Presentation is loading. Please wait.

Presentation is loading. Please wait.

John C. Villforth Lecture 43 rd Annual National Conference on Radiation Control J Thomas Payne PhD.

Similar presentations

Presentation on theme: "John C. Villforth Lecture 43 rd Annual National Conference on Radiation Control J Thomas Payne PhD."— Presentation transcript:

1 John C. Villforth Lecture 43 rd 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 EMI - Electric and Musical Industries Ltd formed March 1931 by merger of UK Columbia Graphophone and Gramophone Company Sir Godfrey Hounsfield ( ) EMI Research Division Nobel Prize Oct. 1, st Clinical scan – Atkinson Morleys Hospital, London

4 EMI Mark I - 1 st Commercial CAT scanner x80 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 ACTA with COLOR A REAL TURKEY Watermelon not a cucumber The RACE begins …..

9 Early CT Physics Paper

10 1 st Gen th Gen rd Gen nd Gen

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

13 CT Units McCullough DFOV units -1.5 McCs ACTA Texas Instruments Computer - hexadecimal Siemens Neurotom 2 NaI detectors

14 CT Units Pfizer 200FS 2 nd Gen. Trans/Rot Siemens Neurotom Mag Tape, Film, Paper printout

15 Original Siemens Somatom

16 The GE Continuum………

17 Picker Green 4 th Generation


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

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

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

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

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

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 TLDs Film

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

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

29 AAPM Report No. 96 January 2008 AAPM website:

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 scanning CTDI vol = CTDI w / pitch CTDI vol Average weighted dose for a helical scan volume Currently displayed for a CT scan technique Remember that CTDI vol is a weighted Dose for plastic cylinder with f-factor for Air It is NOT PATIENT DOSE but a Dose descriptor

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

34 ACR CT Accreditation Dose Limits Old CTDIw (mGy) Current CTDIvol (mGy) XXX Examination Pe diatric Body 5yr old Reference Levels Pass/Fail Criteria Adult Head Adult Abdomen Pe diatric Head 1yr old

35 Why cant there be peace in the valley? Cone beams baby! New Scanners - CT beam is wider than detector Dental 3D CT SPECT/CT

36 Why dont they just measure the dose? What a novel idea – just like the therapy physicists do But I thought we were measuring dose Courtesy of Bob Dixon


38 Develop concept of equilibrium dose D eq and equilibrium dose- pitch product D eq where p 1 x D eq = p 2 x D eq ^

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

40 Future Challenge CTDI vol compared to D eq Phantom material Phantom size Chamber size Acrylic vs High Density Polyethylene 16cm/32cm vs 30cm 100mm Length vs 15mm Length Different :

41 D L (0) and CTDI 100 Equivalence Small ion chamber vs. pencil chamber Integrate charge during axial or helical scan series at an arbitrary pitch p=b/T for a scan length L z = 0 CTDI 100 Pencil chamber Integrate charge for a single axial scan p D 100 (0) = CTDI 100 L

42 Mission Accomplished… Bob Dixon Fearless Leader of TG 111

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

44 AEC systems Z-axis AEC Digital scout mA Modulation During rotation GEAuto mASmart mA (LightSpeed Pro – only) PhilipsDose RightDose Right DOM SiemensCARE Dose 4D ToshibaSure Exposure

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 Its his morning CAT scan CAT Scan Humor …… The End

Download ppt "John C. Villforth Lecture 43 rd Annual National Conference on Radiation Control J Thomas Payne PhD."

Similar presentations

Ads by Google