1. Fast spin echo
단국대학교 영상의학과
유 동 수

2. Contents
FSE의 원리와 특성
: (C)SE와 비교
FSE의 장점,단점
FSE의 변형 22

3. FSE RARE (1986) FSE (Fast spin echo) TSE (Turbo spin echo)
(Rapid Acquisition with Relaxation Enhancement)
FSE (Fast spin echo)
TSE (Turbo spin echo) 21

4. FSE Spin echo의 특성 Fast scan Long TR (Multiple RF pulse, Slice number)
: Image quality ↑, Artifact ↓
Fast scan
Long TR (Multiple RF pulse, Slice number)
- T2강조
Conventional SE
Fast SE
1 NEX
4 NEX
9 min 28 sec
2 min 25 sec 20

5. 주파수 (Frequency) 부호화 경사( Gx )
Spin Echo, k-space
k-space
RF signal (Echo)
위상 (Phase) 부호화 경사 ( Gy )
주파수 (Frequency) 부호화 경사( Gx )
RF Pulse
90°
180°
Fourier Transform
주파수(Frequency) 부호 축 ( Kx)
위상(Phase)부호축 ( Ky)
+ 128
- 128
256개의 phase encoding을 채울 경우 TR 256번을 반복 19

6. FSE vs CSE 18 FSE CSE Time saving No time saving TR TEeff 80
Multiple 180° pulse
FSE
CSE TR
90°
180°
TE30
TE60
TE80
TE100
90°
180°
90°
RF Pulse
위상 (Phase)
부호경사
TE80
K-space
TEeff 80
TE 80
Time saving
No time saving 18

7. FSE vs CSE (CPMG) 17 FSE CSE (CPMG) Single image Time saving
Multiple 180° pulse
CSE (CPMG) TR
90°
180°
TE30
TE60
TE80
TE100
90°
180°
TE30
TE60
TE80
TE100
RF Pulse
위상 (Phase)
부호경사
K-space
TEeff 80
TE30 (PD)
TE60
TE80 (T2WI)
Single image
Time saving
Multiple image
No time saving 17

8. Fast Spin echo - 용어 Echo train length (ETL) Echo train spacing (ETS)
: Number of 180° RF pulse
: Scan time ∝ (1/ETL)
Echo train spacing (ETS)
: Space between 180° RF pulse
Effective echo time (TE eff)
: SE의 TE와 유사하게 사용되나 다른 개념
: TE of k-space mid-line
(위상(Phase) 부호화경사 = 0)
: Echo ↑↑
: Contrast, SNR에 주로 기여
180°
90°
ETS
+ 128
전반적대조도
0 (Ky)
세부묘사
- 128
K-space 16

9. Fast Spin Echo 15 ETL (8) TE5 ETS TE eff SNR, Contrast에 기여 RF Pulse
90°
180°
180°
180°
180°
180°
180°
ETL
(8)
RF Pulse
TE eff
Phase-encoding
gradient
Echo
TE1
TE2
TE3
TE4
TE6
TE7
TE8
TE5
+ 128
0 (Ky)
- 128
Ky=0
SNR, Contrast에 기여 15

10. Effective TE 14 TEeff 40.36 msec 80.72 msec 96.86 msec 137.22 msec
Blurring ↑
T2 effect ↑, SNR ↓
TEeff 40
TEeff 100
TE 40
TE 100 14

11. Echo Train Length 13 ETL 4 ETL 8 ETL 16 ETL 32 10 min 45 sec
TR 5000msec, NEX = 2
ETL 4
ETL 8
ETL 16
ETL 32
10 min 45 sec
5 min 25 sec
2 min 45 sec
1 min 25 sec
ETL ↑ : Time ↓
문제점 : Slice number ↓
보정 : TR ↑, Slice thickness ↑ 13

12. Scan Time Scan Time(SE) = (TR)(Ny)(NEX)
Scan Time(FSE) = (TR)(Ny)(NEX) /ETL Ny
NEX
ETL :
Phase-encoding steps
Number of excitation
Echo Train Length
예제 : TR이 5000 msec, 1NEX, 512 X 512의 해상도로
CSE와 ETL을 16으로 했을 때 FSE에서 영상을 얻는 시간은 ?
CSE
5000(TR) * 512(Ny) * 1(NEX)
= 2560초 (42.7분)
FSE
5000(TR) * 512(Ny) * 1(NEX) / 16
= 160초 (2.7분) 12

13. Advantage Scan time↓: ∝ETL Image quality ↑
: Scan time saving 단계를 trade off – NEX ↑, resolution ↑
Spin echo와 유사한 contrast, imaging parameter
Artifact (motion, susceptibility) ↓
: by 180° refocusing pulse
Shimming magnet ↓ 11

14. Disadvantage Bright fat signal : Fat suppression image
: J-coupling↓, diffusion mediated susceptibility ↓, MTC effect
: Fat suppression image
Conventional SE
Fast SE
Fast SE
Fat suppression 10

15. Disadvantage Magnetic transfer contrast effect ↑
Magnetic susceptibility ( Hmr, Ca+ ) ↓
Conventional SE
Fast SE 9

16. Disadvantage ETL ↑ ↑ Dual TE image Incorrect TEeff
: Reduced coverage (slice number ↓)
Dual TE image
:Time consuming
Incorrect TEeff
: Use multiple TE 8

17. FSE의 변형 3D FSE (+ 3D) GRASE (+ GRE) Fast IR (+ IR) HASTE, SSFSE
(+ Single shot)
(+ Half fourier acquisition) 7

18. 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

19. GRASE (Gradient and Spin Echo)
FSE
GRASE
FSE + GRE
Spin echo를 일부가 GE로 대치
FSE와 유사한 대조도
GRE - Susceptibility ↑ (hemorrhage)
Faster
90°
180°
Gradient echo
Spin echo 5

20. Fast IR (Inversion Recovery)
180° inversion pulse + FSE
Fast STIR, Fast FLAIR
Fast STIR Fast FLAIR
180°
90°
180°
180°
180°
180°
90° TI IR
FSE 4

21. HASTE, SSFSE FSE (Single Shot) + Half fourier acq. Single shot
Frequency encoding ( Kx)
FSE (Single Shot) + Half fourier acq.
Single shot
: 매우 긴 하나의 echo train(64-128개)를 이용
Partial fourier technique
: K-space의 일부에 date를 채움
Phase encoding ( Ky)
K-space
Partial fourier technique
64-128
90°
180° 3

22. HASTE, SSFSE Ultra-fast : 1-2초 (single breath hold)
Abdomen, chest imaging
MRCP Liver MR 2

23. Summary 감사합니다. Spin echo의 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
감사합니다. 1