Part 1 - ncus.orgncus.org/files/spring2014/princip.pdfDoppler Imaging Part 4 Image Processing Advances References Part 1 ... Intensity Measurements Bioeffects Physical Principles 4

1

PRINCIPLES OF SONOGRAPHY

Nate Pinkney

Division of Research

Philadelphia College of Osteopathic Medicine

2014

Principles of Sonography

Part 1

Physical Principles

Intensity Measurements

Bioeffects

Part 2

Pulse-echo Imaging

Image Noise Reduction

Transducer Configurations

Part 3

Hemodynamics

Doppler Imaging

Part 4

Image Processing

Artifacts

Advances

References

Part 1

Physical Principles


Bioeffects

Physical Principles

4

• INFRASOUND = below 20 Hz

• AUDIBLE SOUND = 20 Hz to 20 kHz

• ULTRASOUND = above 20 kHz

o Medical Diagnostic Ultrasound = above 1 MHz

CATEGORIES OF SOUND

5

SOUND VELOCITY

STIFFNESS*

OF MEDIUM

DENSITY OF

MEDIUM

SOUND

VELOCITY

Increase ——————— Increase

Decrease ——————— Decrease

——————— Increase Decrease

——————— Decrease Increase

6

*Stiffness is the primary parameter affecting velocity.

2

SOUND VELOCITIES

Material Meters per second

Air 330

Pure Water 1430

Fat 1450

Soft Tissue 1540

Muscle 1585

Bone 4080 7

•TRANSMIT – Electrical energy to mechanical energy

•RECEIVE – Mechanical energy to electrical energy

PIEZOELECTRIC EFFECT

8

•The fundamental frequency of a transducer

RESONANT FREQUENCY

PIEZOELECTRIC

ELEMENT THICKNESS RESONANT FREQUENCY

Increase Decrease

Decrease Increase

9 10

PIEZOELECTRIC EFFECT

Transmitted pulse Returning echo

Piezoelectric element (s)

Interface

Mechanical

energy

Electrical

energy

Sound waves in a material produce particle motion that is back

and forth along the direction of travel. This back and forth motion,

termed longitudinal wave propagation.

LONGITUDINAL WAVE PROPAGATION

11

WAVE PARAMETERS

Period = 1 Frequency

Wavelength = Velocity Frequency

Pulse Duration = Period x Number of Cycles

Spatial Pulse Length = Wavelength x Number of Cycles

The number of cycles in a pulse is not the same as the

frequency of the sound, which is the number of cycles

per unit time that a transducer, which is operating

continuously, is designed to produce.

