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ABR (NAR) practice questions

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Question 1Breast imaging

A 52-year-old woman has a screening mammogram showing a new 8 mm cluster of fine pleomorphic calcifications in the upper outer quadrant. What is the most appropriate next step?

  1. Six-month follow-up mammography
  2. Stereotactic core needle biopsy Correct answer.
  3. Ultrasound-guided cyst aspiration
  4. Bilateral MRI for screening

Explanation

Fine pleomorphic calcifications that are new or increasing in a cluster carry a substantial risk of ductal carcinoma in situ and warrant tissue sampling. Stereotactic guidance is preferred when the calcifications are visible only on mammography. Short-interval follow-up is reserved for lower-suspicion findings such as scattered punctate calcifications.

Question 2Breast imaging

Which mammographic finding is the classic presentation of a radial scar?

  1. A spiculated architectural distortion with central radiolucency Correct answer.
  2. Diffuse skin thickening without a mass
  3. A solitary group of coarse popcorn calcifications
  4. A circumscribed oval mass with a thin halo

Explanation

A radial scar produces an architectural distortion with spiculated lines radiating from a radiolucent center, often mimicking carcinoma. Because imaging cannot reliably distinguish it from malignancy, core biopsy is typically required. Recognizing the central lucency helps in the differential but does not exclude cancer.

Question 3Breast imaging

What is the primary purpose of adding digital breast tomosynthesis to a screening mammogram?

  1. To eliminate the mediolateral oblique view
  2. To measure breast density automatically
  3. To reduce tissue-overlap masking of cancers Correct answer.
  4. To replace the need for breast compression

Explanation

Tomosynthesis acquires multiple thin-section images through the compressed breast, reducing the masking effect of overlapping fibroglandular tissue. This improves cancer detection and lowers recall rates compared with two-dimensional mammography alone. Compression is still required, and standard views are still obtained.

Question 4Breast imaging

On ultrasound, a simple cyst is characterized by which set of features?

  1. Anechoic, thin-walled, with posterior acoustic enhancement Correct answer.
  2. Hypoechoic, irregular margins, with posterior shadowing
  3. Hyperechoic, lobulated, with internal vascularity
  4. Mixed echogenicity with thick septations and debris

Explanation

A simple cyst is anechoic with smooth thin walls, imperceptible posterior wall, and posterior acoustic enhancement from through-transmission. These features are benign and require no aspiration. Complex features such as thick septa or internal echoes prompt further evaluation.

Question 5Breast imaging

According to the ACR BI-RADS atlas, which category corresponds to a finding that is probably benign and warrants short-interval follow-up?

  1. BI-RADS 2
  2. BI-RADS 5
  3. BI-RADS 4A
  4. BI-RADS 3 Correct answer.

Explanation

BI-RADS 3 designates a finding with a high probability of being benign, generally recommended for short-interval follow-up rather than immediate biopsy. BI-RADS 2 is benign and requires routine screening, while categories 4 and 5 mandate tissue sampling.

Question 6Breast imaging

A 47-year-old woman presents with a palpable, tender, erythematous breast and fever. Ultrasound shows a fluid collection with internal debris and surrounding hyperemia. What is the most likely diagnosis?

  1. Breast abscess Correct answer.
  2. Invasive lobular carcinoma
  3. Fibroadenoma
  4. Fat necrosis

Explanation

Fever, focal tenderness, erythema, and a debris-containing fluid collection with surrounding hyperemia are typical of a breast abscess, often complicating mastitis. Management usually involves ultrasound-guided aspiration or drainage plus antibiotics. Cancer and fat necrosis do not typically present with fever and a purulent collection.

Question 7Breast imaging

Which feature on MRI is most useful for distinguishing a benign fibroadenoma from a malignant mass?

  1. Non-mass enhancement in a ductal distribution
  2. Rim enhancement with central necrosis
  3. Persistent or plateau enhancement kinetics with smooth margins Correct answer.
  4. Washout kinetics with irregular margins

Explanation

Benign fibroadenomas typically show smooth margins and persistent or plateau enhancement on delayed phases. Washout kinetics, irregular margins, and non-mass ductal enhancement are suspicious features associated with malignancy. Kinetic analysis alone is never definitive, but the combination of morphology and kinetics guides management.

