1.5 RPi ultrasound imaging platform · Hacking ultrasound with a DIY dev equipment

2023-05-24 09:25:55

Introduction

This undertaking has a selected goal of offering a low-cost, open supply technological equipment to permit scientists, lecturers, hackers, makers or OSHW followers to hack their option to ultrasound imaging – beneath 500$ – at residence, with no particular tools required.

Goal

The purpose of this undertaking is to construct a small ultrasound imaging {hardware} and software program growth equipment, with the particular purpose of:

constructing an analog “debugging instrument” to discover ultrasound imaging programs.
consolidating existing hardware research;
simplifing / decreasing the price of the equipment;
offering a benchmark of ultrasound programs;
introducing a easy API to regulate {hardware};
having a server which offers uncooked ultrasound information, and for ultrasound imaging, can ship normal DICOM recordsdata;
having a equipment that can be utilized for pedagogical and educational functions – to not point out individuals who wish to perceive ultrasound!

Earlier undertaking has proven the feasibility of the {hardware}, however was not easy sufficient. Let’s maintain the momentum, and use this dev equipment in different tasks as nicely – resembling dopplers or non-destructive testing, totally different tasks utilizing piezos as sensors.

Structure

Ultrasound imaging has advanced for the reason that first ultrasound machine appeared. The primary units have been utilizing single-sensor (transducers) strategies, coupled with mechanical scanning – therefore permitting a single sign processing channel. The structure of such programs, as proven beneath, is well-known and shaped the premise of ultrasound imaging.

This equipment consists of a number of modules primarily constructed from simply obtainable elements – after a brief benchmark of existing ICs. Two digital modules have been particularly designed to supply the fundamental growth equipment.

the Transducer Pulser Module (TPM): designed to supply a exact high-voltage pulse, essential to excite the sensor, whereas remaining sturdy sufficient to be managed by an Arduino;
the Analog Processing Module (APM): designed to accurately course of the uncooked ultrasound electrical sign, whereas simply exposing all middleman alerts, and exposing a digital output to the person
the RPi high-speed ADC makes use of two interleaved AD9200, clocked with the RPi, which reads at 11Msps, resulting in an efficient 22Msps acquisition pace (bottleneck being the RPi copying the ADC values by the GPIOs register to RAM). The alerts may be learn as is (eg in case of analog enveloppe detection) or offset by Vref/2 (to accumulate the uncooked sign). Because of the GPIO essential to run the modules, we’re left with 2×9 GPIO left, leading to a 22Msps, 9 bit ADC. One or two logic alerts can additionaly be sampled – for an exterior motor corridor sensor for instance.

A modular method was chosen to make sure that every key part contained in the ultrasound picture processing can simply get replaced and in contrast with one other module. Every digital module takes the place of a operate within the sign processing chain or permits tapping into the totally different alerts circulating between the blocks.

Earlier experiments have been carried out, to get pictures utilizing totally different digital acquisition programs, resembling a bitscope, a STM32, or a high-speed ADC for beaglebone. The Raspberry Pi was retained ultimately for its ease of use, its value, and neighborhood engaged on it – growing the potential attain of the undertaking.

Meeting information

Required supplies

A pulser board – to generate the excessive voltage pulse to make use of the transducer
An analog front end – to amplify the weak alerts generated by the echoes
an ADC cape – a customized made 11Msps to 22Msps ADC pHAT for Raspberries.
a Raspberry Pi, 0 or W to handle every little thing
the motherboard, v2 – to attach the totally different modules collectively
and a few extras resembling headers, jumpers, and a smallish OLED display screen

For the transducer, one can use both a ATL mechanical probe for instance, or a piezo + servo setup, to mechanically scan the medium to be imaged

Disclaimers

Disclaimer #0: This isn’t a medical ultrasound scanner! It is a growth equipment that can be utilized for pedagogical and educational functions – doable speedy use as a non-destructive testing (NDT) instrument, for instance in metallurgical crack evaluation. As in all electronics, be careful.
Disclaimer #1: although an engineer, this undertaking is the primary of its type, I by no means did one thing associated. It is all however a finalized product.
Disclaimer #2: Ultrasound raises questions. In case you construct a scanner, use warning and good sense!