12

3

3-cycle pulse

longer periods

longer wavelengths

longer pulse duration

longer spatial pulse length

3-cycle pulse

shorter periods

shorter wavelengths

shorter pulse duration

shorter spatial pulse length

SAME DAMPING & AMPLITUDE

DIFFERENT FREQUENCY & PHASE

Frequency = 5.0 MHz Number of Cycles = 3

Period = 0.2 µs

Pulse Duration = 0.6 µs

Wavelength = 0.308 mm Spatial Pulse Length = 0.924 mm


Period = 0.4 µs



13

3-cycle pulse

same periods

same wavelengths

shorter pulse duration

shorter spatial pulse length

4-cycle pulse

same periods

same wavelengths

longer pulse duration

longer spatial pulse length

SAME FREQUENCY, AMPLITUDE, & PHASE

DIFFERENT DAMPING


Period = 0.2 µs


Wavelength = 0.308 mm, Spatial Pulse Length = 1.232 mm


Period = 0.2 µs



14

SAME FREQUENCY & DAMPING

DIFFERENT AMPLITUDE & PHASE

4-cycle pulse

same periods

same wavelengths

same pulse duration

same spatial pulse length

4-cycle pulse

same periods

same wavelengths

same pulse duration

same spatial pulse length


Period = 0.2 µs




Period = 0.2 µs



15

DAMPING vs. BANDWIDTH

DAMPING BANDWIDTH

Increase Increase

Decrease Decrease

16

Pulse-echo

Damped

Wide Bandwidth

CW

Not damped

Narrow Bandwidth

Center frequency = 5.0 MHz Range = 4.9 MHz to 5.1 MHz

Continuous Wave

Bandwidth = 0.2 MHz

Center frequency = 5.0 MHz Range = 3.75 MHz to 6.25 MHz

Number of Cycles = 2

Bandwidth = 2.5 MHz

HIGH DAMPING vs. NO DAMPING

SAME FREQUENCY DIFFERENT DAMPING

17

PRF & PRP

Pulse Repetition Period = 1 Pulse Repetition Frequency

PRF PRP

1000 Hz 1/1000 sec (0.001 sec)

2000 Hz 1/2000 sec (0.0005 sec)

4000 Hz 1/4000 sec (0.00025 sec)

18

4

DUTY FACTOR

Duty Factor = Pulse Duration Pulse Repetition Period

PRF PRP PULSE

DURATION

DUTY

FACTOR

Increase Decrease ———— Increase

Decrease Increase ———— Decrease

———— ———— Increase Increase

———— ———— Decrease Decrease

The duty factor in a pulse-echo system is normally less than 1% (0.01).

Continuous wave (CW) Doppler has a duty factor of 100% (1).

19

(Rayls)

Air 400

Fat 1,380,000

Water 1,430,000

Soft Tissue 1,630,000

Muscle 1,700,000

Bone 7,800,000 20

ACOUSTIC IMPEDANCE

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%)

21

ACOUSTIC COUPLANT

22

Gallstone shadow

SAGITTAL - LIVER, RIGHT KIDNEY

23

TRANSDUCER MATCHING LAYERS

To improve efficiency, increase sensitivity, and

minimize internal reflections in the transducer,

some transducers incorporate intervening

matching layers. The thickness of a matching

layer is typically ¼ - wavelength. The acoustic

impedance of a matching layer should have a

value between the acoustic impedance of the

piezoelectric element and the acoustic

impedance of tissue.

24

5

TRANSDUCER MATCHING LAYERS

Assuming a transducer has two matching layers

between the element and the transducer face, an

example of matching could be:

Piezoelectric element - acoustic impedance = 30,000,000 rayls

First matching layer - acoustic impedance = 16,000,000 rayls

Second matching layer - acoustic impedance = 7,000,000 rayls

Transducer face material - acoustic impedance = 3,600,000 rayls

Acoustic couplant - acoustic impedance = 1,800,000 rayls

Skin - acoustic impedance = 1,700,000 rayls

25

GOOD

GOOD POOR

Interfaces not closely spaced

Closely spaced

RESOLUTION

Closely spaced

26

AXIAL RESOLUTION

(category of spatial resolution)

SCANNED STRUCTURE DISPLAYED IMAGE

27

AXIAL RESOLUTION

SPATIAL PULSE LENGTH AXIAL RESOLUTION (½ SPATIAL PULSE LENGTH)

4 mm 2 mm

3 mm 1.5 mm

2 mm 1 mm

28

LATERAL RESOLUTION


SCANNED STRUCTURE DISPLAYED IMAGE

29

LATERAL RESOLUTION

BEAM-WIDTH

BEAM-WIDTH LATERAL RESOLUTION

4 mm 4 mm

3 mm 3 mm

2 mm 2 mm

30

6

LATERAL RESOLUTION

31

LATERAL RESOLUTION

32

HIGH-FREQUENCY TRANSDUCERS

BETTER RESOLUTION

GREATER ATTENUATION

POORER PENETRATION

LOW-FREQUENCY TRANSDUCERS

POORER RESOLUTION

LESS ATTENUATION

BETTER PENETRATION

RESOLUTION vs. PENETRATION

33

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

34

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 35

ATTENUATION

Attenuation is very high in bone with

high and low frequencies. Conversely,

attenuation is low in fluids (e.g., blood)

and very low in water, even when high

frequencies are used. Regardless of

the medium, penetration is inversely

proportional to the transducer’s

frequency. 36

7

SAGITTAL - LIVER

2.5 MHz 4 MHz 37

SAGITTAL - LIVER, RIGHT KIDNEY

3.5 MHz 5 MHz 38

7.5 MHz

THYROID BREAST

VASCULAR OPHTHALMIC

7 MHz 7 MHz

10 MHz

39


40

SATA

SPTA

SATP (SAPA)

SPTP (SPPA)

Where and when are intensity measurements made?

41

WHERE?

The relationship between ISP and ISA is a

function of beam uniformity ratio (B.U.R.)

42

8

The relationship between ITP(IPA) and ITA is a

function of duty factor (D.F.)

WHEN?

43

WHERE WHEN

SA TA

SP TP(PA)

44

WHERE WHEN

SATA

SPTA

SATP(PA)

SPTP(PA)

45

ISATA ISPTA ISATP (ISAPA) ISPTP (ISPPA)

Lowest Highest

Which method produces the lowest result?

