Development And Optimization Of The Spiral And Rosette Pulse Sequence Trajectories In MRI

The most common sampling pattern in MRI is Cartesian sampling.However,in some specific imaging areas,such as lung and cardiac,respiration and cardiac motion would introduce artifacts along phase encoding.To overcome this kind of issue,a fast and motion-insensitive imaging sequence is in high demand.Radial trajectory and spiral trajectory,as non-Cartesian sampling pattern,have many advantages over under-sampling and multi-echo imaging,which perfectly satisfies the motion insensitivity and fast imaging.Moreover,rosette trajectory,a novel non-Cartesian sampling pattern,has high potential in terms of scanning water-fat separation,noise reduction and quantification imaging due to its sine-like gradient waveform,the feature of crossing K-space center more than once in one TR and spectral response.Compared to radial sampling pattern,spiral trajectory not only is insensitive to motion,but also has higher sampling efficiency.Therefore,we mainly developed spiral sequence protocols,including: 2D spiral sequence,2D balanced Steady State Free Precession(b-SSFP)spiral sequence and three-dimension stark-of-spiral.Nonetheless,the readout direction in spiral varies with the change of time,which makes the spiral trajectory sensitive to B0 field inhomogeneity.Thus,we proposed a field map estimation approach which employed compressed sensing(CS)algorithm to improve the deblurring effect.For rosette imaging,we developed a balanced SSFP rosette trajectory to shorten the TR.Meanwhile,a golden angle rotation method was employed to increase the sampling area.Besides,we also explored the feasibility of fast rosette imaging based on compressed sensing.