Echo Physics Flashcards
What is the definition of strain?
The change in distance between individual speckles in the myocardium
What are the three types of strain and what do they measure?
Longitudinal: measures how the myocardium becomes longer/shorter in the long axis
Radial: measures how the myocardium gets thicker or thinner in the short axis
Circumferential: measures how the circumference of the heart gets larger or smaller
What is the definition of power in ultrasound?
What is the definition of intensity in ultrasound?
Power= amplitude squared Intensity= power per area (watts/cm2)
Describe features of TDI (tissue doppler imaging) in terms of amplitude and velocity
in tissue doppler the signals are higher amplitude and lower velocity whereas in blood doppler imaging amplitude is lower with higher frequency/lower wavelength and higher velocity signals (think of a whale vs dolphin)
as a result, gain settings and power output can be lower
what is the temporal resolution of M-mode vs 2D echo?
1000Hz for M-mode; 100Hz for 2D echo
what is considered low mechanical index
low MI= 0.3 or less
what are the three different ultrasound enhancing agents and what materials are they made of?
Optison= shell made of human serum albumin, octafluoropropane (perflutren) gas Definity= phospholipid shell, octafluoropropane (perflutren) gas Lumason= phospholipid shell, sulfur hexafluoride gas
what variables determine the mechanical index?
mechanical index= peak negative pressure / square root of the transmit frequency (in MHz)
what is considered a high myocardial index
high MI= 0.8 or greater
what is spatial pulse length and how does it influence resolution (i.e. what kind of resolution and how does it impact the resolution)?
spatial pulse length is the length in space of a single pulse (i.e. the wavelength x number of cycles in the pulse); smaller spatial pulse length causes higher axial resolution
