AVR Freaks

they do not. They just put it at your body and see what picture is there. As all the organs have somewhat of a special response to the ping they can build a picture, that is all they go by.

Interesting topic.

Just this month at our ER Doc staff meeting we had a vendor bring in their newest, latest and greatest, ultrasound machine for a demo. 

It costs about $50,000 base price, but I don't recall which probes that included.

Disclaimer: As an old timer, I rarely perform ultrasound myself.  I often order a formal ultrasound study, which is then performed by an ultrasound tech, and is read (interpreted) by a radiologist.  examples might be to examine a patient's heart, wall thickness and motion, and heart valve function; or look at an aorta, (the big blood vessel coming off the heart and supplying blood to the rest of the body), to see if it has an aneurysm, (weak bulging spot in the wall), or a dissection, (a tear within the layers that make up the wall); or an OB scan to see the fetus, (size, development, fetal heart activity,...), or a patient's leg to see if there is a blood clot, (DVT), in the leg; or their eye, (to see if the retina is detaching, etc), or to locate large blood vessels for putting in a "central line", (a really big IV catheter), or to scan the patient's abdomen for blood swishing around inside from a leak somewhere from trauma; or rather frequently to check their gall bladder for gall stones; etc.  The list goes on and on. 

My younger partners learned how to perform many of these ultrasound scans, and interpret them, during their training as an intern and as a resident.  I learned a little of it over the years, but am clearly nowhere near as proficient at it as "the kids".  I'll use the ultrasound for trauma exams when I work on the helicopter, but in the ER I usually rely on the ultrasonographer.

When I think of US in electronics I'm usually thinking of 20 or 40 KHz frequency transducers for ranging or motion detection.  Things like robots tracking parallel to a wall or avoiding an obstacle in front of them, or measuring how full a container is as it is filled, or burglar alarms, etc., all come to mind.

Marine usage for depth finders and submarine locating also use sonar, which is essentially ultrasound in a water medium.

Medical ultrasound is typically performed at 1 - 20 MHz, as an old school engineer I tend to think of that as R.F., not ultrasound...

A single transducer, pencil like probe, can be used to listen to a fetus's heart rate by listening to the doppler shift of the returning ping signals due to the motion of the baby's heart.  The "envelope" of the frequency shift is played through a speaker and one can hear a whoosh, whoosh, ... with each heart beat.  That is perhaps the simplest medical ultrasound device and usage.

One can purchase a fetal heart rate doppler ultrasound these days in stores for ~ $20 USD.

The "probes" come in different frequencies, and as single transducers and as arrays.  How the pings are send, received, and decoded is based upon what one is imaging.  In the old days there was B Mode and M Mode, now days there are too many "Modes" for me to keep up with.

Pretend that the US "beam" was a single, narrow, line/ray/laser beam.

Aim it through one's chest at the patient's heart, for example.

Send a single ping, (for example).

As the US wavefront travels through the body some of the energy is reflected back at every tissue interface, (different tissue density).  So the beam goes through the skin, and hits a chest wall muscle.  Some energy keeps going through the muscle, some is reflected back.  Far side of the muscle it hits some more "soft tissue".  Again, some goes through it, some is reflected back at the interface. It hits the surface of your heart, some is reflected back, some keeps going forward.  It hits the inner chamber of the heart, full of blood, again some is reflected back.  It hits a thin heart valve leaflet, some is reflected back, it hits the back wall of the heart muscle, then more soft tissue, then your back muscles, then your back's skin...

Over time, following the ping, one receives the various reflected pulses.  For a robot looking for an obstacle it is a binary decision, either there is a returned signal within X meters in the front of the robot, or there isn't.   For our patient, above, there are a bunch of reflected signals, all of them important.

