Johannes Töger1,2, Mikael Kanski1, Per M Arvidsson1, Marcus Carlsson1, Sándor J Kovács3, Rasmus Borgquist4, Johan Revstedt5, Gustaf Söderlind2, Håkan Arheden1, and Einar Heiberg1,2,6
1Department of Clinical Physiology, Lund University Hospital, Lund University, Lund, Sweden, 2Department of Numerical Analysis, Centre for Mathematical Sciences, Lund University, Lund, Sweden, 3Department of Internal Medicine, Washington University School of Medicine, St Louis, MO, United States, 4Department of Arrhythmias, Lund University Hospital, Lund University, Lund, Sweden, 5Department of Energy Sciences, Lund University, Faculty of Engineering, Lund, Sweden, 6Department of Biomedical Engineering, Lund University, Faculty of Engineering, Lund, Sweden
Synopsis
Diastolic dysfunction of the left ventricle
(LV) of the heart is a severe condition associated with poor prognosis.
However, objective and reproducible assessment of diastolic function remains a
challenge. We propose a new method using 4D flow MR by quantification of blood
mixing within the LV diastolic vortex-ring. Phantom validation showed fair
agreement between 4D flow MR and planar laser-induced fluorescence (PLIF).
Quantitative vortex-ring mixing differs between healthy controls and patients
with heart failure, which demonstrates its potential as a marker of diastolic
dysfunction.Purpose
Diastolic dysfunction of the left
ventricle (LV) of the heart is commonly seen in cardiac disease and is
associated with poor prognosis.
1 In clinical practice, diastolic dysfunction is diagnosed using a
combination of imaging measures, and the resulting classification may be
ambiguous or inconclusive.
2,3 Therefore, new quantitative physiology-based indices are needed. Diastolic
vortex-ring formation has been proposed as a sensitive marker of diastolic
function.
4 Therefore, our aim is to present and validate a new method for magnetic
resonance (MR) 4D flow quantification of vortex-ring mixing during early, rapid
filling (corresponding to the Doppler E-wave) of the LV as a potential index of
diastolic dysfunction.
Methods
Vortex-ring mixing measurements using 4D
flow MR were validated using planar laser-induced fluorescence (PLIF) in a
previously described phantom setup (Figure 1).5 The phantom setup includes a custom-built pulsatile pump connected
to a nozzle attached to a water tank, where vortex-rings are formed.
Controls
(n=23) and patients with heart failure (n=23) were studied at 1.5T (26
subjects) or 3T (20 subjects) using a previously validated turbo-field echo
(TFE) sequence.5–7 Typical scan parameters were: spatial resolution 3×3×3 mm, flip angle 8°, TR/TE 6.3/3.7 ms, VENC 100
cm/s, temporal resolution 50 ms, SENSE=2 and segmentation factor 2.
Retrospective ECG triggering was used.
For phantom scans, two different methods for phase background correction were used: A) linear
fit of velocities in stationary voxels, and B) subtraction of velocities from a
scan performed with no flow in the tank. For in vivo scans, method A was used in
all subjects.
Vortex-ring volume (VV) was determined using
post-processing of 4D flow using Lagrangian Coherent Structures (LCS, Figure 2).8 The inflowing volume during diastole (VVinflow) was
quantified from through-plane flow in the mitral annulus reconstructed from 4D
flow. The volume mixed into the vortex-ring was then quantified as VVmix-in
= VV–VVinflow. The mixing ratio was defined as MXR = VVmix-in/VV
= 1 – VVinflow/VV.
To test interstudy variability, the full
analysis was carried out for all subjects by two independent observers (JT and
PA). Interobserver variability was defined as the mean and standard deviation
of the differences in MXR between the two observers.
Results
Figure 2 shows LV vortex-ring
mixing in a control subject and a patient with heart failure, using Lagrangian
Coherent Structures8 and Volume Tracking.9
As seen in Figure 3, PLIF validation of 4D
flow MXR showed fair agreement (method A: R2=0.28, mean±SD: 6±7%, method
B: R2=0.45, 1±6%). Interobserver variability for MXR was -4±8% in
controls and -5±9% in patients.
Figure 4 shows quantitative results in controls
and patients. MXR was higher in heart failure patients compared to controls
(28±11% vs 16±10%, p<0.001).
Discussion
The PLIF validation shows that diastolic
vortex-ring mixing can be quantified using MR 4D flow. The importance of phase
background corretion in computing quantitative measures from 4D flow MR is
underscored by the different results for the two background correction methods.
The difference in MXR between controls and
patients may be the result of impaired diastolic function in the heart failure
patients. The specific mechanisms that determine MXR remain to be elucidated,
but likely include LV diastolic suction and load, relaxation and stiffness,10 left atrial pressure, and mitral valve geometry.
Conclusions
Vortex-ring
mixing can be quantified using 4D flow MR. The differences in mixing parameters
observed between controls and patients motivate further investigation of fluid
dynamics based indices of diastolic dysfunction and heart failure.
Acknowledgements
Tomas Hajdu at the
Department of Medical Technology, Skåne University Hospital Lund, Sweden is
acknowledged for design and construction of the phantom equipment.
Ann-Helen Arvidsson, Christel
Carlander, Reza Farazdaghi, Johanna Koul and Lotta Åkesson at the Department of
Clinical Physiology, Lund University Hospital, Lund, Sweden are acknowledged
for assistance in data collection.
This abstract is based
on a paper submitted to and under review in Journal of Magnetic Resonance
Imaging (JMRI) at the time of abstract submission.
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