Radiology and Diagnostic Imaging Exam Prep – Real Practice Questions,
Answers & Detailed Rationales (Updated 2026) 🩻 | Radiographic
Imaging Procedures & Patient Positioning, X-Ray Physics & Exposure
Factors, CT, MRI & Ultrasound Basics, Radiation Protection & Safety
Standards, Anatomy for Diagnostic Imaging, Image Evaluation Techniques,
Clinical Patient Care & Radiologic Technology Review
Question 1: Which imaging modality utilizes ionizing radiation and provides cross-
sectional images by measuring the attenuation of X-rays through different tissues?
A. Magnetic Resonance Imaging
B. Ultrasound
C. Computed Tomography
D. Nuclear Medicine Scintigraphy
CORRECT ANSWER: C. Computed Tomography
Rationale: Computed Tomography (CT) uses rotating X-ray sources and detectors to
acquire multiple projection images, which are reconstructed into cross-sectional slices
based on differential X-ray attenuation by tissues. MRI uses magnetic fields and
radiofrequency pulses without ionizing radiation; ultrasound uses high-frequency sound
waves; nuclear medicine involves radiopharmaceuticals and gamma camera detection,
not X-ray attenuation-based cross-sectional reconstruction.
Question 2: In radiographic imaging, what is the primary purpose of using a grid
between the patient and the image receptor?
A. To increase patient dose for better image quality
B. To reduce scatter radiation reaching the image receptor
C. To magnify the anatomical structures of interest
D. To decrease exposure time and motion artifact
CORRECT ANSWER: B. To reduce scatter radiation reaching the image receptor
Rationale: Grids consist of alternating strips of radiopaque material (usually lead) and
radiolucent interspace material, oriented to absorb scattered photons that deviate from
the primary beam direction. This improves image contrast by reducing fog from
Compton scatter. Grids do increase patient dose slightly due to the need for higher
exposure factors, but their primary function is scatter reduction, not magnification or
exposure time reduction.
Question 3: Which of the following MRI sequences is most sensitive for detecting
acute cerebral ischemia within the first 6 hours of symptom onset?
A. T1-weighted imaging
B. T2-weighted imaging
C. Diffusion-weighted imaging (DWI)
D. Gradient-echo imaging
CORRECT ANSWER: C. Diffusion-weighted imaging (DWI)
,Rationale: DWI detects restricted diffusion of water molecules in cytotoxic edema,
which occurs within minutes of acute ischemic stroke due to failure of energy-
dependent ion pumps. This makes DWI highly sensitive and specific for acute
infarction, often showing abnormalities before changes are visible on CT or
conventional MRI sequences. T1 and T2 sequences typically show changes only after
several hours; gradient-echo is sensitive to hemorrhage but not early ischemia.
Question 4: What is the primary mechanism by which iodinated contrast agents
enhance visibility of vascular structures on CT imaging?
A. They emit gamma rays detectable by the CT scanner
B. They increase the photoelectric effect due to high atomic number
C. They alter the magnetic properties of blood for better MRI signal
D. They absorb ultrasound waves to create acoustic shadowing
CORRECT ANSWER: B. They increase the photoelectric effect due to high atomic
number
Rationale: Iodine (atomic number 53) has a high photoelectric absorption coefficient at
diagnostic X-ray energies. When iodinated contrast is administered intravenously, it
increases X-ray attenuation in blood vessels and perfused tissues, creating greater
contrast between enhanced and non-enhanced structures. This is fundamentally
different from MRI contrast (which affects relaxation times) or ultrasound contrast
(microbubble-based).
Question 5: Which radiographic finding is most characteristic of a tension
pneumothorax on a supine chest X-ray?
A. Deep sulcus sign
B. Silhouette sign
C. Air bronchogram
D. Hampton's hump
CORRECT ANSWER: A. Deep sulcus sign
Rationale: In supine patients, free intrapleural air collects anteriorly and inferiorly,
causing exaggerated lucency of the costophrenic angle—the "deep sulcus sign." This is
a critical finding in trauma imaging. The silhouette sign indicates loss of border
definition between structures of similar density; air bronchograms suggest alveolar
filling processes; Hampton's hump is a wedge-shaped peripheral opacity suggestive of
pulmonary infarction.
