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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


y logo Cancer risk following low-dose radiation

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

y logo nominal beam width

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!


SHA24/018001