ABR (NAR) cheat sheet

BI-RADS density categories: a = almost entirely fatty, b = scattered fibroglandular, c = heterogeneously dense, d = extremely dense; categories c and d may obscure small masses and are associated with reduced mammographic sensitivity.

BI-RADS final assessment categories and management: 0 = incomplete (needs additional imaging), 1 = negative, 2 = benign, 3 = probably benign (short-interval follow-up, typically 6 months), 4 = suspicious (biopsy; subdivided 4A low, 4B moderate, 4C high suspicion), 5 = highly suggestive of malignancy (biopsy), 6 = known biopsy-proven malignancy.

Screening mammography recall rate benchmark is <10%; positive predictive value for biopsy recommended (PPV2) benchmark is 20-40%, and PPV for biopsy performed (PPV3) benchmark is 20-40% per ACR accreditation targets.

Microcalcification descriptors: amorphous (BI-RADS 4B), coarse heterogeneous (4B), fine pleomorphic (4C), fine linear or fine linear branching (4C); punctate and coarse popcorn-like (usually benign, 2). Distribution: diffuse, regional, grouped, linear, segmental (linear and segmental raise suspicion).

US BI-RADS mass descriptors: shape (oval, round, irregular), margin (circumscribed, obscured, microlobulated, indistinct, spiculated), orientation (parallel vs not parallel), echogenicity, posterior features; a nonparallel orientation and spiculated margin are suspicious.

MRI kinetic curve types: persistent (type 1, benign pattern), plateau (type 2, indeterminate), washout (type 3, suspicious); washout kinetics increase suspicion but are not diagnostic alone.

Breast MRI screening indications include BRCA1/2 mutation carriers (annual MRI starting age 25-30), prior chest radiation before age 30 (start 8 years after radiation, not before age 25), and lifetime risk ≥20-25% by validated models.

Sentinel lymph node biopsy is the axillary staging standard for clinically node-negative early breast cancer; axillary lymph node dissection is reserved for clinically node-positive disease or failed sentinel mapping.

Male breast cancer most commonly presents as a subareolar mass; gynecomastia is typically bilateral and flame-shaped, whereas unilateral eccentric mass requires evaluation for carcinoma.

Coronary calcium score (Agatston) is acquired with prospective ECG triggering, 2.5-3 mm slices, and a low tube voltage; a score of 0 confers very low near-term cardiovascular event risk, and scores >400 indicate high risk.

Coronary CTA requires a heart rate typically <65 bpm (beta-blockers) and sublingual nitroglycerin for vasodilation; contraindications include severe asthma, PDE5 inhibitor use within 24-48 h, and renal insufficiency for CTA with contrast.

CAD-RADS categories: 0 = no stenosis, 1 = 1-24%, 2 = 25-49%, 3 = 50-69%, 4 = 70-99% (4A, 4B), 5 = total occlusion; modifiers N (non-diagnostic), S (stent), G (graft).

Left ventricular ejection fraction by MRI is the reference standard; normal LVEF is 55-70%. Late gadolinium enhancement patterns: subendocardial = ischemic, mid-wall = nonischemic (e.g., dilated cardiomyopathy), epicardial = myocarditis.

Cardiac MRI T1 mapping detects diffuse fibrosis (elevated native T1) and amyloidosis (markedly elevated T1 with abnormal nulling); T2 mapping detects myocardial edema.

Stress perfusion MRI: adenosine (140 mcg/kg/min) or regadenoson; a perfusion defect present at stress but not rest indicates ischemia; a defect at both stress and rest indicates infarction.

Aortic dissection Stanford classification: type A involves the ascending aorta (surgical emergency), type B spares the ascending aorta (typically medical management unless complicated).

CT pulmonary angiography for PE: acute PE appears as a central filling defect outlined by contrast; chronic PE shows eccentric, calcified, web-like defects and mosaic perfusion.

Cardiac amyloidosis on bone scintigraphy: grade 2 or 3 myocardial uptake with absent or mild bone uptake (Perugini grading) is highly specific for transthyretin amyloidosis when monoclonal protein is excluded.

CT numbers (Hounsfield units): water = 0, air ≈ -1000, fat ≈ -50 to -100, soft tissue ≈ 20-60, acute hemorrhage ≈ 50-80, bone >300, calcium >130.

Pitch = table feed per rotation / detector collimation; pitch >1 reduces dose and may degrade image quality; pitch <1 increases dose.