Question 8Breast imaging

A screening mammogram shows a new 1.5 cm irregular spiculated mass. The patient is asymptomatic. What is the recommended management?

  1. Ultrasound-guided fine needle aspiration
  2. Image-guided core needle biopsy Correct answer.
  3. Reassurance and clinical follow-up
  4. Repeat mammography in 12 months

Explanation

A new spiculated irregular mass is highly suspicious for malignancy and requires tissue diagnosis, typically by image-guided core needle biopsy. Core biopsy provides histology and biomarker information needed for treatment planning. Fine needle aspiration is inadequate for architectural assessment of a solid mass.

Question 9Breast imaging

Which patient population benefits most clearly from supplemental screening breast MRI according to current guidelines?

  1. Women with a single first-degree relative diagnosed after age 60
  2. Women with dense breasts and no other risk factors
  3. Women with a lifetime breast cancer risk of approximately 20 percent or greater Correct answer.
  4. All women aged 40 to 49 with average risk

Explanation

Major society guidelines recommend annual screening MRI for women whose lifetime risk is roughly 20 percent or greater, including BRCA mutation carriers and those with prior chest radiation. Average-risk women are screened with mammography. Dense breasts alone are not an established indication for MRI.

Question 10Breast imaging

A 60-year-old woman has bloody nipple discharge from a single duct. Mammography is normal. What is the most appropriate next step?

  1. Reassurance without further workup
  2. Three-month repeat mammography
  3. Bilateral screening MRI
  4. Ductography or duct excision for evaluation Correct answer.

Explanation

Spontaneous bloody single-duct discharge raises concern for an intraductal papilloma or carcinoma and requires further evaluation, often with ductography, ductoscopy, or surgical duct excision. Normal mammography does not exclude an intraductal lesion. Reassurance alone is inappropriate.

Question 11Breast imaging

What is the significance of a mammographic finding of skin thickening and trabecular prominence in a non-lactating woman without a palpable mass?

  1. It indicates a simple cyst requiring aspiration
  2. It is a normal variant requiring no follow-up
  3. It confirms a benign fibrocystic change
  4. It may indicate inflammatory carcinoma and warrants prompt evaluation Correct answer.

Explanation

Diffuse skin thickening and trabecular prominence without a discrete mass can be the presenting sign of inflammatory breast carcinoma or may reflect benign causes such as edema or infection. Prompt clinical correlation and imaging, often with biopsy, are required. It is not a normal variant.

Question 12Breast imaging

Which BI-RADS descriptor best characterizes a mass with margins that are completely surrounded by a thin radiolucent halo and are well defined?

  1. Circumscribed Correct answer.
  2. Indistinct
  3. Spiculated
  4. Obscured

Explanation

A circumscribed margin is sharply defined against surrounding tissue and is typical of benign lesions such as cysts and fibroadenomas. Obscured, indistinct, and spiculated margins describe varying degrees of non-sharp borders associated with higher suspicion. The halo sign supports the circumscribed designation.

Question 13Breast imaging

A 45-year-old BRCA1 carrier undergoes annual screening MRI alternating with mammography. She asks why MRI is added. What is the most accurate explanation?

  1. MRI has higher sensitivity for breast cancer in high-risk women than mammography alone Correct answer.
  2. MRI reduces the need for biopsy in high-risk women
  3. MRI eliminates the need for mammography
  4. MRI has higher specificity than mammography

Explanation

In high-risk women, contrast-enhanced MRI detects cancers that mammography misses, particularly in dense breasts, and combined screening improves sensitivity. MRI does not replace mammography and has lower specificity, leading to more false-positive findings and benign biopsies.

Question 14Breast imaging

Which finding on a screening mammogram is most consistent with a benign intramammary lymph node?

  1. A well-circumscribed reniform mass with a radiolucent fatty hilum Correct answer.
  2. A spiculated mass with pleomorphic calcifications
  3. An ill-defined mass with skin tethering
  4. A cluster of branching linear calcifications

Explanation

Intramammary lymph nodes are typically reniform, well circumscribed, and contain a radiolucent fatty hilum. Loss of the fatty hilum or enlargement with irregular margins raises concern for metastasis. The other listed findings are suspicious for primary breast malignancy.

