abdomen ct: customization of ct dose based on … ct... · abdomen ct: customization of ct dose...

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Dushyant Sahani MD Director of CT

Associate Professor of Radiology MGH

email: [email protected]

HARVARD

MEDICAL SCHOOL

MGH Webster Center for Radiation Dose Research and Education

Abdomen CT: Customization of

CT Dose Based on Patients'

Size and Clinical indications

mailto:[email protected]

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MGH CT

CT/PET-CT

18 Scanner

GE=12 16 MDCT=7

8-MDCT=1

64 MDCT=4

Siemens=5 64/Flash

Phillips=1 64 MDCT

2 IR scanners

1 Bariatric Scanner

3 PET/CT

1 PET-CT in NICU

1 Intra-op CT

5 CT’s OCI

1 Portable CT

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CT Operation

CM factors:Vol/rate/conc/Osmol

Power injector:(saline flush)

Positive: Barium/Iodine

Neutral: H2O/VoLumen/Milk

Image processing

Scanner: Speed/resolution/kV-mAs/trigger

Patient: CO/BMI/Indication

Safety: Radiation Dose/AE’s/CIN

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Steps for Lowering Dose

*Provided other scanning factors are kept constant

DECREASE IN

• Tube current • Tube potential • Gantry rotation time * • Scan length • Overlap scanning • Number of scan phases

INCREASE IN • Pitch (Table speed) * •Beam collimation


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Image Quality (IQ) and Dose

Optimum

The best image quality (IQ) per standard radiation dose

is at a point below the shoulder of graph MGH Webster Center for Radiation Dose Research and Education

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156 lbs


CT dose – 1.06 mSv

CT dose – 1.6mSv

CT dose – 6.8 mSv

“Image Quality is in the Eye of the Beholder”

CT dose – 18 mSv

CT dose – 2.2 mSv

430 lbs

162 lbs 151 lbs

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Customize Protocols

• Body part

• Body Size

• Clinical Indication

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MDCT

protocols into 3-4

groups

Low-Contrast I+ phase CECT

(portal/nephro)

Hi-Contrast CTA/CTU/CTC

Arterial phase

Screening Stone/CTC

Post Procedure

Low mA options

kVp+/- (fixed)

Low kVp options

mA optimized

Low kVp

Low mA


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MDCT

protocols into 3-4

groups

Low contrast

I+ phase CECT

(portal/nephro)

High Contrast

CTA/CTU/CTC

Arterial phase

Screening

Stone/CTC

Post Procedure

Low mA options

kVp+/- (fixed)

Low kVp options

mA optimized

Low kVp

Low mA


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Default protocol: IV (I+) and oral (O+) IV contrast portal phase, oral contrast

• Abscess

• Nausea/vomiting/bowel obstruction

• Colitis

• Malignancy… except for hypervasulcar liver lesions

• 10 min delays KUB for bladder cancer history

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Choice of OCM & Its Impact On ATCM & Radiation Dose

The density of OCM is known to affect the automated tube current modulation, in addition to patients body habitus.

Bowel phantom

filled with

respective OCM

A phantom study performed with 5 different OCMs, keeping all parameters same & utilizing ATCM (Noise Index 10). W

AT

ER

VO

LU

ME

N

GA

ST

RO

.

BA

RIU

M 2

%

BA

RIU

M 1

4%

0

2

4

6

8

10

12

14

16

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CT

Dose I

ndex (

CT

DI)

Water VoLumen Gastrografin Barium 2% Barium 14%

CT dose index was calculated & plotted

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SCANNER

TYPE

AEC TRADE

NAME

OPERATOR

CHOSEN

PARAMETER

PATIENT

SIZE AEC

Z-AXIS

AEC

ANGULAR AEC GOAL

(Regardless of

attenuation level)

GE-64 Auto mA

Smart mA

Noise Index

Yes Yes Yes Constant image noise,

within user prescribed

minimum and maximum mA

Toshiba-64 Sure

Exposure

Standard

Deviation

Yes Yes Yes

Siemens-64 CARE Dose

4D

Reference

Effective mAs

Yes Yes Yes Constant image quality, with

reference to a mAs level for an

average sized patient

Philips-64 Dose Right Reference

Image

Yes Yes Yes Same image quality as

reference image.

