I85PREP
⌘ K
DACBR - independent subject foundations study materials
DACBR - independent subject foundations study resources

DACBR - independent subject foundations practice questions

One question at a time. Build your DACBR - independent subject foundations understanding.

First 50 of 190 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Musculoskeletal imaging, trauma and pattern-based differential

A 22-year-old rugby player sustains an acute anterior glenohumeral shoulder dislocation. Following closed reduction, a shoulder MRI is performed. Which combination of osseous and labral lesions is typically identified following an anterior shoulder dislocation?

  1. Reverse Bankart lesion and reverse Hill-Sachs impaction of the anterior humeral head
  2. Bankart lesion (anteroinferior glenoid labral tear) and Hill-Sachs defect (posterolateral humeral head impaction fracture) Correct answer.
  3. Superior labral tear anterior-to-posterior (SLAP lesion) with acromioclavicular dislocation
  4. Subscapularis tendon avulsion with fracture of the lesser tuberosity alone

Explanation

Anterior glenohumeral dislocation classically causes an anteroinferior labral detachment (Bankart lesion), often with glenoid rim fracture (bony Bankart), and a compression fracture on the posterolateral aspect of the humeral head caused by impaction against the anterior glenoid rim during dislocation (Hill-Sachs lesion).

Question 2Musculoskeletal imaging, trauma and pattern-based differential

A 26-year-old soccer player presents with acute knee locking and inability to achieve full extension after a twisting injury. Sagittal knee MRI demonstrates an inner fragment of the medial meniscus displaced into the intercondylar notch, lying anterior and parallel to the intact posterior cruciate ligament, producing a second dark arc of low signal. What pathognomonic MRI sign is this?

  1. Ghost meniscus sign
  2. Fragment-in-notch sign alone without ligamentous relationship
  3. Double PCL sign characteristic of a bucket-handle medial meniscal tear Correct answer.
  4. Empty notch sign characteristic of an anterior cruciate ligament tear

Explanation

The 'double PCL sign' on sagittal MRI is diagnostic of a bucket-handle tear of the medial meniscus (requiring an intact ACL). The displaced inner meniscal fragment lies in the intercondylar notch immediately anterior and inferior to the posterior cruciate ligament (PCL), mimicking a second duplicate PCL.

Question 3Musculoskeletal imaging, trauma and pattern-based differential

A 48-year-old male with poorly controlled diabetes presents with chronic discharging sinus tracts over his left tibia. Radiographs reveal a dense, sclerotic segment of devitalized dead cortical bone separated from viable bone by a radiolucent granulation zone, encased within a thick sheath of subperiosteal reactive new bone with draining defects. What radiological terms correctly describe the dead bone fragment and surrounding reactive bone collar?

  1. Nidus and osteoid osteoma rim
  2. Brodie abscess and Codman triangle
  3. Involucrum and cloaca
  4. Sequestrum (dead bone) and Involucrum (reactive bone sheath) Correct answer.

Explanation

In chronic pyogenic osteomyelitis, a 'sequestrum' is a piece of devitalized, necrotic bone that has become separated from living tissue by granulation tissue. The 'involucrum' is a thick collar of reactive, subperiosteal new bone formed around the sequestrum. Openings within the involucrum that discharge pus and debris to the skin are called 'cloacae'.

Question 4Musculoskeletal imaging, trauma and pattern-based differential

A 15-year-old male presents with deep, progressive pain and swelling in his distal right thigh. Plain radiography demonstrates a mixed lytic and blastic aggressive bone lesion in the distal femoral metaphysis, marked cortical destruction, cloud-like osteoid matrix mineralization, elevation of the periosteum creating a triangular shelf of reactive bone at the margins, and divergent spicules of mineralized bone radiating into the soft tissues. What are these periosteal reactions called?

  1. Fallen fragment sign and soap-bubble pattern
  2. Codman triangle and sunburst (rayos de sol) periosteal reaction indicative of conventional osteosarcoma Correct answer.
  3. Onion-skin laminated periostitis and button sequestrum
  4. Pencil-in-cup deformity and cortical saucerization

Explanation

The 'Codman triangle' (elevation of periosteum by expanding tumor with subperiosteal bone deposition at the periphery) and the 'sunburst' periosteal reaction (osteoblasts producing bone along radially oriented Sharpey fibers) are classic signs of highly aggressive bone malignancy, pathognomonic of conventional intramedullary osteosarcoma.

Question 5Musculoskeletal imaging, trauma and pattern-based differential

An 11-year-old female presents with fever, local tenderness, and an enlarging mass over the mid-shaft of the left fibula. Plain radiography and CT show an ill-defined, permeative ('moth-eaten') osteolytic lesion centered in the diaphysis, associated with multi-layered, concentric, lamellated subperiosteal bone formation and a large, disproportionate soft-tissue mass. What is the diagnosis?

  1. Non-ossifying fibroma (fibroma no osificante)
  2. Osteoid osteoma of the fibular shaft
  3. Ewing sarcoma (sarcoma de Ewing) Correct answer.
  4. Enchondroma with pathological fracture

Explanation

Ewing sarcoma is a highly malignant small round blue cell tumor that typically arises in the diaphysis or metadiaphysis of long bones in children and adolescents. Its radiographic hallmarks are permeative or moth-eaten cortical bone destruction, concentric multi-layered 'onion-skin' periosteal reaction, and a large extraosseous soft-tissue mass.

Question 6Musculoskeletal imaging, trauma and pattern-based differential

A 28-year-old female with closed growth plates presents with knee pain. Radiographs reveal an eccentric, expansile, purely radiolucent osteolytic lesion in the distal femoral epiphysis that extends directly to the subarticular subchondral cortex and abuts the joint line, with a narrow zone of transition but no surrounding sclerotic rim and no matrix calcification. What is the diagnosis?

  1. Chondroblastoma of the epiphysis
  2. Aneurysmal bone cyst of the diaphysis
  3. Osteoblastoma of the posterior neural arch
  4. Giant cell tumor of bone (tumor de células gigantes) Correct answer.

Explanation

Giant cell tumor of bone (GCTB) is a benign but locally aggressive neoplasm occurring almost exclusively in skeletally mature young adults (closed physis). It is characteristically located eccentrically in the epiphysis extending to the subarticular cortex, non-sclerotic at its margin, expansile ('soap-bubble' remodeling), and completely lacks mineralized matrix.

