T2Preparation

class pypulseqpp.sequences.T2Preparation

Bases: RfModule

Adiabatic T2 preparation with tip-down, refocusing and storage pulses.

Refocusing pulses must occur in pairs to cancel their B1-dependent phase. The final half passage is time-reversed and conjugated relative to the first; final_tip selects storage on +z or -z.

Parameters:

• system (pypulseqpp.Opts) – System limits.

• echo_time_s (float) – Preparation echo time (s), first pulse centre to last.

• final_tip ({'up', 'down'}, default='up') – Store on +z (pure T2 weighting) or -z, which starts a T1 recovery as well – see T1T2Preparation.

• n_refocus (int, default=2) – Adiabatic refocusing pulses, spread evenly through the echo time. Must be even; see above.

• half_passage_duration_s (float, default=0.004) – Duration of each half passage (s).

• refocusing_duration_s (float, default=0.01024) – Duration of each refocusing pulse (s).

• adiabaticity (int, default=8) – Sweep-rate margin over the adiabatic condition, for every pulse.

• dwell_s (float, default=1e-05) – RF raster (s).

• spoiling_cycles (float, default=4.0) – Cycles of dephasing the closing spoiler winds across voxel_size_m on each axis. Zero omits the spoiler block.

• voxel_size_m (float, default=0.001) – Length the dephasing is counted over (m).

• labels (sequence of str, default=None) – Counters set to 0 on the first pulse’s block.

Attributes:

• rf_prep (RfEvent) – The half passage that tips down.

• rf_ref (RfEvent) – The refocusing pulse; every repeat plays this one event.

• rf_store (RfEvent) – The reverse half passage that stores what is left.

• wait_first, wait_inner, wait_last (DelayEvent) – The gaps before the first refocusing pulse, between refocusing pulses, and before rf_store. Each is absent when its gap is zero, and wait_inner when there is one refocusing pulse.

• gx_spoil, gy_spoil, gz_spoil (GradEvent) – The closing spoiler.

• prep_labels (LabelSetEvent or list of LabelSetEvent) – One per name in labels.

• echo_time (float) – The preparation echo time achieved on the block raster (s).

Raises:

ValueError – If final_tip is not 'up' or 'down', n_refocus is not a positive even number, a size is out of range, or the echo time is shorter than the pulses themselves.

Examples

>>> import pypulseqpp.sequences as design
>>> import pypulseqpp as pp
>>> prep = design.T2Preparation(pp.Opts(), 50e-3)
>>> round(prep.echo_time * 1e3, 2)
49.99

Tip-down, two refocusing pulses and storage. Over the band the refocusing pulses cover, the module returns the magnetization to +z; what it lost on the way is the T2 weighting:

(svg)

(svg)

Methods

init_module	Build the module's block layout; implemented by the subclass.
publish	Publish events from the caller's locals and register keyword aliases.
register	Publish named events without requiring prior block registration.
sim_rf	Simulate this module's pulse across off-resonance.

Attributes

blocks	Return block tuples in play order, retaining the original event objects.
duration	Duration of the module in seconds.
seq	Sequence holding the module's construction-time block layout.