Echo Basics (M mode, Chamber Assessment, Systolic Function...)

Question 1

Afterload

Answer 1

The force that opposes LV ejection

Question 2

Preload

Answer 2

The force that acts to stretch the myocardial fibers at end diastole and is related to end diastolic volume

Question 3

What conditions cause paradoxical (rightward) motion of the septum in early systole?

Answer 3

-RV volume overload
-LBBB

Question 4

What is the benefit of M mode?

Answer 4

Higher temporal resolution (1000-200 frames per second vs 30-100 frames)

Question 5

What is the average velocity of sound in soft tissue?

Answer 5

1540 m/s

Question 6

Frequency

Answer 6

Number of waves/ sec (Hz)

Question 7

Wavelength

Answer 7

Distance between wave peaks or wave nadir

Question 8

Velocity (formula)

Answer 8

Velocity = frequency x wavelength

Question 9

What is the wavelength of 3 MHz frequency?

Answer 9

0.5mm in soft tissue

Question 10

Amplitude

Answer 10

Difference between maximum and minimum value of a wave

Question 11

Power

Answer 11

Total energy produced each second (W, watts)

Question 12

Intensity

Answer 12

Power / cross-sectional area (W/cm2)

Question 13

Decibel (dB)

Answer 13

10 log (I/Io)
I = measured intensity
Io = is defined as the reference intensity (may be maximum for that machine/probe)

Question 14

Mechanical index

Answer 14

-Measure of potential to produce cavitation (the formation of bubbles within a liquid)

Question 15

Acoustic impedance

Answer 15

-Product of density and velocity of sound (Z = pv)
-Poor transmission of sound from one medium to another if impedances differ significantly
-Interface between materials with dissimilar acoustic impedances reflect sound

Question 16

Specular reflection

Answer 16

-Structures > 1 wavelength
-Angle of reflection = angle of incidence
-Independent of frequency

Question 17

Diffuse reflection

Answer 17

-Specular reflection from an irregular surface
-Sound reflected in may directions

Question 18

Scattering

Answer 18

-Structures < 1 wavelength in diameter
-Omnidirectional
-Frequency dependent (up to fourth power of the frequency)

Question 19

Interference

Answer 19

Algebraic sum of the wave amplitude

Question 20

Speckle

Answer 20

Noise in ultrasound images produced by interference pattern from multiple small reflectors (scatters)

Question 21

Refraction

Answer 21

-Bending of wavefront as sound passes between media with differing propagation velocities
-Snell’s law

Question 22

Diffraction

Answer 22

-Spreading or divergence of a sound beam
-Greater with a smaller source

Question 23

Absorption

Answer 23

-Sound energy is converted to other forms of energy (mainly heat)
-Related to sound frequency, viscosity of medium, and relaxation time of medium

Question 24

Attenuation

Answer 24

-Loss of intensity as the sound wave passes through medium
-Summation of losses due to reflection, scattering, and absorption

Question 25

What is the expected attenuation in soft tissue?

Answer 25

0.5-1.0 dB/ cm/ MHz Ex: For 3MHz signal, assuming 1dB/cm/MHz attenuation -> Half (3dB) of the signal strength is lost for each cm of travel

Question 26

Resonance

Answer 26

Persistent oscillation produces continued ultrasound signal

Question 27

Piezoelectric crystal

Answer 27

-Vibrates with applied alternating current (most efficient when stimulated at its resonant frequency (determined by the crystal thickness) -Also generates current when vibrated -Functions as both transmitter and receiver

Question 28

Backing block

Answer 28

-Limits “ringing” of the crystal to create more discrete ultrasound pulse -Absorbs sound waves directed into transducer

Question 29

Quarter-wavelength Matching Layer

Answer 29

-Provides better acoustic impedance matching between crystal and skin -Significantly improves transmission of ultrasound into tissues and reduces heat at skin surface

Question 30

Narrow band width transducer (high Q factor)

Answer 30

-Crystal allowed to ring freely -More efficient (sensitive) Ex: Choir bell

Question 31

Wide bandwidth transducer (low Q factor)

Answer 31

-Wide range of frequencies sent and received -Short ultrasound pulses -Facilitates harmonic imaging Ex: Cowbell

Question 32

Continuous

Answer 32

-Separate send and receive transducers -CW Doppler

Question 33

Pulsed

Answer 33

-Single transducer alternately sends and receives -PW Doppler, Grayscale imaging, Colorflow imaging

Question 34

Pulse repetition period (PRP)

Answer 34

-Time between pulses -Directly related to the imaging depth

Question 35

Pulse repetition frequency (PRF)

Answer 35

-Inversely related to PRP -Inversely related to imaging depth

Question 36

Duty Factor

Answer 36

-Fraction of PRP that transducer is emitting sound Ex: CW Doppler =1, all pulsed techniques < 1 (usually 0.001 to 0.01)

Question 37

Temporal resolution

Answer 37

-Determined by the frame rate: number of frames/ second -Dependent on the imaging depth (13 used/cm, roundtrip) -Dependent on line density (typically 50-200 lines/frame)

Question 38

Frame rate

Answer 38

-Number of frames per second -Use of multiple beam formers increases frame rate

Question 39

Contrast Resolution

Answer 39

-Ability to discern ‘target’ from background -Dependent on intrinsic physical properties of target and surrounding tissue -Dependent on acquisition and display parameters: frequency, gain, compression, color, etc…

Question 40

Axial resolution

Answer 40

-Determined by spatial pulse length -Resolution = (cycles x wavelength) /2 -Better with higher frequencies, fewer cycles -Pulse length set by manufacturer for probe/frequency -Longer pulse used in harmonic imaging (better separation of fundamental and harmonic signal, slight degradation in axial resolution)

Question 41

Lateral resolution

Answer 41

-Better with narrower beam -Dependent on aperture, frequency (improved at higher frequencies) and focusing -Beam is narrowest at the focal point and diverges rapidly after focal point (poor lateral resolution in far field, especially with small aperture, low frequency, focusing)