Question 7Musculoskeletal imaging, trauma and pattern-based differential

A 45-year-old female presents with bilateral, symmetric joint stiffness and pain in the hands. Posteroanterior hand radiographs demonstrate diffuse periarticular osteopenia, uniform symmetric joint space narrowing, and marginal bone erosions (bare area bone loss) predominantly involving the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints and carpal bones, with total sparing of the distal interphalangeal (DIP) joints. What is the diagnosis?

  1. Rheumatoid arthritis (artritis reumatoide) Correct answer.
  2. Primary nodal osteoarthritis with Heberden nodes
  3. Chronic tophaceous gout
  4. Calcium pyrophosphate dihydrate deposition disease (CPPD)

Explanation

The radiographic hallmarks of rheumatoid arthritis in the hands are symmetric, bilateral involvement of the MCP, PIP, and carpal joints with periarticular osteopenia, uniform joint space loss, and marginal erosions at the 'bare areas' (bone within the capsule devoid of protective cartilage). Complete sparing of the DIP joints is a classic distinguishing feature.

Question 8Musculoskeletal imaging, trauma and pattern-based differential

A 72-year-old postmenopausal female with severe osteoporosis treated with corticosteroids presents with progressive low back and buttock pain without antecedent major trauma. Technetium-99m bone scintigraphy demonstrates an H-shaped or butterfly-shaped pattern of intense radiotracer uptake across both sacral alae and the horizontal sacral body. What pathognomonic sign and diagnosis does this represent?

  1. Paget disease of the sacrum
  2. Honda sign (signo de la Honda) indicative of sacral insufficiency fracture Correct answer.
  3. Chordoma of the sacrum
  4. Metastatic breast carcinoma to the pelvis

Explanation

The 'Honda sign' (H-pattern of tracer uptake on bone scintigraphy or H-shaped low-signal fracture lines with surrounding edema on coronal MRI) is pathognomonic of a bilateral sacral insufficiency fracture. It results from normal physiological stress applied to mineral-deficient, osteoporotic bone.

Question 9Neuroimaging, spinal anatomy and diagnostic reasoning

A 66-year-old male arrives at the emergency department 2 hours after acute onset of right hemiplegia and global aphasia. Emergency non-contrast head CT is performed to evaluate for ischemic stroke. The radiologist calculates the Alberta Stroke Program Early CT Score (ASPECTS). Loss of gray-white matter differentiation is identified in the insular ribbon, lentiform nucleus, and M2 cortical region. What is the patient's ASPECTS score?

  1. 10
  2. 7 Correct answer.
  3. 5
  4. 3

Explanation

The ASPECTS score is a 10-point quantitative topographical CT score for middle cerebral artery (MCA) stroke. Starting from a normal score of 10, one point is subtracted for each defined anatomical area showing early ischemic changes (loss of gray-white differentiation, hypoattenuation). With three involved areas (insular ribbon, lentiform nucleus, M2), the score is 10 - 3 = 7. A score >= 6 is favorable for endovascular thrombectomy.

Question 10Neuroimaging, spinal anatomy and diagnostic reasoning

An unenhanced head CT performed within 90 minutes of acute stroke onset demonstrates spontaneous hyperattenuation of the horizontal M1 segment of the right middle cerebral artery compared to the contralateral side and adjacent brain parenchyma, without parenchymal hemorrhage. What is this crucial early vascular sign called?

  1. Insular ribbon sign
  2. Cord sign of dural sinus thrombosis
  3. Hyperdense middle cerebral artery (MCA) sign Correct answer.
  4. Dense basilar artery sign

Explanation

The 'hyperdense MCA sign' is caused by acute thromboembolic occlusion of the horizontal M1 segment of the middle cerebral artery. The high attenuation (typically > 60-80 HU) is produced by high packed red blood cell and fibrin content within the acute stationary intraluminal thrombus, representing an early marker of large-vessel occlusion.

Question 11Neuroimaging, spinal anatomy and diagnostic reasoning

A 58-year-old male with long-standing poorly controlled arterial hypertension presents with acute headache, nausea, and contralateral dense hemiplegia. An emergent non-contrast head CT demonstrates an acute, homogeneous, hyperdense parenchymal hematoma (measuring 65 to 80 HU) with surrounding hypodense vasogenic edema and local mass effect. What is the most common anatomical site for spontaneous hypertensive intracerebral hemorrhage?

  1. Subcortical lobar frontal white matter
  2. Centrum semiovale
  3. Midbrain tegmentum
  4. Basal ganglia (specifically the putamen and internal capsule) Correct answer.

Explanation

The basal ganglia-predominantly the putamen (50-60%) and thalamus (15-20%)-is the most common anatomical site of spontaneous hypertensive intracerebral hemorrhage. It results from rupture of lipohyalinotic Charcot-Bouchard microaneurysms along the deep lenticulostriate penetrating branches of the middle cerebral artery.

Question 12Neuroimaging, spinal anatomy and diagnostic reasoning

A 21-year-old male sustains head trauma in a boxing match followed by a lucid interval and subsequent rapid neurological deterioration. Non-contrast head CT reveals a hyperdense, biconvex (lentiform) extra-axial collection along the right temporoparietal convexity that does not cross cranial sutures but displaces the dural venous sinus. What is the diagnosis and injured vessel?

  1. Acute subdural hematoma caused by rupture of cortical bridging veins
  2. Acute epidural hematoma caused by laceration of the middle meningeal artery Correct answer.
  3. Chronic subdural hygroma caused by arachnoid membrane tear
  4. Subarachnoid hemorrhage caused by anterior communicating artery aneurysm

Explanation

An acute epidural (extradural) hematoma is classically caused by temporal bone fracture lacerating the middle meningeal artery or its branches. The blood accumulates in the potential space between the inner table of the skull and the periosteal dura mater, forming a high-pressure biconvex (lentiform) collection that is confined by cranial sutures where the dura is tightly attached.

Question 13Neuroimaging, spinal anatomy and diagnostic reasoning

A 52-year-old female presents with progressive focal headaches. Contrast-enhanced brain MRI demonstrates a broad-based, extra-axial, dural-attached mass along the sphenoid ridge. The mass is isointense to cortex on T1 and T2 sequences, enhances vividly and homogeneously with gadolinium, exhibits a tapering peripheral rim of dural enhancement ('dural tail sign'), and induces adjacent hyperostosis of the overlying skull. What is the diagnosis?

