Row-column beamformation project

Project work: Monday, May 29, 13.00-17.00; Tuesday, May 30, 08.00-12.00 and 13.00-17.00; Wednesday, May 31, 13.00-17.00 in the group rooms Building 349, Ground floor Project presentation preparation is Thursday from 8:00-12:00, and the presentations are from 13:00-17:00.

Purpose

A recent paper presents a new row-column (RC) beamformation method, which performs the imaging with orders of magnitude fewer operations (See the paper below by Lasse Thurmann Jørgensen et al.). This exercise aims to implement the new approach and compare the output with the output from the conventional approach (See the paper below by Morten Fischer Rasmussen et al.).

Preparation

1. Read the notes on RC imaging and the papers below.
2. Acquire data with the Verasonics scanner and use Vermon 128+128 RC probe.
3. Finish course exercises regarding RC beamformation

Project description

1. Use simulated RF data from the row-column beamformation exercise from Day 3.
2. Acquire RF data from a wire phantom with the Vermon RC array.

Data processing

• The new beamformer methods consist of stages. The first stage uses the conventional row-column beamformer, and the second stage extrapolates (resamples) the output from the first stage.
• The goal is to beamform a yz-slice (x=0 mm) with an axial and lateral sampling interval of lambda/2 = (c/f₀)/2. This is achieved with the new approach as follows:
  1. For each emission, beamform an axial line directly below the emission source. The sampling interval of the lines should be lambda/8 = (c/f₀)/8, as this ensures accurate second-stage extrapolation. The range of the axial lines should equal (or extend) the axial range of the final output. Store the lines obtained for each emission (do not add them together).
  2. For each axial line, resample the line into a 2D image. The 2D image should have the same image point coordinates as the final yz-slice. The resampling is performed by mapping the image point coordinates onto the axial line. Use the mapping equation below. The coordinate's image value is obtained by interpolating the image value at the mapped position. Use interp1(...,'spline',0).
  3. Lastly, Combine the 2D images resampled for each axial line to obtain the final output (i.e. the beamformed yz-slice).
• Beamform the yz-slice with the conventional beamformer and compare the output with the new beamformer's output. Determine the number of interpolation operations that are performed with the new and conventional approach.
• Compare the two beamformer's output on simulated and measured data.

Debugging hint: Try beamforming the yz-slice with only one emissions. The output from the new and conventional beamforming method should look very similar.

Mapping equation

The following equation maps any (x,y,z)-coordinate onto an axial line located at y = y_v:

Emission source's (y,z)-position: (y_v,z_v)

Receiving element's (x,z)-position: (x_e,z_e)

NB! the above mapping equation assumes z_v.