Cone-beam CT for extremity imaging

Transcription

1 Cone-beam CT for extremity imaging Poster No.: C-0297 Congress: ECR 2011 Type: Scientific Paper Authors: K. Mattila, J. A. Kankare, M. Kortesniemi, J. Salo, N. C Lindfors, J. T. Mattila, S. K. Koskinen ; Turku/FI, Helsinki/FI Keywords: Musculoskeletal joint, CT, Technology assessment, Trauma, Athletic injuries DOI: /ecr2011/C-0297 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 21

2 Purpose To develop a lightweight compact ambulatory imager with ability to produce small isotropic voxels and high-quality 3-D images for diagnostic use in orthopaedic and hand surgery imaging. Images for this section: Fig. 1 Page 2 of 21

3 Methods and Materials The project collaboration started in 2009 Existing technology used in dental CBCT was utilized The technology itself with small gantry allows low patient dose and images with sub-millimeter slice thickness Prototype was build and provided for clinical use in two clinical sites The stability of the apparatus and technical properties were tested and clinical usability developed in collaboration The public authority approvals were obtained as well as approval by ethical committees of Turku and Helsinki University Hospitals. Images for this section: Fig. 1 Page 3 of 21

4 Fig. 2: -Wide collimator angle - beam forms a cone. One flat panel detector used. One rotation only resulting in 300 direction images. Image data read and image volume reconstructed, leading to a cylindrical volume with cone formed heads. Thin slices may be reconstructed due to small isotropic voxels. Radiation dose remains low. Page 4 of 21

5 Results Clinical Research and development Two prototypes have been succesfully manufactured by the vendor (Planmed OY, Helsinki, Finland) and are in preliminary clinical use since 6/2010 The apparatus was first carefully tested using deep frozen pork ankle blocks. Optimal parameters (kvp, mas) for bone and soft tissues were first tested, effect of metal present in the field-of-view as well using different parameter settings. Image quality (SNR/visual testing) was correlated with radiation exposure Optimal settings to obtain excellent image quality with reasonable dosage were found and taken to clinical use Clinical experience More than three hundred examinations have been imaged so far. The product function reliably and it is manually ambulatory The imager can be sited even side by side to other imaging equipment Can be moved if needed in case of trauma patients imaged on patient bed etc. The gantry can be elevated to the shoulder level and lowered down next to the floor level - and addditionally rotated from vertical to horizontal position-allows versatile patient positioning and optimized patient comfort- even weight-bearing CT Functionality Imaging of wrist or elbow in neutral position while sitting on a comfortable patient chair. Imaging injured extremity comfortably without moving patient from the hospital bed or wheel chair. Imaging CT of the lower extremity even in standing position. Isotropic resolution allows reconstructions in any plane as well as 3-D volume rendering. R Verity -technical data Toshiba X-ray tube with tungsten target Anode voltage: up to 96kV, anode current: 1-12mA Page 5 of 21

6 Dual filtration: 0.5mm Cu + 2.5mm Al Pulsed X-ray radiation 20x25cm flat panel detector (amorphous silicon) Pixel size: 127um Imaging modes: 2x2 binning (254um effective pixel size), 4x4 binning (508um effective pixel size) Field of View of approximately 11x16cm Isotropic resolution: 0.2mm (normal mode) / 0.4 mm (low dose mode) 300 projection images acquired over an angle of approximately 210 degrees Scan time: 18 seconds, reconstruction time of s Dimensions (LxWxH): 185cm x 76cm x 160cm Weight approximately 350kg Max. power consumption 1.5kVA, no external cooling needed Radiation Dose Measurement and comparison to MDCT R Exremity CT (Verity ) :Imaging parameters: tube voltage 96 kvp (as mostly used) or 84 kvp, tube current from 1 to 10 ma, exposure time 6 s, DAP ranged from 139 to 1469 mgycm2. Effective doses from 10 to 30 µsv (range of an effective dose from a dental panoramic x-ray scan or a single thorax posterior-anterior projection) MDCT (Siemens Sensation 64) :Peripheral low-dose protocol: 120 kvp, 80 mas, 1 s rotation time, pitch 0.9, scan length of 99 mm Effective dose from 10 to 50 µsv depending on vertical scan location Remarks: Decreasing distance from the trunk region with more radiosensitive organs was related with higher radiation exposure, as scattered radiation from the scan area reaches anatomical regions of pelvis. However, the result is highly dependent also on other imaging parameters, e.g. increasing mas to provide CTDIvol of 15 mgy results in an effective dose of about 200 µsv. Thus, the radiation exposure from MSCT can be an order of magnitude higher compared to peripheral CBCT. However, with appropriately optimized peripheral scan protocol, the exposures of MSCT and CBCT do not necessarily differ significantly. Images for this section: Page 6 of 21