ALARA dose metrics: CTDIvol (volume CT dose index, mGy) and DLP (dose-length product, mGy·cm); effective dose ≈ DLP × k (k ≈ 0.015 mSv/mGy·cm for abdomen).

Contrast phases: unenhanced, arterial (25-35 s), portal venous (60-80 s), delayed (3-5 min); multiphasic liver CT uses unenhanced, arterial, portal venous, and delayed phases.

Dual-energy CT material decomposition uses different attenuation at low and high kVp; applications include virtual noncontrast, iodine maps, and uric acid stone characterization.

CT urography split-bolus technique reduces radiation by combining nephrographic and excretory phases; hematuria workup requires opacification of the collecting system.

Iterative reconstruction and automatic exposure control reduce dose; however, excessive noise reduction can alter lesion conspicuity and should be validated per protocol.

Bowel obstruction on CT: dilated small bowel >3 cm, transition point, and collapsed distal bowel; closed-loop obstruction shows a U- or C-shaped dilated loop with mesenteric vessels converging (whirl sign).

LI-RADS (v2018) major features for HCC: arterial phase hyperenhancement, washout, enhancing capsule, threshold growth, and size; LR-5 requires APHE plus at least one of washout, capsule, or threshold growth in a high-risk patient.

Liver segment anatomy by Couinaud: segment I caudate, II/III left lateral, IV left medial, V-VIII right lobe; the middle hepatic vein separates right and left lobes.

Acute cholecystitis ultrasound: gallstones, wall thickening >3 mm, pericholecystic fluid, and sonographic Murphy sign; HIDA scan is highly sensitive and shows nonvisualization of the gallbladder.

Acute pancreatitis (Atlanta classification): interstitial edematous vs necrotizing; revised Atlanta severity is mild, moderately severe, and severe based on organ failure and local complications.

Crohn disease vs ulcerative colitis: Crohn is transmural, skip lesions, fistulae, and perianal involvement; UC is mucosal, continuous from the rectum, with pseudopolyps and toxic megacolon risk.

Colorectal cancer staging: T1 submucosa, T2 muscularis propria, T3 through muscularis into subserosa, T4 adjacent organs or peritoneal reflection; MRI is preferred for rectal cancer local staging.

Hepatic steatosis on MRI: chemical shift imaging shows signal drop on out-of-phase images; PDFF (proton density fat fraction) is the quantitative reference standard.

GI bleeding localization: tagged RBC scan detects bleeding at ~0.1 mL/min; CT angiography detects ~0.3 mL/min; conventional angiography detects ~0.5 mL/min.

Renal mass Bosniak classification (v2019): category I simple cyst (benign), II benign minimally complex, IIF follow-up, III indeterminate (surgery), IV malignant; enhancing solid components or thickened irregular walls indicate III/IV.

Renal cell carcinoma subtypes: clear cell (most common, hypervascular, VHL), papillary (hypovascular, type 1/2), chromophobe (hypovascular, good prognosis).

Prostate PI-RADS v2.1: score 1-2 very low/low, 3 equivocal, 4 high, 5 very high; DWI is the dominant sequence for peripheral zone, T2 for transition zone.

Testicular torsion: absent or decreased Doppler flow; bell-clapper deformity predisposes; surgical exploration is emergent within 6 hours to preserve testicular viability.

Adrenal incidentaloma: unenhanced CT attenuation <10 HU indicates lipid-rich adenoma; washout >60% at 15 min (absolute) or >40% (relative) supports adenoma.

Ovarian torsion: enlarged edematous ovary with peripheral follicles and twisted vascular pedicle (whirlpool sign); Doppler may be normal in early or intermittent torsion.

Renal stone CT: noncontrast CT is the reference standard; stone density >1000 HU predicts poor shockwave lithotripsy response; Hounsfield density and skin-to-stone distance guide management.

Pheochromocytoma: adrenal mass with high T2 signal (lightbulb sign), marked enhancement; biochemical confirmation with plasma metanephrines; 10% rule for extra-adrenal, bilateral, malignant, and familial associations.

Modified Seldinger technique: needle puncture, guidewire insertion, catheter exchange over wire; the common femoral artery is accessed at the mid-femoral head to reduce pseudoaneurysm and retroperitoneal hemorrhage risk.

Coagulation thresholds before invasive procedures: platelet count >50,000/µL and INR <1.5-1.8 for most percutaneous procedures; higher thresholds for neuroaxial or major surgery.

TACE (transarterial chemoembolization) is indicated for intermediate-stage HCC (BCLC B); TARE (radioembolization with Y-90) is an alternative for portal vein thrombosis or larger tumors.

