Parallel Imaging
Suchandrima Banerjee1

1GE Healthcare, United States


With the increasing use of multicoil array for MR signal reception, and motivated by the need to increase acquisition speed, parallel imaging has become as essential part of MR scans. This talk will aim to impart basic understanding and develop an intuition for underlying concepts of parallel imaging reconstruction with a focus on most widely used methods such as SENSE and GRAPPA. Dynamic acceleration and extension to non-cartesian trajectories will be touched upon and the impact of parallel imaging reconstruction on signal-to-noise will be discussed.

Target Audience

Physicists and engineers new to the field and clinicians looking to acquire a better understanding of parallel imaging.


-To provide a brief background on parallel imaging developments.

-To introduce various methods of parallel imaging, and discuss the similarities and differences between the methods

-To discuss SNR measurement for images obtained with Parallel Imaging

-To help develop an understanding of the use cases and limitations of highly accelerated imaging


Need for increasing scan throughput and reducing chances of incidence of motion greatly motivate acceleration of MR scans. With the proliferation of multiple channel receive coils, acquired MR data is typically overdetermined. For these reasons, parallel imaging which constitutes of under sampling the MR data and synthesizing/estimating the missing data using the redundancy of multi-coil signal reception has become an integral part of MR exams, and an enabler for many static as well as dynamic MR techniques in clinical settings.


While many different parallel imaging techniques have been published in the literature since the publication of the SMASH [3] method in 1997, the underlying concept for all these methods is that MR data is undersampled, and the missing information is estimated by exploiting spatially varying sensitivity of coil elements in the receiver array. One way of categorizing the techniques is on the basis of how they estimate coil sensitivities-methods such as SMASH[3], SENSE [4-5] and SPACE-RIP [6] estimate the coil sensitivity information explicitly while AUTO-SMASH [7], PILS[9], GRAPPA [10] and APPEAR [13] implicitly use the sensitivity information for reconstruction to avoid some of the challenges associated with explicit estimation of the sensitivities.While a comprehensive review of all proposed parallel imaging techniques is beyond the scope of this discussion, some of the most widely used techniques such and SENSE and GRAPPA and a combination of the approaches [14] will be described in detail. Design choices such as size of calibration data, kernel size and regularization parameter will also be discussed. Dynamic parallel imaging [15-18] and pseudo-Cartesian/Non Cartesian approaches [19-21] to parallel imaging will also be touched upon.

Results and Discussion:

Higher acceleration factors can come at the expense of image artifacts and loss of diagnostic quality which is why acceleration factor for a specific MR protocol should be chosen carefully. Parallel imaging reconstruction also leads to spatially varying noise enhancement which makes signal-to-noise ratio calculation more complicated, and can impact MR image derived measurements. Some of these caveats will be addressed briefly in this talk.


No acknowledgement found.


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Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)