Uozu city/jp, Minatoku, Tokyo/JP Bones, Extremities, CT, Surgery, Physics, Artifacts, Image verification /ecr2014/C-0462

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1 Metal Artifact Reduction Algorithm enablesreduce metal artifacts and improvement of diagnosis in the postoperative Pedicle screws implant for Spinal Fusion: A Phantom Study Poster No.: C-0462 Congress: ECR 2014 Type: Scientific Exhibit Authors: T. Nomizu, A. Muramori, A. Tokunaga, T. Osonoi, T. Fujioka ; Uozu city/jp, Minatoku, Tokyo/JP Keywords: Bones, Extremities, CT, Surgery, Physics, Artifacts, Image verification DOI: /ecr2014/C-0462 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 18

2 Aims and objectives Introduction Since Computed Tomography was developed in 1972, it has continually developed, and it now constitutes powerful instruments in diagnosis. As a non-invasive imaging technique, the use of CT has become essential, especially since the advent of Multi Detector-law CT (MDCT) in the 2000 years, which led to improve z-axis temporal resolution and spatial resolution. However, CT image is deteriorated by the presence of metal objects. Images of patients with metal implants such as pedicle screws for spinal fusion suffer from artifacts, generally in the form of bright and dark streaks, cupping and capping; these artifacts are mostly appeared due to quantum noise, scattered radiation and beam hardening [1] [2]. Metal artifacts reduce image contrast and obscure the detail of objects, thus impairing the detectability of structures of interest; in the worst case, this can make a diagnosis impossible. It is important to diagnose as the presence or absence of loosening in the CT examination of postoperative pedicle screws implant for spinal fusion. However, in many cases, metal artifacts inhibit the result of diagnostics.(fig.1) Page 2 of 18

3 Fig. 1: Fig.1 Postoperative Pedicle screws implant for Spinal Fusion images in FBP References: Department of Radiology, Toyama Rousai Hospital - Uozu city/jp CT images without metal artifact cannot obtain using filtered back projection (FBP). Metal Artifact Reduction for Orthopedic Implants Algorithm (O-MAR, PHILIPS Healthcare) can reduce adverse effects of metal objects. Purpose O-MAR is generally used for reducing the metal artifact reduction. However, although not shown about O-MAR is useful to diagnose as the presence or absence of loosening in the CT examination of postoperative pedicle screws implant for spinal fusion. The purpose of this study was to evaluate the improvement of diagnostic performance by O-MAR in the case of postoperative pedicle screws implant for spinal fusion. Page 3 of 18

4 Images for this section: Fig. 1: Fig.1 Postoperative Pedicle screws implant for Spinal Fusion images in FBP Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Page 4 of 18

5 Methods and materials We developed the phantom which simulate the state of postoperative pedicle screws implant for spinal fusion. This phantom which has 8cm in diameter made by acrylic cylinder This phantom is defined as mimic vertebra. It has two holes which simulate loosening and non-loosening after surgery(fig.2). Fig. 2: Fig.2 Phantom of simulating the state of postoperative pedicle screws implant for spinal fusion References: Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Hole of non-loosening was 6 mm in diameter, hole of loosening was 10 mm in diameter. Titanium alloy screws were inserted into those holes. This phantom with those screws was encapsulated in the JIS Z-4923 water phantom(kyoto Kagaku). Page 5 of 18

6 Therefore, it was a structure in which water is filled in the hole loosening of acrylic(fig.3). Fig. 3: Fig.3 Phantom of simulating the state of postoperative pedicle screws implant for spinal fusion References: Department of Radiology, Toyama Rousai Hospital - Uozu city/jp This phantom was placed which those screws were inclined 10 degrees to the X-Y direction. The iso-center was placed at the center of the phantom. We scanned the phantom with 128 Slice CT (Ingenuity CT, PHILIPS Healthcare). Scan parameters were fixed as follows; tube voltage: 120 kv, effective tube current-time products: 400 mas/slice, resolution: high resolution(small focus), rotation time: 0.5sec/ rot, helical pitch: 0.3, slice thickness/slice increment : 0.67mm/0.33mm. The reconstruction filter function was set to Y-Detail (YD) and display field of view (DFOV) was 200 mm. Image reconstruction types were used FBP and O-MAR. Method1, Visual evaluation of loosening and non-loosening detectability We compared the visibility of FBP image with O-MAR image. Page 6 of 18

