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MEDICAL IMAGING

MEDICAL IMAGING. Dr. Hugh Blanton ENTC 4390. There has been an alarming increase in the number of things I know nothing about!. Lecture 1. INTRODUCTION. INTRODUCTION TO MEDICAL IMAGING. Medical imaging of the human body requires some form of energy.

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MEDICAL IMAGING

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  1. MEDICAL IMAGING Dr. Hugh Blanton ENTC 4390

  2. There has been an alarming increase in the number of things I know nothing about! Dr. Blanton ENTC 4390 --Introduction 2

  3. Lecture 1 INTRODUCTION

  4. INTRODUCTION TO MEDICAL IMAGING • Medical imaging of the human body requires some form of energy. • In radiology, the energy used to produce the image must be capable of penetrating tissues. • The electromagnetic spectrum outside the visible light region is used for • x-ray imaging, • magnetic resonance imaging, and • nuclear medicine. • Mechanical energy, in the form of high-frequency sound waves, is used in ultrasound imaging. Dr. Blanton ENTC 4390 --Introduction 4

  5. INTRODUCTION TO MEDICAL IMAGING • With the exception of nuclear medicine, all medical imaging requires that the energy used to penetrate the body’s tissues also interact with those tissues. • Absorption, • Attenuation, and • Scattering. Dr. Blanton ENTC 4390 --Introduction 5

  6. INTRODUCTION TO MEDICAL IMAGING • If energy were to pass through the body and not experience some type of interaction (e.g., absorption, attenuation, scattering), • then the detected energy would not contain any useful information regarding the internal anatomy, and • thus it would not be possible to construct an image of the anatomy using that information. Dr. Blanton ENTC 4390 --Introduction 6

  7. INTRODUCTION TO MEDICAL IMAGING • In nuclear medicine imaging, radioactive agents are injected or ingested, and it is the metabolic or physiologic interactions of the agent that give rise to the information in the images. Dr. Blanton ENTC 4390 --Introduction 7

  8. The power levels used to make medical images require a balance between patient safety and image quality. Dr. Blanton ENTC 4390 --Introduction 8

  9. History, Basic Principles, & Modalities Class consists of: • Deterministic Studies - distortion - impulse response - transfer functions All modalities are non-linear and space variant to some degree. Approximations are made to yield a linear, space-invariant system. • Stochastic Studies SNR (signal to noise ratio) of the resultant image - mean and variance Dr. Blanton ENTC 4390 --Introduction 9

  10. Wilhelm Röntgen, Wurtzburg Nov. 1895 – Announces X-ray discovery Jan. 13, 1896 – Images needle in patient’s hand – X-ray used presurgically 1901 – Receives first Nobel Prize in Physics – Given for discovery and use of X-rays. Radiograph of the hand of Röntgen’s wife, 1895. Dr. Blanton ENTC 4390 --Introduction 10

  11. Röntgen’s Setup Röntgen detected: • No reflection • No refraction • Unresponsive to mirrors or lenses His conclusions: • X-rays are not an EM wave • Dominated by corpuscular behavior Dr. Blanton ENTC 4390 --Introduction 11

  12. Projection X-Ray Disadvantage: Depth information lost Advantage: Cheap, simple attenuation coefficient Measures line integrals of attenuation Film shows intensity as a negative ( dark areas, high x-ray detection Dr. Blanton ENTC 4390 --Introduction 12

  13. Sagittal Coronal Dr. Blanton ENTC 4390 --Introduction 13

  14. Body Structure

  15. Directional Terms • Anatomical position • Beginning reference point • Body upright • Facing front • Arms at side, palms forward • Feet parallel Dr. Blanton ENTC 4390 --Introduction 15

  16. Directional Terms Dr. Blanton ENTC 4390 --Introduction 16

  17. Planes of Division • Frontal plane • Coronal plane • Divides body into anterior, posterior parts Dr. Blanton ENTC 4390 --Introduction 17

