Simultaneous parallel inclined readout image technique

Abstract 

Sensitivity-encoded phase undersampling has been combined with simultaneous slice excitation to produce a parallel MRI method with a high volumetric acquisition acceleration factor without the need for auxiliary stepped field coils.

Dual-slice excitation was produced by modulating both spin and gradient echo sequences at ±6 kHz. Frequency aliasing of simultaneously excited slices was prevented by using an additional gradient applied along the slice axis during data acquisition. Data were acquired using a four-channel receiver array and ×4 sensitivity encoding on a 1.5 T MR system. The simultaneous parallel inclined readout image technique has been successfully demonstrated in both phantoms and volunteers. A multiplicative image acquisition acceleration factor of up to ×8 was achieved. Image SNR and resolution was dependent on the ratio of the readout gradient to the additional slice gradient. A ratio of approximately 2:1 produced acceptable image quality. Use of RF pulses with additional excitation bands should enable the technique to be extended to volumetric acquisition acceleration factors in the range of ×16–24 without the SNR limitations of pure partially parallel phase reduction methods.

Keywords: Parallel MRI, Fast MRI, Frequency oversampling, B₁ array coils, Sensitivity encoding, SENSE, SMASH