Gradient- and spin-echo (GRASE) MR imaging: a long-existing technology that may find wide applications in modern era

Comparison of Compressed Sensing and Gradient and Spin-Echo in Breath-Hold 3D MR Cholangiopancreatography: Qualitative and Quantitative Analysis

“…Although direct comparison of qualitative scores between the two different studies is difficult, background suppression for BH-GRASE-MRCP was better in our study compared to He et al, (4.02 vs. 3.885), while background suppression for BH-CS-MRCP was quite similar (4.46 vs. 4.628). As GRASE is inherently a combination of gradient echo and FSE [ 30 ], susceptibility effects in proximity to air-tissue interfaces arising from the gradient-echo [ 31 ] could lead to unwanted signal loss and thus may hide the small duct, such as 2nd level IHD or PD. Moreover, GRASE has been reported to show blurring related to the point-spread-function arising from T2 and T2* decay [ 32 ], which, with matrix size settings during a limited imaging time, impairs spatial resolution and could be inadequate for showing small ducts [ 20 ].…”

Magnetic resonance cholangiopancreatography at 3T in a single breath-hold: comparative effectiveness between three-dimensional (3D) gradient- and spin-echo and two-dimensional (2D) thick-slab fast spin-echo acquisitions

“…Although not a severe problem at field strengths of 1.5 Tesla or lower, the SAR issue becomes critical at 3.0 Tesla or higher because power deposition scales more than linearly with the main field strength (10). One approach that may surrogate FSE in 3D MRCP is to insert a series of gradient echoes during each echo spacing interval in a way similar to echo-planar imaging (11), such that the amount of data obtained per single refocusing RF pulse can be increased. This method, termed the gradient-and spin-echo (GRASE) sequence (12,13), has recently been employed for 3D MRCP at 3.0 Tesla.…”

“…Despite of the obvious advantage of 3D GRASE for MRCP in terms of motion immunity as compared with 3D FSE at identical SAR, there are potential issues to be explored regarding this technique. Since GRASE is essentially a hybrid of gradient echo and FSE (11), susceptibility effects near air-tissue interfaces due to the gradient-echo nature (16) could possibly lead to undesired signal loss and hence may obscure particularly the pancreatic ducts. In addition, GRASE is known to exhibit point-spread-function-related blurring due to T2 and T2* decaying (17) which, along with matrix size settings within limited scan time, trades off the spatial resolution and could thus be detrimental for depicting small ducts.…”

“…Inferiority of 3D GRASE to 2D thick-slab FSE MRCP in RAD, RPD, and PDD is attributed to difference in in-plane spatial resolution because of the small size of these ducts (15). Despite that the voxel volume of 1.51×1.53×1.20 mm 3 in 3D GRASE MRCP was theoretically adequate in resolving these ducts, the actual spatial resolution could easily be impeded by residual subject motion and point-spread-function blurring (11,17). Here the very short scan time of 2D thick-slab FSE MRCP plus its high in-plane resolution provided important advantage for depiction of small ducts compared with 3D GRASE MRCP.…”

“…On the other hand, balanced steadystate free precession and fast-recovery FSE are two different readout design alternatives to GRASE, probably promoted by different manufacturers and thus hard to compare under the same system platform. In fact, to our knowledge, 3D GRASE so far does not seem to be widely employed for MRCP by other manufacturers (11). Nevertheless, balanced steady-state free precession is known to exhibit banding artifacts particularly prominent at high fields (28), whereas fast-recovery FSE exhibiting exactly the same SAR issue as 3D FSE might restrict MRCP applications to field strengths of 1.5 Tesla or lower (4,27).…”