Experiments

Introduction

This project has a specific target of providing a low-cost, open source technological kit to allow scientists, academics, hackers, makers or OSHW fans to hack their way to ultrasound imaging - below 500$ - at home, with no specific equipment required. This piece of hardware follows the murgen dev-kit and the echomods, previous iterations. Those were simpler, less robust and less cost-efficient than this kit.

ice40 - a specificity

This board builds in particular on the famouse ice40 FPGA family which is low-cost, … and open-sourced.

It can use the “Project IceStorm”, which aims at reverse engineering and documenting the bitstream format of Lattice iCE40 FPGAs and providing simple tools for analyzing and creating bitstream files.

There’s a bit of action around these FPGAs these days, be it for tools, extensions, DIP designs,… and I thought using those for a ultrasound imaging device would permit to mix both FPGA and OpenSource.

How is this better?

Compared to previous iteration, this setup is:

Objective

The aim of this project is to build a small ultrasound imaging hardware and software development kit, with the specific goal of:

Previous projects has shown the feasibility of the hardware, but was not simple enough. Let’s keep the momentum, and use this dev kit in interesting ways.

What can be done with this hardware?

This board has been developped for pedagogical purposes, to understand how ultrasound imaging and non-desctrucive testing work. This structure can be used to develop:

Why are you doing this ? or besides pedagogical uses of your prototype, we want to know if you are thinking about other applications ? Where your prototype can be more useful? In Africa for example, can your prototype solve some problems?

General principles of ultrasound imaging

Using echoes to map interfaces

Medical ultrasound is based on the use of high frequency sound to aid in the diagnosis and treatment of patients. Ultrasound frequencies range from 2 MHz to approximately 15 MHz, although even higher frequencies may be used in some situations.

The ultrasound beam originates from mechanical oscillations of numerous crystals in a transducer, which are excited by electrical pulses (piezoelectric effect). The transducer converts one type of energy into another (electrical <–> mechanical/sound).

The ultrasound waves (pulses of sound) are sent from the transducer, propagate through different tissues, and then return to the transducer as reflected echoes when crossing an interface. The returned echoes are converted back into electrical impulses by the transducer crystals and are further processed - mostly to extract the enveloppe of the signal, a process that transforms the electrical signal in an image - in order to form the ultrasound image presented on the screen.

Ultrasound waves are reflected at the surfaces between the tissues of different density, the reflection being proportional to the difference in impedance. If the difference in density is increased, the proportion of reflected sound is increased and the proportion of transmitted sound is proportionately decreased.

If the difference in tissue density is very different, then sound is completely reflected, resulting in total acoustic shadowing. Acoustic shadowing is present behind bones, calculi (stones in kidneys, gallbladder, etc.) and air (intestinal gas). Echoes are not produced on the other hand if there is no difference in a tissue or between tissues. Homogenous fluids like blood, bile, urine, contents of simple cysts, ascites and pleural effusion are seen as echo-free structures.

Creating a 2D image

If the process is repeated with the probe sweeping the area to image, one can build a 2D image. In practice, in the setups we’ll be discussing, this sweep is done with a transducer coupled to a servo, or using a probe that has an built-in motor to create the sweep.

Plugging the Pi to an existing probe

Not a first shot

  1. A beaglebone black had been used with its high-speed DAQ to be connected to an existing mechanical probe, with some results.
  2. The next step has been to interface a Raspberry Pi W to this probe through the 24Msps Pi ADC pHAT, to see if one can get the same quality of image, and produce a ultrasound loop. This was summarized here

Comparing improvements on signal capture

Below is represented the improvement in signal capture.

This setup

Picture of the setup

Results

Making it better

I’ll definitely need to use the on-board Time Gain Compensation, did the tests on the benchmark unit.. but haven’t been using it on this rig.

What’s next?

  1. Just a name … Kruizinga ;)
  2. Plugin a real probe (I’m thinking about Shenzen, there are good prodes)
  3. Assembling with an old ultrasound machine.

Working together

Who’s working on this?

A summary of the contributors using this family of hardware is detailed below. Some continents are still to be represented!

And you?

Articles

Under CC-BY-4.0, main article here