Which method produces the highest result?

46

Bioeffects

47

HEAT (Thermal)

CAVITATION (Mechanical)

Stable

Transient

48

BIOEFFECTS CATEGORIES

9

MECHANICAL INDEX

THERMAL INDEX

49

SAFETY INDICES MECHANICAL INDEX

MI

A value used as a guide in

determining the probability of

mechanical bioeffects (mainly

cavitation) occurring

50

THERMAL INDEX

TI

A value used to estimate the

rise in temperature in ºC

51

ALARA “As low as reasonably achievable”

Nonfocused: SPTA < 100 mW / cm2 (0.1 Watt per square centimeter)

Focused: SPTA < 1 W / cm2

52

Part 2

Pulse-echo Imaging



Pulse-echo Imaging

54

10

Pulse-echo Imaging

Voltage

Sound

55

Display Modes

56

Display Modes

B-SCAN (2-D) M-MODE

57

2-D 3-D

Display Modes

58

TRANSDUCER EXCITATION

AND OUTPUT POWER

TRANSMITTER

TRANSMIT POWER

OUTPUT

ACOUSTIC POWER

ENERGY OUTPUT

59

The frequency of the sound is not affected. MAXIMUM ONE - HALF

OUTPUT POWER SETTINGS

60

11

TIMING

PRF

61

Pulse-repetition frequency is not

the same as transducer frequency.

RECEIVER

TGC

GAIN

MASTER GAIN

OVERALL GAIN

62

Receiver controls do not affect the patient.

TIME GAIN COMPENSATION

63

TGC

INCORRECT SETTINGS

64

DYNAMIC RANGE (category of contrast resolution)

DYNAMIC RANGE

COMPRESSION

LOG-COMPRESSION

COMPRESS

65 30 dB

DYNAMIC RANGE

50 dB

Decreased dynamic

range; increased compression; smaller

range of displayed gray

levels; reduced

contrast resolution

Increased dynamic

range; decreased compression; wider

range of displayed

gray levels; improved

contrast resolution

66

12


67

NOISE REDUCTION

Methods commonly used to suppress noise

and improve signal-to-noise ratio include:

• Rejection

• Frame averaging

• Frequency compounding

• Harmonic Imaging

68

NOISE REDUCTION

USING REJECT

BEFORE REJECT AFTER REJECT

anechoic low-level echoes

(noise)

69

FRAME AVERAGING

Frame averaging (persistence) reduces

image noise by averaging and overlapping

sequential real-time frames to provide

spatial smoothing of the image.

70

FREQUENCY COMPOUNDING

Frequency compounding is a method of

transmitting a single broadband pulse and

then using different receive frequency sub-

bands. It reduces speckle and electronic

noise to improve axial and contrast

resolutions.

71


CONVENTIONAL IMAGE

FREQUENCY COMPOUNDING AT 10 MHz

72

13


CONVENTIONAL IMAGE

FREQUENCY COMPOUNDING AT 14 MHz

73

HARMONIC IMAGING

Harmonic echoes are non-linear, high

frequency signals created when a contrast

agent or tissue interacts with ultrasound

energy during pulse-echo and Doppler

studies.

74

HARMONIC IMAGING

Harmonic imaging is a procedure in which

the receiver detects only echoes at the

second harmonic, which is twice the

fundamental (transmitted) frequency.

75

HARMONIC IMAGING

Harmonic imaging, by reducing unwanted

artifacts caused by interaction with the

fundamental frequency sound waves,

provides improved contrast resolution, and

reduced visible noise.

76

HARMONIC IMAGING

By reducing side lobes and slice thickness, it

improves lateral resolution. However, the

lower fundamental frequency produces a

longer spatial pulse length resulting in

somewhat degraded axial resolution.

77

HARMONIC IMAGING

Some harmonics are “native” to specific

types and characteristics of tissue and are

often produced without the use of a contrast

agent.

78

14

HARMONIC IMAGING

Pulse inversion harmonic imaging is a non-

linear imaging method specifically made for

enhanced detection of microbubble

ultrasound contrast media. Pulse inversion

harmonic imaging has half the frame rate as

conventional imaging. Axial resolution is

somewhat improved compared to

fundamental harmonic imaging.

