7/28/2017. Michael Speidel. University of Wisconsin - Madison

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1 Scanning-Beam Digital X-ray (SBDX) is a technology for real-time fluoroscopy and angiography in the cardiac cath lab Michael Speidel Characterized by high speed beam scanning with a 2D array of focal spots University of Wisconsin - Madison AAPM 17 DEPARTMENT OF Medical Physics UNIVERSITY OF WISCONSIN SCHOOL OF MEDICINE AND PUBLIC HEALTH Learning Objectives 1. Describe operating principles 2. Understand potential clinical benefits 3. Overview of studies and challenges Triple Ring Technologies, Inc. 2 Traditional x-ray tube: single focal spot Multisource: Spatially distributed, addressable focal spots With SBDX, the primary goal is to bring an advantageous geometry to fluoroscopy and angiography. Fixed SBDX geometry is a form of very fast tomosynthesis (1 scan/s). Scanning x-ray beam Two potential benefits stem from this geometry: Mechanical constraints in multi-view imaging modalities Can enable fast imaging without mechanical motion 1. Features that improve dose efficiency 2. Depth-resolved image guidance tools Multihole collimator Scanning Electron beam 3 4 Inverse geometry fluoroscopy Composite display Single-plane Tomosynthesis 3D device tracking from tomosynthesis 2D array of focal spots and multihole collimator Full scan every 1/1 s Tomosynthesis recon 32 plane x 1 Hz Imaging volume Composite recon at 1 frame/s 2D array of focal spots Triple Ring, Inc. 6 1

2 Multihole collimator X-ray beam Up to 100 x 100 holes with 2.3 mm pitch Specifications 1 kv, 0 ma 100 x 100 collimator holes 0.68 mm focal spot diam. 2.3 mm focal spot pitch 1.04 ms time 0.24 ms move time Deflection coils Electron gun Electron beam 1 ms time Al filter water coolant Be window W / Re target ~1 mm thick Multi-pass blockwise raster scan Multi-pass lowers peak target temperature Blockwise method limits motion blurring Dt/2 Dt Dt/2 Temperature reduction Time Speidel MA, Wilfley BP, Star-Lack JS, et al., Med Phys 33, 2714 (06). 7 8 must capture an image for each collimator hole illumination 1.04 ms ms move = 1.28 ms/hole 781,20 fps Very high speed, very low counts per image Real-time reconstruction is performed on multiple s Front-end processing Tomosynthesis recon 32 plane x mm 1 stacks/sec Composite recon, & 3D catheter tracking 1 frame/s Specifications 2 mm thick CdTe Readout every 1.28 ms 10.6 x.3 area 0.33 mm elements Single discriminator threshold (Triple Ring Technologies, Inc.) 40 Gbps Accumulate and bin images Raw data storage 32 TB Plane stacks CPU Live Display Live Display Speidel MA, Tomkowiak MT, Raval AN, et al., Proc. SPIE 9412:9412W (1). 9 Speidel MA, Tomkowiak MT, Raval AN, et al., Proc. SPIE 9412:9412W (1). 10 The risk of radiation-induced skin injury and stochastic carcinogenesis are an ongoing concern Dose Efficiency Improvements to system dose efficiency can enable dose reduction without loss of SNR Depth Resolved Image Guidance SDNR C P A (1 SF)DQE A system efficiency factors ent obj T pat ent fluence

3 SNR Entrance R/min exposure (R/min) Narrow-beam scanning with a large air gap reduces detected scatter: Inverse geometry spreads out the x-rays: Regional adaptive exposure (RAE) 1 : At collimator holes corresponding to high transmission regions, turn off beam current for some scan passes ~7% SF No grid Thick CdTe detector 1/r 2 Chest phantom 2 Image with normal scan Bright lung region Image with RAE scan 2-0% SF with grid Thin CsI detector Conventional Inverse 1/r 2 Conventional ~2x larger field Inverse Relative dose to film at Burion S, Speidel MA, Funk T, Med Phys 40:01911 (13). 2. McCabe BP, PhD thesis (12) 14 Upper limit on x-ray output, and SNR, because: 1. Tight collimation limits usable primary x-rays per electron delivered to the anode 2. Electrons are concentrated in a smaller physical focal spot area, for given effective focal spot (no line focus principle) On the other hand 1. Dose efficient system requires less primary x-ray output 2. Short times support high current density (0 ma / mm 2 for 0.68 mm 1kV) Collimated X-ray beam Electron beam Iodine SNR and exposure on previous-gen SBDX system, for acrylic phantoms 1 At 1 kv, 107% to 69% of conventional II/CCD SNR in cardiac cine mode While delivering 61% to 8% of the exposure This prompted an upgrade which doubled x-ray beam and detector width Iodine Signal-to-Noise Entrance Exposure SBDX at 123 R/min II/CCD cine II/CCD cine 1 kvp II/CCD kvp SBDX at 1 kvp SBDX at 1 kvp Cine SBDX at mode equal kvp 100 SBDX at equal kvp SBDX at 18 R/min 70 kvp kvp 9.3 R/min phantom thickness ( thickness ( acrylic) phantom thickness thickness ( acrylic) Previous generation Current generation Speidel MA, et al., Med Phys 33, 2728 (06). 16 SBDX was temporarily located in the UW Hospital cardiac cath lab, next to a clinical flat panel system Clinical Flat Panel SBDX System SBDX (composite display) In an IRB-approved study, consented patients requiring diagnostic coronary angiography received standard-of-care angiogram on the clinical system SBDX angiogram acquired with same catheter placement and approximately same contrast injection technique. 37 angiogram pairs, 19 subjects, lbs. Subjective IQ scale (4 interventional cardiologist readers) 2.4 cgy/min at reference point Average IQ score: cgy/min (39% conventional) Average IQ score: Unpublished result 18 3

4 Z-plane SBDX System SBDX System 40. cgy/min Avg. IQ score: cgy/min (28% conventional) Avg IQ score: cgy/min Avg IQ score: cgy/min (32% conventional) Avg IQ score: 3.8 Unpublished result 19 Unpublished result Clinical problem: Many non-coronary procedures require navigation of catheter devices inside relatively large 3D spaces deg Each composite image frame is formed from a stack of 32 planes with mm spacing Anterior plane (iso + 4. ) 2D projection format gives limited guidance Composite Example: Catheter ablation of left atrial fibrillation 4 32 plane x 0. Posterior plane (iso - 1. ) (x obj, y obj ) Input plane stack Spatial filtering Localize in X-Y space For each object z obj = p z i z i i Speidel et al., Med Phys 37: 6377 (10) Z Localize along Z-axis Sharpness p(z) 23 Dunkerley DAP, Speidel MS, RSNA 16 Annual Meeting (16)

5 e Multi-source x-ray tube designs enable fast imaging and provide a way to bring a new geometry to a clinical application Financial support provided by NIH Grant R01 HL Thank You! SBDX uses an electronically scanned 2D array of focal spots and high speed detector to perform tomosynthesis at 1 frame/s X-ray output limitations and reconstruction optimization are design challenges The geometry enables features that can improve dose efficiency and simultaneously provide unique 3D image guidance capabilities. Technical support provided by Triple Ring Technologies, Inc. Tobias Funk, PhD Paul Kahn UW-Madison collaborators: David Dunkerley, PhD Jordan Slagowski, MS Amish Raval, MD Michael Tomkowiak, PhD Bradley McCabe, PhD Wisconsin Institutes for Medical Research (WIMR) University of Wisconsin - Madison 2 26