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The ACR CT Accreditation The ACR CT Accreditation Program and the Medical Program and the Medical
PhysicistPhysicist
Maynard High, PhDNew York Medical College
with the most kind assistance of
Cynthia McCollough, PhDMayo Clinic
Aim of CT AccreditationAim of CT Accreditation
• Peer Review and Evaluation of facility, including:– personnel qualifications– image quality– quality control procedures– patient radiation exposure
Positive Outcomes of CT Positive Outcomes of CT Accreditation Process from Accreditation Process from the Viewpoint of a Satisfied the Viewpoint of a Satisfied
UserUser• Technologist:
– involvement in performance evaluation
• Technologist, radiologist, and physicist:– increased awareness of patient dose
• Patient:– review and possible modification of scan
protocols affecting dose and image quality
Financials of CT Financials of CT Accreditation Accreditation
• Costs are not insignificant: – ~ $5K for 1 CT site with phantom
• Some insurers now require CT accreditation:
• Many more insurers will require CT accreditation within a year:
CT PROGRAM STATISTICS CT PROGRAM STATISTICS April 2003April 2003
• 200 applications received• 40 facilities accredited • ??% passed on 1st attempt
– too early in program for statistics– failures about 50% clinical / 50%
phantom
The Application ProcessThe Application Process
• Submission of site info and personnel credentials
• Acquisition of ACR CT phantom• Submission of CT data and images
– clinical images– phantom images– dose measurements
Personnel CredentialsPersonnel Credentials
• Radiologist:– Competence, continuing experience,
CME
• Technologist:– Competence, CME
• Medical Physicist:– Competence, CME
Medical Physicist Medical Physicist CredentialsCredentials
1) RECOMMEND ABR certification in – Diagnostic Radiological Physics or– Radiological Physics
2) Be Familiar with CT 3) Be in accordance with ACR
Standard for CME– no specific requirement for CT CME
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ACR Standard for CME:ACR Standard for CME:Medical Physicist Medical Physicist
• 150 hrs/3 yrs (Category 1,2 and MEP)– this 150 hrs includes the 60 hrs below– Category 2 includes meeting attendance,
self-study, teaching, publications,peer-review activities, etc
• 60 hrs/3 years (Category 1 or MEP)
The Application ProcessThe Application Process
• Submission of site info and personnel credentials
• Acquisition of ACR CT phantom• Submission of CT data and images
– clinical images– phantom images– dose measurements
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
ACR CT Phantom Information Courtesy of
CYNTHIA McCOLLOUGH, PHD
• All slides of this format and color scheme were kindly loaned to me for use in this talk by Cynthia McCollough, PhD, Chairperson of the ACR CT Accreditation Physics Subcommittee
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Physics Subcommittee
• Cynthia McCollough, Ph.D., Chair
• Tom Payne, Ph.D.
• Mike McNitt-Gray, Ph.D.
• Tom Ruckdeschel, M.S.
• Jim Brink, M.D.
• ACR: Pam Wilcox, Penny Butler, Krista Bush, Chris Riha
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Consensus Opinion re: Accreditation Phantom and Film
• Single phantom design must be used• No existing phantom had all desirable test objects• Solid one-piece construction, 20-cm diameter• Test objects must be simple to evaluate• Objects and tests must be extendable to spiral• Dosimetry will be CTDI100-based in PMMA• Assessment of phantom images will be film-based
until ACR converts to digital submission process
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
The ACR CT phantom was designed to examine a broad range of scanner parameters
Positioning Accuracy CT # Accuracy Slice Width Accuracy Low Contrast Resolution High Contrast (Spatial) Resolution Image Uniformity and Noise Image Artifacts Distance Measurement Accuracy Section Sensitivity Profiles
ACR Accreditation Application ACR Accreditation Application TestsTests
• Align light accuracy• Align table to gantry• Table/gantry tilt• Scout slice
localization accuracy• Table incr. accuracy• Slice thickness• CT#
accuracy/linearity• Hard-copy display
• Image Quality– high contrast
resolution– low contrast resolution– image uniformity– noise– artifact evaluation
• CTDI• Patient dose for
exams
Physicist’s Annual CT Survey Physicist’s Annual CT Survey (ACR)(ACR)
• Align light accuracy• Align table to gantry• Table/gantry tilt• Scout slice
localization accuracy• Table incr. accuracy• Slice thickness• CT#
accuracy/linearity• Video display• Hard-copy display
• Image Quality– high contrast resolution– low contrast resolution– image uniformity– noise– artifact evaluation
• CTDI• Patient dose for exams• Safety evaluation• Required State tests
Technologist CT QC (ACR)Technologist CT QC (ACR)
• Align light accuracy• Slice thickness• CT# accuracy• Video display• Hard-copy display