79

HARMONIC IMAGING

CONVENTIONAL IMAGE

TISSUE HARMONIC IMAGING

80

HARMONIC IMAGING

CONVENTIONAL IMAGE

HARMONIC IMAGING

81

HARMONIC IMAGING

CONVENTIONAL IMAGE

HARMONIC IMAGING

82


83

Ultrasound

Transducers

84

15

85

(FLAT) LINEAR ARRAY

86

Labeled “L”

87

(FLAT) LINEAR ARRAY

FETUS 88

(FLAT) LINEAR ARRAY IMAGE

89

(FLAT) LINEAR ARRAY IMAGES

90

(FLAT) LINEAR ARRAY

16

THYROID AND LEFT CAROTID

TRANSMIT

FOCAL

ZONES

91

(FLAT) LINEAR ARRAY IMAGE

MULTI-DIMENSIONAL LINEAR ARRAY

ELEMENT CONFIGURATION

92

A “multi-dimensional array (also called 1.5 dimensional array), with a matrix of

elements along the “width” plane (often called “elevation or z-axis”) improves

elevational resolution by reducing the slice thickness.” A reduced slice thickness

decrease chances of a tissue averaging artifact.

(FLAT) LINEAR ARRAY

93

(FLAT) LINEAR ARRAY STEERED-LINEAR ARRAY IMAGE

94

CURVED-LINEAR (CONVEX) ARRAY

95

Labeled “C”

96


17

97


LIVER AND RIGHT KIDNEY 98

CURVED-LINEAR (CONVEX) ARRAY IMAGE

PHASED ARRAY

99

Labeled “P” or “S”

PHASED ARRAY

100

ABDOMEN

PHASED ARRAY IMAGE

101

PHASED ARRAY

102

18

HEART, 4-CHAMBER VIEW

PHASED ARRAY IMAGE

103

VECTOR (TRAPEZOIDAL) ARRAY

104

Labeled “V”

ABDOMEN 105

VECTOR (TRAPEZOIDAL) ARRAY IMAGE

CAROTID ARTERY 106

VECTOR (TRAPEZOIDAL) ARRAY IMAGE

Part 3

Hemodynamics

Doppler Imaging

Hemodynamics

108

19

Cardiopulmonary

Systemic

MAJOR SYSTEMS OF

CARDIOVASCULAR CIRCULATION

109

Kinetic

Potential

110

ENERGY

Combination of the kinetic

energy (blood flow) and the

potential energy (blood

pressure) present.

111

TOTAL FLUID ENERGY

P The difference in pressure

(pressure drop) between the

two ends of a vessel or the

difference in pressure across a

valve.

112

GRADIENT

POISEUILLE’S LAW

113

Increases with increasing

hematocrit (red cell volume).

114

VISCOSITY (Internal friction)

20

Aorta 4%

Large Arteries 5%

Main Branches 10%

Terminal branches 6%

Arterioles 41%

Capillaries 27%

Total venous 7%

100% 115

PERCENTAGE OF RESISTANCE IN

THE VASCULAR SYSTEM

• plug

•laminar (parabolic)

• disturbed

• turbulent 116

FLOW PATTERNS

• occurs during systole in large vessels

117

PLUG FLOW

• thought to exist in the majority of

vessels

118

LAMINAR FLOW

• caused by high peak velocities, curving,

branching, and divergence

• often produces bruits

119

DISTURBED FLOW

• often at the location of a stenosis

• significant pressure gradients are

present

120

TURBULENT FLOW

21

BERNOULLI EFFECT

The Bernoulli Effect describes the

relationship between changes in

fluid flow and changes in

pressure energy.

Q = V x A (flow = velocity x area)

121

BERNOULLI EFFECT

A reduction in pressure

accompanies an increase

in flow.

122

• causes a significant

reduction in the amount

of blood flow distal to the

location of the stenosis

CRITICAL STENOSIS

123

abdominal aorta 90% area reduction

carotid artery 75% area reduction

CRITICAL STENOSIS

In the abdominal aorta, a 90% reduction (10% remaining) in area

is required before the stenosis is critical, while in the carotid

artery a 75% reduction (25% remaining) in area is characterized

as critical. A 75% area reduction is equivalent to a 50% diameter

reduction, often called a 50% stenosis.

124

Doppler Imaging

125

DOPPLER

During Doppler operation, the reflected sound has the same frequency as the

transmitted sound if the blood is stationary.

SAME

FREQUENCY

TRANSDUCER

126

22

DOPPLER

During Doppler operation, the reflected sound has a lower frequency if the

blood is moving away from the sound source.

LOWER

FREQUENCY

TRANSDUCER

127

DOPPLER

During Doppler operation, the reflected sound has a higher frequency if the

blood is moving toward the sound source.