  1. Metastatic breast adenocarcinoma to the skull vault
  2. Acoustic vestibular schwannoma
  3. Dural arteriovenous fistula
  4. Benign intracranial meningioma Correct answer.

Explanation

Meningiomas are the most common extra-axial intracranial neoplasms in adults. Classic features include a broad dural base, homogeneous and vivid contrast enhancement, adjacent hyperostosis or reactive bone remodeling, a CSF or vascular cleft separating it from brain parenchyma, and the classic 'dural tail sign' representing reactive dural thickening.

Question 14Neuroimaging, spinal anatomy and diagnostic reasoning

A 60-year-old male with treated bronchogenic adenocarcinoma develops confusion and ataxia. Contrast-enhanced brain MRI reveals multiple, well-circumscribed, round, enhancing nodules located specifically at the corticomedullary (gray-white matter) junctions of both cerebral hemispheres, associated with disproportionately severe, finger-like vasogenic edema in the deep white matter. Which pathophysiology explains this characteristic anatomical distribution?

  1. Embolic hematogenous tumor seeding trapped within the microvasculature at the junction where vessel caliber abruptly narrows Correct answer.
  2. Retrograde perineural tumor extension along the olfactory nerve branches
  3. Direct trans-ependymal cerebrospinal fluid seeding through the ventricles
  4. Local microglial transformation triggered by systemic paraneoplastic antibodies

Explanation

Hematogenous cerebral metastases lodge predominantly at the corticomedullary junction because penetrating arterial vessels undergo an abrupt reduction in caliber at the transition between gray and white matter, functioning as a microvascular filter that traps circulating tumor emboli. Disproportionate vasogenic edema results from tumor-secreted VEGF disrupting the blood-brain barrier.

Question 15Neuroimaging, spinal anatomy and diagnostic reasoning

A 28-year-old male presents with adult-onset focal epilepsy. High-resolution brain MRI demonstrates a 6 mm unilocular cystic lesion in the parietal cortex with CSF-like signal intensity on T1 and T2 sequences. Within the cyst, a 1 mm eccentric, hyperintense mural nodule representing the invaginated scolex ('hole-with-a-dot' sign) is clearly visualized, without surrounding edema or capsule enhancement. According to the Escobar classification of neurocysticercosis, which stage is this?

  1. Granular-nodular stage
  2. Vesicular stage (viable cyst) Correct answer.
  3. Colloidal vesicular stage
  4. Nodular calcified stage

Explanation

In neurocysticercosis (Taenia solium), the vesicular stage represents viable larval cysts. The cyst fluid is clear (matching CSF), the wall is thin and non-enhancing, and the eccentric invaginated scolex appears as a discrete internal nodule ('hole-with-a-dot' sign). Host immune tolerance prevents surrounding edema during this stage.

Question 16Neuroimaging, spinal anatomy and diagnostic reasoning

A 29-year-old female presents with acute unilateral optic neuritis, followed 8 months later by sensory ataxia. Brain MRI demonstrates multiple ovoid T2/FLAIR hyperintense demyelinating plaques oriented perpendicular to the lateral ventricles along subependymal venules ('Dawson fingers'), in addition to juxtacortical, infratentorial, and cervical spinal cord lesions. Which disease does this imaging pattern definitively indicate?

  1. Multiple sclerosis (esclerosis múltiple) Correct answer.
  2. Neuromyelitis optica spectrum disorder (NMOSD)
  3. Acute disseminated encephalomyelitis (ADEM)
  4. Cerebral autosomal dominant arteriopathy (CADASIL)

Explanation

'Dawson fingers' are classic imaging features of multiple sclerosis on sagittal T2/FLAIR MRI, caused by perivenular demyelination extending radially perpendicular to the lateral ventricles. Combined with typical lesions in juxtacortical, infratentorial, and spinal cord locations, they fulfill the McDonald imaging criteria for dissemination in space.

Question 17Neuroimaging, spinal anatomy and diagnostic reasoning

A 32-year-old diver hits his head on the seabed following a shallow dive. Axial cervical spine CT demonstrates bilateral fractures through both the anterior and posterior arches of the atlas (C1 vertebra), with lateral displacement of the lateral masses of C1 relative to the articular pillars of C2 exceeding a combined total of 7 mm on coronal reformations (Spence rule). What is the specific eponym for this cervical spine burst fracture?

  1. Hangman's fracture of C2
  2. Clay-shoveler fracture of C7
  3. Jefferson burst fracture of C1 Correct answer.
  4. Chance distraction fracture

Explanation

A Jefferson fracture is a burst fracture of the atlas (C1) caused by severe axial loading driving the occipital condyles into the lateral masses. It classically produces a four-part fracture involving both the anterior and posterior arches. A combined lateral displacement of C1 lateral masses > 7 mm signifies rupture of the transverse atlantal ligament, establishing mechanical instability.

Question 18Thoracic and cardiovascular imaging patterns

A 42-year-old male evaluated within Cuba's Programa Nacional de Control de la Tuberculosis presents with chronic cough, night sweats, and weight loss. A posteroanterior chest radiograph reveals an apical cavitary lesion with thick, irregular walls in the right upper lobe, associated with adjacent micronodular and fibrotic opacities. Which radiological feature most strongly supports active post-primary pulmonary tuberculosis?

  1. Homogeneous basilar consolidation with air bronchograms and blunting of the costophrenic angle
  2. A thin-walled round radiolucency with an internal mobile dependent mass and air-crescent sign
  3. Thick-walled cavitary lesions located in the apical and posterior segments of the upper lobes with endobronchial tree-in-bud satellite opacities Correct answer.
  4. Diffuse bilateral symmetric interstitial reticular opacities with predominant honeycombing in the lung bases

Explanation

Post-primary (reactivation) pulmonary tuberculosis typically involves the apical and posterior segments of the upper lobes or the superior segment of the lower lobes. Active disease is characterized by thick-walled cavitation accompanied by bronchogenic dissemination manifesting as centrilobular nodules and branching 'tree-in-bud' opacities on imaging, consistent with MINSAP tuberculosis surveillance guidelines.

Question 19Thoracic and cardiovascular imaging patterns

A 35-year-old female presents with sudden high fever, pleuritic chest pain, and rust-colored sputum. Chest radiography reveals homogeneous opacification of the right middle lobe with crisp inferior margination along the major fissure and sharp superior margination along the minor fissure. The right heart border is obscured on the frontal view. What radiological sign does this border obscuration represent?

