John C. Villforth Lecture 43rd 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” The next phase “Equivalent Dose” 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 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 First CT scanner in U.S. Mayo Clinic Rochester, MN June 1973 EMI Mark I Polaroid film hard copy Water bag diaphragm Wow ! Could get a paper printout !!! CT Advantage over plain film Linear Attenuation map • No superimposition • Improved image contrast 0.5% versus 10% The RACE begins….. ACTA with COLOR - 1974 A REAL TURKEY Watermelon not a cucumber Early CT Physics Paper 1st Gen. 1972-73 2nd Gen. 1974-76 3rd Gen. 1976-78 4th Gen. 1978-79 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 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 Varian Pfizer CT Units 1974-78 ACTA 2” NaI detectors Siemens Neurotom Texas Instruments Computer - hexadecimal McCullough DFOV units -1.5 McC’s CT Units 1974-78 Pfizer 200FS 2nd Gen. Trans/Rot Siemens Neurotom Mag Tape, Film, Paper printout Original Siemens Somatom The GE Continuum……… Picker “Green” 4th Generation 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 Modern CT – Covers Off! We have come along way Baby !!! X-ray Tube Housing HV Transformer Detector array HV Transformer 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 !!!! 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) SPIRAL CT 1996 – 2004 and beyond… SPEED BABY !!! Slide – complements Willi Kalender 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 Spiral CT Slip-ring technology Higher power Tubes Interpolation algorithms Detector B Detector A Radiation Dose - Early measurements Medical Physicists get thee to measuring ! Radiation Dose - Early measurements Surface dose and inside a humanoid phantom Patient Dose and Dose Measurement • TLD’s • Film In comes CTDI circa 1980 ~ 8 years from 1st CT CT Dose “Queen” – Cynthia McCollough PhD Thomas Ruckdeschel, MS Alliance Medical Physics Tom Payne, PhD Abbott Northwestern Hosp. Krista Bush, RT(CT) ACR Michael McNitt-Gray, PhD UCLA School of Medicine Cynthia McCollough, PhD Mayo Clinic “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 AAPM Report No. 96 January 2008 AAPM website: http://www.aapm.org/pubs/reports/RPT_96.pdf AAPM Report No. 96 January 2008 AAPM Report No. 96 January 2008 Weighted ave 1/3, 2/3 W. Leitz IEC Remember that CTDIvol is a weighted Dose for “plastic cylinder” with f-factor for “Air” It is NOT PATIENT DOSE but a Dose descriptor CTDI concept can be used for Helical scanning CTDIvol = CTDI w / pitch CTDIvol Average weighted dose for a helical scan volume Currently displayed for a CT scan technique CTDI ion chamber (100 mm long) CTDI100 Acrylic CTDI phantoms 32 cm diameter (body) 16 cm diameter (head) Holes for measurements ACR CT Accreditation Dose Limits Reference Levels Examination Adult Head Old CTDIw (mGy) 60 Pass/Fail Criteria Current CTDIvol (mGy) CTDIvol (mGy) 75 80 Adult Abdomen 35 25 30 Pediatric Body 25 20 25 X X X 5yr old Pediatric Head 1yr old 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 Courtesy of Bob Dixon Why don’t they just measure the dose? But I thought we were measuring dose What a novel idea – just like the therapy physicists do http://www.aapm.org/pubs/reports/RPT_111.pdf Develop concept of “equilibrium dose” Deq and “equilibrium dose- pitch product” ^D where p1 x Deq = p2 x Deq eq AAPM TG200 CT Phantom 30cm Diameter 60 cm Length (multi-section) High Density Polyethylene (HDPE) Courtesy John Boone PhD Future Challenge CTDI vol compared to Deq Different : Phantom material Acrylic vs High Density Polyethylene Phantom size 16cm/32cm vs Chamber size 30cm 100mm Length vs 15mm Length DL(0) and CTDI100 Equivalence L/2 1 ion chamber vs. DSmall L (0) f ( z ) d z b L / 2 pencil chamber p D100(0) = 1 CTDI 100 T 50 mm f ( z)dz 50 mm CTDI100 CTDI Pencil 100 chamber L Integrate charge during axial or helical scan series at an arbitrary pitch p=b/T for a scan length L z=0 Integrate charge for a single axial scan Mission Accomplished… Bob Dixon Fearless Leader of TG 111 Dose Reduction Techniques Automatic Exposure Control (AEC) Iterative Reconstruction Techniques AEC systems Z-axis AEC “Digital scout” mA Modulation During rotation GE Auto mA Smart mA (LightSpeed Pro – only) Philips Dose Right Dose Right DOM Siemens CARE Dose 4D CARE Dose 4D Toshiba Sure Exposure 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 CAT Scan Humor …… The End “”It’s his morning CAT scan “