Hung Phi Do1 and Krishna S Nayak2
1Department of Physics and Astronomy, University of Southern California, Los Angeles, CA, United States, 2Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, United States
Synopsis
Modiļ¬ed Look-Locker Inversion Recovery (MOLLI)
provides the highest precision and reproducibility for myocardial T1 mapping,
and extracellular volume (ECV) mapping. In this work, we determine its
effectiveness for measuring myocardial blood flow (MBF), based on apparent-T1
mapping under two conditions, slice-selective inversion and non-selective
inversion. We demonstrate that MOLLI provides measured MBF comparable to the
reference FAIR-SSFP ASL method.Background
Myocardial blood flow
(MBF) is an important indicator of micro-vascular and coronary artery
dysfunction. Arterial spin labeled (ASL) CMR is a non-contrast technique that can
quantitatively measure MBF either using signal subtraction
1-4 or apparent T
1
approaches.
5,6 MOLLI has been shown to provide the highest precision and
reproducibility among T
1 mapping methods.
7 This study investigates
the feasibility of using MOLLI 5(3)3
8 apparent T
1 mapping for MBF
quantification in humans. We compare MOLLI-based ASL with conventional
flow-sensitive alternating inversion recovery (FAIR) ASL
9.
Methods
Our Institutional Review Board approved the study
protocol, and informed consent was provided by all subjects. Six healthy adults
were enrolled in the study (5M/1F, age 22-32). Two subjects received a second
scan on a separate day, resulting in a total of 8 datasets. All experiments
were performed on a 3T scanner (Signa Excite HDxt, GE Healthcare). MOLLI 5(3)38 and FAIR sequences were performed in all subjects. Scan time was 3 min for
FAIR (7 breath-holds) and 1 min for MOLLI (2 breath-holds, 1 with
slice-selective inversion, and the other with non-selective inversion). Imaging
parameters were the same for both methods: FOV=180-280 mm, slice thickness = 10
mm, matrix size = 96x96, GRAPPA factor =1.6.9 Flip angle was 500
and 350 for FAIR and MOLLI, respectively.
The myocardium was
manually segmented for global and per-segment (6 segments) analysis. MBF in
FAIR was analyzed in the same manner as described previously.4 MBF in MOLLI
was quantified using the equation MBF= λ/T1blood (T1NS/T1SS-1).10 Where λ and T1blood were chosen consistently with MBF quantification in FAIR
which are 1 ml/g and 1650ms, respectively. T1NS and T1SS
were obtained using nonlinear regression from MOLLI slice-selective inversion
and non-selective inversion series, respectively. Global and per-segment MBF of
the two methods were compared using paired Student’s t-test. Results were
reported as mean ± SD.
Results
Figure 1 shows T
1
maps acquired from MOLLI using slice-selective inversion (left) and
non-selective inversion (right) from a representative subject. Global and
per-segment T
1NS and T
1SS are summarized in the
Table 1, consistent with MOLLI literature
range of 1005 to 1296 ms.
11 T
1NS was significantly higher than T
1SS
(p<0.001) that is consistent with inflow of fresh blood to the imaging slice
as shown in
Figure 2. There was no
significant difference between global and per-segment MBF measured from the
MOLLI compared to those measured in the reference FAIR method (p>0.57) as
shown in
Figure 3. Scatter and Bland-Altman analysis show no
significant bias measured MBF from the two methods.
Conclusions
This study
demonstrates the feasibility of using MOLLI for assessment of MBF on healthy
subjects. The preliminary results show that MBF measured from MOLLI is in good
agreement with that measured in the reference FAIR method. Multi-slice MOLLI has
been routinely used in clinic. MOLLI ASL would simultaneously provide both MBF
and T
1 maps. Complete physiological noise analysis is a work in
progress.
Acknowledgements
American Heart
Association 13GRNT13850012; Wallace H. Coulter Foundation Clinical
Translational Research Award.References
1. Zun Z et al., Magn Reson Med. 2009; 62(4):975-83.
2. Wang DJJ et al., Magn Reson Med. 2010; 64(5):1289-95.
3. Zun Z et al., iJACC. 2011; 4(12):1253-61.
4. Do HP et al., J Cardiovasc Magn Reson. 2014; 16:15.
5. Zhang H et al., Magn Reson Med. 2005; 53(5):1135-42.
6. Northrup BE et
al., J Cardiovasc Magn Reson. 2008;
10:53.
7. Roujol S et al., Radiology. 2014; 272(3):683-9.
8. Kellman et al., J Cardiovasc Magn Reson. 2014; 16:2.
9. Jao TR et al., Proc. SCMR. 2016 (accepted)
10. Belle V et al., J Magn Reson Imaging. 1998:8:1240-45
11. Knobelsdorff-Brenkenhoff F et al., J
Cardiovasc Magn Reson. 2013; 15:53.