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INTRODUCTION to Radiology

INTRODUCTION to Radiology. Carol P. Becker, M.D. Acknowledgements: N.E. Diethelm, M.D., E.Blaudeau,M.D. Diagnostic Radiology. Radiographs – X-rays, plain films, XR Fluoroscopy – “Fluoro” Tomography – “Tomo” (planar, helical) Urography - IVP Ultrasound - US Computed Tomography - CT

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INTRODUCTION to Radiology

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  1. INTRODUCTION to Radiology Carol P. Becker, M.D. Acknowledgements: N.E. Diethelm, M.D., E.Blaudeau,M.D..

  2. Diagnostic Radiology • Radiographs – X-rays, plain films, XR • Fluoroscopy – “Fluoro” • Tomography – “Tomo” (planar, helical) • Urography - IVP • Ultrasound - US • Computed Tomography - CT • Magnetic Resonance Imaging - MRI • Nuclear Medicine – NM • Breast Imaging - Mammography, US, MRI

  3. More photons strike the film => film appears blacker Fewer photons strike the film => film appears whiter www.med.harvard.edu/JPNM/TF03_04/Sept2/CXR.jpg

  4. 1895: Roentgen discovers X-rays (XRAYs wife’s handby accident)

  5. Ionization • An atom which loses an electron is ionized • Photons having  15electron volts can produce ionization in atoms and molecules • X-Rays, Gamma Rays, and certain types of UV Radiation are Ionizing Radiation

  6. Ionizing Radiation in Radiology • Patients undergoing these types of studies are exposed to Ionizing Radiation: • Radiographs • Fluoroscopy/Conventional Angiography • CT • Nuclear Medicine

  7. IONIZING RADIATION • Ionizing Radiation can be carcinogenic and, to the fetus, mutagenic or even lethal

  8. Goals of Radiation Safety • Eliminate deterministic effects • Reduce incidence of stochastic effects

  9. Exposure to Ionizing Radiationcauses two types of effects • Deterministic Effects: A minimum threshold dose must be attained for the effect to occur. Examples include cataract formation, skin reddening (erythema), and sterility. Also referred to as “non-stochastic” effects • Stochastic Effects: The effect may (potentially) occur following any amount of exposure – there is no threshold. Examples include cancer and genetic defects.

  10. RADIATION SAFETY • PLEASE REVIEW RADIATION SAFETY MATERIAL IN THE SYLLABUS ON WEBSITE (ON YOUR OWN). • INCLUDES RADIATION GUIDELINES FOR PREGNANT PATIENT

  11. What is an X-ray? • X-rays are very short wavelength electromagnetic radiation. Shorter wavelength, greater energy/greater the ability to penetrate matter • X-rays are described as packets of energy called Quanta or Photons • Photons travel at the speed of light • Photon energy measured in Electron Volts

  12. Effects of varying types of tissue and varying thickness same tissue www.med.harvard.edu/JPNM/TF03_04/Sept2/CXR.jpg

  13. X-ray beamabsorption and attenuation • X-Rays passing through matter becomeATTENUATEDvia absorption and scatter. • With increasing atomic number comes increasing attenuation by the material

  14. X-ray beamabsorption and attenuation • X-Rays passing through matter become ATTENUATED via absorption and scatter. • For a given thickness, the greater the physical density (gm/cc) of a material, the greater its ability to absorb or scatter X-Rays. Lead >Aluminum

  15. Attenuation and Hounsfield unitsversus window and level settings for image display Gas -1,000 HU Soft tissue +20 to +100 HU Fat -100 HU Bone +1,000 HU Water 0 HU 1 2 3

  16. LIMITING YOUR EXPOSURE:You do the math! • Doubling your distance from the X-ray tube reduces your exposure by a factor of four • Tripling your distance from the X-ray tube reduces your exposure by a factor of nine!

  17. Lumbar spine, lateral view Fluoroscopy : intervertebral disc space http://www.orthoassociates.com/images/Image_discogram.jpg

  18. Clinical Medical Specialtiesthat rely on radiation Diagnostic and Interventional Radiology • Imaging (CT, XRAY) • Nuclear Medicine • Interventional procedures Radiation Oncology: The therapeutic use of radiation.

  19. RADIOGRAPH History:weight loss. Diagnosis: Mets or Multiple myeloma

  20. Radiographic Densities • Metal Very White • Bone White • Water Gray • Fat Gray-Black • Air Black • Metal is most Radiodenseor Radiopaque. • Air is most Radiolucent.