  18. Planes of Division • Sagittal plane • Divides body into right, left portions • If plane cuts midline, called midsagittal or medial plane Dr. Blanton ENTC 4390 --Introduction 18

  19. Planes of Division • Transverse plane • Divides body into superior, inferior parts Dr. Blanton ENTC 4390 --Introduction 19

  20. Dr. Blanton ENTC 4390 --Introduction 20

  21. Anatomical Directions • Anterior (ventral) = toward front of body • Posterior (dorsal) = toward back of body • Medial = toward midline of body • Lateral = toward side of body • Proximal = nearer to reference point • Distal = farther from reference point Dr. Blanton ENTC 4390 --Introduction 21

  22. Body Cavities • Dorsal cavity contains: • Cranial cavity • Spinal cavity Dr. Blanton ENTC 4390 --Introduction 22

  23. Body Cavities (cont’d) • Ventral cavity contains: • Thoracic cavity • Diaphragm • Separates • thoracic cavity and • abdominal cavity Dr. Blanton ENTC 4390 --Introduction 23

  24. Body Cavities (cont’d) • Abdominopelvic cavity: • Abdominal cavity • Pelvic cavity • Peritoneum Dr. Blanton ENTC 4390 --Introduction 24

  25. Body Regions • Imaginarily divided into 9 regions Dr. Blanton ENTC 4390 --Introduction 25

  26. Body Regions • Midline sections: • Epigastric = above stomach • Umbilical = umbilicus or navel • Hypogastric = below the stomach Dr. Blanton ENTC 4390 --Introduction 26

  27. Body Regions (con’t) • Lateral sections: • Right and left hypochondriac • Positioned near ribs, specifically cartilages Dr. Blanton ENTC 4390 --Introduction 27

  28. Body Regions (con’t) • Right and left lumbar • Positioned near small of back (lumbar region) Dr. Blanton ENTC 4390 --Introduction 28

  29. Body Regions (con’t) • Right and left iliac • Named for upper bone of hip (ilium) • Also called inguinal region (referring to groin) Dr. Blanton ENTC 4390 --Introduction 29

  30. Body Positions • Anatomical • Standing erect, facing forward, arms at sides, palms forward, toes pointed forward • Prone • Lying face down • Supine • Lying face up Dr. Blanton ENTC 4390 --Introduction 30

  31. X-Ray

  32. Early Developments • Intensifying agents, contrast agents all developed within several years. • Creativity of physicians resulted in significant improvements to imaging. - found ways to selectively opacify regions of interest - agents administered orally, intravenously, or via catheter Dr. Blanton ENTC 4390 --Introduction 32

  33. Later Developments More recently, physicists and engineers have initiated new developments in technology, rather than physicians. 1940’s, 1950’s Background laid for ultrasound and nuclear medicine 1960’s Revolution in imaging – ultrasound and nuclear medicine 1970’s CT (Computerized Tomography) - true 3D imaging (instead of three dimensions crammed into two) 1980’s MRI (Magnetic Resonance Imaging) PET ( Positron Emission Tomography) Dr. Blanton ENTC 4390 --Introduction 33

  34. Computerized Tomography (CT) 1972 Hounsfield announces findings at British Institute of Radiology • Hounsfield, Cormack receive Nobel Prize in Medicine (CT images computed to actually display attenuation coefficient m(x,y)) Important Precursors: 1917 Radon: Characterized an image by its projections 1961 Oldendorf: Rotated patient instead of gantry Result: Dr. Blanton ENTC 4390 --Introduction 34

  35. First Generation CT Scanner Acquire a projection (X-ray) Translate x-ray pencil beam and detector across body and record output Rotate to next angle Repeat translation Assemble all the projections. Dr. Blanton ENTC 4390 --Introduction 35

