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Image Quality in Cardiac Angiography

Image Quality in Cardiac Angiography. L 8. Are these statements “True” or “False”?. Image quality of coronary angiography is commonly measured objectively using well-defined objective criteria. Recommended acquisition frame rate for coronary angiography in adult is 30 fps.

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Image Quality in Cardiac Angiography

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  1. Image Quality in Cardiac Angiography L 8

  2. Are these statements “True” or “False”? • Image quality of coronary angiography is commonly measured objectively using well-defined objective criteria. • Recommended acquisition frame rate for coronary angiography in adult is 30 fps. Lecture 8: Image Quality in Cardiac Angiography

  3. Educational Objectives • Components of image quality • Determinants of cardiac angiographic image quality • How to assess image quality of cardiac angiographic images? • Some Quality Criteria for assessing cardiac angiographic images Lecture 8: Image Quality in Cardiac Angiography

  4. Is this coronary angiography of good quality? Lecture 8: Image Quality in Cardiac Angiography [ video clip]

  5. Quality of cardiac images • Background • cardiac cine-angiographic images should allow the cardiologist to evaluate the anatomic (and sometimes functional) details which are relevant for clinical decision making • Variables • technical performance of the imaging system • patient cooperation • angiographic technique Lecture 8: Image Quality in Cardiac Angiography

  6. An angiography series consists of multiple still images in quick succession Lecture 8: Image Quality in Cardiac Angiography

  7. Quality of each still image contributes to overall quality of the whole angiography series Lecture 8: Image Quality in Cardiac Angiography

  8. Quality of cardiac images • Background • cardiac cine-angiographic images should allow the cardiologist to evaluate the anatomic (and sometimes functional) details which are relevant for clinical decision making Lecture 8: Image Quality in Cardiac Angiography

  9. Quality of cardiac images • Image (“photographic”) quality • sharpness • contrast • noise • “Content” • foreshortening? • overlap? • delineate the lesion? • composition • enough information? Lecture 8: Image Quality in Cardiac Angiography

  10. Is this acquisition run long enough to give adequate information • (“tell the story”)? • Is the acquisition run too long? • Are there “wasted/unnecessary” frames? cine [ video clip]

  11. Content and composition • What do you think about this picture? • Too many extra things that make it difficult to know where emphasis should lie. Lecture 8: Image Quality in Cardiac Angiography

  12. Content and composition • Lesson: • Include only the area of interest when taking photography  coronary angiogram Lecture 8: Image Quality in Cardiac Angiography

  13. 3 main quality parameters for still image • Sharpness • Contrast • Noise • Contrast – “to detect the object” • Sharpness / spatial resolution – “to characterize the object” • Noise – “uneven brightness graininess of image” Lecture 8: Image Quality in Cardiac Angiography

  14. Focal Point Unsharpness Lecture 8: Image Quality in Cardiac Angiography

  15. Pulsed Fluoroscopy Fluoroscopic pulsing X rays are produced during a small portion of the video frame time. The narrower the pulse width, the sharper the image. ( “Faster shutter speed” in camera ) Lecture 8: Image Quality in Cardiac Angiography

  16. Medical Imaging is the Process of Converting Tissue Characteristics into a Visual Image (shades of gray or colour) Lecture 8: Image Quality in Cardiac Angiography

  17. Image = “shadow” Relies on various degree of “lucency” or opacity Requires point source 3D object --> 2 D image (projection) Imaging with X ray Lecture 8: Image Quality in Cardiac Angiography

  18. Contrast • Contrast  difference • An object within the body will be visible in an image only if it has sufficient physical contrast relative to surrounding tissue. • Contrast of an image  difference in • shades of gray • light intensities • colours Lecture 8: Image Quality in Cardiac Angiography

  19. Increasing Contrast Sensitivity Increases Image Contrast and the Visibility of Objects in the Body Lecture 8: Image Quality in Cardiac Angiography

  20. Contrast Sensitivity • relates to the system's ability to translate physical object contrast into image contrast. • characteristics of the imaging method, and the variables of the particular imaging system Lecture 8: Image Quality in Cardiac Angiography

  21. Effect of Contrast Sensitivity on Object Visibility Lecture 8: Image Quality in Cardiac Angiography

  22. Lossy compression Lecture 8: Image Quality in Cardiac Angiography

  23. “Lossy” compression  loss of details 1:1 1:50 1:80 Lecture 8: Image Quality in Cardiac Angiography

  24. Lecture 8: Image Quality in Cardiac Angiography

  25. Factors Affecting Angiographic Image Contrast • Subject contrast • Vessel size • X ray kV (lower contrast at > 75 kV) • Scatter • Patient thickness along beam • X ray beam area (FOV and collimation) • Image intensifier veiling glare • Digital image processing Lecture 8: Image Quality in Cardiac Angiography

  26. Dose vs. Noise 2 µR per frame 15 µR per frame 24 µR per frame Lecture 8: Image Quality in Cardiac Angiography

  27. Relationship between Image Quality and Dose • Detection is limited by NOISE. • Acceptable noise depends on TASK. • Noise  1 / • Acceptable dose level depends on TASK Lecture 8: Image Quality in Cardiac Angiography

