Free ARRT Radiography Practice Test

Answer: C. A longer SID means less beam divergence, so structures that sit away from the image receptor are magnified less. That's why the heart's size can be judged on a 72-inch PA chest. A is backwards: a longer SID needs more mAs to keep receptor exposure, not less. B and D aren't the reason for the distance standard.

Source: UMS Radiographic Procedures Review — Chest, PA chest

Answer: A. Use two patient-specific identifiers, such as name and date of birth, and have the patient state them. The Joint Commission says a room number is not an acceptable identifier (C). A yes/no question (B) invites an anxious or hard-of-hearing patient to agree with the wrong name, so open-ended questions are standard good practice. A family member's word (D) isn't verification against the order.

Source: The Joint Commission — Two Patient Identifiers FAQ

Answer: D. The filament circuit heats the tungsten filament until electrons boil off its surface. That's thermionic emission, and it supplies the electrons that kVp then accelerates toward the anode. Characteristic interactions (A) happen at the target after the electrons arrive. The step-up transformer (B) provides kilovoltage, not electrons. Compton interactions (C) are photon events, not an electron source.

Source: Radiopaedia — Thermionic emission

Answer: B. Receptor exposure is directly proportional to mAs, so going from half the target to the target means doubling 10 mAs to 20 mAs. The grain is quantum mottle: too few photons reached the detector. A smoothing filter (C) can hide it cosmetically but can't add the missing signal. Cutting mAs (A) makes it worse. Dropping kVp about 15% (D) roughly halves receptor exposure, canceling the mAs increase.

In AAPM terms, half the target exposure is a deviation index of about −3.

Sources: Radiopaedia — Quantum noise · AAPM Report 116 executive summary

Answer: C. When the hand is rotated about 45°, the fingers drop toward the IR. If they aren't supported parallel to it, the phalanges foreshorten and the IP joints close. A radiolucent step sponge fixes that. Letting the fingertips rest on the IR (D) is the error itself. Over-rotating (A) causes metacarpal overlap. Angling the CR (B) doesn't correct finger position.

Sources: Radiopaedia — Hand (oblique view) · UMS — Hand

Answer: A. Treating the patient as a rough point source, intensity follows the inverse square law: double the distance and exposure falls to (1/2)², or one-quarter. Scatter does go in all directions (D), which is exactly why distance works in every direction. One-half (B) is the linear mistake.

Source: Radiopaedia — Inverse square law

Answer: D. Typical ripple: single-phase about 100%, three-phase six-pulse about 13–14%, three-phase twelve-pulse about 4%, high-frequency about 1% or less. Lower ripple means a more nearly constant voltage, a higher average photon energy, and more efficient x-ray production.

Source: Radiopaedia — Ripple

Answer: A. With 15° caudal angulation exiting at the nasion, the petrous ridges land in the lower third of the orbits. The foramen magnum (B) is where the dorsum sellae belongs on an AP axial (Towne). Ridges just below the maxillary sinuses (C) is the Waters criterion. D isn't produced by a correctly angled Caldwell.

Source: UMS — Skull, PA axial (Caldwell)

Answer: C. When a patient is unconscious, can't give consent, and needs urgent care, consent is implied. An unresponsive patient can't give oral consent (B), and a radiographer can't consent on the patient's behalf (A). Waiting for a guardian (D) would delay necessary emergency care.

Source: Cornell LII Wex — Implied consent

Answer: A. Bremsstrahlung ("braking") radiation forms when a projectile electron slows near a target nucleus. Below 70 kVp the beam is essentially all bremsstrahlung. Above 70 kVp, tungsten K-characteristic x-rays (about 69.5 keV) appear but still make up only around 15%. Photoelectric and coherent interactions (C, D) happen in the patient, not in the tube.

Source: Radiopaedia — Bremsstrahlung

Answer: D. A 15% kVp increase roughly doubles receptor exposure, so mAs is halved: 70 × 1.15 = 80.5, so about 80 kVp at 10 mAs. Patient dose drops by about a third, not half, because entrance dose scales roughly with kVp² × mAs (1.15² × 0.5 ≈ 0.66). The tradeoff is lower subject contrast. A raises dose. B doubles receptor exposure. C halves it.

