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CT Scanning and Patient Dose Past Present and Future

CT Scanning and Patient Dose Past Present and Future. John C. Villforth Lecture 43 rd Annual National Conference on Radiation Control J Thomas Payne PhD. Outline Evolution of CT scanners 1971 to the present ………… Early Dose Measurements CTDI from “soup to nuts”

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CT Scanning and Patient Dose Past Present and Future

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  1. CT Scanning and Patient DosePast Present and Future John C. Villforth Lecture 43rd Annual National Conference on Radiation Control J Thomas Payne PhD

  2. Outline • Evolution of CT scanners • 1971 to the present ………… • Early Dose Measurements • CTDI from “soup to nuts” • The next phase “Equivalent Dose”

  3. CT – The beginning Sir Godfrey Hounsfield (1919-2004) EMI Research Division Nobel Prize - 1979 Oct. 1, 1971 1st Clinical scan – Atkinson Morley’s Hospital, London EMI - Electric and Musical Industries Ltd formed March 1931 by merger of UK Columbia Graphophone and Gramophone Company

  4. EMI Mark I - 1st Commercial CAT scanner 1972 • 80x80 Matrix • Water bath • 10 minute scan time • Two (2) 13mm slices Early EMI CT Head Scans, 80x80 Matrix

  5. First CT scanner in U.S. • Mayo Clinic • Rochester, MN • June 1973

  6. EMI Mark I Polaroid film hard copy Water bag diaphragm Wow ! Could get a paper printout !!!

  7. CT Advantage over plain film • Linear Attenuation map • No superimposition • Improved image contrast • 0.5% versus 10%

  8. The RACE begins….. • ACTA with COLOR - 1974 A REAL TURKEY Watermelon not a cucumber

  9. Early CT Physics Paper

  10. Oh those GENERATIONS !!!! 1st Gen. 1972-73 2nd Gen. 1974-76 3rd Gen. 1976-78 4th Gen. 1978-79

  11. CT Units 1974-78 over 18 vendors, 29 models ACTA Artronix – 1110 Neuro CAT AS&E CGR Elscint - Scanex EMI – Mark I, CT5005, CT1010 GE– CT/N, CT/T 6800,7800 Ohio-Nuclear– Delta 50,25, 110,150,190 Omnimedical– Omni 4001

  12. CT Units 1974-78 over 18 vendors, 29 models Pfizer– 200FS, 4000 Philips– Tomoscan Picker– Synerview 300,600 Searle– Photrax 4000 Siemens– Siretom, Somatom Syntex – System 60 Technicare - 2060 Toshiba Varian Pfizer Varian

  13. CT Units 1974-78 ACTA 2” NaI detectors Texas Instruments Computer - hexadecimal Siemens Neurotom McCullough DFOV units -1.5 McC’s

  14. CT Units 1974-78 Pfizer 200FS 2nd Gen. Trans/Rot Siemens Neurotom MagTape, Film, Paper printout

  15. Original Siemens Somatom

  16. The GE Continuum………

  17. Picker “Green” 4th Generation

  18. And the Winner is……. 3rd Generation - Fastest scan time Improvements 1980-90 and beyond 512x512 matrix - 1981 Slip-rings for X-ray tube – continuous rotation Faster data transmission – brush contactors / wireless Multiple detector rows – Multislice 1998 Dual tube – super FAST Cardiac.. 16, 64, 128, 256 Slice scanners Large Detector size +30cm coverage

  19. Modern CT – Covers Off! We have come along way Baby !!! X-ray Tube Housing HV Transformer Detector array HV Transformer

  20. In the early 80’s along comes a new kid on the block Nuclear Magnetic Resonance --- MRI Many projected demise of CT Here lies “CAT Scanner” Killed by MRI But wait - SPIRAL CT may save the day !!!!

