Medical Imaging Midterm 2 Notes

What is required to operate a fluoroscopic unit in CA?

permit and passing test score

What was the first fluoro unit, as well as other WW1 fluoro components made of?

ZnCdS

What color light did the first fluoro unit emit?

dim green

What was a critical flaw in the early days of fluoro?

lackluster protective units

Who is given credit for the first handheld fluoro unit?

Marie Curie

What was the resolution like for the first handheld fluoro unit?

low resolution

What was the intended purpose for the first handheld fluoro unit?

aimed to quickly locate shrapnel/foreign objects in bodies

What was the #1 concern that led to the creation of CA’s fluoro permit?

genetic dose

What does a fluoro permit allow?

operation of equipment, movement of patient under fluoro, setting technique, plugging in equipment

What term defines the peeling of tissue due to damage?

desquamation

What is the maximum time for fluoro in a medical procedure?

no limit

What is the #1 exposure risk for workers and patients?

fluoroscopy

What act compelled manufacturers to report radiation burn cases?

Safe Medical Devices Act (SMDA)

What resulted from the SMDA?

Lengthy Interventional Procedures

What is another name for Lengthy Interventional Procedures?

coronary angiography

Is the conventional fluoro system digital or non-digital?

non-digital

What is the most common TV camera tube?

Vidicon

What is the function of a camera tube in a fluoro system?

converts light from II to electronic pulses

What is created when x-rays enter a patient?

remnant pattern of information

What does the II output?

bright light

If there is too little or too much light, where does the ABC send a signal?

to the AEC

What does ABC stand for?

automatic brightness control

What does AEC stand for?

automatic exposure control

When the AEC receives a signal from the ABC, what is adjusted?

technique (kVp and mAs)

What is the ultimate goal the AEC is trying to reach?

automatic brightness stabilization (ABS)

What happens to occupational and patient dose when light within the II increases?

dose increases

What is the total resolution of a standard fluoro system?

2 lp

What is the resolution of an II’s input phosphor?

4 lp

What is the resolution of an II’s output phosphor?

2 lp

If the input phosphor receives more dose, what will the output phosphor emit?

more light

What draws the electrostatic image to the output phosphor?

electrostatic focusing lens

What type of potential difference is the electrostatic image drawn through in an II?

positivity-biased

What is an input phosphor made of?

cesium iodide

What is the diameter of an input phosphor?

9 inches

What is the photocathode composed of?

antimony trisulfide

What does the photocathode emit?

electrons

What is the potential difference across a standard image intensifier?

25 kV

What is the maximum entrance dose for a manual exposure control of the II?

5 R/min

What is the federal regulation for the maximum entrance dose for the AEC?

10 R/min

What is the maximum entrance dose for a high level exposure control?

20 R/min

What is CA’s maximum average patient entrance dose?

5 R/min

What is the function of evacuated glass in an II?

creates vacuum for tube

What does the input phosphor of an II receive?

remnant pattern/radiation from patient

What does the input phosphor of an II create?

light

What does the photocathode of an II receive?

light from input screen

What does the photocathode of an II produce?

electrons

What are photocathodes of the II made of?

antimony trisulfide

What is sprayed on top of photocathodes to prevent them from chemically interacting with the input screen?

plastic film

What is the function of electrostatic lens in the II?

keep pattern in place as electrons move through II, preventing distortion

What is the relationship between electrostatic lens and spatial resolution?

maintain spatial resolution

What is the function of the accelerating anode in the II?

draws electrostatic image forward

How fast do electrons accelerate through the II?

at half the speed of light

What does the output phosphor of the II receive?

electrons

What is the output phosphor of the II made of?

ZnCdS

Why did output phosphors switch from CeI to ZnCdS?

longer lifespan, added durability

What color light do output screen emit?

green

What is the “ground” of an II made of?

aluminum

What is the function of a “ground” of an II?

prevents light from reentering tube and affecting the positive bias, pulls off electrons that hit output screen

What is are other terms used to refer to high level control (HLC)?

boost

What are the limits to the mag mode in fluoro?

no limit

What are the limits to spot films/camera spots in fluoro?

no limit

What is the exposure limit for a radiology worker under the age of 18?

0.5 Rem per year

What is the exposure limit for a radiology worker over the age of 18?

5 Rem per year

What is the exposure limit for a public member?

0.1 Rem

What is the exposure limit for a fetus?

0.5 Rem per 9 months or 0.05 Rem per month

In CA, when is dose measured for pregnant workers?

organogenesis

What is skin dose measured as?

first 4 cm into patient

What term defines the difference in brightness between the output phosphor to the input phosphor?

brightness gain

What term describes the difference in the diameters of the input and output phosphors?

minification

How is brightness gain calculated?

multiply minification gain by flux gain

What term describes how accelerated the electrons in the II are?

flux gain

What is the standard range for flux gain?

50-100

What is the typical range for brightness gain?

3000-4000

What happens to dose when magnification increases?

dose increases

What happens to the focal point in the II when voltage increases?

focal point moves back

What occurs in the II when an image is magnified in fluoro?

less electrons hit output phosphor, leading to less light

How does magnification affect resolution and contrast?

increases resolution and contrast

What is the lead equivalency value for an input phosphor?

2 mm Pb

What is another term for the input phosphor?

primary beam

What is another term for the remnant image the input phosphor receives?

primary beam

Why must the fluoro tube and II carriage be detented?

ensure primary barrier receives all of primary beam

What is the “jail box” of the II?

grid

When should grids be removed?

for peds and parts smaller than 10 cm

How close should the II be to the patient?

as close as possible

Where is the average patient entrance dose measured for under-table tubes?

1 cm above the table

Where is the average patient entrance dose measured for over-table tubes?

30 cm off above the table

For under-table tubes, what is the set entrance dose if the tube is 12’’ from the patient?

5 R

For under-table tubes, what is the set entrance dose if the tube is 18’’ from the patient?

3.3 R

What is the federal regulation for the distance between the patient and the tube?

15’’

What is the federal regulation for the distance between the patient and the tube for a C-Arm?

12’’

Why is high kVp used for a traditional fluoro technique?

maximizes absorption of given contrast by matching the average energy of the beam

What is the contrast k-shell binding energy?

33-35 keV

Why is low mAs used for a traditional fluoro technique?

helps decrease heat on target and extend fluoro time indefinitely

What is the range of mA used in fluoro procedures?

0.5-3 mA

How is the probability of scatter interaction demonstrated with the sideways pear?

high probability of scatter traveling in a certain direction if point of interaction to wall of pear is longer

Where does most scatter travel?

forward from the patient

As you move closer to the II, what happens to the amount of scatter?

decreases

What is the required lead equivalency that the bucky slot of a x-ray and fluoro unit have?

0.5 mm Pb

What is the recommended thickness for aprons?

0.5 mm Pb

How much mm of Pb equivalence should a mobile wall have?

1 mm Pb eq