Source: How Radiology Works — The 15% rule

Answer: B. An AP thumb needs extreme medial rotation of the hand so the thumbnail side lies flat on the IR, centered to the first MCP joint. A PA thumb (C) adds OID and magnification. A describes a lateral thumb. D is neither centering nor rotation for the thumb.

Source: UMS — Fingers and thumb, AP thumb

Answer: C. Less irradiated tissue means less patient dose and less scatter produced. A higher-ratio grid (A) reduces scatter at the detector but requires more exposure, so dose goes up. A shorter SID (B) raises entrance skin dose. Opening the field (D) does the opposite of what's needed.

Sources: Image Gently — Digital radiography · Image Wisely — Fluoroscopy checklists

Answer: A. Rectifiers keep current flowing one way through the tube, protecting it and making every half-cycle useful. Raising voltage to kilovolts (B) is the step-up transformer's job. Filament heating (C) belongs to the filament circuit.

Source: Radiopaedia — High-voltage generator

Answer: D. A correct Waters places the OML at 37° to the IR, which drops the petrous ridges just below the maxillary sinuses. Ridges over the sinuses mean the chin wasn't extended enough. Tucking the chin (A) makes it worse. The Waters uses a perpendicular CR to the IR, not a caudal angle (B).

Source: UMS — Paranasal sinuses, parietoacanthial (Waters)

Answer: B. Battery is intentional harmful or offensive contact without consent, and the patient's refusal withdrew consent. Assault (A) is causing fear of contact without the contact itself. Libel (C) is written defamation. Res ipsa loquitur (D) is a negligence doctrine, "the thing speaks for itself."

Source: Cornell LII Wex — Battery

Answer: B. Inverse square law: 2.0 × (100/200)² = 2.0 × 0.25 = 0.5 mGy. 1.0 mGy (C) applies distance linearly. 0.25 mGy (A) squares twice. 4.0 mGy (D) inverts the ratio.

Source: Radiopaedia — Inverse square law

Answer: D. The exposure maintenance formula is the inverse square law turned around: new mAs = old mAs × (new SID / old SID)² = 10 × (72/40)² = 10 × 3.24 = 32.4 mAs. 18 mAs (C) uses the ratio without squaring it. 5.6 mAs (A) moves in the wrong direction.

Source: Calculation from the inverse square law — Radiopaedia — Inverse square law

Answer: D. The air kerma at the center of the beam doesn't change, but the area goes from 100 cm² to 400 cm². Four times the area means four times the DAP. That's four times as much tissue irradiated and more scatter produced, which is the radiation-protection case for tight collimation in one number. "The same" (B) reflects only the center-of-field air kerma.

Source: Calculation from the DAP definition given in the stem. DAP meters are listed under Radiation Protection in ARRT's 2022 Radiography content specifications.

Answer: B. Ten posterior ribs above the diaphragm is the standard criterion for a good inspiration. Seven (A) is a poor inspiration. Clavicles above the apices (C) describes an AP lordotic. Equidistant sternal clavicle ends (D) is the check for rotation, not inspiration.

Source: UMS — Chest, image evaluation

Answer: C. The induction motor's stator sits outside the tube envelope and the rotor sits inside, spinning the anode. The electron beam hits a moving track, so heat spreads around the circumference instead of one spot. The heel effect (B) still exists. Focal spot size (A) is set by the filament, the focusing cup, and the target angle.

Source: Varex Imaging — How x-ray tubes work

Answer: A. Ulnar deviation elongates the scaphoid and opens the spaces around it. Radial deviation (B) is used to open the medial (ulnar-side) carpals instead. 45° medial rotation (D) moves the wrist into a medial oblique rather than opening the scaphoid.

Source: UMS — Wrist, PA ulnar deviation

Answer: D. With 30° caudad to the OML (or 37° to the IOML), the dorsum sellae and posterior clinoids project inside the foramen magnum. If they fall outside it, check the CR angle and the head's flexion before repeating.

