Reducing distortion in EPI using partial Fourier encoding in the kx-direction

where ΔB0(r) represents a field inhomogeneity, FOVpe is the phase-encoding FOV, and Tro = Nro * Δtro is the readout time for one k-space line (or echo spacing), and Nro is the number of samples in the readout direction. From Eq. 1, one can reduce geometric distortion by reducing FOVpe and/or by reducing Tro. The former can be achieved by accelerating the traversal of kspace with parallel imaging [2-4], whilst the latter can be achieved by reducing the readout width Nro. To shorten the EPI readout and TE, the acquisition is often used with partial Fourier (PF) imaging in the ky-direction. Particularly with higher field strength, the shorter readout train decreases blurring; while the smaller achievable TE increases SNR (offset by less data acquired per readout), increases the # slices/TR, and can decrease T2-shine-through in diffusion-weighted imaging for high matrix sizes. In this abstract, PF-encoding in EPI is performed instead in the kx-direction and compared with images acquired with PF in the ky-direction. As shown in Fig. 1, the echo spacing between two consecutive echoes is reduced (Fig. 1b) – resulting in reduced geometrical distortion while keeping the SNR approximately equivalent. This approach can reduce geometric distortion by ~20% compared with EPI images acquired with PF in ky.