Publication for the Philips MRI Community Issue 47 2012/3 Liver imaging beyond expectations with Ingenia Contributed by John Penatzer, RT, MR clinical product specialist, Cleveland, OH, USA Publication for the Philips MRI Community ISSUE 47 2012/3 Ingenia s dstream technology as upgrade for Achieva, Intera Bonn proves the power of Ingenia 3.0T in prostate imaging Leuven sees high quality, large coverage head-neck MRI with Ingenia Partnership with Barrow Neurological Institute: research to make clinical MR faster and better Designed with patients in mind This article is part of FieldStrength issue 47 2012/3
38 Application tips Contributed by John Penatzer, RT, MR clinical product specialist, Cleveland, Ohio, USA Ingenia s dstream architecture delivers the first fully digital RF coils to the market, with their high SNR and superb ds-sense performance providing the opportunity to create new strategies for abdominal imaging leading to enhanced patient care. Ingenia users can perform liver imaging at higher SENSE factors than ever before in order to increase image quality and reduce examination times. Liver imaging beyond expectations with Ingenia TIP 1 Use ds-sense for sharper T2 single shot imaging Before the introduction of Ingenia, parallel imaging with SENSE was typically applied in the anterior-posterior (AP) phase encoding dimension and found to deliver high quality outcomes using typical speed up factors of 2 in multislice acquisitions. The advantage SENSE delivered to body imaging included higher temporal resolution, reduced blurring for single shot acquisitions, decreased distortions for EPI and shorter breath hold (BH) times. AP SENSE factor 2, shot length 349 ms., shot length 275 ms. With Ingenia, the next innovation in SENSE is made available. Improved robustness, image quality and speed can be demonstrated with ds-sense. This is made possible by next generation SENSE algorithms and the smart digital coil design. These advancements make higher SENSE factors feasible by changing phase encoding from AP to RL. This change allows for improved image quality in T2 single shot (SSH) acquisitions by shortening the shot length, which leads to sharper images. By increasing SENSE factors, a shorter shot length can be demonstrated. This leads to reduced image blur due to improved point spread function (PSF). 38 FieldStrength - Issue 47-2012 / 3
TIP 2 Use high SENSE factors for sharper DWI Applying the same approach to DWI leads to reduced EPI readouts and decreased bandwidth. This image comparison demonstrates reduced distortion and EPI ghosting due to the reduction in EPI factor and water-fat-shift (WFS). b0 b20 b1000 b0 b20 b1000 AP SENSE factor 2, EPI factor 119, WFS 43 RL SENSE factor 5, EPI factor 75, WFS 24 TIP 3 Novel strategy for further improvement The RL SENSE approach requires phase oversampling in order to avoid fold-over from the arms placed at the patient s side. Oversampling requires additional phaseencoding lines, increasing the shot length or EPI encoding steps and leading to a lower effectiveness of this approach. Arms down, shot length 306 ms Arms up, shot length 254 ms. However, oversampling could be turned off if the arms were positioned above the head and therefore outside of the imaging field. Until now this has not been considered, since bore size limited the ability to position the patient comfortably for the period of time needed to acquire the exam (routinely 30-40 minutes). Ingenia s wider bore allows the arms to be placed over the head in a more comfortable position, which allows use of the smaller FOV in the RL direction. This reduces the number of acquired phase encoding steps and further improves the quality of the single shot and DWI images. Blurring is reduced due to the shorter shot lengths. Another advantage is the reduced aliasing artifacts seen, due to absence of additional tissue outside the anatomy of interest. With the novel strategy of arms up and RL ds-sense, the shot length and image sharpness of single shot BH imaging approach those of a multi-shot gated technique. Multi-shot respiratory triggered, conventional AP SENSE factor 2, shot length 154 ms. Single shot 20 sec BH, novel strategy RL SENSE factor 4, shot length 208 ms. CONTINUE FieldStrength 39
Application tips TIP 3 continued With ds-sense, a higher SENSE factor reduces shot length and improves image sharpness. Comparison with the arms-down images again demonstrates the increased sharpness with ds-sense. Conventional, AP SENSE factor 2, shot length 349 ms. Novel ds-sense strategy with arms up,, shot length 235 ms. Arms down,, shot length 315 ms. DWI scanning with the novel strategy also reduces distortion artifacts and blurring caused by T2* decay. By applying the novel approach to 3D volumetric imaging, the advantage of reduced BH times at high SENSE factors is seen. This can improve BH compliance or be traded in for higher resolution in the currently accepted BH time. A higher SENSE factor can be used to reduce scan time. AP SENSE factor 2 1.75 mm isotropic resolution, 16 sec BH. 1.75 mm isotropic resolution, 9 sec BH. DWI, AP SENSE factor 3, EPI factor 31 Novel strategy, DWI, RL SENSE factor 5, EPI factor 25 The higher SENSE factor can also be used to increase resolution within a reasonable BH time. Additional advantages of high SENSE factors are the possibility to significantly reduce BH times for dynamic imaging. As SENSE reduces the number of RF pulses applied, specific absorption rates (SAR) are also reduced, leading to further scan time reduction or lower power deposition to the patient which is especially important at higher field strengths. 1.5 mm isotropic resolution, 13 sec BH. 1.3 mm isotropic resolution, 19 sec BH. 40 FieldStrength - Issue 47-2012 / 3
TIP 4 Improved examination workflow As shown, the novel ds-sense strategy can improve image quality and/ or reduce scan times. Comparing the same sequences acquired with AP to the ds-sense approach demonstrates a time saving of 38 seconds. This ds-sense approach provides the opportunity to further reduce total examination time by reducing the number of required breath holds, so that the total time saving increases to even further (55 seconds). Shortened breath hold times also increase patient compliance and provide opportunities for interleaving the various scans to take advantage of so-called dead time in the exam strategy. Combining these time savings with the image quality improvements previously discussed, results in the possibility to obtain a high quality MRI study of the liver in examination times that now approach those of CT. Routine liver exams 3.0T SENSE conventional Ingenia 3.0T ds-sense novel strategy T2 Cor BH 23 sec (2 x 12 sec) T2 Cor BH 18 sec mdixon All 20 sec mdixon All 13 sec mdixon W 17 sec per phase mdixon W 9 sec per phase BB DWI BH 13 sec BB DWI BH 11 sec T2 Tra BH 25 sec (2 x 13 sec) T2 Tra BH 17 sec T2 FS Tra BH 25 sec (2 x 13 sec) T2 FS Tra BH 17 sec Examples from Ingenia 3.0T with the novel RL ds-sense approach: T2W coronal mdixon All Dynamic mdixon W DWI T2W T2W SPAIR FieldStrength 41