7 Fig. 1: -Testing parameter settings: Axial pork ankle with a fracture. kvp 88- different mass Page 7 of 21

8 Fig. 2: Testing image quality: kvps with different currencies, effect on noise Page 8 of 21

9 Fig. 3: -Pork ankle. Sagittal 2mm reconstructions CBCT vrs MDCT 64sl. Page 9 of 21

10 Page 10 of 21

11 Fig. 4: -Metal implant with several screws on a fractured pork ankle block. Fig. 5: -Imager functionality Page 11 of 21

12 Fig. 6: -Chronic wrist pain, no history of recent trauma. Extremity CT reveals a fracture non-union of the hook of hamate. Fig. 7: - 11 year-old patient with wrist pain, scaphoid fracture non-union. Comparison of 0.4 vrs 2mm sagittal reconstructions. Page 12 of 21

13 Fig. 8: -58 year-old patient with a tibia plateau fracture, unsatisfactory result of previous surgery, deep depression of the joint surface demonstrated on CBCT, 2mm reconstructions Page 13 of 21

14 Fig. 9: - A patient with Charcot-Marie-Tooth -disease. Unstable TC- joint, severe osteoarthrosis, high longitudinal arch, subtalar and midtalar joints stable. Abnormal posture much worse on weight-bearing images than on those obtained while sitting. Page 14 of 21

15 Conclusion Discussion Limitations Limited FOV (11x16cm)--only extremities can be imaged, small gantry size-hip, shoulder, bilateral feet out of range Relative long scan time: 18 seconds- artifacts due to movement possible CBCT method related image artifacts Difficult to obtain good soft tissue contrast and scale tissues in Hounsfield units Stitching software for reconstructing whole foot images from forefoot to hindfoot so far missing Advantages Small, manually ambulatory Versatile patient positioning Upper arm, standard neutral position Lower leg knee ankle, foot-eiher weight bearing, or sitting on a comfortable patient chair, or can be moved next to the patient bed, allows imaging without lifting patient Image quality is considered excellent, comparable to big multi slice whole body scanners, small isotropic voxels allow image reconstructions in any plane as well as 3-D volume rendering The patient dose measurements show doses closer to plain film examination than multi-slice CT Reasonable size investment Tecnology inexpensive Siting in existing radiography room without investing to constructing new space as in case of installing a whole body scanner Can be easily moved to new position if alterations in patient flow in the hospital/department (ambulatory, wheels) Stand alone in cliniques with sufficient number of extremity imaging (trauma, chronic), or can be used to streamline patient flow in busy departments with squeezed whole body scanners Conclusions Extremity CT starts new era in orthopedic musculoskeletal imaging Page 15 of 21

16 Allows obtaining volumetric data with either the joint in functional position, or using weight bearing, previously impossible on whole body CT scanners. Image quality is considered excellent, comparable to big multi slice whole body scanners, small isotropic voxels allow image reconstructions in any plane as well as 3-D volume rendering. Low radiation dose makes it not only an alternative for CT, but also for plain radiographs. Images for this section: Page 16 of 21

17 Fig. 1 Page 17 of 21

18 Fig. 2 Page 18 of 21

19 References Reichardt B, Sarwar A, Bartling S, Cheung A,Grasruck M, Leidecker C, Bredella M, YT, Gupta R. Musculoskeletal applications of flat-panel volume CT. Skeletal Radiol (2008) 37: Schulze D, Heiland M, Thurmann H and Adam G. Radiation exposure during midfacial imaging using 4- and 16-slice computed tomography, cone beam computed tomography systems and conventional radiography. Dentomaxillofacial Radiology (2004) 33, Biswas D, Bible J, Bohan M, Simpso A, Whang P, Grauer J. Radiation Exposure from Musculoskeletal Computerized Tomographic Scans. J Bone Joint Surg Am. 2009;91: Faccioli N, Foti G, Barilari M, Atzei A, Mucelli R.Finger fractures imaging: accuracy of cone-beam computed tomogrphy and multislice computed tomography. Skeletal Radiol (2010 )39: Gupta R, Cheung A, Bartling S, Lisauska J, Grasruck M, Leidecker C, Schmidt B, Flohr T, Brady T. Flat-panel Volume CT: Fundamentaal principles, Technology, and Applications. RadioGraphics (2008) 28: Images for this section: Page 19 of 21

20 Fig. 1 Page 20 of 21

21 Personal Information Acknowledgements: Special thanks to Jouni Uusi-Simola and Anne-Mari Vitikainen, HUS Helsinki Medical Imaging Center and Department of Physics, University of Helsinki and Lauri Seppälä, Planmed OY for contributing in radiation dose measurements. Page 21 of 21