  36. Reconstruction from Back Projection 1.Filter each projection to account for sampling data on polar grid 2. Smear back along the “line integrals” that were calculated by the detector. Dr. Blanton ENTC 4390 --Introduction 36

  37. Modern CT Scanner From Webb, Physics of Medical Imaging Dr. Blanton ENTC 4390 --Introduction 37

  38. Computerized Tomography (CT), continued Early CT Image Current technology Dr. Blanton ENTC 4390 --Introduction 38

  39. Inhalation Dr. Blanton ENTC 4390 --Introduction 39

  40. Exhalation Dr. Blanton ENTC 4390 --Introduction 40

  41. Nuclear Medicine - Grew out of the nuclear reactor research of World War II • Discovery of medically useful radioactive isotopes 1948 Ansell and Rotblat: Point by point imaging of thyroid 1952 Anger: First electronic gamma camera • Radioactive tracer is selectively taken up by organ of interest • Source is thus inside body! • This imaging system measures function (physiology) • rather than anatomy. Dr. Blanton ENTC 4390 --Introduction 41

  42. Nuclear Medicine, continued Very specific in imaging physiological function - metabolism - thyroid function - lung ventilation: inhale agent Advantage: Direct display of disease process. Disadvantage: Poor image quality (~ 1 cm resolution) Why is resolution so poor? Very small concentrations of agent used for safety. - source within body Quantum limited: CT 109 photons/pixel Nuclear ~100 photons/pixel Tomographic systems: SPECT: single proton emission computerized tomography PET: positron emission tomography Dr. Blanton ENTC 4390 --Introduction 42

  43. Combined CT / PET Imaging Dr. Blanton ENTC 4390 --Introduction 43

  44. Comparison of Modalities Why do we need multiple modalities? Each modality measures the interaction between energy and biological tissue. - Provides a measurement of physical properties of tissue. - Tissues similar in two physical properties may differ in a third. Note: - Each modality must relate the physical property it measures to normal or abnormal tissue function if possible. - However, anatomical information and knowledge of a large patient base may be enough. - i.e. A shadow on lung or chest X-rays is likely not good. Other considerations for multiple modalities include: - cost - safety - portability/availability Dr. Blanton ENTC 4390 --Introduction 44

  45. X-Ray Measures attenuation coefficient Safety: Uses ionizing radiation - risk is small, however, concern still present. - 2-3 individual lesions per 106 - population risk > individual risk i.e. If exam indicated, it is in your interest to get exam Use: Principal imaging modality Used throughout body Distortion: X-Ray transmission is not distorted. Dr. Blanton ENTC 4390 --Introduction 45

  46. Ultrasound Measures acoustic reflectivity Safety: Appears completely safe Use: Used where there is a complete soft tissue and/or fluid path Severe distortions at air or bone interface Distortion: Reflection: Variations in c (speed) affect depth estimate Diffraction: λ ≈ desired resolution (~.5 mm) Dr. Blanton ENTC 4390 --Introduction 46

  47. Magnetic Resonance (MR) Multiparametric M(x,y,z) proportional to ρ(x,y,z) and T1, T2. (the relaxation time constants) Velocity sensitive Safety: Appears safe Static field - No problems -Some induced phosphenes Higher levels - Nerve stimulation RF heating: body temperature rise < 1˚C - guideline Use: Distortion: Some RF penetration effects - intensity distortion Dr. Blanton ENTC 4390 --Introduction 47

  48. Clinical Applications - Table Dr. Blanton ENTC 4390 --Introduction 48

  49. Clinical Applications - Table Dr. Blanton ENTC 4390 --Introduction 49

  50. Economics of modalities: X-Ray: Cheapest Ultrasound:~ $100K – $250K CT: $400K – $1.5 million (helical scanner) MR:$350K (knee) - $4.0 million Service: Annual costs Hospital must keep uptime Staff: Scans performed by technologists Hospital Income: Competitive issues Significant investment and return Dr. Blanton ENTC 4390 --Introduction 50

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