This is work in progress and subject to change.

Data Storage and Description

Parameters

At the toplevel, the parameter file contains variables for describing the ultrasound system, transducers, acquisition setup, and UFF information. Optional parameters are in italics.

System Parameters

This is stored in the variable system and describes the acquisition system. This will contain information about make and model of the ultrasound system, serial numbers, hardware/firmware/software revisions or versions, etc.

Probes

List of probes (transducer arrays, hydrophones) used in the measurement.

Acquisition Setup

The scan sequence is stored in the variable scan_sequence.

• transform - geometric transform of the scan sequence relative to the probe
• sound_speed - speed of sound in m/s
• transmit_waves - list of transmit waves
  • transform - this describes to focus point or wave direction. For a spherical wave, the rotation applied on the position describes the focus point or virtual source location. For a plane wave, the transform's position has no meaning.
  • wave_type - enumerated type (converging, diverging, plane, cylindrical, photoacoustic)
  • apodization - analytical apodization window
    • window - text describing the window, e.g., Hamming, Gauss, Tukey with parameter
    • f_number - F# of the aperture
  • excitation - the excitation waveform
    • pulse_shape - text describing the pulse shape, e.g., sinusoidal, square wave, chirp; including necessary parameters
    • waveform - sampled waveform in units normalized to system transmit voltage
    • sampling_frequency - sampling frequency of waveform in Hz

• ultrasound_events - list of unique ultrasound events (emissions and associated receptions)

  • transform
  • event_category - text descriptive of the event and used in generating the storage path for the data
  • active_probe - reference to the emitting probe
  • active_waves - list of transmit waves in the event
    • wave - reference to wave in transmit_waves
    • time_offset - temporal offset relative to start of event
    • weight - weight of wave in event (unitless between -1 and +1). This may be used to describe pulse inversion sequences.
    • active_aperture_center - coordinate of the center of the active aperture in the coordinate system of the active probe [m]
  • channel_mapping - mapping of transmit channels to transducer elements. Note that one channel may connect to multiple elements, but one element may only be connected to one channel. Element indices relate to probe definition.
  • transmit_delays - the transmit delays on channels in seconds as set in the hardware
  • excitations - matrix of excitation waveforms with dimensions number of samples in longest excitation by number of transducer elements. If necessary, excitation waveforms are zero-padded at the end of the waveform to match the number of samples in the longest waveform. Normalized amplitude relative to tx voltage. Sampled at fs tx. This is intended to be as close as possible to the hardware.
  • sampled_channels_setup - description of sampled channel data. If more than one probe is used in reception, this is a list of setups.
    • probe - reference to the receiving probe
    • time_start_sampling - time offset when sampling starts relative to start of event
    • sampling_frequency_channels - sampling frequency of recorded data in Hz
    • modulation_frequency - modulation frequency of IQ data (optional) [Hz]
    • channel_mapping - mapping of receive channels to transducer elements
    • tgc_profile - the analog TGC profile in dB sampled at sampling_frequency_tgc
    • sampling_frequency_tgc - sampling rate of the TGC profile in Hz.
  • beamformed_lines_setup - description of beamformed lines
  • TBD - allow description in terms of beam space or line space

• sequence_order - sequence of ultrasound events and respective time stamps

  • event - list of references to the unique event
  • time_stamp - list of starting times of events relative to frame starting time [s]
• start_time - time stamp for the beginning of the scanning, ISO 8601:2005 section 4.3.2 basic format with local time without difference to UTC, e.g., 20180406T091930 is April 6th 2018, 19 minutes and 30 seconds after 9 AM in whichever timezone the measurement is made. Comment: I think local time makes most sense, especially for in-vivo scans (was it morning, just after lunch, etc. for the patient/volunteer), while difference to UTC does not provide useful information as I see it.
• country_code - ISO 3166-1 Alpha-2 country code for the country where the scan was conducted. Mandatory for in-vivo scans.