Advantages of the Spin Echo-type Radial Scan of the Cranial Region

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1 Advantages of the Spin Echo-type Radial Scan of the Cranial Region Poster No.: C-0969 Congress: ECR 2013 Type: Scientific Exhibit Authors: T. Gomi 1, M. Hasegawa 2, N. Murata 2, A. Tabata 2, M. Tsunoo 2, M. Nagamoto 2, Y. Iizuka 2, N. Hattori 2, E. Kohda 2 ; 1 Tokyo-Meguro/JP, 2 Tokyo/JP Keywords: DOI: Artifacts, Imaging sequences, MR, Neuroradiology brain /ecr2013/C-0969 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 9

2 Purpose T1-weighted imaging (T1WI) using spin echo (SE) is generally used for enhanced magnetic resonance imaging (MRI) of the head. However, with this method, the posterior fossa cannot be clearly visualized because of flow-related artifacts arising from blood vessels. Even with flow compensation, it is difficult to eliminate these artifacts completely (1, 2). In recent years, reports have described a countermeasure for flow-related artifacts using the radial scan method based on periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER, BLADE) (3, 4). Most of these are reports of techniques using T1-weighted fluid attenuated inversion recovery (FLAIR) BLADE combining fast spin echo (FSE) with a radial scan (5, 6). With T1-weighted FLAIR BLADE, suppression of flow-related artifacts is greater than with flow compensation, but compared with SE, the scan time is extended, and the contrast enhancement is different(6). On the other hand, it is also possible to suppress flow-related artifacts using T1WI of the RADial Acquisition Regime (RADAR)-SE, a method combining RADAR (7, 8, 9) and SE. RADAR-SE is an imaging method where only one SE signal is collected per repetition time (TR). Further, RADAR-SE can arbitrarily determine whether to place a number of SE signals in parallel within each blade. However, unlike FSE, in RADAR-SE each echo signal in the blade is collected with each separate TR. Therefore, RADAR-SE differs from previously reported radial scan techniques in terms of points not arising in FLAIR or FSE. Moreover, it is possible to shorten the imaging time of RADAR-SE compared to that of conventional SE by using RADAR-SE together with Rapid Acquisition through Parallel Imaging Design (RAPID) (10), a method of parallel imaging. The objective of the present study was to examine the advantages of using RADAR-SE combined with RAPID in clinical cases. Methods and Materials All imaging was conducted using a 1.5 T MRI system. MRI technique RADAR-SE is a method to fill the k-space using a trajectory rotated with the center of the k-space as its axis. The RADAR-SE method helps acquire a single echo signal within each TR. At this point a change occurs in the ratio of the readout gradient magnetic field pulses of the two axes within the slice and the k-space fills up. Therefore, it becomes possible to acquire an echo time (TE) with the same value in all echo modes. Page 2 of 9

3 RADAR-RAPID decreases the number of blades and shortens the imaging time by thinning out the number of echo signals to be measured. Since the total number of echoes stays constant, the number of blades decreases as the EF increases. In image reconstruction, an algorithm is used to generate the aliasing for each blade. Clinical study Patients were imaged using SE and RADAR-SE combined with Rapid pulse sequences with equal imaging time, and they were then evaluated for artifact of the RADAR-SE and SE images. We examined enhanced cranial MR images of 31 consecutive cases, acquired from July- November, The ethics committee of our institution approved this study and written consent was obtained from all patients. The patients comprised 18 men and 13 women, ranging in age from 21 to 91 years (average: 62.4±17.6). Diagnoses were as follows: meningioma, n=4; angioma cavernosum, n=2; brain metastasis, n=13 (from lung cancer, n=11; esophageal cancer, n=1; and bladder cancer, n=1); multiple sclerosis, n=1; multiple lymphoma, n=1; Bechet disease of the central nervous system, n=2; angioblastoma, n=1; symptomatic reduced pressure of the cerebrospinal fluid,n=1; glioma, n=5; and germinoma, n=1. Gd-DTPA, 0.2 ml/kg, was injected intravenously as contrast medium. The imaging parameters for RADAR-SE were FOV: 24x24 cm; TR: 500 ms; TE: 12 ms; slice thickness: 5.0 mm; matrix: 320x264; NSA; 1; RAPID: 1.5; and scan time: 1 min 31 sec. The parameters for SE were FOV: 24x24cm; TR: 500ms; TE: 12 ms; slice thickness: 5.0 mm; matrix: 256x200; NSA: 1; RAPID: off; and scan time: 1 min 29 sec with flow compensation. The images acquired by SE and RADAR-SE were evaluated independently by two radiologists. Flow-related artifacts were evaluated on a four-point scoring system (0 = no artifact, 1 = slight, 2 = moderate, 3 = severe). Statistical analysis We used the Wilcoxon's signed rank test to evaluate the difference between SE and RADAR-SE for the severity of flow-related artifacts in the clinical study. A p-value of less than 0.05 was considered to be significant. Results Page 3 of 9

4 In the clinical study the flow-related artifacts were 0.03±0.53 (Reader 1) and 0.00±0.47 (Reader 2) for RADAR-SE and 1.77±0.76 (Reader 1) and 2.29±0.94 (Reader 2) for SE (Table 1). A significant decrease in flow-related artifacts was seen on RADAR-SE images (Fig. 1, 2). Images for this section: Table 1: Scores for severity of artifacts on RADAR-SE and SE images Data are expressed as mean±standard deviation. The severity of artifacts was evaluated using a four-point scoring system (0 = no artifact, 1 = slight, 2 = moderate, 3 = severe). Page 4 of 9

