Fluence Field Modulated X-ray CT using Multiple Aperture Devices. Acknowledgements

Transcription

1 Fluence Field Modulated X-ray CT using Multiple Aperture Devices Joseph W. Stayman 1, Aswin J. Mathews 1, Wojciech Zbijewski 1 Grace Gang 1, Jeffrey H. Siewerdsen 1 Satomi Kawamoto 2 Ira Blevis 3, Reuven Levinson 3 1 Department of Biomedical Engineering, Johns Hopkins University 2 Department of Radiology, Johns Hopkins Hospital 3 Philips Medical Systems Johns Hopkins University Schools of Medicine and Engineering Faculty and Scientists Tharindu De Silva Grace Gang Matthew Jacobson Alejandro Sisniega Wojciech Zbijewski Acknowledgements Clinicians John Carey Gary Gallia Kelvin Hong A Jay Khanna Doug Reh Marc Sussman Clifford Weiss AIAI Laboratory Advanced Imaging Algorithms and Instrumentation Lab aiai.jhu.edu web.stayman@jhu.edu I-STAR Laboratory Imaging for Surgery, Therapy, and Radiology istar.jhu.edu jeff.siewerdsen@jhu.edu Students Qian Cao Sarah Ouadah Sureerat Reaungamornrat Steven Tilley II Ali Uneri Jennifer Xu Esme Zhang Funding NIH U01EB (Stayman) Presented at SPIE-Medical Imaging

2 Beam Shaping in Computed Tomography Bowtie Filters Shape via variable thickness Reduce dynamic range of data Help to homogenize noise X-ray Source Limitations Static beam shape Patients are not circular/symmetric Patient positioning (not centered) Patient Detector Split bow-tie designs Fluence Field Modulation Strategies Piecewise linear design Fluid-filled designs (Hsieh, Pelc, Medical Physics, 2013) (Szczykutowicz, Hermus, SPIE, 2015) Presented at SPIE-Medical Imaging

3 Challenges for Fluence Field Modulation in CT Practical implementations require Compact design Limited space for actuators (limited size/number) Limited thickness of attenuators Fast actuation Modern CT spins ~3-5 Hz Min-to-max modulation <100 ms Multiple Aperture Device (MAD) Concept X-ray Source X-rays MAD Filter Patient Detector MAD Features: Binary filter (0% or 100% pass) Small actuation distances (1 period) Thin design (e.g. a few mm of tungsten) Spectrally neutral Presented at SPIE-Medical Imaging

4 Multiple Aperture Device (MAD) Concept X-ray Source X-rays MAD Filter Patient Detector MAD Features: Binary filter (0% or 100% pass) Small actuation distances (1 period) Thin design (e.g. a few mm of tungsten) Spectrally neutral Design Goals Desire smooth fluence patterns Avoid seeing fine MAD structure Principles Local fluence determined by amount of blockage Blockers are too small to resolve (determined by pitch) Individual MAD Design SDD SMD MAD pitch FS X-ray Focal Spot MAD Plane MAD Pitch = FS 1 SMD SDD Detector Plane Presented at SPIE-Medical Imaging

5 Illustration of Single MAD Design - Simulation Constant Optimal Pitch Design Linearly Decreasing Bar Widths Position at MAD (mm) Presampling Fluence at Detector Plane Position at Detector (mm) Sampled Fluence at Detector Detector Element Dual MAD Design MAD Pitch (P) MAD Pitch (P) b 1 (0) b 1 (1) b 1 (2) MAD #1 d(0) d(1) d(2) b 2 (0) b 2 (1) b 2 (2) MAD #2 Dx Presented at SPIE-Medical Imaging

6 MAD Transmission MAD Transmission MAD Transmission Transmission with Relative Motion (Dx) and d-offsets Offset to Right Offset to Left Offset to Center b 1 (0) d = 0 b 1 (0) d = (b 1 -b 2 ) b 1 (0) d = (b 1 -b 2 )/2 b 2 (0) Dx b 2 (0) Dx b 2 (0) Dx Dx Dx Dx Position at MAD (mm) Position at MAD (mm) Position at MAD (mm) Illustration of Fluence Patterns for a Specific Goal Desired Fluence Achieved Fluence Presented at SPIE-Medical Imaging

7 Detector Physical Experiments and Fabrication Object Stage MAD Stages X-ray Source Test-bench Features Stable controllable motion Step-and-shoot, pulsed x-rays kvp, 80 kw, w/ pulse width modulation Flat-panel detector 43x43 cm 2 MAD stages, 2.5 mm steps, 1 mm encoders a = mm 320 mm dia SDD (1040 mm) SAD (803 mm) MADs SMD (341 mm) Source fs ~ 1.19 mm Detector Practical Considerations for Fabrication Focused MAD filters a Dz MAD1 MAD2 Focal Spot Measurements Focal Spot Pinhole Image Variable Line Pairs Projection Image Presented at SPIE-Medical Imaging

8 Slot Thickness (mm) Stayman et al. (Johns Hopkins University) MAD Construction Tungsten Laser Sintering Tungsten Powder 3D CAD File Laser Powder Bed Fusion EDM Wire Cutting and Mounting Single MAD Design to Flatten Fluence for 32 cm Phantom 0.8 Designed Slot Thickness: 1-b 1 (x) Aperture Position (mm) Normalized Detector Signal: Blank Scan 3D Printed Tungsten MAD Minimum Feature Size: ~100 mm Focused at 341 mm Thickness: 1.5 mm Normalized Detector Signal: 32 cm CTDI Phantom Presented at SPIE-Medical Imaging

9 Sample Reconstruction with MAD Filtering Sample Projection CatPhan Resolution Phantom FBP Reconstruction of Test-Bench Data 360 Acquisition, 360 angles, 80 kvp, 10 ma, 50 ms pulses, 180 mas total Sample Projection Sample Reconstruction with MAD Filtering CatPhan Resolution Phantom FBP Reconstruction of Test-Bench Data 360 Acquisition, 360 angles, 80 kvp, 10 ma, 50 ms pulses, 180 mas total Presented at SPIE-Medical Imaging

10 Conclusion Presented a novel FFM design Based on MAD filtration Compact design Large scale shaping with small actuation levels Ongoing Work Dual-MAD Experiments Integration in a commercial CT gantry Conclusion / Ongoing Work Presented at SPIE-Medical Imaging