  1. Golden S sign of Golden
  2. Westermark sign
  3. Cervicothoracic sign
  4. Silhouette sign of Felson Correct answer.

Explanation

Felson's silhouette sign occurs when two structures of the same radiographic density are in direct anatomical contact, obliterating their shared optical margin. Because the right middle lobe anatomically abuts the right atrium, consolidation of the middle lobe silhouettes and obscures the right cardiac border.

Question 20Thoracic and cardiovascular imaging patterns

A 58-year-old post-surgical patient develops sudden dyspnea and tachycardia. Computed tomography pulmonary angiography (CTPA) is performed. Which imaging finding constitutes the direct, definitive diagnostic sign of acute pulmonary embolism?

  1. A complete or partial intraluminal filling defect surrounded by contrast medium forming acute angles with the arterial wall on axial sections Correct answer.
  2. Wedge-shaped peripheral consolidation representing pulmonary infarction with surrounding ground-glass halo
  3. Focal dilatation of the main pulmonary artery trunk exceeding 29 mm without intraluminal filling defects
  4. Abrupt tapering of peripheral segmental vessels with local pleural reaction alone

Explanation

The definitive direct sign of acute pulmonary thromboembolism on contrast-enhanced CTPA is an intraluminal filling defect that is completely occlusive or partially surrounded by contrast material, typically forming acute angles with the vascular wall ('polo-mint' sign in cross section or 'railroad-track' sign on longitudinal views).

Question 21Thoracic and cardiovascular imaging patterns

A 64-year-old heavy smoker presents with hemoptysis. A chest CT reveals a 2.8 cm solitary pulmonary nodule in the left upper lobe. Which morphological feature identified on high-resolution thin-section CT carries the highest positive predictive value for primary bronchogenic carcinoma?

  1. Smooth, round margins with concentric 'target-like' laminated calcification
  2. Corona radiata with fine, radiating spiculation and pleural tagging Correct answer.
  3. Central coarse 'popcorn' calcification with well-defined borders
  4. Extensive internal macroscopic fat attenuation measuring -60 to -100 Hounsfield Units

Explanation

The presence of radiating spiculated margins ('corona radiata') reflects malignant cellular infiltration along adjacent bronchoarterial sheaths, pulmonary septa, and lymphatics, carrying a positive predictive value for malignancy exceeding 90%. Pleural indentation or tagging further increases malignant probability.

Question 22Thoracic and cardiovascular imaging patterns

A 60-year-old male with a 40 pack-year smoking history undergoes high-resolution chest CT (HRCT). The images demonstrate bilateral, non-tapering dilatations of small radiolucent spaces centered around the terminal bronchioles in the upper lobes, with intact surrounding lung parenchyma and thin, barely perceptible walls. Which subtype of emphysema does this describe?

  1. Panlobular (panacinar) emphysema
  2. Paraseptal (distal acinar) emphysema
  3. Centrilobular (centriacinar) emphysema Correct answer.
  4. Cicatricial (irregular) emphysema

Explanation

Centrilobular emphysema is the classic smoking-related emphysema, characterized on HRCT by focal areas of low attenuation centered around the centrilobular core artery within the secondary pulmonary lobule, predominantly affecting the apical and posterior segments of the upper lobes.

Question 23Thoracic and cardiovascular imaging patterns

A 67-year-old male presents with progressive exertional dyspnea and bibasilar end-inspiratory Velcro crackles. Volumetric high-resolution CT (HRCT) of the chest without contrast reveals subpleural, basal-predominant reticular opacities with architectural distortion, traction bronchiectasis, and multilayered subpleural honeycombing, in the absence of micronodules, extensive ground-glass opacity, or mosaic perfusion. Which diagnostic pattern is established?

  1. Definite Non-Specific Interstitial Pneumonia (NSIP)
  2. Cryptogenic Organizing Pneumonia (COP)
  3. Hypersensitivity Pneumonitis (HP) with airway trapping
  4. Definite Usual Interstitial Pneumonia (UIP) pattern Correct answer.

Explanation

Under international and Cuban thoracic consensus guidelines, the presence of subpleural, basilar-predominant reticulation, traction bronchiectasis, and definite honeycombing in the absence of atypical features meets the strict HRCT criteria for a Definite Usual Interstitial Pneumonia (UIP) pattern, obviating the need for surgical lung biopsy in the appropriate clinical context.

Question 24Thoracic and cardiovascular imaging patterns

A 22-year-old trauma victim is maintained in the supine position following a high-speed vehicular collision. An anteroposterior supine bedside chest radiograph is obtained. Which radiological sign indicates the presence of an occult pneumothorax in the supine projection?

  1. Deep sulcus sign with abnormal deepening and radiolucency of the ipsilateral costophrenic angle Correct answer.
  2. Prominent air bronchograms extending to the periphery of the lower lung zone
  3. Elevated hemidiaphragm with ipsilateral mediastinal shift
  4. Homogeneous apical cap opacity with thickening of the apical extrapleural fat

Explanation

In supine patients, intrapleural free air collects anteriorly and basally rather than at the apex. It outlines the anterior costophrenic gutter, producing an abnormally deep, sharp, and hyperlucent costophrenic angle known as the 'deep sulcus sign,' which is a critical sign of occult pneumothorax on supine chest films.

Question 25Thoracic and cardiovascular imaging patterns

A 62-year-old male with long-standing uncontrolled arterial hypertension presents with acute, tearing substernal chest pain radiating to his interscapular region. Contrast-enhanced thoracic CT angiography reveals an intimal flap originating immediately distal to the origin of the left subclavian artery, extending distally along the descending thoracic aorta into the abdominal aorta. What is the correct classification of this condition?

  1. Stanford Type A aortic dissection
  2. Stanford Type B (DeBakey Type III) aortic dissection Correct answer.
  3. Penetrating atherosclerotic ulcer without intramural hematoma
  4. Traumatic aortic pseudoaneurysm of the aortic isthmus

Explanation

Stanford Type B dissections involve exclusively the descending aorta distal to the origin of the left subclavian artery (corresponding to DeBakey Type III), without involvement of the ascending aorta. Stanford Type A dissections involve the ascending aorta and represent surgical emergencies, whereas uncomplicated Type B dissections are primarily managed with rigorous medical hemodynamic control.