HIGHER

FREQUENCY

TRANSDUCER

128

f

DOPPLER SHIFT

129

DOPPLER SHIFT EXAMPLE

TRANSMITTED

FREQUENCY

RECEIVED

FREQUENCY

DOPPLER SHIFT

f DIRECTION OF

FLOW TO SOUND

5 MHz 4.995 MHz 0.005 MHz

(5 kHz) Away

5 MHz 5.005 MHz 0.005 MHz

(5 kHz) Toward

130

DOPPLER SHIFT FORMULA

An increase in blood velocity produces an increase in the Doppler shift.

An increase in the transmitted frequency produces an increase in the Doppler shift.

A Doppler angle of 0º produces the maximum possible Doppler shift.

A Doppler shift is not produced when the Doppler angle is 90º.

Doppler angle: the angle

between the direction of

propagation of the ultrasound wave and the

direction of blood flow

131

DOPPLER RELATIONSHIPS

TRANSMITTED FREQUENCY

fo

DOPPLER ANGLE

q

BLOOD

VELOCITY

V

DOPPLER SHIFT

f

Increase ———— ———— Increase

Decrease ———— ———— Decrease

———— Increase ———— Decrease

———— Decrease ———— Increase

———— ———— Increase Increase

———— ———— Decrease Decrease

132

23

q cos q fo = 2.5 MHz fo = 5.0 MHz

0 1 3226 Hz 6452 Hz

30 0.867 2794 Hz 5588 Hz

45 0.707 2281 Hz 4562 Hz

60 0.5 1613 Hz 3226 Hz

75 0.259 835 Hz 1670 Hz

90 0 0 Hz 0 Hz

Doppler shifts (f) for

V = 100 cm per second

c = 1550 meters per second

DOPPLER CALCULATIONS

133

A Doppler system is capable of measuring only the Doppler shift. It calculates

the blood velocity.

An increase in the Doppler shift produces an increase in the calculated blood

velocity.

BLOOD VELOCITY FORMULA

134

SPECTRAL DOPPLER

FFT DISPLAY:

POSITIVE DOPPLER SHIFT

WITHOUT SPECTRAL BROADENING

FFT DISPLAY:

POSITIVE DOPPLER SHIFT

WITH SPECTRAL BROADENING

FREQUENCY

SCALES

135

DOPPLER GAIN SETTING NORMAL DOPPLER GAIN SETTING TOO HIGH

DOPPLER GAIN

136

WALL FILTER SETTING NORMAL WALL FILTER SETTING TOO HIGH

WALL FILTERS

137

NON-IMAGING CW 2-D IMAGING AND CW

(Duplex)

CW SPECTRAL DOPPLER

138

24

NON-IMAGING CARDIAC CW DOPPLER TRANSDUCER

CW SPECTRAL DOPPLER

139

CW DOPPLER DETECTING SHIFTS FROM MORE THAN ONE VESSEL

CW SPECTRAL DOPPLER

140

2-D AND CW DOPPLER WITH SPECTRUM ANALYZER DISPLAY

CW SPECTRAL DOPPLER

141

PW TRANSMITTING PW RECEIVING

PW SPECTRAL DOPPLER

142

NON-IMAGING PW 2-D IMAGING AND PW

(Duplex)

PW SPECTRAL DOPPLER

143

PW SPECTRAL DOPPLER

144

2-D AND PW DOPPLER WITH SPECTRUM ANALYZER DISPLAY

25

NORMAL SAMPLE VOLUME WITH

NO SPECTRAL BROADENING

LARGER THAN NORMAL SAMPLE VOLUME

WITH SPECTRAL BROADENING

PW SPECTRAL DOPPLER

145

PW TRANSDUCERS USED FOR

TRANSCRANIAL DOPPLER

PW SPECTRAL DOPPLER

146

PW - ALIASING

WRAP-AROUND

147

HIGH VELOCITY FLOW

NYQUIST LIMIT EXCEEDED

PW - ALIASING

148

NYQUIST LIMIT = PRF ÷ 2

SAME DOPPLER SHIFT BUT ALIASING

ELIMINATED

SCALE ADJUSTED TO INCREASE THE

PULSE DOPPLER PRF AND RAISE THE

NYQUIST LIMIT

PW - ALIASING

149

ALIASING


SAME DOPPLER SHIFT BUT ALIASING

ELIMINATED

BASE LINE LOWERED TO INCREASE

THE PULSE DOPPLER PRF AND RAISE

THE NYQUIST LIMIT

PW - ALIASING

150

ALIASING


26

ALIASING ELIMINATED

DOPPLER ANGLE INCREASED

SCALE, BASELINE, AND PRF UNCHANGED

PW - ALIASING

151

ALIASING


PW - ALIASING

ALIASING ELIMINATED

TRANSDUCER FREQUENCY DECREASED

SCALE, BASELINE, AND PRF UNCHANGED

152

ALIASING


NYQUIST LIMIT EXCEEDED, BUT NO WRAP-AROUND

PW - ALIASING

153

NYQUIST LIMIT

NYQUIST LIMITS

(PRF 2)

PRF N.L.