Question 6: What is the recommended annual occupational dose limit for the lens
of the eye for radiation workers, according to the International Commission on
Radiological Protection (ICRP)?
A. 15 mSv
B. 20 mSv
,C. 50 mSv
D. 150 mSv
CORRECT ANSWER: A. 15 mSv
Rationale: The ICRP reduced the annual equivalent dose limit for the lens of the eye
from 150 mSv to 20 mSv averaged over 5 years (with no single year exceeding 50 mSv) in
2011, and many jurisdictions have adopted a stricter 15 mSv/year limit based on
emerging evidence of radiation-induced cataracts at lower doses. This reflects
heightened protection for radiosensitive ocular tissues. Options B, C, and D represent
outdated or incorrect values.
Question 7: In ultrasound imaging, what artifact is characterized by equally spaced,
parallel lines deep to a strong reflector, caused by reverberation of the sound
beam?
A. Shadowing
B. Enhancement
C. Ring-down artifact
D. Comet-tail artifact
CORRECT ANSWER: C. Ring-down artifact
Rationale: Ring-down artifact appears as a series of parallel lines extending deep to a
highly reflective interface (e.g., gas or metal) due to continuous oscillation of the
reflector or trapped gas bubbles re-emitting sound. It is distinct from comet-tail artifact
(a short, tapering series of echoes), shadowing (signal loss behind attenuating
structures), or enhancement (increased brightness behind fluid-filled structures).
Question 8: Which of the following is a contraindication to administering
gadolinium-based contrast agents in MRI?
A. History of asthma
B. Estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73m²
C. Claustrophobia
D. Presence of a titanium orthopedic implant
CORRECT ANSWER: B. Estimated glomerular filtration rate (eGFR) < 30
mL/min/1.73m²
Rationale: Severely impaired renal function (eGFR < 30) significantly increases the risk
of nephrogenic systemic fibrosis (NSF), a rare but serious condition associated with
certain linear gadolinium agents. Asthma is not a direct contraindication (though
caution with any contrast is prudent); claustrophobia may require sedation but does not
preclude contrast use; titanium implants are MRI-safe and do not interact with
gadolinium.
Question 9: What is the primary advantage of digital radiography (DR) over
computed radiography (CR)?
, A. Lower initial equipment cost
B. Higher spatial resolution
C. Immediate image availability and wider dynamic range
D. Reduced need for radiation protection measures
CORRECT ANSWER: C. Immediate image availability and wider dynamic range
Rationale: DR systems use direct or indirect flat-panel detectors that provide near-
instantaneous image display and possess a wider exposure latitude (dynamic range)
than CR, reducing repeat exams due to exposure errors. CR uses photostimulable
phosphor plates requiring separate scanning, causing delay. DR does not inherently
offer higher spatial resolution than CR, and radiation protection requirements remain
unchanged.
Question 10: Which radiographic view is optimal for evaluating the scaphoid bone
for occult fracture?
A. Posteroanterior (PA) wrist
B. Lateral wrist
C. PA with ulnar deviation (scaphoid view)
D. Oblique wrist
CORRECT ANSWER: C. PA with ulnar deviation (scaphoid view)
Rationale: Ulnar deviation elongates and unfolds the scaphoid, minimizing
foreshortening and superimposition from adjacent carpal bones, thereby improving
detection of fractures. Standard PA, lateral, or oblique views may miss nondisplaced
scaphoid fractures due to overlapping structures. This specialized projection is critical
in trauma evaluation when clinical suspicion remains high despite normal initial films.
Question 11: In nuclear medicine, what does the term "half-life" refer to regarding a
radiopharmaceutical?
A. Time required for the biological elimination of 50% of the agent
B. Time for the radioactivity of the isotope to decrease by 50% due to physical decay
C. Duration of optimal imaging window after administration
D. Period during which the agent remains bound to its target receptor
CORRECT ANSWER: B. Time for the radioactivity of the isotope to decrease by 50%
due to physical decay
Rationale: Physical half-life is an intrinsic property of a radionuclide, defined as the time
required for half of the radioactive atoms to undergo decay, independent of biological
processes. Biological half-life refers to elimination by physiological mechanisms;
effective half-life combines both. The imaging window and receptor binding duration are
clinical considerations but not the definition of half-life.
Question 12: Which finding on a non-contrast head CT is most suggestive of an
acute subdural hematoma?