Question 26Thoracic and cardiovascular imaging patterns

On an upright posteroanterior chest radiograph, what is the classic radiological finding that represents the accumulation of at least 175 to 200 mL of free pleural fluid in the dependent hemithorax?

  1. Flattening of the ipsilateral hemidiaphragm with contralateral tracheal deviation
  2. Perihilar cuffing with bat-wing alveolar infiltrates
  3. Blunting of the lateral costophrenic angle with a concave-upward fluid curve (meniscus sign) Correct answer.
  4. Triangular retrocardiac opacity silhouetting the left pulmonary artery

Explanation

On an erect frontal chest radiograph, free fluid first accumulates in the posterior costophrenic sulcus (visible at ~50 mL on lateral views) and then fills the lateral costophrenic angle (visible at 175-200 mL), forming a classic homogeneous opacity with a superior concave-upward border known as the meniscus sign.

Question 27Thoracic and cardiovascular imaging patterns

A 48-year-old female presents with bilateral ptosis, diplopia, and progressive muscle fatigue. A contrast-enhanced chest CT reveals a smooth, lobulated, homogeneous soft-tissue mass located in the prevascular (anterior) mediastinum, positioned immediately anterior to the ascending aorta and superior vena cava, with no macroscopic fat or calcification. Which condition is the most likely diagnosis?

  1. Posterior neurogenic schwannoma
  2. Substernal multinodular goiter with colloid cysts
  3. Mature cystic teratoma
  4. Thymoma associated with myasthenia gravis Correct answer.

Explanation

Thymoma is the most common primary tumor of the anterior (prevascular) mediastinum in adults and is strongly associated with myasthenia gravis (present in up to 30-50% of thymoma cases). On CT, it typically appears as a homogeneous, smooth, or lobulated anterior mediastinal soft-tissue mass.

Question 28Thoracic and cardiovascular imaging patterns

A 52-year-old female with a history of recurrent childhood pulmonary infections presents with chronic purulent sputum production and hemoptysis. A high-resolution chest CT (HRCT) demonstrates an internal bronchial luminal diameter substantially exceeding the diameter of its accompanying pulmonary artery branch in the right lower lobe, accompanied by peribronchial wall thickening and lack of peripheral bronchial tapering. Which pathognomonic CT sign does this represent?

  1. Signet ring sign indicative of bronchiectasis Correct answer.
  2. Gloved-finger sign indicative of allergic bronchopulmonary aspergillosis
  3. Crazy-paving pattern indicative of pulmonary alveolar proteinosis
  4. Comet tail sign indicative of round atelectasis

Explanation

The 'signet ring sign' on HRCT is diagnostic of bronchiectasis. The dilated bronchus viewed in cross-section appears as a ring of soft tissue representing the thickened bronchial wall, adjacent to a smaller opacified circular pulmonary arteriole, resembling a signet or pearl ring (bronchoarterial ratio > 1.0 to 1.5).

Question 29Thoracic and cardiovascular imaging patterns

A 40-year-old female with systemic lupus erythematosus presents with dyspnea, orthopnea, and distant heart sounds. A posteroanterior chest radiograph demonstrates marked symmetrical enlargement of the cardiac silhouette with a globular, flask-like or 'water-bottle' contour and sharp margins, without pulmonary venous congestion. What is the most likely diagnosis?

  1. End-stage dilated cardiomyopathy with biventricular failure
  2. Large pericardial effusion Correct answer.
  3. Severe mitral stenosis with giant left atrium
  4. Large mediastinal liposarcoma encasing the great vessels

Explanation

Rapid or massive accumulation of pericardial fluid causes generalized enlargement of the cardiac shadow with smooth, rounded contours and sharp cardiophrenic angles, classic for the 'water-bottle' or flask-shaped heart. The absence of pulmonary congestion helps distinguish simple pericardial effusion from true congestive heart failure.

Question 30Abdominal and pelvic imaging: localization and pattern analysis

A 19-year-old male presents to the emergency surgical service with 24 hours of periumbilical pain radiating to the right iliac fossa, fever, and rebound tenderness. Graded-compression ultrasonography of the right lower quadrant is performed. Which combination of sonographic findings establishes the definitive diagnosis of acute appendicitis?

  1. Compressible tubular structure measuring 4 mm in outer diameter with peristalsis
  2. Collapsed blind-ending loop surrounded by clear ascites with normal wall thickness
  3. Non-compressible, blind-ending tubular structure with an outer diameter greater than 6 mm, target sign on cross-section, and hyperemic wall on color Doppler Correct answer.
  4. Echogenic mucosal focus with posterior acoustic shadowing inside the terminal ileum

Explanation

The established sonographic criteria for acute appendicitis on graded compression include an aperistaltic, non-compressible blind-ending tubular structure with an outer diameter exceeding 6 mm, mural thickening (> 2 mm), a 'target' or 'halo' pattern in transverse section, appendiceal wall hyperemia on color Doppler, and prominent echogenic periappendiceal fat stranding.

Question 31Abdominal and pelvic imaging: localization and pattern analysis

A 44-year-old multiparous woman presents with severe right upper quadrant pain, nausea, vomiting, and low-grade fever after consuming fatty foods. Transabdominal ultrasonography reveals impacted stones in the gallbladder neck, diffuse gallbladder wall thickening of 5 mm, pericholecystic fluid, and exquisite focal tenderness when the transducer directly compresses the visible gallbladder. What is this crucial clinical-ultrasound finding called?

  1. Courvoisier sign
  2. Rovsing sign
  3. Blumberg sign
  4. Sonographic Murphy sign Correct answer.

Explanation

The sonographic Murphy sign refers to maximal focal tenderness elicited by direct mechanical compression with the ultrasound probe over the visualized gallbladder. Combined with gallstones, wall thickening (> 3 mm), and pericholecystic fluid, its positive predictive value for acute calculous cholecystitis exceeds 92%.

Question 32Abdominal and pelvic imaging: localization and pattern analysis

A 68-year-old male with a history of peptic ulcer disease presents with sudden, catastrophic epigastric pain and board-like abdominal rigidity. On a supine abdominal radiograph, gas is seen outlining both the inner mucosal and outer serosal surfaces of the small bowel wall. What is this classic radiographic sign of massive pneumoperitoneum?