  21. Nuclear Medicine • Most imaging modalities detect changes in gross anatomy • However, most NM exams rely on changes in physiology to detect disease. • Radionuclides • Produce ionizing radiation • Administered I.V., orally, SubQ

  22. Normal bone scan mets Posterior Anterior Anterior Posterior Diethelm MD Lisa

  23. Nuclear Medicine • Photonsemitted by radioisotopes are detected by Sodium Iodide crystals. Brightness of light emitted depends on the energy of the photon • Photodetectors convert the light into an electronic signal, which a computer converts to diagnostic images………

  24. PET – CT Fusion Scanner • Combines Positron Emission Tomography (PET) and Helical CT • PET detects area of increased metabolic activity as indicated by uptake of radioactive glucose ( by tumor, infection) • PET data is then “fused” with CT data to produce an image showing increased glucose uptake superimposed upon exquisite anatomic detail of helical CT

  25. Multi-Detector(Helical) CTmultiple planes of detectors in the gantry • Technical innovation allows • faster scanning • over a much longer range • with even better image quality • Radiation exposure greater than single-detector CT • “Total body” CT in trauma pts

  26. HOUNSFIELD UNIT SCALE • Compares attenuation of each tissuethrough which the x-ray beam passes with the attenuation of WATER.

  27. Hounsfield Unit Scale (CT Attenuation) • Gas (Air) -1,000 HU • Fat -100 HU • Water 0 HU • Soft tissue +20 to +100 HU • Bone +1,000 HU

  28. CT • Contrast resolution far superior to plain radiographs, but spatial resolution inferior to XR • Thinly collimated x-ray beam passes through a “slice” of the patient’s body while the x-ray tube moves in an arc around the patient • Electronic detectors, placed opposite the x-ray tube, convert the attenuated x-ray beam into electrical pulses.Computers convert this data to a gray-scale image

  29. MAIN ADVANTAGES OF CT OVER MRI • Rapid scan acquisition • Visualization of cortical boneand soft tissue calcifications

  30. MRI: Main Disadvantages • Poor visualization of cortical bone and soft tissue calcifications (vs. CT, x ray) • Long imaging times (in general) • Limited spatial resolution • Patient cooperation is needed • Some medical devices prohibitive

  31. MRI • Nuclei with odd #’s of nucleons (protons and neutrons) align themselves with external Magnetic Field • A Radio Frequency pulse perturbs this nuclear alignment, resulting in release of radio frequency energy from the nucleus • The scanner converts this released radio frequency into diagnostic images • Tissues that contain the most hydrogen (water, fat) generally have the strongest signal

  32. CONTRAINDICATIONS for MRI SCANNING: • Pacemakers, pacing wires (RF current can induce cardiac arrhythmias, burns) • Cerebral aneurysm clips (movement, burns, induced electrical currents) • Implants (insulin pumps, cochlear implants, neurostimulator, drug infusion pumps, penile and dental implants) • Intra-orbital metallic fragments (may deflect in magnetic field, causing injury/blindness), XRay orbits if unsure

  33. Ultrasound • Exploits differences in acoustic properties of adjacent organs to produce images Ultrasound and MRI are Non- Ionizing

  34. Ultrasound • Nonionizing • Multiplanar • Applications include OB/GYN, Cardiac, Abdominal, Non-Invasive Vascular, Intraoperative, and Neonatal Brain imaging • Limited in skeletal imaging, but can be useful in muscle and tendon imaging

  35. ULTRASOUND1794: Lazzaro Spallanzani figures out that flying bats avoid obstacles in the dark by using reflected echoes of high frequency sound inaudible to humans

  36. Contrast Media • Most viscera are of water-density or close to it • Contrast media are materials we introduce to better define anatomy and pathologic changes

  37. Barium enema www.philips.com/ Main/products/xray/ Assets/images/dose Wise/urf2_large.jpg

  38. Common Indications for IV Contrast in CT • To visualize blood vessels (Aortic injury, Abdominal Aortic Aneurysm, Pulmonary Embolus) • To evaluate for primary or metastatic tumor • To evaluate for infections or inflammatory processes • To evaluate for traumatic injury

  39. Iodinated Contrast Reactions Mild Warmth, metallic taste, N/V, HA, Dizziness, Tachycardia, sneezing, coughing, erythema, Moderate Agitation, bradycardia, hypotension, wheezing, urticaria (“hives”), itching Severe Pulm edema, shock, CHF, cardiac arrest, laryngospasm, laryngeal edema, apnea, seizure, coma

  40. MRI Contrast Media • Gadolinium • Paramagnetic (radiopaque) • IV • NSF/ check GFR=renal function

  41. PACS Training • PictureArchiving and CommunicationSystem • Digital system for storage, retrieval, and display of imaging studies • MCLNO has gone completely filmless =PACS is your only access to your patients’ images • Therefore, you are encouraged to learn to use PACS

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