Source: UMS — Skull, AP axial (Towne)

Answer: C. Respondeat superior ("let the master answer") makes an employer liable for an employee's acts within the scope of employment. Res ipsa loquitur (A) lets negligence be inferred from the event itself. Stare decisis (B) is following precedent. Primum non nocere (D) means "first, do no harm," an ethical principle, not a liability doctrine.

Source: Cornell LII Wex — Respondeat superior

Answer: A. Low-energy photons add to entrance dose but rarely contribute to the image. Filtering them out raises the beam's average energy (beam hardening) and lowers skin dose. It does the opposite of B, doesn't change the kVp setting (C), and isn't a scatter-control device (D).

Source: Radiopaedia — Filters

Answer: D. The Privacy Rule allows disclosure for treatment without authorization, and the minimum-necessary standard doesn't apply to treatment disclosures. A, B, and C have no treatment, payment, or operations purpose and need the patient's authorization.

Sources: 45 CFR 164.506(c) · HHS — Disclosures for treatment, payment, and operations

Answer: A. Fluid settles and air rises only when the patient is upright, and only a horizontal beam can show the flat interface between them. Angling the CR on an upright patient blurs that line.

Source: UMS — Paranasal sinuses

Answer: A, B, and C. Lower pulse rates, last-image hold, and collimation all cut beam-on dose. Magnification mode (D) raises the dose rate, so the lowest practical magnification is the goal. Keeping the image receptor close to the patient lowers dose, so increasing the gap (E) raises it.

Source: Image Wisely — Fluoroscopy checklists

Answer: C. Going from no grid to a grid: new mAs = old mAs × grid conversion factor = 5 × 5 = 25 mAs. The grid absorbs scatter and some primary radiation, so exposure has to go up. Dividing (A) is the reverse move, used when removing a grid.

Source: Calculation using the grid conversion factor given in the stem. Grids appear under Image Acquisition in ARRT's content specifications.

Answer: D. With the wrist hyperextended and the CR about 25–30° to the long axis of the hand, the beam looks down the carpal canal, showing the pisiform and the hamulus in profile. A is the ulnar-deviation PA. B is the lateral-rotation elbow oblique.

Source: UMS — Wrist, Gaynor-Hart

Answer: C. Photoelectric probability rises roughly with Z³ and falls roughly with 1/E³, so high-Z bone absorbs far more photons than soft tissue. That differential absorption is subject contrast. Compton scatter (A) depends little on atomic number and degrades contrast. Pair production (D) needs photon energies above 1.02 MeV, far outside diagnostic radiography.

Source: Radiopaedia — Photoelectric effect

Answer: A. Equal distances between each sternoclavicular joint and the spine mean no rotation. B is the inspiration check. C shows the shoulders were rolled forward. D describes a lordotic projection.

Source: UMS — Chest, image evaluation

Answer: B. Effective focal spot size ≈ actual focal spot × sin(target angle). A smaller angle gives a smaller effective spot and better detail. The cost is a stronger heel effect and less field coverage, the reverse of D.

Source: Radiopaedia — Line focus principle

Answer: D. NIOSH guidance for repositioning up in bed calls for a friction-reducing device and two or three caregivers, or more for heavier patients. It says this isn't a one-person task and that there's no safe way to manually lift an adult. Keep the load close and avoid twisting the spine (B) or reaching with extended arms (C). Pulling by the arms (A) can injure the patient's shoulders.

Source: NIOSH Publication 2009-127 — Safe patient handling

Answer: C. Stationary fluoroscopes must keep the source at least 38 cm from the skin, and mobile units at least 30 cm (B). Specific surgical applications may go shorter, but never below 20 cm. Small C-arms (maximum SID under 45 cm, made on or after June 10, 2006) have a separate 19 cm limit for extremity use. A longer source-to-skin distance lowers entrance skin dose.

