic voltages (VMHD). VMHD becomes significant during systole when rapidly ejected blood from the left ventricle into the aortic arch interacts with the strong magnetic field (B0 )o f the MRI [1]. Due to this relationship, we hypothesized that blood flow as a function of time in the cardiac cycle and left ventricular Stroke Volume (SV) could be derived using VMHD extracted from intra-MRI ECG. This method would allow for real-time beat-to-beat SV estimation during clinical MR scanning and cardiac MRI stress testing. This non-invasive real-time physiological measure of patient condition can be provided with the described software processing during conventional cardiac MRI routines, and potentially replace Invasive Blood Pressure during complex interventional procedures.

Myocardial perfusion quantification using simultaneously acquired 13NH3-ammonia PET and dynamic contrast-enhanced MRI in patients at rest and stress

Systematic differences with respect to myocardial perfusion quantification exist between DCE‐MRI and PET. Using the potential of integrated PET/MRI, this study was conceived to compare perfusion quantification on the basis of simultaneously acquired 13NH3‐ammonia PET and DCE‐MRI data in patients at rest and stress.

Gradient-induced voltages on 12-lead ECGs during high-duty-cycle MRI sequences and a theoretically-based method to remove them

Background An MRI-compatible 12-lead ECG platform, equipped with MRI-gradient induced-voltage removal hardware and magneto-hydrodynamic voltage removal software [1], was previously applied to physiological monitoring and synchronization of cardiac imaging of patients inside MRI. This approach had limited success for highduty-cycle [(total Gradient-ramp-time per R-R)/(R-R time) >20%] MRI sequences, such as Steady State Free Precession (SSFP), Short-TR Gradient Echo (GRE), and Short-TR Fast Spin Echo. The study objective is to measure and develop a method to remove gradient-induced voltages on 12-lead ECGs during high-duty-cycle MRI sequences.

Computation of the gradient-induced electric field noise in 12-lead ECG traces during rapid MRI sequences

Background Successful physiological monitoring using a 12-lead ECG during MR imaging is essential for safe conduction of cardiovascular interventions within a MR scanner. However, ECG artifacts induced by magnetic field gradients severely affect the signal quality and fidelity. Previously, the gradient-induced artifacts were reduced by blocking ECG transmissions during all gradient ramps [1], which has been shown feasible while the method is not suitable for short-TR sequences. Theoretical and experimental

Comparing 3DQRS and VCG approaches for ECG QRS detection within 1.5T, 3T and 7T MRI

Background Electrocardiograms (ECGs) obtained within High-field MRIs are distorted due to the Magneto-hydrodynamic (MHD) effect. Blood plasma electrolytes ejected into the aorta during early systole interact with the strong magnetic field of the MR scanner to produce a MHD-induced voltage (VMHD) [1]. The VMHD overlay on ECG traces can result in intermittent QRS detection. Vectorcardiogram (VCG) based gating approaches have been conventionally adapted in most MRI scanners [2], but may fail at high field strengths [3]. Recently, a multiple ECG channel cross-correlation based algorithm, 3DQRS, has been developed to provide increased sensitivity levels in these environments [4]. The 3DQRS approach constructs a 3-D ECG representation, where the third dimension, in addition to voltage and time, is deemed a channels axis, formed from concurrent viewing of the precordial leads V1-V6. This study quantitatively compares 3DQRS and VCG approaches at a variety of MRI field strengths to assess the robustness of these methods.

3T cardiac imaging with on-line 12-lead ECG monitoring

Background We previously demonstrated rapid detection of acute ischemia inside MRI using a prototype MRI-conditional 12-lead ECG system [1] equipped with hardware to remove artifacts produced by the MRI gradients. We also synchronized [2] high-field (1.5-7T) scanners using triggers from 12-lead traces following Magneto-HydroDynamic voltage removal. A commercial 12-lead ECG system might allow performing MR imaging studies with a greater risk of ischemic events, as well as the execution of high-risk MRI-guided interventions, such as ventricular tachycardia ablation. Our objective is to validate the performance of an alpha-site version of a commercial MRI-compatible 12-lead ECG system during cardiac imaging at 3T.