  21. SPIRAL CT introduced 1989 Willi Kalender, W. Seissler, E. Klotz, P Vock “Spiral volumetric CT with single-breathhold technique, continuous transport and continuous scanner rotation” Radiology (1990), 176:181-183 Pitch = Table speed (mm/rot) / Beam Width (mm)

  22. SPIRAL CT 1996 – 2004 and beyond… SPEED BABY !!! Slide – complements Willi Kalender

  23. SPIRAL CT and even Dual Tube Multiple detector rows – Multislice 1998 Dual tube – super FAST Cardiac.. Large Detectors – 256 Slice Tube A Siemens Definition Tube B Detector B Spiral CT Slip-ring technology Higher power Tubes Interpolation algorithms Detector A

  24. Radiation Dose - Early measurements Medical Physicists get thee to measuring !

  25. Radiation Dose - Early measurements Surface dose and inside a humanoid phantom

  26. Patient Dose and • Dose Measurement • TLD’s • Film

  27. In comes CTDI circa 1980 ~ 8 years from 1st CT

  28. CT Dose “Queen” – Cynthia McCollough PhD • Thomas Ruckdeschel, MS • Alliance Medical Physics Tom Payne, PhD Abbott Northwestern Hosp. • Krista Bush, RT(CT) ACR • Cynthia McCollough, PhD • Mayo Clinic Michael McNitt-Gray, PhD UCLA School of Medicine “CT Dose Index and Patient Dose: They are Not the Same Thing” Cynthia McCollough PhD et.al. , Radiology, Vol. 259:No:2,311-316, May 2011

  29. AAPM Report No. 96 • January 2008 AAPM website: http://www.aapm.org/pubs/reports/RPT_96.pdf

  30. AAPM Report No. 96 • January 2008

  31. AAPM Report No. 96 • January 2008 Weighted ave 1/3, 2/3 W. Leitz IEC

  32. CTDI concept can be used for Helical scanningCTDIvol = CTDI w / pitch Remember that CTDIvol is a weighted Dose for “plastic cylinder” with f-factor for “Air” It is NOT PATIENT DOSE but a Dose descriptor CTDIvol Average weighted dose for a helical scan volume Currently displayed for a CT scan technique

  33. CTDI ion chamber (100 mm long)CTDI100 • Acrylic CTDI phantoms • 32 cm diameter (body) • 16 cm diameter (head) • Holes for measurements

  34. ACR CT Accreditation Dose Limits Pass/Fail Criteria Reference Levels Examination Adult Head Adult Abdomen Pediatric Body 5yr old Pediatric Head 1yr old

  35. Why can’t there be peace in the valley? New Scanners - CT beam is wider than detector Cone beams baby! Dental 3D “CT” SPECT/CT

  36. Courtesy of Bob Dixon Why don’t they just measure the dose? What a novel idea – just like the therapy physicists do But I thought we were measuring dose

  37. http://www.aapm.org/pubs/reports/RPT_111.pdf

  38. Develop concept of “equilibrium dose” Deq and “equilibrium dose- pitch product” Deq where p1 x Deq = p2 x Deq ^

  39. AAPM TG200 CT Phantom Courtesy John Boone PhD 30cm Diameter 60 cm Length (multi-section) High Density Polyethylene (HDPE)

  40. Future Challenge CTDIvolcompared to Deq Different : Phantom material Phantom size Chamber size Acrylic vs High Density Polyethylene 16cm/32cm vs 30cm 100mm Length vs 15mm Length

  41. CTDI100 Pencil chamber z = 0 Integrate charge for a single axial scan DL(0) and CTDI100 Equivalence Small ion chamber vs. pencil chamber p D100(0) = CTDI100 L Integrate charge during axial or helical scan series at an arbitrary pitch p=b/T for a scan length L

  42. Mission Accomplished… Bob Dixon Fearless Leader of TG 111

  43. Dose Reduction Techniques Automatic Exposure Control (AEC) Iterative Reconstruction Techniques

  44. AEC systems

  45. Iterative Reconstruction Techniques • GE ASiR ™ • Adaptive Selective Iterative Reconstruction • Noise reduction technique • works on projection data in recon space • not an image filter in image space • Typical 40-50% dose reduction

  46. CAT Scan Humor …… The End “”It’s his morning CAT scan “

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