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Dushyant Sahani MD Director of CT
Associate Professor of Radiology MGH
email: dsahani@partners.org
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
2
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
MGH Webster Center for Radiation Dose Research and Education
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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
MGH Webster Center for Radiation Dose Research and Education
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
MGH Webster Center for Radiation Dose Research and Education
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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
MGH Webster Center for Radiation Dose Research and Education
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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
18
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
MGH Webster Center for Radiation Dose Research and Education
• 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
MGH Webster Center for Radiation Dose Research and Education
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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
18
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
MGH Webster Center for Radiation Dose Research and Education
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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
20
Effect of kVp: Hypervascular Lesions
Hepatic Arterial Phase: Multiple Adenomas
kVp
80
mAS
330
kVp
140
mAs
58
21
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
MGH Webster Center for Radiation Dose Research and Education
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
MGH Webster Center for Radiation Dose Research and Education
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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%
MGH Webster Center for Radiation Dose Research and Education
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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
33
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
36
MGH CT Dose Fact Sheet
37
=
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
MGH Webster Center for Radiation Dose Research and Education
39
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
MGH Webster Center for Radiation Dose Research and Education
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