Virtual scanner

The stand-ins for the scanner: the cache played, an analytic phantom acquired along the trajectory it plays or the blocks it plays simulated on isochromats, and the raw data sent as the scanner’s reconstruction client sends them; and the blocks the cache plays, written as a Pulseq file for a simulator that reads one.

The design calls, the IR, the reconstruction proxy and the reconstruction plugins are the production code; what each stand-in exercises, and the signal model, are described in The virtual scanner. Positions are in metres and k-space locations in 1/m, along the physical axes: the logical axes turned by the prescription’s rotation, the identity unless one is given. Chemical shifts are in ppm from water, and frequencies in Hz from the scanner’s centre frequency.

Acquisition

Object	Description
trajectory	The k-space location of every ADC sample the cache beside a sequence file plays.
acquire	The samples the cache beside a sequence file acquires of a phantom, demodulated as the playout demodulates.
simulate	The samples the cache beside a sequence file acquires of isochromats, the blocks it plays played on them in turn.
excited	The slabs the excitation pulses of the cache beside a sequence file excite, found by playing each on a line of isochromats along its gradient; none where one excites the whole phantom.
Slabs	Slabs of the physical frame, each the isochromats that see a field within its bounds during a pulse, so that an isochromat’s own frequency moves its slab; the region a phantom is sampled in.

Bloch simulation

The Bloch equation with relaxation, integrated on isochromats in the frame rotating at the reference frequency, as The virtual scanner states it. Times are in seconds, gradients in Hz/m and RF fields in Hz.

Object	Description
Isochromats	Isochromats, and the magnetisation the Bloch equation carries from one block to the next; one block’s events played on them.
Repetitions	Repetitions of a sequence of blocks that differ in their phase offsets, phase encodings and readout directions, played in turn from the affine map one repetition applies to each isochromat.
RigidMotion	A subject moving as a rigid body, a rotation about a centre and a translation as functions of time, which isochromats are given as their motion.

Scan clock and sound

Object	Description
Scan	The cache beside a sequence file played on isochromats as simulate() plays it, against a scan clock, in spans carrying their readouts and the sound of their gradients.
Chunk	A span of a scan between two block boundaries: its bounds in scan time, its readouts and its sound.
SAMPLE_RATE	MATLAB Pulseq’s audio sample rate, which a scan’s sound takes unless given another.

External simulators

Object	Description
export	Write the blocks the cache beside a sequence file plays as one Pulseq 1.5.1 file, and return the receiver phase of every readout.

Phantom

Object	Description
Phantom	Ellipses whose signals add, received by one coil or several of analytic sensitivity, placed in the physical frame by a rotation and a position; sampled as isochromats for the Bloch simulation.
BrainWeb	BrainWeb’s normal brain, downloaded on first use, placed head first and supine with its tissues’ T1, T2 and proton density, in the field its susceptibility adds to B0; sampled as isochromats for the Bloch simulation.
Ellipse	An ellipse of uniform magnetization in a plane of constant z, of one chemical shift and one pair of relaxation times.
localizer	The axial, coronal and sagittal images of a phantom’s proton density through a point, as DICOM, drawn from its ground truth with no sequence played.

Coils

Object	Description
Coil	The RF coils of an exam, fixed in the physical frame: the transmit and receive sensitivities of BART’s coil models, sampled by bartorch, or of each coil’s field maps, the default shim a single-channel pulse plays through, and the VOP limits of mapped transmit coils.
COILS	The virtual scanner’s coils by name, transmit/receive: the body coil both ways, the body coil with a 48-channel receive head array, and an 8-channel parallel-transmit head coil with a 32-channel receive head array.

Reconstruction client

Object	Description
send	Send one series to a reconstruction proxy as the scanner’s client sends it, each readout as it is acquired; return what comes back.
record	Write one series to an ISMRMRD file as send sends it.
Console	A scanner console’s calls answered in process: the design calls on the interpreter’s text blocks, an exam’s coil and localizer, and a scan of a stored design whose clock and DICOM images stream back, reconstructed by a proxy or in process; pulserver console serves them over a WebSocket.