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CT Scanning and Patient Dose Past Present and Future

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Presentation on theme: "CT Scanning and Patient Dose Past Present and Future"— Presentation transcript:

1 CT Scanning and Patient Dose Past 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 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 4th Gen

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 Toshiba Varian Pfizer Varian

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

14 CT Units 1974-78 Siemens Neurotom Mag Tape, Film, Paper printout
Pfizer 200FS 2nd Gen. Trans/Rot Siemens Neurotom Mag Tape, 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 and beyond 512x512 matrix 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: 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 Medical Physicists get
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 , 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 CTDIvol = 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 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

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 Old CTDIw (mGy) Current CTDIvol (mGy) 60 75 80 35 25 30 20 X 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 Why don’t they just measure the dose?
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


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

41 DL(0) and CTDI100 Equivalence
Small ion chamber vs. pencil chamber z = 0 CTDI100 Pencil chamber Integrate charge for a single axial scan 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 (LightSpeed Pro – only)
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 Toshiba Sure 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 CAT Scan Humor …… The End “”It’s his morning CAT scan “

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