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AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationCT Acceptance Testing & QCDianna Cody, Ph.D.Jim Kofler, Ph.D.

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationDisclosures Jim Kofler, Ph.D.– None Dianna Cody, Ph.D.– MTMI, paid speaker– Fulbright & Jaworski, expert witness

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationContributors Jim Kofler, Ph.D.Dustin Gress, M.S.Jessica Nute, M.S.John Rong, Ph.D.Brandan Darensbourg, B.S.

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationLearning Objectives Understand the essential components of an annualCT test process Recognize the value of implementing a daily CTquality control process Understand the basic components of a daily CTquality control program

AAPM 2012 Summer School on Medical Imaging using Ionizing Radiationoutline Acceptance testing– What to watch out for?– New stuff [Flash, GSI, 420 heads,etc] Daily QC– Why bother?– What to expect? Artifacts– Make it part of daily QC– Consider adding large phantom artifact scan

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationAcceptance Testing Basics (ACR QC Man.)––––––––Protocol reviewRx & light alignmentImage thicknessTable travelBeam widthContrast resolutionSpatial resolutionCT number accuracy– Artifact evaluation– Dosimetry– CT scanner monitor

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationBasic Tests Protocol Review––––Pediatric Head & AbdomenAdult Head & AbdomenHigh Resolution ChestNeuro CT Perfusion (if performed) Consider– Acquisition details– Reconstruction details– CTDIvol & DLP

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationNewer Technology Additional tests to consider––––IQ for both tubes (separately if possible)Dose for each tube (test A B, A alone, calculate B)Dose for kV switching (dual-energy) acquisitionsCardiac dose (use 32cm CTDI phantom, ECG input forcoronary artery exam)– Ped dose (ACR – 16cm CTDI on table top)– 420 head scans

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationNew technology with ? tests Iterative reconstruction– Phantom vs clinical

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationOrgan dose reductionCT vendors starting to design exposures specificallyto reduce organ dose Siemens Flash scanner “X-care” feature Up to 40% breast dose reduction How to verify this? Point dosimeter?

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 1How should the radiation exposure measurement for acardiac CT exam be performed?1%54%1%41%3%a)b)c)d)e)Axial-Sequential scan mode, 16cm CTDI phantomAxial-Sequential scan mode, 32cm CTDI phantomHelical scan mode, 16cm CTDI phantomHelical scan mode, 32cm CTDI phantomIt is not feasible to assess radiation exposure fromthis exam

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 1 - keyHow should the radiation exposure measurement for acardiac CT exam be performed?a) Axial-Sequential scan mode, 16cm CTDI phantomb) Axial-Sequential scan mode, 32cm CTDI phantomc) Helical scan mode, 16cm CTDI phantomd) Helical scan mode, 32cm CTDI phantome) It is not feasible to assess radiation exposure fromthis examKofler, et al. Radiology RSNA proceedings, p1065, 2008

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 2How can the radiation exposure from the secondary x-ray tube in adual-source CT scanner be evaluated without resorting to using servicemode?8%86%1%2%3%a)b)c)d)e)Measure A tube, measure A B tube. A – (A B) B aloneMeasure A tube, measure A B tube. (A B) - A B aloneMeasure A tube, measure A B tube. (A B) A B aloneMeasure B tube aloneCannot be done reliably without service mode

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 2 - keyHow can the radiation exposure from the secondary x-ray tube in adual-source CT scanner be evaluated without resorting to usingservice mode?a) Measure A tube, measure A B tube. A – (A B) B aloneb) Measure A tube, measure A B tube. (A B) - A B alonec) Measure A tube, measure A B tube. (A B) A B aloned) Measure B tube alonee) Cannot be done reliably without service modeKofler, et al. Radiology RSNA proceedings, p1065, 2008

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationCT Quality Control Purpose– Technology becoming more complicated, moreoversight needed– Field becoming more quantitative, more focus onnumerical values in CT images– Improved reliability may result in fewer repeat exams– Overall improvement in quality

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationQuality Control in CT Daily QC– Typically performed and recorded by technologistoperator PRIOR to first patient of the day– Should be streamlined – both easy and fast to complete– Some method for recording results should be in place(easy & fast)– Electronic recording best – provides efficient methodfor plotting results for improved interpretation

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationDAILY QC? Have you gone completely insane?Have you no regard for clinical throughput?My techs would never put up with this Etc Will soon be part of the ACR CT QC Manual Drives home the importance of confirming scanneris operating at a minimally acceptable level

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationOver 100 scanner years of CT QC Data Mix of GE & Siemens CT scannersRoutine, Interventional, Hybrid areasDaily QC on water phantomUsed Mfr tolerances (for most part)Images sent to off-line computer for analysisCompiled over 100 scanner years of data

AAPM 2012 Summer School on Medical Imaging using Ionizing Radiation

AAPM 2012 Summer School on Medical Imaging using Ionizing Radiation

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationWhat to test? Noise (Standard Deviation) in water phantom (Get mean water value for free – record that, too) Artifacts Not so bad, eh?

