Tuesday, May 3, 2016

Grey Scale

The amount of energy (pressure) reflected by the impedance mismatch at the interface determines the brightness or grey scale displayed on the image.

When the reflected pressure energy strikes the transducer crystals it deforms them and gets converted to an electrical pulse.  The imaging system then divides the pulse based on strength into different categories that get assigned different shades of grey.  The weaker the electrical signal the darker the shade of grey assigned to it.  The strongest portion of the signal gets the brightest (white) shade of grey assigned to it.

We can then use these different shades of grey to characterize tissue types such as blood, liver, muscle, etc:

Wednesday, April 13, 2016


Sound traveling through a medium with a uniform density and stiffness will continue to travel until it runs out of energy.  However when sound encounters an interface between two mediums with different impedance values some of the sound energy is reflected back and some of the energy passes through the interface.

The amount of energy that reflects and the amount that passes through the interface is determined by the difference in impedance values of the two mediums.  The greater the impedance mismatch the greater the amount of reflected energy.

A good example of this is gall stones.  Sound energy travels very well through both bile at about 1500 meters per second and calcified stones around 4000 meters per second because they are both very stiff and non compressible.  However the impedance mismatch between the bile and the stone is very high so all the sound energy is reflected at the leading edge of the interface and virtually none is passing through the interface.  Because there is no energy passing through the interface we see a shadow behind the stone.

Wednesday, April 6, 2016


Sound travels through a medium by compressing the molecules of the medium using the pressure created by the mechanical wave I discussed in the last post.  The amount of pressure created starts at the crystal in the transducer. 

When the crystal is exposed to an electrical impulse it reacts by getting thicker and thinner in a repetitive cycle ringing much like a tuning fork oscillates back and forth after being struck.  When the crystal thickens it transmits a wave of high pressure to the medium just like pressing on your arm with your finger, as it relaxes and gets thinner the pressure reduces.  This creates the typical sine wave used to represent sound waves. 

When the wave of high pressure enters the medium it compresses the medium and then the medium relaxes.  The medium and strength of the wave both determine how far the energy travels in the medium.

Monday, April 4, 2016

Back to basics physics

Lets start at the beginning, what is sound?

Sound is a series of pressure waves, these are sometimes described as mechanical waves.  To exist, a mechanical wave requires a medium to travel through. 

Stiffness and density are the two primary characteristics that determine how well a mechanical wave can travel through a medium. 

The ease or difficulty a medium presents to the passage of the mechanical wave is called impedance and determines the propagation speed.

The next post will discuss how sound propagates through a medium

Thursday, October 11, 2012

Sorry I have been gone so long

I have been very busy for awhile and not able to keep up with my writing.  I will try to do better.  I left off with a conversation about venous reflux going so I will use that to get started again with.

Stay tuned...TJ

Monday, July 18, 2011

Venous Reflux Testing

There have been many discussions on various websites regarding venous reflux testing.  One of the greatest areas of contention is the complexity of the exam and how long it should take.

I have worked with physicians that want to know one thing, is there treatable reflux or not.  Then there are the physicians that want every vessel, varicosity, and perforator investigated and documented.  Somewhere in the middle is an appropriate protocol for diagnosing relevant reflux while at the same time protecting the sonographer from repetitive motion injuries.  I know what works for my sonographers and my physicians and will post a protocol that I have had in place for over 10 years with good results.  However I would like to know how everyone else approaches the inherent challenges associated with this testing modality.

Also if there is interest I can post a worksheet I have developed that documents consistently and conveys the data clearly.  It is a compilation of worksheets from labs all over the country.

Wednesday, July 13, 2011

boundary waters june 2011

Got to spend a week in the Boundary waters of northern minnesota with my brother doing some fishing and just relaxing. Here are some of the pictures I took. I am still trying to identify the bird so if you have any idea what kind it is let me know.