Source: 21 CFR 1020.32(g)

Answer: A, B, and C. Geometric unsharpness = focal spot size × OID / SOD. A smaller focal spot shrinks it, and so does a longer SID with the same OID, because SOD grows. Motion blur destroys detail no matter the geometry. mAs and kVp (D, E) change receptor exposure and contrast, not geometric sharpness.

Sources: How Radiology Works — Magnification and blurring · Motion is listed under spatial resolution in ARRT's content specifications

Answer: A. About 45° of lateral rotation separates the radial head, neck, and tuberosity from the ulna. Medial rotation (B) shows the coronoid process in profile instead. On the AP (C) and lateral (D), the radial head partly overlaps the ulna.

Source: UMS — Elbow, AP obliques

Answer: C. With the left side down and a horizontal beam, free air rises to the right side and outlines against the liver, away from the gastric air bubble. The patient should lie on that side at least 5 minutes, with 10–20 minutes preferred, so air can collect. A supine film (D) can't show an air–fluid interface. An immediate exposure (B) doesn't give air time to move.

Source: UMS — Abdomen series, lateral decubitus

Answer: D. Posterior cervical obliques show the foramina on the side away from the IR, so the LPO shows the right side. Anterior obliques (RAO/LAO, with a caudal angle) show the side closest to the IR. Lumbar obliques follow the opposite rule (see HSP-07).

Source: UMS — Cervical spine, AP axial oblique

Answer: A. The backup timer is a safety cap that prevents overexposure and tube overload if the AEC doesn't stop the exposure, for example when the wrong chamber is selected or anatomy isn't over the chamber. Federal rules cap AEC exposures at 51 kVp and above at 60 kWs or 600 mAs per exposure (2,000 mAs below 51 kVp). The shortest exposure the AEC can end is a different setting, the minimum response time (B).

Sources: 21 CFR 1020.31(a)(3)(iii) · Radiologica — Automatic exposure control

Answer: B. A nasal cannula is a low-flow device used at about 1–6 L/min. A non-rebreather (A) needs at least 10–15 L/min. A simple face mask (C) needs at least about 6 L/min so the patient doesn't rebreathe CO₂. A bag-valve mask (D) is for assisted ventilation. Don't change the ordered flow yourself; report concerns to the responsible clinician.

Source: Open RT text (WTCS) — Medical gas therapy devices

Answer: D. Compton scattering dominates in soft tissue at diagnostic energies and is the main source of scattered radiation. Most worker dose comes from that patient scatter, not the tube itself. Staff should never be in the primary beam (B), and leakage (A) is limited by the tube housing.

Sources: Health Physics Society — Ask the Experts, q9545 · Radiopaedia — Compton effect

Answer: C. 88 mGy/min is the normal-mode limit, traditionally quoted as 10 R/min. 176 mGy/min (D) is allowed only under high-level control with continuous manual activation. 44 mGy/min (B) is the rate above which the unit must have automatic exposure rate control. The limit is measured at a defined reference point, such as 1 cm above the tabletop for an under-table tube, not at the patient's skin.

Source: 21 CFR 1020.32(d)

Answer: C. SOD = SID − OID = 80 cm. Magnification factor = SID/SOD = 100/80 = 1.25. Image size = 8 × 1.25 = 10 cm. 6.4 cm (A) applies the factor backward.

Source: How Radiology Works — Magnification and blurring

Answer: D. A lateral elbow is flexed 90°, and superimposed epicondyles confirm no rotation. A full-extension lateral (A) hides the fat pads and the olecranon relationship. B describes the lateral-rotation oblique.

Source: UMS — Elbow, lateral

Answer: C. Free air rises, so the side in question goes up: a left pneumothorax needs a right lateral decubitus. Fluid does the opposite. A suspected left pleural effusion goes left side down (A).

Source: UMS — Chest, clinical applications

Answer: B. Minimum response time is the shortest exposure the AEC can end. If a thin part at high mA needs less time than that, the exposure runs long and the image is overexposed. Lower the mA or use a manual technique. A thick part (A) needs a long exposure, so the minimum isn't the issue. A short backup time (D) causes underexposure.

