Hyperpolarized Xe-129 in the Rat

Report
Determining Whole Lung
Perfusion Using
Hyperpolarized Xe-129 MRI
Ian Gerard
Department of Medical Biophysics
University Of Western Ontario
Six Week Project
MR Imaging Basics
B1
Sample
RF Coil
Gradient Coil Set
Magnet
z
z
m
x
y
x
y
Hyperpolarized Media
Isotope
Spin
* 107 rad s/T
P (ppm)
1H
1/2
1/2
1/2
-1/2
26.75
20.37
6.73
7.40
5.11
3.89
1.28
1.41
3He
13C
129Xe
(For T = 300 K and B0 = 3 T )
M  NmP
In General
P  Pth105
After Hyper-polarization Method
Gas Exchange Model
TTR
Cc(r,t)
Lc
Ct(r,t)
Lt
Ca(t)
FIN
ra
Xe
VA
Xe
Xe
D 2C ( r , t )
r 2
Xe
Xe
FOUT
-
C ( r , t )
t
0
Xe
Gas
Tissue
Capillary
Fig 1: Alveolar-Capillary model of Mansson [2].
Va is the alveolar volume measured at standard
temperature and pressure. ra is the radius of the
alveolus. Lt and Lc are the compartment lengths for
tissue and capillary. C(r,t) is the xenon concentration
in each respective compartment as a function of
distance and time. F is the rate of pulmonary flow.
Fin=Fout.
-t

TTR 
t

S ( ) S0 1 e
 + S1t


S1  αλpl (1 – H)F
Methods
Medical Air & O2
Ventilator
3He
Or
129Xe
3T MRI Scanner
Heater
Rb Reservoir
Polarization Cell
Gas Cylinder
89% 4He
10% N2
1% Xe
794.8nm
Circular Polarizer
Magnet
Polarized 129Xe Out
Polarized 129Xe and 3He
Valve
Assembly Acid Port
Ventilator
Pilot Results: Xenon
Pulse Sequence
Chemically Selective Saturation Recovery (CSSR)
90o
90o
RF Pulse
~193ppm
t i
f
Loop
N. Abdeen et al (2006)
t
Dissolved
Gas Phase
Phase Maximized Minimized
Spectroscopy After Applying
Pulse Sequence
S (t )  S0 (1 - e -t / TTr ) + S1t
Mansson Model:
S (t )  S0 (1 - e -t / TTr ) + S1t
Valid for all time.
Tissue Spectroscopy and Model
Fit
Mansson Model:
S (t )  S0 (1 - e -t / TTr ) + S1t
Results: Representative Figure
S (t )  S0 + S1t
Linear fit applied to
long time values
Slope and intercept
values are S1 and S0
respectively and used to
calculate lung perfusion
Calculated Lung Perfusion
Typical Perfusion value from control rat 1.2 ± 0.2
Mansson et al.
Rat Number
Rat 1
Rat 2
Rat 3
PIP (cmH20)
Mean Perfusion
(ml s-1/ml) ± Std
7 ± 0.1
0.74 ± 0.05
11 ± 0.1
1.01 ± 0.01
12 ± 0.1
1.17 ± 0.03
17 ± 0.1
1.29 ± 0.04
7 ± 0.1
0.84 ± 0.05
12 ± 0.1
1.07 ±0.02
17 ± 0.1
1.36 ± 0.05
11 ± 0.1
1.14 ± 0.15
13 ± 0.1
1.34 ±0.06
15 ± 0.1
1.40 ± 0.05
Perfusion and PIP
• Appears to
be some
relationship
between PIP
value and
Perfusion
Discussion
• Values agree with control perfusion from
Mansson et al.
• Something interesting may be happening at
low pressure.
• There may be a relationship between
Perfusion and PIP
• Hematocrit and typical perfusion values
used were for Wistar rats while SpragueDawley rats were actually used but
assumed equal for the project
Conclusions and Future Work
• Successfully able to estimate whole lung
perfusion using Mansson model and other
minor assumptions
• Investigate the effects of low PIP on
perfusion
• Next Step: Create a perfusion map
determining lung perfusion on a pixel by
pixel basis
Acknowledgements
Heather Cadieux
Eugene Wong
Jake Van Dyk
Funding:
Giles Santyr
Matthew Fox
Alexei Ouriadov
Ryan Kraayvanger
William Dominguez
Wilfred Lam
Peggy Xu
Adam Farag
Marcus Couch
Lynda McCaig
Ruud Veldhuizen
Jim Lewis

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