  1. Rigler sign (double wall sign) Correct answer.
  2. Football sign
  3. Inverted V sign
  4. Chilaiditi sign

Explanation

Rigler's sign (double wall sign) occurs when free intraperitoneal gas outlines the outer serosal surface of the bowel wall while normal intraluminal gas outlines its inner mucosal surface, making both sides of the bowel wall distinctly visible as a sharp linear stripe on supine radiographs.

Question 33Abdominal and pelvic imaging: localization and pattern analysis

A 60-year-old female with a prior history of open hysterectomy presents with cramping abdominal pain, obstipation, and bilious vomiting. Contrast-enhanced abdominal CT shows multiple small bowel loops dilated to 3.8 cm with intraluminal air-fluid levels, an abrupt transition point in the right lower quadrant, and collapsed distal ileal loops and colon. No intraluminal mass, mural hematoma, or inflammatory stranding is identified at the transition point. What is the most likely etiology?

  1. Adenocarcinoma of the small bowel
  2. Postoperative peritoneal adhesive band Correct answer.
  3. Gallstone ileus with Rigler triad
  4. Ileocolic intussusception

Explanation

Postoperative peritoneal adhesions account for 60-75% of mechanical small bowel obstructions. On CT, an adhesive band typically manifests as an abrupt discrete transition point from dilated to collapsed loops without intrinsic mural thickening, soft-tissue mass, or abnormal calcification.

Question 34Abdominal and pelvic imaging: localization and pattern analysis

A 38-year-old male with acute small bowel obstruction undergoes emergency abdominal CT. The scan demonstrates a C-shaped loop of distended fluid-filled small bowel with two transition points converging at a single anatomical site, severe mesenteric vessel twisting ('whirl sign'), engorged mesenteric veins, and diminished mural enhancement of the closed loop. What critical condition does this signify?

  1. Simple paralytic ileus secondary to hypokalemia
  2. Uncomplicated distal partial adhesive obstruction
  3. Closed-loop small bowel obstruction with impending strangulation and ischemia Correct answer.
  4. Acute pseudomembranous colitis with toxic megacolon

Explanation

A closed-loop obstruction occurs when a bowel segment is occluded at two points along its length (e.g., beneath an adhesive band or internal hernia), trapping secretions and gas. The mesenteric 'whirl sign', converging vascular pedicles, and poor mural enhancement indicate vascular compromise, representing a surgical emergency to prevent transmural necrosis and perforation.

Question 35Abdominal and pelvic imaging: localization and pattern analysis

An 82-year-old institutionalized male with chronic constipation presents with massive abdominal distension and obstipation. An abdominal radiograph reveals a huge, ahaustral, gas-distended loop of large bowel arising from the pelvis and projecting toward the right upper quadrant, with its medial walls converging toward the left lower quadrant, resembling a bent inner tube or coffee bean. Which diagnosis is confirmed?

  1. Sigmoid volvulus Correct answer.
  2. Cecal volvulus
  3. Acute appendiceal mucocele
  4. Intussusception of the transverse colon

Explanation

Sigmoid volvulus accounts for the vast majority of colonic volvulus cases in elderly patients. Torsion of the redundant sigmoid loop on its mesentery produces the classic 'coffee-bean' or bent inner-tube sign, with the apex pointing toward the right upper quadrant and the converging limbs arising from the left lower quadrant.

Question 36Abdominal and pelvic imaging: localization and pattern analysis

A 38-year-old asymptomatic woman undergoes an abdominal ultrasound, revealing a well-defined, homogeneous, hyperechoic mass measuring 3.5 cm in hepatic segment VII. A multiphase contrast-enhanced CT of the liver is performed. Which dynamic enhancement pattern is pathognomonic for a cavernous hepatic hemangioma?

  1. Intense, rapid homogeneous enhancement in the early arterial phase with immediate washout in the portal venous phase
  2. Early, peripheral, nodular, discontinuous enhancement during the arterial phase with progressive, centripetal 'puddle' fill-in on portal venous and delayed phases Correct answer.
  3. Homogeneous arterial enhancement with non-enhancing central stellate scar that enhances on delayed phases
  4. Continuous thick, irregular rim enhancement with central non-enhancing necrosis

Explanation

Cavernous hemangioma is the most common benign mesenchymal hepatic tumor. Its diagnostic hallmark on multiphase CT/MRI is peripheral, globular, nodular discontinuous enhancement on the arterial phase, followed by progressive centripetal fill-in that matches the attenuation of the blood pool (aorta and portal vein) on delayed scans.

Question 37Abdominal and pelvic imaging: localization and pattern analysis

A 54-year-old male with chronic hepatitis B and cirrhosis undergoes liver ultrasound surveillance, which identifies a new 2.4 cm nodule in segment VI. Multiphase dynamic contrast CT is performed. Which dynamic enhancement behavior confirms the non-invasive diagnosis of Hepatocellular Carcinoma (HCC) without requiring biopsy according to AASLD and Cuban oncology guidelines?

  1. Peripheral nodular discontinuous puddling with complete delayed centripetal fill-in
  2. Persistent hypovascularity on all phases with marked delayed capsular retraction
  3. Non-rim arterial phase hyperenhancement followed by delayed-phase or portal venous phase 'washout' with an enhancing pseudo-capsule Correct answer.
  4. Uniform target-like peripheral halo on portal venous phase with no arterial enhancement

Explanation

In cirrhotic livers, the non-invasive diagnostic criteria for HCC (LI-RADS LR-5 / AASLD / Cuban clinical consensus) are met when a nodule >= 10 mm exhibits non-rim arterial phase hyperenhancement (APHE) followed by 'washout' appearance in the portal venous or delayed phase, often accompanied by an enhancing fibrous pseudocapsule.

Question 38Abdominal and pelvic imaging: localization and pattern analysis

A 32-year-old female taking oral contraceptives undergoes an abdominal MRI for non-specific upper abdominal discomfort. A solitary, well-circumscribed 4.5 cm liver lesion is identified. It shows bright, homogeneous enhancement on the arterial phase with rapid return to isointensity relative to liver on the portal phase, and contains a central stellate scar that is hypointense on T1, hyperintense on T2, and shows delayed gadolinium enhancement. What is the diagnosis?

  1. Hepatic adenoma (inflammatory subtype)
  2. Fibrolamellar hepatocellular carcinoma
  3. Biliary cystadenoma
  4. Focal nodular hyperplasia (FNH) Correct answer.

