Image Production Test 1

When did name change from technician to technologist?

1964

when were xrays discovered

nov 8, 1895

who discovered xrays

Wilhelm Conrad Roentgen

what was the first taken xray

mrs roentgens hand

how long did the first xray take

15 min

explain the first xray

-300 yrs of cumulative effort
-used partially evacuated crookes tube
-put platinocyanide paper over tube
-no visible light but paper emitted light

fluorescence

emission of visible light resulting from ionizing light emitting phosphors

when was roentgen awarded the first nobel prize

1901

radiation

enengy in transit in form of high speed particles and elecomagnetic waves

Xrays are ionizing. what does this mean?

have enough energy to seperate molecules or remove electrons from atoms

what kind of wavelength lengths do ionizing beams have

short

gamma radiation

electomagnetic waves or photons emitted from nucleus. stronger than xrays

beta radiation

high speed particles, indentical to electrons emitted from nucleus

alpha radiation

particle emitted from nucleus with 2 protons and 2 neutrons

xrays

electromagnetic waves or photons not emitted from nucleus but emitted by energy changes in electrons

describe xrays

-energy changes occur in xray tube by slowing down
-have no definite max range, however energy of photons decreases w thickness of absorber

explain how wavelengths affect penetration

shorter wavelengths (like xrays) are able to penetrate materials

waves

variation in disturbance that transfers energy point to point

wavelength

distance from peak to peak

describe the relationship between wavelength and photon strength

the shorter the wavelength, the stronger the photon

photon

particles of light transported in discrete packages

maxwell theory

xrays travel at constant speed of light and produce frequencies of vibration w a directly proportional wavelength between each frequency

MAIN CONCEPT of maxwell theory

the higher the kvp, the shorter the wavelength and vice versa

frequency

the number of wave cycles to pass a given point per unit of time

quantum theory (photon theory)

explains xrays as a "shower" of photons

10 properties of xrays

1. can penetrate materials that absorb/reflect light
2. cause certain subject to fluoresce
3. can penetrate solids and opaque materials
4. produce biological changes that can stimulate/ retard growth
5. travel in straight lines and can scatter
6. travel at speed of light
7. can ionize gas
8. have no mass and no electrical charge
9. are invisible
10. cannot be focused by a lens

shielding

highly debated topic, 6 vs. 12 ft debate

3 components of xray

1. vacuum tube (evacuated)
2. heated cathode
3. rotating anode

heated cathode

negative electrode

rotating anode

postive electrode

evacuated

free from air

an xray tube is a diode. what does this mean?

it is an evacuated tube w 2 electrodes

what happenes to the area covered by radiation if you increase collimation

if you increase collimation, the area covered by the radiation decreases

what 3 conditions must be present for xray to take place?

1. source of electrons
2. means to free electrons from cloud
3. means to slow them down

Explain the "source of electrons" needed for xray to occur

- need dedicated circuit
-cathode becomes incondescent
-electrons dont move yet, they need an applied force

Describe the cathode

negatively charged electrode and source of electrons
has two filaments: small used for lower exposures, large used for high exposures

what is the relationship between the temperature of the cathode filament and electrons?

the temperature of the cathode filament controls the quantity of electrons

What conditions will increase along with the increase of quantity of electrons?

1. Ma
2. current
3. filament temp
4. heat

What happens to the sharpness of an image as the beam spreads?

as a beam spreads, the sharpness of an image decreases

What is the relationship between focal spot and sharpness of image detail?

Inverse, as the focal spot size increases, the sharpness goes down

Explain "means to free electrons from cloud" needed to take xray

- electrons in cloud until force is applied
-they are repelled from cathode to anode via thermionic emission
-kvp pushes electrons out of cathode
-when electron hits anode, it becomes a photon

Explain "Means to slow electrons down" needed to take xray

-done by anode

Why is the anode made of all metals and used to slow electrons down? (3 reasons)

1. high melting point
2. high atomic number
3. good conducters of heat

How do we control the quantity of exposure to a patient?

mAs

How do we control the quality of exposure (absorbed dose)?

kVp

Explain the physical process of an xray

prepare rotor and expose

What does "expose" mean

applies kvp to free electrons and push towards the anode

As Kvp increases, what other factors will also increase?

1. strength of electrons
2. penetrating power of photons
3. quality

As kvp increases, what factors will decrease?

