Arab Board Radiology Final Written cheat sheet

MCA territory infarct: loss of insular ribbon, obscured lentiform nucleus, and cortical swelling within 3-6 h; hyperdense MCA sign reflects thrombus.

ASPECTS: 10-point scoring of 10 MCA regions on non-contrast CT; each affected region subtracts 1 point; score ≤7 suggests large core.

ICH on CT: hyperdense acute blood; use ABC/2 (A×B×C/2) for volume; intraventricular extension and hydrocephalus worsen prognosis.

SAH: non-contrast CT sensitivity ~100% within 6 h, falls after 5-7 days; xanthochromia in CSF peaks at 12 h-2 weeks.

Acute spinal cord compression: epidural mass, cord signal change on T2; cauda equina shows nerve root clumping and enhancement.

Herniation syndromes: subfalcine (ACA), uncal (CN III palsy, PCA infarct), tonsillar (respiratory arrest); midline shift >5 mm is significant.

Huntington and CJD: caudate atrophy with boxcar ventricles; CJD shows cortical ribboning and basal ganglia hyperintensity on DWI/FLAIR.

Head and neck: nodal necrosis and extracapsular spread are key prognostic features in squamous cell carcinoma; retropharyngeal nodes are first-echelon.

Pituitary macroadenoma: snowman appearance with suprasellar extension; microadenoma best seen as delayed enhancing lesion on dynamic MRI.

Fleischner criteria: incidental solid nodule ≥8 mm needs PET/CT or tissue sampling; ≤6 mm in low-risk needs no routine follow-up.

Nodule growth: volume doubling time 100-400 days favors malignancy; <30 days suggests infection; >400 days suggests benign.

Honeycombing with basal and subpleural predominance indicates usual interstitial pneumonia (UIP); traction bronchiectasis supports fibrosis.

PE on CTPA: filling defect in contrast-opacified artery; right heart strain shows RV/LV ratio >1.0 and septal bowing.

Mosaic attenuation: air trapping on expiratory scans favors small airways disease; normal expiration favors vascular cause.

Mediastinal compartments: anterior (thymoma, teratoma, thyroid, lymphoma), middle (nodes, cysts), posterior (neurogenic tumors).

Sarcoidosis: bilateral hilar and right paratracheal lymphadenopathy with perilymphatic nodules; lambda sign on gallium.

Pneumothorax on supine radiograph: deep sulcus sign and increased hemidiaphragm lucency; tension shows mediastinal shift.

Coronary CTA: calcium score >400 limits specificity; use prospective ECG gating and beta-blockers to target heart rate <65 bpm.

Aortic dissection: Stanford A involves ascending aorta and needs urgent surgery; Stanford B is managed medically unless complicated.

IMH and PAU are variants of acute aortic syndrome; IMH shows crescent high attenuation without flow on non-contrast CT.

Cardiac MRI: delayed enhancement with subendocardial pattern favors ischemic disease; mid-wall favors non-ischemic cardiomyopathy.

Myocardial iron overload shows low T2* (<20 ms); amyloid shows diffuse subendocardial enhancement and abnormal nulling.

Acute myocarditis: Lake Louise criteria (edema on T2, non-ischemic LGE, increased T1/T2 mapping).

Aortic stenosis grading: severe when peak velocity ≥4 m/s, mean gradient ≥40 mmHg, or valve area <1.0 cm².

Pulmonary hypertension on CT: main pulmonary artery ≥29 mm and PA:aorta ratio >1 suggests elevated pressure.

LI-RADS: LR-5 requires arterial hyperenhancement plus washout, capsule, or threshold growth in at-risk liver.

Liver segment anatomy by Couinaud uses hepatic veins and portal vein bifurcation; segment I is the caudate lobe.

Acute appendicitis: dilated appendix >6 mm, wall thickening, periappendiceal fat stranding; appendicolith in ~30%.

Bowel obstruction: dilated loops >3 cm (small bowel) or >6 cm (colon); transition point and air-fluid levels are key.

Crohn disease: transmural inflammation, skip lesions, creeping fat, and comb sign (engorged vasa recta).

Pancreatitis: interstitial vs necrotizing; necrosis is non-enhancing and predicts worse outcome; Balthazar grading predicts severity.

Biliary: Mirizzi syndrome is common hepatic duct compression by a stone in the cystic duct or gallbladder neck.

Hepatic hemangioma: peripheral nodular enhancement with centripetal fill-in; no washout; high T2 signal (lightbulb).

Bosniak classification: category I-II benign; IIF needs follow-up; III and IV need surgery; enhancement and nodularity define higher categories.

Renal cell carcinoma: clear cell shows avid enhancement and washout; papillary is hypovascular; chromophobe is homogeneous.

Prostate PI-RADS: score 4-5 lesions in peripheral zone show marked restricted diffusion; transition zone uses T2 as dominant sequence.

