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ultrasound imaging systems electronic assembly

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Model No:	ultrasound imaging systems pcb assembly

Country	CN
Payment Term	T/T

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Instrumentation medical devices ultrasound imaging systems
pcba assembly electronics oem contract manufacturing services OEM CEM EMS experience
company-China Shenzhen Topscom

 
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Medical ultrasound (also known as
diagnostic sonography or ultrasonography) is a diagnostic imaging technique
based on the application of ultrasound. It is used to see internal body
structures such as tendons, muscles, joints, vessels and internal organs. Its
aim is often to find a source of a disease or to exclude any pathology. The
practice of examining pregnant women using ultrasound is called obstetric
ultrasound, and is widely used.


 


Ultrasound is sound waves with frequencies
which are higher than those audible to humans (>20,000 Hz). Ultrasonic
images also known as sonograms are made by sending pulses of ultrasound into
tissue using a probe. The sound echoes off the tissue; with different tissues
reflecting varying degrees of sound. These echoes are recorded and displayed as
an image to the operator.


 


Many different types of images can be
formed using sonographic instruments. The most well-known type is a B-mode
image, which displays the acoustic impedance of a two-dimensional cross-section
of tissue. Other types of image can display blood flow, motion of tissue over
time, the location of blood, the presence of specific molecules, the stiffness
of tissue, or the anatomy of a three-dimensional region.


 


Compared to other prominent methods of
medical imaging, ultrasound has several advantages. It provides images in
real-time, it is portable and can be brought to the bedside, it is
substantially lower in cost, and it does not use harmful ionizing radiation.
Drawbacks of ultrasonography include various limits on its field of view
including patient cooperation and physique, difficulty imaging structures
behind bone and air, and its dependence on a skilled operator.


 


Doppler ultrasonography


Spectral Doppler scan of the common carotid
artery


 


Colour Doppler scan of the common carotid
artery


Sonography can be enhanced with Doppler
measurements, which employ the Doppler effect to assess whether structures
(usually blood)[16] are moving towards or away from the probe, and its relative
velocity. By calculating the frequency shift of a particular sample volume, for
example flow in an artery or a jet of blood flow over a heart valve, its speed
and direction can be determined and visualised. This is particularly useful in
cardiovascular studies (sonography of the vascular system and heart) and
essential in many areas such as determining reverse blood flow in the liver
vasculature in portal hypertension. The Doppler information is displayed
graphically using spectral Doppler, or as an image using color Doppler
(directional Doppler) or power Doppler (non directional Doppler). This Doppler
shift falls in the audible range and is often presented audibly using stereo
speakers: this produces a very distinctive, although synthetic, pulsating
sound.


 


All modern ultrasound scanners use pulsed
Doppler to measure velocity. Pulsed wave machines transmit and receive series
of pulses. The frequency shift of each pulse is ignored, however the relative
phase changes of the pulses are used to obtain the frequency shift (since
frequency is the rate of change of phase). The major advantages of pulsed
Doppler over continuous wave is that distance information is obtained (the time
between the transmitted and received pulses can be converted into a distance
with knowledge of the speed of sound) and gain correction is applied. The
disadvantage of pulsed Doppler is that the measurements can suffer from
aliasing. The terminology "Doppler ultrasound" or "Doppler
sonography", has been accepted to apply to both pulsed and continuous Doppler
systems despite the different mechanisms by which the velocity is measured.


 


It should be noted here that there are no
standards for the display of color Doppler. Some laboratories show arteries as
red and veins as blue, as medical illustrators usually show them, even though
some vessels may have portions flowing towards and portions flowing away from
the transducer. This results in the illogical appearance of a vessel being
partly a vein and partly an artery. Other laboratories use red to indicate flow
toward the transducer and blue away from the transducer. Still other
laboratories prefer to display the sonographic Doppler color map more in accord
with the prior published physics with the red shift representing longer waves
of echoes (scattered) from blood flowing away from the transducer; and with
blue representing the shorter waves of echoes reflecting from blood flowing
toward the transducer. Because of this confusion and lack of standards in the
various laboratories, the sonographer must understand the underlying acoustic
physics of color Doppler and the physiology of normal and abnormal blood flow
in the human body (see Red shift


 


Although Angiography and Venography which
both use X-ray and contrast injection material are more accurate than Doppler
Sonography, Doppler Sonography may be chosen because it is faster, less
expensive, and non-invasive.


 

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