1. wavelength
2. patient dose

What is the relationship between kvp and mas? How do they affect each other?

Kvp can affect mas but mas cant affect kvp because it is unable to penetrate

Define focal spot

area on rotating anode where the electron beam strikes
have two tracks, small and large. tracks are related to the quantity of electrons they recieve

what is the relationship between focal spot and resolution

inverse, as focal spot increase, resolution decreases

why do focal spots have 2 tracks?

related to sharpness/spatial resolutions

what is the ONLY thing a focal spot size can affect

resolution

what factors can affect resolution?

1. focal spot size
2. SID
3. OID

actual focal spot

area where electrons actually strike anode in tube
determines electric load

effective (projected) focal spot size

area where protons strike the film
determines sharpness

line focus principle

a principle that automatically occurs because of anode angle in tube, size of area electrons strike in tube is larger than projected on IR

Advantage of line focus principle

provides detail of small focal spot and allows large amount of heat dissipation

What is the MAIN CONCEPT of the line focus principle

the lower the target angle, the smaller the effective focal spot, the more resolution

what is the most common target angles and what is ours?

12-17, ours is 12

what is the relationship between angle and resolution?

inverse, as angle decreases, resolution increases

Why is a 12-17 degree angle considered best?

1. balance between resolution and tube load of photons exiting tube
2. less that 12 photons can bounce back to cathode
3. more than 17 photons can be absorbed into target material
4. info is lost everytime beam spreads so you want to keep it as streamlined as possible

penumbra

false image, unsharpness

umbra

true image, sharpness

what is the relationship between penumbra and umbra

inverse, as penumbra goes up, umbra goes down

Problems associated with focal spot

1. Space change
2. blooming
3. etching

Explain the "space change" problem

can become larger and expand causing blooming

explain the "blooming" problem

expanding beyond normal diameter. some is expected and tolerated

explain the "etching" problem

damage to anode via small cracks due to thermal shock

define resolution

ability to distinguish between any 2 adjacent details as seperate and distinct

how can resolution be tested?

with a focal spot test tool

How do you decide between dose and resolution?

1. patient age (tolerance)
2. part under exam
3. amount of needed exposure
4. sex (childbearing)
5. diagnosis

ALARA prinicple

as low as reasonably achievable REGARDING PT DOSE

What body parts are most sensitive to radiation?

eyes, thyroid, gonads

4 prime factors needed to produce radiographs?

1. ma
2. time
3. kvp
4. distance (SID)

Which of the prime factors is controlled by a generator but set by an RT?

Ma
time
kvp

which of the prime factors is controlled and set by an RT?

SID

Define mAS

the measure of quantity of electrical current flowing through a circuit

what role does mAs play?

- controls density in film
-responsible for controlling intensity, but not strength of beam
- in digital it can affect amount of radiation to IR, as well as patient dose

as mA increases, what other factors also increase

- heat production
-quantity of electrons produced
- time
-pt dose

How does mAs affect contract

has no direct effect on contrast because it is unable to penetrate

what does mAs represent?

number of electrons passing through point in time

what does Ma and time together control?

total amount of photons produced at tube

density

overall blackening present on image

explain the difference between dark/light images and their density

darker images have higher density, lighter images have lower density

brightness

measurement of luminance of area in a image displayed on a monitor

what is the relationship between density and brightness?

they are opposites

optimum intensity

ideal amount of light for human vision

what is the relationship between mas and density?

proportional, as mas increases so does density

in the digital world, what is the relationship between mas and brightness?

inverse, as mas increases, brightness decreases

define time

designated length of xray exposure the patient is subjected to

Milliampere

number of electrons emitted from filament, determines heat

Explain linearity and how mAs behaves as such

if mas doubles, intensity doubles and density should be approx double on final image
- doubling mas from 10 to 20 would be a 100% increase
- this also results in doubling the dose to patient

Reciprocity Law

mA and time are inversely proportional to achieve some density

what is the reciprocity law formula?

ma1/ma2= sec 2/sec1

What factor would you want to decrease to decrease chance of motion?

time

when does the combo of mA & time matter?

does affect mAs output but affects patient dose and resolution

What factors are linear?

- mAs and denisty
- mAs and dose

Explain linearity

-important for patient dose
-cant be observed