Sources: Radiologica — Automatic exposure control · 21 CFR 1020.31(a)(3)(ii)

Answer: A. Insulin without food is a classic setup for low blood sugar, and shaking, sweating, and confusion are typical signs. Get help right away under your facility's emergency protocol. No contrast has been given (C), and hyperglycemia (B) tends to develop over hours with thirst and frequent urination.

Source: CDC — Low blood sugar (hypoglycemia)

Answer: D. Units made before June 10, 2006 have a cumulative timer, preset to no more than 5 minutes, that signals when it completes. Units made on or after that date must display fluoroscopy time at the operator's position and signal at each 5 minutes. The purpose is awareness of beam-on time, a direct driver of patient dose.

Source: 21 CFR 1020.32(h)

Answer: C. External rotation puts the humerus in a true AP, with the greater tubercle in profile on the lateral side. Internal rotation turns the humerus lateral and puts the lesser tubercle (A) in profile medially. The glenoid cavity (D) is shown in profile on the Grashey (see EX-09).

Source: UMS — Shoulder, AP external and internal rotation

Answer: A. Raising one arm over the head and dropping the other shoulder separates the shoulders and shows the cervicothoracic junction. The open-mouth view (B) is for C1–C2. Flexion (D) shows motion, not the C7–T1 region hidden by the shoulders.

Source: UMS — Cervical spine, cervicothoracic (swimmer's) lateral

Answer: A, B, and D. C. difficile calls for contact plus standard precautions. Gown and gloves are appropriate for contact with the patient or environment. When spore contamination is likely, soap-and-water handwashing physically removes spores; alcohol-based hand rub does not kill C. difficile spores, so C is wrong. Use an EPA-registered disinfectant with a sporicidal claim for contaminated equipment and surfaces. N95 respirators (E) are for airborne hazards, not routine C. difficile contact precautions.

Sources: CDC — Transmission-Based Precautions · CDC — Clinical Safety: Hand Hygiene for Healthcare Workers · CDC — C. diff clinical guidance

Answer: D. When the part isn't parallel to the IR, its projected length shrinks: foreshortening. Elongation (A) comes from the opposite setup, where the part is parallel to the IR and the tube is angled along its long axis.

Source: University of Mustansiriyah lecture — Distortion

Answer: B. Effective dose and equivalent dose use the sievert. Absorbed dose and air kerma use the gray. Exposure uses coulombs per kilogram (C/kg). SI units are the primary units on the ARRT radiography exam.

Source: U.S. NRC — Measuring radiation

Answer: C. Normally the humeral head sits over the center of the "Y." Beneath the coracoid (anterior) means anterior dislocation. Beneath the acromion (posterior) means posterior dislocation (B).

Source: UMS — Shoulder, scapular Y

Answer: C. NCRP Report 116 recommends 50 mSv per year, with a cumulative limit of 10 mSv × age. The NRC's federal rule for radioactive materials uses the same 0.05 Sv. X-ray equipment is regulated by the states. 1 mSv (A) is the annual limit for members of the public. 150 mSv (D) is the NRC's annual limit for the lens of the eye, not effective dose.

Sources: 10 CFR 20.1201 · Health Physics Society — Ask the Experts, q11553

Answer: Q → S → P → R → T. Indirect conversion goes x-ray → light → charge → readout → digital value. Direct-conversion detectors use amorphous selenium to turn x-rays straight into charge, skipping the light stage. That's the difference the exam usually tests.

Source: Radiopaedia — Flat panel detector

Answer: D. On an AP lordotic, the clavicles project nearly horizontal and above the apices, so the apices are clear of them. On a PA (A) and an AP supine (C), the clavicles overlie the apices.

Source: UMS — Chest, AP lordotic

Answer: C. CDC tells patients with suspected or confirmed infectious TB to wear a surgical or procedure mask, if possible, during transport and around others. The mask contains their respiratory droplets. Staff entering the patient's room wear fit-tested respirators (N95), not the patient (A). TB needs airborne precautions, not contact precautions alone (D).

