longitudinal magnetisation

longitudinal magnetisation

An MRI term for the component of the net magnetisation vector that moves in the direction of the static magnetic field. After RF excitation, the component returns to equilibrium at a rate defined by the time constant T1.
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The difference signal between the longitudinal magnetisation of the control and label images ([DELTA]M) is
A modification of the Bloch equation for longitudinal magnetisation to include the flow effect according to Fick's principle (difference between delivery and clearance of substance in blood is proportional to the local flow) has been introduced by Detre and Williams [19]:
where [M.sub.0] is the longitudinal magnetisation of the tissue at the equilibrium and M, Ma, and Mv are the time-dependent longitudinal magnetizations of the tissue, arterial, and venous blood, respectively.
Additionally, labelled blood flow leads to a time-dependent decrease in the longitudinal magnetisation [M.sub.0] with an apparent time constant T1 app; its magnitude depends on the T1 relaxation time of tissue and blood flow, given by
and in the case of a steady state, [M.sub.0] decrease to longitudinal magnetisation in steady state [M.sub.ss], and the solution is given by
(iii) And the magnetisation relaxation function, M (t), is the fraction of the remaining longitudinal magnetisation that is carried by the tagged water at time t after arrival.
The signal intensity improves with the higher value of TR by allowing maximum recovery of longitudinal magnetisation.4
Sine TR controlled the recovery of longitudinal magnetisation of tissues, at higher values of TR the difference between longitudinal magnetisation was more prominent among tissues.

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