7 Window center and window width of all images was set at 400/2000. This evaluation was performed by one radiologist and one orthopedic surgeon and two radiographers independently. The radiologist and orthopedic surgeon has experience in CT for orthopedic and two staff radiographer has experience in MDCT operator. All readers were blinded to the two kinds of images setting. The score of visibility is defined as follows. The loosening and non-loosening holes were evaluated by two scores as visible or invisible. Method2, Measurement Metal Artifact Value In order to analyze the artifact of O-MAR and FBP quantitatively, we measured the Metal Artifact Value. The objective noise was defined as the standard deviation (SD) of the measured density. 2 ² The Metal Artifact Value (MAV) was defined as: MAV =#(SD o-sd r)[3] 2 2 ' SD o ' is the desired image (FBP or O-MAR) of ROI, 'SD r ' is the Reference FBP image of ROI. Therefore, MAV approaches zero in case of few metal artifacts. ROI were set three positions. ROI #1 was placed in the water portion of the image. ROI #2 was placed in an acrylic portion on mimic vertebra. In addition, ROI #3 was placed between the non-loosening hole and the loosening hole of the acrylic portion on mimic vertebra. (Fig.4). In order to compare MAV, we measured reference FBP image without metal object. Measured points of ROI were same as ROI#1, ROI#2, ROI#3. Page 7 of 18

8 Fig. 4: Fig.4 ROI(s) for Metal Artifact value mesurement References: Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Page 8 of 18

9 Images for this section: Fig. 2: Fig.2 Phantom of simulating the state of postoperative pedicle screws implant for spinal fusion Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Page 9 of 18

10 Fig. 3: Fig.3 Phantom of simulating the state of postoperative pedicle screws implant for spinal fusion Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Page 10 of 18

11 Fig. 4: Fig.4 ROI(s) for Metal Artifact value mesurement Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Page 11 of 18

12 Results Result1, Visual evaluation of loosening and non-loosening detectability Visibility of non-loosening hole In case of FBP image, non-loosening hole was not determined as non-loosening hole. All readers' score was same. In case of O-MAR image, non-loosening hole was determined as non-loosening hole due to reduction of metal artifacts. All readers' score was same. Visibility of loosening hole In case of FBP image, loosening hole was not determined as loosening hole. All readers' score was same. In case of O-MAR image, loosening hole was determined as loosening hole due to reduction of metal artifacts. All readers' score was same(fig.5). Page 12 of 18

13 Fig. 5: Fig.5 Two kinds of Images of Phantom of simulating the state of postoperative pedicle screws implant for spinal fusion References: Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Result2, Measurement Metal Artifact Value In case of FBP image compared to Reference FBP image, MAV increased in all three ROI(s). In case of O-MAR image compared to Reference FBP image, MAV recovered and approached the MAI of Reference FBP image in all three ROI(s). Therefore, O-MAR indicates higher effect of reducing Metal Artifact than FBP(Fig.6). Fig. 6: Fig.6 Compared Metal artifact value of FBP with O-MAR References: Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Page 13 of 18

14 Images for this section: Fig. 5: Fig.5 Two kinds of Images of Phantom of simulating the state of postoperative pedicle screws implant for spinal fusion Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Page 14 of 18

15 Fig. 6: Fig.6 Compared Metal artifact value of FBP with O-MAR Department of Radiology, Toyama Rousai Hospital - Uozu city/jp Page 15 of 18

16 Conclusion Conclusion O-MAR can reduce metal artifacts and maintain the shape of objects. Therefore O-MAR can improve diagnosis of the postoperative Pedicle screws implant for Spinal Fusion. Acknowledgment I am deeply grateful to Mr. Kazumichi Tanaka (Kaetsu Hospital, Niigata Pref, Japan ) & Mr. Junichi Kitaori (PHILIPS Healthcare, Tokyo, Japan). Page 16 of 18

17 Personal information Toshiyuki Nomizu Radiographer. Department of Radiology, Toyama Rousai Hospital Uozu city,toyama.japan. Page 17 of 18

18 References Oliver Watzke., Willi A. Kalender. A pragmatic approach to metal artifact reduction in CT: merging of metal artifact reduced images. Eur Radiol (2004) 14: Metal Artifact Reduction for Orthopedic Implants (O-MAR). Philips HealthCare System 2012 [available URL : clinical.netforum.healthcare.philips.com/us_en/explore/white-papers/ct/ Metal-Artifact-Reduction-for-Orthopedic-Implants-(O-MAR)]. Xiao Zhu Lin., Fei Miao,. et al. High-Definition CT Gemstone Spectral Imaging of the Brain: Initial Results of Selecting Optimal Monochromatic Image for Beam-Hardening Artifacts and Image Noise Reduction. J Comput Assist Tomogr 2011;35: Page 18 of 18