Reducing dose in Cardiac CT Koen Nieman, MD, PhD
Thoraxcenter, Erasmus Medical Center Departments of Cardiology & Radiology Rotterdam, The Netherlands
Public awareness
y logo More powerful scanners Wider coverage 14-18mSv 10-15mSv
8.6mSv 6-7mSv
2-5mSv/yr
0.1mSv CXR * ECG-Pulsing
Natural background
4-CTA
16-CTA
64-CTA
Stress Tc99
Picano E, BMJ 2003; Jakobs, Eur. Radiology ‘02
Lifetime attributed risk of cancer incidence (%)
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0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
1/143
“A single coronary CT scan causes cancer in 1/143 20-years-old women�
1/284 1/686
20
1/446 1/1007
40
1/1241 1/1338 1/3261
60
80
Lifetime attributed risk of cancer incidence (%)
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
1/143
“A single coronary CT scan causes cancer in 1/143 20-years-old women�
1/284 1/686
20
1/446 1/1007
40
1/1241 1/1338 1/3261
60
80
Cancer risk
Risk at low exposure
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• Based on high-dose atom bomb exposure • Dose uncertainties • Irradiation quality • Extrapolation to lowdose medical exposure
Radiation dose
Cancer risk
Risk at low exposure
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• Extrapolation to lowdose medical exposure • Natural cancer incidence • Quadratic-linear? • Hormesis?
Radiation dose
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407,000 radiation workers, 15 countries
Average exposure: 19 mSv
Excess relative risk: 2% per 19 mSv Cardis et al, 2005
Dose Calculations CT Dose Index (CTDI100, C/kg)
Weigthed CTDI
Integrated, absorbed radiation from a single acquisition (slice) by a 100-mm ionization chamber
(CTDIw, gray)
Inhomogneous attenuation = ⅔CTDIedge+ ⅓ CTDIcenter
Volume CTDI
= CTDIw / pitch
(CTDIvol )
Dose-length pr. (DLP, mGy*cm)
Effective dose (E, mSv)
= CTDIvol * scan length
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Z-axis
Z-axis
= k * DLP kheart = 0.014 Z-axis
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Why is the dose of cardiac CT so high?
Pitch 2
Pitch 0.5
tube current
3D dataset
Noise & detail Axial source images
Using Radiation More Efficiently
Continuous scanning 50%
RR-interval
ECG-Triggered tube modulation
*Hausleiter, et al, Circulation 2006
36% off*
Continuous scanning 50%
RR-interval
ECG-Triggered tube modulation
Optimization of tube modulation
Continuous scanning 50%
RR-interval
ECG-Triggered tube modulation
>50% off*
Optimization of tube modulation
Prospective ECG-triggering
*Hausleiter, et al, AJR 2010
Prospectively triggering
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Arterially Corrected Transposition High heart rate Prospective triggering (80kV) DLP 101 (1.4 mSv)
Protection II Hausleiter, JACCimg 2010 RR 31% (P<0.001) 120kV 100kV
12.2 8.4
NS 3.30 3.28
Dose (mSv)
Image Quality
400 non-obese patients prospectively randomized
Arterially Corrected TGA High heart rate Prospective triggering (80kV) DLP 101 (1.4 mSv)
Arterial Switch
Repeat scanning
20079 64-DSCT Spiral mode, wide pulsing 120 kV; 412 mAs DLP 1636 23 mSv
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20112 128-DSCT Sequential, narrow pulsing 100 kV; 259/370 mAs DLP 176 2.5 mSv
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Staged Approach Achenbach, Eur Rad 2010 Axial 100kV 330mAs
11/56
Min-Dose spiral Spiral 120kV 400mAs
9.8
9.8 4/55 2/65
Non-diagn
3.4
3.4
4.4
1.5 Dose (mSv)
Total Dose (mSv)
Randomized trial (N=176)
High-pitch spiral CT “Flash”
250ms
Table feed ≤430 mm/s
HR 49 /min, 100 kV DLP 54 (0.76 mSv)
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High-pitch spiral CT “Flash”
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N=50; HR<60/min; <100kg Sensitivity Specificty PPV NPV
100% 80% 72% 100%
250ms
Effective dose 0.78 mSv Table feed ≤430 mm/s
Achenbach, JACCimg 2011
Spiral scan mode (Helical scan)
Retrograde ECG gating
Prosp. trigg. tube modulation (Pulsing)
Axial scan mode (Step and shoot)
Prospective ECG triggering
Tube output extension (Padding)
High-pitch spiral (Flash)
Prospective ECG triggering
High-pitch, Axial & Spiral
