Fabian Tobias Gutjahr1, Thomas Kampf1, Stephan Michael Guenster1, Volker Herold1, Patrick Winter1, Xavier Helluy2, Wolfgang Bauer3, and Peter Jakob1
1Experimental Physics V, University of Wuerzburg, Wuerzburg, Germany, 2NeuroImaging Centre, Ruhr University, Bochum, Germany, 3Department of Internal Medicine 1, Universitaetsklinikum Würzburg, Wuerzburg, Germany
Synopsis
A fast method for the measurement of myocardial perfusion in mice is presented. Using an efficient retrospective data selection and weighting process in combination with a model based reconstruction perfusion maps can be acquired within 3.5min.Purpose
T1
based arterial spin labeling (ASL) perfusion measurements have become
the de facto (1-2) standard for myocardial perfusion mapping in mice. Yet
there has been an increased interest in first pass perfusion
measurements (3-4) due to the high acquisition speed. In this work we want
to demonstrate an ASL method that is nearly as fast as first pass
measurements while retaining the advantages of ASL measurements.
Methods
In
(5) a retrospectively triggered method using a model
based reconstruction has been demonstrated. Retrospective
triggering and breath gating leads to undersampling. A model based method is used to extrapolate missing data directly in k-space. Data acquired during a 30% window around the desired
position in the cardiac cycle is accepted for reconstruction. In order to use the acquired
data more efficiently, data further away from the desired position in the cardiac
cycle can be used to improve the reconstruction. To prevent smeared images, data
are weighted before the interpolation. Weighting is done in
dependence of the position in k-space and in the cardiac cycle. A
proposed weighting scheme can be seen in Fig. 1. In the k-space center the selection is more strict so intensity variations due to blood flow and cardiac motion do not influence the image intensity, which would lead to incorrect T1 fits. Using a numerical
phantom the sharpness of the acquired images was assessed. The gain
in accepted data can be used to shorten the measurement time
significantly.
Results
Data
from a wider range of the heart cycle are
used for reconstruction. Perfusion measurements of murine myocardium
were acquired in less than 3.5 minutes with a native inplane resolution of (230µm)
2. A
comparison
of the results from the reconstruction with a fixed 30% window and
the weighted selection can be seen in Fig.
2.
The quality of the
maps is improved while the
heart phase and k-space
dependent weighting
prevents loss in image sharpness.
Conclusion
A
fast method for T1 measurements and perfusion mapping using a
retrospectively triggered reconstruction is demonstrated. The
acquisition time of 3.5 min is comparable to first pass methods while
all the advantages (eg. repeatability, noninvasiveness, low
preparational effort) of arterial spin labeling perfusion
measurements are retained.
Acknowledgements
This work was supported by grants from the Deutsche Forschungsgemeinschaft (SFB 688 B5, Z02) and the Bundesministerium für Bildung und Forschung (BMBF01 EO1004)References
(1) Campbell-Washburn et al. Magn Reson Med. 2013 Jan;69(1):238-47. doi: 10.1002/mrm.24243. Epub 2012 Mar 12.Cardiac arterial spin labeling using segmented ECG-gated Look-Locker FAIR: variability and repeatability in preclinical studies.
(2) Vandsburger et al. Magn Reson Med. 2010 Mar;63(3):648-57. doi: 10.1002/mrm.22280.Improved arterial spin labeling after myocardial infarction in mice using cardiac and respiratory gated look-locker imaging with fuzzy C-means clustering
(3) Naresh et al., Magn Reson Med. 2015 Jul 20. doi: 10.1002/mrm.25769. Repeatability and variability of myocardial perfusion imaging techniques in mice: Comparison of arterial spin labeling and first-pass contrast-enhanced MRI.
(4) Coolen et al. Magn Reson Med. 2010 Dec;64(6):1658-63. doi: 10.1002/mrm.22588. Mouse myocardial first-pass perfusion MR imaging.
(5) Gutjahr et al., Magn Reson Med. 2014 Dec 1. doi: 10.1002/mrm.25526. Quantification of perfusion in murine myocardium: A retrospectively triggered T1-based ASL method using model-based reconstruction