Question 15Breast imaging

A 55-year-old woman has a 2 cm invasive ductal carcinoma that is estrogen receptor positive, progesterone receptor negative, and HER2 negative. Which statement about staging with imaging is most appropriate?

  1. Routine bone scan is required for all stage I breast cancers
  2. Axillary ultrasound with biopsy of suspicious nodes guides surgical planning Correct answer.
  3. Sentinel lymph node biopsy is unnecessary when axillary ultrasound is normal
  4. PET-CT is standard for every newly diagnosed breast cancer

Explanation

Axillary ultrasound with biopsy of suspicious nodes can identify nodal metastasis preoperatively and inform the choice between upfront surgery and neoadjuvant therapy. Systemic staging with bone scan or PET-CT is reserved for patients with symptoms or high-risk features, not routine early disease. Sentinel node biopsy remains standard when nodes appear clinically negative.

Question 16Breast imaging

A nonpalpable mammographic abnormality is visible only on one view and cannot be localized on ultrasound. Which technique is most appropriate for tissue sampling?

  1. Ultrasound-guided core biopsy
  2. Excisional biopsy without wire localization
  3. Fine needle aspiration without imaging guidance
  4. Stereotactic vacuum-assisted core biopsy Correct answer.

Explanation

Stereotactic guidance uses the mammographic projection to localize findings seen on mammography but not sonographically, such as microcalcifications. Vacuum-assisted devices obtain adequate tissue for calcifications. Ultrasound guidance cannot target a lesion that is not sonographically visible, and unguided excision risks missing the lesion.

Question 17Breast imaging

A woman with a newly diagnosed breast cancer is found to have a single 1 cm suspicious axillary node. Which statement best describes the current role of axillary staging in this setting?

  1. Axillary imaging cannot alter surgical management
  2. Complete axillary dissection is always required before systemic therapy
  3. Ultrasound-guided biopsy of the suspicious node can confirm metastasis and inform neoadjuvant planning Correct answer.
  4. Sentinel lymph node biopsy should be omitted because the node is suspicious

Explanation

Biopsy of a suspicious axillary node confirms nodal status and can guide the decision for neoadjuvant chemotherapy and the extent of axillary surgery. Sentinel lymph node biopsy remains an option in selected patients with limited nodal disease, and axillary dissection is increasingly reserved for residual disease or specific indications. Imaging findings strongly influence surgical planning.

Question 18Cardiovascular imaging

On a noncontrast chest CT, which coronary artery is most reliably identified coursing in the anterior interventricular groove?

  1. Right coronary artery
  2. Left anterior descending artery Correct answer.
  3. Posterior descending artery
  4. Left circumflex artery

Explanation

The left anterior descending artery runs in the anterior interventricular sulcus, making it the most consistently visible coronary artery on noncontrast CT because of its superficial location and surrounding epicardial fat. The circumflex and right coronary arteries lie in the atrioventricular grooves, and the posterior descending artery is a distal branch in the inferior interventricular groove.

Question 19Cardiovascular imaging

A coronary calcium score of 0 on a noncontrast ECG-gated CT most strongly indicates which of the following?

  1. A very low likelihood of obstructive coronary artery disease Correct answer.
  2. Presence of hemodynamically significant myocardial ischemia
  3. A high likelihood of significant stenosis requiring catheterization
  4. Complete absence of any noncalcified plaque

Explanation

A zero calcium score confers a very low probability of obstructive coronary artery disease and carries strong negative prognostic value. However, it does not exclude noncalcified (soft) plaque, and it says nothing about functional ischemia, so it cannot rule out unstable angina from a noncalcified lesion.

Question 20Cardiovascular imaging

Which measurement best defines left ventricular hypertrophy by echocardiography according to ASE guidelines?

  1. Left ventricular mass indexed to body surface area Correct answer.
  2. Left atrial volume indexed to body surface area
  3. Left ventricular ejection fraction below 50%
  4. Mitral annular early diastolic velocity

Explanation

Left ventricular hypertrophy is defined by increased left ventricular mass, which is indexed to body surface area to account for body size. Ejection fraction, left atrial volume, and tissue Doppler velocities describe systolic function, chamber dilation, and diastolic function respectively, not hypertrophy.

