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CTCA Dose Reduction & Image Quality Improvement Strategy in NDH

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:.

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CTCA Dose Reduction & Image Quality Improvement Strategy in NDH

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  1. CTCA Dose Reduction & Image Quality Improvement Strategy in NDH Speaker: Au Chun Yu Edmund Chong Siu King Windy North district Hospital HKRA AGM 2011

  2. In NDH: • CT machine: GE Lightspeed VCT, 64MSCT • Over 500 cases done (since 2008): • Cardiac CT booked daily • several sub – stages:

  3. NDH vs other standards:

  4. Results: • Analyzed statistically • Maintain diagnostic quality • Radiation protection

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

  6. 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

  7. Image Quality:

  8. 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

  9. Before & After… …

  10. kVp modification: • kVp adjustment according to patient’s body weight • Radiation dose is proportional to the square of kVp

  11. mA modification: • Mean dose reduction: 20%

  12. Scan length modification: • Reduction of 1cm: dose savings of 1 mSv • Radiation dose reduction: 20%

  13. Contrast volume: • Reduction of contrast : • Decrease probability of allergic reaction • Faster contrast rate: • Better contrast resolution

  14. Protocol selection:

  15. Protocol selection: • The most dose-efficient method of ECG-synchronized: • Snapshot pulse • Dose reduction by 64% (compared with segment)

  16. Snapshot pulse: • X-ray on/off is triggered by ECG R-peak with user selectable time off • Radiation exposure is about 4 times less

  17. Limitation: • HR <60bpm • Stable rhythms dependence • Allow limited phase reconstruction: • only 3-4 % phase • Insufficient for functional analysis & Electrophysiology (EP) • NDH decision: • Segment

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

  19. Patient preparation:

  20. Breathing technique: • Options for different types of patient: • Important in evaluation of time for stable HR after breath-hold

  21. Beta-blocker: • Lower heart beat and stabilize rhythm : • Improve temporal resolution • Options for scanning protocol selection • Flowchart of beta-blocker standardized

  22. Flow chart of beta blocker:

  23. 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

  24. Scanning Protocol checklist: • Test dose: • Calculation of delay time • Contrast volume depends on delay time

  25. Technique Modification:(pathology-related)

  26. 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

  27. Future directions in NDH:

  28. 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

  29. 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

  30. 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…

  31. Reference: • Mayo J.R., Leipsic J.A. Radiation dose in cardiac CT AJR 2009; 192:646-653 • Pannu H., Alvarez Jr. W., Fishman E.k. β-Blockers for Cardiac CT: A Primer for the Radiologist. AJR2006;186:341-345 • Weigold W.G. Cardiovascular computed tomography: current and future scanning system design. Cardiac CT Imaging 2010;1:21-27 • 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 • Chan I.Y.F. A brief review of CT coronary angiogram. The Hong Kong medical diary 2007;12:3 • Sun Z. Multislice CT angiography in coronary artery disease: technical developments, radiation dose and diagnostic value. World J cardiol2010 26; 2(10):333-343 • 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

  32. Reference: • 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 • Sun Z. Multislice CT angiography in cardiac imaging: prospective ECG-gating or retrospective ECG-gating?. Biomed Imaging Intervention Journal 2010; 6(1):e4 • Kopp AF, Kuttner A, Trabold T, et al. Multislice CT in cardiac and coronary angiography. The British Journal of Radiology 2004; 77:S87-S97 • Alkadhi H. Radiation dose of cardiac CT- what is the evidence?. European Society of Radiology 2009; 19:1311-1315 • 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 • Hausleiter J, Meyer T, Hermann F, et al. Estimated radiation dose associated with cardiac CT angiography. JAMA 2009; 301(5):500-506 • 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 • Jean-Francois P & Hicham TA. Strategies for reduction of radiation dose in cardiac multislice CT. European Radiology. Springer-Verlag 2007 • 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

  33. ~THANK YOU~

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