• Image Quality– high contrast
resolution– low contrast
resolution– image uniformity– noise– artifact evaluation
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
4 3 2 1
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4 cm
Head Foot
AlignmentAlignment
CT # CT #
Slice widthSlice width
Low contrast Low contrast resolutionresolution
Uniformity Uniformity & noise & noise
Distance Distance accuracy accuracy
& SSP& SSP
High contrast High contrast resolutionresolution
Technologist and Phantom Technologist and Phantom TestingTesting
• Try to give technologist responsibility for accreditation phantom testing– best done together with physicist– helps technologist better understand the
physicist’s annual survey (ACR required)– helps the physicist understand how
technologist sets up protocols (useful information for annual survey)
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Site Scanning Data Form• Site or manufacturer-recommended protocols
– Adult Head: Routine head CT for evaluation of patient with headaches to exclude neoplasms
– High Resolution Chest: CT exam of the chest for evaluation of diffuse lung disease
– Adult Abdomen: Routine oncologic CT survey of the abdomen for detection of possible liver metastases
– Pediatric Abdomen: CT examination of pediatric (approx. 5 years old) abdomen for the evaluation of blunt trauma injuries
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
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Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Instruction Manual• Detailed step by step scan and analysis
instructions• Tells which set of scan parameters to use to
acquire which phantom images• Data sheet provides cells for measured and
calculated data• W/L and location on film grid given for all
images to be filmed• Dose measurement and calculation methods
Test 1: Phantom and Test 1: Phantom and Scanner Alignment Scanner Alignment
• Align Module 1 to lasers• Scan with Hi Res Chest protocol
• Prescribe a scan at center of Module 4 ie, 120 mm superior
• Scan with Hi Res Chest protocol
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Air ≈ -1000 HU
Water ≈ 0 HU
Polyethylene ≈ -97 HU
“Bone” ≈ +910 HU
Acrylic ≈ +120 HU
MODULE 1
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
High-resolution chest technique
Must see all four BBs(in Modules 1 & 4)
Longer wire must have same number of lines above and below (±1)
Wires are 0.5 mm apart in z-direction
WW = 1000WL = 0
DATA FORMDATA FORM
Test 2: CT Number Test 2: CT Number Calibration and Slice Calibration and Slice
ThicknessThickness• Align Module 1 to lasers• Scan with Adult Adomen protocol & all
kVp’s available• Record all HU and slice thickness• Also scan with 3, 5, 7 mm & hi res chest
slice thickness• Record water HU and slice thickness for
each scan.
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Adult abdomen technique
CT number measured in 5 materials
CT number of water measured at several scan widths and kVps
WW = 400WL = 0
“Bone”
Water
Poly
Acrylic Air
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
11/2 = 5.5
10/2 = 5
Adult abdomen technique
Scan width measured at several scan widths
WW = 400WL = 0
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Test 3: Low Contrast Test 3: Low Contrast ResolutionResolution
• Scan Module 2 with Abdomen and Head protocols
• Record the smallest rod seen
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
25 mm
6 mm
5 mm
4 mm
3 mm
2 mm
Low contrast = 6 HU ± 0.5 HU
MODULE 2
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Adult abdomen and head techniques
Record diameter of the smallest set of rods for which all 4 rods can be seen
ROI check of absolute contrast using large rod
WW = 100WL = 100
DATA FORMDATA FORM
Test 4: Uniformity, Noise, Test 4: Uniformity, Noise, Artifacts, and Distance Artifacts, and Distance
AccuracyAccuracy• Scan Module 3 with Abdomen
protocol• Record HU & SD in center• Record HU at 12, 3, 6, 9 o’clock• Examine for artifacts and record• Check distance accuracy (optional)
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
MODULE 3
100 mm
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Adult abdomen and head techniques
Measure uniformity and noise
Assess for artifacts
Measure distance accuracy(optional) WW = 100
WL = 0
DATA FORMDATA FORM
Test 5: High Contrast Test 5: High Contrast ResolutionResolution
• Scan Module 4: – Hi Resolution Chest protocol– Abdomen protocol
• Record limiting lp/mm
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
12
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Bar patterns:lp/cm MODULE 4
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Adult abdomen, adult head and high-resolution chest techniques
Record the first highest frequency bar pattern for which the bars and spaces merge
WW = 100WL 1100
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
WW = 400WL = 0
CT ART?