Question 21Cardiovascular imaging

On cardiac MRI, late gadolinium enhancement in a subendocardial to transmural distribution within a coronary territory most suggests which etiology?

  1. Hypertrophic cardiomyopathy
  2. Ischemic myocardial scar Correct answer.
  3. Cardiac amyloidosis
  4. Myocarditis

Explanation

Ischemic scar follows a coronary vascular territory and begins in the subendocardium, which is most vulnerable to ischemia, then extends outward. Amyloidosis, myocarditis, and hypertrophic cardiomyopathy typically produce nonischemic patterns such as global subendocardial, midwall, or patchy enhancement.

Question 22Cardiovascular imaging

Which echocardiographic view is most appropriate for measuring the proximal ascending aortic diameter at the sinuses of Valsalva?

  1. Parasternal long-axis view Correct answer.
  2. Apical four-chamber view
  3. Suprasternal notch view
  4. Subcostal four-chamber view

Explanation

The parasternal long-axis view displays the aortic root perpendicular to the ultrasound beam, allowing accurate caliper measurement at the sinuses of Valsalva, sinotubular junction, and proximal ascending aorta. The apical and subcostal views show the aorta obliquely or not at all, and the suprasternal view is used for the distal arch and descending aorta.

Question 23Cardiovascular imaging

A 62-year-old with atypical chest pain undergoes coronary CT angiography. A 1.5 mm noncalcified plaque causes 40% diameter narrowing in the mid-LAD. How should this finding be classified?

  1. Severe stenosis
  2. Mild stenosis Correct answer.
  3. Moderate stenosis
  4. Occlusion

Explanation

By CAD-RADS and conventional CCTA grading, diameter stenosis below 50% is classified as mild. Moderate stenosis spans roughly 50-69%, severe stenosis 70% or greater, and occlusion means complete absence of antegrade flow.

Question 24Cardiovascular imaging

A patient with suspected acute aortic dissection has a normal-appearing ascending aorta on noncontrast CT but a crescentic high-attenuation collection in the aortic wall. What is the most likely diagnosis?

  1. Intramural hematoma Correct answer.
  2. Penetrating atherosclerotic ulcer
  3. Aortic intramural thrombus without dissection
  4. Ruptured aortic aneurysm

Explanation

A crescentic high-attenuation thickening of the aortic wall on noncontrast CT represents acute intramural hematoma, a variant of acute aortic syndrome without a visible intimal flap. Penetrating ulcer shows a focal contrast-filled outpouching, and rupture shows contrast extravasation or periaortic hematoma.

Question 25Cardiovascular imaging

Which finding on resting echocardiography most specifically supports the diagnosis of cardiac tamponade in a patient with a large pericardial effusion?

  1. Right ventricular diastolic collapse Correct answer.
  2. Left ventricular ejection fraction of 45%
  3. Moderate mitral annular calcification
  4. Left atrial spontaneous echo contrast

Explanation

Right ventricular diastolic collapse occurs when intrapericardial pressure exceeds right ventricular diastolic pressure, a hallmark of tamponade physiology. Reduced ejection fraction, annular calcification, and atrial echo contrast are unrelated to the hemodynamic compromise of tamponade.

Question 26Cardiovascular imaging

In cardiac MRI, which sequence is most useful for quantifying myocardial edema in acute myocarditis?

  1. Cine steady-state free precession imaging
  2. First-pass perfusion imaging
  3. T2-weighted or T2 mapping imaging Correct answer.
  4. Phase-contrast flow imaging

Explanation

T2-weighted imaging and T2 mapping detect increased myocardial water content, which is the MRI signature of edema in acute myocarditis. First-pass perfusion assesses microvascular blood flow, cine imaging assesses function and motion, and phase-contrast imaging quantifies flow volumes.

Question 27Cardiovascular imaging

A 70-year-old with known aortic stenosis has a peak velocity of 4.2 m/s and a mean gradient of 45 mm Hg on echocardiography. How is the stenosis severity classified?

  1. Mild aortic stenosis
  2. Severe aortic stenosis Correct answer.
  3. Sclerocalcific valve without stenosis
  4. Moderate aortic stenosis

Explanation

Severe aortic stenosis is defined by a peak velocity of at least 4.0 m/s or a mean gradient of at least 40 mm Hg. Moderate disease corresponds to a peak velocity of 3.0-3.9 m/s and mean gradient of 20-39 mm Hg, while mild disease is below those thresholds.

