Doppler Ultrasonography - Science topic

From one of the best group in the field :

That is so general question which will lead you to get more general answer. Being more specific would help a lot. Understanding the source of the problem is the first step you can do. Then having some ideas about how does it influence the ultrasound probe? If you say that it is the LED source causing this problem, try to cover it!! ;)

The left hepatic vein can sometimes be harder to profile if the liver is echogenic and the patient is large. But no difference in the middle and right that I am aware of.

Hi. Do you use artificial intelligence for this measure?

Please remember that continuous wave ultrasound at the focal point of a transducer in a fluid medium like tissue culture or flask can generate fluid streaming and depending on the conditions cavitation which can be locally destructive. This is not relevant to pulsed wave ultrasound used medically for diagnostic studies in intact bodies. 

Federico,

If you are interested in flow volume, yes, the systolic diameter is the significant one, as most of flow occurs during the systolic phase. Accurate absolute flow volume, however, is rarely of clinical interest: person-to-person variation, as well as the impedance of the vasculature, varies so much that there is no "correct" volume flow like 37C for temperature. What is generally clinically significant are  gross changes, e.g. no flow indicating a blockage, or high flow indicating a hemorrhage, or relative changes, e.g. change in cerebral flow while holding your breath.

Various methods have been proposed for determining the lumen. One method that is appealing to engineers, is to use a narrow beam, and then a beam wide enough to ensure full insonation of the vessel, and look at the difference in backscattered energy at the same distance (so the attenuation is the same); if you know the diameter of the narrow beam, the ratio of the wide to narrow backscatter energy times the diameter of the narrow beam gives the lumen cross-section. (To do this right you must take into account the non-uniformities of the beams, so its not so simple -- or often used.)

See David Evans's publications for real expertise in this and other areas of transcranial Doppler measurements.

Regards,

David

Since the kidneys are retroperitoneal structures, air will stay anterior to them and they will be visible from a posterior approach without reverberation artefacts. You willl obviously not be able to use an anterior or lateral approach.

Several good answers here.  For a minimal TOF measurement in a fluid you need to have several (more than 2-3) wavelengths  of travel in the fluid, though with correlation you can improve this at the expense of more complex signal processing.  if the tube bore is too small to permit this, then you must position the transducers such that beam reflections are used between the transmitter and receiver, i.e. single reflection V path, 3 reflection W path.   The transducer design is really important in all this.   The main points are

1. ensure a single mode (mentioned above) is transmitted into the pipe wall.   When an acoustic pulse encounters an interface between two materials of different acoustic impedance (plastic vs steel for example) refraction occurs which bends the path according to Snells law.  What also happens is that two or more vibrational modes are generated.   Most commonly a longitudinal wave (vibration along axis of propagation) will create a Shear wave (vibration perp to axis of propagation).  these wave travel at different sound velocities and can arrive at your receiver in overlapping fashion, corrupting the measurement.   With knowledge of the material properties of the pipe and transducer you can select a transducer angle that will produce only a shear wave.  this works by using a steep enough angle to exceed the critical angle of the LONG wave.   there is a calculator for this here:   http://alturl.com/qpsw9

2.  You also need to ensure sufficient energy is coupled into the pipe wall.  This means the acoustic impedance of the transducer facing material (matching layers or delay line) has a sound speed very close to the pipe material.  if not, then most of the energy will be reflected instead of transmitted at both the receive and transmit sides of the system.  

3.  You want a narrow unfocused beam so that the energy goes where you want.  a small crystal is a bad choice.  A point source is completely omnidirectional while a large surface is completely directional.  so you need to use the largest crustal that is practical for the geometries you are working with.   It is not uncommon to see 3-4" diameter transducers used in large pipeline applications for example.

4.  If you are doing time domain processing, a simple envelope detector (precision rectifier followed by an integrator) can be fed into a PLL along with the transmit (reference) signal to generate the TOF error voltage.  from there it is trivial to measure the voltage and convert it to flow.

If you are attempting to build a general purpose instrument that can handle multiple pipe sizes, fluid types, etc the complexity goes up from here.   These are just the basics required.

Dear Ehab,

I just wanted to add

duplex uses pulsed wave Doppler techniques

one single elements transmits the US wave and receives it

in contrary to continuous wave Doppler

here you have to 2 elements 

one is sending - one receiving

Doppler was from Austria and described the Doppler effect in 1843 in prag

New US systems use Duplex only

color, power or spectral wave Doppler

best regards

ferdinand

All you can do with a single element transducer is generate shear waves near the focus.  You would need a second transducer to track the shear wave and calculate displacement/speed.  The Olympus transducer at 2.2 MPa should be fine for generating shear waves (use ~1 ms pulse duration at a low duty cycle). A phased array can be used to both generate and track shear waves. 

Hi...I am not sure if it will help you a bit....However, I can suggest you two websites with some US images of the breast, though they do not provide a real database: http://www.medison.ru/uzi/eng/all/mammography.htm