DABR Qualifying (Core)
DABR – AMERICAN BOARD OF RADIOLOGY DIPLOMATE |
QUALIFYING (CORE) | EXAM QUESTIONS AND CORRECT
ANSWERS | 2026/2027
THE AMERICAN BOARD OF RADIOLOGY — DIPLOMATE (DABR)
QUALIFYING (CORE)
1. At diagnostic x-ray energies above about 30 keV, which photon
interaction predominates in soft tissue?
A. Coherent (Rayleigh) scattering
B. Compton scattering
C. Pair production
D. Photoelectric absorption
B. Compton scattering — Compton scatter dominates in low-Z soft
tissue across most of the diagnostic range and is the main source of
scatter that degrades contrast.
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, DABR Qualifying (Core)
2. The probability of photoelectric absorption varies approximately
with which relationship?
A. Z/E
B. E³/Z³
C. Z³/E³
D. Z²·E
C. Z³/E³ — Photoelectric absorption rises sharply with atomic number
and falls steeply with photon energy, which is why it drives contrast for
bone, iodine and barium.
3. The K-edge of iodine, which makes it an effective contrast agent at
typical diagnostic energies, is approximately:
A. 33 keV
B. 12 keV
C. 50 keV
D. 69 keV
A. 33 keV — Iodine's K-shell binding energy is about 33.2 keV, close to
the mean energy of many diagnostic beams, maximizing photoelectric
absorption.
4. Increasing kVp while keeping mAs constant will most directly:
A. Have no effect on patient dose
B. Decrease the number of photons reaching the detector
C. Decrease beam penetration and increase subject contrast
D. Increase beam penetration and decrease subject contrast
D. Increase beam penetration and decrease subject contrast —
Higher kVp produces more energetic, penetrating photons, so Compton
scatter increases relative to photoelectric absorption and contrast falls.
Page 2 of 53
, DABR Qualifying (Core)
5. Regarding the anode heel effect, the x-ray beam intensity is:
A. Uniform across the field
B. Greater on the anode side of the field
C. Greater on the cathode side of the field
D. Greatest at the central ray only
C. Greater on the cathode side of the field — Photons exiting toward
the anode side travel through more target material and are attenuated,
so the cathode side is more intense.
6. The SI unit used to express effective dose is the:
A. Coulomb per kilogram (C/kg)
B. Becquerel (Bq)
C. Sievert (Sv)
D. Gray (Gy)
C. Sievert (Sv) — Effective dose applies radiation and tissue weighting
factors to absorbed dose and is expressed in sieverts.
7. Tissue weighting factors used in calculating effective dose account
for:
A. The depth of each organ below the skin surface
B. Differences in organ sensitivity to stochastic radiation effects
C. Differences in biological effectiveness of radiation types
D. The density of each organ
B. Differences in organ sensitivity to stochastic radiation effects —
Tissue weighting factors reflect each organ's relative contribution to
overall stochastic detriment, mainly cancer risk.
8. If the distance from a point x-ray source is doubled, the beam
intensity becomes:
A. Twice the original
B. Unchanged
C. One quarter of the original
D. One half of the original
C. One quarter of the original — By the inverse square law, intensity
falls with the square of distance, so doubling distance reduces it to 1/4.
Page 3 of 53
, DABR Qualifying (Core)
9. The half-value layer (HVL) of an x-ray beam is the thickness of
material that:
A. Absorbs all photons below 50 keV
B. Reduces the beam intensity to 50% of its initial value
C. Doubles the mean energy of the beam
D. Reduces the beam energy by half
B. Reduces the beam intensity to 50% of its initial value — HVL is
the standard measure of beam quality; it is the thickness that cuts
exposure rate to one half.
10. Adding aluminum filtration to an x-ray beam primarily:
A. Hardens the beam and reduces patient skin dose
B. Increases the number of low-energy photons
C. Softens the beam and increases contrast
D. Improves spatial resolution
A. Hardens the beam and reduces patient skin dose — Filtration
removes low-energy photons that would be absorbed in skin without
contributing to the image, raising mean beam energy.
SECTION 2: RADIATION BIOLOGY, SAFETY AND REGULATIONS
11. Under NRC regulations, the annual occupational total effective dose
equivalent limit for an adult radiation worker is:
A. 20 mSv (2 rem)
B. 150 mSv (15 rem)
C. 50 mSv (5 rem)
D. 1 mSv (0.1 rem)
C. 50 mSv (5 rem) — US federal regulations (10 CFR 20) set the whole-
body occupational limit at 50 mSv per year.