Uterine fibroid embolization (UAE) targets the uterine arteries; pregnancy is a contraindication; ovarian failure risk is low but higher in older patients.

IVC filter indications: contraindication to anticoagulation, recurrent PE despite anticoagulation, and preoperative prophylaxis in selected high-risk patients; retrieval is preferred when anticoagulation is safe.

Radiofrequency ablation vs microwave ablation: RFA is limited by heat-sink effect near vessels and by charring; microwave ablation achieves larger, more uniform zones and is less heat-sink dependent.

Postembolization syndrome: fever, pain, and nausea after embolization, typically self-limited and managed supportively; it must be distinguished from abscess and infarction.

Contrast-induced nephropathy prevention: hydration with isotonic saline, use lowest contrast volume, and avoid nephrotoxins; bicarbonate and N-acetylcysteine have limited evidence.

T1 relaxation time: recovery of longitudinal magnetization; short TR and short TE produce T1-weighted images (fat bright, fluid dark). T2: decay of transverse magnetization; long TR and long TE produce T2-weighted images (fluid bright).

Gadolinium shortens T1 and T2; nephrogenic systemic fibrosis risk is associated with linear agents and severe renal impairment (eGFR <30), so macrocyclic agents are preferred in at-risk patients.

Diffusion-weighted imaging: restricted diffusion shows high signal on DWI and low signal on ADC; high cellularity (tumors, abscess, acute infarct) restricts diffusion.

Susceptibility artifact from metal is reduced by fast spin echo, short TE, increased bandwidth, and view angle tilting; gradient echo sequences worsen susceptibility.

MR safety: patients with pacemakers require MRI-conditional devices; ferromagnetic intraocular foreign bodies are an absolute contraindication; gadolinium is avoided in pregnancy unless strongly indicated.

MR spectroscopy: choline elevated and NAA decreased in brain tumors; lactate doublet indicates anaerobic metabolism; citrate and choline peaks in prostate cancer.

Fat suppression techniques: chemical shift (frequency-selective), STIR (short tau inversion recovery, robust to field inhomogeneity), and Dixon (water-fat separation).

MR elastography measures liver stiffness; values ≥2.5-3.0 kPa suggest significant fibrosis; it is less reliable in inflammation or congestion.

Fracture descriptors: location, pattern (transverse, oblique, spiral, comminuted), displacement, angulation, rotation, and articular involvement; Salter-Harris types I-V in pediatric physeal fractures.

Bone tumor location and age: epiphysis = chondroblastoma (child) or giant cell tumor (adult); metaphysis = osteosarcoma, osteochondroma, nonossifying fibroma; diaphysis = Ewing sarcoma, lymphoma, osteoid osteoma.

Osteosarcoma: aggressive periosteal reaction (Codman triangle, sunburst), medullary sclerosis; peak age 10-20 years, metaphysis of long bones around the knee.

Ewing sarcoma: permeative diaphyseal lesion with onion-skin periosteal reaction; peak age 5-15 years; translocation t(11;22).

Rotator cuff tear: supraspinatus most commonly involved; MRI shows tendon discontinuity, fluid-filled gap, and retraction; subacromial-subdeltoid bursitis often coexists.

ACL tear: secondary signs include bone contusion at the lateral femoral condyle and posterior tibial plateau, anterior tibial translation, and pivot-shift bone contusions.

Osteomyelitis: MRI is the most sensitive modality; decreased T1 marrow signal and increased T2/STIR signal with enhancement; sinus tract and sequestrum suggest chronic infection.

Avascular necrosis: early MRI shows serpiginous low T1 signal and double-line sign on T2; femoral head is the classic site; risk factors include corticosteroids, alcohol, and sickle cell disease.

Ischemic stroke CT: early signs include insular ribbon sign, loss of gray-white differentiation, and hyperdense MCA sign; ASPECTS score ≤6 predicts poor outcome and affects thrombectomy eligibility.

Alberta Stroke Program Early CT Score (ASPECTS): 10-point scale; each affected region subtracts 1 point; scores ≥6 generally favor endovascular therapy within 24 h in selected patients.

Intracerebral hemorrhage: hyperdense on noncontrast CT; spot sign on CTA predicts expansion; hypertension is the most common cause; amyloid angiopathy in lobar hemorrhage in elderly.

Brain metastasis vs abscess: abscess shows restricted diffusion centrally with ring enhancement; metastasis typically has central necrosis without restricted diffusion and occurs at gray-white junction.

