Dushyant V. Sahani, M.DDushyant V. Sahani, M.D

Director of CTAssociate Professor of Radiology Massachusetts General Hospital

Harvard Medical SchoolEmail-dsahani@partners.org

Director of CTAssociate Professor of Radiology Massachusetts General Hospital

Harvard Medical SchoolEmail-dsahani@partners.org

Low kV Imaging: Indication, Application and Innovation

HARVARDMEDICAL SCHOOL

DisclosuresDisclosures

• MGH has research agreement –GE Health Care–Siemens Medical Systems

• MGH has research agreement –GE Health Care–Siemens Medical Systems

Which of the following is NOTtrue Regarding CT Dose?

Which of the following is NOTtrue Regarding CT Dose?

A. There is a linear relationship between tube current (mA) and dose

B. Tube potential (kVp) has a quadratic relationship with dose (dose kVp2)

C. Thinner slices increases image noise and dose

D. Patient with a larger body size require substantially higher dose for a diagnostic image quality

E. Arterial phase acquisition delivers more radiation than venous phase

A. There is a linear relationship between tube current (mA) and dose

B. Tube potential (kVp) has a quadratic relationship with dose (dose kVp2)

C. Thinner slices increases image noise and dose

D. Patient with a larger body size require substantially higher dose for a diagnostic image quality

E. Arterial phase acquisition delivers more radiation than venous phase

Factors that Influence DoseFactors that Influence Dose

Beam Quality

Collimation

Patient Size & anatomy

dose kVp2 Tube potential

Exposure timedose mAS

Tube Current

Benefits of low-kV selectionBenefits of low-kV selection• Increased

iodine contrast– CTA studies

• Increased iodine contrast

– CTA studies

Stiller et al, Eur J Radiol. 2011Perisinakis et al, Br J Radiol. 2011Utsunomiya et al, Eur Radiol. 2010 Marin et al, Radiology. 2010 Kim et al, AJR. 2010. Hunsaker AR. AJR. 2010 Godoy MC. Eur J Radiol. 2010 Feuchtner GM. Eur J Radiol. 2010

140 kV 100 kV

CTA: Visualization of renal artery branches

CTA: Visualization of renal artery branches

50 keV 70 keV 90 keV 120 kVp

Pinho D et al. Eur Radiol 2012

Effect of kV: Hypervascular Lesions

Hepatic Arterial Phase: Multiple Adenomas

kVp 80

mAS330

kVp 80

mAS330

kVp 140

mAs58

kVp 140

mAs58

Benefits / Challenges of low-kV selection

Benefits / Challenges of low-kV selection

8

– Reduction in radiation dose

• Small and medium size patientsdose ≈ kV2

100 kV / 440 mA 120 kV / 350 mA

NOISE

Siegel MJ Radiology 2004Huda, et al., Med Phys 2004Nakayama, et al. AJR 2006McCollough C, ISMDCT 2012

“Appropriateness of using lower-kV is highly dependent on patient size and CT indication”

MDCT protocols into 3-4

groups

Low-ContrastI+ phase CECT(portal/nephro)

Hi-ContrastCTA/CTU/CTCArterial phase

ScreeningStone/CTC

Post Procedure

Low mA optionskVp+/- (fixed)

Low kVp options mA optimized

Low kVp Low mA

MGH

Strategies for kV selectionStrategies for kV selection• Body weight

• Body mass index (BMI)–<25, 25-30, >30

• Abdominal width– < 30 cm=80*/100#

– 30-45 cm=100*/120#

– 45-50 cm=120*/120#

– >50 cm=140*/140#

• *=CTA, #=CECT

• Body weight

• Body mass index (BMI)–<25, 25-30, >30

• Abdominal width– < 30 cm=80*/100#

– 30-45 cm=100*/120#

– 45-50 cm=120*/120#

– >50 cm=140*/140#

• *=CTA, #=CECT

Workflow

Huda et al, Radiology 2000Nakayama et al, AJR 2006Schindera et al, Radiology 2008Szucs-Farkas et al, Invest Rad 2008Guimarães et al, Radiology 2010McCollough S IS-MDCT 2012

kVp Selection Based on Body Weight & Indication: CTA

120kvp 100kvp 80kvp

kVp 80-100

mA/mAs= 550/280

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

> 300 lbs= 140 kVpCT dose – 2.2 mSv

162 lbs-80 kVp

CT Cholangiography CT Cholangiography

<200 lbs >200 lbs

kV=80 kV=100

mA=350 350

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

Benadryl

Yeh B et al. Radiology 2005

Diagnostic Arterial Phase CTDiagnostic Arterial Phase CT

Siemens 64 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 20 100 250 0.89

201-300 lbs 120 220 1.3 120 75-550 1.375 22 120 220 0.89

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

100 kV selection for <200 lbs patients

DLP 580

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

Low kVp Imaging

Stone Protocol : Initial and FU CT

Siemens Flash(initial/follow up)

GE HD(initial/follow up) Phillips

Weight kV Ref mA kV Auto mA(min-max)

Noise index kV mAs

< 200lbs 120/80 100/40 120/80 75-250/50-150 26/30 120/80 120

201-300 lbs 120/80 100/40 120/100 75-350/50-150 26/30 120/80 120

> 300 lbs 120/80 100/40 120/100 75-350/50-150 26/30 120 160

FU: 80 kV<200 lbs & 100 kV> 200lbs

Post-IntereventionPost-IntereventionSiemens 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

Automated kV selction (CARE kV-Siemens)

Automated kV selction (CARE kV-Siemens)

• Automatically recommends the optimal kV setting– individual patient – specific exam

• Information from topogram– user-chosen

contrast-to-noise ratio

• Automatically recommends the optimal kV setting– individual patient – specific exam

• Information from topogram– user-chosen

contrast-to-noise ratio

205lbs

120kV

100kV

CT dose – 7.1 mSv CT dose – 11.7 mSv

138lbs

100kV

CT dose – 2.8 mSv

120kV

CT dose – 7.3 mSv

120kV

19

kV selection - CARE kV

kV selected (compared to a weight-based protocol)

kV selected

Automated kV selectionAutomated kV selection• Automatic kV selection is feasible

–Simple workflow – technologists• > 50 % of the patients kV selected lower

than the weight-based protocol• Provides Diagnostic image quality with a

lower dose• When iterative technique is combined with

CARE kV there is further drop in the radiation dose

• Automatic kV selection is feasible–Simple workflow – technologists

• > 50 % of the patients kV selected lower than the weight-based protocol

• Provides Diagnostic image quality with a lower dose

• When iterative technique is combined with CARE kV there is further drop in the radiation dose

Summary Summary • kV optimization in CT

– dual benefit of higher iodine attenuation and low dose

• Several approaches available– kV selection based on body size and indication

• Small and average size patients can be scanned using <120 kV– High contrast studies allow low kV application without image

quality limitations – In larger patients 120/140 kV– Automated kV selection is promising

• Applications– improved detection and characterization– Evaluation of vascular structures. – Reduce iodinated contrast material dose

• kV optimization in CT – dual benefit of higher iodine attenuation and low dose

• Several approaches available– kV selection based on body size and indication

• Small and average size patients can be scanned using <120 kV– High contrast studies allow low kV application without image

quality limitations – In larger patients 120/140 kV– Automated kV selection is promising

• Applications– improved detection and characterization– Evaluation of vascular structures. – Reduce iodinated contrast material dose