Electrical Impedance Tomography for
Assessing Ventilation/Perfusion Mismatch
for Pulmonary Embolism Detection without
Interruption in Respiration
D T Nguyen1, A Thiagalingam2 , A Bhaskaran2, M A Barry2,
J Pouliopoulous2, C Jin1 and A McEwan1
1
School of Electrical and Information Engineering, The University of Sydney,
New South Wales, Australia
2 Department of Cardiology, Westmead Hospital, New South Wales, Australia
Outline
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Motivations
Overview
Materials and Methods
Results
Discussion
Future works
Motivation
• Pulmonary perfusion is important:
– Pulmonary embolism (PE)
• together with VTE: fifth most cause of death in Australia
– Pulmonary Artery Hypertension, etc.
• Electrical Impedance Tomography of the lung:
– Highly valuable tool for ventilation monitoring
• Why not pulmonary perfusion too?
– Possible but hard!
– Low signal to noise ratio (SNR) (with blood pulsatile signal)
• Borges et al. 2012 and Frerichs et al. 2002:
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–
–
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Contrast impedance bolus based on hypertonic NaCl to improve SNR
10 ml of 20% NaCl and 5.6% NaCl, respectively
Medium animal study (23 kg piglets)
2 minutes of apnea
Pulmonary Embolism
• 1.08 in 1000 people affected
• Pregnant, hospitalized patients are at 100 times
higher risk
• Non-specific symptoms: chest pain, shortness of
breath
• No positive predictive molecular marker: D-dimer
test
• Imaging diagnosis: CTPA and V/Q
R A Douma et al. (2010)
CTPA scan
(W S Choe et al. (2011))
V/Q Scan
(Wikipedia)
Overview of this study
• Use of contrast enhanced EIT for V/Q scan
• Low concentration saline as contrast
– 60 ml of 3% saline solution
• No apnea
• Artificially induced PE in large ovine model
(N=3, 83.7 ± 7.7 kg )
Materials and Methods
• Animal:
– Ovine model: 3 males,
Merino cross, 83.7 ±
7.7 kg, healthy
– Mechanically ventilated
(inspiration to
expiration ratio of
1:1.5)
– Under general
anesthesia
Materials and Methods (cont.)
• Agilis catheter (St Jude
Medicals):
– From right femoral vein
to IVC for contrast
injections
• Electrode rings:
– 32 electrodes for EIT
– Novel multi-point,
bronze coated
electrodes
Materials and Methods (cont.)
• Pulmonary embolism induction:
– Artificially induced
– Balloon catheter blocking blood supply in one the of
pulmonary arteries
• 3 Injection repetitions with PE and 3 without
Before Balloon inflation
Balloon inflated
Balloon deflated
Methods
• EIT:
– Swisstom Pioneer, 32 electrodes
– 5 mA, 100 kHz
– 10 frames per second
• GREIT reconstruction (EIDORS 3.7, Matlab 2014a)
 a 64 x 64 rasterized image/frame
• Time difference:
v = v(t)- v0
• 2.5 D model
2
1.5
L
R
1
0.5
0
4
3
2
1
2
0
1
0
-1
-1
-2
-2
-3
-3
Posterior
EIT image analysis
Raw EIT
Image
series
• 64 x 64
• Ventilation + Contrast
dilution
• Daubechies level 4
Filtered • 8 level decompositions
EIT image • Only keep levels 7 and 8
series
• Using ventilation signal
• Thresholding of FFT within
ROIs
definition respiration range
• For each ROI (left or right lung)
• Ventilation: sum of all
frequencies within respiration
Ventilation
range (of raw series)
and
Perfusion • Perfusion: from filtered series
estimation • Averaged V and Q for each ROI
R
L
Results – Perfusion at baseline
R
Dorsal
Results – Perfusion with defect
(right lung PE)
R
Dorsal
Results - Ventilation
Baseline
R
Dorsal
Right Lung PE
Results – Change in Perfusion due to PE
R
Dorsal
R
Dorsal
Quantitatively
• Compute and compare right lung to left lung (R2L) V and Q in
each state (PE and baseline) of all subjects.
• Significant change in
perfusion
• Reduction in R2L
because of right lung PEs
• Insignificant change in
ventilation
• S3: imbalance in ventilation
but normal perfusion
Discussion
• Contrast dilutions at each pixel after filtering is
similar to literature
• Dilution curve can be extracted with filtering
• In three subjects with induced PE, we showed
that contrast enhanced EIT can detect the
change in perfusion
Future works
• This is a pilot study for proof of concept
• Lots more to be done:
– Localization of the defects
– Superimpose perfusion and ventilation images
– More data required for optimization of the algorithm
 sensitivity and specificity
– Gold standard comparison
• But it’s worth it:
– Diagnosis of PE in “difficult patients” (renal problems,
pregnant, highly instrumented, etc.)
– Monitoring during treatment
– Radiation free routine check for at risk patients
Thanks
• To my co-authors
• Westmead Vivarium and research holding staffs
• And past colleagues:
– Dr William Chik
– Dr Roman Kosobrodov
• Supporting organizations:
– University of Sydney, Westmead and ARC grant
Thank you for listening !!!