Source: CDC — Guidelines for preventing the transmission of M. tuberculosis (MMWR 2005), Minnesota Department of Health copy

Answer: A. Posterior lumbar obliques show the joints closest to the IR, the "Scottie dog" side, so the RPO shows the right side. Compare HSP-05: posterior cervical obliques show the side away from the IR. Keep the two rules separate.

Source: UMS — Lumbar spine, posterior oblique

Answer: B. Lymphocytes are highly radiosensitive even though they're mature and don't divide, a well-known exception to the Law of Bergonié and Tribondeau. Nerve cells, muscle cells, and mature red cells (A, C, D) are among the most radioresistant.

Source: Stanford EHS — Biological effects of radiation

Answer: D. Beam intensity is greater on the cathode side, so the thicker part goes there. On an AP thoracic spine, that means the lower thoracic region under the cathode and the head toward the anode. A and B say the same wrong thing.

Source: Radiopaedia — Anode heel effect

Answer: A. The patient rotates 35–45° toward the affected side, placing the scapula parallel to the IR so the glenoid is seen in profile. The supraspinatus outlet (D) is the Neer projection.

Source: UMS — Shoulder, Grashey

Answer: C. A single dosimeter goes at collar level outside the apron, where it estimates dose to the unshielded head, neck, and eyes. Some programs add a second badge under the apron at the waist (A), but with one badge, the collar is the place.

Source: Image Wisely — Fluoroscopy checklists

Answer: D. A: 1 ÷ (2 × 0.1 mm) = 5 lp/mm. B: 1 ÷ (2 × 0.2 mm) = 2.5 lp/mm. Smaller pitch means higher limiting resolution, so A wins. C forgets the factor of 2. DQE (B) describes detection efficiency, not sampling limits.

Source: Calculation from the formula given in the stem. Pixel pitch, detector elements, and Nyquist frequency are listed under digital spatial resolution in ARRT's 2027 content specifications.

Answer: A. Fomites are inanimate objects that carry an infectious agent, a form of vehicle-borne indirect transmission. Vectors (B) are living carriers such as mosquitoes or ticks. Droplets (C) are direct transmission.

Source: CDC — Principles of Epidemiology, Lesson 1, Section 10

Answer: C. Expiration and a recumbent position both raise the diaphragm, putting the lower ribs against the denser abdomen. Ribs above the diaphragm use the opposite: upright and full inspiration (A).

Source: UMS — Ribs

Answer: D. The line from the lower edge of the upper incisors to the mastoid tips should be perpendicular to the IR. Incisors over the dens mean the chin is too low, so raise it. If the base of the skull overlaps the dens, the chin is too high, so flex (A).

Source: Radiopaedia — Cervical spine (odontoid view)

Answer: A. Stochastic effects have no threshold. Their probability, not their severity, rises with dose. Cancer is the classic example. Erythema, cataract, and epilation (B, C, D) are deterministic effects (tissue reactions): they have a threshold, and severity rises with dose.

Source: Stanford EHS — Biological effects of radiation

Answer: C. The AEC keeps exposing until its selected chamber gets enough radiation. Behind the dense mediastinum and spine, that takes longer, so the air-filled lungs receive too much. For a PA chest, the outer chambers behind the lungs are normally selected.

Source: Radiopaedia — Automatic exposure control

Answer: B. Medial rotation of 30–40° opens the lateral side of the foot: the cuboid in profile, the sinus tarsi, and the third through fifth metatarsal bases. The sesamoids (A) need a tangential projection.

Source: UMS — Foot, AP medial oblique

Answer: D. Optically stimulated luminescence dosimeters use carbon-doped aluminum oxide (Al₂O₃:C). Light makes them release a signal proportional to dose. Heating lithium fluoride (A) describes a TLD.

Sources: Landauer — Luxel+ dosimeter · AAPM — OSL dosimetry presentation

Answer: B. Window width controls contrast: a narrower range of values spread across the gray scale looks more contrasty. Window level controls brightness. Neither changes the detector's spatial resolution (D).

