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Generic structure
Each dataset is comprised of two fields: data and meta. The data itself is kept in ''ChDataset.data'', an array with 7 dimensions: [nRanges, nAzChannels, nElChannels, nTxAz, nTxEl, nPackets, nFrames].
| Dimension | Description |
|---|---|
| nRanges | Number of samples in the depth dimension (z). The number of samples is determined by the sampling frequency and range (min and max depths) |
| nAzChannels | Number of transducer crystals in the azimuth direction (x) |
| nElChannels | Number of transducer crystals in the elevation direction (y) |
| nTxAz | Number of transmit directions in azimuth to form a given frame |
| nTxEl | Number of transmit directions in elevation to form a given frame |
| nPackets | Number of packets. For compounding, this is the number of ''low resolution'' shots to sum into the final ''high resolution'' image |
| nFrames | Number of acquisition frames |
The metadata can be found in the field ''ChDataset.meta'' and includes information about the system settings, as well as the probe and scanning sequence used and the phantom imaged. A more detailed description of the metadata can be found in the sections below.
Metadata fields
Probe
The Probe structure contains useful information, such as the element geometry and element-to- channel pinout, as detailed below.
| Field | Description |
|---|---|
| name | Probe name |
| nElementsAz/El | Number of elements in azimuth and elevation |
| elSizeAz/El | Element width (azimuth) and height (elevation) [m] |
| kerfAz/El | Kerf in azimuth and elevation [m] |
| pitchAz/El | Pitch in azimuth and elevation [m] |
| xdcSizeAz/El | Probe size in azimuth and elevation [m] |
| tx_probe_origo | Probe origin, as considered by the transmit beamforming (x,y,z) [m] |
| rx_probe_origo | Probe origin, as considered by the receive beamforming (x,y,z) [m] |
| el_focus | Elevation focal depth [m] |
| type | Type of transducer: phased_array, phased_2d_array, muxed_2d_array |
| elementPos | Coordinates of the transducer elements (nAz x nEl x [x,y,z]) [m] |
| connectorPinout | System pinout (elementPos are a regular grid, but the system might scramble the channels) |
| channelIndex | Channel index for every physical element |
| nMuxAz/El | Number of multiplexing blocks in azimuth and elevation |
| muxerPos | Coordinates of the muxing blocks used for beamforming (nMuxAz x nMuxEl x [x,y,z]) [m] |
| muxMode | Description of the muxing mode used ('muxedArray' or 'fullChannel') |
Sequence
The Sequence structure has been designed considering a simplex imaging mode. This may have to be adapted once we move to more complex imaging sequences.
| Field | Description |
|---|---|
| nFrames | Number of frames acquired |
| nTxAx/El | Number of transmit directions per frame in azimuth and elevation |
| txFocalDepth | Focal depth of the transmissions [m] |
| compoundingMode | Type of coumpounding sequence |
| nCompoundAz/El | Number of compounding shots in azimuth and elevation |
| openingAngle | Acquisition opening angle (Az, El) [deg] |
| nMLAs | Number of MLAs in azimuth and elevation |
| nMLTs | Number of MLTs in azimuth and elevation |
| txEvents | Structure with the transmit events |
| nPackets | Number of data packets |
| f0 | Pulser centre frequency [Hz] |
| chSampleTime | Time vector for channel data [s] |
| chRangeMin/Max | Min and max acquisition range [m] |
| Muxing | Structure with the multiplexing settings |
When multiplexing is used, each txEvent may be transmitted multiple times with different aperture layouts. Additional information regarding txEvent repetition is stored in the field ''Sequence.Muxing''. This includes the number of repetitions and the elements used for each firing.
| Field | Description |
|---|---|
| nMuxRounds | Number of multiplexing firings into the same direction |
| T_First | Index of the first transmit element for each transmission (from the focal law) |
| R_First | Index of the first receive element for each transmission (from the focal law) |
| activeTxElm | List of elements active in each transmission |
| activeRxElm | List of elements active in each reception |
The txEvents structure contains additional information related to the transmit events, such as beam direction and apodization.
| Field | Description |
|---|---|
| txAngle | Angle of the transmit beam (azimuth and elevation) [deg] |
| txFocus | Coordinates of the focal point for each transmission (x,y,z) [m] |
| txApod* | Transmit apodization used |
| txOrigo | Origin of the active transmit aperture (x,y,z) [m] |
| txActiveAper | List of active elements for each transmission |
| txTimeZero | Time-zero for each transmit beam (useful when multiple beams are transmitted sequentially) [s] |
| txPolarity | Pulser polarity (+1, -1, or eventually other reconstruction code) |
| rxActiveAper | List of active elements for each reception |
Note: each field may have N rows, where N is the number of MLTs.
Phantom
The Phantom structure is specially useful in the case of simulation datasets, as it provides the ground-truth for the tissue data.
| Field | Description |
|---|---|
| name | Name of the phantom |
| scat_pos | Coordinates of the scatterers in the medium (x,y,z) [m] |
| scat_amp | Amplitude of the scatterers in the medium |
Updated