Glioblastoma: irregular ring enhancement, central necrosis, surrounding edema, and high choline/NAA ratio on MR spectroscopy; IDH wild-type and MGMT promoter status guide prognosis.

Multiple sclerosis: periventricular, juxtacortical, infratentorial, and spinal cord lesions; dissemination in space and time (McDonald criteria); Dawson's fingers on sagittal FLAIR.

Pituitary macroadenoma: >10 mm, suprasellar extension, optic chiasm compression; prolactinoma is the most common functioning adenoma and is treated with dopamine agonists.

Spinal cord compression: MRI is the modality of choice; metastatic epidural compression requires urgent steroids and radiation or surgery; cauda equina syndrome is a surgical emergency.

ACR Appropriateness Criteria provide evidence-based imaging recommendations by clinical scenario; they are not mandatory but support ordering decisions.

Radiation dose: effective dose is a population-averaged risk estimate; natural background is ~3 mSv/year; a chest CT is ~7 mSv, and a chest radiograph is ~0.1 mSv.

BI-RADS, LI-RADS, PI-RADS, and CAD-RADS are standardized reporting systems that improve communication and auditability; use the current version in reports.

Informed consent for contrast: discuss benefits, risks (allergic reaction, nephrotoxicity), and alternatives; document pregnancy status and renal function as appropriate.

Peer review and QA: RADPEER is a common peer-review tool; discrepancies are scored by clinical significance; the goal is system improvement, not individual punishment.

Medicare reimbursement: global vs professional vs technical components; the technical component covers equipment and staff; the professional component covers interpretation.

Contrast reaction treatment: mild urticaria treated with antihistamines; anaphylactoid reaction treated with epinephrine, oxygen, IV fluids, and airway support.

Error and safety: wrong-site procedures require time-out verification; handoff communication (SBAR) reduces errors; report critical findings directly and document the communication.

V/Q scan interpretation (PIOPED): high probability = ≥2 large mismatched segmental defects; very low probability = nonsegmental defects or matched defects; a normal scan effectively excludes PE.

Bone scan: increased uptake at sites of osteoblastic activity; three-phase bone scan (flow, blood pool, delayed) distinguishes osteomyelitis from cellulitis; tagged WBC scan improves specificity for osteomyelitis.

Thyroid uptake and scan: Graves disease shows diffusely increased uptake; subacute thyroiditis shows low uptake; a cold nodule requires ultrasound and possibly FNA.

PET/CT with FDG: high uptake in aggressive tumors, infection, and inflammation; FDG is not tumor-specific; SUVmax is a semiquantitative measure influenced by many factors.

Sentinel lymph node mapping uses Tc-99m sulfur colloid or tilmanocept; the sentinel node is the first draining node; blue dye and gamma probe complement each other.

Myocardial perfusion imaging: stress and rest images; reversible defect = ischemia; fixed defect = infarction; normal perfusion excludes significant CAD with high negative predictive value.

Radioiodine therapy for hyperthyroidism or thyroid cancer uses I-131; pregnancy and breastfeeding are absolute contraindications; radiation safety instructions are required.

Renal scintigraphy: MAG3 is preferred for renal function and transplant evaluation; DMSA binds cortical tubules and is used for cortical scarring; captopril renography for renovascular hypertension.

Pediatric radiation sensitivity is higher than in adults; use child-size protocols, lower kVp/mAs, and limit multiphase studies; thyroid and gonadal shielding per policy.

Pyloric stenosis: ultrasound shows thickened pyloric muscle (>3 mm) and elongated canal (>15 mm); typically presents at 3-6 weeks with nonbilious projectile vomiting.

Intussusception: ultrasound shows target sign or pseudokidney; contrast or air enema is both diagnostic and therapeutic; ileocolic is most common.

Malrotation with midgut volvulus: upper GI series shows corkscrew duodenum and abnormal duodenojejunal junction; surgical emergency.

Necrotizing enterocolitis: prematurity, feeding intolerance, pneumatosis intestinalis, portal venous gas; perforation is a surgical emergency.

Developmental dysplasia of the hip: ultrasound is used before ossification (before 4-6 months); Graf classification; Pavlik harness for early treatment.

Pediatric brain tumors: medulloblastoma (posterior fossa, fourth ventricle), pilocytic astrocytoma (cerebellar hemisphere, cystic with mural nodule), ependymoma (fourth ventricle, plastic).

Skeletal survey for suspected nonaccidental trauma: includes skull, spine, ribs, and long bones; healing fractures of different ages are suspicious; follow-up survey in 2 weeks.