Basic rules of ultrasound imaging

Utilizing echoes to map interfaces

Medical ultrasound relies on using excessive frequency sound to assist within the prognosis and therapy of sufferers. Ultrasound frequencies vary from 2 MHz to roughly 15 MHz, though even greater frequencies could also be utilized in some conditions.

The ultrasound beam originates from mechanical oscillations of quite a few crystals in a transducer, that are excited by electrical pulses (piezoelectric impact). The transducer converts one kind of power into one other (electrical <–> mechanical/sound).

The ultrasound waves (pulses of sound) are despatched from the transducer, propagate by totally different tissues, after which return to the transducer as mirrored echoes when crossing an interface. The returned echoes are transformed again into electrical impulses by the transducer crystals and are additional processed – largely to extract the enveloppe of the sign, a course of that transforms {the electrical} sign in a picture – to be able to kind the ultrasound picture offered on the display screen.

Ultrasound waves are mirrored on the surfaces between the tissues of various density, the reflection being proportional to the distinction in impedance. If the distinction in density is elevated, the proportion of mirrored sound is elevated and the proportion of transmitted sound is proportionately decreased.

If the distinction in tissue density could be very totally different, then sound is totally mirrored, leading to complete acoustic shadowing. Acoustic shadowing is current behind bones, calculi (stones in kidneys, gallbladder, and so on.) and air (intestinal fuel). Echoes aren’t produced alternatively if there isn’t any distinction in a tissue or between tissues. Homogenous fluids like blood, bile, urine, contents of easy cysts, ascites and pleural effusion are seen as echo-free constructions.

Making a 2D picture

If the method is repeated with the probe sweeping the realm to picture, one can construct a 2D picture. In follow, within the setups we’ll be discussing, this sweep is completed with a transducer coupled to a servo, or utilizing a probe that has an built-in motor to create the sweep.

Experiments

What may be carried out with this {hardware}?

This dev equipment has been developped for pedagogical functions, to grasp how ultrasound imaging and non-desctrucive testing work. This construction can be utilized to develop:

different modalities of ultrasound imaging – and be used as a platform for A-mode, or B-mode imaging;
it will also be used for array imaging – the modules can be utilized with a multiplexer for do artificial aperture beamforming;
new sign processing strategies;
check transducers – which can be utilized as nicely for upkeep and repairs of ultrasound probes;
different non-destructive testing equipment.

Why are you doing this ? or in addition to pedagogical makes use of of your prototype, we wish to know in case you are interested by different purposes ? The place your prototype may be extra helpful? In Africa for instance, can your prototype resolve some issues?

Benchmark of acquisition

The primary acquisition, used as a reference, is thru the ADCs of a STM32F205 (feather WICED) – reaching a whooping 1.7Msps (did not grasp the interleaved mode..). Even at these speeds, one can see some options of an ultrasound picture, on a wire-phantom. Nonetheless, decision is not that nice, let’s examine if that may be improved?

The Raspberry Pi experiment setup

It may be famous that the ADC used within the experiments beneath is working at half its acquisition pace, as a consequence of a blunder – soldering two pins of the second ADC collectively. Nonetheless, the 9-bit, 11Msps ADC works comparatively nicely to analyse the uncooked sign in addition to the enveloppe.

It is a image from a first test with all customized made modules, together with raspberry ADC.

The picture is created from a wire phantom, based mostly on a stripboard with a 2.54mm pitch. Wire phantoms are sometimes used as calibration units, and to evaluate the lateral and axial decision of a sensor.

Prices of the supplies

Raspberry Dev Equipment

Utilizing a less complicated linux-enabled controler (the omnipotent Pi in its RPi 0 or Pi W) for the dev equipment. Price of supplies goals at being as little as doable, beneath the five hundred$.

