1970 Projection Radiography 2D projection of 3D anatomy

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1 Speakers: L. N. Rothenberg, Ph.D. Computed Tomography G. D. Clarke, Ph.D. Magnetic Resonance Imaging J. A. Zagzebski, Ph.D. Ultrasonic Imaging August 1, 2012 Lawrence N. Rothenberg, Ph.D. Keith S. Pentlow, M.Sc. Department of Medical Physics Memorial Sloan Kettering Cancer Center e mail: rothenbl@mskcc.org 1970 Projection Radiography 2D projection of 3D anatomy What about conventional tomography? With x ray tube moving above the table and the image receptor moving in a parallel plane below the table, we can get only coronal or sagittal slices. Out of plane anatomy blurred over the image 3 4 Complex Tomography for Coronal Images Philips Polytome & CRG Stratimatic Can we use screen film to get axial cuts? Toshiba found a way to do that 5 6 1

2 TAT Transverse Axial Tomography: Toshiba Unit in Radiation Oncology Toshiba TAT 7 8 CT Overview CT Overview and History CT was first introduced in Britain in The Nobel Prize for Medicine was awarded in 1979 to Godfrey Hounsfield of Britain (CT scanner) and Alan Cormack of the US (image reconstruction). It s advantages over radiography are: Conventional radiography suffers from collapsing of 3D structures onto a 2D image. Although spatial resolution is lower in CT, low contrast resolution is far superior in CT, allowing for the first time the direct visualization of soft tissue organs and tumors CT development EMI Mk1 head only scanner, introduced st generation, i.e. translate-rotate geometry, parallel rays, pencil beam, one NaI detector t per slice 180 rotation, 5 mins per acquisition 5 mins per reconstruction 2 slices produced Initially 80 x 80 matrix Water bag/box for bolus At Cornell NY Hospital Neuroradiology 12 2

3 EMI Electric & Musical Industries, Ltd. CT Acquisition CT Reconstruction I t I e t o ln( I o / I ) t t G. Hounsfield and His Lab CT 3 Projections, 7 Rays Each EMI CT Scanning Motion First Patient Scans Ambrose at Atkinson Morley s Hospital in London Patient with suspected frontal lobe tumor Mayo Clinic, NY Hospital and others in US Problem for Physicists: How to measure patient dose? Led to MSAD and CTDI

4 EMI CT Head Image What to call this process? Computerized Axial Tomography CAT Computerized Transaxial Tomography CTT Gray scale 80 x 80 CRT and Polaroid image and paper printout provided 5 minute scan 5 minute reconstruction It looks just like the cross-sectional anatomy books (Your 8/1/2012 smart phone has much AAPM History more Symposium computing 2012 power than the EMI computer had!) 19 Computed Tomography CT 20 Even Peanuts got into the act! Research and Development Goals Faster in slice scanning 5 min 20s 5s 3 s 1s 0.8s 0.5 s 0.3 s Faster image reconstruction 5 min a few seconds Better resolution in all three dimensions 80 x x x x x 1024 We can now achieve sub mm resolution in 3D Faster coverage of the entire body Minutes a few seconds Two Images Radiography Computed Tomography Projection Radiography vs. CT

5 CT Reconstruction I t I e t o ln( I o / I ) t t The Mathematicians Johan Radon Radon Transform 2D and 3D reconstruction from infinite projections Alan Cormack unaware of Radon s work, developed reconstruction technique in South Africa Nobel Prize with Hounsfield in 1979 David Kuhl reconstruction techniques for PET Shepp and Logan developed reconstruction algorithms 3 Projections, 7 Rays Each st Generation: Rotate Translate 2 nd Generation: Rotate Translate w Small Fan Beam 5 Minute Scan Time Second Scan, 30 detectors, 10 deg fan, required bolus 28 Robert Ledley, D.D.S. (d. 7/24/12) and the ACTA Body and Head Scanner CT development Ohio-Nuclear Delta50 head and body scanner (covers removed), introduced nd generation, i.e. translate-rotate geometry, parallel rays, pencil beam, three NaI detectors per slice 180 rotation, 1-3 mins per acquisition (2 slices) 256 x 256 matrix Shaped filters Images in color, CT number range 0 to 200, no bolus required

6 Early CT System Components 3 rd Generation: Rotate Rotate w Wide Fan Beam Polaroid Camera later replaced by laser imager, now images go directly to PACS 31 Scan times as low as 0.33 sec, 800 detectors, deg fan, 360 deg rotation 32 3 rd Generation 4 th Generation s of stationary detectors, x-ray tube rotates 360 deg,no ring artifacts 34 4 th Generation Scanner (AS&E) CT Numbers Hounsfield Units (HU) (x, y) - CT# (x, y) 1000 water water CT# (water) = 0 CT# (air) = CT# (soft tissue) = -300 to +100 CT# (bone, I) = up to Originally EMI used +/-500, Ledley used