5 Fig. 1: (a) SE, (b) RADAR-SE The flow-related artifacts observed on SE are suppressed on RADAR-SE, and the cerebellar metastasis, which was unclear on SE, is clearly depicted(arrow). Page 5 of 9

6 Fig. 2: (a) SE, (b) RADAR-SE The flow-related artifacts observed on SE are suppressed on RADAR-SE, but streak artifacts are present(arrow). Page 6 of 9

7 Conclusion In clinical images, flow-related artifacts decrease significantly on RADAR-SE compared with SE images. Although flow compensation is adopted as a countermeasure for flow-related artifacts in SE, it cannot completely suppress these artifacts after injection of contrast medium (1, 2). Suppression of flow-related artifacts is also possible by adoption of T1W-FLAIR-BLADE (5, 6), but this technique has the disadvantage of drastically extending the imaging time compared with conventional SE (6). Furthermore, the black blood method and other methods of suppressing flow-related artifacts are limited in the number of slices and the length of imaging time possible (11). It is also possible to decrease the flow-related artifacts in high resolution 3D T1W images such as those acquired using 3D volume interpolated breath hold examination (VIBE) and magnetization prepared rapid acquisition gradient echo (MR RAGE), but the contrast enhancement decreases compared with SE (12). Motion-sensitized driven-equilibrium (MSDE) has also been proposed as a method for suppression of flow-related artifacts (13), but deterioration in the uniformity of the image and signal to noise ratio (SNR) is observed when MSDE is applied in combination (14). It is also reported to produce false positive results (15). By incorporating parallel imaging techniques, RADAR-SE can acquire images in the same scan time. It can also suppress flow-related artifacts, but it has the disadvantage of producing streak artifacts. However, in this study there were a few cases. RADAR-SE therefore appears to be a useful imaging method in cases prone to flow-related artifacts. The number of actual cases in the current study was small, future studies need to include a larger number of cases. In conclusion, we studied the characteristics of RADAR-SE, a type of radial scan, which allows suppression of flow-related artifacts without increasing scanning time. We demonstrated the advantages of RADAR-SE used together with RAPID for cranial imaging. References 1) Felmlee JP, Ehman RL, Spatial presaturation : a method for suppressing flow artifacts and improving depiction of vascular anatomy in MR imaging. Radiology 1987; 164: Page 7 of 9

8 2) Mitchell DG, Ortega H, Mohamed F, Tascyian T, Vinitski S. Aortic ghost artifact in ultrashort TE multislice gradient echo MR imaging is not increased by paramagnetic enhancement. Magn Reson Med 1993; 29: # Pipe JG: Motion correction with PROPELLER MRI: application to head motion and free-breathing cardiac imaging.magn Reson Med 1999, 42, ) Pipe JG, Farthing VG, Forbes KP. Multishot diffusion-weighted FSE using PROPELLER MRI. Magn Reson Med 2002; 47: ) Naganawa S, Satake H, Iwao S, et al. Contrast-enhanced MR imaging of the brain using T1-weighted FLAIR with BLADE compared with a conventional spin-echo sequence. Eur Radiol 2008; 18: ) Özlem Alkan, Osman K#z#k#l#ç, Tülin Y#ld#r#m, Sedat Alibek. Comparison of contrast-enhanced T1-wieghted FLAIR with BLADE, and spin-echo T1-weighted sequences in intracranial MRI. Diagn Interv Radiol 2009; 15: ) Takizawa M, Takahashi T. Robust radial sampling correction algorithm eliminating motion artifacts for body imaging. 22nd Annual Scientific Meeting of ESMRMB, Basle, Switzerland 2005 (Poster 425). 8) Takizawa M, Takahashi T, Robust correction algorithm for radial sampling on open MRI system, In: Proceedings of ISMRM workshop on non-cartesian MR, Sedona, USA 2007 (Abstract 3). 9) Takizawa M, Ito T, Itagaki H, et al. Modified Echo Peak Correction for Radial Acquisition Regime(RADAR). MRMS 2009; ) Kamada Y, Takizawa M, Taniguchi Y, Takahashi T, Development of Parallel Imaging for Radial Scan in the Head Region,In: Proceeding of the 38th Annual meeting of the JSMRM, 2010, Abstract T (Article in Japanese) 11) Amano Y, Takagi R, Takahara K, Kumazaki T. Contrast-enhanced T1-weighed black blood fast spin echo MR imaging of the brain. Technique for suppression of enhancing venous signal. Acta Radiol 2001; 42: ) Wetzel SG, Johnson G, Tan AG, et al. T1-weghted gradient echo imaging of the brain with a volumetric interpolated examination. AJNR Am Jneuroradiol 2002; 23: ) Wang J, Yarnykh VL, Hatsukami T, et al. Improved suppression of plaquemimicking artifacts in black-blood carotid atherosclerosis imaging using a multislice motion-sensitized driven-equilibrium (MSDE) turbo spin-echo (TSE) sequence. Magn Reson Med 2007; 58: Page 8 of 9

9 14) Inoue Y, Nakagawa K, Komaki S, et al. Parameters of MSDE Imaging Techniques to evaluate plaque - Investigated using Phantom Studies Chugoku-Shikoku Forum for Radiological Technology 2010; 6: No 72. (Article in Japanese) 15) Nagao E, Yoshimura T, hiwatishi A, et al. 3D Turbo Spin-Echo Sequence with Motion- Sensitized Driven-Equilibrium Preparation for Detection of Brain Metastases on 3T MR Imaging. AJNR 2011; 32: Personal Information gomi@oha.toho-u.ac.jp Page 9 of 9