Medical Imaging Analysis

Medical Imaging SystemX-ray Computed Tomography (CT) Magnetic Resonance Imaging (MRI)

Ultrasound Nuclear Medicine

Position Emission Tomography (PET)

Characteristics of Diagnostic Ultrasound

• Non-invasive.• Safe (under regulations).• Real-time.• Reflection mode (similar to RADAR).• Blood flow imaging.• Portable.• Body type dependent.

Clinical Applications

• OB/GYN, vascular, cardiac, transcranial, abdominal, musculoskeletal, endo-vaginal, endo-rectal, ocular, intra-vascular, …etc.

(From www.acuson.com)

B-mode Image Fundamentals

Ultrasonic Array Transducers

(From www.acuson.com)

Beamformation Using Arrays

Sum

mation

Delay C

ontrol

Weighting

• Focusing the ultrasound energy– Delay and weighted sum

• Fixed focusing on transmit and dynamic focusing on receive

• The beam quality is poor in the out of transmit focused region

Focusing

Single zone focusing Multi-zone focusing Dynamic focusing

f

f1

f2

f3

• Resolution Point Spread Function (PSF)

• Contrast Contrast to Noise Ratio (CNR)

Point Spread Function

• 點的影像仍是點嗎 ?• Image of a point is point spread function (PSF).• 和電路學的 impulse response 相同觀念。

Input LTI System Output

電路學 Impulse LTI circuit Impulse Response

影像 Point LTI System Point Spread Function

Single zone tx focusing Multi-zone tx focusing

speckle

Frame rate

Dynamic range

2cm

4cm

6cm

Sample Image

Range Beam Plots

Speckle

• Left: T甲狀腺， J為頸靜脈，C為頸動脈• Right: RV右心室，LV左心室

TC

JLV

RV

T

C

J

RV

LV

Speckle• granular noise• common in all phase sensitive imaging system

Simulated US image Imaged object

Speckle

3dB

Speckle

• Speckle reduces the detect ability

Imaged objectSimulated US image

6dB

Speckle

Imaged objectSimulated US image

Speckle

US sensor

11

jeaA a1: amplitude

1: phase

N: # of scatterers

N

i

ijiea

NA

1

1

Phasor representation

Speckle• Assumption

– ai: Gaussian distribution (central limit theorem, N ~10) i: uniform distribution between and -

(scatterers in the sample volume are randomly located)

• I: intensity, exponential distribution

• E: amplitude, Rayleigh distribution

1I

I

ISNR

(Multiplicative noise)

2222

1

I

I ep

2

2

22

E

E eE

p

91.1

EE

ESNR

I

PI

E

PE

Speckle• US image is usually displayed on log scale

)(log10)()(0

10 I

IIfdBD

(Additive noise)

Taylor series expansion about I

)()()( ' IfIIIfdBD =>

dBD 34.4

CNR

• Contrast to noise ratio (CNR) determines the contrast resolution of a image

• Intensity can be viewed as signal and standard deviation can be viewed as noise

outoutI ininI

outin

outin IICNR

I : intensity (mean2)

:standard deviation (std2)

Work• HW1

– Estimate PSF size, speckle std (dB, theoretical value ~ 4.34 dB), speckle histogram (back to linear) for both single zone tx focusing and multi-zone tx focusing and make a discussion about the results.

• HW 2 – Repeat 1. under a different B-mode gain, and compare the results

with those of 1.

• HW 3 – Estimate CNRs in the focused region and in the out of focused regi

on.

• HW4 – Carotid color doppler and PW images of yours

Work – HW1

Single zone tx focusing Multi-zone tx focusing

speckle

Frame rate

Dynamic range

2cm

4cm

6cm

Speckle histogram

(gray to dB, and then dB back to linear)

and std (gray to dB)

0 5 10 15 20 25 30 35 40 45-30

-25

-20

-15

-10

-5

0

(gray to dB)

Work – HW2

Higher B-mode gain Lower B-mode gain

Work – HW3

Work – HW4

• Carotid Color Doppler

Work – HW4

• Carotid PW

Carotid

Carotid Color Doppler

Carotid PW

GE 超音波儀器操作說明

A-mode & B-mode

displayreceive signal

processingT/R

switch

pulser

transducer

received signal

• A-scan, one-dimensional

• B-scan, two-dimensional

linear sector curved linear

easy access limited access easy access

limited field of view large field of view large field of view

Color Flow Doppler (CFD)

multiple firings

multiple gates

zero velocity, black dark

bright

bright

red

blue

positive velocity

negative velocity

• The ultrasonic data acquisition process in Color Doppler is similar to that in B-mode except that the ultrasonic pulse needs to be fired multiple times along the same direction sequentially before moving to the next beam.

Pulse Wave Doppler (PWD)D

epth

(F

ast T

ime

Inde

x)

Firing Number(Slow Time Index)

1 2 3 4 5 6 7

Vessel Wall

Vessel Wall

Doppler Signals

PRI

Frame Grabber (UPG401B, UPMOST Corp.)

超音波影像擷取架構圖

仿體

GE Medical SystemLOGIQ 500 MD

Transducer

18 cm

2

4

6

8

10

12

14

16

.

.

.

.

.

.

.

. . . .

. . . .

.

....

.

... .

.

... .

1 2 3 4

3 cm

Axial Resolution

Axial Resolution

Axial Resolution

Horizontal Spacing

Vertical Spacing Gray Scale Target

16.5 cm

仿體 (Phantom)Model: Grey Scale Phantom RMI 403GS LE

http://www.gammex.com/403GSLE.htm

仿體 (Phantom) 詳細規格

醫用超音波儀器 (1)

GE Medical SystemLOGIQ 500 MD

Linear Array

仿體

ON/OFF

醫用超音波儀器 (2)

B-mode GainDepthDoppler Mode

面版說明

Frame Grabber (UPG401B, UPMOST Corp.)

Image Output

醫用超音波儀器 (3)影像輸出

影像擷取程式 (1)

執行 UPMOST 程式

執行 Capture 選項

選項： 1.1. Single FrameSingle Frame 2.Video2.Video

執行 File 選項

選項： 1. Save Single FrameSave Single Frame 2. Save Captured 2. Save Captured Video AsVideo As

影像擷取程式 (2)

超音波影像 LOAD 到 MATLAB

RAW_Image = imread(‘ 檔名’ ,’.bmp’);

Gray_Image = rgb2gray(RAW_Image) ; % Convert to GRAYSCALE

DoubleImage = double(Gray_Image) / 255 ;% Convert to DOUBLE format

( 副檔名 )