Post on 12-Jan-2016
description
RF Coil Design Optimization in Cervical Carotid Imaging
Rock Hadley
MIRL Symposium
Sundance
September 13, 2002Go Take
A Hike!
4-channel commercial Neurovascular volume coil
home-built bilateral 4-elementcarotid Phased-array coil
Available Carotid Coils
• bilateral 4-element carotid PA coil
• 300% SNR improvement over anterior neck coil
• commercial anterior neck coil
Dedicated Carotid Coils
Coil Comparisons
0 20 40 60 80 100 120 1400
50
100
150
200
250Torso PA Chest Dual PA Head Dual PA GE Head Carotid PA Inverted Dual PANVPA1 NVPA2a NVPA2b NVPA3
image slice number
circle ofWillis
carotid bifurcation
aortic arch
rela
tive
SN
R
50 100 150 200 250 300 350 400 450 500
50
100
150
200
250
300
350
400
450
500bz contour
cross-sectional contour plots
Magnetic Field of a Circular Loop
axial-component(signal component)
magnitude(all field components)
coil
signalshadow
coilaxis
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150
1
2
3
4
5
6
7
8
9
10
11
12
vessel depth (cm)
optim
ized
coi
l rad
ius
(cm
) 45cm vessel length25cm vessel length5cm vessel length 1cm vessel length
long vesselsopt coil radius = vessel depth
very short vesselsopt coil diameter = vessel depth
Coil Design Issues
coil x
coil axis
vessel
surface
depth
aortic arch bifurcation circle of Willis
Simulation Model
= 0.3, r = 73 (muscle)
= 0, r = 1 (air)
figure of merit = average SNR along entire vessel(weighting of specific vessel points optional)
0
1
2
3
4
5
6
7
8
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8 0
1
2
3
4
5
6
7
8
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8 0
1
2
3
4
5
6
7
8
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
-1
0
1
2
3
4
5
6
7
8
9
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8 0
2
4
6
8
10
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
80
2
4
6
8
10
12
14x 10
-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
80
2
4
6
8
10
12
14
16
18
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
0
0.5
1
1.5
2
2.5
x 10-6
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
0
0.5
1
1.5
2
2.5
3
3.5
x 10-6
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5x 10
-6
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
x 10-6
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
x 10-6
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
x 10-6
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5x 10
-6
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
0
0.5
1
1.5
2
2.5
3
x 10-6
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
0
0.5
1
1.5
2
x 10-6
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
80
5
10
15x 10
-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8 0
2
4
6
8
10x 10
-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
-1
0
1
2
3
4
5
6
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
-1
0
1
2
3
4
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8 -0.5
0
0.5
1
1.5
2
2.5
3
3.5
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8 -0.5
0
0.5
1
1.5
2
2.5
x 10-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8-5
0
5
10
15
20
25x 10
-8
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
-0.5
0
0.5
1
1.5
2
2.5x 10
-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
80
0.5
1
1.5
2
2.5x 10
-7
vessel length(cm)
vess
el d
epth
(cm
)
0 5 10 15 20
0
1
2
3
4
5
6
7
8
Simulation Model
Example Simulation
optimal coil array radius (cm) position (cm)
coil 1 3 3
coil 2 2 8
coil 3 2 12
coil 4 2 16
coil 5 4 22
• 24 cm vessel length- 6 cm depth at aortic arch
- 3 cm depth at carotid bifurcation
- 9 cm depth at circle of Willis
• Results:
0 5 10 15 20 25
0
2
4
6
8
10
12
14
vessel position (cm)
vess
el d
ep
th (
cm)
aorticarch
circleof
Willis
flatsurface
bifurcation
simulated vessel structure
Coil1
Coil2
Coil3
Coil4
Coil5
0 5 10 15 20 250
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
vessel length (cm)
rela
tive
SN
R
optimum SNR for a 6,3,9 x 25cm length vessel
0 5 10 15 20 250
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
vessel length (cm)
rela
tive
SN
R single 10 cm radius coil
0 5 10 15 20 250
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
vessel length (cm)
rela
tive
SN
R5 coil array single 10 cm radius coil
Simulation Results
Conclusions
• This simulation tool provides a method for the study of optimum coil arrays for various carotid artery anatomy
• Number of channels needed for optimal carotid imaging is about 16 – 20 channels
Future Work
• Minimize magnetic and electric coupling between coils to determine proper coil overlap
• Adapt to non-planer surfaces to more closely match the anatomy of the shoulders, head, and neck
50 100 150 200 250 300 350 400 450 500
50
100
150
200
250
300
350
400
450
500bz contour
Coil Properties
magnetic field of a circular loop(cross-sectional contour plots)
axial-component(signal component)
magnitude(all field components)
coil
signalshadow
coilaxis
1 2 3 4 5 6 7 8 9 100.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1optcoil.results.24fov.639realvessel
# of coils
max
SN
R
Simulation Results
RF Coil Design Optimization in Cervical Carotid Imaging
Rock Hadley
MIRL Symposium
Sundance
September 13, 2002
Go Take
A Hike!
1 2 3 4 5 6 7 8 9 100
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
coil radius (cm)
rela
tive
nois
e (a
rbitr
ary
units
)
sample noise ohmic noise combined noise
commercial neurovascularvolume coil
home-built bilateral 4-elementcarotid Phased-array coil
Coil Options for Carotid Imaging
Methods: Neurovascular Coil
Dual PA Coil
/4 triaxbalun cables
C1
C2
LL
C1
C2
C2
C2
C2
C2
D1
C3C3
Coil layout
Gap on backside of copper substrate
(Hayes et al. Magn Reson Med 18:309-319, 1991)
Methods: Ladder Coil Set UP
coil 3 / 5 slabs
coil 2 / 3 slabs
coil 1 / 4 slabs
+ GE standard head coil (GE Head)+ Commercial Neurovascular PA coils (NVPA)
Torso PA Chest Dual PA Inverted Dual PA
Carotid PA Head Dual PA
0 5 10 15 20 250
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
vessel length (cm)
rela
tive
SN
R
5 coil array single 10 cm radius coil
Purpose
• Develop a coil for MRA screening from the aortic arch to the top of the head
• Use dedicated coil elements for each section of specific anatomy
• Ability to use the same coil for high-resolution imaging of suspect regions