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Neefjes, et al, Eur Rad 2012
Per-segment performance 100 90 80 70 60 50 40 30 20 10 0
N=549 (267 CAG <5wks) HR<65/min randomize
Hi-pitch Axial spiral narrow 0.7 1.6
high-pitch spiral axial - narrow axial - wide spiral
Sens
Spec
PPV
NPV
2.7 4.7
HR>65/min randomize
Axial wide
Spiral wide
4.1 7.5
5.7 10.2
100kV 120kV (mSv)
P<0.001 (all)
Mode Selection
Heart rhythm Completely regular
Completely irregular
<60/min
Axial (narrow)
Spiral (systolic)
>80/min
Axial (wide)
Spiral (no pulsing)
Heart Rate
Additional variables: age, indication, alternatives, scanner, etc
Flash Example
250ms
Table feed â&#x2030;¤430 mm/s
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Flash Example
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(Adult) Congenital Heart Disease Where MRI runs short….. • • • • • • • • •
Right ventricle RV outflow tract / PR Pulmonary arteries & aorta Pulmonary & systemic veins Collaterals & AV malformations Coronary anomalies Myocardial mass Poor acoustic window ICD / claustrophobia
ARCAPA Abberant RCA from the pulmonary artery
4 years-old boy High heart rate Axial CT DLP = 25 (0.35 mSv)
Ventricular Septal Defect
Resuscitation @ 2 weeks SR 155 / min High-pitch spiral CTA DLP 6 (0.08 mSv)
Practicalities in pediatric cardiac CT • Contrast injection: 2-3 cc / kg body weight • Vacuum pillow fixation • Sedation usually unnecessary with highpitch scan protocols (scan time <1 sec) • Low kV scanning (80 kV 70 kV) • DLP < 10 in infants (non-gated) • Beam hardening!
4 MoB
4 MoB
Hypoplastic left heart with subvalvular VSD, banding pulmonary arteries, stent ductus Botalli CT: imaging aorta
Hypoplastic Left Heart (1M) after bilateral PA banding and ductus stenting
High-pitch spiral CT DLP 3 (0.04 mSv)
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Iterative Reconstruction Filtered back projection
Iterative reconstruction
Model
Adaptation Verification
SD-HU(Ao) = 25.2
SD-HU(Ao) = 17.5
Reconstruction
FBP vs Iterative Recon
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ERASIR, Leipsic, AJR 2011 NS 98.5 99.3
RR 44% (P<0.001)
650 450
4.2 2.3
mA
Dose (mSv)
Interp
Consecutive populations 331 (FBP) vs 243 (243)
FBP ASIR
Decreasing Exposure
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Dose saving & requirements
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Measure
Requirements
Disqualified
ECG-modulation High-pitch spiral
Regular heart rate Low heart rate
Narrow range
Cooperation
Reduce mA/kV
Small size
Arrhythmia Tachycardia Multi-phase need Non-cooperating CABG Obesity
Accept inferior image quality
Less extensive disease
Thicker slices
Lower detail requirement
Calcifications Stents Calcifications Stents
Can the calcium scan save dose? Symptomatic patients undergoing CTA • 0.3 – 1 mSv • Reduce scan range • Decision to CTA
>400 zero
CCS
100-400 10-100 <10
N/A (N=3)
<50% (N=4)
>50% (N=58)
Nieman, AJC 2011
CTA
N/A >50% (N=5) (N=3) Normal or <50% stenosis (N=167)
Tips and tricks
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• • • • •
Lower heart rate (quality and dose) Use axial mode as default scan mode 100kV for patients <75kg Narrow scan range (longitudinal) Use calcium score
• • •
Benefits should outweigh the risks Dose reduction possible without losing quality Diagnostic rather than esthetic image quality
Register & Compare
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Protection 1, Hausleiter, JAMA 2009
Conclusions: ALARA
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Dose requirement
Dose saving potential
Necessity vs Risk
Multiphase imaging Stent imaging High-risk r/o CAD Low-risk r/o CAD Calcium imaging Graft patency Cardiac morphology Non-gated imaging
Obese and atrial fibrillation
Elderly patient, in an emergency situation without alternatives
Co-operative, thin and low, regular heart rate
Elective exam in a child or non X-ray alternatives
63 year-old woman • • • • • • •
Symptoms of CHF Decreased LVF Dilated LV/LA Mitral regurgitation Tricuspid regurgitation Atrial fibrillation His ablation (VVI-PM)
Trans-Thoracic Echocardiography
Diagnosis? 1. 2. 3. 4. 5.
