Technological development for applying MR Elastography to shoulder muscles

Transcription

1 Technological development for applying MR Elastography to shoulder muscles Poster No.: C-1003 Congress: ECR 2016 Type: Scientific Exhibit Authors: D. Ito 1, T. Numano 1, T. Onishi 1, K. Mizuhara 1, K. Takamoto 2, H. Keywords: DOI: Nishijyou 2 ; 1 Tokyo/JP, 2 Toyama/JP Tissue characterisation, Inflammation, Image verification, Imaging sequences, Computer Applications-General, MR, Elastography, Soft tissues / Skin, Musculoskeletal soft tissue, MR physics /ecr2016/C-1003 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 13

2 Aims and objectives Palpation remains the fundamental clinical tools to diagnose abnormal stiffness changes in soft tissue. However, palpation is subjective, and detecting stiffness changes is impossible in deep tissues. MR elastography (MRE) is possible to quantitatively measure stiffness of both superficial and deep tissues (1). For throwing athletes, shoulder injuries are more common than any other body part injures, and rotator cuff (supraspinatus, infraspinatus, teres minor, subscapular muscle) injures are often caused (2). Among rotator cuff, it is difficult that the supraspinatus muscle is directly palpated, because it is not anatomically located in superficial. Therefore, the supraspinatus muscle may be the object which is suitable for stiffness measurement by using MRE. The purpose of this study was technological development for applying the MRE technique to the supraspinatus muscle. Page 2 of 13

3 Methods and materials All MRE experiments were performed on a clinical MR imager (Achieva 3.0T; Philips Healthcare, Best, The Netherlands) while using a shoulder coil with the subject in the supine position. Power amplifier (XTi 1000; Crown, IN USA) and a pneumatic pressure generator (Subwoofer TIT320C-4 12"; Dayton Audio, OH, USA) units were used to supply vibration to a vibration pad (Fig. 1a) which was designed by using a 3D printer (3Dtouch; 3D System, SC, USA). The vibration pad was placed over the trapezius muscle on the proximal side of the supraspinatus muscle, and was secured with Velcro straps and an auxiliary tool (Fig. 1a) which was designed by using a 3D printer. Figure 2b-d showed fixing method of the vibration pad. MRE acquisitions were performed with a gradient-echo type multi-echo MR sequence developed by Numano et al (3). In this method, the readout gradient has an effect which sensitizes the tissue motion by vibrations. If readout's gradient lobes are synchronized with vibrations, the readout gradient has the maximum effect. This synchronization can be easily achieved by adjusting the period of bipolar readout gradient lobes and the gap between the first and next echo (#TE) of a multi-echo sequence. We conducted MRE of the supraspinatus muscle at 75 Hz and 100 Hz vibrations, and it was synchronized with 5ms of #TE. The MR phase images (wave image) were recorded with the following parameters: acquisition matrix, 8 number of averages, 2 SENSE reduction factor, 20 flip angle, mm 2 field of view, 5 mm slice thickness, 2.3 ms 1st echo time, 20 ms repitation time, and 80 s total scan time (four vibration phase offsets). In addition, the wave image data were collected in two different readout directions (x, y). Readout direction x was parallel to the orientation of the supraspinatus muscle, and y was perpendicular to it. All wave images were processed by a phase unwrapping and a Gaussian spatial filter (MRE/Wave, MAYO CLINIC) after cutting out the region of the supraspinatus muscle from the obtained images. The regions of interest (ROIs) was set along the inner surface of the supraspinatus muscle (Fig. 2b), and a profile was drawn along the wave propagation in the supraspinatus muscle (Fig. 2c). The ROIs were used to measure the mean amplitude value (MAV) of the propagating wave in the supraspinatus muscle by using the amplitude images (MRE/Wave, MAYO CLINIC). Otherwise, the profile was used to measure the wavelengths (Fig. 2d). Assuming that the supraspinatus muscle was linearly elastic, isotropic, homogeneous, and incompressible, the shear modulus (µ), which represented the local elasticity, was calculated using following equation: µ = #f 2 # 2 Page 3 of 13

4 where # is the supraspinatus muscle density (#1000 kg/m 3 ), f is the frequency and # is the wavelength. Three healthy volunteers in this MRE study. All volunteer studies were done after obtaining informed consent from all volunteers and being approved by our institutional ethnic review board. Page 4 of 13

5 Images for this section: Fig. 1: a: The vibration pad (left) and the auxiliary tool (right). b-d: Fixing method of the vibration pad. - Tokyo/JP Page 5 of 13

6 Fig. 2: a: Axial magnitude image of the supraspinatus muscle. b: This image was made by fusion of the amplitude image with the magnitude image. The yellow ellipse indicates the ROIs of the supraspinatus muscle. c: This image was made by fusion of the wave image with the magnitude image. The yellow line indicates the profile drawn through the propagated wave. d: Representation of the wave traveling along the profile. - Tokyo/JP Page 6 of 13