Explanation

Focal nodular hyperplasia (FNH) is a benign, non-neoplastic liver lesion resulting from a hyperplastic response to a pre-existing congenital vascular malformation. On MRI, its classic feature is vivid, homogeneous arterial enhancement with isointensity on portal/delayed phases, and a pathognomonic central stellate scar that is T2 hyperintense and shows characteristic delayed contrast enhancement.

Question 39Abdominal and pelvic imaging: localization and pattern analysis

A 26-year-old female presents with recurrent crampy abdominal pain, non-bloody diarrhea, low-grade fever, and weight loss. CT enterography demonstrates discontinuous segments of transmural mural hyperenhancement, marked submucosal edema, mesenteric fibrofatty proliferation ('creeping fat'), and engorged vasa recta perpendicular to the bowel wall ('comb sign') in the terminal ileum. What is the diagnosis?

  1. Crohn's disease (enfermedad de Crohn) Correct answer.
  2. Ulcerative colitis (colitis ulcerosa)
  3. Ischemic colitis
  4. Infectious typhlitis (neutropenic enterocolitis)

Explanation

Transmural inflammation, skip lesions (discontinuous involvement), mesenteric fibrofatty proliferation ('creeping fat'), and the 'comb sign' (mesenteric vascular engorgement of the vasa recta) are hallmark CT enterography findings of active Crohn's disease, distinguishing it from mucosal-limited ulcerative colitis.

Question 40Abdominal and pelvic imaging: localization and pattern analysis

A 45-year-old male presents with progressive dysphagia to both liquids and solids, accompanied by regurgitation of undigested food. A dynamic fluoroscopic barium swallow reveals marked dilatation and tortuosity of the esophageal body, absent primary peristalsis, and smooth, symmetric, tapered narrowing of the distal gastroesophageal junction. What classic radiological sign is demonstrated?

  1. Corkscrew esophagus
  2. Feline esophagus
  3. Apple-core defect
  4. Bird-beak (pico de pájaro) sign Correct answer.

Explanation

The 'bird-beak' (pico de pájaro) sign is pathognomonic of achalasia on barium esophagography. It results from persistent, failure of relaxation of the lower esophageal sphincter (LES) producing smooth, symmetric tapering at the gastroesophageal junction beneath a dilated, aperistaltic esophagus.

Question 41Pediatric, obstetric and breast imaging foundations

A premature neonate born at 30 weeks of gestation develops grunting, tachypnea, and severe intercostal retractions 2 hours after birth. A bedside frontal neonatal chest radiograph demonstrates diffuse, symmetrical fine reticulogranular opacities ('ground-glass' appearance) throughout both lung fields, accompanied by prominent air bronchograms extending into the lung periphery and generalized low lung volumes. What is the diagnosis?

  1. Meconium aspiration syndrome
  2. Transient tachypnea of the newborn (wet lung)
  3. Respiratory Distress Syndrome (hyaline membrane disease) Correct answer.
  4. Congenital diaphragmatic hernia

Explanation

Respiratory Distress Syndrome (RDS / hyaline membrane disease) is caused by surfactant deficiency in premature infants. Its classic radiographic triad consists of uniform, fine reticulogranular (ground-glass) opacities, prominent air bronchograms extending into peripheral airways, and diffuse hypoexpansion (low lung volumes).

Question 42Pediatric, obstetric and breast imaging foundations

An 8-month-old infant presents with bouts of severe inconsolable colicky crying, vomiting, and passage of dark red 'currant-jelly' stools. Abdominal ultrasound demonstrates a multi-layered, concentric mass measuring 3.2 cm in the right upper quadrant, showing a 'doughnut' or 'target' appearance in transverse plane and a 'pseudokidney' appearance in longitudinal plane. If there are no signs of peritonitis or perforation, what is the initial non-operative therapeutic procedure of choice?

  1. Ultrasound- or fluoroscopy-guided pneumatic (air) or hydrostatic reduction under controlled pressure Correct answer.
  2. Immediate exploratory laparotomy with bowel resection
  3. High-dose intravenous methylprednisolone administration
  4. Placement of a transjugular intrahepatic portosystemic shunt

Explanation

In uncomplicated pediatric ileocolic intussusception (without peritonitis, pneumoperitoneum, or hemodynamic shock), image-guided pneumatic (air enema) or hydrostatic reduction is the standard of care, with success rates exceeding 80-90%. Air pressure is strictly monitored (typically <= 100-120 mmHg in infants).

Question 43Pediatric, obstetric and breast imaging foundations

A 52-year-old asymptomatic female undergoes routine screening mammography within the Cuban National Breast Cancer Control Program (Programa Nacional de Detección Precoz del Cáncer de Mama). Both craniocaudal and mediolateral oblique views reveal symmetrical, radiolucent fibroglandular patterns without masses, architectural distortion, or microcalcifications. Under the ACR BI-RADS system, how should this screening mammogram be classified?

  1. BI-RADS 0: Incomplete assessment
  2. BI-RADS 3: Probably benign finding
  3. BI-RADS 1: Negative (completely normal mammogram, routine screening recommended) Correct answer.
  4. BI-RADS 4: Suspicious abnormality

Explanation

BI-RADS 1 denotes a completely negative, normal examination with no masses, architectural distortion, or suspicious calcifications. The management recommendation is to continue routine age-appropriate screening as outlined in national health guidelines.

Question 44Pediatric, obstetric and breast imaging foundations

On diagnostic magnification mammography, a cluster of microcalcifications is detected in the upper outer quadrant of the left breast. The calcifications are thin, irregular, branching, casting-type calcifications (< 0.5 mm) with varying shapes and discontinuous linear fragments tracing along the ductal system. Under the BI-RADS lexicon, which morphological type and assessment category is this?

  1. Round and punctate microcalcifications; BI-RADS 2
  2. Coarse 'popcorn-like' calcifications; BI-RADS 2
  3. Milk of calcium in microcysts; BI-RADS 2
  4. Fine linear and fine-linear branching (casting) microcalcifications; BI-RADS 4C or 5, highly suspicious for ductal carcinoma in situ (DCIS) Correct answer.

Explanation

Fine linear and fine-linear branching (casting) microcalcifications are thin, irregular calcifications filling the lumen of malignant ducts in ductal carcinoma in situ (DCIS) or high-grade invasive ductal carcinoma. They carry the highest positive predictive value for breast malignancy (> 70-90%) and are categorized as BI-RADS 4C or 5, requiring stereotactic or vacuum-assisted biopsy.