7 CT Numbers Hounsfield Units (HU) Survey of Early CT Units Hounsfield units = 1000 x ( - water ) / water David White s Phantoms TLD and Film Dosimetry Dr. White s tissue formulations used in many commercial phantoms 39 Scanners with 180 deg or 360 deg rotation, and possibly with overscan 40 Survey of Early CT Units CT in Popular Scientific Press Note color image displays Manufacturers Pfizer/A.S. & E Elscint EMI General Electric Ohio-Nuclear Philips Picker Searle Siemens Varian*

8 5 th Generation: Electron Beam CT (EBCT) EBCT Imatron, (later marketed by Picker, then Siemens, then bought by GE), introduced 1980 s R. Robb at Mayo Clinic Electron Beam CT (sometimes called 5 th generation), stationary scintillator-photodiode detectors, scanning electron beam on stationary target ring, fan beam, four (eight) slice 216 rotation, 50 millisecs per acquisition (8 slices) CT Image Display Window/Level Detectors/Detector Arrays Xenon Gas CT was the first widely used digital imaging system Solid State Detectors Helical Slip Ring Scanners

9 Early Slip Ring Scanning HV Slip Rings Closed Tunnel Size reduction & continuous rotation slip rings 1987 Improved high voltage generator technology made units smaller Slip ring technology enabled them to be placed on the rotating part of gantry This permitted continuous rotation without interscan delays Set the stage for spiral scanning 49 Key: 1. Tube, 2. Collimator, 3. Tube Controller, 4. HV Gen (-), 5. Detector, 6. DAS, 7. HV Gen (+), H. OB Comp., 9. Stat Comp. 50 Size reduction Many components now in gantry or under the desk Spiral CT (Also Helical) 1989 table movement ( mm) per rotation Pitch collimator width ( mm) at isocenter Multi-slice or multi-detector row CT Multi-slice or multi-detector row CT Driven by X-ray tube heat loading Faster scans More practical thin slices Improved spiral interpolation MDCT 53 Or even 64 or 320 rows 54 9

10 Reconstruction Example: Iterative Reconstruction Filtered Backprojection Iterative Reconstruction - Slow Reconstruction Algorithms- GE Phantom Soft Standard Lung Multiplanar Reconstruction Detail Bone Edge Multiplanar Images Isotropic Resolution Volume Rendering

11 Reprojection Techniques Adaptive Statistical Iterative Reconstruction (ASIR) advanced reconstruction technique that reduces image noise and improves low contrast detectability and image quality. Higher diagnostic performance at lower dose Up to 40% less dose with no loss of image quality Improves low contrast detectability up to 30% 61 non-asir ASIR Noise=25.9 Noise= 16.5 AAPM History Symposium 8/1/ Computed Tomography Big Bore CT for Radiation Oncology EMI Mk I Multi-slice CT PET-CT Angio-CT 63 Note: Hopefully the caption above refers to the scanner, not to me! Slice CT (Toshiba) From Popular Science magazine

12 Flat Panel Cone Beam CT Cone Beam CT in Radiation Oncology 1 MV Source Accelerator 2 kv Flat Panel Imager 3 MV Flat Panel Imager 4 kv Source X-ray Tube /1/2012 AAPM History From Symposium Lovelock Dental Cone Beam CT 1 X-ray Tube 2 Flat Panel Imager 1 2 Ionizing Radiation! From Dental Planet CT History Information W. Kalender, PMB 51, R29 R43, 2006 Siemens web site Impact Scan.org Google Wikipedia Many other sources 71 Further Reading for CT RSNA/AAPM Teaching Modules: CT Image Quality and Protocols CT Systems Radiation Dose in CT: Cardiac CT Physics of Cardiac Imaging with Multiple Row Detector CT Mahesh and Cody. RadioGraphics 2007 Managing Radiation Use in Medical Imaging: A Multifaceted Challenge. Hricak, Brenner et al Radiology March

13 Thanks for slides to: J. Anthony Seibert, Ph.D., 2011 President AAPM, Professor UC Davis, Radiological and Medical Physics Society of NY (RAMPS) October 5, Maynard High, Ph.D., Medical Physicist, Westchester Medical Center, NY. The Essential Physics of Medical Imaging 2 nd Edition. J.T. Bushberg, J.A. Seibert, E.M. Leidholdt and J.M. Boone, Lippincott Williams and Wilkins Publisher, 2002 and 3 rd Edition 2012 D. Michael Lovelock, Ph.D., Associate Attending Physicist, MSKCC 73 Sources of Dose/Risk Information ACR & RSNA radiologyinfo.org Image Gently for Pediatric Exams imagegently.org Image Wisely for Adult Exams imagewisely.org FDA Radiological Health IAEA Radition Protection of Patients rpop.iaea.org They don t just look for illegal nuclear weapons! 74 13