Carmosino

Chris Macgowan

Joshua van Amerom

Lars Grosse-Wortmann

Laskey

Milnor

Parker

Peter Leimbigler

Shi-Joon Yoo

Weinberg

English

PubMed

Springer - Publisher Connector

WORKSHOP PRESENTATION Open Access
Measurement of pulmonary arterial pulse wave
reflection from single-slice phase-contrast and
steady-state free precession MRI
Peter Leimbigler1*, Joshua van Amerom1,2, Lars Grosse-Wortmann2,3, Shi-Joon Yoo2,3, Chris Macgowan1,2
From 15th Annual SCMR Scientific Sessions
Orlando, FL, USA. 2-5 February 2012
Summary
Pulmonary arterial hypertension (PAH) is associated
with elevated pulmonary vascular resistance, resulting in
increased reflection of pressure and flow waves from
distal vessels1. The gold standard for assessing PAH is
right heart catheterization, an invasive procedure that
carries a 5% risk of major complications2. We validate a
noninvasive method for quantifying pulmonary arterial
reflection using phase-contrast (PC) and steady-state
free precession (SSFP) sequences acquired in a single
slice.
Background
An arterial segment approximates a hydraulic transmis-
sion line terminated distally by a reflection site that par-
tially reflects forward-traveling pressure and flow (q)
waves back toward the heart3. Due to finite pulse wave
velocity (PWV), backward-traveling waves are minimal
in early systole (Figure 1); since arterial cross-sectional
area (a) increases roughly linearly with pressure, PWV =
∂q(t)/∂a(t). Combining this with the water hammer
equation yields an expression for the backward flow
wave4:
<center>qb(t) = [qmeas(t) - PWV×a(t)]/2,</center>from
which arterial reflection magnitude (R) can be computed
in the frequency domain:
<center>R(ω) = Qb(ω)/Qf(ω).</center>
Methods
The right pulmonary artery in three healthy adult volun-
teers was imaged on a 1.5 T MR system (Siemens, Ger-
many) using retrospectively ECG-gated cine PC and
SSFP sequences to quantify blood velocity and vessel
cross-section, respectively. PC and SSFP images were
co-registered in MATLAB (The MathWorks, USA). The
arterial lumen was outlined semi-automatically using
Segment (Medviso, Sweden), yielding flow and area time
series that were resolved into forward and backward
flow waves in MATLAB. The frequency-domain ratios
of backward to forward flow waves yielded estimates of
R which were then averaged over the fundamental heart
frequency and the next two harmonics3 and compared
to literature values using a two-tailed Student’s t-test.
Results
The single-slice MRI method reliably resolved forward
and backward flows in vivo (Figure 2), enabling noninva-
sive measurement of normal right pulmonary arterial
reflection magnitudes, R (SD) = 0.34 (0.05), statistically
equivalent (p = 0.74) to invasively measured literature
values5 of R (SD) = 0.33 (0.13).
Conclusions
The feasibility of single-slice MRI measurement of pul-
monary arterial reflection in healthy adults motivates
follow-up studies in adult and pediatric patient popula-
tions and lays the groundwork for noninvasive assess-
ment of pulmonary hypertension.
Funding
This study was supported by the Canadian Institutes of
Health Research (App #199854).
Author details
1Medical Biophysics & Medical Imaging, University of Toronto & Hospital for
Sick Children, Toronto, ON, Canada. 2Diagnostic Imaging, Hospital for Sick1Medical Biophysics & Medical Imaging, University of Toronto & Hospital for
Sick Children, Toronto, ON, Canada
Full list of author information is available at the end of the article
Leimbigler et al. Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1):W35
http://www.jcmr-online.com/content/14/S1/W35
© 2012 Leimbigler et al; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Children, Toronto, ON, Canada. 3Labatt Family Heart Centre, Toronto, ON,
Canada.
Published: 1 February 2012
References
1. Weinberg , et al: Circulation. 2004, 110(17):2609-17.
2. Carmosino , et al: Anesth Analg. 2007, 104(3):521-7.
3. Milnor : Hemodynamics., 2 1989.
4. Parker : Med Biol Eng Comp. 2009, 47(2):175-88.
5. Laskey , et al: J Am Coll Cardiol. 1993, 21(2):406-12.
doi:10.1186/1532-429X-14-S1-W35
Cite this article as: Leimbigler et al.: Measurement of pulmonary arterial
pulse wave reflection from single-slice phase-contrast and steady-state
free precession MRI. Journal of Cardiovascular Magnetic Resonance 2012 14
(Suppl 1):W35.
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Figure 1 Illustration of single-slice wave separation. Before the
onset of backward waves, flow and area are related by the constant
factor PWV. Backward-traveling flow and area waves are equal in
form but opposite in sign, and are proportional to the difference
between PWV × area and flow.
Figure 2 Flow wave separation in the right pulmonary artery of
Subject 1 calculated from an initial MR study and a repeat scan 36
days later. Reflection magnitudes and standard deviations are
tabulated for all subjects. Scan parameters were TR/TE = 9.8/2.2 ms,
192 × 192 matrix, 28 × 28 cm2 FOV, 2 averages, flip angle = 10°
(PC) and 45° (SSFP). The root-mean-variances of the forward,
measured and backward flow waves between scans were 11, 16
and 8 ml/s, respectively.
Leimbigler et al. Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1):W35
http://www.jcmr-online.com/content/14/S1/W35
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Measurement of pulmonary arterial pulse wave reflection from single-slice phase-contrast and steady-state free precession MRI

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Journal of Cardiovascular Magnetic Resonance

Leimbigler Peter

van Amerom Joshua

Grosse-Wortmann Lars

Yoo Shi-Joon

Macgowan Chris

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Cite this article as: Leimbigler et al.: Measurement of pulmonary arterial pulse wave reflection from single-slice phase-contrast and steady-state free precession MRI.

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Measurement of pulmonary arterial pulse wave reflection from single-slice phase-contrast and steady-state free precession MRI

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