Ovarian mass: simple cyst <5 cm in premenopausal needs no follow-up; complex or solid features raise O-RADS category.

Adnexal torsion: enlarged edematous ovary with peripheral follicles and twisted pedicle; Doppler may be normal.

Renal artery stenosis: Doppler peak systolic velocity >180-200 cm/s and tardus-parvus waveform distally.

Testicular mass: seminoma is homogeneous and hypointense on T2; non-seminoma is heterogeneous with hemorrhage and necrosis.

Bladder cancer staging: muscle invasion (T2) changes management; VI-RADS uses DWI and dynamic contrast for staging.

Bone tumor: osteosarcoma shows aggressive periosteal reaction (Codman triangle, sunburst); Ewing shows onion-skin periosteal reaction.

Simple bone cyst: centrally lucent, fallen fragment sign; aneurysmal bone cyst shows fluid-fluid levels.

Osteomyelitis: earliest sign is periosteal reaction or soft tissue swelling; MRI shows marrow edema and rim-enhancing abscess.

Rotator cuff: supraspinatus most commonly torn; full-thickness tear shows tendon gap and fluid; MRI arthrography improves sensitivity.

Meniscal tear: grade 3 signal reaches articular surface; horizontal cleavage in older patients; displaced fragment = bucket-handle.

ACL tear: primary sign is discontinuity and increased signal; secondary signs include bone contusion and pivot-shift edema.

Stress fracture: earliest on MRI (bone marrow edema); radiographs lag 2-3 weeks; scintigraphy is sensitive but nonspecific.

Sarcoma staging: compartmental extent and neurovascular involvement determine resectability; MRI is modality of choice.

BI-RADS categories: 0 incomplete, 1 negative, 2 benign, 3 probably benign (<2% malignancy), 4 suspicious, 5 highly suggestive (≥95%), 6 known malignancy.

Screening mammography detects microcalcifications best; clustered pleomorphic or linear branching calcifications are suspicious.

Mass descriptors: shape, margin (circumscribed vs spiculated), and density; spiculated high-density mass is highly suspicious.

Ultrasound: oval, circumscribed, parallel orientation suggests benign; irregular, non-parallel, hypoechoic with shadowing is suspicious.

MRI kinetics: rapid initial rise with delayed washout favors malignancy; persistent enhancement favors benign.

Ductal carcinoma in situ: often calcifications only; comedo type shows linear branching calcifications and higher grade.

Sentinel node biopsy is standard for axillary staging in clinically node-negative invasive cancer.

Male breast cancer: subareolar mass; gynecomastia is flame-shaped and bilateral, sparing the subareolar fat.

Neonatal bowel: malrotation shows corkscrew sign on upper GI; volvulus is a surgical emergency.

Intussusception: target sign on ultrasound; contrast enema is both diagnostic and therapeutic in stable patients.

Pyloric stenosis: hypertrophied pylorus >3 mm thick and >14 mm long on ultrasound; target sign on radiograph.

Necrotizing enterocolitis: pneumatosis intestinalis, portal venous gas, and pneumoperitoneum are key signs.

Developmental dysplasia of the hip: ultrasound before 6 months (alpha angle <60° abnormal); radiograph after 4-6 months.

Medulloblastoma arises in the cerebellar vermis and shows restricted diffusion; ependymoma arises in the fourth ventricle floor.

Neuroblastoma: calcification, crosses midline, elevated catecholamines; Wilms tumor arises in kidney and displaces it.

Congenital diaphragmatic hernia: bowel in thorax, mediastinal shift, hypoplastic lungs; mortality predicted by liver herniation.

Child abuse: metaphyseal corner fractures and posterior rib fractures are highly specific for non-accidental trauma.

Seldinger technique: needle, wire, catheter; confirm wire position before catheter advancement.

Embolization agents: coils for large vessels, particles for tumor/bleeding, glue for varices, and gelfoam for temporary occlusion.

TACE is used for intermediate-stage HCC; radioembolization (Y-90) requires shunt evaluation with macroaggregated albumin.

Portal hypertension: TIPS reduces portosystemic gradient; target gradient 8-12 mmHg; encephalopathy is a major complication.

Aortic aneurysm EVAR: landing zones and neck morphology determine feasibility; endoleak types I-IV guide management.

Nephrostomy and biliary drainage: confirm position and drainage; hematuria and cholangitis are common complications.

Radiofrequency ablation: heat-based; ground-pad placement and impedance monitoring are important; avoid near large vessels (heat sink).

Vertebroplasty: cement leakage into veins or spinal canal is the main risk; use high-viscosity cement and fluoroscopic guidance.

FDG-PET: uptake reflects glucose metabolism; SUVmax is semiquantitative; physiologic uptake in brain, heart, kidneys, and bladder.

Bone scan: Tc-99m MDP; three-phase study for osteomyelitis; superscan shows diffuse uptake with absent renal uptake.