Question 28Cardiovascular imaging

On a cardiac CT, which feature most reliably distinguishes an acute from a chronic distal aortic occlusion?

  1. Presence of extensive collateral vessels and calcified chronic thrombus Correct answer.
  2. Presence of a small pericardial effusion
  3. Presence of left ventricular hypertrophy
  4. Presence of coronary artery calcification

Explanation

Chronic occlusion typically develops extensive collateral circulation and shows calcified, organized thrombus, whereas acute occlusion lacks well-formed collaterals and may show a fresh thrombus with an abrupt cutoff. Pericardial effusion, ventricular hypertrophy, and coronary calcification are unrelated to the acuity of aortic occlusion.

Question 29Cardiovascular imaging

In echocardiography, which parameter is used to estimate right ventricular systolic pressure?

  1. Pulmonary vein systolic flow reversal
  2. Mitral inflow E/A ratio
  3. Inferior vena cava collapsibility
  4. Tricuspid regurgitation peak velocity Correct answer.

Explanation

Right ventricular systolic pressure is estimated from the tricuspid regurgitation jet velocity using the modified Bernoulli equation (4v squared) plus right atrial pressure. The E/A ratio reflects left ventricular diastolic function, pulmonary vein flow reversal indicates elevated left atrial pressure, and IVC collapsibility estimates right atrial pressure alone.

Question 30Cardiovascular imaging

A patient with hypertrophic cardiomyopathy undergoes cardiac MRI. Which enhancement pattern is most characteristic?

  1. Epicardial enhancement of the lateral wall
  2. Patchy midwall enhancement at right ventricular insertion points Correct answer.
  3. Diffuse global subendocardial enhancement
  4. Subendocardial enhancement along the LAD territory

Explanation

Hypertrophic cardiomyopathy characteristically shows patchy, often midwall, late gadolinium enhancement at the right ventricular insertion points and within the most hypertrophied segments. Subendocardial enhancement in a coronary territory indicates ischemic scar, global subendocardial enhancement suggests amyloidosis, and lateral epicardial enhancement suggests myocarditis.

Question 31Cardiovascular imaging

Which coronary CT angiography finding is most associated with a higher risk of future acute coronary syndrome, independent of stenosis severity?

  1. Anomalous origin of the circumflex from the right sinus
  2. High-risk plaque features such as positive remodeling and low attenuation Correct answer.
  3. Mild diffuse luminal narrowing without plaque
  4. Coronary artery calcification confined to a single vessel

Explanation

High-risk plaque features, including positive remodeling, low-attenuation plaque, spotty calcification, and the napkin-ring sign, predict future acute coronary events independent of the degree of stenosis. Simple calcification, anomalous origin, and diffuse mild narrowing without discrete plaque do not carry the same vulnerable-plaque risk.

Question 32Cardiovascular imaging

On cardiac MRI, a patient with severe aortic regurgitation shows a regurgitant fraction of 45% by phase-contrast imaging. What does this value indicate?

  1. Moderate aortic regurgitation
  2. Normal physiologic regurgitation
  3. Mild aortic regurgitation
  4. Severe aortic regurgitation Correct answer.

Explanation

By MRI phase-contrast quantification, a regurgitant fraction of 40% or greater indicates severe aortic regurgitation. Mild disease is generally below 20%, and moderate disease falls roughly between 20% and 39%, while normal physiologic regurgitation is trivial.

Question 33Cardiovascular imaging

A patient with suspected cardiac sarcoidosis undergoes FDG-PET combined with cardiac MRI. Which pattern most supports active inflammation?

  1. Absent myocardial FDG uptake with normal perfusion
  2. Diffuse homogeneous myocardial FDG uptake suppressed by a high-fat diet
  3. Focal myocardial FDG uptake corresponding to areas of late gadolinium enhancement Correct answer.
  4. Pericardial FDG uptake alone

Explanation

Active cardiac sarcoidosis shows focal or patchy myocardial FDG uptake that matches regions of late gadolinium enhancement on MRI, reflecting inflammation. Physiologic myocardial uptake is normally suppressed by dietary preparation, and isolated pericardial uptake is nonspecific.

