Philadelphia College of Osteopathic Medicine 2016...
Transcript of Philadelphia College of Osteopathic Medicine 2016...
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OB/Gyn (Core) Ultrasound
Principles of Ultrasound
Physics and Instrumentation
Nathan Pinkney, BS, CDOS
Philadelphia College of Osteopathic Medicine
2016 ULTRASOUND
CATEGORIES OF SOUND
• INFRASOUND = below 20 Hz
• AUDIBLE SOUND = 20 Hz to 20 kHz
• ULTRASOUND = above 20 kHz
o Medical Diagnostic Ultrasound = above 1 MHz
SOUND VELOCITIES
Material Meters per second
Air 330
Pure Water 1430
Fat 1450
Soft Tissue 1540
Muscle 1585
Bone 4080
•TRANSMIT – Electrical energy to mechanical energy
•RECEIVE – Mechanical energy to electrical energy
PIEZOELECTRIC EFFECT
PIEZOELECTRIC EFFECT
Transmitted pulse
Piezoelectric element (s)
Interface
Mechanical
energy
Electrical
energy
Returning echo
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ACOUSTIC IMPEDANCE
(Rayls)
Air 400
Fat 1,380,000
Water 1,430,000
Soft Tissue 1,630,000
Muscle 1,700,000
Bone 7,800,000
INTERFACE MATERIALS & ECHO STRENGTH
Soft Tissue to Muscle - Weak (1%)
Fat to Soft Tissue - Weak (1%)
Soft Tissue to Bone - Strong (50%)
Blood to Plaque - Strong (50%)
Soft Tissue to Air - Very Strong (100%)
GRAY SCALE ASSIGNMENT RESOLUTION
Interfaces not closely spaced
Closely spaced
GOOD
GOOD POOR
Closely spaced
AXIAL RESOLUTION
SCANNED STRUCTURE DISPLAYED IMAGE
LATERAL RESOLUTION
SCANNED STRUCTURE DISPLAYED IMAGE
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HIGH-FREQUENCY TRANSDUCERS
BETTER RESOLUTION
GREATER ATTENUATION
POORER PENETRATION
LOW-FREQUENCY TRANSDUCERS
POORER RESOLUTION
LESS ATTENUATION
BETTER PENETRATION
RESOLUTION & PENETRATION
The fundamental frequency of a transducer
RESONANT FREQUENCY
PIEZOELECTRIC
ELEMENT THICKNESS RESONANT FREQUENCY
Increase Decrease
Decrease Increase
2 MHz 2.25 MHz 2.5 MHz
TRANSDUCER FREQUENCIES
5 MHz 7 MHz 7.5 MHz
10 MHz 12 MHz 15 MHz
3 MHz 3.5 MHz 4 MHz
TRANSDUCER FREQUENCY ATTENUATION PENETRATION HALF INTENSITY DEPTH
Increase Increase Decrease Decrease
Decrease Decrease Increase Increase
ATTENUATION COEFFICIENT:
(in tissue)
a = - 0.5 dB per cm per MHz
HALF INTENSITY DEPTH:
(in tissue)
H.I.D. = 6 divided by frequency
ATTENUATION
IN TISSUE:
Attenuation = 0.5 dB per cm per MHz
H.I.D. = 6 ÷ Frequency
Frequency -dB per cm Half-Intensity-Depth
2 MHz 1 3 cm
2.25 MHz 1.125 2.67 cm
2.5 MHz 1.25 2.4 cm
3 MHz 1.5 2 cm
3.5 MHz 1.75 1.71 cm
4 MHz 2 1.5 cm
5 MHz 2.5 1.2 cm
7 MHz 3.5 0.86 cm
7.5 MHz 3.75 0.8 cm
10 MHz 5 0.6 cm
15 MHz 7.5 0.4 cm
HEAT (Thermal)
CAVITATION (Mechanical)
Stable
Transient
ULTRASOUND BIOEFFECTS
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ALARA
“As low as reasonably achievable”
Pulse-echo Imaging
Voltage
Sound
TRANSDUCER EXCITATION
AND OUTPUT POWER
TRANSMITTER
TRANSMIT POWER
OUTPUT
ACOUSTIC POWER
ENERGY OUTPUT
The frequency of the sound is not affected.
TIMING
PRF
Pulse-repetition frequency is not
the same as transducer frequency.