V/Q scan: high-probability pattern is ≥2 segmental mismatched perfusion defects; PIOPED criteria guide probability.

Thyroid: I-131 therapy for hyperthyroidism and differentiated cancer; pregnancy is an absolute contraindication.

Sentinel node: Tc-99m sulfur colloid or blue dye; preoperative lymphoscintigraphy maps drainage.

DOTATATE PET: somatostatin receptor imaging for neuroendocrine tumors; higher sensitivity than octreotide scan.

Myocardial perfusion: stress-rest reversibility indicates ischemia; fixed defect indicates scar.

PSMA PET: prostate cancer staging and recurrence; higher sensitivity than conventional imaging at low PSA.

Attenuation: I = I0 × e^(-μx); half-value layer (HVL) = 0.693/μ; HVL increases with beam energy.

CT numbers: Hounsfield units = 1000 × (μ_tissue − μ_water)/μ_water; water = 0, air = −1000, bone = +1000.

MRI: T1 and T2 relaxation; TR controls T1 weighting, TE controls T2 weighting; fat is bright on T1.

MRI safety: ferromagnetic projectiles, heating, and acoustic noise; pacemakers and implants need MR-conditional status.

Ultrasound: frequency and resolution are inversely related; higher frequency improves resolution but reduces penetration.

Radiation dose: effective dose in mSv; CT abdomen ~10 mSv; chest radiograph ~0.1 mSv.

ALARA and dose reduction: tube current modulation, iterative reconstruction, and appropriate collimation.

Image quality: contrast, spatial resolution, noise, and artifacts; quantum mottle is photon-starvation noise.

Linear-quadratic model: survival fraction = e^-(αD + βD²); α/β ratio is ~10 for tumors and ~2-3 for late-responding tissues.

Radiosensitivity: Bergonie-Tribondeau law - rapidly dividing, undifferentiated cells are most sensitive.

Fractionation spares late effects because repair of sublethal damage is greater in late-responding tissues.

Stochastic effects (cancer, hereditary) have no threshold; deterministic effects (skin, cataract) have thresholds.

Cataract threshold ~0.5 Gy; erythema ~2 Gy; permanent sterility higher; use ICRP thresholds.

Occupational dose limit: 20 mSv/year averaged over 5 years (50 mSv in any single year); public limit 1 mSv/year.

Pregnancy: lead apron and dose monitoring; fetal dose <50 mGy generally considered low risk.

Shielding: half-value layer and tenth-value layer; lead equivalence of aprons is typically 0.35-0.5 mm Pb.

Justification and optimization are core principles: every examination must have a clinical indication and be optimized for dose.

Radiation incidents: report to the regulator; investigate root cause; document corrective actions.

Contrast safety: check renal function and allergy history; premedicate high-risk patients; anaphylaxis management with epinephrine.

Gadolinium: NSF risk with linear agents in severe renal impairment; macrocyclic agents are preferred in renal failure.

Peer review and audit: structured reporting, double reading, and discrepancy review improve diagnostic quality.

Communication of critical results: closed-loop communication documented in the record.

Consent: informed consent for invasive procedures; document risks, benefits, and alternatives.

Infection control: standard precautions, sterile technique for interventions, and safe sharps disposal.

CT colonography: requires bowel preparation, insufflation, and both supine and prone positioning; polyps ≥6 mm are reported.

Ischemic colitis: thumbprinting, wall thickening, and watershed distribution (splenic flexure).

SMA syndrome: duodenal obstruction from narrow aortomesenteric angle (<25°) and distance (<8 mm).

Cirrhosis: nodular contour, enlarged caudate lobe, and portal hypertension signs (varices, splenomegaly, ascites).

Cholangiocarcinoma: peripheral mass-forming type shows delayed enhancement; hilar type causes biliary obstruction.

Gastric cancer: CT staging evaluates wall invasion and nodes; peritoneal deposits are a key limitation.

Appendiceal mucocele: cystic mass with mural calcification; avoid rupture during surgery.

Hepatic abscess: rim-enhancing collection with central low attenuation; gas may be present.

Osteoarthritis: joint space narrowing, subchondral sclerosis, osteophytes, and subchondral cysts.

Rheumatoid arthritis: symmetric erosions, periarticular osteopenia, and MCP/PIP involvement; sparing of DIP joints.

Gout: juxta-articular erosions with overhanging edges and tophi; preservation of joint space until late.

CPPD: chondrocalcinosis in menisci and triangular fibrocartilage; degenerative changes in atypical joints.

Ankylosing spondylitis: sacroiliitis, syndesmophytes, and bamboo spine; MRI shows bone marrow edema early.

Bone density: DXA T-score ≤ −2.5 defines osteoporosis; −1.0 to −2.5 is osteopenia.

Avascular necrosis: early MRI shows double-line sign; late shows sclerosis and collapse.

Soft tissue sarcoma: MRI for local staging; heterogeneity and necrosis suggest higher grade.