Answers & Detailed Rationales (Updated 2026) 🩻 | Radiographic
Imaging Procedures & Patient Positioning, X-Ray Physics & Exposure
Factors, CT, MRI & Ultrasound Basics, Radiation Protection & Safety
Standards, Anatomy for Diagnostic Imaging, Image Evaluation Techniques,
Clinical Patient Care & Radiologic Technology Review
Question 1: Which imaging modality utilizes ionizing radiation and provides cross-
sectional images by measuring the attenuation of X-rays through different tissues?
A. Magnetic Resonance Imaging
B. Ultrasound
C. Computed Tomography
D. Nuclear Medicine Scintigraphy
CORRECT ANSWER: C. Computed Tomography
Rationale: Computed Tomography (CT) uses rotating X-ray sources and detectors to
acquire multiple projection images, which are reconstructed into cross-sectional slices
based on differential X-ray attenuation by tissues. MRI uses magnetic fields and
radiofrequency pulses without ionizing radiation; ultrasound uses high-frequency sound
waves; nuclear medicine involves radiopharmaceuticals and gamma camera detection,
not X-ray attenuation-based cross-sectional reconstruction.
Question 2: In radiographic imaging, what is the primary purpose of using a grid
between the patient and the image receptor?
A. To increase patient dose for better image quality
B. To reduce scatter radiation reaching the image receptor
C. To magnify the anatomical structures of interest
D. To decrease exposure time and motion artifact
CORRECT ANSWER: B. To reduce scatter radiation reaching the image receptor
Rationale: Grids consist of alternating strips of radiopaque material (usually lead) and
radiolucent interspace material, oriented to absorb scattered photons that deviate from
the primary beam direction. This improves image contrast by reducing fog from
Compton scatter. Grids do increase patient dose slightly due to the need for higher
exposure factors, but their primary function is scatter reduction, not magnification or
exposure time reduction.
Question 3: Which of the following MRI sequences is most sensitive for detecting
acute cerebral ischemia within the first 6 hours of symptom onset?
A. T1-weighted imaging
B. T2-weighted imaging
C. Diffusion-weighted imaging (DWI)
D. Gradient-echo imaging
CORRECT ANSWER: C. Diffusion-weighted imaging (DWI)
,Rationale: DWI detects restricted diffusion of water molecules in cytotoxic edema,
which occurs within minutes of acute ischemic stroke due to failure of energy-
dependent ion pumps. This makes DWI highly sensitive and specific for acute
infarction, often showing abnormalities before changes are visible on CT or
conventional MRI sequences. T1 and T2 sequences typically show changes only after
several hours; gradient-echo is sensitive to hemorrhage but not early ischemia.
Question 4: What is the primary mechanism by which iodinated contrast agents
enhance visibility of vascular structures on CT imaging?
A. They emit gamma rays detectable by the CT scanner
B. They increase the photoelectric effect due to high atomic number
C. They alter the magnetic properties of blood for better MRI signal
D. They absorb ultrasound waves to create acoustic shadowing
CORRECT ANSWER: B. They increase the photoelectric effect due to high atomic
number
Rationale: Iodine (atomic number 53) has a high photoelectric absorption coefficient at
diagnostic X-ray energies. When iodinated contrast is administered intravenously, it
increases X-ray attenuation in blood vessels and perfused tissues, creating greater
contrast between enhanced and non-enhanced structures. This is fundamentally
different from MRI contrast (which affects relaxation times) or ultrasound contrast
(microbubble-based).
Question 5: Which radiographic finding is most characteristic of a tension
pneumothorax on a supine chest X-ray?
A. Deep sulcus sign
B. Silhouette sign
C. Air bronchogram
D. Hampton's hump
CORRECT ANSWER: A. Deep sulcus sign
Rationale: In supine patients, free intrapleural air collects anteriorly and inferiorly,
causing exaggerated lucency of the costophrenic angle—the "deep sulcus sign." This is
a critical finding in trauma imaging. The silhouette sign indicates loss of border
definition between structures of similar density; air bronchograms suggest alveolar
filling processes; Hampton's hump is a wedge-shaped peripheral opacity suggestive of
pulmonary infarction.
Question 6: What is the recommended annual occupational dose limit for the lens
of the eye for radiation workers, according to the International Commission on
Radiological Protection (ICRP)?
