GROG Based Sensitivity Map Estimation for Radial Data in MRI
mahwish khan1, Taquwa Aslam1, and Hammad Omer1

1Electrical Engineering, COMSATS institute of information technology, Islamabad, Pakistan

Synopsis

The estimation of receiver coil sensitivity profiles is required for many PMRI algorithms including CG-SENSE. Conventionally,CG-SENSE uses pre-scan method to estimate the sensitivity maps for which a separate scan is required. The novelty in this work is the use of GROG gridding on the central region of the acquired under-sampled cardiac radial data to estimate the receiver coil sensitivities using Eigen-value method. The results show that GROG based sensitivity map estimation (proposed method) is an effective method without any requirement of a prior scan or body coil image.

Purpose

The estimation of receiver coil sensitivity profiles is required for many Parallel imaging algorithms including CG-SENSE [1]. Conventionally, CG-SENSE uses pre-scan method [2] to estimate the sensitivity maps for which a separate scan is required. This paper proposes the use of GROG [3] to estimate sensitivity maps without any need to acquire a separate scan.

Materials and Methods

CG-SENSE is an iterative algorithm used in PMRI which requires sensitivities of the receiver coils for MR image reconstruction from under-sampled data. GROG [3] has been recently proposed to grid non-Cartesian data sets in a Cartesian fashion. Eigen-value method [4] is an implicit technique of estimating the sensitivity maps using a series of Eigen-value decompositions. The proposed method starts with the acquired radially under-sampled data (cardiac data in this paper). The central region of the acquired data (window size of 24x24 in this paper) is cropped and Grog gridding is applied to get the Cartesian estimate of this data. The inverse FFT of this Cartesian k-space provides a low resolution image. In this paper, the sensitivity maps are estimated from these low resolution images obtained after GROG gridding using (1) Pre-scan method [2] and (2) Eigen-value method [4]. The novelty in this work is the use of GROG gridding on the central region of the acquired under-sampled radial data to estimate the receiver coil sensitivities using Eigen-value method[4]. The reconstructions are performed on cardiac data obtained using 3T Skyra Siemens scanner at Case Western Reserve University, USA which contains 30 channel cardiac coils with 80 measurement frames in radial form 256×144×30 at TR=2.94ms with real-time, free-breathing and no ECG gating. The acquired data is under-sampled for different acceleration factors retrospectively. Artifact Power [5] is used to test the quality of the reconstructed images.

Results and Discussion

Figure1 shows the reconstructed cardiac images for different acceleration factors (AF) using the sensitivity maps estimated from the proposed method with CG-SENSE. Figure2 shows the reconstructed cardiac images obtained using the sensitivity maps estimated from the pre-scan method with CG-SENSE. Figure 3-a and 3-b compare Artifact Power (AP) and PSNR for the reconstructed images. The results show low artifact power and high PSNR (as desired) in the reconstructed images for all the acceleration factors using the proposed method. This shows that the proposed method successfully estimates sensitivity maps without the need of a separate scan providing good reconstruction results.

Conclusion

GROG based sensitivity map estimation (proposed method) is an effective method to estimate receiver coil sensitivity profiles without any requirement of a prior scan or body coil image.

Acknowledgements

COMSATS institute of information technology, Islamabad, Pakistan.

References

[1] Nicole Seiberlich, Non-Cartesian Parallel Imaging Reconstruction, Journal of Magnetic Resonance Imaging, Volume 40, Issue 5, pages 1022–1040, November 2014.

[2] Klaas P. Pruessmann, SENSE: Sensitivity Encoding for Fast MRI, Magnetic Resonance in Medicine 42:952–962 (1999) Magnetic Resonance in Medicine 42:952–962 (1999).

[3] Nicole Seiberlich, Reconstruction of Under-sampled Non-Cartesian Data Sets Using Pseudo-Cartesian GRAPPA in Conjunction With GROG, Journal of Magnetic Resonance Imaging, Volume 59, Issue 5, pages 1127–1137, May 2008.

[4] Michael Lustig, ESPIRiT – An Eigenvalue Approach to Autocalibrating Parallel MRI: Where SENSE meets GRAPPA, 19th Annual Meeting of ISMRM, Montreal, Canada, 2011.

[5] Omer H, Dickinson R, British Chapter of the ISMRM, Annual Meeting 2010, Nottingham, UK.

Figures

Figure(1) Reconstructed cardiac images using sensitivity maps estimated from the proposed method with CG-SENSE

Figure(2) Reconstructed cardiac images using sensitivity maps estimated from the pre-scan method with CG-SENSE

Figure3 (a) AP of the reconstructed images for different AF for the proposed method.

Figure 3 (b) PSNR of the reconstructed images for different AF for the proposed method



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