AbdomenCT:When,HowwithWhatProtocol
Mannudeep K.Kalra,MD
WebsterCenterforQualityandSafety
Massachusetts General HospitalHarvard Medical School
IndicationDrivenAbdomenCTProtocols
Protocol Clinical Reasons Specific instructions
Routine Abdomen Masses, infections, pain, cancer staging (non-abdominal primary)
No routine non-contrast before contrast
CT urinary calculi Suspected or known renal colic Follow up stone CT at lower dose than initial
CT hematuria < 40 years: non-contrast CT- Stone – No post contrast
> 40 years: non-contrast & post-contrast
CT adrenal protocol Characterize adrenal nodule seen on chest or routine abdomen
All phases through adrenal region only
CT colonography Screening exam, completion colonography Lowest dose abdominal CT
CT biphasic liver When MR can not be performed in patients with suspected liver malignancies
Arterial phase: Lower kV Arterial phase: Liver only
Portal venous phase: entire abdomen
SpecificAbdominalCTProtocols
Scanprotocolsmustbeginwithclinicalindications.
Eachscanprotocolshouldthenaddress••Numberofscanphasesrequired••Scanrangeforeachphase••Scanparametersforeachphase••Doseadjustmentforpatientsize
Need:Indicationdrivenprotocols?
••Urinarystones••CTcolonography••CTenterography
Certainthingscanbeseenatreduceddose
••Lowattenuationliverlesions••Pancreaticneoplasms••Solidrenaltumors
Othersneedhigherdoseforassessment
CTColonography<CTurinarycalculi<CTroutineabdomen<CTbiphasicortriphasicliverprotocol
AbdomenCT:TubeCurrent
Ensuredoseadjustmenttopatientsize
••UseAEC(CareDose4D)andnotfixedmAs••AdjustQRMfordifferentclinicalindications••LowermAsforurinarystones/CTcolonography••LowermAsforiterativereconstructionsthanFBP
TubeCurrent:
65 kg115 kg
50 mAs3.4 mGy
Obese
200 mAs14 mGy
339 mAs23 mGy
200 mAs14 mGy
Average/slim
100 mAs6.7 mGy
50 mAs3.4 mGy
Routine Abdomen: Use AEC
KVandAbdominalCT
KVselection:UseCareKV
WitholderCTandFBP:120kV
WithIR,innon-obesepatientsat100kV
CTAandarterialphaseCTat≤100kV
ForceCTwithhighermAslimit(800-1300mAs)areexpectedtoincreaseuseoflowerkVinabdomen.
kV,DoseandHU
kVp: 140 120 (-35% dose) 100 (-50% dose) HU: 300 357 470
ScanLength:AbdominalCT
Indication CoverageRoutineorR/O Dome ofliver- pubic symphysis
Delays Throughlesiononly(not entireorgan)
Kidney stoneCTUrography Top ofkidneys- Symphysis
Dual phaseliver Arterial: LiverPortalvenous:Entireabdomen
Appendixinyoungpatients Limitedcoverage:L3tosymphysis
Chest-Abdomen CT
Minimize scan overlap
BenignDisease:YoungPatientsEx: Appendicitis
Limited coverage: L3 to SPAEC for size adapted dose
8YO/28kg?Appy
DSCT(Force)CarekV,refkV90AdmireA3
NormalAppendixMesentericAdenitis
Enteroclysis
94 kgDefinition EdgeCare kV, Ref kV 120 QRM 250 mAsSafire S3
NumberofscanseriesforabdomenCT• Unfortunately,repeatedscanningiscommoninabdomen• Routinepre-contrastpriortopost-contrastCTshouldbeavoided• Whenperformingmultiplephases,questionneedandtechnique
Abdominal CT: Multiphase exams
Multiple phases Questions to ask and answerNeed? Routine non-contrast phase before post-contrast: No
Routine arterial and venous phases: NoRoutine delayed images: No
