Imaging Principles Unit 1

anode

positive terminal of xray tube; stops electrons

cathode

negative terminal of xray tubes; source of electrons

filament

spiral wires made with thoriated tungsten where thermionic emission takes place

focusing cup

made of stainless steel or nickel; small depression in cathode assembly that narrows down thermionic cloud as it drives to anode

actual focal spot

the physical portion of the focal track (on anode) that is impacted; location that is actually hit by electrons

effective focal spot

the area of the focal spot that is shot out of the tube; only spot where xrays can leave the tube through port window

anode heel effect

anode heel gets in the way of xrays trying to leave the tube causing the cathode side to have greater intensity xrays than the anode side

electromagnetic radiation (EM)

a form of energy that is a result of electric and magnetic disturbances in space

electromagnetic spectrum

describes the different forms of electromagnetic radiation

photon or quantum

electromagnetic energy in a discrete or quantized amount that acts like a bundle or packet of energy much like a particle

wavelength

distance from crest to crest or trough to trough

frequency

number of waves that pass a specific point in a given time frame or number of cycles per second

mAs (milli ampere seconds)

primary control of xray exposure and radiographic density; measure of the quantity of electrical current flowing though a circuit

kVp (kilovoltage peak)

primary control of quality of beam; measure of electrical force or pressure behind a current of electricity

SID (source to image detector)

AKA FFD or TFD; distance from the source (machine) to the image receptor (IR)

OID (object to image detector)

AKA OFD; distant from object (person) to image receptor (IR)

SOD (source to object)

AKA SSD; distance from source (machine) to the object (person)

Inverse square law

the intensity of radiation in inversely proportional to the square of the distance between the receiver and emitter

Line focus principle

the size of the effective focal spot can be changed by changing the actual focal spot through changing the angle of the target anode. decreased angle= decreased effective focal spot= increased detail

the size of the actual focal spot

the effective focal spot is controlled by?

density changes when distance is changed with a direct relationship to account for the changes in intensity and density

explain the correction formula

density maintenance formula and direct square law

what’s another name for the correction formula?

Brem’s and characteristic

what are the two types of target interactions?

-photon orbits around the nucleus (not hitting anything) losing some power which becomes the xray

-closer to the nucleus = more power

explain Brem’s interactions

-photon knocks an inner shell electron out of its orbit creating a characteristic cascade and 57.5 Kev xrays

explain characteristic interactions?

photoelectric absorption, coherent scattering, Compton scattering, pay production, photodisintegration

what are the 5 types of photon/matter interactions

photon knock an inner shell electron out of orbit and ceases to exist. Causes ionization of atom; responsible for image contrast

explain photoelectric absorption

photon interacts with outer shell electron, electron vibrates and releases photon with same energy in a different direction

explain coherent scattering

more common scattering; photon knocks outer shell electron out of orbit (ionizing atom) and move in a different direction with lower energy

explain Compton scattering

high energy photon encounter nucleus creating two electrons. the negation is immediately absorbed. the positron pairs with an electron disappearing and creating 2 new photons moving in opposite directions (Annihilation reaction); not worried about in dx

explain pair production

extremely high energy photon hits nucleus and blows up atom; what radiation therapy does

explain photodisintegration

radio, microwave, infrared, visible, ultraviolet, xray, gamma ray

list the energies on the electromagnetic spectrum from longest to shortest wavelength.

3×10^8 m/sec or 186400 mi/sec

what are the ways the speed of light can be represented?

radiation that is composed of photons that were not produce at the focal spot; can cause ghosting of primary beam

explain off focus radiation

stator

made of induction motor electromagnets; only part that is outside the vacuum; causes the rotor to turn the anode

rotor

made of hollow copper cylinder attached to anode by molybdenum shaft, inside stator and envelope

envelope

aka tube; metal or glass; maintains the vacuum

housing

controls leakage and prevents scatter radiation; space is filled with oil to cool tube

sufficient density to show an image of tissue adequately penetrated and sharply defined

define diagnostic radiograph

10^-10 m

what is an xrays wavelength

thermionic emmsion

process by which we collect electrons that are kicked out of group in focusing cup

15-17 degrees

what target angle do we use in dx?

differential absorption

xray image result from the difference between those xrays absorbed photoelectrically in the patient and those transmitted in the IR

a source of electrons, an appropriate target material, a high voltage, and a vacuum

what conditions are necessary for electrical production of xrays?

0.1-0.2 mm thick, 1-2 mm wide by 7-15 mm long

filament measurements