Source: Radiopaedia — Windowing

Answer: C. Protective isolation keeps infectious agents away from a patient whose immune defenses are very low. CDC's term for the room setup is a "Protective Environment." Protecting others from the patient (A) is what transmission-based precautions do.

Source: CDC — Isolation precautions glossary

Answer: A. The malleoli don't lie in a true coronal plane. Rotating the leg 15–20° medially brings the intermalleolar line parallel to the IR and opens all three sides of the mortise.

Source: UMS — Ankle, AP mortise

Answer: D. Stop the injection as soon as extravasation is suspected. The ACR recommends examining the patient, elevating the affected extremity, and using either cold or warm compresses; evidence does not establish one compress temperature as clearly superior. The patient should receive instructions about worsening pain, swelling, sensory change, reduced motion, or skin injury. Squeezing or massaging the site (B) is not recommended.

Source: ACR Manual on Contrast Media — “Extravasation of Contrast Media”

Answer: A. Mottle is a shortage of signal, and only more photons fix it. Edge enhancement (B) and narrower windowing (C) make noise more visible. Lowering kVp at the same mAs (D) sends even fewer photons to the detector.

Source: Radiopaedia — Quantum noise

Answer: B. The CR enters at the base of the third metatarsal at 40° cephalad to the long axis of the foot. That shows the calcaneus from the tuberosity to the talocalcaneal joint.

Sources: Radiopaedia — Calcaneus (axial view) · UMS — Calcaneus

Answer: Q → P → R. According to CDC, the full hematopoietic syndrome appears at about 0.7–10 Gy (mild symptoms possibly from 0.3 Gy), the GI syndrome above about 10 Gy, and the cardiovascular/CNS syndrome above about 50 Gy. The order follows tissue radiosensitivity: bone marrow stem cells, then the gut lining, then the far more resistant nervous system.

Source: CDC — Acute radiation syndrome: information for clinicians

Answer: C. In the RAO, barium flows toward the pylorus and duodenum, filling the bulb and C-loop in profile. The LPO (A) is the reverse: barium shifts to the fundus and the bulb fills with air for a double-contrast view.

Source: UMS — Upper GI series

Answer: A. Scatter is greatest where the beam enters the patient, on the tube side. The patient's body attenuates much of it toward the receptor side, so stand next to the image receptor.

Sources: Image Wisely — Fluoroscopy checklists · Health Physics Society — Ask the Experts, q9545

Answer: D. Processing software analyzes a histogram of the anatomy inside the collimated area. If it can't find the borders, or the field holds multiple exposures or large raw-beam areas, it identifies the values of interest incorrectly. That throws off both the exposure indicator and the displayed image.

Source: AAPM Report 116 executive summary

Answer: B. Rotating the legs internally 15–20° puts the femoral necks parallel to the IR and largely hides the lesser trochanters. A clearly visible lesser trochanter with foreshortened necks means the legs are externally rotated. A is the correction.

Source: UMS — Pelvis

Answer: C. The ACR classifies "facial edema with dyspnea" as severe. Without the breathing difficulty, facial swelling alone would rate lower. Stay with the patient, call for help, and start the facility's emergency response; a radiologist or physician directs treatment. Onset within minutes rules out a delayed reaction (D).

Source: ACR Manual on Contrast Media · ACR severity table reproduced in Insights into Imaging, Table 3

Answer: A. At saturation, every pixel in the area is forced to the maximum value, and the differences between tissues are gone. No windowing (B, D) can bring back data that was never recorded. If the lost anatomy matters, the image has to be repeated.

Source: AAPM Report 116 executive summary

Answer: A. The rule: under 19 cm, angle 3–5° caudad; 19–24 cm, perpendicular; over 24 cm, angle 3–5° cephalad. Angling to match the tibial plateau opens the joint space. Watch for study sources that reverse this rule.

Source: UMS — Knee and patella

Answer: C. Image Gently's message is "child-size" technique: measure the child and adjust, because one size doesn't fit all. Adult technique (A) or doubled technique (B) overexposes the child.

