INTRODUCTION to Radiology Carol P. Becker, M.D. Acknowledgements:

INTRODUCTION to Radiology Carol P. Becker, M.D. Acknowledgements:

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

Magnetic Resonance Imaging - MRI Nuclear Medicine NM Breast Imaging - Mammography, US, MRI 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 1895: Roentgen discovers X-rays (XRAYs wifes hand by accident) Ionization An atom which loses an electron is

ionized Photons having 15 electron volts can produce ionization in atoms and molecules X-Rays, Gamma Rays, and certain types of UV Radiation are Ionizing Radiation Ionizing Radiation in Radiology Patients undergoing these types of

studies are exposed to Ionizing Radiation: Radiographs Fluoroscopy/Conventional Angiography CT Nuclear Medicine IONIZING RADIATION Ionizing Radiation can be carcinogenic and, to the fetus, mutagenic or even lethal

Goals of Radiation Safety Eliminate deterministic effects Reduce incidence of stochastic effects Exposure to Ionizing Radiation causes 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 nonstochastic effects Stochastic Effects: The effect may (potentially) occur following any amount of exposure there is no threshold. Examples include cancer and genetic defects. RADIATION SAFETY

PLEASE REVIEW RADIATION SAFETY MATERIAL IN THE SYLLABUS ON WEBSITE (ON YOUR OWN). INCLUDES RADIATION GUIDELINES FOR PREGNANT PATIENT 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 Effects of varying types of same tissue tissue and varying thickness

www.med.harvard.edu/JPNM/TF03_04/Sept2/CXR.jpg X-ray beam absorption and attenuation X-Rays passing through matter become ATTENUATED via absorption and scatter. With increasing atomic number comes increasing attenuation by the material

X-ray beam absorption 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 Attenuation and Hounsfield units

Gas -1,000 HU versus Fat -100 HU Water 0 HU 1 +20 to +100 HU windowSoft

andtissue level settings for image Bone +1,000 HU display 2 3

1. brighamrad.harvard.edu/ .../hc ache/333/ full.html 2. http://r ad.usuhs.mil/ rad/ home/ abd_CT6.jpg 3. www.netmedicine.com/ xray/c tscan/ img_ct/ct a19b.jpg 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! Lumbar spine, lateral view Fluoroscopy : intervertebral disc space http://www.orthoassociates.com/images/Image_discogram.jpg Clinical Medical Specialties

that rely on radiation Diagnostic and Interventional Radiology Imaging (CT, XRAY) Nuclear Medicine Interventional procedures Radiation Oncology: The therapeutic use of radiation. RADIOGRAPH History:weight

loss. Diagnosis: Mets or Multiple myeloma Radiographic Densities

Metal Bone Water Fat Air Very White White

Gray Gray-Black Black Metal is most Radiodense or Radiopaque. Air is most Radiolucent. 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 Normal bone scan mets Posterior Anterior

Posterior Anterior Diethelm MD Lisa Nuclear Medicine Photons emitted 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 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 Multi-Detector (Helical) CT multiple 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 HOUNSFIELD UNIT SCALE

Compares attenuation of each tissue through which the x-ray beam passes with the attenuation of WATER. 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 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 patients body while the x-ray tube moves in an arc around the patient

Electronic detectors, placed opposite the xray tube, convert the attenuated x-ray beam into electrical pulses.Computers convert this data to a gray-scale image MAIN ADVANTAGES OF CT OVER MRI Rapid scan acquisition Visualization of cortical bone and soft tissue

calcifications 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 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 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 Ultrasound Exploits differences in acoustic

properties of adjacent organs to produce images Ultrasound and MRI are Non- Ionizing 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 ULTRASOUND 1794: Lazzaro Spallanzani figures out that flying bats avoid obstacles in the dark by using reflected echoes of high frequency sound inaudible to humans

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 Barium enema www.philips.com/

Main/products/xray/ Assets/images/dose Wise/urf2_large.jpg 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 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 MRI Contrast Media Gadolinium Paramagnetic (radiopaque) IV

NSF/ check GFR=renal function PACS Training Picture Archiving and Communication System 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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