Transcript In NDH

CTCA Dose Reduction &
Image Quality Improvement
Strategy in NDH
Speaker: Au Chun Yu Edmund
Chong Siu King Windy
HKRA AGM 2011
North district Hospital
 CT machine: GE Lightspeed VCT, 64MSCT
 Over 500 cases done (since 2008):
 Cardiac CT booked daily
 several sub – stages:
Protocol selection
Scanning
parameters
Scanning range
Breath-hold
preparation
premedication
Contrast volume
NDH vs other standards:
GE suggestion:
International:
NDH:
kVp:
120
100
80-100
Tube current
modulation:
~650mA;
30%-80%
~600mA;
30%-80%
<500mA;
40%-80%
Scan coverage:
Superior: 2cm
above carina
Inferior: base of
heart
Superior: sufficiently include LAD
Inferior: sufficiently include PLB &
PDA
Contrast volume: 80ml; 5ml/s
80ml; 5ml/s
60-65ml;
5-5.5ml/s
Protocol
selection:
Pulse
Pulse/Segment
Segment
Breathing
technique:
inspiration
Not applicable
Inspiration/
suspension
Beta-blocker:
HR:>70bpm
HR>70bpm
HR:>65bpm
mSv
11
7-12
7.88
 Analyzed statistically
 Maintain diagnostic quality
 Radiation protection
Effective Radiation Dose (mSv)
Effective Radiation Dose
of CTCA in 2010 in NDH
14
12
10
8
6
4
2
0
1
2
3
4
5
6
7
8
Month
9
10 11 12
Limited conditions:
 Limited pre-medication:
 Beta-blocker prescribed by Cardiac department
 CT machine: GE Lightspeed VCT, 64MSCT
 Maintain high image quality for reporting
Outcome:
 International standard dose for CTCA in 64MSCT :
 7-12mSv
 Average effective dose in NDH (2010):
 7.88mSv
 ~10% Dose reduction throughout 2010
 Organized, structured & optimized protocol agreed
with radiologists
 Successful training program for junior radiographers
Image Quality:
Subjective: (analyzed by the radiologists)
Image noise
Overall image quality with diagnostic confidence level
Objective:
Image noise

standard deviation of the density (in HU) within a large region of interest.
Contrast-to-noise ratio (CNR):


Signal-to-noise ratio
Noise:


Contrast –to-noise ratio
CNR = (HU LV Chamber – HU LV wall)/noise
Signal-to-noise ratio (SNR):