A. 15 mSv
B. 20 mSv
,C. 50 mSv
D. 150 mSv
CORRECT ANSWER: A. 15 mSv
Rationale: The ICRP reduced the annual equivalent dose limit for the lens of the eye
from 150 mSv to 20 mSv averaged over 5 years (with no single year exceeding 50 mSv) in
2011, and many jurisdictions have adopted a stricter 15 mSv/year limit based on
emerging evidence of radiation-induced cataracts at lower doses. This reflects
heightened protection for radiosensitive ocular tissues. Options B, C, and D represent
outdated or incorrect values.
Question 7: In ultrasound imaging, what artifact is characterized by equally spaced,
parallel lines deep to a strong reflector, caused by reverberation of the sound
beam?
A. Shadowing
B. Enhancement
C. Ring-down artifact
D. Comet-tail artifact
CORRECT ANSWER: C. Ring-down artifact
Rationale: Ring-down artifact appears as a series of parallel lines extending deep to a
highly reflective interface (e.g., gas or metal) due to continuous oscillation of the
reflector or trapped gas bubbles re-emitting sound. It is distinct from comet-tail artifact
(a short, tapering series of echoes), shadowing (signal loss behind attenuating
structures), or enhancement (increased brightness behind fluid-filled structures).
Question 8: Which of the following is a contraindication to administering
gadolinium-based contrast agents in MRI?
A. History of asthma
B. Estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73m²
C. Claustrophobia
D. Presence of a titanium orthopedic implant
CORRECT ANSWER: B. Estimated glomerular filtration rate (eGFR) < 30
mL/min/1.73m²
Rationale: Severely impaired renal function (eGFR < 30) significantly increases the risk
of nephrogenic systemic fibrosis (NSF), a rare but serious condition associated with
certain linear gadolinium agents. Asthma is not a direct contraindication (though
caution with any contrast is prudent); claustrophobia may require sedation but does not
preclude contrast use; titanium implants are MRI-safe and do not interact with
gadolinium.
Question 9: What is the primary advantage of digital radiography (DR) over
computed radiography (CR)?
, A. Lower initial equipment cost
B. Higher spatial resolution
C. Immediate image availability and wider dynamic range
D. Reduced need for radiation protection measures
CORRECT ANSWER: C. Immediate image availability and wider dynamic range
Rationale: DR systems use direct or indirect flat-panel detectors that provide near-
instantaneous image display and possess a wider exposure latitude (dynamic range)
than CR, reducing repeat exams due to exposure errors. CR uses photostimulable
phosphor plates requiring separate scanning, causing delay. DR does not inherently
offer higher spatial resolution than CR, and radiation protection requirements remain
unchanged.
Question 10: Which radiographic view is optimal for evaluating the scaphoid bone
for occult fracture?
A. Posteroanterior (PA) wrist
B. Lateral wrist
C. PA with ulnar deviation (scaphoid view)
D. Oblique wrist
CORRECT ANSWER: C. PA with ulnar deviation (scaphoid view)
Rationale: Ulnar deviation elongates and unfolds the scaphoid, minimizing
foreshortening and superimposition from adjacent carpal bones, thereby improving
detection of fractures. Standard PA, lateral, or oblique views may miss nondisplaced
scaphoid fractures due to overlapping structures. This specialized projection is critical
in trauma evaluation when clinical suspicion remains high despite normal initial films.
Question 11: In nuclear medicine, what does the term "half-life" refer to regarding a
radiopharmaceutical?
A. Time required for the biological elimination of 50% of the agent
B. Time for the radioactivity of the isotope to decrease by 50% due to physical decay
C. Duration of optimal imaging window after administration
D. Period during which the agent remains bound to its target receptor
CORRECT ANSWER: B. Time for the radioactivity of the isotope to decrease by 50%
due to physical decay
Rationale: Physical half-life is an intrinsic property of a radionuclide, defined as the time
required for half of the radioactive atoms to undergo decay, independent of biological
processes. Biological half-life refers to elimination by physiological mechanisms;
effective half-life combines both. The imaging window and receptor binding duration are
clinical considerations but not the definition of half-life.
Question 12: Which finding on a non-contrast head CT is most suggestive of an
acute subdural hematoma?
