SPECIAL IMAGINGADVANCED IMAGING INTRODUCTION TO DIGITAL RADIOGRAPHY

1
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

2
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

3
DO THE TOMOMOTION WITH ME!

• X-RAY TUBE IS ATTACHED TO THE IMAGE RECEPTOR
  (BUCKY).
• TUBE MOVES IN ONE DIRECTION, BUCKY IN ANOTHER

4
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

5
TOMOGRAPHY ANGLES

• Determines the thickness of the cut
• More Angle thinner cut

6
THE ARC

• SHOULD BE LONG ENOUGH TO ACCOMMODATE EXPOSURE TIME

7
WORDS TO AVOID

• CUT!
• SLICE!
• SECTION IS THE BEST DESCRIPTION!

8
TYPES OF TOMOGRAPHY UNITS

• Conventional Movement
• Linear
• Circular
• Elliptical
• Hypocycloidal
• Trispiral

9
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

10
CT

• Conventional tomography produces coronal and
  sagital images
• CT produces transaxial images

11
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

12
CT HISTORY (KEY WORDS)

• Godfrey Hounsfield
• EMI scanner
• 1st generation
• 2nd generation
• 3rdgeneration
• 4th generation
• 5th generation

13
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

14
HIGH VOLTAGE GENERATOR

• ACCOMMODATES HIGHER ROTOR SPEEDS
• POWER SURGES OF PULSED SYSTEMS
• IN THE GANTRY

15
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

16
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 timeend of scanning to image
  appearance

17
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

18
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)

19
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

20
DIGITAL RADIOGRAPHYCR AND DR

• REFERENCES Digital Radiography and PACS, Carter
• Rad. Imaging and Exposure, Fauber

21
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

22
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

23
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

24
LUT????

• LOOK-UP TABLE
• SEE PAGE 115-116 (Carter et al)
• REMEMBER EACH PIXEL HAS ITS 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.j
  pg
• To be continued in LAB on March 31/April 4

25
(No Transcript)