Aortic stenosis Coronary anomaly Moderate pulmonary regurgitation Patent ductus arteriosis Something else?
TTE versus CT
Anomalous Left Coronary Artery from the Pulmonary Artery (Bland-Garland-White)
ALCAPA
ALCAPA
Cardiac Surgery • LCA re-implantation • Mitral valve annuloplasty • Tricuspid valve annuloplasty
Follow-up • Progressive fatigue • Perciardial effusion without evident tamponade • Video-assisted thoracoscopy and drainage
Follow-up • Progressive fatigue • Perciardial effusion without evident tamponade • Video-assisted thoracoscopy and drainage
Follow-up
Healthy 70 years-old man (RR)
• • • •
Progressive dyspnea uphill hiking, no CHF Sx ASA, statin, amlodipine (HTN 140/90) Non-specific ECG, “Normal” echo, LDL 4.6, normal Hb,TSH 2011: X-ECG, 150/124W, 75% THR, no ischemia
Calcium Scan
Proceed to CT angiography?
Calcium Scan
Proceed to CT angiography?
CT Angiography LAD
CT Angiography LCX
Next step Progressive dyspnea, no chest pain, fairly normal exercise test, normal echo, high calcium score, 2VD cannot be ruled out 1. 2. 3. 4. 5.
Reassurance Medical treatment Non-invasive ischemia testing Cardiac cath Find non-cardiac cause
Stress Myocardial Perfusion CT Adenosine Contrast
>10’
Contrast
Coronary angiography Myocardial perfusion
<10’
Late Enhancement
CT Perfusie Imaging LAD
1
2
2
3
1 3
CT Perfusie Imaging LAD
1
2
2
3
1 3
Cath angio / FFR Left dominance Distal LM > 50% Diagonal >50% LCx > 50%
FFR 0.45 FFR 0.51 FFR 0.66
Radiation Exposure
Calcium scan 0.57 mSv
CTA 3.63 mSv Total effective dose 12.10 mSv
CT-MPI 7.90 mSv
Dynamic DSCT MPI Bamberg et al, Radiology 2011 33 high risk patients CTA + dynamic CT MPI CAG + FFR (50-85%)
Per vessel
Se
Sp PPV NPV
CTA (>50%)
91
69
79
85
CTA (FFR)
100 51
47
100
CTA/MBF (FFR)
93
75
97
87
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Scanner
Reference
N
Population
Se
Sp
Kurata
16CT (stat)
SPECT-MPI
12
Susp CAD
90
79
George
64/256CT (stat) QCA/SPECT
27
Pos SPECT
81
85
Blankstein
64DSCT (stat)
QCA/SPECT
33
SPECT/ICA
93
74
Ho
128DSCT (dyn)
SPECT
35
Recent MPI
83
78
Ko
64DSCT (stat)
MRI
41
Known CAD
91
72
Tamarapoo 64DSCT (stat)
SPECT
30
Pos SPECT
92
86
Weininger
128DSCT (dyn)
MRI
20
Acute CP
93
99
Feuchtner
128DSCT (stat)
MRI
30
Kwn/susp. CAD
96
95
Bamberg
128DSCT (dyn)
FFR
36
Kwn/susp. CAD
93
87
Ko
320CT
FFR
42
Kwn CAD
76
84
Pooled
306
88.3 83.1
Stress Perfusion Scan Modes Static perfusion Single dataset “single” phase
Kurata, JCircJ 2005 Blankstein, JACC 2009
Dynamic perfusion Altern.table position
Hattori, JCircJ 1998 (EBCT) Bamberg, Radiology 2011 (DSCT)
Full coverage
George, JACC 2006 George, Circ CV Img 2009
Thank you!