T. Stan Gregory

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.

Magnetohydrodynamic-Driven Design of Microscopic Endocapsules in MRI

Microscopic medical robots capable of translating in a bloodstream or similar liquid represent a new type of therapeutic technology for surgical interventions. This study aims to characterize a new MRI compliant method of propulsion for swimming robots using the magnetohydrodynamic effect (MHD). An MHD drive is a method of propulsion employing only electromagnetic elements, without the need for moving mechanical parts. By utilizing MHD voltages induced within the MRI magnetic field, the opportunity to propel a device and provide imaging simultaneously is presented. We hypothesized that a wireless MHD-driven thruster could be developed to control endocapsules within the MRI magnetic field. A model capsule was constructed and evaluated in a scaled MRI-environment, and subsequently, tested for MRI-compatibility at 3 T. Dynamic performance of the endocapsule was characterized as input power was varied. In the scaled MRI environment, a peak force of 0.31 mN was observed, providing evidence that an MHD-driven endocapsule is possible in an MRI environment. Increased forces will be obtainable with increases in magnetic field strength and applied power.

Continuous Rapid Quantification of Stroke Volume Using Magnetohydrodynamic Voltages in 3T Magnetic Resonance Imaging

Background—To develop a technique to noninvasively estimate stroke volume in real time during magnetic resonance imaging (MRI)–guided procedures, based on induced magnetohydrodynamic voltages (VMHD) that occur in ECG recordings during MRI exams, leaving the MRI scanner free to perform other imaging tasks. Because of the relationship between blood flow (BF) and VMHD, we hypothesized that a method to obtain stroke volume could be derived from extracted VMHD vectors in the vectorcardiogram (VCG) frame of reference (VMHDVCG). Methods and Results—To estimate a subject-specific BF–VMHD model, VMHDVCG was acquired during a 20-s breath-hold and calibrated versus aortic BF measured using phase-contrast magnetic resonance in 10 subjects (n=10) and 1 subject diagnosed with premature ventricular contractions. Beat-to-beat validation of VMHDVCG-derived BF was performed using real-time phase-contrast imaging in 7 healthy subjects (n=7) during 15-minute cardiac exercise stress tests and 30 minutes after stress relaxation in 3T MRIs. Subject-specific equations were derived to correlate VMHDVCG with BF at rest and validated using real-time phase-contrast. An average error of 7.22% and 3.69% in stroke volume estimation, respectively, was found during peak stress and after complete relaxation. Measured beat-to-beat BF time history derived from real-time phase-contrast and VMHD was highly correlated using a Spearman rank correlation coefficient during stress tests (0.89) and after stress relaxation (0.86). Conclusions—Accurate beat-to-beat stroke volume and BF were estimated using VMHDVCG extracted from intra-MRI 12-lead ECGs, providing a means to enhance patient monitoring during MR imaging and MR-guided interventions.

Magnetic resonance conditional paramagnetic choke for suppression of imaging artifacts during magnetic resonance imaging

Higher risk patient populations require continuous physiological monitoring and, in some cases, connected life-support systems, during magnetic resonance imaging examinations. While recently there has been a shift toward wireless technology, some of the magnetic resonance imaging devices are still connected to the outside using cabling that could interfere with the magnetic resonance imaging’s radio frequency during scanning, resulting in excessive heating. We developed a passive method for radio frequency suppression on cabling that may assist in making some of these devices magnetic resonance imaging compatible. A barrel-shaped strongly paramagnetic choke was developed to suppress induced radio frequency signals which are overlaid onto physiological monitoring leads during magnetic resonance imaging. It utilized a choke placed along the signal lines, with a gadolinium solution core. The choke’s magnetic susceptibility was modeled, for a given geometric design, at increasing chelate concentration levels, and measured using a vibrating sample magnetometer. Radio frequency noise suppression versus frequency was quantified with network-analyzer measurements and tested using cabling placed in the magnetic resonance imaging scanner. Temperature-elevation and image-quality reduction due to the device were measured using American Society for Testing and Materials phantoms. Prototype chokes with gadolinium solution cores exhibited increasing magnetic susceptibility, and insertion loss (S21) also showed higher attenuation as gadolinium concentration increased. Image artifacts extending <4 mm from the choke were observed during magnetic resonance imaging, which agreed well with the predicted ∼3 mm artifact from the electrochemical machining simulation. An accompanying temperature increase of <1 °C was observed in the magnetic resonance imaging phantom trial. An effective paramagnetic choke for radio frequency suppression during magnetic resonance imaging was developed and its performance demonstrated.

Magnetohydrodynamic Voltage Recorder for Comparing Peripheral Blood Flow

Blood flow is a clinical metric for monitoring of cardiovascular diseases but current measurements methods are costly or uncomfortable for patients. It was shown that the interaction of the magnetic field (B0) during MRI and blood flow in the body, through the magnetohydrodynamic (MHD) effect, produce voltages (VMHD) observable through intra-MRI electrocardiography (ECG), which are correlated with regional blood flow. This study shows the reproducibility of VMHD outside the MRI and its application in a portable flow monitoring device. To recreate this interaction outside the MRI, a static neodymium magnet (0.4T) was placed in between two electrodes to induce the VMHD in a single lead ECG measurement. VMHD was extracted, and integrated over to obtain a stroke volume metric. A smartphone-enabled device utilizing this interaction was developed in order to create a more accessible method of obtaining blood flow measurements. The portable device displayed a <6% error compared to a commercial recorder, and was able to successfully record VMHD using the 0.4T magnet. Exercise stress testing showed a VMHD increase of 23% in healthy subjects, with an 81% increase in the athlete. The study demonstrates a new device utilizing MHD interactions with body circulation to obtain blood flow metrics.

Defining the Relationship of Magnetohydrodynamic Voltages and Magnetic Field Strength

The magnetohydrodynamic (MHD) effect is observed in flowing electrolytic fluids and their interactions with magnetic fields. The magnetic field (B0), when perpendicular with the electrolytic fluid flow (μ), causes the shift of the charged particles in the fluid to shift across the length of the vessel (L) normal to the plane of B0 and flow, creating a voltage (VMHD) observable through voltage potential measurements across the flow (Eqn. 1)[1].

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

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

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

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