1. SPECIAL IMAGING/ADVANCED IMAGING INTRODUCTION TO DIGITAL RADIOGRAPHY
Tomography- Chapter 15, pg 265- Bushong
CT –Chapter 23
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 SCANNER GANTRY
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 time=end 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 RADIOGRAPHY CR 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 IT’S OWN GRAY VALUE pg 73 (Carter et al)
Pixel is a picture element
Contains bits of information
Make up the matrix
To be continued in LAB on March 31/April 4