Publications by authors named "Bryant T Svedin"
Purpose: Implement simultaneous proton resonance frequency (PRF) shift and T measurements with equivalent temporal resolution using a single reference variable flip angle method. This novel method allows for simultaneous thermometry in both aqueous and fatty tissue.
Methods: This method acquires a single reference image at the lower flip angle and all dynamic images at the higher angle.
Article Synopsis
- The study aims to create a model that links the duration and symmetry of k-space-weighted image contrast (KWIC) windows to the temporal resolution in ultrasound imaging.
- A modulation analysis of temperature measurements was conducted, leading to the comparison of simulated and experimental results using different KWIC window setups.
- Findings reveal that the effectiveness of KWIC reconstructions varies with object size, with shorter window durations improving accuracy but potentially reducing precision; symmetric windows minimize response delays but complicate reconstruction timings.
Purpose: To study the accuracy and precision of T estimates using the Variable Flip Angle (VFA) method in 2D and 3D acquisitions.
Methods: Excitation profiles were simulated using numerical implementation of the Bloch equations for Hamming-windowed sinc excitation pulses with different time-bandwidth products (TBP) of 2, 6, and 10 and for T values of 295 ms and 1045 ms. Experimental data were collected in 5° increments from 5° to 90° for the same T and TBP values.
Purpose: Implement and evaluate a 3D MRI method to measure temperature changes with high spatial and temporal resolution and large field of view.
Methods: A multiecho pseudo-golden angle stack-of-stars (SOS) sequence with k-space weighted image contrast (KWIC) reconstruction was implemented to simultaneously measure multiple quantities, including temperature, initial signal magnitude M(0), transverse relaxation time ( T2*), and water/fat images. Respiration artifacts were corrected using self-navigation.
Purpose: To develop a method for rapid prediction of the geometric focus location in MR coordinates of a focused ultrasound (US) transducer with arbitrary position and orientation without sonicating.
Methods: Three small tracker coil circuits were designed, constructed, attached to the transducer housing of a breast-specific MR-guided focused US (MRgFUS) system with 5 degrees of freedom, and connected to receiver channel inputs of an MRI scanner. A one-dimensional sequence applied in three orthogonal directions determined the position of each tracker, which was then corrected for gradient nonlinearity.
Purpose: To develop reliable three-dimensional (3D) segmented echo planar imaging (seg-EPI) proton resonance frequency (PRF) temperature monitoring in the presence of respiration-induced B0 variation.
Methods: A free induction decay (FID) phase navigator was inserted into a 3D seg-EPI sequence before and after EPI readout to monitor B0 field variations. Using the field change estimates, the phase of each k-space line was adjusted to remove the additional phase from the respiratory induced off-resonance.