![]() The TR used in TSE is often much longer than that used in conventional spin-echo. The opposite is true of short turbo factors. Long turbo factors also lead to more T2 contrast. The scan time is therefore reduced to 1/16 of the originalSelection of a long turbo factor means many of lines of k-space are filled every TR so the scan time decreases. 16) TR periods must elapse to complete the scan. In FSE, using the same parameters but selecting a turbo factor of 16, 16 phase-encoding steps are performed every TR. Assuming 1 NSA is also selected, 256 TR periods must elapse to complete the scan. For example:In conventional spin-echo, if a 256 phase matrix is selected, 256 phase encodings are per- formed. The higher the turbo factor, the shorter the scan time, as more phase-encoding steps are performed per TR. This number is called the turbo factor or the echo train length (ETL). The number of 180° RF rephasing pulses performed every TR corresponds to the number of spin-echoes produced in the echo train and the number of lines of k-space filled with data from these echoes. This is achieved by using several 180 deg RF-RP's to produce several spin echoes to form an echo train. the scan time is reduced by performing more than one phase encoding step and subsequently filling more than one line of k space per TR. As a result k space is filled more efficiently, and the scan time decreases. The number of phase encoding steps is maintained so that the phase matrix is unchanged however in TSE, the number of phase encoding steps per TR is increased. ![]() the scan time is decreased by modifying the phase matrix component of this equation. ![]() The scan time is a function of the TR, the number of signal averages (NSA) and the phase matrix. Also known as RARE (Rapid Acquisition with Relaxation Enhancement) a spin echo pulse sequence but with scan times that are much shorter than conventional spin echo. ![]()
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