Ultrasound Principle超音波原理

Diagnosis Imaging System

影像診斷系統

振幅Amplitude

Wavelength 波長

Pressuremaximum

Pressureminimum

1 Cycle

週期1 Cycle

週期1 Cycle

週期

Sound wave

• Amplitude

• Frequency

• Velocity

Sound wave

dB

MHz 1,000,000 次 / 秒

1540 m/s in body

Propagated

wave

Refracted

wave

Refracted

waveReflected

wave

Reflected

wave

Medium #1 Medium #2

折射與反射

• Power … watt

• Intensity… watt / cm2

– Loudness or strength

• Decibel notation …dB = 10 log 10 ( ----- )

I

I0

dB Intensity Ratio Amplitude Ratio

70 10,000,000 10,00060 1,000,000 1,00050 100,000 32040 10,000 10030 1,000 3220 100 1010 10 3.2 0 1 1-10 0.1 0.32-20 0.01 0.1

Power and Intensity

Gain

結果 : 超音波頻率提升 ,穿透力卻下降

Reflection

Absorption

Scattering

Frequency Penetration

Frequency Vs Penetration 頻率與穿透力的關係

Frequency Vs Resolution 頻率與解像度的關係

Higher Frequency can

Reflect smaller objects

超音波頻率提升解像度也會提升

ResolutionElevation

Axis

Lateral

Spatial ResolutionSpatial Resolution

Frequency

Transmit

Signal process

Focusing Steering Channel ….

Acoustic lance

Matching Layer

CrystalAbsorbing material

Resolution

Contrast ResolutionContrast Resolution

Compress

Compress

ExpandSoft Tissue

Strongreflection

Weakreflection

Acoustic Signal

Visual light

Dynamic Range

Beamfomer

Transducer

Beamfomer

一條音束從發射到接收要花多少時間？Suppose depth = 16 cm , sound speed 1540 m/s16 x 2 / 1540 2 / 10000 second

一個 frame 0.025 second要花 30 ~ 40 Hz

1231211st Frame

2nd Frame 123121

VariableGain Stage

ImageProcessingMemory

ScanConverter

SignalProcessing

Display

Xducer

Receiver

Xmitter

GainTGCLGC

B/WContrast

Color/HuePost-processColorizationAnnotation

Measurement

LoopQuick review

Mode control2D, B (Sector,Linear, convex)MDopplerColorAQ

Image Format ZoomImage & B/W InvertDual Image

Pre-processingCompressionPersistence

Xmit FocusDepth

Frequency

Signal process

Post-processing Curves

Post-processing

Gray Level before Post-processing Curves

Gra

y L

evel

aft

er P

ost

-pro

cess

ing C

urves

Input level

Output level

Post-processing:,藉由特殊電腦影像處理 改變不,同組織的相對灰度顯示 例如

Tissue Boundary, Thrombus等.會更加明顯而獲致最佳解像度

B ModeColorFlow

Image Doppler

Spectrum

AnatomyAnatomy

FunctionFunction

ViabilityViability

InformationInformationManagementManagement

TGC

Gain

Dynamic Range

Focus

Depth

Signal process / Control