  28. Lecture 8: Image Quality in Cardiac Angiography

  29. Image Quality • 3 parameters are interdependent. • Aim  usable image, not a perfect image. •  image contrast  low kVp  large patient exposure dose •  kVp   patient dose; image contrast •  receptor input dose   patient exposure;  image noise • Optimal compromise set of exposure parameters that preserve diagnostic quality image contrast at an acceptable image noise level while minimizing patient dose Lecture 8: Image Quality in Cardiac Angiography

  30. Effect of X ray Beam Penetration on Contrast, Body Penetration, and Dose Lecture 8: Image Quality in Cardiac Angiography

  31. In general, every X ray system produces a range of energies Beam energy: High energy X rays: poor contrast and low skin dose Low energy X rays: high image contrast but high skin dose Middle energy X rays: high contrast for iodine and moderate skin dose Lecture 8: Image Quality in Cardiac Angiography

  32. The goal is to shape the beam energy spectrum for the best contrast at the lowest dose. An improved spectrum with 0.2 mm Copper filtration is depicted by the dashes: Beam energy: Low-contrast high energy x rays are reduced by lower kVp Filtration reduces poorly penetrating low energy x rays Middle energy x rays are retained for best compromise on image quality and dose Lecture 8: Image Quality in Cardiac Angiography

  33. Scatter and Veiling Glare depend on FOV Lecture 8: Image Quality in Cardiac Angiography

  34. Image Quality Radiation Dose Lecture 8: Image Quality in Cardiac Angiography

  35. Is there difference in Quality of Coronary Angiographic Images?

  36. Types of technical deficiencies in 308 cineangiograms(Leape, Am Heart J 2000;139:106-13) N % Lecture 8: Image Quality in Cardiac Angiography

  37. Percentage of inadequate studies by different hospitals (Leape, Am Heart J 2000;139:106-13) In 12/29 hosp. 50% of studies had deficencies 6 of these are teching hosp.

  38. + 288% + 41% + 113% mean fluoroscopy time, frame number and dose-area product (DAP) in some European centers during coronary angiography Neofotistou, ER 2003 Lecture 8: Image Quality in Cardiac Angiography

  39. DIMOND 3 data mean number of series projections’ distribution focus-detector mean distances Lecture 8: Image Quality in Cardiac Angiography

  40. Imaging Assessment Strategy

  41. Image assessment strategy • Observer-based Observations • traditional method for field analysis, QC • “subjective” • not sensitive to small difference in image quality • Physics-based measurement • traditionally performed by vendors • “objective” • not usually performed under realistic clinical conditions Lecture 8: Image Quality in Cardiac Angiography

  42. Quality evaluation of angiographic imagesMethod 1: Objective, physics-based measurements. Based on measurement of some physical parameters • system transfer factor K • spatial resolution (MTF, modulation transfer function) • detective quantum efficiency (DQE) • noise They are rather complex and rarely applied to daily practice Lecture 8: Image Quality in Cardiac Angiography

  43. Quality evaluation of angiographic imagesMethod 2: Subjective methods • test objects or phantoms • they are able to simulate the same radiation conditions as the part of the body • they describe behaviour of radiology equipment in specific operating condition • evaluation of clinical images • allow evaluation of the overall performance including patient’s collaboration and technique Lecture 8: Image Quality in Cardiac Angiography

  44. test objects Lecture 8: Image Quality in Cardiac Angiography

  45. Line Pair Test Objects 1 Megapixel Digital Cine film Lecture 8: Image Quality in Cardiac Angiography

  46. Lecture 8: Image Quality in Cardiac Angiography

  47. ACC Expert Consensus Document on Radiation Safety in the Practice of Cardiology JACC Vol. 31, No. 4, March 15, 1998:892-913 • risks of radiation exposure to medical professionals in many aspects of cardiology, including catheterization, electrophysiology, and nuclear cardiology. • Background on radiation physics and biology, as well as recommendations to reduce radiation exposure and provide for operator safety during pregnancy or when pregnancy is planned. • Emphasis is placed on the ALARA principle, and includes recommendations for training and discussion of shielding options and monitoring badges Lecture 8: Image Quality in Cardiac Angiography

  48. American College of Cardiology Training Statement on Recommendations for the Structure of an Optimal Adult Interventional Cardiology Training ProgramJACC 1999; 34:2141-7 • Training in radiology imaging and radiation safety • Principles of X-ray imaging, quantitative coronary arteriography, operation of cineflurographic X-ray equipment, operation of digital video imaging systems, radiation biology and radiation protection Lecture 8: Image Quality in Cardiac Angiography

  49. Evaluation of Clinical Coronary Angiographic Images

  50. Quality in invasive cardiology and scientific societies Scientific societies implemented guidelines to guarantee adequate level of quality and performance of invasive cardiology • training of operators • quantitative standards to maintain the expertise in coronary angiography or angioplasty • quality-assurance programme Pepine, J Am Coll Cardiol 1995;25:14–6 Miller, Can J Cardiol 1996;12:470–2 Cowley, Cathet Cardiovasc Diagn 1993;30:1–4 Heupler, Cathet Cardiovasc Diagn 1993;30:191–200 Scanlon, J Am Coll Cardiol 1999;33:1756–824 Lecture 8: Image Quality in Cardiac Angiography

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