MEDICAL PHYSICS ABR FINAL PAPER
PRACTICE QUESTIONS WITH VERIFIED
ANSWERS PACKAGE
●● Why is rhenium mixed with tungsten in a filament?
Answer: Prevent cracking with repeated heating/cooling
●● K edge of Iodine
Answer: 33.2 keV
●● K shell binding energy of tungsten
Answer: 69.5 keV
●● Max energy of the xray that is created at the anode
Answer: Can't be higher than the energy of the electron that created it
(which maxes at the voltage between the cathode and anode in kV)
●● K-shell binding energy proportional to...
Answer: Z^2
●● Auger electron
,Answer: Inner shell electron gets ionized, another drops down, emits
energy but this energy ionizes another (outer shell) electron. No x-rays
produced
●● What elements tend to make Auger electrons?
Answer: Lower Z. This is also why you pick high Z for anodes
●● Relationship between Z and amount of Bremsstrahlung
Answer: Directly proportional
●● Type of shielding to use when blocking beta emitters (like a syringe
full of Y90)
Answer: Low Z shield (like plastic) because high Z shield will create
tons of Bremsstrahlung xrays
●● Double the mA
Answer: Double the intensity of the energy spectrum
●● Increase kVP by 15%
Answer: Double intensity of energy spectrum
●● Average energy of the xrays is based on the...
Answer: kVP, unrelated to mA
,●● Average energy relative to kVP
Answer: Approximately 50% (prob slightly less) of the kVP
●● Things to do when you xray a baby
Answer: Lower the kVP (you don't need as much to penetrate), keep
mAs similar or slightly lower
Dont use a grid
●● Focal spot
Answer: Part of the anode where bombardment/xray production takes
place
●● Smaller focal spot
Answer: Better spatial resolution, worse heat dissipation
●● Actual focal spot vs apparent focal spot
Answer: Actual focal spot is on the target. Apparent focal spot is on the
patient
●● Which focal spot determines the blur?
, Answer: The apparent focal spot (on the patient), not the actual focal
spot on the anode
●● Steeper (smaller) anode angle
Answer: Makes a smaller apparent focal spot, but the actual focal spot is
also smaller so heat dissipation can be a problem
●● "Blooming" of the focal spot
Answer: Happens when you have high mA, low kVP. Imagine crowded
low energy electrons that are bumping each other when theyre going
from cathode to anode.
●● Heel effect
Answer: Xrays that are closer to the anode side had to travel through
more attenuating material and are less intense. Remember "cathode to
chest wall"
●● How to improve heel effect
Answer: Smaller film size, larger source to image distance, larger (less
steep) anode angle
●● Heel "cutoff"
Answer: Smaller (steeper) anode angle results in worse heel effect
PRACTICE QUESTIONS WITH VERIFIED
ANSWERS PACKAGE
●● Why is rhenium mixed with tungsten in a filament?
Answer: Prevent cracking with repeated heating/cooling
●● K edge of Iodine
Answer: 33.2 keV
●● K shell binding energy of tungsten
Answer: 69.5 keV
●● Max energy of the xray that is created at the anode
Answer: Can't be higher than the energy of the electron that created it
(which maxes at the voltage between the cathode and anode in kV)
●● K-shell binding energy proportional to...
Answer: Z^2
●● Auger electron
,Answer: Inner shell electron gets ionized, another drops down, emits
energy but this energy ionizes another (outer shell) electron. No x-rays
produced
●● What elements tend to make Auger electrons?
Answer: Lower Z. This is also why you pick high Z for anodes
●● Relationship between Z and amount of Bremsstrahlung
Answer: Directly proportional
●● Type of shielding to use when blocking beta emitters (like a syringe
full of Y90)
Answer: Low Z shield (like plastic) because high Z shield will create
tons of Bremsstrahlung xrays
●● Double the mA
Answer: Double the intensity of the energy spectrum
●● Increase kVP by 15%
Answer: Double intensity of energy spectrum
●● Average energy of the xrays is based on the...
Answer: kVP, unrelated to mA
,●● Average energy relative to kVP
Answer: Approximately 50% (prob slightly less) of the kVP
●● Things to do when you xray a baby
Answer: Lower the kVP (you don't need as much to penetrate), keep
mAs similar or slightly lower
Dont use a grid
●● Focal spot
Answer: Part of the anode where bombardment/xray production takes
place
●● Smaller focal spot
Answer: Better spatial resolution, worse heat dissipation
●● Actual focal spot vs apparent focal spot
Answer: Actual focal spot is on the target. Apparent focal spot is on the
patient
●● Which focal spot determines the blur?
, Answer: The apparent focal spot (on the patient), not the actual focal
spot on the anode
●● Steeper (smaller) anode angle
Answer: Makes a smaller apparent focal spot, but the actual focal spot is
also smaller so heat dissipation can be a problem
●● "Blooming" of the focal spot
Answer: Happens when you have high mA, low kVP. Imagine crowded
low energy electrons that are bumping each other when theyre going
from cathode to anode.
●● Heel effect
Answer: Xrays that are closer to the anode side had to travel through
more attenuating material and are less intense. Remember "cathode to
chest wall"
●● How to improve heel effect
Answer: Smaller film size, larger source to image distance, larger (less
steep) anode angle
●● Heel "cutoff"
Answer: Smaller (steeper) anode angle results in worse heel effect