Page 4 of 53
DABR – AMERICAN BOARD OF RADIOLOGY DIPLOMATE |
QUALIFYING (CORE) | EXAM QUESTIONS AND CORRECT
ANSWERS | 2026/2027
THE AMERICAN BOARD OF RADIOLOGY — DIPLOMATE (DABR)
QUALIFYING (CORE)
1. At diagnostic x-ray energies above about 30 keV, which photon
interaction predominates in soft tissue?
A. Coherent (Rayleigh) scattering
B. Compton scattering
C. Pair production
D. Photoelectric absorption
B. Compton scattering — Compton scatter dominates in low-Z soft
tissue across most of the diagnostic range and is the main source of
scatter that degrades contrast.
Page 1 of 53
, DABR Qualifying (Core)
2. The probability of photoelectric absorption varies approximately
with which relationship?
A. Z/E
B. E³/Z³
C. Z³/E³
D. Z²·E
C. Z³/E³ — Photoelectric absorption rises sharply with atomic number
and falls steeply with photon energy, which is why it drives contrast for
bone, iodine and barium.
3. The K-edge of iodine, which makes it an effective contrast agent at
typical diagnostic energies, is approximately:
A. 33 keV
B. 12 keV
C. 50 keV
D. 69 keV
A. 33 keV — Iodine's K-shell binding energy is about 33.2 keV, close to
the mean energy of many diagnostic beams, maximizing photoelectric
absorption.
4. Increasing kVp while keeping mAs constant will most directly:
A. Have no effect on patient dose
B. Decrease the number of photons reaching the detector
C. Decrease beam penetration and increase subject contrast
D. Increase beam penetration and decrease subject contrast
D. Increase beam penetration and decrease subject contrast —
Higher kVp produces more energetic, penetrating photons, so Compton
scatter increases relative to photoelectric absorption and contrast falls.
Page 2 of 53
, DABR Qualifying (Core)
5. Regarding the anode heel effect, the x-ray beam intensity is:
A. Uniform across the field
B. Greater on the anode side of the field
C. Greater on the cathode side of the field
D. Greatest at the central ray only
C. Greater on the cathode side of the field — Photons exiting toward
the anode side travel through more target material and are attenuated,
so the cathode side is more intense.
6. The SI unit used to express effective dose is the:
A. Coulomb per kilogram (C/kg)
B. Becquerel (Bq)
C. Sievert (Sv)
D. Gray (Gy)
C. Sievert (Sv) — Effective dose applies radiation and tissue weighting
factors to absorbed dose and is expressed in sieverts.
7. Tissue weighting factors used in calculating effective dose account
for:
A. The depth of each organ below the skin surface
B. Differences in organ sensitivity to stochastic radiation effects
C. Differences in biological effectiveness of radiation types
D. The density of each organ
B. Differences in organ sensitivity to stochastic radiation effects —
Tissue weighting factors reflect each organ's relative contribution to
overall stochastic detriment, mainly cancer risk.
8. If the distance from a point x-ray source is doubled, the beam
intensity becomes:
A. Twice the original
B. Unchanged
C. One quarter of the original
D. One half of the original
C. One quarter of the original — By the inverse square law, intensity
falls with the square of distance, so doubling distance reduces it to 1/4.
Page 3 of 53
, DABR Qualifying (Core)
9. The half-value layer (HVL) of an x-ray beam is the thickness of
material that:
A. Absorbs all photons below 50 keV
B. Reduces the beam intensity to 50% of its initial value
C. Doubles the mean energy of the beam
D. Reduces the beam energy by half
B. Reduces the beam intensity to 50% of its initial value — HVL is
the standard measure of beam quality; it is the thickness that cuts
exposure rate to one half.
10. Adding aluminum filtration to an x-ray beam primarily:
A. Hardens the beam and reduces patient skin dose
B. Increases the number of low-energy photons
C. Softens the beam and increases contrast
D. Improves spatial resolution
A. Hardens the beam and reduces patient skin dose — Filtration
removes low-energy photons that would be absorbed in skin without
contributing to the image, raising mean beam energy.
SECTION 2: RADIATION BIOLOGY, SAFETY AND REGULATIONS
11. Under NRC regulations, the annual occupational total effective dose
equivalent limit for an adult radiation worker is:
A. 20 mSv (2 rem)
B. 150 mSv (15 rem)
C. 50 mSv (5 rem)
D. 1 mSv (0.1 rem)
C. 50 mSv (5 rem) — US federal regulations (10 CFR 20) set the whole-
body occupational limit at 50 mSv per year.
Page 4 of 53