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationWhich scanners to test (daily QC)? Routine bread-and-butter CT scanners Interventional scanners Hybrid CT scanners– PET/CT– SPECT/CT CT Simulation scanners

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationWater phantom scan parameters? Recommend: Manufacturer’s specification– Must follow specified protocol parameters– Want to use vendor noise test criteria– Most efficient for following up test with service

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationStd. Dev. QC – plotted in histogram form Criteria may need adjustment? (GE VCT)Current limitsMore appropriate?

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 3If the water phantom test result passes each day, why botherto record it?75%1%0%23%1%a) There can be a lot of value in examination of longterm QC datab) Federal law demands itc) All state regulations require itd) ACR CT Accreditation program requires ite) AAPM insists on it

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 3 - keyIf the water phantom test result passes each day, whybother to record it?a) There can be a lot of value in examination oflong-term QC datab) Federal law demands itc) All state regulations require itd) ACR CT Accreditation program requires ite) AAPM insists on itAdvances in Medical Physics 2008. Wolbarst,Mossman, Hendee. Page 52.

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 4You are preparing to launch a new hybrid scanning service (nuclearmedicine combined with CT). What do you expect the reaction willbe regarding your CT QC instructions from the )Who needs QC?Why bother to record results?Is that all we have to do? You’re kidding, right?What a waste of time!We don’t do QC around here.

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 4 - keyYou are preparing to launch a new hybrid scanningservice (nuclear medicine combined with CT). What doyou expect the reaction will be regarding your CT QCinstructions from the technologist/operator staff?a) Who needs QC?b) Why bother to record results?c) Is that all we have to do? You’re kidding, right?d) What a waste of time!e) We don’t do QC around here.Advances in Medical Physics 2008. Wolbarst, Mossman,Hendee. Page 59.

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationCT Artifacts Artifact analysis should be incorporated into dailyQC scan program Hunting for artifacts is essentially different fromrecognizing them (maybe) on water images Appropriate window/level settings are critical Can be readily accomplished in stack mode

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationArtifact scan parameters? Medical Physicist’s judgement We recommend:– AXIAL-SEQUENTIAL scan mode!– Detector configuration with smallest sample detectors inz-direction to see subtle problems soonest (checkingchannel balance)– Detector configuration that samples entire detector arrayin z-direction to check entire extent

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationWhat to expect? Mostly ringsFrom subtle to severeOften resolved by repeating air calibration processExamples

AAPM 2012 Summer School on Medical Imaging using Ionizing Radiation

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationDon’t rely on automated manufacturer’s checksBoth scans passed daily “constancy” test

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationStreaks more frequently appearing 2008

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationLarge Phantom Artifact Scan20cm48cmWeekly to Monthly?“Best Practice”

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationMore frequent problem on 16-slice than on 64-slice scanners

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationWhat to use for large phantom? Often something suitable is provided with scannerby manufacturer– 48cm or 35cm diameter If nothing is readily available, try the 32cm CTDI May need to push phantom suppliers to offerthese?

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationDon’t be surprised If you try this, you may see issues that have notbeen recognized For a large group of scanners, this could cause areal mess Suggest phased in implementation Be ready with a triage approach (worst artifact getsserviced first, etc )

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationPatient image artifacts Helicopter blade head example – combination ofhelical pitch 1 exam and swallowing (unluckytiming). Others we have observed recently

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationCombination ofswallowing at justthe right (wrong)moment, pitch 1

AAPM 2012 Summer School on Medical Imaging using Ionizing Radiation

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 5A ring artifact has emerged on a daily water phantom QCimage. What is the most logical course of action?1%0%2%6%91%a) Shut the scanner down and wait for service.b) Ignore it and get on with the patient exams.c) Repeat the scan without changing anything – maybeit will just go away.d) Request a calibration service from the field engineere) Run an air calibration scan procedure, then repeatthe QC scan.

AAPM 2012 Summer School on Medical Imaging using Ionizing RadiationSAMs question 5 - keyA ring artifact has emerged on a daily water phantom QCimage. What is the most logical course of action?a) Shut the scanner down and wait for service.b) Ignore it and get on with the patient exams.c) Repeat the scan without changing anything – maybe itwill just go away.d) Request a calibration service from the field engineere) Run an air calibration scan procedure, then repeat theQC scan.Advances in Medical Physics 2008. Wolbarst, Mossman,Hendee. Page 55.