Ambiguity in Doppler shift frequency information when true Doppler shift exceeds 1/2 pulse repetition frequency (PRF)
Color Doppler US
Approximates mean velocity and direction of flow within vessel or tissue through color coding, superimposing this color onto vessels in grayscale image
Color coding represents direction of flow in relation to transducer
By default, blood flow coming toward transducer is red
By default, blood flow going away from transducer is blue
Important to remember that color coding can be changed by user
Doppler effect
Frequency change of reflected sound based on movement of source of sound relative to receiver
Frequency perceived by receiver will be higher if source moving toward receiver
Frequency perceived by receiver will be lower if source moving away from receiver
Differences in transmitted vs. perceived frequencies from blood scatters can be used to quantify direction, magnitude, or intensity of blood flow
Doppler shift: Difference between transmitting and reflected frequency emitted from transducer
Defined as ΔF = 2F₀V cos Ø/c
ΔF is Doppler shift
F₀ is transmit frequency
V is velocity of blood flow
Ø is angle of incidence between US beam and direction of blood flow
c is speed of sound in tissue
Notice that Doppler shift is highly dependent on angle of incidence and can be maximized with Ø = 0° or minimized with Ø = 90°
PRF
Number of pulses of US occurring in 1 second
IMAGING ANATOMY
Anatomic Considerations
Vascular Variations Visible on Color Doppler
Physical Considerations
CLINICAL IMPLICATIONS
Clinical Importance
DIAGNOSTIC CHECKLIST
Selected References
Jenssen C et al: [Ultrasound artifacts and their diagnostic significance in internal medicine and gastroenterology - part 2: color and spectral Doppler artifacts.] Z Gastroenterol. 54(6):569-78, 2016
Rubens DJ et al: Doppler artifacts and pitfalls. Radiol Clin North Am. 44(6):805-35, 2006
Wells PN: Ultrasound imaging. Phys Med Biol. 51(13):R83-98, 2006
Kremkau FW: Doppler color imaging. Principles and instrumentation. Clin Diagn Ultrasound. 27:7-60, 1992
Related Anatomy
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Related Differential Diagnoses
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References
Tables
Tables
KEY FACTS
Terminology
Anatomy Imaging Issues
Physiology
Basic Imaging Considerations
TERMINOLOGY
Synonyms
Color flow imaging (CFI)
Definitions
Aliasing
Ambiguity in Doppler shift frequency information when true Doppler shift exceeds 1/2 pulse repetition frequency (PRF)
Color Doppler US
Approximates mean velocity and direction of flow within vessel or tissue through color coding, superimposing this color onto vessels in grayscale image
Color coding represents direction of flow in relation to transducer
By default, blood flow coming toward transducer is red
By default, blood flow going away from transducer is blue
Important to remember that color coding can be changed by user
Doppler effect
Frequency change of reflected sound based on movement of source of sound relative to receiver
Frequency perceived by receiver will be higher if source moving toward receiver
Frequency perceived by receiver will be lower if source moving away from receiver
Differences in transmitted vs. perceived frequencies from blood scatters can be used to quantify direction, magnitude, or intensity of blood flow
Doppler shift: Difference between transmitting and reflected frequency emitted from transducer
Defined as ΔF = 2F₀V cos Ø/c
ΔF is Doppler shift
F₀ is transmit frequency
V is velocity of blood flow
Ø is angle of incidence between US beam and direction of blood flow
c is speed of sound in tissue
Notice that Doppler shift is highly dependent on angle of incidence and can be maximized with Ø = 0° or minimized with Ø = 90°
PRF
Number of pulses of US occurring in 1 second
IMAGING ANATOMY
Anatomic Considerations
Vascular Variations Visible on Color Doppler
Physical Considerations
CLINICAL IMPLICATIONS
Clinical Importance
DIAGNOSTIC CHECKLIST
Selected References
Jenssen C et al: [Ultrasound artifacts and their diagnostic significance in internal medicine and gastroenterology - part 2: color and spectral Doppler artifacts.] Z Gastroenterol. 54(6):569-78, 2016
Rubens DJ et al: Doppler artifacts and pitfalls. Radiol Clin North Am. 44(6):805-35, 2006
Wells PN: Ultrasound imaging. Phys Med Biol. 51(13):R83-98, 2006