novelmethodfort2

Novelmethodfort2 - Novel sequence for accurate multi-slice T2-rexometry with insensitivity to refocusing pulse profiles and reduced SAR G S Pell1 A

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Novel sequence for accurate, multi-slice T2-rexometry with insensitivity to refocusing pulse profiles and reduced SAR G. S. Pell 1 , A. B. Waites 1 , D. F. Abbott 1 , R. S. Briellmann 1 , G. D. Jackson 1 1 Brain Research Institute, Heidelberg West, Victoria, Australia Introduction: T2 has been found to be a sensitive indicator of conditions such as temporal lobe epilepsy and schizophrenia. Its acquisition in the clinical context is usually carried out with a multi-echo CMPG sequence. The method is disadvantaged however by limitations that are principally a result of the multiple refocusing 180° pulses in the sequence (1). Power deposition limits the number of slices that can be acquired. The accuracy of the T2 measurements are affected by stimulated echoes from the edges of the slice selective 180° pulses that modulate the measured T2. An apparent T2 measurement is therefore the result of such a study and this will likely deviate from the true T2. This report describes a novel rapid sequence for T2 relaxometry that enables accurate measurement of T2 with insensitivity to the refocusing pulse profile and with reduced SAR. The sequence : The pulse sequence shown in Fig. 1 is based on a standard FSE multiple spin echo train of 90 x °-[180 y °] NE pulses where NE is the desired number of echoes. With an incrementing phase encode pulse, T2-weighted images are produced at NE unique echo times. For multi-slicing, the sequence needs to be repeated for the desired number of times. In the new sequence, the slice selective 180° is replaced by a non-selective composite refocusing pulse, [90 x °-180 y °-90 x °] (2). This pulse has improved robustness to B1 inhomogeneities. More significantly, the lack of a slice selection gradient across the
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This note was uploaded on 02/27/2008 for the course EE 591 taught by Professor Nayak during the Fall '07 term at USC.

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