Turboprop IDEAL: A motion‐resistant fat–water separation technique

Abstract

Suppression of the fat signal in MRI is very important for many clinical applications. Multi-point water-fat separation methods, such as IDEAL (Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation), can robustly separate water and fat signal, but inevitably increase scan time, making separated images more easily affected by patient motions. PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) and Turboprop techniques offer an effective approach to correct for motion artifacts. By combining these techniques together, we demonstrate that the new TP-IDEAL method can provide reliable water-fat separation with robust motion correction. The Turboprop sequence was modified to acquire source images, and motion correction algorithms were adjusted to assure the registration between different echo images. Theoretical calculations were performed to predict the optimal shift and spacing of the gradient echoes. Phantom images were acquired, and results were compared with regular FSE-IDEAL. Both T1-and T2-weighted images of the human brain were used to demonstrate the ef- Key words: fat suppression; IDEAL; PROPELLER; TurboporpRobust water-fat separation is very important in many clinical applications, and can improve clinical diagnosis in applications for which the bright fat signal could otherwise obscure underlying pathology. For example, when T1-shortening contrast agents such as gadolinium are used to visualize lesions in T1-weighted imaging, or in T2-weigthed imaging where the edema or tumors appear bright, it is very important to suppress the fat signal effectively.Various techniques have been proposed to suppress the fat signal. One can use RF pulses to selectively excite the water signal or suppress the fat signal (1-3), or use a short TI recovery (STIR) technique (4 -6) to null the fat signal. However, these techniques are usually sensitive to B0 or B1 field inhomogeneities, and sometimes fail to provide reliable separation (suppression) in clinical applications. Multi-point water-fat separation methods (7-15) exploit the difference in chemical shifts between water and fat to separate them, and are less affected by field inhomogeneities.Source images from multi-point water-fat separation techniques can be processed differently. Dixon's method (7) and its variations (8 -11,14) have been widely used. IDEAL (Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation) (15) is a recently proposed multi-point water fat separation technique. Combined with a region-growing algorithm (16), IDEAL has great robustness and SNR efficiency, making it suitable for many clinical applications (15,17,18). However, the requirement of acquiring multiple images may increase total scan time and make IDEAL images more prone to motion artifacts. Variations of IDEAL techniques have been proposed (19 -23) to reduce scan time and motion artifacts, however the remaining artifacts may still be a problem.PROPELLER (Periodically Rotated Overlapp...

Chemical shift encoding‐based water–fat separation methods

“…While only different variants of Cartesian gradient‐echo and fast or turbo spin‐echo imaging were illustrated in the examples, Dixon methods are applicable in conjunction with most sequences and sampling strategies. They have been demonstrated in balanced steady‐state free precession imaging (FIESTA/bFFE/TrueFISP) , as well as with radial, spiral, and PROPELLER k ‐space trajectories . The most notable exception is still Cartesian EPI, as mentioned previously.…”

Dixon water‐fat separation in PROPELLER MRI acquired with two interleaved echoes

“…The proposed approach with two interleaved echoes has a number of advantages over previously presented multiecho approaches . Most importantly, data can be acquired more SNR‐efficient with a low sampling bandwidth.…”

GESFIDE-PROPELLER Approach for Simultaneous R2 and R2* Measurements in the Abdomen

“…However, fat saturation methods can be relatively sensitive to B 0 and B 1 inhomogeneities, resulting in partial or failed fat suppression. Huo et al (26) recently proposed another approach for the Turboprop-IDEAL sequence to reduce chemical-shift artifacts by acquiring blade-pairs for each blade with opposite readout directions; however, this approach increases the total imaging time by a factor of 2. Further investigations to compare and optimize fat signal suppression approaches for these PROPELLER-based GESFIDE methods could be valuable to improve image quality and R2/R2* measurement accuracy.…”