the acr ct accreditation program and the medical - acr ct

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)

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


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


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


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


4 3 2 1

20 c

m

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)


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

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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


Air ≈ -1000 HU

Water ≈ 0 HU

Polyethylene ≈ -97 HU

“Bone” ≈ +910 HU

Acrylic ≈ +120 HU

MODULE 1


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.


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


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


25 mm

6 mm

5 mm

4 mm

3 mm

2 mm

Low contrast = 6 HU ± 0.5 HU

MODULE 2


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)


MODULE 3

100 mm


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


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5 9

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Bar patterns:lp/cm MODULE 4


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


WW = 400WL = 0

CT ART?

At soft-tissue window settings these streaks are visible and not of concern

DATA FORMDATA FORM


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


CTDI Measurements:CTDI Measurements: Adult Head Adult Head

• 16 cm PMMA

• Phantom in head holder


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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


Center

Measurement 1 (mR) 197


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




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)


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


CTDIw (mGy) 19.0





Dose Length Product =(CTDIvol) * (total length of scan)


CTDIw (mGy) 19.0





ESTIMATEDESTIMATED Effective Dose =(DLP) * (Tissue Weighting Factor)


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


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


• 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

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


• 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


• ACR CT Accreditation process is very worthwhile for PATIENT: – better image quality– probably lowered dose


• 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

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