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Try adding DA figs
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mathieuboudreau committed Oct 4, 2024
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---
title: Transmit and Receive RF field amplitudes
title: Double Angle method(s)
subtitle: Double Angle technique
date: 2024-07-25
authors:
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template: Fig. %s
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:::{attention}
:class: attentionDraft
:name: attentionDraft
This content of this section is still a work-in-progress and has not been proofread and/or reviewed.
:::

This pulse sequence uses a 180 degree spin-echo refocusing pulse and acquires two images using an excitation pulse α and 2α. It assumes that there is full signal recovery (long TR), and because it refocuses T2*, it eliminates signal variability caused by B0 in the resulting B1 map (Insko and Bolinger 1993). Alternatively, a gradient echo could be used?

Assuming an an refocusing pulse is used (i.e. isn’t dependent on B1), we can develop the equation for a gradient echo and spin echo case.
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B1=arcos(M22M)nominal
(7)

Figure 2. B1 computed from analytical GRE equations for DA sequence

:::{figure} #daFig1cell
:label: daPlot1
:enumerator: 4.2
B1 computed from analytical GRE equations for DA sequence
:::

This equation is also used for alpha-180 spin echo pulses, however it assumes no dependency on of the refocusing pulse on B1. Figure 3 explores this using Bloch simulations

Figure 3. B1 computed from bloch simulations for ideal spin echo and refocusing pulse where FA = 180*B1
:::{figure} #daFig2cell
:label: daPlot2
:enumerator: 4.3
B1 computed from bloch simulations for ideal spin echo and refocusing pulse where FA = 180*B1
:::


:::{figure} #daFig3cell
:label: daPlot3
:enumerator: 4.4
B1 computed from bloch simulations for spin echo with refocusing pulse where FA = 180*B1,, and composite pulse 90x-180y-90x where each 90 and 180 are also multiplied by B1.
:::

Figure 4. B1 computed from bloch simulations for spin echo with refocusing pulse where FA = 180*B1,, and composite pulse 90x-180y-90x where each 90 and 180 are also multiplied by B1.

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