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SPECIAL IMAGING/ADVANCED IMAGING INTRODUCTION TO DIGITAL RADIOGRAPHY. Tomography- Chapter 21- Bushong CT –Chapter 29 Bushong/Chapter 22-Bontrager MRI – Chapter 24, Bontrager CR/DR- Chapters 1,4, 7-Carter Chapter 12 - Fauber. FACTS ABOUT TOMOGRAPHY.

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special imaging advanced imaging introduction to digital radiography

SPECIAL IMAGING/ADVANCED IMAGINGINTRODUCTION TO DIGITAL RADIOGRAPHY

Tomography- Chapter 21- Bushong

CT –Chapter 29 Bushong/Chapter 22-Bontrager

MRI – Chapter 24, Bontrager

CR/DR- Chapters 1,4, 7-Carter

Chapter 12 - Fauber

facts about tomography
FACTS ABOUT TOMOGRAPHY
  • Conventional radiography-structures are superimposed
  • Before widespread use of CT and MRI, tomography was the procedure of choice
  • TOMOGRAPHY isolates and visualizes a particular section of the body. Blurs out structures above and below the area of interest
do the tomomotion with me
DO THE “TOMOMOTION” WITH ME!
  • X-RAY TUBE IS ATTACHED TO THE IMAGE RECEPTOR (BUCKY).
  • TUBE MOVES IN ONE DIRECTION, BUCKY IN ANOTHER
fulcrum point of pivot
FULCRUM (POINT OF PIVOT)
  • FACTS ABOUT THE FULCRUM
  • LIES IN OBJECT PLANE
  • OBJECTS ABOVE AND BELOW THE FULCRUM ARE PROJECTED TO VARIOUS LOCATIONS ON IMAGE RECEPTOR
  • FULCRUM IS USUALLY ADJUSTABLE
  • DETERMINES WHAT SECTION OF THE BODY IS NEEDED TO BE VISUALIZED
tomography angles
TOMOGRAPHY ANGLES
  • Determines the thickness of the “cut”
  • More Angle = thinner cut
the arc
THE ARC
  • SHOULD BE LONG ENOUGH TO ACCOMMODATE EXPOSURE TIME
words to avoid
WORDS TO AVOID
  • CUT!
  • SLICE!
  • SECTION IS THE BEST DESCRIPTION!
types of tomography units
TYPES OF TOMOGRAPHY UNITS
  • Conventional Movement
    • Linear
    • Circular
    • Elliptical
    • Hypocycloidal
    • Trispiral
types of tomography units1
TYPES OF TOMOGRAPHY UNITS
  • Zonography
  • Panoramic Tomography
    • All tomography exams increase patient dose. A 16 film tomographic exam can equal patient dose of several rad.
  • Stereoradiography
  • Magnification Radiography
slide10
CT
  • Conventional tomography produces coronal and sagital images
  • CT produces transaxial images
ct simplified
CT SIMPLIFIED
  • Rotating x-ray source
  • Fan shaped beam
  • Multiple stationary detectors
  • Tube rotates around body-translation
  • Body attenuates x-ray beam
  • The attenuated beam (pixel) is assigned a CT number (Hounsfield unit)
  • Computer calculates attenuation of the individual voxels- three dimensional tissue volumes (height, width, depth)-pg 732-Bontrager
ct history key words
CT HISTORY (KEY WORDS)
  • Godfrey Hounsfield
  • EMI scanner
  • 1st generation
  • 2nd generation
  • 3rdgeneration
  • 4th generation
  • 5th generation
components of a ct scanner gantry
COMPONENTS OF A CT SCANNERGANTRY
  • Detectors, track for x-ray tube
    • Scintillation, gas filled,
    • High frequency circuit (Low frequency circuit is located in CT room)
  • X-ray tube (8,000,000+ HU)
  • Collimation
    • Two collimators
    • prepatient
      • Determines dose profile and patient dose
    • and predetector
      • Determines sensitivity profile and slice thickness
high voltage generator
HIGH VOLTAGE GENERATOR
  • ACCOMMODATES HIGHER ROTOR SPEEDS
  • POWER SURGES OF PULSED SYSTEMS
  • IN THE GANTRY
patient support table
Patient support table
  • Table indexes ( moves at a preset distance when the exam begins)
  • Movement must be reproducible within 1 mm
  • In spiral CT table moves continuously
  • Weight limit of 450 lbs, made with low atomic number
computer system
$$$$COMPUTER SYSTEM$$$$
  • 1/3 the cost of the entire system
  • The “brains” of the CT unit
  • May calculate up to 250,000 mathematical equations simultaneously
  • Reconstruction time=end of scanning to image appearance
operating consoles
Operating Consoles
  • Dual Monitors
  • Operator-turns CT scanner on and off
  • Selects and can control the protocol which is
    • Predetermined
    • Includes kVp, mAs, pitch, FOV,slice thickness, table indexing, reconstruction, algorithms and display windows
  • KVP and mAs preselected as is focal spot size
    • kVp usually in excess of 120 kVp
    • Usual mA station is 100 mA in continuous beam and several hundred mA in pulsed beam
  • Physicians viewing console
spatial resolution
SPATIAL RESOLUTION
  • DEPENDENT ON:
  • Focal spot size (not operator controlled: pre determined)
  • Beam collimation
  • Detector size
  • Matrix and pixel size(Larger matrices with smaller pixels= better spatial resolution)
slide19
MRI
  • Magnetize the atomic nuclei in hydrogen atoms
  • Bombard these atoms with radiofrequency waves
  • Hydrogen atoms absorb RT and re-emit back as radiowaves.
  • Signals are sent to computer to construct an image
digital radiography cr and dr

DIGITAL RADIOGRAPHYCR AND DR

REFERENCES: Digital Radiography and PACS, Carter

Rad. Imaging and Exposure, Fauber

cr vs dr
CASSETTE BASED DR

CR: -Imaging plate composed of photostimulable phosphor-Barium fluorohalide crystals doped with europium-Do not fluoresce when hit by x-ray photons, store energy instead.-laser releases the stored energy in a form of light-Collected by photomultiplier tube and converted to digital data.

CASSETTE-LESS SYSTEM

INDIRECT CAPTURE

X-RAYS CONVERTED TO LIGHT

LIGHT DETECTED BY AN AREA CCD OR TFT (THIN FILM TRANSISTOR)

CONVERTED TO ELECTRICAL SIGNAL

DIRECT CAPTURE/CONVERTS X-RAY INTO AN ELECTRICAL SIGNAL

DETECTOR REPLACES THE CONVENTIONAL BUCKY

CR VS DR
processing
PROCESSING
  • Film – image produced by interaction of the chemicals with the exposed silver halide crystals
  • CR- Computer near the reader (digitizer)
  • DR –computer next to the console
technique
TECHNIQUE
  • FILM – NON-LINEAR RESPONSE (THINK OF CHARACTERISTIC CURVE)
  • CR/DR – kVP influences subject contrast but radiographic contrast is controlled by the LUT
  • CR/DR –mAs affects pt. exposure and image noise but density is controlled by image processing algorithms (with LUT)
  • CR/DR – more sensitive to scatter
slide24
LUT????
  • LOOK-UP TABLE
  • SEE PAGE 115-116 (Carter et al)
  • REMEMBER EACH PIXEL HAS IT’S OWN GRAY VALUE pg 73 (Carter et al)
    • Pixel is a picture element
    • Contains bits of information
    • Make up the matrix
    • http://photo.net/equipment/digital/basics/pixels.jpg
    • To be continued in LAB on March 31/April 4
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