Same length? Length for some phases can be less: YesEx: arterial phase liver or pancreas can be smaller lengthEx: Delayed phase: through the lesion only
Same dose? Some phases can be acquired at lower dose: YesNon-contrast: Lower dose Arterial phase: Lower KV to reduce doseIterative reconstruction technique to enable dose reduction
MultiphaseLiverCT:DoseReduction
Arterialphase:LowerkV(100)LiveronlycoverageAEC Portalvenousphase:
LongercoverageAEC
AdrenalProtocol
•MultiphaseCT• Scanlength:
• T11- L2• Adrenalsonly
•120kV•AEC• IRtechniques
CTForHematuria:DecreasingScanPhases
Unenhanced CT50 mL IV contrast bolus
250 mL saline drip infusion
Wait 15 minutes (Prone)
100 mL IV contrast @ 3 mL/sec
Scan at 100-sec. delay Maher MM, Kalra MK, et al. BJR 2004
Non-contrastlimit coverage: kidneys to SPLower dose ( - 50%)AEC and IR
Post Contrast:Wider coverage AEC
IterativeReconstruction(IR)inAbdomen
SeveralstudieshaveshownreducedradiationdoseswithIRinabdomenCT
ExtentofdosereductionwithIRrelativetofilteredbackprojectionvariesbyclinicalindicationandpatientsize
Generally,30-50%dosereductioncanbeanticipatedvsFBPforabdominalCT
IRIS 200 mAs
FBP 200 mAs FBP 100 mAs
IRIS 100 mAs
FBP 50 mAs
IRIS 50 mAs
Itera
tive
reco
nstru
ctio
n (IR
IS, S
iem
ens)
redu
ce im
age
nois
e in
low
dos
e C
T
FBP 200 mA FBP 160 mA FBP 80 mA
S1 80 mA S2 80 mA S3 80 mA
S1, S2, and S3 represent increasing strength of Safire ( Siemens) for noise reduction
Iterative reconstruction help reduce image noise in low dose CT
WhatelseishighcontrastinAbdomen?
Highcontrast=KidneystonesCalciumVsSofttissues
DoseReduction
CT Colonography
30-40 mAs: 100-120 kV
Flat polyp (8 mm)
2-4 mGy
High tissue contrast between air and colonic wall and lesions enable dose reduction
FBP300mAs 140kV30mGy 200mAs 120kV13mGy
100mAs 120kV7mGy 50mAs 120kV3.4mGy
350mAs 120kV24mGy
Kidney stone CT: Seen at Lower Dose
65 kg BMI 26
UrinaryStoneCT
(A)CT images of 60-year-old man acquired with fixed current (A) and
(B) AEC show a tiny calculus (arrow) in left renal pelvis. AEC (B) enabled 50% dose reduction compared to fixed current technique.
Tube Potential 120 KV commonly (100 kV< 60 kg)
Tube current (prefer AEC)
About 30-50% lower than routine abdomen
Image thickness (mm) 2.5- 5mm
CTDI vol 2-6 mGy (size based)
A BFixed mA Use AEC (NI 20)
HighContrastinAbdomen
CTA(aorta,liver,renal)+CTenterography
LowerKV=lowerDose
ThePotentialandTheCurrent:Routine
WithATPS,dosereductionof18%withkV+AECversusAECaloneWithATPSalone,35%lowerdoseforchest&42%lowerdoseforabdominalCT
CTAbdomen:AutomaticKVisDefault
Protocol type Ref KV Setting
Pediatric abdomen Non-contrast Portal venous phaseArterial phase
100 kV100 kV80 kV
3712
Adult abdomen Non-contrast Kidney stonePortal venous phaseArterial phase
120 kV100 kV120 kV100 kV
33711
Contrast Savings
LowkV&IodineConcentration
120 Ref kV400 mg% Iodine
80-100 kV270 mg% Iodine
Summary
NeedforclinicalindicationbasedCTprotocols
1AvoidroutinemultiphaseCTprotocols
2Reducescanlengthwhenpossibleformulitphase CT
3UseAEC
4UselowerkVforsmallerpatientsparticularlywithIR
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