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

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!

X-RAY TUBE IS ATTACHED TO THE IMAGE RECEPTOR (BUCKY).

TUBE MOVES IN ONE DIRECTION, BUCKY IN ANOTHER

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

Determines the thickness of the “cut”

More Angle = thinner cut

THE ARC

SHOULD BE LONG ENOUGH TO ACCOMMODATE EXPOSURE TIME

WORDS TO AVOID

CUT!SLICE! SECTION IS

THE BEST DESCRIPTION!

TYPES OF TOMOGRAPHY UNITS

Conventional Movement Linear Circular Elliptical Hypocycloidal Trispiral

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

CT

Conventional tomography produces coronal and sagital images

CT produces transaxial images

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)

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

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

ACCOMMODATES HIGHER ROTOR SPEEDS

POWER SURGES OF PULSED SYSTEMS

IN THE GANTRY

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

$$$$COMPUTER SYSTEM$$$$

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

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

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)

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 RADIOGRAPHYCR AND DR

REFERENCES: Digital Radiography and PACS, CarterRad. 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

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

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

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