ARFI

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Introduction[edit]

Acoustic Radiation Force Imaging, or ARFI, is a method where high power ultrasonic waves are used to displace tissue for the purpose of tissue characterization and measurements.

The basic process is as follows:

  • Acoustic waves deposits energy into the tissue.
  • This energy generates a force that causes displacement of the tissue.
  • These motions are used to derive information about the tissue.
ARFI Focused Beam

Implementation[edit]

Pulse Sequencing[edit]

The basic sequence for programming ARFI is as follows:

  • Acquire imaging line/lines (used as a reference)
  • Apply the push pulse (a long transmit)
  • Acquire imaging line/lines afterward to use for tracking
ARFI Sequence

System Requirements[edit]

To perform the sequence above, an ultrasound system must be composed of:

  • Programmable sequencer
  • Transmit pulses with long durations up to 500 microsec
ARFI Sequence

Texo Implementation (6.1)[edit]

The Texo SDK can be used to program the ARFI sequence. Below is some pseudo-code for programming the Texo sequence:

// 1) program reference scanlines
...

// 2) program the push pulse
// transmit aperture
tx.aperture = 64;
// transmit center element
tx.centerElement = pushLine + 0.5;
// fill out the entire transmit pulse train (48 cycles)
tx.pulseShape= "+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-";
// repeat the transmit pulse train as many as required (maximum 255)
tx.txRepeat = 20;
// push duration + additional wait time
rx.customLineDuration = pushDuration * 1000;
// no acquisition for ARFI pulse
rx.acquisitionDepth = 0;
// add the push pulse to the sequence
texo->addLine(tx, rx);

// 3) program tracking scanlines
...

Measurements[edit]

Electronic Measurements[edit]

The figures below show some measurements from an oscilloscope attached to a Sonix RP system.

ARFI Scope Measurements

Acoustic Measurements[edit]

The needle hydrophone results can be shown below.

ARFI Hydrophone Measurements

Displacement Measurements[edit]

The figure below shows the resulting displacement from an ARFI sequence.

  • 100 microsec push duration
  • 1 kHz RF sampling
  • Displacement profile at push location shown below
ARFI Displacment

Remaining Issues[edit]

  • Hold over effect
    • The switching from short pulses to long pulses introduces artifacts in the echo signal that appear in the displacement estimates. The user need to make sure enough delay exist between the push pulse and the imaging pulse. This can be controlled by the customLineDuration parameter.
  • Voltage Droop
    • Ideally the amplitude should stay steady during the transmit push pulses.