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Speaker: Au Chun Yu Edmund Chong Siu King Windy North district Hospital HKRA AGM 2011.

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Presentation on theme: "Speaker: Au Chun Yu Edmund Chong Siu King Windy North district Hospital HKRA AGM 2011."— Presentation transcript:

1 Speaker: Au Chun Yu Edmund Chong Siu King Windy North district Hospital HKRA AGM 2011

2  CT machine: GE Lightspeed VCT, 64MSCT  Over 500 cases done (since 2008):  Cardiac CT booked daily  several sub – stages: Protocol selectionScanning parameters Scanning range Breath-hold preparation premedicationContrast volume

3 GE suggestion:International:NDH: kVp: 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 60-65ml; 5-5.5ml/s Protocol selection: PulsePulse/SegmentSegment Breathing technique: inspirationNot applicableInspiration/ suspension Beta-blocker:HR:>70bpmHR>70bpmHR:>65bpm mSv

4  Analyzed statistically  Maintain diagnostic quality  Radiation protection

5  Limited pre-medication:  Beta-blocker prescribed by Cardiac department  CT machine: GE Lightspeed VCT, 64MSCT  Maintain high image quality for reporting

6  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


8  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 noiseOverall image quality with diagnostic confidence level Objective: Image noiseContrast –to-noise ratioSignal-to-noise ratio


10  kVp adjustment according to patient’s body weight  Radiation dose is proportional to the square of kVp Stage 1:Stage 2:Stage 3: >80kg120 kVp80 kVp100kVp <80kg80kVp

11  Mean dose reduction: 20% Stage 1:Stage 2: mA:Manual mA: >500 Tube current modulation: <500; 40%-80% Mean Dose: (DLP/mGY-cm)

12  Reduction of 1cm: dose savings of 1 mSv  Radiation dose reduction: 20% Stage 1:Stage 2: Superior aspect:2 cm superior to carina of trachea Sufficiently include LAD Inferior aspect:Base of heartSufficiently include PLB & PDA Mean Dose: (DLP/mGY-cm)

13  Reduction of contrast :  Decrease probability of allergic reaction  Faster contrast rate:  Better contrast resolution GE suggestion:International:NDH: 80ml; 5ml/s 60-65ml; 5-5.5ml/s

14 Snapshot pulse (HR 30-65BPM) Prospective ECG gating Snapshot segment (HR 30-74BPM) Snapshot burst (HR ) Retrospective ECG gating

15  The most dose-efficient method of ECG-synchronized:  Snapshot pulse  Dose reduction by 64% (compared with segment) Case #Mean dose (DLP/mGy-cm) LowestHighestAverage DLP/slice Burst pulse segment

16  X-ray on/off is triggered by ECG R-peak with user selectable time off  Radiation exposure is about 4 times less


18  Pros:  Helical continuous data acquisition  Favor retro-reconstruction  Option for different cardiac pattern;  Enable cardiac function analysis  Larger volume coverage  i.e. bypass graft


20  Options for different types of patient:  Important in evaluation of time for stable HR after breath-hold Stage 1:Stage 2: Breathing technique:Inspiration onlyInspiration/suspension

21  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

22 <65 bpm (1) >65 bpm Stable irregular PulseSegment 1 st β medication 30 mins <65 bpm (1) >65 bpm 2 nd β medication 30 mins <65 bpm (1) >65 bpm Calcium score + consult radiologist

23  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

24  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


26  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


28  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

29  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

30  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…

31 1.Mayo J.R., Leipsic J.A. Radiation dose in cardiac CT AJR 2009 ; 192: Pannu H., Alvarez Jr. W., Fishman E.k. β -Blockers for Cardiac CT: A Primer for the Radiologist. AJR 2006 ;186: Weigold W.G. Cardiovascular computed tomography: current and future scanning system design. Cardiac CT Imaging 2010 ;1: 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 ;34(1): 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 ; 2(10): Hospital Authority. Hospital Authority Statistical Report [homepage on the Internet] [cited 2011 Apr 9]. Available from: Hospital Authority, Statistics and Workforce Planning Department Web site:

32 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): 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: Sun Z, Ng KH. Multislice CT angiography in cardiac imaging. Part III: radiation risk and dose reduction. Singapore Med J 2010; 51(5): Hausleiter J, Meyer T, Hermann F, et al. Estimated radiation dose associated with cardiac CT angiography. JAMA 2009; 301(5): 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: Jean-Francois P & Hicham TA. Strategies for reduction of radiation dose in cardiac multislice CT. European Radiology. Springer- Verlag 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


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