Image Encoding With Blipped Gradients in an Echo Train

An MRI scanner was designed and built to encode $k$ -space points in the spin echoes occurring between $180^{\circ }$ pulses in an echo train by using blipped $B_0$ gradient pulses applied just prior to those spin echoes.

The proposed MRI scanner is a modification of an original design that used TRansmit Array Spatial Encoding (TRASE), a built-in $B_0$ gradient, and a thin RF coil defining a single axial slice. However, for TRASE, the thin profile coil needed a spatially uniform $B_1$ phase, and this proved difficult to achieve. We therefore replaced the RF encoding coil with a low-power $B_0$ gradient coil. This removed the need for a uniform spatial $B_1$ phase for the single slice RF coil to achieve Fourier image encoding. The pulse sequence then sent all $180^{\circ }$ transmit RF pulses through the one remaining single slice RF coil with $B_0$ gradient pulses applied between the RF pulses. The spin echoes between the RF pulses were received and used to define the $k$ -space points in one transverse direction. Image encoding in the perpendicular transverse direction was accomplished via frequency encoding within the built-in transverse $B_0$ gradient. Mineral oil phantoms were used to establish a proof-of-concept for the blipped-gradient imaging approach.

The phantom images give a proof-of-concept level verification of the blipped-gradient MRI design.

With work to address engineering imperfections, a blipped-gradient approach could be used to achieve the extreme Size, Weight, and Power (SWaP) requirements for a spaceworthy MRI.