AEC/ATCM on Different Scanners

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ATCM: Noise Index • Noise index: on GE MDCT, used to choose the

desired image quality for scans

• Lower the noise index, higher the image quality

• Auto mA: when the mA varies throughout the scan

Higher, unnecessary mA in the

pelvis due to increased

presence of bones and fat

Can reduce mA without

compromising diagnostic ability

Unfortunately, only one NI for

each scan

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Weight Noise Index

kVp mA

< 136 lbs 12.5 100 75-250

136-200 lbs 15 120 75-350

200-300 lbs 18 120 75-450

> 300 lbs 18 120-140 75-650

Weight & Indication Adapted

Protocols

Routine

Abdomen


• Average CTDI (mGy) values were

significantly lower in all noise indexes for

the study group when compared to the

control group (17%-35%)

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Siemens (Care Dose 4D)

GE 16/64 (Auto mA 3D)

Phillips 64 (Z-DOM)

Weight

kV Ref mA Pitch kV

Auto mA

(min-max)

Pitch Noise index

kV mAs Pitch

< 135 lbs

120

200 1.2

120

75-250

1.375

12

120

250 1.1 136-200

lbs 75-350 15

201-300 lbs

75-450 17

> 300 lbs 200 0.95 75-550 0.984 18 280 0.891

Weight Based CT Protocol: Routine Abdomen

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Weight Noise Index

kVp mA Ref mAS

mAs/ Pitch

< 200 lbs 15 100-120 75-450 200 220

> 200 lbs 18 120 75-550 250 250

Weight & Indication Adapted

Protocols Cancer Follow-up


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Contribution Specific Optimization of Each Phase

mAs: 186

mAs: 67 mAs: 56

Portal

phase Noise

Index: 12

Delaye

d

phase Noise

Index: 20

60% lower dose on delayed

phase

mAs: 158 120

kVp

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MDCT

protocols into 3-4

groups

Low contrast

I+ phase CECT

(portal/nephro)

High Contrast

CTA/CTU/CTC

Arterial phase

Screening

Stone/CTC

Post Procedure

Low mA options

kVp+/- (fixed)

Low kVp options

mA optimized

Low kVp

Low mA


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Low kV imaging: Exploiting the k-edge of Iodine

Indication 140 kV 100 kV

Stiller W. Eur J Radiol. 2011

Perisinakis K. Br J Radiol. 2011.

Utsunomiya D. Eur Radiol. 2010

Marin D. Radiology. 2010

Marin D. Radiology. 2010.

Kim JE, AJR. 2010.

Hunsaker AR. AJR. 2010

Godoy MC. Eur J Radiol. 2010

Feuchtner GM. Eur J Radiol. 2010

Sahani DV. AJR 2007

Kalva S. J Comput Assist Tomogr. 2006

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Effect of kVp: Hypervascular Lesions

Hepatic Arterial Phase: Multiple Adenomas

kVp

80

mAS

330

kVp

140

mAs

58

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Low kVp Issues: Image Noise

kV=100/mA440 kV 124/mA 350

dose kVp2 Tube potential

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Arterial Phase CT

Siemens Flash GE 64 Phillips 64

Parameters

kV Ref mA

Pitch kV

Auto mA

(min-max)

Pitch Noise index

kV mAs Pitch

<200 lbs 100

200 1.3

100

75-550 1.375 18 120 250 0.89

200 1.3 75-550 1.375 20 120 250 0.89

201-300 lbs

120 250 1.3 120 75-550 1.375 22 120 250 0.89

> 300 lbs 120 250 1.3 120 150-550 0.984 28 120 280 0.89

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DLP 580

33 yr old, 67 kg women= kV 100/120, DLP=538

Low kVp Imaging

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kVp Selection Based on Body

Weight & Indication: CTA

40 % Dose Reduction

120kvp 100kvp 80kvp

kVp 80-100

mA= 75-550


200-300 lbs >150-200 lbs < 150 lbs

> 300 lbs= 140 kVp

dose kVp2 Tube potential

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Liver CTA-Pre-surgical

Planning

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CT Cholangiography Protocol: Following CTA