At soft-tissue window settings these streaks are visible and not of concern
DATA FORMDATA FORM
The Application ProcessThe Application Process
• Submission of site info and personnel credentials
• Acquisition of ACR CT phantom• Submission of CT data and images
– clinical images– phantom images– dose measurements
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Dose Information for ACR Accreditation
• Submit calculations of CTDIvol, DLP and Effective Dose using the site’s measured CTDIw and the reported scan acquisition parameters (pitch)– Routine head (cerebrum)– Adult abdomen– Pediatric abdomen (5 y.o)
• CDTI phantom acquisition must be filmed
CTDI Measurements:CTDI Measurements: Adult Body Adult Body
• 32 cm PMMA
• Phantom on table
• 12 o’clock & isocenter
CTDI Measurements:CTDI Measurements: Pediatric Body Pediatric Body
• 16 cm PMMA
• Phantom on table
• 12 o’clock & isocenter
CTDI Measurements:CTDI Measurements: Adult Head Adult Head
• 16 cm PMMA
• Phantom in head holder
• 12 o’clock & isocenter
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RADIATION DOSIMETRY RADIATION DOSIMETRY FORMFORM
Dose Calculator Spreadsheet (Exposure) CTAP ID Number 00019
Section 11 - Radiation Dosimetry ( Adult Body)
CTDI Body Phantom (32-cm diameter PMMA Phantom) Measured Calculated Film
kVp 120 Page:Box
mA 240
Exposure time per rotation (s) 0.8
Z axis collimation T (mm)1 3.75
# data channels used (N)1 4
Axial (A): Table Increment (mm) = (I)1
OR Helical (H): Table Speed (mm/rotation) = (I) 11.25
Active Chamber length (mm) 100
Chamber correction factor 0.97
T, N, I and Pitch (P) T, N, I and Pitch (P)
• Some scanners do not display collimation width, T.
• Can be determined from P = I / N*T
• Conversion table for GE on ACR website.
Axial or Helical?Axial or Helical?
• ALL CTDI data must be acquired using a single axial (non-helical) scan
• Correction for helical pitch will be made in CTDIvol calculation
RADIATION DOSIMETRY RADIATION DOSIMETRY FORMFORM
Center
Measurement 1 (mR) 197
Measurement 2 (mR) 199
Measurement 3 (mR) 199 2:9
Average of above 3 measurements (mR) 198.3
Body CTDI at isocenter in phantom (mGy) 11.2
12 o'clock position
Measurement 1 (mR) 401
Measurement 2 (mR) 422
Measurement 3 (mR) 401
Average of above 3 measurements (mR) 408.0
Body CTDI at 12 o'clock position in phantom (mGy) 23.0
CTDIw (mGy) 19.0
CTDIw = 1/3 (CTDIcenter)+2/3 (CDTIedge)
RADIATION DOSIMETRY RADIATION DOSIMETRY FORMFORM
CTDIw (mGy) 19.0
Clinical exam dose estimates (using measured CTDIw and site's Adult Abdomen Protocol from Table 1)
CTDIvol (mGy) =CTDIw*N*T/I 25.4
DLP (mGy-cm) =CTDIvol*25 634.2
Eff Dose (mSv) =DLP*0.015 9.5
Pitch correction: 19.0 * 4/3 = 25.4
RADIATION DOSIMETRY RADIATION DOSIMETRY FORMFORM
CTDIw (mGy) 19.0
Clinical exam dose estimates (using measured CTDIw and site's Adult Abdomen Protocol from Table 1)
CTDIvol (mGy) =CTDIw*N*T/I 25.4
DLP (mGy-cm) =CTDIvol*25 634.2
Eff Dose (mSv) =DLP*0.015 9.5
Dose Length Product =(CTDIvol) * (total length of scan)
RADIATION DOSIMETRY RADIATION DOSIMETRY FORMFORM
CTDIw (mGy) 19.0
Clinical exam dose estimates (using measured CTDIw and site's Adult Abdomen Protocol from Table 1)
CTDIvol (mGy) =CTDIw*N*T/I 25.4
DLP (mGy-cm) =CTDIvol*25 634.2
Eff Dose (mSv) =DLP*0.015 9.5
ESTIMATEDESTIMATED Effective Dose =(DLP) * (Tissue Weighting Factor)
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
Reference Doses
• Concept has been shown to lower dose average in other modalities and/or other countries
• Represent the upper third or quartile of doses sampled from clinical practice
• Do not represent ideal or suggested doses
• Identify when dose are unusually high
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
European Guidelines
Exam CTDIw DLP Eff. DoseHead 60 1050 2.4Chest 30 650 11.1Abd 35 800 12.0Pelvis 35 600 11.4Chest/Abd/Pel 2050 34.5
From European Commission EUR 16262European Guidelines on Quality Criteria for Computed Tomography
Copyright 2003 C.H. McCollough, Ph.D. and the ACR. Used with permission.
