Cardiac and Respiratory Self-Gated 4D Multi-Phase Steady-State Imaging with Ferumoxytol Contrast (MUSIC)
Fei Han1, Ziwu Zhou1, Takegawa Yoshida1, Kim-Lien Nguyen1,2, Paul J Finn1, and Peng Hu1

1Radiology, University of California, Los Angeles, Los Angeles, CA, United States, 2Division of Cardiology, Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, CA, United States

Synopsis

We proposed a cardiac and respiratory self-gated, 4D multi-phase steady-state imaging with contrast (MUSIC) technique for detailed evaluation of cardiovascular anatomies. A rotating cartesian k-space sampling pattern was designed that integrates frequently sampled k-space centerline as self-gating signal and allows retrospective data-binning based on derived motion signal. Phantom and in-vivo results on 7 clinical indicated pediatric CHD patients show that the proposed self-gated MUSIC could potentially eliminates the need of external physiological signal for motion gating, has increased scan efficiency while maintaining or exceeding the image quality of the original MUSIC.

Purpose

Conventional contrast-enhanced MRA is generally performed without cardiac gating due to the time constraint imposed by breath-hold and the first passage of the gadolinium based agent and therefore provides limited delineation on blood vessels that are subject to cardiac motion. To address this issue, we recently proposed the MUSIC1 approach that acquires cardiac-phase-resolved 4D images without breath-holds during the steady-state distribution of ferumoxytol, an intra-vascular contrast agent. Using ECG and airway pressure signal for motion gating, the MUSIC has been routinely applied in our institution on pediatric patients with congenital heart disease (CHD) and provides exquisitely detailed information on both intra- and extra-cardiac vascular anatomy1. However, the airway pressure signal is only available when general anesthesia (GA) is performed and the ECG signal is not always reliable especially in high field strength due to interference from the RF pulses and gradients. To overcome these limitations, we propose the self-gated MUSIC (sgMUSIC) where a retrospective motion self-gating strategy is used to eliminate the need for external physiological signal and make the MUSIC potentially available on general patient population. In this study, we tested the sgMUSIC on pediatric CHD patients underwent GA so that the derived motion signal can be validated against the recorded physiological signal and the sgMUSIC images compared with original MUSIC.

Methods

(a)Data Acquisition: A 3D GRE sequence is modified using ROtating Cartesian K-space (ROCK) where kykz views of 3D Cartesian grid were reordered using quasi-spiral pattern with each arm starts from the outer k-space and ends at the center(Fig.1a). The arms are rotated using segmented golden ratio2 in which the entire k-space is divided into N=7 angular segments, each segment is sampled using golden ratio and different segments are sampled in a pseudo-random order. The extra degree of randomness ensures more uniform k-space sampling even after data sorting. (b)Data Sorting: Cardiac and respiratory self-gating signal was derived from the repeatedly sampled centerline (kykz=0) using cross-correlation3 and further separated by band-pass filter. The acquired data is then retrospectively soft-gated4 based on the derived respiratory self-gating signal and sorted into different cardiac phase based on the derived cardiac self-gating signal. (c)Image Reconstruction: 3D images were reconstructed independently for each cardiac phase using ESPIRiT, a compressed sensing and parallel imaging combined approach5. The data sorting and image reconstruction algorithms were implemented in our GPU-accelerated image reconstruction framework5 so that 4D images are available at the scanner console 5-8 minutes after the scan. (d)Phantom Experiment: Static phantom experiment was performed to validate the ROCK pattern in different settings: 1) direction of quasi-spiral arms (inward vs. outward); 2) rotating strategy (segmented golden ratio vs. golden angle). Data was sorted using physiological signal recorded from previous patient scans. (e)In-vivo Experiment: 7 clinically indicated pediatric CHD patients (aged 1 month to 8 years) underwent GA with controlled mechanical ventilation were included in this study. 4mg-Fe/kg ferumoxytol was administrated. The sgMUSIC was performed after standard clinical protocol, which includes the original MUSIC with matching resolution. Sequence parameters included: 0.9/2.9ms, FA=25°, 500x300x150, 0.8-1.0mm3 isotropic resolution, 9 phases, TA=5±1.5min. The self-gated images were reconstructed without using ECG or ventilator pressure signal. (f)Image Evaluation: Subjective image quality scores were visually assessed on original MUSIC and sgMUSIC in 3 different anatomical regions by a cardiologist using criteria listed in Table 1.

