Unrewound gradients (as implemented in spirals) caus ValueError in Sequence validtation
Description
In the current implementation, when specifying no rewind for spiral gradients in seqdefs.readout
a cmrseq.Sequence
object is returned. The per-block validation does not fail as no 0. magnitude point is appended to the gradient waveform, thereby not resulting in a slew-rate violation. The validation of the all combined gradient blocks (introduced in !59 (merged)) within a sequence fails as the return to 0 gradient magnitude is automatically appended.
However, non-rewound spirals (and gradient blocks in general) are a desired feature, if combined with other subsequent gradients.
Proposed solution
Instead of returning a Sequence
object, I would propose to just return the Gradient block which does not have to adhere with the sequence validation per se. As soon as it is inserted into sequence the validation will fail again, yielding desired behaviour.