• ACR CT Dose Reference Values– Adult Head 60 mGy– Adult Abdomen 35 mGy– Pediatric (5yr old) Abdomen 25 mGy
• Currently no pass/fail criteria– ACR will require documentation detailing either
site’s justification or corrective action– At renewal (3 yrs), reference doses will become
pass/fail
• Analysis of ACR data will determine future Analysis of ACR data will determine future reference dose values (likely CTDIreference dose values (likely CTDIvolvol))
Case History #1:Case History #1:Are CT Reference Doses Are CT Reference Doses
Useful?Useful?• High posterior fossa CTDIw observed• Parameters examined with
radiologists• New parameters proposed• Image quality evaluated• New protocol instituted• (New CTDIw) < 1/2 (Old CTDIw) !
Case History #1:Case History #1:Are CT Reference Doses Are CT Reference Doses
Useful?Useful?
Study OLD NEWtype mAs collimation CTDIw mAs collimation CTDIw
(mm) (cGy) (mm) (cGy)
Adult Post Fossa 480 2.5 / 2i 13.6 300 5.0 / 2i 6.0
Head Cerebrum 240 7.5 / 2i 4.6 300 7.5 / 2i 6.0
I have used similar reference dose methodologies to lower CTDI at several sites.
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The Accreditation ApprovalThe Accreditation Approval (or not) Report (or not) Report
• Review report with physicists, radiologists, and technologists
• Contains peer review feedback on – clinical images– performance from phantom data– dose
• May initiate protocol changes
ACCREDITATION APPROVAL REPORT: ACCREDITATION APPROVAL REPORT: CLINICALCLINICAL
Case History #2: Case History #2: Accreditation Peer ReviewAccreditation Peer Review
• Recommended P>1 for pediatric sinus• Parameters examined with technologists• Retrospective thin slice recons not
possible for P>1 : This is common req.• Displayed CTDIw not decreased
significantly for P>1.• Conclusion: P<1 clinically justified.
ACCREDITATION APPROVAL REPORT: ACCREDITATION APPROVAL REPORT: PHANTOMPHANTOM
ACCREDITATION APPROVAL REPORT: ACCREDITATION APPROVAL REPORT: PHANTOMPHANTOM
My Personal Conclusions: My Personal Conclusions: PhantomPhantom
• ACR CT Phantom can be used for all routine CT performance evaluation
• Single phantom allows intercomparison of CT units
• Not so useful where manufacturer gives specifications for their phantom– acceptance testing– noise, uniformity, low contrast, MTF
My Personal Conclusions: My Personal Conclusions: ProgramProgram
• ACR CT Accreditation process is very worthwhile for TECHNOLOGIST: – increased involvement in
performance evaluation– increased awareness of patient dose
and of parameters affecting dose
My Personal Conclusions: My Personal Conclusions: ProgramProgram
• ACR CT Accreditation process is very worthwhile for RADIOLOGIST: – increased awareness of patient dose
and of parameters affecting dose– review and possible modification of
scan protocols affecting dose and image quality
My Personal Conclusions: My Personal Conclusions: ProgramProgram
• ACR CT Accreditation process is very worthwhile for PATIENT: – better image quality– probably lowered dose
My Personal Conclusions: My Personal Conclusions: ProgramProgram
• ACR CT Accreditation process is very worthwhile for MEDICAL PHYSICIST: – better communication with
Radiologist and Technologist– increased interest and knowledge re:
multi-slice CT scanners– more respect and popularity
Thank YouThank You