In Burst experiments, the read gradient is much larger then the other imaging gradients, hence, only translation along this gradient direction will cause appreciable image artefacts. If j is the echo number, that assumes values from 1 to n (n = total number of echoes), the result of the integration in [1] is a polynomial function of the second order in j:.[3] a, b and c are constants that contain information about the read gradient strength, G R, the  -pulse separation, , and the velocity along the read direction, v R. Spins that moving in the presence of a magnetic field gradient, G, accumulate a phase,  (t), (additional to that corresponding to their normal Larmor precession) which is given by, [1] where R(t) is the spin position at time t. The signal is therefore multiplied by a phase factor:. [2] The Burst sequence gradient scheme causes a complex phase modulation of the signal. In fact, Equation 1 needs to be solved for each pulse/echo pair. Translation Artefacts in Burst Imaging C.A. Wheeler-Kingshott 1,2, Y. Crémillieux 3, S.J. Doran 1 1 School of Physics and Chemistry, University of Surrey, Guildford, GU2 5XH (UK); 2 Now at NMR Unit, Dept. Clinical Neurology, Institute of Neurology, UCL, London WC1N 3BG (UK); 3 Laboratoire de RMN, Université Claude Bernard Lyon 1, Lyon (F) Coherent macroscopic motion of the sample during MRI experiments can lead to image artifacts that seriously impair the diagnostic utility or quantitative accuracy of the data obtained. In vivo applications of MRI are particularly susceptible to this kind of distortion because of the natural rhythms, pulsatile flows and involuntary motion of the subject. Burst is an alternative ultra-fast single-shot technique, with advantages over commercially available fast sequences, such as insensitivity to magnetic susceptibility differences, low RF power deposition and low acoustic noise. Although Burst has a number of disadvantages, too, it has considerable potential in certain niche areas, such as single-shot multi-slice imaging [1] outside the head. Burst uses long and very large read gradients during excitation and acquisition. Hence, it is very sensitive to motion along the read direction. The effect of rotating the sample during Burst acquisition has been previously discussed [2]. Here we present the problem of the sample moving during the experiment at a constant known speed. The images are affected by a complicated artefact that results from a phase modulation of the k-space data, typical of Burst experiments. Knowledge of the phase map associated with the sample translation can be used to correct the images. Introduction [1] Crémillieux et al., MRM 38: (1997); [2] Wheeler-Kingshott et al, in Proc. ISMRM 1986 (1999); [3] Zha et al., MRM 33: (1995); Discussion and Conclusions AcknowledgementsReferences n  -pulses are applied during a continuous gradient, along the read direction, to frequency encode the magnetisation. A 180 º soft pulse, followed by a read gradient, refocuses n spin echoes, one from each pulse. The phase encoding gradient is also applied during the excitation and it is set to make each echo correspond to a different k-space line. In the hypothesis of independent pulses (linear approximation), it is possible to assume that :  the transverse magnetisation created by each pulse, experiences a read gradient of the same amplitude, but different length from that experienced by the transverse magnetisation created by the other pulses. Exactly the same is true for the phase gradient.  coherent motion will affect the magnetisation created by each pulse differently. The Spin-Echo Burst Sequence and its Characteristics [2]  Phantom data confirmed the theory and image correction was possible using a pre-acquired phase map.  The distortion problem does not preclude the use of Burst for fast scanning. An appropriate selection of the read direction, accompanied by triggering can reduce or even eliminate the possibility of distortion due to sample rotation and where this proves impossible the above correction can be applied.  A navigated version of the sequence could help in dealing with the high sensitivity of Burst to motion.  The high sensitivity of Burst to motion can cause severe image artefacts because of the high read gradients applied for a relatively long time.  Translation during conventional experiment affects each line of k- space in the same way. In the case of Burst each line of k-space suffers a different phase shift.  We have presented experimental results with images reconstructed in the presence of moderate translation. This study was part of a PhD thesis funded jointly by SMIS (Guildford, UK and the EPSRC. Translation of the Sample During the Experiment: The Special Behaviour of Burst Method and Results Rf Slice Read Phase 180 Selective PulseBURST ExcitationEchoes Acquisition  TT T ref GRGR GRGR GSGS G ref G PE  Pulse corresponding to echo j Echo j A B C D We acquired a set of SE Burst images on a SMIS 2.0T small bore horizontal system. With a device built by SMIS (Guildford, England) we could translate a gelatine phantom, along the axis of the magnet at different constant velocities. Figure 1 shows the images acquired with G R  z and v = 8, 12 and 16 mm s -1. Image distortion occurred only when the translation of the phantom was parallel to the read gradient, i.e., v  G R.. Coronal and transverse views acquired with v  G R were not affected by the motion. To correct the distortions, resulting from the complicated phase modulation of the signal described above, we acquired a non-phase encoded data-set with exactly the same protocol. From this data-set it is possible to derive the exact phase map to correct the original data and reconstruct images that are free from artefacts. The corrected images are displayed below the corresponding original images. v = 8 mm s -1 v = 12 mm s -1 v = 16 mm s -1 v = 16 mm s -1 Original Coronal Views G R  v Corrected Coronal Views G R  v Original Coronal and Transverse Views G R  v