CTCA Dose Reduction & Image Quality Improvement Strategy in NDH
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Transcript of CTCA Dose Reduction & Image Quality Improvement Strategy in NDH
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Speaker: Au Chun Yu EdmundChong Siu King WindyNorth district Hospital
CTCA Dose Reduction & Image Quality Improvement Strategy in NDH
HKRA AGM 2011
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In NDH: 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
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NDH vs other standards:GE suggestion:
International: NDH:
kVp: 120 100 80-100Tube current modulation:
~650mA; 30%-80%
~600mA; 30%-80%
<500mA; 40%-80%
Scan coverage: Superior: 2cm above carinaInferior: 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
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Results:
Analyzed statistically Maintain diagnostic quality Radiation protection
1 2 3 4 5 6 7 8 9 10 11 120
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4
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Effective Radiation Dose of CTCA in 2010 in NDH
MonthEffec
tive
Rad
iati
on D
ose
(mSv
)
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Limited conditions: Limited pre-medication:
Beta-blocker prescribed by Cardiac department
CT machine: GE Lightspeed VCT, 64MSCT
Maintain high image quality for reporting
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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
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Image Quality:
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Analysis of Image quality:
Noise:
standard deviation of the density (in HU) within a large region of interest.
Contrast-to-noise ratio (CNR):
CNR = (HU LV Chamber – HU LV wall)/noise
Signal-to-noise ratio (SNR):
SNR = HU coronary artery lumen/noise
Subjective: (analyzed by the radiologists)Image noise Overall image quality with diagnostic confidence level
Objective:Image noise Contrast –to-noise ratio Signal-to-noise ratio
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Before & After… …
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kVp modification:
kVp adjustment according to patient’s body weight
Radiation dose is proportional to the square of kVp
Stage 1: Stage 2: Stage 3:>80kg 120 kVp 80 kVp 100kVp<80kg 80kVp
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mA modification:
Mean dose reduction: 20%
Stage 1: Stage 2:mA: Manual mA:
>500
Tube current modulation:
<500; 40%-80%
Mean Dose:(DLP/mGY-cm)
635.76 507.90
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Scan length modification:
Reduction of 1cm: dose savings of 1 mSv
Radiation dose reduction: 20%
Stage 1: Stage 2:Superior aspect: 2 cm superior to
carina of tracheaSufficiently include
LADInferior aspect: Base of heart Sufficiently include
PLB & PDAMean Dose:
(DLP/mGY-cm)637.5 512.05
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Contrast volume:
Reduction of contrast : Decrease probability of allergic reaction
Faster contrast rate: Better contrast resolution
GE suggestion: International: NDH:80ml; 5ml/s 80ml; 5ml/s 60-65ml;
5-5.5ml/s
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Protocol selection:
Snapshot pulse (HR 30-65BPM)
Prospective ECG gating
Snapshot segment(HR 30-74BPM)
Snapshot burst(HR 75-113)
Retrospective ECG gating
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Protocol selection:
The most dose-efficient method of ECG-synchronized: Snapshot pulse Dose reduction by 64% (compared with segment)
Case # Mean dose (DLP/mGy-
cm)
Lowest Highest Average DLP/slice
Burst 21 723.94 548.67 899.75 3.73pulse 4 197.46 105.10 315.56 0.99
segment
136 548.54 349.54 879.08 2.78
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Snapshot pulse: X-ray on/off is triggered by ECG R-peak with user
selectable time off
Radiation exposure is about 4 times less
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Limitation: HR <60bpm Stable rhythms dependence Allow limited phase reconstruction:
only 3-4 % phase Insufficient for functional analysis & Electrophysiology (EP)
NDH DECISION:SEGMENT
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Snapshot segment: Pros:
Helical continuous data acquisitionFavor retro-reconstruction
Option for different cardiac pattern;Enable cardiac function analysis
Larger volume coverage i.e. bypass graft
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Patient preparation:
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Breathing technique:
Options for different types of patient:Important in evaluation of time for
stable HR after breath-hold
Stage 1: Stage 2:Breathing technique: Inspiration only Inspiration/suspension
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Beta-blocker:
Lower heart beat and stabilize rhythm : Improve temporal resolution Options for scanning protocol selection
Flowchart of beta-blocker standardized
Stage 1: Stage 2:Heart rate: >70 bpm >65 bpm
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Flow chart of beta blocker:<65 bpm
(1)>65 bpm
Stable irregular
Pulse
Segment
1st β medication
30 mins
<65 bpm(1)
>65 bpm
2nd β medication30 mins
<65 bpm(1)
>65 bpm
Calcium score + consult radiologist
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Patient Preparation checklist: 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
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Scanning Protocol checklist:
Test dose: Calculation of delay time Contrast volume depends on delay time
1. Scout view:
2. Calcium score:If score >400 consult radiologist
3. Test dose:20ml IOP370 at 5ml/s + saline at 5ml/s
4. Contrast scan protocol selection:
Burst/Segment/Pulse mode
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Technique Modification:
(pathology-related)
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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
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Future directions in NDH:
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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
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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
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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…
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Reference:1. Mayo J.R., Leipsic J.A. Radiation dose in cardiac CT AJR 2009; 192:646-6532. Pannu H., Alvarez Jr. W., Fishman E.k. β-Blockers for Cardiac CT: A Primer for the Radiologist.
AJR 2006;186:341-3453. Weigold W.G. Cardiovascular computed tomography: current and future scanning system
design. Cardiac CT Imaging 2010;1:21-274. 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
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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
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Reference: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
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