HESI RADIOLOGY EXIT EXAM PREP VERSION 3 2026/2027
ELSEVIER EVOLVE – COMPREHENSIVE RADIOLOGIC SCIENCES
COMPETENCY ASSESSMENT
SECTION 1: RADIATION PHYSICS (QUESTIONS 1-10)
Question 1
What is the primary source of radiation used in diagnostic radiography?
A) Alpha particles
B) Beta particles
C) X-rays produced by an X-ray tube
D) Gamma rays from radioactive isotopes
Answer: C) X-rays produced by an X-ray tube
Rationale: Diagnostic radiography uses X-rays produced by an X-ray tube. X-rays are a
form of electromagnetic radiation produced when high-speed electrons collide with a
metal target (tungsten) in the X-ray tube. Alpha particles (A) and beta particles (B) are
particulate radiation used in nuclear medicine but not in general radiography. Gamma
rays (D) are used in nuclear medicine (gamma cameras) but not in general radiography.
X-rays have high energy and short wavelength, allowing them to penetrate tissue.
Question 2
Which component of the X-ray tube is the source of electrons?
A) Anode
B) Cathode
C) Stator
D) Glass envelope
,Answer: B) Cathode
Rationale: The cathode is the negative electrode in the X-ray tube and contains the
filament (usually tungsten) that emits electrons when heated (thermionic emission). The
anode (A) is the positive electrode that receives the electrons and produces X-rays (the
target). The stator (C) is part of the induction motor that rotates the anode. The glass
envelope (D) encloses the tube and maintains a vacuum. The cathode current controls
the number of electrons (tube current, mA), which determines the quantity of X-rays
produced.
Question 3
The quantity of X-rays produced is primarily controlled by:
A) Kilovoltage peak (kVp)
B) Milliamperage (mA) and exposure time (seconds)
C) Focal spot size
D) Added filtration
Answer: B) Milliamperage (mA) and exposure time (seconds)
Rationale: The quantity of X-rays (number of X-ray photons) is directly proportional to
the milliamperage (mA) and exposure time (seconds). The product of mA and time is mAs
(milliampere-seconds). mAs controls the total number of electrons striking the anode,
which determines the number of X-ray photons produced. Kilovoltage peak (kVp) (A)
controls the quality (energy/penetrating power) of X-rays, not the quantity. Focal spot
size (C) affects spatial resolution but not quantity. Added filtration (D) removes low-
energy X-rays (beam hardening) but does not increase quantity.
Question 4
The quality (energy/penetrating power) of X-rays is primarily controlled by:
A) Milliamperage (mA)
B) Exposure time (seconds)
C) Kilovoltage peak (kVp)
,D) Focal spot size
Answer: C) Kilovoltage peak (kVp)
Rationale: Kilovoltage peak (kVp) controls the maximum energy of X-ray photons (peak
energy in kiloelectron volts, keV). Higher kVp produces X-rays with higher energy (more
penetrating power), which affects the quality of the image (contrast). Lower kVp
produces lower energy X-rays (less penetrating), which increases subject contrast. kVp
also affects the quantity of X-rays proportionally to the square of kVp. mA (A) and
exposure time (B) control quantity, not quality. Focal spot size (D) affects spatial
resolution, not X-ray quality.
Question 5
The primary function of the grid in radiography is to:
A) Increase the X-ray beam intensity
B) Reduce scatter radiation reaching the image receptor
C) Increase patient dose
D) Decrease image contrast
Answer: B) Reduce scatter radiation reaching the image receptor
Rationale: The grid is placed between the patient and the image receptor. Its primary
function is to absorb scatter radiation (Compton scatter) produced within the patient,
which reduces image fog and improves image contrast. Scatter radiation degrades image
quality by adding unwanted exposure to the image receptor without diagnostic
information. Grids are typically used for body parts thicker than 10-12 cm and for higher
kVp techniques. Option A: grids do not increase beam intensity; they reduce it (grid
factor). Option C: grids increase patient dose because the technique must be increased
to compensate for grid absorption. Option D: grids improve contrast, not decrease it.
Question 6
Which of the following is a characteristic of X-rays?
, A) They are visible light
B) They are a form of ionizing radiation
C) They are produced by radioactive decay
D) They have a long wavelength
Answer: B) They are a form of ionizing radiation
Rationale: X-rays are a form of ionizing radiation, meaning they have enough energy to
remove electrons from atoms (ionization), which can cause biological damage (DNA
damage). X-rays are invisible (A) and cannot be seen by the human eye. They are
produced by an X-ray tube (C), not by radioactive decay (gamma rays are produced by
radioactive decay). X-rays have short wavelengths (D) (0.01-10 nanometers), shorter than
visible light. The ionizing nature of X-rays requires radiation protection measures (time,
distance, shielding).
Question 7
The inverse square law states that the intensity of radiation is:
A) Directly proportional to the square of the distance from the source
B) Inversely proportional to the square of the distance from the source
C) Directly proportional to the distance from the source
D) Inversely proportional to the distance from the source
Answer: B) Inversely proportional to the square of the distance from the source
Rationale: The inverse square law states that the intensity of radiation (I) is inversely
proportional to the square of the distance (d) from the source: I1/I2 = (d2)2/(d1)2. As
distance doubles, the intensity decreases to one-quarter (1/4). As distance triples,
intensity decreases to one-ninth (1/9). This principle is used in radiation protection to
reduce exposure (increasing distance from the source). It applies to point sources of
radiation (X-ray tube, radioactive source). For example, if the distance from the X-ray
tube is doubled, the exposure to the patient or technologist decreases by a factor of 4.
