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Fast spin echo
단국대학교 영상의학과 유 동 수
Contents
FSE 의 원리와 특성 : (C)SE 와 비교
FSE 의 장점 , 단점
FSE 의 변형
22
FSE
21
RARE (1986) (Rapid Acquisition with Relaxation Enhancement)
FSE (Fast spin echo) TSE (Turbo spin echo)
FSE Spin echo 의 특성 : Image quality ↑, Artifact ↓ Fast scan Long TR (Multiple RF pulse, Slice number) - T2 강조
Conventional SE Fast SE
1 NEX 4 NEX
20
9 min 28 sec 2 min 25 sec
Spin Echo, k-space
Fourier Transfor
m
k-space
주파수 (Frequency) 부호 축 ( Kx)
19
256 개의 phase encoding 을 채울 경우 TR 256 번을 반복위
상(P
hase
)부호
축 (
Ky
)
+ 128
- 128
0
RF signal (Echo)
위상 (Phase) 부호화 경사 ( Gy )
주파수 (Frequency) 부호화 경사 ( Gx )
RF Pulse
90° 180° 90°
FSE vs CSE
18
90° 180° 90°
TE80
90° 180° 180° 180° 180° 90°
TE30 TE60 TE80 TE100
CSEFSE
TR
위상 (Phase)부호경사
RF Pulse
Multiple 180° pulse
TE 80
Time saving
K-space
TEeff 80
No time saving
FSE vs CSE (CPMG)
17
90° 180° 180° 180° 180° 90°
TE30
TE60
TE80
TE100
90° 180° 180° 180° 180° 90°
TE30 TE60 TE80 TE100
CSE (CPMG)FSE
TR
위상 (Phase)부호경사
RF Pulse
Multiple 180° pulse
TE30 (PD)
TE60 TE80 (T2WI)
Single image
Time saving
K-space
TEeff 80
Multiple image
No time saving
Fast Spin echo - 용어
Echo train length (ETL) : Number of 180° RF pulse : Scan time ∝ (1/ETL)
Echo train spacing (ETS) : Space between 180° RF pulse
Effective echo time (TE eff) : SE 의 TE 와 유사하게 사용되나 다른 개념 : TE of k-space mid-line ( 위상 (Phase) 부호화경사 = 0) : Echo ↑↑ : Contrast, SNR 에 주로 기여
16
180° 180° 180° 180° 180° 180° 180° 180°90°
ETS
ETL
K-space
전반적대조도
세부묘사
+ 128
- 128
0 (Ky)
Fast Spin Echo
RF Pulse
Phase-encodinggradient
Echo
TE5
TE1 TE2 TE3 TE4 TE
6 TE7 TE8
ETS
90°
180° 180° 180° 180° 180° 180°
TE eff
15
ETL
(8)
Ky=0 SNR, Contrast 에 기여
+ 128
- 128
0 (Ky)
Effective TE
TEeff 40.36 msec 80.72 msec 96.86 msec 137.22 msec
14
T2 effect ↑, SNR ↓Blurring ↑
TE 40 TE 100
TEeff 40 TEeff 100
Echo Train Length
ETL 4 ETL 8 ETL 16 ETL 32
TR 5000msec, NEX = 2
10 min 45 sec 5 min 25 sec 2 min 45 sec 1 min 25 sec
13
ETL ↑ : Time ↓
문제점 : Slice number ↓
보정 : TR ↑, Slice thickness ↑
Scan Time(SE) = (TR)(Ny)(NEX)
Scan Time
Scan Time(FSE) = (TR)(Ny)(NEX) /ETL
NyNEXETL
:::
Phase-encoding stepsNumber of excitationEcho Train Length
12
예제 : TR 이 5000 msec, 1NEX, 512 X 512 의 해상도로 CSE 와 ETL 을 16 으로 했을 때 FSE 에서 영상을 얻는 시간은 ?
CSE
5000(TR) * 512(Ny) * 1(NEX)
= 2560 초 (42.7 분 )
FSE
5000(TR) * 512(Ny) * 1(NEX) / 16
= 160 초 (2.7 분 )
Advantage
Scan time↓: ETL∝
Image quality ↑ : Scan time saving 단계를 trade off – NEX ↑, resolution ↑
Spin echo 와 유사한 contrast, imaging parameter
Artifact (motion, susceptibility) ↓ : by 180° refocusing pulse
Shimming magnet ↓
11
Disadvantage
Bright fat signal : J-coupling↓, diffusion mediated susceptibility ↓, MTC effect
: Fat suppression image
10
Conventional SE Fast SE
Fat suppression
Fast SE
Disadvantage
Magnetic transfer contrast effect ↑ Magnetic susceptibility ( Hmr, Ca+ ) ↓
Conventional SE Fast SE
9
Disadvantage
ETL ↑ ↑
: Reduced coverage (slice number ↓)
Dual TE image :Time consuming
Incorrect TEeff
: Use multiple TE
8
FSE 의 변형
3D FSE (+ 3D)
GRASE (+ GRE)
Fast IR (+ IR)
HASTE, SSFSE (+ Single shot) (+ Half fourier acquisition)
7
3D FSE
Phase encoding : z 방향 (Nz) 을 추가 Multiple slices → Slap Scan time = (TR*NEX*Ny*Nz)/ETL More scan time Thinner image
2D Image
3D Image
6
GRASE (Gradient and Spin Echo)
FSE + GRE Spin echo 를 일부가 GE 로 대치 FSE 와 유사한 대조도 GRE - Susceptibility ↑ (hemorrhage)
Faster
90°
180° 180° 180°
Gradient echo Spin echo
FSE
GRASE
5
Fast IR (Inversion Recovery)
180° inversion pulse + FSE Fast STIR, Fast FLAIR
FSE
90° 180° 180° 180° 180° 90°180°
IR
TI
Fast STIR Fast FLAIR
4
HASTE, SSFSE
FSE (Single Shot) + Half fourier acq. Single shot : 매우 긴 하나의 echo train(64-128 개 ) 를 이용 Partial fourier technique
: K-space 의 일부에 date 를 채움
Frequency encoding ( Kx)
Phas
e en
codi
ng (
Ky)
Partial fourier technique
K-space
90° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180°
3
64-128
HASTE, SSFSE
Ultra-fast : 1-2 초 (single breath hold) Abdomen, chest imaging
MRCP Liver MR
2
Summary
Spin echo 의 특성
Fast scan ∝ETL
Advantage : Image quality ↑, Artifact↓
Disadvantage : Fat signal ↑, Slice number ↓
ETL, ETS, TE eff
Advance of HW, pulse sequence – better image quality
1
감사합니다 .