Question 45Pediatric, obstetric and breast imaging foundations

A 28-year-old primigravida attends her first-trimester prenatal genetic ultrasound under the Cuban National Maternal-Child Health Program (PAMI). The examination is performed between 11 weeks 0 days and 13 weeks 6 days of gestation. To obtain a scientifically valid and standardized measurement of fetal Nuchal Translucency (NT) according to Fetal Medicine Foundation (FMF) and PAMI protocols, which criterion is mandatory?

  1. The crown-rump length (CRL) must be between 20 mm and 40 mm with the fetal neck in extreme hyperextension
  2. The image must show a mid-sagittal view of the fetal profile with the fetal neck in a neutral position, magnifying the head and thorax to fill the screen, placing calipers strictly on the inner borders of the nuchal line Correct answer.
  3. The measurement must be obtained on a transverse axial plane through the fetal cerebellum
  4. The calipers must be placed on the outer skin margin and outer surface of the amnion

Explanation

Standardized FMF and PAMI guidelines require: (1) crown-rump length between 45 mm and 84 mm (11+0 to 13+6 weeks); (2) strict mid-sagittal section showing the echogenic tip of the nose, rectangular shape of the palate, and translucent diencephalon; (3) neutral fetal neck position; (4) maximum magnification (fetal head and thorax filling >= 75% of the screen); and (5) calipers placed strictly on the inner borders of the echogenic lines defining the translucency.

Question 46Pediatric, obstetric and breast imaging foundations

A 22-year-old pregnant woman at 21 weeks of gestation undergoes routine fetal anatomical survey under PAMI. Axial cranial sonography demonstrates inward scalloping of the frontal bones ('lemon sign') and caudal displacement of the cerebellum with an anteriorly curved, crescentic cerebellar contour obliterating the cisterna magna ('banana sign'), accompanied by ventriculomegaly. Which major congenital anomaly is indicated by these cranial signs?

  1. Holoprosencephaly
  2. Dandy-Walker malformation
  3. Open neural tube defect (spina bifida / myelomeningocele with Chiari II malformation) Correct answer.
  4. Agenesis of the corpus callosum

Explanation

The 'lemon sign' (frontal calvarial collapse caused by reduced intracranial pressure) and 'banana sign' (downward herniation and curvature of the cerebellar hemispheres through the foramen magnum obliterating the cisterna magna) are cranial sonographic markers of Chiari II malformation, present in > 95% of fetuses with open spina bifida (myelomeningocele).

Question 47Imaging physics, beam interactions and useful calculations

A 45-year-old patient undergoes an urgent contrast-enhanced abdominal CT for suspected acute intra-abdominal pathology. According to radiation protection standards and ALARA principles reinforced in Cuban radiological practice, which parameter adjustment provides the most substantial reduction in patient radiation dose while maintaining diagnostic image quality?

  1. Activating automated tube current modulation based on patient body habitus attenuation Correct answer.
  2. Increasing peak tube potential to the scanner maximum of 140 kVp
  3. Decreasing detector pitch to less than 0.5 without changing tube current
  4. Extending anatomical scan length to include the entire thoracic cage routinely

Explanation

Automated tube current modulation (ATCM) adjusts the mA dynamically in the x, y, and z axes according to patient anatomical attenuation profiles, achieving dose reductions of 20% to 50% without compromising diagnostic image fidelity. This is a foundational principle of radiation protection under ALARA and international standards adopted by the Cuban radiological system.

Question 48Imaging physics, beam interactions and useful calculations

While performing a spectral Doppler interrogation of the common carotid artery, the radiologist observes that the peak systolic velocity waveforms appear wrapped around and displayed in the reverse channel at the bottom of the tracing. Which machine adjustment correctly resolves this Doppler aliasing artifact?

  1. Switching to a higher ultrasound transducer frequency
  2. Increasing the Pulse Repetition Frequency (PRF) or velocity scale Correct answer.
  3. Increasing the Doppler gain to maximum output
  4. Steering the Doppler angle closer to 90 degrees relative to flow

Explanation

Spectral Doppler aliasing occurs when the Doppler frequency shift exceeds the Nyquist limit (one-half of the pulse repetition frequency: PRF/2). Increasing the PRF raises the Nyquist limit, allowing high systolic velocities to be displayed without waveform cut-off or directional wrapping.

Question 49Imaging physics, beam interactions and useful calculations

In conventional radiography, an anti-scatter grid is placed between the patient and the image receptor when imaging thick anatomical regions such as the pelvis or spine. What is the primary physical trade-off associated with utilizing a higher grid ratio?

  1. Improved spatial resolution accompanied by a reduction in patient radiation dose
  2. Decreased radiographic contrast accompanied by severe geometric magnification
  3. Superior scatter radiation clean-up and improved contrast, requiring an increase in patient exposure (mAs) Correct answer.
  4. Complete elimination of penumbra with decreased x-ray tube anode heating

Explanation

Higher grid ratios (e.g., 12:1 or 16:1) absorb a higher percentage of scattered Compton photons, resulting in marked improvement in radiographic contrast. However, because the lead strips also absorb a proportion of primary diagnostic photons (grid cut-off and attenuation), the Bucky factor increases, necessitating higher mAs and consequently higher patient radiation dose.

Question 50Imaging physics, beam interactions and useful calculations

A patient with suspected diffuse axonal injury undergoes brain MRI. Which magnetic resonance sequence utilizes gradient echoes without refocusing 180-degree radiofrequency pulses, providing the highest sensitivity for detecting microscopic blooming artifacts from intracellular and extracellular petechial hemosiderin deposits?

  1. T2-weighted fast spin-echo (FSE)
  2. Diffusion-weighted imaging with b=0 s/mm²
  3. T1-weighted fluid-attenuated inversion recovery (FLAIR)
  4. Susceptibility-weighted imaging (SWI) or T2*-weighted gradient-recalled echo Correct answer.

Explanation

Susceptibility-weighted imaging (SWI) and T2*-weighted GRE sequences lack 180-degree refocusing pulses, making them exquisitely sensitive to magnetic field inhomogeneities caused by paramagnetic blood breakdown products (hemosiderin and deoxyhemoglobin). This creates prominent local signal loss ('blooming artifact'), detecting tiny petechial hemorrhages in diffuse axonal injury.