Question 34Cardiovascular imaging

In a patient with a mechanical aortic valve, which imaging modality is preferred for assessing valve function and complications when echocardiography is limited?

  1. Cardiac CT with retrospective ECG gating Correct answer.
  2. Coronary calcium scoring
  3. Resting nuclear perfusion imaging
  4. Non-gated chest CT

Explanation

Retrospectively ECG-gated cardiac CT allows evaluation of mechanical valve leaflet motion, pannus, thrombus, and perivalvular complications with reduced motion artifact. Non-gated CT suffers from motion artifact, calcium scoring does not assess valve function, and nuclear perfusion evaluates myocardial ischemia rather than prosthetic valve integrity.

Question 35Computed tomography

In CT physics, what does the term 'window width' control on a displayed image?

  1. The range of CT numbers mapped to the visible gray scale Correct answer.
  2. The slice thickness selected at the scanner console
  3. The rotation speed of the gantry during acquisition
  4. The physical field of view reconstructed from the raw data

Explanation

Window width sets the span of Hounsfield units that are displayed as shades between black and white; a narrow width increases contrast but reduces the range shown. Window level, by contrast, centers that span on a chosen CT number.

Question 36Computed tomography

Which CT number approximately corresponds to water on the Hounsfield scale?

  1. 0 Correct answer.
  2. 1000
  3. 40
  4. -1000

Explanation

The Hounsfield scale is anchored with water at 0 HU and air at about -1000 HU. Tissues are then described relative to these fixed reference points.

Question 37Computed tomography

A CT image is described as having high spatial resolution. What does this most directly mean?

  1. The scanner can image a very long anatomical range in one rotation
  2. The displayed gray scale spans a very wide range of CT numbers
  3. The image has very little quantum mottle in uniform regions
  4. Small high-contrast structures can be distinguished as separate objects Correct answer.

Explanation

Spatial resolution describes the ability to separate small, closely spaced objects, usually assessed with high-contrast phantoms. It is distinct from low-contrast detectability, which depends heavily on noise.

Question 38Computed tomography

During a helical CT acquisition, pitch is defined as table travel per gantry rotation divided by which quantity?

  1. The scan field of view diameter
  2. The reconstructed slice thickness
  3. The nominal beam collimation width Correct answer.
  4. The total scan length

Explanation

Pitch compares table feed per rotation with the beam width (collimation) so that it is dimensionless. A pitch of 1 means the table advances one beam width per rotation.

Question 39Computed tomography

Which artifact appears as dark streaks between two dense objects such as metal implants or high-contrast bone?

  1. Photon starvation
  2. Beam-hardening streaks Correct answer.
  3. Partial volume artifact
  4. Ring artifact

Explanation

Beam hardening occurs because polychromatic x-rays lose low-energy photons preferentially in dense material, producing cupping and dark bands between dense structures. Ring artifact and photon starvation have different appearances and causes.

Question 40Computed tomography

A technologist increases the tube current-time product (mAs) while all other parameters are unchanged. What is the expected effect on image noise?

  1. Noise increases because more photons create scatter
  2. Noise is unchanged because mAs only affects dose
  3. Noise decreases approximately as the square root of mAs increases Correct answer.
  4. Noise decreases linearly with mAs

Explanation

Quantum noise is inversely proportional to the square root of the number of detected photons, so quadrupling mAs roughly halves noise. The relationship is not linear, which is why large mAs increases yield diminishing noise reduction.

Question 41Computed tomography

A protocol uses 120 kVp but the patient's large size yields excessive noise. Which change most directly increases photon penetration and reduces noise?

  1. Reducing the detector collimation
  2. Raising kVp to 140 Correct answer.
  3. Lowering kVp to 100
  4. Increasing the reconstruction kernel sharpness

Explanation

Higher kVp raises beam energy and penetration, so more photons reach the detector through a large patient, reducing noise and beam hardening. The trade-off is lower iodine contrast and higher dose per mAs.

Question 42Computed tomography

Which parameter most directly determines the reconstructed slice thickness in multidetector CT?