Merely the servo and transducer module (cletus) — get for 80$ (The place? Recycling a transducer from ebay, servo from wherever (Amazon?))
The Pi Coronary heart of the echOmods (tomtom) — get for 10$ (The place? Get the Pi W from plenty of sources)
Utilizing a twin ADC raspberry pHAT for 20Msps+ acquisition (elmo) — get for 99$ (The place? OSHPark, MacroFab, Tindie)
Goblin: a TGC-Envelop-ADC module (goblin) — get for 149$ (The place? Customized made, get the Gerbers, or buy it preassembled on Tindie, or contact @kelu124)
Tobo: the HV-pulser (tobo) — get for 120$ (The place? Customized made, get the Gerbers, buy it preassembled on tindie or contact @kelu124)

Whole price of the set: 458$

Some outcomes: alerts and pictures

I am getting comparable pictures utilizing the analog enveloppe detection (acquired by the DAQ, by a monitor uncovered on the Analog Processing Module), in comparison with the digital enveloppe detection, as described beneath, once more on the wire phantom:

The identical process was utilized to accumulate the enveloppe created by the analog enveloppe detection, uncovered on the Analog Processing Module:

Plugging the Pi to an present probe

A beaglebone black had been used with its high-speed DAQ to be linked to an present mechanical probe, with some results. The subsequent step has been to interface the Pi to this probe by the 24Msps Pi ADC pHAT, to see if one can get the identical high quality of picture, and produce a ultrasound loop. The setup appears to be like as beneath:

It produced ultimately truly good pictures:

together with particulars of the processing chain (see the work jupyter notebook):

Classes on the way in which

Begin with widespread parts and modules: I had been fairly presumptuous to try to create one thing from scratch. Do your homeworks, evaluate
Modular design is the way in which to go. Discussing in numerous communities, there are solely so many designs that did not fail within the first time. Make modules out of your designs, in order that if one half fails, you are not left with nothing however a brand new bill from the PCBA.
Share: the world of open-source is superior. There are many good concepts round, and folks haven’t got the time to implement them. There are different individuals who wish to implement stuff. Merge the 2. Get pleasure from!
Do what you want: do not do what you do not like. Discover help – even when it is PCBA – on your designs. Typically, it is good to depend on professionals to do your designs cleanly. Or possibly somebody might be blissful to evaluate the designs. It does rely.
Doc: a simple factor to say.. nevertheless it needs to be repeated. Do not hesitate to make use of/make instruments to help this quest, it makes your life soooo a lot simple. All of this gitbook is generated on the fly – my rule of thumb is: Do not write something twice.

What’s subsequent?

On a {hardware} aspect:

The pulser-module design makes use of solely two inputs and one excessive voltage supply. Nonetheless, the chip permits extra advanced makes use of as a pulser, which may be additional explored.
A multiplexer module can be utilized, to interface this single channel equipment with an array probe. Doing this is able to allow to do artificial aperture imaging, and to characterize as nicely every factor within the array.
A complete area left unexplored to date is that of the transducer. As the important thing sensor within the equipment, it could be attention-grabbing to discover related applied sciences to develop an open and accessible transducer.
Fairly curiously, I might like to merge all modules as soon as once more on one RaspberryPi3-compatible hat. I would like nonetheless to chop some prices on the pulser aspect and enhance its robustness.

On a software program aspect:

The Raspberry Pi can be utilized a bit extra. From a software program viewpoint, the modules might be wirelessly managed, leveraging the present wi-fi communication channel, in order that researchers can use a single unit for a laboratory, managed from private computer systems.
The pictures will have to be saved in a DICOM-compatible format.

On the OSH aspect undertaking – the contribution of a instrument to the neighborhood:

A marketing campaign ought to begin quickly to make the ADC accessible. It appears there is a demand for top pace DAQ there. Simply want to substantiate the PCBA.