Reconstruction clients

The reconstruction client is the scanner-side program that streams the raw data of each series to the reconstruction proxy and returns the images to the console. It connects to the proxy’s TCP port (Running the services), sends one series per connection as MRD messages, and reads what the reconstruction returns on the same connection.

The proxy replaces the encoding counters, flags, encoding spaces and trajectory of the series with those the sequence states (Raw-data enrichment and routing). The client therefore sends what the scanner measured, the identity of the design the series was played from and the reconstruction plugin to run, and leaves the Pulseq structure of the scan to the proxy.

Messages

A series is sent in this order:

Message	Identifier	Content
CONFIG	2	The reconstruction plugin, as a bare name or the path of its <plugin>.py file, or as either under parameters.config of a JSON, YAML or XML text
HEADER	3	The MRD XML header, once
ACQUISITION	1008	One per readout of the sequence chain, in play order
WAVEFORM	1026	Optional, anywhere after the header: physiological waveforms, passed to the reconstruction unchanged
CLOSE	4	The end of the series

The design names no reconstruction, so the proxy refuses a series whose config names none, unless it forwards with a --forward-config. A path ending in .py names the plugin its file is called, without the extension; the proxy searches its own --plugins directories for that name, whatever the path’s directory.

The client then reads until the proxy’s CLOSE: images (IMAGE, 1022), DICOM datasets (DICOM_WITHNAME, 1018) and texts (TEXT, 5), in the order the reconstruction produces them. A text beginning pulserver: reports a series that failed. A refused series receives that text and a CLOSE at once; the proxy then discards what the client still sends until it closes the connection, so the client can finish sending and read the reason.

Header

Element	Requirement	Use
pulserver_design, a userParameterString	Required	The identifier of the design the interpreter plays, from the GENERATED or IMPORTED reply: 18 hexadecimal digits, which are three 24-bit integers of six digits each
experimentalConditions.H1resonanceFrequency_Hz	Required by the MRD schema	DICOM ImagingFrequency
acquisitionSystemInformation.receiverChannels	Optional	The coil count of a reconstruction buffer laid out before its first acquisition
ExamID, a userParameterString, or else studyInformation.studyInstanceUID, or else studyInformation.studyID	Optional	The exam; the series of one exam share its exam cache, and a series without one is an exam of its own
fov_offset_mm, a userParameterString	Optional	The position of the field-of-view centre, three millimetres along the logical readout, phase and slice axes separated by spaces; a difference from the offset the design was converted at is applied to the samples as a receive phase. Without it, the converted offset
subjectInformation, studyInformation, measurementInformation, acquisitionSystemInformation	Optional	Copied into the DICOM datasets; relativeTablePosition is not
measurementInformation.measurementID	A non-negative integer when systemVendor names GE	The DICOM series number on a GE system
encoding	Optional	Replaced by one encoding space per subsequence, and one more for the navigator readouts of a subsequence that has them. The reconstruction space is the sequence’s matrix size and field of view; the encoded space of a Cartesian space has the readout widened to the full echo, oversampling included, and its field of view in proportion. The encoding limits are the extremes of the counters the readouts reach, centred on the k-space centre line and partition the sequence defines. A matrix size or field of view the sequence does not define is kept from the client’s encoding at the same index
sequenceParameters	Optional	TR, TE, TI and flip angles replaced by those the sequence defines; TR and TE it does not define are measured by pypulseqpp’s test_report_dict, flip angles it does not define are the distinct values of rf_flip_angles

A header that the ISMRMRD schema does not accept, or that names no design of the store, is refused before any acquisition is read.

Acquisitions

The proxy matches acquisitions to readouts by their position in the stream, so the client sends every readout the sequence chain plays, those of dummy scans, noise scans and navigators included, and no other.

Field	Client	Proxy
number_of_samples	The sample count of the readout’s ADC event	Checked
active_channels, data	The samples, demodulated by each ADC’s frequency and phase offsets	Multiplied by the phase a field-of-view offset adds to a readout under a moving gradient, and by any phase modulation the sequence file stores
scan_counter	0 on every acquisition, or increasing by one from any start	Checked
flags	None, or LAST_IN_MEASUREMENT on the last acquisition	Replaced
idx, sample_time_us, encoding_space_ref	Any value	Replaced
center_sample	Any value	Replaced, except on a readout whose k-space location does not change
trajectory_dimensions, traj	Any value	Replaced on a readout whose k-space location changes, in 1/m along the sequence’s gradient axes
measurement_uid, position, read_dir, phase_dir, slice_dir, patient_table_position, acquisition_time_stamp, physiology_time_stamp, user_int, user_float	The scanner’s values, as MRD defines them	Passed on unchanged; an image takes them from its reference acquisition

A series is refused, and its reconstruction stopped, when an acquisition has a sample count other than its readout’s, when the scan counters skip or repeat one, when an acquisition before the last is flagged LAST_IN_MEASUREMENT, or when the stream carries more or fewer acquisitions than the chain plays.

See also

• Running the services — starting the proxy.

• Raw-data enrichment and routing — enrichment and routing.

• Designs and the design store — the design store and the identifier of a design.

• ReconProxy — the proxy.