ctca dose reduction & image quality improvement strategy in ndh
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CTCA Dose Reduction & Image Quality Improvement Strategy in NDH. Speaker: Au Chun Yu Edmund Chong Siu King Windy North district Hospital. HKRA AGM 2011. In NDH:. CT machine: GE Lightspeed VCT, 64MSCT Over 500 cases done (since 2008): Cardiac CT booked daily several sub – stages:. - PowerPoint PPT PresentationTRANSCRIPT
Speaker: Au Chun Yu EdmundChong Siu King WindyNorth district Hospital
CTCA Dose Reduction & Image Quality Improvement Strategy in NDH
HKRA AGM 2011
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
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
Results:
Analyzed statistically Maintain diagnostic quality Radiation protection
1 2 3 4 5 6 7 8 9 10 11 120
2
4
6
8
10
12
14
Effective Radiation Dose of CTCA in 2010 in NDH
MonthEffec
tive
Rad
iati
on D
ose
(mSv
)
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:
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
Before & After… …
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
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
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
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
Protocol selection:
Snapshot pulse (HR 30-65BPM)
Prospective ECG gating
Snapshot segment(HR 30-74BPM)
Snapshot burst(HR 75-113)
Retrospective ECG gating
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
Snapshot pulse: X-ray on/off is triggered by ECG R-peak with user
selectable time off
Radiation exposure is about 4 times less
Limitation: HR <60bpm Stable rhythms dependence Allow limited phase reconstruction:
only 3-4 % phase Insufficient for functional analysis & Electrophysiology (EP)
NDH DECISION:SEGMENT
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
Patient preparation:
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
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
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
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
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
Technique Modification:
(pathology-related)
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…
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