Dushyant V. Sahani, M.DDushyant V. Sahani, M.D
Director of CTAssociate Professor of Radiology Massachusetts General Hospital
Harvard Medical [email protected]
Director of CTAssociate Professor of Radiology Massachusetts General Hospital
Harvard Medical [email protected]
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
Top Related