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Transcript of SPECIAL IMAGING/ADVANCED IMAGING INTRODUCTION TO DIGITAL RADIOGRAPHY Tomography- Chapter 15, pg 265-...
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SPECIAL IMAGING/ADVANCED IMAGINGINTRODUCTION TO DIGITAL
RADIOGRAPHY
Tomography- Chapter 15, pg 265- BushongCT –Chapter 23MRI – Chapter 24, BontragerCR/DR- Chapters 1,4, 7-Carter Chapter 12 - Fauber
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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
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DO THE “TOMOMOTION” WITH ME!
X-RAY TUBE IS ATTACHED TO THE IMAGE RECEPTOR (BUCKY).
TUBE MOVES IN ONE DIRECTION, BUCKY IN ANOTHER
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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
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TOMOGRAPHY ANGLES
Determines the thickness of the “cut”
More Angle = thinner cut
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THE ARC
SHOULD BE LONG ENOUGH TO ACCOMMODATE EXPOSURE TIME
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WORDS TO AVOID
CUT!SLICE! SECTION IS
THE BEST DESCRIPTION!
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TYPES OF TOMOGRAPHY UNITS
Conventional Movement Linear Circular Elliptical Hypocycloidal Trispiral
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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
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CT
Conventional tomography produces coronal and sagital images
CT produces transaxial images
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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
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CT HISTORY (KEY WORDS)
Godfrey Hounsfield EMI scanner 1st generation 2nd generation 3rdgeneration 4th generation 5th generation
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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
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HIGH VOLTAGE GENERATOR
ACCOMMODATES HIGHER ROTOR SPEEDS
POWER SURGES OF PULSED SYSTEMS
IN THE GANTRY
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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
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$$$$COMPUTER SYSTEM$$$$
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
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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
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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)
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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
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DIGITAL RADIOGRAPHYCR AND DR
REFERENCES: Digital Radiography and PACS, CarterRad. Imaging and Exposure, Fauber
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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
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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
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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
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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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