ECHO-TIME REDUCTION FOR SUBMILLIMETER RESOLUTION IMAGING WITH A 3D PHASE ENCODE TIME REDUCED ACQUISITION METHOD

To achieve optimal image quality and highest spatial resolution for in ner ear imaging with a 3D gradient echo sequence, it is necessary to m inimize susceptibility dephasing effects by using very short TE. Fract ional RF pulses and echoes can yield short TE for moderate spatial res olution; however, for voxel size of less than 1 mm, TE is limited by t he phase encode gradients. We present a method to obtain very short ef fective TE by using short triangular shaped phase encode gradients to sample the central portions of k-space and progressively longer trapez oidal gradients for the outer portions of k-space. A 3D pulse sequence employing the modified phase encoding scheme for both in-plane and sl ice phase encoding directions was implemented and tested on phantoms a nd in vivo. The effective TE equals the minimal TE used for the centra l k-space portions. Submillimeter resolution (0.35 x 0.35 x 0.7 mm(3)) images of the inner ear were obtained with effective TE of 3.2 ms and were compared with standard 3D images with TE of 8 ms. With this pron ounced TE reduction, the susceptibility artifacts at air/fluid interfa ces are significantly reduced.