If one aims the beam at the patient's heart valve, and plots the return signals as a function of time, across the screen, (penetration depth on the vertical axis, time on the horizontal axis), one sees a bunch of lines across the screen.  Each line is a reflection from the US energy hitting a different tissue.  The vertical axis is time or depth or distance the ping traveled.  So I see nice stationary lines at different depths, and can see how thick your skin is, how thick your muscle layer is, how think your heart wall is...

Down near the bottom of the screen I see a saw tooth waveform across the screen.   That means that the distance from the probe was changing, nearer-farther, back and forth, over time.  That thin line is your heart valve's leaflet, moving back and forth as the valve opens and closes with each heart beat.

Still with me?  This is a lot easier to explain to someone with a probe in hand, and an image in front of you...

Now let's step it up a notch.  Instead of one transducer element, let's have an array, so I can see the reflections along a beam from multiple "parallel" beams, simultaneously.  Now instead of a 1-D image vs Time, display I can have a 2-D image vs time display, and I can see a lot more information in the image.  (2-D, I see depth into tissue and tissue reflections along one axis, (each beam), and I see the second axis as the stack up of parallel beams, now giving me a 2_D image, or a 'Plane", i.e. a cross sectional cut.  Time is an additional dimension.)

Now I use my wrist to orient the linear array's beams so that they slice through the patient's body at just the right orientation in 3-D space to visualize what I want to see, (your gall bladder, your appendix, your heart, ...).  Recall that the beams are not narrow like a laser beam, but they are still pretty narrow, and I am essentially visualizing "planes", slices through the patient's body.

So cool, especially to see it in action, rather than listen to my description of it.

Now add color to the Doppler shift and I can see the velocity and direction of the blood flowing through your heart value.  Does the valve work, or is it leaking backflow of blood when it is supposed to be closed?

If I am looking at your forearm, trying to find a vein in which to start an iv, I can see the round cross sections of arteries and veins, as their walls, and the blood within them, are different acoustic densities than the soft tissue in which they lie.  Both look like round circles in cross section.  How do I know which is the artery, which I (usually) want to avoid, and the vein, which I'm looking for?  If I now gently press the transducer against the skin then the low pressure, soft walled, vein collapses and flattens out.  The high pressure, muscularly walled artery maintains its circular cross section.  Easy.

Now I can use my wrist to rotate the transducer array 90-ish degrees an instead of seeing the vein in cross section, I can see the pipe running lengthwise through your arm.

There are now many different scanning "Modes", and image reconstruction techniques, all designed to optimize obtaining certain information.  An ultrasonographer doing a formal heart US might take an hour of waving the probe over your chest, aiming the beam at certain parts of your heart, in certain angles, and with different scanning modes, to obtain all of the images and data needed for the formal echocardiogram report.  When I do a trauma "FAST" exam, looking at about 4 items, it takes < 1 minute to do the procedure.

The coolest development in US, in my opinion, is 3-D obstetric ultrasounds.  One can generate a 3-D appearing image of the fetus.  Totally useless for me in the ER, and our new $50K+ machines can't even generate one of these images, but still so cool to look at.  Google 3D fetal ultrasound, then click on images, to see a bunch of baby ultrasound images, all generated with "sound" waves and echo data analysis.  This makes "The Hunt for Red October" sonar look like the dark ages of crystal radios.

Wiki Medical Ultrasound has a very cool photo of an US video image of a heart showing the four chambers of the heart and two of the four valves, with their leaflets opening and closing.

I should have just referred to this page image and not tried to write my own comments!

Oh well, hopefully that helps a little bit.

JC, ER Doc, but definitely NOT an ultrasound expert! 

Edit: typo

"Give me a ping, Vasili. One ping only, please."

Thanks Bill, I got my daily Dave injection. One can never stop there, so that's a couple of hours I'm never getting back :)

It's interesting how expectations have changed. For something of that complexity, cost and production quantity, having field mods is expected. Most of the 'fixes' these days are software updates. These could incorporate new fpga bitstreams or workarounds for silicon errors along with bug fixes/enhancements for the code itself. Thus the 'fixes' are invisible.