Parameters 16-MDCT 64-MDCT

DC (mm) 0.5-0.75 0.5-0.625

Pitch 1-1.3 1-1.3

kV 80 80

Slice venous (mm) 2-3 2-3

Contrast 20 mL Cholografin (50%) mixed in 80mL saline and drip infused over 30-40 before scanning

Premedication Benadryl

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CT Cholangiography

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MDCT

protocols into 3-4

groups

Low contrast

I+ phase CECT

(portal/nephro)

High Contrast

CTA/CTU/CTC

Arterial phase

Screening Stone/CTC

Post Procedure

Low mA options

kVp+/- (fixed)

Low kVp options

mA optimized

Low kVp

Low mA


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Top of diaphragm to lower border of ischium

Top of L-1 to upper border of symphysis

Limit Coverage: Kidney Stone

Limit Scanning Area

Dose Reduction by 20%


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Weight Noise Index

mA Ref mAS

< 200 lbs 25 75-250 100

> 200 lbs 25 75-350 120

Kidney Stone Protocols

Noise Index -20 Noise Index -25 Noise Index -30

15-20% reduction 15-20% reduction

Total 30-40 % Dose Reduction MGH Webster Center for Radiation Dose Research and Education

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Stone Protocol: Initial and FU

Siemens Flash (initial/follow up)

GE HD (initial/follow up)

Phillips

Parameters

kV Ref mA Pitch kV

Auto mA

(min-max)

Pitch Nois

e index

kV mAs Pitch

< 200lbs 120/80 100/40

0.6

120/80

75-250/50-

150 1.375 26/30

120/80

120

1.1 201-300

lbs 120/80 100/40

120/100

75-350/50-

150 1.375 26/30

120/80

120

> 300 lbs 120/80 100/40 120/100

75-350/50-

150 1.375 26/30 120 160

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+ +

+

Limit

Scanning area

Increase Noise

Index

Low kVp

Increase slice thickness

Include coronal reformations

Total Dose Reduction

by 40-70% from

Standard dose

DLP

1000 mGy-cm

DLP

200 mGy-cm

Summary of Strategies for Dose Reduction

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Post- Inetrevention/ Pancreatitis

Siemens GE

Parameters

kV Ref mA

Pitch kV Auto mA

(min-max)

Pitch Noise index

<200 lbs 80 40 0.6 100 50-250 1.375 30

201-300 lbs 80 40 0.6 120 50-250 1.375 30

> 300 lbs 100 40 0.6 120 50-350 1.375 30

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Post IR Catheter/Pancreatitis FU

156 lbs

CT dose – 1.06 mSv

CT dose – 1.6mSv

CT dose – 6.8 mSv

151 lbs

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MGH CT Dose Fact Sheet

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MGH CT Dose Fact Sheet

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=

2 View KUB = 0.6 – 1.2 mSv CT KUB = < 1 mSv

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Summary

• CT dose is the biggest threat to radiology dept

• Critical to invest efforts in lowering CT dose

• Optimize CT protocols based on body size, age and clinical indications

• Weight adapted mA and kVp reductions

• Limit scan acquisition phases and scan length

• Use thicker slices (5 mm) and include Multiplanar reconstructions


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MDCT

protocols into 3-4

groups

Low-Contrast I+ phase CECT

(portal/nephro)

Hi-Contrast CTA/CTU/CTC

Arterial phase

Screening Stone/CTC

Post Procedure

Low mA options

kVp+/- (fixed)

Low kVp options

mA optimized

Low kVp

Low mA


abdomen ct: customization of ct dose based on … ct... · abdomen ct: customization of ct dose...

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