Results

The time series of SG projections from static phantom (Fig.1b) shows that the inward quasi-spiral arm could significantly reduce the eddy-current interference in self-gating signal because an adjacent k-space line is acquired in previous TR instead of a distant one in the case of outward arm. The k-space patterns (Fig.1c) show the segmented golden ratio provides more uniform k-space sampling even after data sorting. Fig.2 shows the in-vivo result from a 3-month-old female where the derived SG signal corresponds well with the recorded physiological signal and the sgMUSIC images using self-gating signal have similar quality with the ones using recorded physiological signal. When compared with the original MUSIC acquired using with 4X GRAPPA, the sgMUSIC acquisition took less time due to the use of variable density sampling pattern and non-linear image reconstruction algorithm. Scores in Table.2 shows that the sgMUSIC maintains or exceeding the image quality of original MUSIC, with significant improvement in 1 of 3 regions. (P<0.05) The volumetric images allows reformatting into arbitrary planes for visualization of detailed vascular structures (Fig.3).

Conclusion

The proposed cardiac and respiratory self-gated MUSIC eliminates the need of external physiological signal for motion gating, has slightly increased scan efficiency, while maintaining or exceeding the image quality of the original MUSIC.

Acknowledgements

NIH 1R01HL127153

References

1. Han, F., Rapacchi, S., Khan, S., Ayad, I., Salusky, I., Gabriel, S., Plotnik, A., Finn, J. P. and Hu, P. (2015), Four-dimensional, multiphase, steady-state imaging with contrast enhancement (MUSIC) in the heart: A feasibility study in children. Magn Reson Med, 74: 1042–1049. doi: 10.1002/mrm.25491

2. Han, F., Zhou, Z., Rapacchi, S., Nguyen, K.-L., Finn, J. P. and Hu, P. (2015), Segmented golden ratio radial reordering with variable temporal resolution for dynamic cardiac MRI. Magn Reson Med. doi: 10.1002/mrm.25861

3. Hu, P., Hong, S., Moghari, M. H., Goddu, B., Goepfert, L., Kissinger, K. V., Hauser, T. H., Manning, W. J. and Nezafat, R. (2011), Motion correction using coil arrays (MOCCA) for free-breathing cardiac cine MRI. Magn Reson Med, 66: 467–475. doi: 10.1002/mrm.22854

4. Cheng, J. Y., Zhang, T., Ruangwattanapaisarn, N., Alley, M. T., Uecker, M., Pauly, J. M., Lustig, M. and Vasanawala, S. S. (2015), Free-breathing pediatric MRI with nonrigid motion correction and acceleration. J. Magn. Reson. Imaging, 42: 407–420. doi: 10.1002/jmri.24785

5. Uecker, M., Lai, P., Murphy, M. J., Virtue, P., Elad, M., Pauly, J. M., Vasanawala, S. S. and Lustig, M. (2014), ESPIRiT—an eigenvalue approach to autocalibrating parallel MRI: Where SENSE meets GRAPPA. Magn Reson Med, 71: 990–1001. doi: 10.1002/mrm.24751

6. Han, F., Zhou, Z., Sung, K., Finn, J. P. and Hu, P. A Low-Cost, Clinical Friendly Non-Linear Parallelized MR Image Reconstruction Framework: Initial Proof of Concept on Pediatric Contrast Enhanced MRA Application. Proceedings ISMRM 23rd Scientific Sessions, 2015, Toronto.

Figures

Fig.1 (a) the proposed ROCK pattern. (b) The time series of self-gating projections on static phantom shows that the inward quasi-spiral arm could significantly reduce the eddy-current interference in self-gating signal. (c) The kykz sampling pattern using segmented golden ratio, due to the extra degree of randomness, is more uniform than that of conventional golden ratio, both after a retrospective data sorting using recorded physiological signal in previous patient scan.

Fig.2 Data acquired on a 3 month-old female. Derived SG signal correlates well with the recorded physiological signal (a). The SG-MUSIC reconstructed using SG signal (d) has comparable image quality with the ones from a separated reconstruction using recorded physiological signal based on the same data (c). SG-MUSIC has shorter scan time yet better image quality (c,d) than the original MUSIC (b). (RESP airway pressure signal, RSG respiratory SG, CSG cardiac SG, TA acquisition time)

Table 2. Image Quality Scoring Criteria

Table 1. Image Quality Score of original MUSIC vs. self-gated MUSIC. (*) denotes statistical significance (P<0.05)

Fig.5 The 4D volumetric sgMUSIC images allows retrospective reformatting into arbitrary planes for visualization of detailed cardiac and vascular structures including major branches of coronary arteries.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
1077