  1. Detector row configuration and reconstructed section width Correct answer.
  2. Tube current
  3. Gantry rotation time
  4. Reconstruction field of view

Explanation

Slice thickness is set by the detector configuration during acquisition and by the reconstructed section width chosen at the console. Rotation time and tube current affect temporal and noise characteristics, not section thickness.

Question 43Computed tomography

A CT study uses a filtered back projection reconstruction. Which statement best describes the role of the reconstruction filter (kernel)?

  1. It alters the trade-off between spatial resolution and image noise Correct answer.
  2. It removes patient motion by correcting raw data
  3. It sets the tube voltage for the next acquisition
  4. It determines the pitch used during helical scanning

Explanation

Reconstruction kernels are convolution filters that emphasize either sharpness (high resolution, more noise) or smoothness (less noise, lower resolution). The choice is made at reconstruction and does not change acquisition parameters.

Question 44Computed tomography

During a CT fluoroscopy-guided biopsy, the operator stands close to the gantry. Which practice best reduces occupational dose while maintaining workflow?

  1. Stepping on the pedal continuously during the procedure
  2. Removing the table-side lead drape to improve visibility
  3. Using intermittent exposure with last-image hold and maximizing distance Correct answer.
  4. Using continuous fluoroscopy at high mA

Explanation

Intermittent exposure and last-image hold reduce beam-on time, and distance reduces scatter dose because exposure falls with the inverse square of distance. Shielding drapes add protection rather than being removed.

Question 45Computed tomography

A CT dose index is reported as CTDIvol = 20 mGy and the dose-length product is 400 mGy·cm. What scan length was used?

  1. 80 cm
  2. 40 cm
  3. 10 cm
  4. 20 cm Correct answer.

Explanation

DLP equals CTDIvol multiplied by the scanned length, so length equals DLP divided by CTDIvol. Here 400 mGy·cm ÷ 20 mGy gives 20 cm.

Question 46Computed tomography

Which situation most increases the risk of partial volume averaging on a CT image?

  1. A small structure whose thickness is less than the reconstructed slice width Correct answer.
  2. A scan performed at high kVp
  3. A scan reconstructed with a smooth kernel
  4. A large homogeneous organ imaged with thin slices

Explanation

Partial volume averaging occurs when a structure occupies only part of a voxel, so its attenuation is averaged with surrounding tissue. Thin slices reduce this effect by shrinking voxel dimensions along z.

Question 47Computed tomography

A patient with a very large body habitus is scanned with a fixed mAs protocol. Which artifact is most likely to appear?

  1. Out-of-field artifact from arms at the side
  2. Motion blur from cardiac pulsation
  3. Metallic bloom
  4. Photon starvation streaks Correct answer.

Explanation

Large attenuation reduces the number of photons reaching detectors, producing noisy streaks known as photon starvation. Increasing mAs or kVp or using automatic exposure control mitigates it.

Question 48Computed tomography

A CT image shows ring artifacts centered on the isocenter. Which cause is most consistent with this appearance?

  1. A miscalibrated or defective detector channel Correct answer.
  2. Incorrect window level
  3. Patient motion during the scan
  4. Beam hardening from dense bone

Explanation

Ring artifacts arise when one detector channel consistently records an incorrect signal, so the error is projected as a circle across all views. Detector calibration and phantom quality assurance help detect this.

Question 49Computed tomography

A helical scan uses a pitch greater than 1. What is the most relevant consequence for image quality and dose?

  1. Increased slice thickness because of interpolation
  2. Faster coverage with reduced dose but potentially more noise and artifact Correct answer.
  3. Slower coverage with higher dose and improved low-contrast detectability
  4. No change in dose because pitch does not affect exposure

Explanation

Higher pitch increases table speed, shortening scan time and reducing dose for a given mAs, but fewer projections per location can increase noise and artifact. Modern scanners use interpolation to maintain image quality.

Question 50Computed tomography

A dual-energy CT dataset is used to create a virtual monoenergetic image at 40 keV. What is the primary expected benefit?

  1. Improved temporal resolution
  2. Increased iodine contrast Correct answer.
  3. Lower patient dose
  4. Reduced metal artifact

Explanation

Low-keV virtual monoenergetic images sit closer to iodine's k-edge, boosting iodine attenuation and contrast enhancement. High-keV images instead reduce beam hardening and metal artifact.