RECEIVER
TGC
GAIN
MASTER GAIN
OVERALL GAIN
Receiver controls do not affect the patient
TIME GAIN COMPENSATION
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OBSTETRICAL IMAGE
B-SCAN
Display Modes
B-SCAN (2-D) M-MODE
PATIENT-ORIENTED B-SCAN PLANES OBSTETRICAL IMAGES
2D 3D/4D
3D/4D
Freehand 3D, often called manual 3D uses a
standard 2D transducer and produces a static
volumetric image after the transducer is slowly
moved along a scan plane.
Automatic 3D requires a dedicated transducer and
can produce a volumetric image from a fixed
transducer position.
4D also requires a dedicated transducer, but the
volumetric image is displayed in real-time.
Ultrasound Transducers
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FLAT-LINEAR ARRAY
(linear array)
Labeled “L”
FLAT-LINEAR ARRAY
(linear array)
FLAT-LINEAR ARRAY
(linear array)
EMBRYO
FLAT-LINEAR ARRAY
(linear array) CURVED-LINEAR ARRAY
(convex array)
Labeled “C”
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CURVED-LINEAR ARRAY
(convex array)
CURVED-LINEAR ARRAY
(convex array)
CURVED-LINEAR ARRAY
(convex array)
FIBROID UTERUS
CURVED-LINEAR ARRAY
(convex array)
EMBRYO AND OVARIAN CYST
CURVED-LINEAR ARRAY
(convex array)
FETUS
CURVED-LINEAR ARRAY
(convex array)
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FETUS
CURVED-LINEAR ARRAY
(convex array)
ENDOVAGINAL TRANSDUCER
CURVED-LINEAR ARRAY
(convex array)
ENDOVAGINAL TRANSABDOMINAL
SAGITTAL SCAN PLANES
ENDOVAGINAL UTERUS
CURVED-LINEAR ARRAY
(convex array)
PHASED ARRAY
(electronically steered)
Labeled “P” or “S”
FETAL HEAD
PHASED ARRAY
(electronically steered)
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FETUS
PHASED ARRAY
(electronically steered)
ENDOVAGINAL
TRANSDUCER
PHASED ARRAY
(electronically steered)
ENDOVAGINAL UTERUS
PHASED ARRAY
(electronically steered)
PHASED / VECTOR ARRAY
(trapezoidal array)
Labeled “V”
FETUS
PHASED / VECTOR ARRAY
(trapezoidal array) ULTRASOUND ARTIFACTS
REVERBERATION
ENHANCEMENT
SHADOWING
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Doppler Imaging
DOPPLER
SAME
FREQUENCY
TRANSDUCER
During Doppler operation, the reflected sound has the same frequency as the
transmitted sound if the blood is stationary.
DOPPLER
LOWER
FREQUENCY
TRANSDUCER
During Doppler operation, the reflected sound has a lower frequency if the
blood is moving away from the sound source.
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DOPPLER
HIGHER
FREQUENCY
TRANSDUCER
During Doppler operation, the reflected sound has a higher frequency if the
blood is moving toward the sound source.
SPECTRAL & COLOR-FLOW DOPPLER
KEY ITEMS
FOR REVIEW
#1
Frequencies used for medical
diagnostic ultrasound are:
#1
Frequencies used for medical
diagnostic ultrasound are:
above 1 MHz
CATEGORIES OF SOUND
• INFRASOUND = below 20 Hz
• AUDIBLE SOUND = 20 Hz to 20 kHz
• ULTRASOUND = above 20 kHz
o Medical Diagnostic Ultrasound = above 1 MHz
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#2
The average sound velocity in
soft tissue is:
#2
The average sound velocity in
soft tissue is:
1540 meters per second
SOUND VELOCITIES
Material Meters per second
Air 330
Pure Water 1430
Fat 1450
Soft Tissue 1540
Muscle 1585
Bone 4080
#3
High frequency transducers
provide improved resolution and:
#3
High frequency transducers
provide improved resolution and:
poor penetration
HIGH-FREQUENCY TRANSDUCERS
BETTER RESOLUTION
GREATER ATTENUATION
POORER PENETRATION
LOW-FREQUENCY TRANSDUCERS
POORER RESOLUTION
LESS ATTENUATION
BETTER PENETRATION
RESOLUTION & PENETRATION
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#4
Major categories of ultrasound
bioeffects are heat and:
#4
Major categories of ultrasound
bioeffects are heat and:
cavitation
HEAT (Thermal)
CAVITATION (Mechanical)
Stable
Transient
ULTRASOUND BIOEFFECTS #5
Two basic scanning formats are:
#5
Two basic scanning formats are:
linear and sector
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