1 kHz (1000 Hz) 500 Hz

2 kHz (2000 Hz) 1000 Hz

3 kHz (3000 Hz) 1500 Hz

4 kHz (4000 Hz) 2000 Hz

5 kHz (5000 Hz) 2500 Hz

6 kHz (6000 Hz) 3000 Hz

NYQUIST LIMIT

154

CW – NO ALIASING

155

PW - VELOCITY CORRECT:

PROPER ANGLE-CORRECT

PW - VELOCITY INCORRECT:

IMPROPER ANGLE-CORRECT

VELOCITY

SCALES

ANGLE-CORRECT

156

27

(peak systolic - end diastolic)

÷ mean

PULSATILITY INDEX:

(PI)

157

(peak systolic - end diastolic)

÷ peak systolic

RESISTIVITY INDEX:

(RI)

158

COLOR-FLOW IMAGING

159

COLOR-FLOW IMAGING

STANDARD

COLOR MAP

160

COLOR-FLOW IMAGING

ENHANCED

COLOR MAP

161

COLOR-FLOW IMAGING

STANDARD

COLOR MAP

162

28

COLOR-FLOW IMAGING

COLOR

VARIANCE MAP

163

CAROTID

COLOR-FLOW IMAGING

164

2-D, SPECTRAL DOPPLER, & COLOR-FLOW

DOPPLER ECHOCARDIOGRAPHIC STUDY (Triplex)

COLOR DOPPLER

SAMPLE ANGLES

COLOR-FLOW IMAGING

STANDARD

COLOR

MAP

165

COLOR-FLOW DOPPLER

COLOR-FLOW IMAGING

166

COLOR-FLOW DOPPLER POWER DOPPLER

COLOR-FLOW & POWER DOPPLER IMAGING

167

POWER DOPPLER & SPECTRAL DOPPLER

168

29

Part 4

Image Processing

Ultrasound Artifacts

Sonographic Advances

Image Processing

170

Image Storage, Display

and Recording

171

Digital scan converter

172

173

GRAY SCALE ASSIGNMENT

PRE PROCESSING (category of contrast resolution)

NUMBER OF BITS IN A

DIGITAL MEMORY AND

NUMBER OF GRAY SHADES

(based on 2n)

bits gray shades

4 16

5 32

6 64

7 128

8 256

9 512

10 1024 174

30

4 BITS (16 GRAY SHADES) 8 BITS (256 GRAY SHADES)

The greater the bit density, the better the contrast resolution.

175

BIT DEPTH

(category of contrast resolution)

PIXEL MATRIX SIZE


262,144 PIXELS 65,536 PIXELS

The greater the number of pixels, the better the spatial resolution.

176

POST PROCESSING (category of contrast resolution)

GRAY-SCALE MAPPING BY DIFFERENT SETTINGS

OF THE POST PROCESSING CONTROL

177

MAGNIFICATION

ZOOM

MAG

RES

SCALE

SIZE

FOV

WRITE

READ

178

WRITE MAGNIFICATION

NORMAL SIZE

PRIOR TO MAGNIFICATION

AFTER WRITE MAGNIFICATION

NO CHANGE IN THE NUMBER OF

DISPLAYED PIXELS 179

READ MAGNIFICATION

NORMAL SIZE

PRIOR TO MAGNIFICATION

AFTER READ MAGNIFICATION

A REDUCTION IN THE NUMBER OF

DISPLAYED PIXELS 180

31

Recording devices

181

Recording devices

BLACK & WHITE PAGE PRINTER HARD-COPY

182

Recording devices

COLOR PAGE PRINTER HARD-COPY

183

RECORDING DEVICES

HARD-COPY

A color ink-jet printer operates by propelling drops of ink of various

colors onto standard paper.

