ABR Medical Physics Certification Examination
Exam Questions and Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
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1. Which of the following is the main mechanism of x-ray production
in a diagnostic x-ray tube?
A. Characteristic and Bremsstrahlung radiation
B. Cherenkov radiation
C. Compton scattering
D. Photoelectric effect
A. Characteristic and Bremsstrahlung radiation
X-rays are produced in a tube primarily by Bremsstrahlung (deceleration
of electrons in the target) and characteristic radiation (electrons filling
inner shell vacancies).
2. The half-value layer (HVL) of an x-ray beam is defined as the
thickness of material required to reduce the beam intensity to:
A. 25%
B. 50%
C. 75%
D. 100%
B. 50%
The HVL is the thickness of a specified material that reduces the
intensity of the x-ray beam by half.
3. In radiotherapy, the primary purpose of a flattening filter is to:
A. Reduce patient dose
, B. Remove low-energy photons
C. Produce a uniform dose distribution across the field
D. Increase beam energy
C. Produce a uniform dose distribution across the field
Flattening filters are designed to make the intensity profile of the
photon beam uniform across the field for standard treatments.
4. Which interaction predominates for 1 MeV photons in soft tissue?
A. Photoelectric effect
B. Compton scattering
C. Pair production
D. Coherent scattering
B. Compton scattering
At intermediate energies (around 1 MeV), Compton scattering is the
dominant interaction in soft tissue.
5. The unit Gray (Gy) is used to measure:
A. Absorbed dose
B. Equivalent dose
C. Activity
D. Exposure
A. Absorbed dose
1 Gy = 1 joule/kg and measures the energy deposited per unit mass of
tissue.
6. In MRI, T1 relaxation time refers to:
A. Spin-spin relaxation
B. Spin-lattice relaxation
C. Free induction decay
D. Chemical shift
, B. Spin-lattice relaxation
T1 measures the time constant for the recovery of longitudinal
magnetization along the magnetic field.
7. In CT imaging, increasing the tube current (mA) will primarily:
A. Increase spatial resolution
B. Increase image noise
C. Increase patient dose
D. Reduce scan time
C. Increase patient dose
Increasing mA increases the number of x-ray photons, which raises the
patient dose without significantly affecting spatial resolution.
8. The purpose of a bowtie filter in CT is to:
A. Improve temporal resolution
B. Reduce beam hardening and patient dose
C. Increase image contrast
D. Increase tube output
B. Reduce beam hardening and patient dose
Bowtie filters shape the x-ray beam intensity, reducing unnecessary
dose at the periphery and minimizing artifacts.
9. The Compton effect results in:
A. Absorption of photon
B. Scattering of photon with energy loss
C. Production of positrons
D. No change in photon direction
B. Scattering of photon with energy loss
Compton scattering causes deflection of the photon and energy transfer
to an electron.
Exam Questions and Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. Which of the following is the main mechanism of x-ray production
in a diagnostic x-ray tube?
A. Characteristic and Bremsstrahlung radiation
B. Cherenkov radiation
C. Compton scattering
D. Photoelectric effect
A. Characteristic and Bremsstrahlung radiation
X-rays are produced in a tube primarily by Bremsstrahlung (deceleration
of electrons in the target) and characteristic radiation (electrons filling
inner shell vacancies).
2. The half-value layer (HVL) of an x-ray beam is defined as the
thickness of material required to reduce the beam intensity to:
A. 25%
B. 50%
C. 75%
D. 100%
B. 50%
The HVL is the thickness of a specified material that reduces the
intensity of the x-ray beam by half.
3. In radiotherapy, the primary purpose of a flattening filter is to:
A. Reduce patient dose
, B. Remove low-energy photons
C. Produce a uniform dose distribution across the field
D. Increase beam energy
C. Produce a uniform dose distribution across the field
Flattening filters are designed to make the intensity profile of the
photon beam uniform across the field for standard treatments.
4. Which interaction predominates for 1 MeV photons in soft tissue?
A. Photoelectric effect
B. Compton scattering
C. Pair production
D. Coherent scattering
B. Compton scattering
At intermediate energies (around 1 MeV), Compton scattering is the
dominant interaction in soft tissue.
5. The unit Gray (Gy) is used to measure:
A. Absorbed dose
B. Equivalent dose
C. Activity
D. Exposure
A. Absorbed dose
1 Gy = 1 joule/kg and measures the energy deposited per unit mass of
tissue.
6. In MRI, T1 relaxation time refers to:
A. Spin-spin relaxation
B. Spin-lattice relaxation
C. Free induction decay
D. Chemical shift
, B. Spin-lattice relaxation
T1 measures the time constant for the recovery of longitudinal
magnetization along the magnetic field.
7. In CT imaging, increasing the tube current (mA) will primarily:
A. Increase spatial resolution
B. Increase image noise
C. Increase patient dose
D. Reduce scan time
C. Increase patient dose
Increasing mA increases the number of x-ray photons, which raises the
patient dose without significantly affecting spatial resolution.
8. The purpose of a bowtie filter in CT is to:
A. Improve temporal resolution
B. Reduce beam hardening and patient dose
C. Increase image contrast
D. Increase tube output
B. Reduce beam hardening and patient dose
Bowtie filters shape the x-ray beam intensity, reducing unnecessary
dose at the periphery and minimizing artifacts.
9. The Compton effect results in:
A. Absorption of photon
B. Scattering of photon with energy loss
C. Production of positrons
D. No change in photon direction
B. Scattering of photon with energy loss
Compton scattering causes deflection of the photon and energy transfer
to an electron.
