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  • 1

    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

    mailto:dsahani@partners.org

  • 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 CTs OCI

    1 Portable CT

  • 3

    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/AEs/CIN

  • 4

    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

  • 5

    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

  • 6

    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

  • 7

    Customize Protocols

    Body part

    Body Size

    Clinical Indication

  • 8

    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

  • 9

    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

  • 10

    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

  • 11

    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

  • 12

    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

  • 13

    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

  • 14

    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%)

  • 15

    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

  • 16

    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

  • 17

    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

  • 19

    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

  • 22

    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

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

  • 23

    DLP 580

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

    Low kVp Imaging

  • 24

    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

  • 25

    Liver CTA-Pre-surgical

    Planning

  • 26

    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

  • 27

    CT Cholangiography

  • 28

    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

  • 29

    Top of diaphragm to lower bor

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