Message Types

ID 1: MRD_MESSAGE_CONFIG_FILE

ID

Config File Name

2 bytes

1024 bytes

unsigned short

char

This message type is used to send the file name of a configuration file (local on the server file system) to be used during reconstruction. The file name must not exceed 1023 characters and is formatted as a null-terminated, UTF-8 encoded char string.

ID 2: MRD_MESSAGE_CONFIG_TEXT

ID

Length

Config Text

2 bytes

4 bytes

length * 1 byte

unsigned short

uint32_t

char

Alternatively, the text contents of a configuration file can be sent directly via the data stream. The length is sent as an uint32_t. Configuration text is sent as a UTF-8 encoded char string.

In addition to specifying a configuration “preset” to be executed on the server, it is often desirable to modify specific parameters of the configuration, such as filter strength or the toggling of intermediate outputs for debugging purposes. While individual parameters are specific to a given pipeline and server, the format of this configuration is standardized to enable interoperable communications between various clients and servers.

ID 3: MRD_MESSAGE_HEADER

ID

Length

XML Header Text

2 bytes

4 bytes

length * 1 byte

unsigned short

uint32_t

char

Metadata for MRD datasets are stored in a flexible XML formatted MRD header. The header length is sent as an uint32_t and the text is sent as a UTF-8 encoded char string.

ID 4: MRD_MESSAGE_CLOSE

ID

2 bytes

unsigned short

This message type consists only of an ID with no following data. It is used to indicate that all data related to an acquisition/reconstruction has been sent. The client will send this message after sending the last data (raw, image, or waveform) message. The server will also send this message after sending the last data (raw, image, or waveform) message back to the client.

ID 5: MRD_MESSAGE_TEXT

ID

Length

Text

2 bytes

4 bytes

length * 1 byte

unsigned short

uint32_t

char

Informational (logging) text can be sent using this message type, typically from the reconstruction side to the acquisition/client side. The length of message text is sent as an uint32_t while the text is sent as a UTF-8 encoded char string. These messages are optional and their timing is not guaranteed.

ID 1008: MRD_MESSAGE_ACQUISITION

ID

Fixed Raw Data Header

Trajectory

Raw Data

2 bytes

340 bytes

number_of_samples * trajectory_dimensions * 4 bytes

number_of_channels * number_of_samples * 8 bytes

unsigned short

mixed

float

float

This message type is used to send raw (k-space) acquisition data. A separate message is sent for each readout. A fixed AcquisitionHeader contains metadata such as encoding loop counters. Three fields of the data header must be parsed in order to read the rest of the message:

  • trajectory_dimensions: defines the number of dimensions in the k-space trajectory data component. For 2D acquisitions (kx, ky), this is set to 2, while for 3D acquisitions (kx, ky, kz), this is set to 3. If set to 0, the trajectory component is omitted.

  • number_of_samples: number of readout samples.

  • active_channels: number of channels for which raw data is acquired.

Trajectory data is organized by looping through the dimensions first then the samples:

  • For 2D trajectory data:

    Sample 1 Sample 2 ... Sample n
    kx ky kx ky kx ky

  • For 3D trajectory data:

    Sample 1 Sample 2 ... Sample n
    kx ky kz kx ky kz kx ky kz

Raw data is organized by looping through real/imaginary data, samples, then channels:

Channel 1 Channel 2 ... Channel n
Sample 1 ... Sample n Sample 1 ... Sample n Sample 1 ... Sample n
Re Im Re Im Re Im Re Im Re Im Re Im Re Im Re Im Re Im

ID 1022: MRD_MESSAGE_IMAGE

ID

Fixed Image Header

Attribute Length

Attribute Data

Image Data

2 bytes

198 bytes

8 bytes

length * 1 byte

matrix_size[0] * matrix_size[1] * matrix_size[2] * channels * sizeof(data_type)

unsigned short

mixed

uint_64

char

data_type

Image data is sent using this message type. The fixed image header contains metadata including fields such as the ImageType (magnitude, phase, etc.) and indices such as slice and repetition number. It is defined by the ImageHeader struct. Within this header, there are 3 fields that must be interpreted to parse the rest of the message:

  • matrix_size: This 3 element array indicates the size of each dimension of the image data.

  • channels: This value indicates the number of (receive) channels for which image data is sent

  • data_type: This value is an MRD_DataTypes enum that indicates the type of data sent. The following types are supported:

    Value

    Name

    Type

    Size

    1

    MRD_USHORT

    uint16_t

    2 bytes

    2

    MRD_SHORT

    int16_t

    2 bytes

    3

    MRD_UINT

    uint32_t

    4 bytes

    4

    MRD_INT

    int32_t

    4 bytes

    5

    MRD_FLOAT

    float

    4 bytes

    6

    MRD_DOUBLE

    double

    8 bytes

    7

    MRD_CXFLOAT

    complex float

    2 * 4 bytes

    8

    MRD_CXDOUBLE

    complex double

    2 * 8 bytes

Attributes are used to declare additional image metadata that is not present in the fixed image header. In general, this data is sent as a UTF-8 encoded char string (not null-terminated), with the length sent first as an uint_64 (not uint_32!). These are interpreted as an XML formatted set of image MetaAttributes.

Image data is organized by looping through matrix_size[0], matrix_size[1], matrix_size[2], then channels. For example, 2D image data would be formatted as:

Channel 1 ... Channel n
y1 ... yn y1 ... yn
x1 ... xn x1 ... xn x1 ... xn x1 ... xn x1 ... xn x1 ... xn

ID 1026: MRD_MESSAGE_WAVEFORM

ID

Fixed Waveform Header

Waveform Data

2 bytes

40 bytes

channels * number of samples * bytes

unsigned short

mixed

uint32_t

This message type is used to send arbitrary waveform data (e.g. physio signals, gradient waveforms, etc.). The fixed waveform data header contains metadata as defined by the WaveformHeader.

The channels and number_of_samples members fields must be parsed in order to read the rest of the message. Waveform data is sent as an uint32_t array, ordered by looping through samples and then through channels:

Channel 1 Channel 2 ... Channel n
w1 ... wn w1 ... wn w1 ... wn