High field MRI - University of Nottingham

Trends in Static Magnetic Field
Exposure due to MRI
Penny Gowland
Magnetic Resonance Centre
University of Nottingham
Future trends
Overview
• The numbers of patients exposed
• The field strength of exposure
– Why high field ?
– Changes in magnet design
• The ranges of applications
• The classes of staff exposed
• The alternatives
Number of scanners in the UK
400
2000-3000
Increasing at
scan per
30-40 p.a.
scanner
Embedded table (double click
to see it)
p.a.
350
300
250
200
150
100
50
3
20
0
1
20
0
9
19
9
7
19
9
5
19
9
3
19
9
19
9
1
0
1-2% of the UK population
have an MRI scan every year
800,000
scans p.a.
in UK,
capacity will
increase
10% soon
MagNET
New title slide to break up presentation
Field strength trends
MR market share
>=1,5T
1899
Embedded1,0T
excel file
0,5T - 0,7T
<0,5T
583
161
03
20
01
20
99
19
97
19
95
19
93
19
91
19
89
19
87
19
85
97
19
19
83
70%
65%
60%
55%
50%
45%
40%
35%
30%
25%
20%
15%
10%
5%
0%
Projected market
100%
>=3T
1.5T
1.0-0.5T
0% 1999
2004
Embedded image
2009
<0.5T
Ultrahigh field
• High field milestones:
– 8T to Ohio State University 1998
– 7T to Minnesota 1999
Try to put some sort of image on every
slide
(depending on audience and the
– 9.4T to Minnesota
2003
the talk)
• Expected world market forpoint
7T ofwhole
body is
~ 10 to 15 systems (expected to increase
significantly over the next 5 years)
• Magnex and Oxford both shipped 9.4T whole
body scanners last year.
Why high field?
Whyhigh field ?
• Signal:
– SNR ~ Bo
• Chemical shift:
– CS ~ Bo  
• Susceptibility
These were ticks and crosses.. Look
what can happen to fonts when ppt files
are moved between computers
 DB ~ Bo  
• RF heating:
– SAR ~ Bo2 
• Relaxation times:
– T1 increased;  
– T2/T2* decreased 
Wicklow, Washington University, St. Louis
Using increased S/N
• Increase spatial resolution
– Microscopy, fibre tracking
– Thinner slices
• Increased temporal resolution
– Dynamic imaging
• Shorter experiments
– reduced imaging time
– reduced susceptibility artefacts
T2 weighted Tx/Rx Quad Head
1024 Matrix, 4 mm,TE 80, TR 4s
High spatial resolution- hair folicles
4.7 T
Zoomed in corner of image
Roger Ordidge,
UCL
Anatomical imaging in MS
Suspected MS
1.5 T
640 x 1024
Custom animation
Dept. of Radiology, University of Bonn, Germany
256 x 512
3.0 T
Summary
• This magnet is great!
  Bo
Embedded equation
Insert> Object> Equation
To get colour right,
Right click> Format object> Picture>
Recolour
Acknowledgements
• My family