SPECIAL IMAGINGADVANCED IMAGING INTRODUCTION TO DIGITAL RADIOGRAPHY

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SPECIAL IMAGINGADVANCED IMAGING INTRODUCTION TO DIGITAL RADIOGRAPHY

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X-RAY TUBE IS ATTACHED TO THE IMAGE ... Tube rotates around body-translation. Body attenuates ... X-ray tube (8,000,000 HU) Collimation. Two collimators ... – PowerPoint PPT presentation

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Title: 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????