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

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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

5