SNR = HU coronary artery lumen/noise
Before & After… …
>80kg
<80kg
Stage 1:
Stage 2:
Stage 3:
120 kVp
80 kVp
100kVp
80kVp
 kVp adjustment according to patient’s body weight
 Radiation dose is proportional to the square of kVp
Stage 1:
mA:
Mean Dose:
(DLP/mGY-cm)
Stage 2:
Manual mA:
>500
Tube current
modulation:
<500; 40%-80%
635.76
507.90
Mean dose reduction: 20%
Stage 1:
Stage 2:
Superior aspect:
2 cm superior to
carina of trachea
Sufficiently include
LAD
Inferior aspect:
Base of heart
Sufficiently include
PLB & PDA
Mean Dose:
(DLP/mGY-cm)
637.5
512.05
 Reduction of 1cm: dose savings of 1 mSv
Radiation dose reduction: 20%
Contrast volume:
GE suggestion:
International:
NDH:
80ml; 5ml/s
80ml; 5ml/s
60-65ml;
5-5.5ml/s
 Reduction of contrast :
 Decrease probability of allergic reaction
 Faster contrast rate:
 Better contrast resolution
Snapshot pulse
(HR 30-65BPM)
Prospective ECG gating
Snapshot segment
(HR 30-74BPM)
Snapshot burst
(HR 75-113)
Retrospective ECG gating
Case #
Mean dose
(DLP/mGy-cm)
Lowest
Highest
Average
DLP/slice
Burst
21
723.94
548.67
899.75
3.73
pulse
4
197.46
105.10
315.56
0.99
segment
136
548.54
349.54
879.08
2.78
 The most dose-efficient method of ECG-synchronized:
 Snapshot pulse
 Dose reduction by 64% (compared with segment)
 X-ray on/off is triggered by ECG R-peak with user
selectable time off
Radiation exposure is about 4 times less
 HR <60bpm
 Stable rhythms dependence
 Allow limited phase reconstruction:
 only 3-4 % phase
 Insufficient for functional analysis & Electrophysiology (EP)
 Pros:
 Helical continuous data acquisition
Favor retro-reconstruction
Option for different cardiac pattern;
Enable cardiac function analysis
 Larger volume coverage
i.e. bypass graft
Patient preparation:
Breathing technique:
Breathing technique:
Stage 1:
Stage 2:
Inspiration only
Inspiration/suspension
 Options for different types of patient:
Important in evaluation of time for stable
HR after breath-hold
Beta-blocker:
Heart rate:
Stage 1:
Stage 2:
>70 bpm
>65 bpm
 Lower heart beat and stabilize rhythm :
 Improve temporal resolution
 Options for scanning protocol selection
 Flowchart of beta-blocker standardized
Flow chart of beta blocker:
<65 bpm
>65 bpm
(1)
Stable
Pulse
1st β medication
irregular
Segment
30 mins
<65 bpm
>65 bpm
(1)
2nd β medication
30 mins
<65 bpm
>65 bpm
(1)
Calcium score + consult radiologist
 No caffeine & smoking 12 hrs before exam
 Prepare for contrast CT scan
 i.e. fasting, Metformin, LMP
 Steroid cover
 Measure resting heart rate (HR):
 Below 70 bpm: preferable
 >70 bpm: consult radiologist for medication
 Breathing instruction rehearsal:
 Evaluate the time of stable HR after breath-hold
 IV access: 18 gauge(5ml/sec), right-sided preferable
1. Scout view:
2. Calcium score:
If score >400  consult radiologist
3. Test dose:
20ml IOP370 at 5ml/s + saline at 5ml/s
 Test dose:
 Calculation of delay time
 Contrast volume depends on delay time
4. Contrast scan protocol selection:
Burst/Segment/Pulse mode
Grafting:
 Bypass grafting implant of left internal mammary artery (LIMA) to LAD
 Right IMA or inferior epigastric artery grafting to RCA
 Increase scan coverage superiorly
 Only segment protocol applicable
Future directions in NDH:
Future directions in NDH:
 Cross-departmental communication:
 Improve pre-medication prescription
 Pulse scanning protocol trial
 Further radiation dose reduction
 BMI (body mass index) dependent:
 Develop all-rounded & more precise kVp modification
Conclusion:
 Radiation dose reduction with satisfactory image
quality
 Structured ,organized & optimized protocol
 Ease the workflow of CT cardiac exam
 Improve efficiency and effectiveness for both radiologists
and radiographers
 Junior radiographers gain confidence in Cardiac CT
training program
Acknowledgements:
 Mr Ho (DM), Mr Wong (SR) & Mr Leung (SR) of NDH
 Ms Tracy Chan, Mr Eddy Chan & Mr Wayne Li
 Staff of NDH Radiology department
 Cardiac team of NDH
 HKRA
 Patients involved…
1.
Mayo J.R., Leipsic J.A. Radiation dose in cardiac CT AJR 2009; 192:646-653
2.
Pannu H., Alvarez Jr. W., Fishman E.k. β-Blockers for Cardiac CT: A Primer for the Radiologist.
AJR 2006;186:341-345
3.
Weigold W.G. Cardiovascular computed tomography: current and future scanning system
design. Cardiac CT Imaging 2010;1:21-27
4.
Araoz P.A, Kirsch J., Primak A.N., Braun N. N., Saba O., Williamson E. E., Harmsen W.S.,
Mandrekar J. N., McCollough C. H.. Dual-source computed tomographic temporal resolution
providers higher image quality than 64-detector temporal resolution at low heart rates. J
Comput Assist Tomogr. 2010;34(1):64-69
5.
Chan I.Y.F. A brief review of CT coronary angiogram. The Hong Kong medical diary 2007;12:3
6.
Sun Z. Multislice CT angiography in coronary artery disease: technical developments, radiation
dose and diagnostic value. World J cardiol 2010 26; 2(10):333-343
7.
Hospital Authority. Hospital Authority Statistical Report 2008-2009. [homepage on the
Internet]. 2010 [cited 2011 Apr 9]. Available from: Hospital Authority, Statistics and Workforce
Planning Department Web site: http://www.ha.org.hk/upload/publication_15/281.pdf
8.
Hirai N, Horiguchi J, Fujioka C, et al. Prospective versus Retrospective ECG-gated 64-Detector Coronary CT Angiography:
Assessment of Image Quality, Stenosis, and Radiation Dose. Radiology 2008; 248(2):424-430
9.
Sun Z. Multislice CT angiography in cardiac imaging: prospective ECG-gating or retrospective ECG-gating?. Biomed Imaging
Intervention Journal 2010; 6(1):e4
10.
Kopp AF, Kuttner A, Trabold T, et al. Multislice CT in cardiac and coronary angiography. The British Journal of Radiology 2004;
77:S87-S97
11.
Alkadhi H. Radiation dose of cardiac CT- what is the evidence?. European Society of Radiology 2009; 19:1311-1315
12.
Sun Z, Ng KH. Multislice CT angiography in cardiac imaging. Part III: radiation risk and dose reduction. Singapore Med J 2010;
51(5):374-380
13.
Hausleiter J, Meyer T, Hermann F, et al. Estimated radiation dose associated with cardiac CT angiography. JAMA 2009; 301(5):500506
14.
Hausleiter J, Meyer T, Hadamitzky M, et al. Radiation dose estimates from cardiac multislice computed tomography in daily practice:
impact of dofferent scanning protocols on effective dose estimates. Circulation 2006; 113:1305-1310
15.
Jean-Francois P & Hicham TA. Strategies for reduction of radiation dose in cardiac multislice CT. European Radiology. SpringerVerlag 2007
16.
Ohnesorge BM, Westerman BR, Schoepf UJ. Scan Techniques for Cardiac and coronary artery imaging with multislice CT.
Contemporary Cardiology: CT of the heart: principles and applications. Human Press. Totowa. NJ
~THANK YOU~