Ch 1 Intro Flashcards
How many kHz is u/s?
Above 20 kHz (higher than humans can hear)
What is u/s?
-Non invasive way of looking inside human body
-2D/3D anatomic + flow imaging uses u/s
U/s is accomplished by using what technique?
Pulse-echo technique
What is the pulse-echo technique?
-Pulses of sound get sent into the tissues
-Echoes returning from the tissues provide anatomic info
How many pulses per scan line with the pulse-echo technique?
1 pulse = 1 scan line
(therefore, multiple scan lines are used to create an image)
Once the u/s instrument processes the returning echoes, how will it present them?
As visible dots, which form the anatomic image
Are all of the u/s pulses reflected back?
No - most of the original pulses continue on to be reflected from deeper structures
The brightness of the dot corresponds to what?
Echo strength (based on medium acoustic impedance)
The location of the dot corresponds to what?
The echo return time
Strengths of the reflected + transmitted pulses are determined by what?
The impedances of the 2 mediums at the boundary
Explain the variables in the acoustic impedance formula: Z = p x c
Z: acoustic impedance
p: density of medium
c: velocity
(measured in Rayls)
List the 3 types of 2D scan formats?
-Linear
-Sector (phased)
-Combination (curvilinear)
List 4 things about the linear format?
-Closely spaced parallel vertical scan lines
-Pulses travel in same direction
-Different starting points for each subsequent pulse
-Produces rectangular display
List 3 things about the sector format?
-Slice of pie display
-Each pulse originates from same starting point
-Subsequent pulses go out in slightly different directions
List 3 things about the combination (sector + linear) format?
-Pulses originate from different starting points (linear)
-Each pulse travels in a slightly different direction from the previous pulse (sector)
-Curved display
What is volume imaging?
3D imaging:
-Where 3D echo data is acquired by many 2D sections of echo info
-Then forms a 3D volume of data
What is the doppler effect?
Change in frequency of sound waves due to a moving object
What is the doppler effect used to detect in u/s?
Tissue motion
What does the doppler effect measure in u/s?
The velocity + direction of blood flow (RBCs) within vessels + the heart
What 3 forms is doppler info presentable in?
-Audible
-CD
-Spectral doppler
What does CD detect?
Direction of blood flow
What is CD?
A color coded presentation of doppler info superimposed on grey scale images
What does spectral doppler calculate?
Flow velocity data
What 2 places is spectral doppler info applied to?
-To loudspeakers for audible evaluation
-To spectral displays for quantitative analysis
2 types of spectral doppler?
-PW (pulse wave)
-CW (continuous wave)
Differentiate PW + CW doppler?
PW: samples RBC movement + direction at a SPECIFIC location (spectral window)
CW: continuously transmits + receives u/s waves to detect higher flow velocities along ENTIRE cursor line (no spectral window)
What is power doppler used for?
-To display low flow velocities
-Superior in detecting the presence OR absence of flow
(can NOT determine direction of blood flow)
What is acoustic impedance?
-It describes how much resistance an u/s beam encounters as it passes through a tissue
-Determines how much of the sending sound beam is reflected back into the 1st medium + how much is transmitted into 2nd medium
The greater or smaller the difference in acoustic impedance’s will result in stronger echoes?
Greater - producing higher % of reflection too