7 Results This study used 75 and 100 Hz vibrations, respectively. Higher frequencies have shorter wavelengths and better resolution but lower penetration ability. A waveform generator for the supraspinatus muscle needs higher frequencies to provide high resolution, because the supraspinatus muscle is small. In this study, the wave image represented clear wave propagation in the supraspinatus muscle at 100Hz vibration. Therefore, we validated the change in wave propagation in the supraspinatus muscle depending on the readout direction at 100 Hz vibration. Figure 3 demonstrates the change in the mean relative MAV of the supraspinatus muscle in three volunteers depending on the readout direction, normalized with MAV in the y readout direction. The mean relative MAV in the x readout direction decreased more than 50 % it in the y readout direction. Figure 4 showed the wave images from one of three volunteers in the supraspinatus muscle. The wave images in the x readout direction and in the y readout direction are showed Fig. 4a and 4b, respectively. These images were magnitude images overlaid with the wave image. In the case of the x readout direction, the wave image represented unclear wave propagation in the supraspinatus muscle, and the wavelength cannot be measure. In the case of the y readout direction, the wave image represented clear wave propagation along the orientation of the supraspinatus muscle, and the wavelength can be measure. The mean stiffness value of the supraspinatus muscle in three volunteers was 10.3 ± 3.14 (mean ± SD) kpa in the y readout direction. Fig. 5 showed the movie of wave image and magnitude fusion images in the supraspinatus muscle. Page 7 of 13

8 Images for this section: Fig. 3: Mean relative (MAV normalized with MAV in the y-direction) in three volunteers vs. the readout gradient direction (x or y). The mean relative MAV in x-direction decreased more than 50% compared with it in y-direction. Bars show standard deviations. - Tokyo/JP Page 8 of 13

9 Fig. 4: Each image was made by fusion of the wave image with the magnitude image. The Green arrows indicate the readout gradient direction. - Tokyo/JP Fig. 5: Movie of wave image and magnitude fusion images in the supraspinatus muscle. - Tokyo/JP Page 9 of 13

10 Conclusion The results demonstrate that MRE is applicable to the supraspinatus muscle by using this MRE technique. This MRE technique successfully represented clear wave propagation along the orientation of the supraspinatus muscle in the y readout direction (Fig. 4b). In the case of the y readout direction, the readout gradient is sensitized the perpendicular wave displacement to the orientation of the supraspinatus muscle. In addition, Fig. 3 demonstrates that the wave displacement was occurring mainly perpendicular direction to the orientation of the supraspinatus muscle. Previous studies (4) have demonstrated the wave propagation follows the muscle fibers. Morphologically, the supraspinatus muscle is one of the uni-circumpennate muscles and is formed that the arraying direction of the muscle fibers is diagonal to the orientation of the supraspinatus muscle. Fig. 6 showed schematic illustrations of the fusiform muscle and the uni-circumpennate muscle (supraspinatus muscle). In the proximal side of the supraspinatus muscle, the fiber orientation of the supraspinatus muscle is close parallel and is similar to the fusiform muscle. Therefore, in the proximal side of the supraspinatus muscle, it is assumed that the wave propagated along the orientation of the supraspinatus muscle as if the supraspinatus muscle is one of the fusiform muscles. The fusiform muscles may be easy to measure the stiffness compared to uni-circumpennate muscles, because the fiber orientation of the fusiform muscle is a simple structure. In this MRE technique, it is recommended that the stiffness of the supraspinatus muscle is measured in the proximal side of the supraspinatus muscle with the y readout direction. Page 10 of 13

11 Images for this section: Fig. 6: a: Schematic illustration of the the fusiform muscle. b: Schematic illustration of the uni-circumpennate muscle (supraspinatus muscle) - Tokyo/JP Page 11 of 13

12 Personal information Daiki ITO, R.T. Graduate Student Dept. of Radiological Sciences Graduate School of Human Health Sciences Tokyo Metropolitan University , Higashiogu, Arakawa-ku, Tokyo Japan D. ITO, T.NUMANO, T.ONISHI Tokyo Metropolitan University K.MIZUHARA Tokyo Denki University K.TAKAMOTO, H.NISHIJYOU Toyama University Page 12 of 13

13 References 1. Muthupillai R, Lomas DJ, Rossman PJ, et al. Magnetic resonance elastography by direct visualization of propagating acoustic strain waves. Science 1995; 269: Yanagisawa O, Niitsu M, Takahashi Y, et al. Magnetic resonance imaging of the rotator cuff muscles after baseball pitching. J Sports Med Phys Fitness 2003; 43: Numano T, Kawabata Y, Mizuhara K, et al. A simple method for MR elastography: a gradient-echo type multi-echo sequence. Magn Reson Imaging 2015; 33: Debernard L, Robert L, Charleux F, et al. Characterization of muscle architecture in children and adults using magnetic resonance elastography and ultrasound techniques. J Biomech 2011; 44: Page 13 of 13