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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” - PowerPoint PPT Presentation
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John C. Villforth Lecture43rd 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”
EMI - Electric and Musical Industries Ltd formed March 1931 by merger of UK Columbia Graphophone and Gramophone Company
Sir Godfrey Hounsfield (1919-2004)EMI Research DivisionNobel Prize - 1979
Oct. 1, 19711st Clinical scan – Atkinson Morley’s Hospital, London
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 ClinicRochester, MNJune 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%
ACTA with COLOR - 1974
A REAL TURKEY
Watermelon not a cucumber
The RACE begins…..
Early CT Physics Paper
1st Gen. 1972-73
4th Gen. 1978-793rd Gen. 1976-78
2nd Gen. 1974-76
CT Units 1974-78 over 18 vendors, 29 modelsACTAArtronix – 1110 Neuro CAT
AS&ECGRElscint - 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
ToshibaVarian Varian
Pfizer
CT Units 1974-78
McCullough DFOV units -1.5 McC’s
ACTA
Texas Instruments Computer - hexadecimal
Siemens Neurotom
2” NaI detectors
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
HV Transformer
HV Transformer
Detector array
X-ray Tube Housing
In the early 80’s 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
Pitch = Table speed (mm/rot) / Beam Width (mm)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), 176:181-183
SPIRAL CT introduced 1989
SPIRAL CT 1996 – 2004 and beyond… SPEED BABY !!!
Slide – complements Willi Kalender
Multiple detector rows – Multislice 1998Dual tube – super FAST Cardiac..Large Detectors – 256 Slice
Tube A
Tube B Detector B
Detector A
SPIRAL CT and even Dual Tube
Siemens Definition
Spiral CTSlip-ring technologyHigher power TubesInterpolation algorithms
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
Cynthia McCollough, PhDMayo Clinic
Tom Payne, PhD Abbott Northwestern Hosp.
Michael McNitt-Gray, PhD UCLA School of Medicine
Krista Bush, RT(CT) ACR
Thomas Ruckdeschel, MSAlliance Medical Physics
“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. 96January 2008
AAPM website:http://www.aapm.org/pubs/reports/RPT_96.pdf
AAPM Report No. 96January 2008
AAPM Report No. 96January 2008
Weighted ave 1/3, 2/3 W. Leitz IEC
CTDI concept can be used for Helical scanning
CTDIvol = CTDI w / pitch
CTDIvol
Average weighted dose for a helical scan volumeCurrently displayed for a CT scan technique
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 ion chamber (100 mm long) CTDI100
Acrylic CTDI phantoms32 cm diameter (body)16 cm diameter (head)Holes for measurements
ACR CT Accreditation Dose Limits
OldCTDIw (mGy)
CurrentCTDIvol (mGy) CTDIvol (mGy)
60 75 80
35 25 30
25 20 25
X X X
Examination
Pediatric Body5yr old
Reference LevelsPass/Fail Criteria
Adult Head
Adult Abdomen
Pediatric Head1yr old
Why can’t there be peace in the valley?
Cone beams baby!
New Scanners - CT beam is wider than detector
Dental 3D “CT”SPECT/CT
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
Courtesy of Bob Dixon
http://www.aapm.org/pubs/reports/RPT_111.pdf
Develop concept of “equilibrium dose”Deq and “equilibrium dose- pitch product”Deq where p1 x Deq = p2 x Deq
^
AAPM TG200 CT Phantom Courtesy John Boone PhD
30cm Diameter60 cm Length (multi-section)High Density Polyethylene (HDPE)
Future ChallengeCTDI vol compared to Deq
Phantom material
Phantom size
Chamber size
Acrylic vs High Density Polyethylene
16cm/32cm vs 30cm
100mm Length vs 15mm Length
Different :
DL(0) and CTDI100 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
CTDI100
Pencil chamber
Integrate charge for a single axial scan
p D100(0) = CTDI100
mm
mm
zdzfT
CTDI
50
50
100 )(1
L
2/
2/
)(1
)0(L
L
L zdzfb
D
Mission Accomplished… Bob Dixon
Fearless Leader of TG 111
Automatic Exposure Control (AEC)Iterative Reconstruction Techniques
Dose Reduction Techniques
AEC systems
Z-axis AEC“Digital scout”
mA ModulationDuring 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 spaceTypical 40-50% dose reduction
“”It’s his morning CAT scan “
CAT Scan Humor ……The End