Source: Image Gently — Digital radiography

Answer: B. The LAO and RPO open the splenic flexure. The RAO and LPO (A, C) open the hepatic flexure. A memory hook: anterior obliques open the flexure on the side down, and posterior obliques open the side up.

Source: UMS — Contrast enema, obliques

Answer: A. DICOM is the international standard for medical images and related information. HL7 (B) carries clinical and administrative text messages, such as orders and reports. HIPAA (C) is a privacy law, not a data standard.

Source: DICOM — About

Answer: D. The ACR–National Kidney Foundation consensus uses eGFR to stratify risk. Patients with eGFR under 30 mL/min/1.73 m² who aren't on dialysis are higher risk and are candidates for preventive IV fluids. Metformin is held only when eGFR is under 30 or there's acute kidney injury.

Sources: RSNA — ACR–NKF contrast consensus · ACR Manual on Contrast Media

Answer: C. Higher-energy photons penetrate tissues more evenly, with less differential absorption and more Compton scatter, so subject contrast drops. With mAs lowered to compensate, patient dose goes down, not up (D). On digital systems, displayed contrast is largely set by processing (the LUT and window width).

Source: How Radiology Works — Contrast-to-noise ratio

Answer: B. The oxygen enhancement ratio compares the dose needed for the same effect under hypoxic and oxygenated conditions. It's about 3 for x-rays (low-LET radiation) and smaller for high-LET radiation.

Source: ICRPaedia — Oxygen enhancement ratio

Answer: D. The cross-table lateral uses a horizontal beam and raises the unaffected leg, so the injured leg never has to move. Frog-leg positions (A, B) require abducting and rotating the injured leg and are contraindicated when a fracture is suspected.

Sources: UMS — Hip, axiolateral (Danelius-Miller) · Radiopaedia — Hip (horizontal beam lateral view)

Answer: A. The medial condyle extends lower than the lateral one, and the slight cephalic angle lines up their distal margins. Limiting flexion to 20–30° avoids tightening the muscles and tendons that hold the patella in place.

Source: UMS — Knee and patella, lateral knee

Answer: C. The ACR–SPR practice parameter calls for screening and, when pregnancy status is still uncertain, notifying the radiologist before the study. The patient, referring physician, and radiologist then decide whether to proceed, modify, or postpone. Proceeding (A, B) skips that decision. Rescheduling on your own (D) leaves the ordering team uninformed.

Source: ACR–SPR Practice Parameter for Imaging Pregnant or Potentially Pregnant Patients with Ionizing Radiation (rev. 2023), §III.B–E

Answer: B. The RAO rotation separates the esophagus from the spine so it sits in the clear space between the vertebral column and the heart. On a straight PA or AP, it overlies the spine (A).

Source: UMS — Esophagus, RAO

Answer: B. The limit is 2% of the distance from the source to the center of the light field (the SID, when the IR is perpendicular to the beam). 2% × 100 cm = 2 cm. A routine collimator QC test checks this, because a misaligned field irradiates tissue you didn't intend to include or cuts off anatomy you did.

Source: 21 CFR 1020.31(d)(2)(i)

Answer: A. Barium (B) that leaks into the peritoneal cavity can cause peritonitis, so known or strongly suspected GI perforation is a contraindication to barium. Water-soluble contrast is generally preferred.

Source: Radiopaedia — Barium sulfate

Answer: C. 10 × log₁₀(2) ≈ 3, so DI +3 is about double the target exposure, and DI −3 is about half (B). DI is logarithmic, so it doesn't read as a percent (A) or a simple multiple (D). A DI near 0 means the detector exposure matched the target for that exam.

Source: AAPM Report 116 executive summary

Answer: B. With the patient prone and the lower leg raised 40–50°, the CR is angled to match, perpendicular to the lower leg, to open the intercondylar fossa. The Holmblad method gets a similar result by kneeling (about 60–70° flexion) with the CR perpendicular to the IR.

Source: UMS — Knee and patella, Camp-Coventry and Holmblad