ARRT - Image Production

two photographic properties

exposure and contrast

two geometric properties

spatial resolution and distortion

increase of receptor exposure: variables

• mAs: increase

• kVp: increase

• SID: decrease

• grid ratio: decrease

• beam restriction: decrease

• patient factor thickness: decrease

increase of contrast: variables

• kVp: decreases

• grid ratio: increases

• beam restriction: increases

• patient factor thickness: decreases

increase of spatial resolution: variables

• OID: decreases

• SID: increases

• focal spot size: decreases

• patient factor thickness: if the patient is larger and there is more OID, it creates magnification which decreases resolution

increase of distortion: variables

• OID: increases

• SID: decreases

• patient factor thickness: if the patient is larger and there is more OID, it creates magnificiation which increases distortion

x-ray production starting with the source of free electrons

1. electrons at the cathode filament get boiled (thermionic emission)

2. gets so hot it creates free electrons

3. kVp accelerates electrons

what is thermionic emission

boiling of electrons

what are 3 productions of scatter

1. beam restriction

2. patient thickness

3. kVp

what is the purpose of a grid

a contrast device at a risk of patient dose

another name for distortion

magnification

draw out the x-ray tube with anode on right side

what is the role of the glass envelope and what is it made out of

creates a free air vacuum around cathode and anode, to protect tube from oxidation

• made out of metal, ceramic, or pyrex (borosilicate) glass

what is the role of the tube (metal/lead) housing

prevent xrays emitted throughout exam room, absorbs all the xray photons

what end of the tube has the filament and focusing cup

cathode

what are the type of anodes

stationary anode: electron beam is focused on specific place on anode, heat is on one small area. simple design, but low heat capacity so only for low exposures (only dental machines)

rotating anode: electron beam on a rotating disk, increase of heat capacity

what is the tube housing leakage minimum

0.88 mGy/hr

what is an induction motor

turns anode without actually touching anode, incudes anode to spin

3 induction motors

stators: electromagnets around rotor, induce turning of rotor

rotor: attaches anode disk that rotates

bearings: in between rotor and xray tube, low friction spheres that allow free rotation of rotor (the sound we hear when we take xrays)

Define anode heel effect

affects intensity of the xray beam. there are fewer xray photons on the anode side due to xrays getting absorbed within anode heel

• putting a body part on the anode side on the least dense portion of patient, gives an even exposure

Why is the beam more intense on the cathode end?

has higher intensity of xray photons

If the degree of anode angle decreases - will that increase or decrease the anode heel effect?

typical anode angle and relationship with anode heel effect

between 6 to 20 degrees

• the lesser the anode angle, the higher the anode heel effect

what is line focus principle and what does it affect

relationship between actual focal spot on anode and effect focal spot that extends from anode

• affects heat capacity, spatial resolution, and beam coverage

• Which is larger, Actual focal spot or Effective focal spot? (line focus principle)

• larger actual focal spot

actual focal spot vs effective focal spot

• actual focal spot: size of cathode filament, and this is where electrons convert to xray on ANODE

• effective focal spot: width of xray beam, it reflects off the anode down. affects penumbra and spatial resolution

If you decrease anode angle (choose a small focal spot) how will that affect the effective focal spot size? 

small focal spot will lower penumbra and increase spatial resolution (which is good)

Which focal spot is the one goes toward the patient?

effective focal spot

what is tube loading

heat created in the xray tube

calculation of tube loading

heat units = kVp x mA x seconds x W (waveform factor)

what kind of focal spot is needed for large exposure techniques

small actual focal spot

as effective focal spot size increases, spatial resolution ____

increases

which set of shutters blocks most of the off-focus radiation

first set

what is off focus radiation

areas outside the focal spot and travels at wider angles than the primary xray beam

How long would it take the anode to cool completely after using a 120,000 heat unit exposure

10 minutes

during the histogram process, the computer may identify off-focus radiation as

values of interest

difference between series and parallel circuits

series: all components are connected end to end, if one component fails the entire circuit fails

parallel: has different components, if one fails it still keeps going on.

draw the xray circuit

What is the incoming voltage coming into the circuit?

220 volts, but we need more for an xray and we need kilovolts

• Which transformer comes first in the circuit?

autotransformer

• What is the role of the autotransformer?

supply a precise voltage to the filament circuit and to the high-voltage circuit of the x-ray imaging system

• without it we cant change kvp to different settings

• The autotransformer works on what type of induction?

self induction

• What is the role of the step up transformer?

increases the voltage from volts to kilovolts

• What is the role of the step down transformer?

steps down voltage and amperage, which increas heat and xrays coming out. ALL AC

• The step up & step down transformers work on what type of induction?

mutual induction

• What is the role of the rectifier?

turn AC wave to DC wave

• What is the difference between direct and alternating current

alternating current (AC): reversing polarity, electrons move in both directions (that allow transformers to work)

direct current (DC): one polarity, electrons travel in one direction

• What works on alternating current in the circuit?

autotransformer

• What works on direct current in the x-ray circuit?

xray tube

• What is the rheostat? 

variable resister that is a mA selector in the filament

• When a technologist increases the mA on the control panel, what factors will also increase?

• increases current to the filament, heat, # of electrons flowing in xray tube, and xrays coming out

what is an ammeter

measuring deviced hooked up in a series circuit

• measured by amps

what is a voltmeter

measuring device hooked up in a parallel circuit

• measured in volts

what is a capacitor

storage for electricity

current in filament has to be

3-6 amperes so that thermionic emission takes place