184

RECORDING DEVICES

MAGNETIC TAPE RECORDER NOT HARD-COPY

185

NOT HARD-COPY

RECORDING DEVICES

Optical disk (e.g., CD, DVD) recorders can also record static and live

images. Like magnetic recording devices, playback equipment is

required to view the recorded information. Optical storage media is not

affected by external magnetic fields.

186

32

RECORDING DEVICES

PACS WORKSTATIONS

187

NOT HARD-COPY

YES NO

HARD COPY?

188


189

REVERBERATION

ENHANCEMENT

SHADOWING


190

Reverberation

Reverberation is sometimes identified as:

Ring down

Comet tail 191

Enhancement and Shadowing

192

33

Enhancement and Shadowing

Refractive shadowing is sometimes identified as:

Edge shadowing 193

Enhancement

Enhancement is sometimes identified as:

Posterior enhancement

Distal enhancement

Good through transmission

194

Shadowing - fetus

Bone is a source of acoustic shadows.

195

Shadowing - carotid

Calcified plaque is a source of acoustic shadows.

196

Sonographic Advances

197

VOLUME RENDERING

(3D/4D/MPR)

198

34

3-D

Freehand 3-D, often called manual 3-D

uses a standard 2-D transducer and

produces a static volumetric image after the

transducer is slowly moved along a scan

plane.

199

3-D

Automatic 3-D requires a dedicated

transducer and can produce a volumetric

image from a fixed transducer position.

200

4-D

4-D also requires a dedicated transducer,

but the volumetric image is displayed in

real-time.

201

MPR

Volume-rendering capabilities also permit

multi-planar reconstruction, which is the

process of reconstructing 2-D

images from the original volume data set

in three different planes from original 2-D

scans obtained in a single plane.

202

MPR

MULTI-PLANAR RECONSTRUCTION

203

SPATIAL COMPOUNDING

204

35

SPATIAL COMPOUNDING

Spatial compounding is the process of

steering ultrasound beams “off-axis” to

provide multiple transmit angles, or “lines

of sight” while combining them in real-time

during a single cross-sectional scan. Tissue

interfaces are encountered from numerous

directions rather than from a single direction.

205

SPATIAL COMPOUNDING

Spatial compounding eliminates certain

artifact patterns to provide a more realistic

anatomic representation. Reducing the

acoustic shadows enables the scanner to

essentially “see around” obstructions.

206

SPATIAL COMPOUNDING

CONVENTIONAL IMAGE SPATIAL COMPOUNDING

207

SPATIAL COMPOUNDING

CONVENTIONAL IMAGE SPATIAL COMPOUNDING 208

SPATIAL COMPOUNDING

CONVENTIONAL IMAGE SPATIAL COMPOUNDING 209

EXTENDED FIELD-OF-VIEW

210

36


CONVENTIONAL IMAGES

EXTENDED FOV

211


CONVENTIONAL IMAGE

EXTENDED FOV

212


213


214

ELASTOGRAPHY

(Elasticity Imaging)

215

ELASTOGRAPHY

The physics of elasticity is based

on mechanics and relates to the

distortions, which occur when

matter is subjected to an external

force or stress.

216

37

ELASTOGRAPHY

Elastography uses the deformability

and the elastic and relative stiffness

properties of tissues to determine the

likelihood of abnormality.

217

ELASTOGRAPHY

Elastography-based palpation using

the ultrasound transducer is a real-

time technique that improves the

differentiation of benign and

malignant disease in a range of

clinical applications.

218

ELASTOGRAPHY

CONVENTIONAL IMAGE

ELASTOGRAPHY

219

ELASTOGRAPHY

BREAST ELASTOGRAPHY

220

ELASTOGRAPHY

RECTAL ELASTOGRAPHY

221

References

38

223

RESOLUTION CATEGORIES

• lead zirconate titanate

• barium titanate

• lead metaniobate

• lead titanate

PIEZOELECTRIC CERAMICS

The ceramic material in a transducer has piezoelectric

characteristics because it was polarized while at a

temperature above its Curie point. If a transducer is

sterilized by heating it above the Curie point,

depolarization may result.