Question 8
ELSEVIER EVOLVE – COMPREHENSIVE RADIOLOGIC SCIENCES
COMPETENCY ASSESSMENT
SECTION 1: RADIATION PHYSICS (QUESTIONS 1-10)
Question 1
What is the primary source of radiation used in diagnostic radiography?
A) Alpha particles
B) Beta particles
C) X-rays produced by an X-ray tube
D) Gamma rays from radioactive isotopes
Answer: C) X-rays produced by an X-ray tube
Rationale: Diagnostic radiography uses X-rays produced by an X-ray tube. X-rays are a
form of electromagnetic radiation produced when high-speed electrons collide with a
metal target (tungsten) in the X-ray tube. Alpha particles (A) and beta particles (B) are
particulate radiation used in nuclear medicine but not in general radiography. Gamma
rays (D) are used in nuclear medicine (gamma cameras) but not in general radiography.
X-rays have high energy and short wavelength, allowing them to penetrate tissue.
Question 2
Which component of the X-ray tube is the source of electrons?
A) Anode
B) Cathode
C) Stator
D) Glass envelope
,Answer: B) Cathode
Rationale: The cathode is the negative electrode in the X-ray tube and contains the
filament (usually tungsten) that emits electrons when heated (thermionic emission). The
anode (A) is the positive electrode that receives the electrons and produces X-rays (the
target). The stator (C) is part of the induction motor that rotates the anode. The glass
envelope (D) encloses the tube and maintains a vacuum. The cathode current controls
the number of electrons (tube current, mA), which determines the quantity of X-rays
produced.
Question 3
The quantity of X-rays produced is primarily controlled by:
A) Kilovoltage peak (kVp)
B) Milliamperage (mA) and exposure time (seconds)
C) Focal spot size
D) Added filtration
Answer: B) Milliamperage (mA) and exposure time (seconds)
Rationale: The quantity of X-rays (number of X-ray photons) is directly proportional to
the milliamperage (mA) and exposure time (seconds). The product of mA and time is mAs
(milliampere-seconds). mAs controls the total number of electrons striking the anode,
which determines the number of X-ray photons produced. Kilovoltage peak (kVp) (A)
controls the quality (energy/penetrating power) of X-rays, not the quantity. Focal spot
size (C) affects spatial resolution but not quantity. Added filtration (D) removes low-
energy X-rays (beam hardening) but does not increase quantity.
Question 4
The quality (energy/penetrating power) of X-rays is primarily controlled by:
A) Milliamperage (mA)
B) Exposure time (seconds)
C) Kilovoltage peak (kVp)
,D) Focal spot size
Answer: C) Kilovoltage peak (kVp)
Rationale: Kilovoltage peak (kVp) controls the maximum energy of X-ray photons (peak
energy in kiloelectron volts, keV). Higher kVp produces X-rays with higher energy (more
penetrating power), which affects the quality of the image (contrast). Lower kVp
produces lower energy X-rays (less penetrating), which increases subject contrast. kVp
also affects the quantity of X-rays proportionally to the square of kVp. mA (A) and
exposure time (B) control quantity, not quality. Focal spot size (D) affects spatial
resolution, not X-ray quality.
Question 5
The primary function of the grid in radiography is to:
A) Increase the X-ray beam intensity
B) Reduce scatter radiation reaching the image receptor
C) Increase patient dose
D) Decrease image contrast
Answer: B) Reduce scatter radiation reaching the image receptor
Rationale: The grid is placed between the patient and the image receptor. Its primary
function is to absorb scatter radiation (Compton scatter) produced within the patient,
which reduces image fog and improves image contrast. Scatter radiation degrades image
quality by adding unwanted exposure to the image receptor without diagnostic
information. Grids are typically used for body parts thicker than 10-12 cm and for higher
kVp techniques. Option A: grids do not increase beam intensity; they reduce it (grid
factor). Option C: grids increase patient dose because the technique must be increased
to compensate for grid absorption. Option D: grids improve contrast, not decrease it.
Question 6
Which of the following is a characteristic of X-rays?
, A) They are visible light
B) They are a form of ionizing radiation
C) They are produced by radioactive decay
D) They have a long wavelength
Answer: B) They are a form of ionizing radiation
Rationale: X-rays are a form of ionizing radiation, meaning they have enough energy to
remove electrons from atoms (ionization), which can cause biological damage (DNA
damage). X-rays are invisible (A) and cannot be seen by the human eye. They are
produced by an X-ray tube (C), not by radioactive decay (gamma rays are produced by
radioactive decay). X-rays have short wavelengths (D) (0.01-10 nanometers), shorter than
visible light. The ionizing nature of X-rays requires radiation protection measures (time,
distance, shielding).
Question 7
The inverse square law states that the intensity of radiation is:
A) Directly proportional to the square of the distance from the source
B) Inversely proportional to the square of the distance from the source
C) Directly proportional to the distance from the source
D) Inversely proportional to the distance from the source
Answer: B) Inversely proportional to the square of the distance from the source
Rationale: The inverse square law states that the intensity of radiation (I) is inversely
proportional to the square of the distance (d) from the source: I1/I2 = (d2)2/(d1)2. As
distance doubles, the intensity decreases to one-quarter (1/4). As distance triples,
intensity decreases to one-ninth (1/9). This principle is used in radiation protection to
reduce exposure (increasing distance from the source). It applies to point sources of
radiation (X-ray tube, radioactive source). For example, if the distance from the X-ray
tube is doubled, the exposure to the patient or technologist decreases by a factor of 4.
Question 8
