Ultrasound Theory waves+medical use

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18 Terms

1
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What kind of waves are ultrasounds?

  • nonionizing

  • Mechanical waves (produce deformation of material thru contact forces)- results in perturbation (atoms shifted)

2
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What is mechanical wave stress?

The force that acts per a unit of area, indicates how intense the force acting on each atom will be

  • Parallel application (normal)

  • Perpendicular (shear)

  • Shortens bonds- compressive

  • Lengthen bonds- tensile

<p>The force that acts per a unit of area, indicates how intense the force acting on each atom will be</p><ul><li><p>Parallel application (normal)</p></li><li><p>Perpendicular (shear)</p></li><li><p>Shortens bonds- compressive</p></li><li><p>Lengthen bonds- tensile</p></li></ul><p></p>
3
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What are the processes referred to when the stresses are small?

The deformation is proportional to the stress and so is considered an elastic process— if stress is large, it can results in deformation or fracture.

4
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Explain transverse wave as a type of mechanical wave

Perturbations in X or Y axis result in oscillations in perpendicular direction (Z)- hence transverse waves are shear waves

<p>Perturbations in X or Y axis result in oscillations in perpendicular direction (Z)- hence transverse waves are shear waves</p><p></p>
5
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Explain longitudinal wave as a type of mechanical wave

Result due to pertrubation on Z axis, oscillation occurs same direction in which wave advances, hence they are waves of compression and tension (normal)

<p>Result due to pertrubation on Z axis, oscillation occurs same direction in which wave advances, hence they are waves of compression and tension (normal)</p><p></p>
6
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What are the sounds frequency categories?

  • infrasound: less than 20 Hz

  • Sound: between 20Hz and 20KHz

  • Ultrasounds: greater than 20 KHz

7
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How are US waves used for medical purposes?

Diagnosis: Waves reflected by interior of body are registered and observed (piezoelectric crystal in device transmits its vibration to the mediums around it when subjected to voltage- it is called a transducer and acts as a source and reciever for waves)- echo reflected back is interpreted and creates image

Treatment:

  • lithotripsy-generate pressure waves and sear waves in kidney stones to break them into smaller parts

  • high-intenisty ultrasound (HIFU)- possible to destroy certain brain cells responsible for tremblinng in Parkinson’s disease.

8
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Explain the echo grayscale for ultrasound

White/bright lines=big echo (echogenic), max intensity—inhomogenous materials like bones, calcium, metal(high attenuation+absorption)

Gray= solid tissues (intermediate attenuation)

Dark/black lines=no or almost no echo (an-echoic or non-echogenic)—fluids and air filled cavities (low attenuation+absorption)

9
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<p>What is teh ultrasound doppler effect?</p>

What is teh ultrasound doppler effect?

When ambulance is still and it generates a siren sound the sound propagates equally all aorund it, but when ambulance begins to move the sound becomes clustered in the front of the ambulance and expands near the back, hence the pitch chnages at the different locations— this can also be applied to red blood cells reflecting US waves moving thru the bloodstream, the velocity of these RBCs can be calculated by using the frequency of the reflected wave.. hence the equation in the image below can be used:

<p>When ambulance is still and it generates a siren sound the sound propagates equally all aorund it, but when ambulance begins to move the sound becomes clustered in the front of the ambulance and expands near the back, hence the pitch chnages at the different locations— this can also be applied to red blood cells reflecting US waves moving thru the bloodstream, the velocity of these RBCs can be calculated by using the frequency of the reflected wave.. hence the equation in the image below can be used:</p><p></p>
10
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What is ultrasound doppler displacement?

Using the logic from the doppler effect with RBC, the angle at which the US waves hit and are therefore reflected back can be viewed in time to get a doppler shift that is eiether negative of positive, telling whether they are moving aaway(negative) or towrads(positive) the transducer

<p>Using the logic from the doppler effect with RBC, the angle at which the US waves hit and are therefore reflected back can be viewed in time to get a doppler shift that is eiether negative of positive, telling whether they are moving aaway(negative) or towrads(positive) the transducer</p><p></p>
11
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What is the thermal index (TI)

Energy being absorbed by tissue- increasing temperature

TI reflects the power absorbed in a specific tissue ccompraed to the power needed to increase 1Cº of that specific tissue- the ratio has t be smaller than one in order for the temperature increase to be safe

12
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What is the Mechanical index (MI)?

If the US oscillates too lowly it can produce something that will locally increase the pressure (bubbles) dangerous in the body- causing a spontaneous change from vapour to liquid phase wheen pressure falls below Pvapour (this is called cavitation)))- the mechanical index is defined by the equation in the image. It is proportional to peak negative prssure p= and hence local pressure— MI has to be lower than 1.9

<p>If the US oscillates too lowly it can produce something that will locally increase the pressure (bubbles) dangerous in the body- causing a spontaneous change from vapour to liquid phase wheen pressure falls below Pvapour (this is called cavitation)))- the mechanical index is defined by the equation in the image. It is proportional to peak negative prssure p= and hence local pressure— MI has to be lower than 1.9</p><p></p>
13
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What equipment is required for US

  • Transducer/probe containing piezoelectric quartz crystal

    • Curvilinear: used to check abdomen, low frequencies, more pentrance, less resolution

    • Linear: used to see superficial structures like skin, high frequency, lower penetrance, higher resolution

  • Patient contact required

  • Connecter/cable to US machine

  • Images seen on monitor in real time

14
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What is posterior acoustic shadowing and what is posterior acoustic enhancement?

Shadowing occurs when there is a region that doenst le US go thruCalci in kidney and gallbladder cause posterior acoustic shadowing, hepatic cyst (cystic structure typically fillled with liquid) shows posterior acoustic enhancement.

<p>Shadowing occurs when there is a region that doenst le US go thruCalci in kidney and gallbladder cause posterior acoustic shadowing, hepatic cyst (cystic structure typically fillled with liquid) shows posterior acoustic enhancement.</p>
15
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Doppler effecr usage in imaging explain

Can be used to determine blood movement and when color is added to blood moving towards or away from transducer, the imaging can be helpful:

<p>Can be used to determine blood movement and when color is added to blood moving towards or away from transducer, the imaging can be helpful:</p>
16
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What is power doppler?

Checks vasculature, only to see movement, not direction

<p>Checks vasculature, only to see movement, not direction</p>
17
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What is a pulsed doppler

Allows to quntify velocity and determine flow direction.. towards tranducer (posittive velocity) away (negative).

<p>Allows to quntify velocity and determine flow direction.. towards tranducer (posittive velocity) away (negative).</p><p></p>
18
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What are the advantages and limitations of US?

Adavantges:

  • no ionizing radiation

  • Protable, fast

  • In real time

  • Gives guidance for invasive procedures

  • Many perspective+angles

  • Cheap

Limitations:

  • operator needs experience

  • Csnnot penetrate bone or air filled structures

  • Limited in patients with obesity (low penetration)