224

WAVE PARAMETERS

DAMPING FREQUENCY PERIOD WAVELENGTH NUMBER OF

CYCLES

PULSE

DURATION

SPATIAL

PULSE LENGTH

———— Increase Decrease Decrease ———— Decrease Decrease

———— Decrease Increase Increase ———— Increase Increase

Increase ———— ———— ———— Decrease Decrease Decrease

Decrease ———— ———— ———— Increase Increase Increase

225

RANGE EQUATION (in tissue)

Distance to the reflector

= 0.77 x round trip time

TIME TO THE REFLECTOR

(ONE WAY)

DISTANCE TO THE REFLECTOR

(ONE WAY)

ROUND TRIP

TIME

ROUND TRIP DISTANCE

6.5 µs 10 mm (1 cm) 13 µs 20 mm (2 cm)

5 µs 7.7 mm (0.77 cm) 10 µs 15.4 mm (1.54 cm)

The range equation assumes a velocity (speed of sound) of 1540

meters per second. Variations in the speed of sound have an effect

on the distance accuracy of a pulse-echo system, resulting in axial

errors.

226

ACOUSTIC IMPEDANCE

z = r x c

(density x velocity)

DENSITY VELOCITY ACOUSTIC

IMPEDANCE

Increase ———— Increase

Decrease ———— Decrease

———— Increase Increase

———— Decrease Decrease

227

PRF ÷ FRAME RATE = ACOUSTIC LINES

1000 Hz ÷ 10 Hz = 100

1000 Hz ÷ 20 Hz = 50

1500 Hz ÷ 10 Hz = 150

1500 Hz ÷ 20 Hz = 75

2000 Hz ÷ 10 Hz = 200

2000 Hz ÷ 20 Hz = 100

228

LINE DENSITY (category of spatial resolution)

The frame rate is the image update rate.

The higher the frame rate, the better the

temporal resolution.

39

LINE DENSITY

DISPLAY

DEPTH PRF

CHANCE OF DEPTH

AMBIGUITY

FRAME RATE ACOUSTIC

LINES

Increase Decrease Decrease ——–—-—- Decrease

Decrease Increase Increase —————- Increase

—————— —————— —————— Increase Decrease

—————— —————— —————— Decrease Increase

229

The number of acoustic lines in a frame

does not affect lateral resolution.

Prefix Factor Decimal Multiplier Symbol

pico (trillionth) 10-12 0.000000000001 p

nano (billionth) 10-9 0.000000001 n

micro (millionth) 10-6 0.000001

milli (thousandth) 10-3 0.001 m

centi (hundredth) 10-2 0.01 c

deci (tenth) 10-1 0.1 d

deca (ten) 101 10 D

hecta (hundred) 102 100 h

kilo (thousand) 103 1000 k

mega (million) 106 1000000 M

giga (billion) 109 1000000000 G

tera (trillion) 1012 1000000000000 T

ENGINEERING & SCIENTIFIC NOTATION

230

Binary Decimal

128 64 32 16 8 4 2 1 100 10 1

0 0 0 0 0 0 0 0 = 0

0 0 0 0 0 0 0 1 = 1

0 0 0 0 1 0 1 0 = 1 0

0 0 0 0 1 1 1 1 = 1 5

0 0 1 0 0 0 0 0 = 3 2

0 1 0 0 0 0 0 0 = 6 4

1 0 0 0 0 0 0 0 = 1 2 8

1 1 1 1 1 1 1 1 = 2 5 5

8-BIT BINARY NUMBERS

231

Decibels do not represent actual power, intensity, or amplitude, but rather how

much difference exists between two levels. For power or intensity, each 3 dB

represents a factor of 2. A 3 dB increase is double the power or intensity.

A 3 dB decrease is half the power or intensity.

DECIBELS dB Power or Intensity ratio Amplitude ratio

(Amplitude ratio) 2 (Power or Intensity ratio)½

-9 0.125 0.354

-6 0.25 0. 5

-3 0.5 0.707

0 1 1

+3 2 1.414

+6 4 2

+9 8 2.83

+10 10 3.16

+20 100 10

+30 1000 31.6

+40 10000 100

+50 100000 316

+60 1000000 1000

232

INTENSITY

POWER ÷ AREA

POWER BEAM DIMENSIONS AREA INTENSITY

100 mw 1 cm x 1 cm 1 cm2 100 mW / cm2

100 mw 1.414 cm X 1.414 cm 2 cm2 50 mW / cm2

100 mw 2 cm x 2 cm 4 cm2 25 mW / cm2

50 mw 1.414 cm x 1.414 cm 2 cm2 25 mW / cm2

233

Questions?

Nate Pinkney

Division of Research

Philadelphia College of Osteopathic Medicine

2014

WWW.SONICORINC.COM

WWW.SONICORINC.COM

Documents

Part 1 - ncus.orgncus.org/files/spring2014/princip.pdfDoppler Imaging Part 4 Image Processing Advances References Part 1 ... Intensity Measurements Bioeffects Physical Principles 4