OMSB Diagnostic Radiology (OEDR) cheat sheet

Effective dose = absorbed dose (Gy) x radiation weighting factor (wR) x tissue weighting factor (wT); SI unit is the sievert (Sv).

CTDIvol reflects dose per unit volume; dose-length product (DLP) = CTDIvol x scan length, and effective dose approximates DLP x k (body region conversion factor).

ALARA is operationalized by mAs (tube current-time product) as the primary dose lever; kVp changes dose roughly with the square to the 2.5 power of the kilovoltage.

Automatic exposure control modulates mAs to reach a preset detector signal; noise index and reference mAs determine image noise, not kVp.

Hounsfield unit = 1000 x (mu_tissue - mu_water) / (mu_water); water is 0 HU by definition, air about -1000 HU.

In MRI, the static field B0 (tesla) aligns protons; the Larmor frequency = gamma x B0, with gamma about 42.58 MHz/T for hydrogen.

In ultrasound, axial resolution improves with higher frequency (shorter wavelength) but penetration decreases; lateral resolution depends on beam width and transducer aperture.

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

Pregnancy shielding: lead apron attenuation follows exponential absorption, so half-value layer and beam quality determine shielding thickness, not simply 0.5 mm Pb for all energies.

Silhouette sign: loss of a normal border occurs when the adjacent structure has the same radiographic density, localizing opacity to the contiguous lobe.

Air bronchograms indicate alveolar airspace disease; their absence suggests pleural, mediastinal, or atelectatic (airway-obstructed) processes.

The mediastinum is divided by the lateral chest radiograph into anterior, middle, and posterior compartments; the posterior compartment contains the esophagus, descending aorta, and neural foramina.

Honeycombing with basal and subpleural predominance plus traction bronchiectasis indicates usual interstitial pneumonia (UIP) pattern.

Centrilobular nodules with tree-in-bud branching suggest infectious bronchiolitis; perilymphatic nodules suggest sarcoidosis or lymphangitic spread.

The Fleischner Society recommends follow-up CT for incidentally detected solid nodules greater than 6 mm in patients at risk; subsolid nodules require longer follow-up.

Pneumothorax on supine radiograph shows the deep sulcus sign; tension pneumothorax shows mediastinal shift away from the affected side.

Pulmonary embolism on CT pulmonary angiography is diagnosed by an intraluminal filling defect; right ventricular enlargement (RV/LV ratio greater than 1) indicates right heart strain.

Coronary calcium score (Agatston) is quantified on non-contrast ECG-gated CT; scores above 400 indicate high risk and reduce the specificity of CT coronary angiography.

Coronary CT angiography requires a low and regular heart rate, typically below 65 bpm, achieved with beta-blockade; prospective triggering lowers dose versus retrospective gating.

Cardiac MRI late gadolinium enhancement shows myocardial scar or fibrosis; subendocardial distribution suggests ischemic etiology, mid-wall or epicardial suggests non-ischemic.

Aortic dissection is classified by the Stanford system: type A involves the ascending aorta (surgical emergency), type B spares it.

Acute aortic intramural hematoma appears as a crescentic high-attenuation thickening on non-contrast CT without a visible intimal flap.

Cardiac amyloidosis shows diffuse subendocardial late gadolinium enhancement and abnormal myocardial nulling; T1 mapping and ECV are supportive.

CT pulmonary angiography for pulmonary hypertension shows a main pulmonary artery diameter greater than 29 mm and right-to-left ventricular ratio greater than 1.

Aortic stenosis severity on echocardiography is graded by peak velocity, mean gradient, and continuity-equation valve area; low-flow low-gradient requires dobutamine stress.

Acute appendicitis on CT shows an enlarged appendix greater than 6 mm with periappendiceal fat stranding and an appendicolith.

The CT findings of bowel ischemia include wall thickening, pneumatosis intestinalis, portal venous gas, and absent or diminished mural enhancement.

Cirrhosis is diagnosed by surface nodularity, caudate-to-right-lobe hypertrophy, and a nodular regenerating liver with portal hypertension signs.

LI-RADS categorizes observations in at-risk livers from LR-1 (definitely benign) to LR-5 (definitely HCC) and LR-M (malignant, not specific for HCC); LR-5 requires arterial phase hyperenhancement with washout and capsule or threshold growth.

Choledocholithiasis is best detected on MRCP or endoscopic ultrasound when common bile duct stones are suspected but CT is negative.

Bowel obstruction on CT is characterized by dilated loops with a transition point; closed-loop obstruction shows a U- or C-shaped loop with radial mesenteric vessels.

Acute pancreatitis severity is graded by the revised Atlanta classification: interstitial edematous versus necrotizing, with organ failure determining severity.

Hepatic steatosis is suggested by liver attenuation less than spleen on unenhanced CT or by signal drop on out-of-phase MRI.

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

Bosniak classification of cystic renal masses: category I and II are benign; IIF requires follow-up; III and IV are surgical.

Urolithiasis is detected on non-contrast CT with sensitivity near 97%; stone size and location predict spontaneous passage.

Prostate cancer is assessed with PI-RADS v2.1 on multiparametric MRI; a score of 3 or higher in the peripheral zone warrants targeted biopsy.

Ovarian torsion shows an enlarged edematous ovary with peripherally displaced follicles and a twisted vascular pedicle.

Endometrial cancer staging uses depth of myometrial invasion; MRI with dynamic contrast improves detection of cervical stromal involvement.

Renal artery stenosis is suggested by a kidney length difference greater than 1.5 cm and delayed enhancement on contrast studies.

Testicular torsion is a surgical emergency; Doppler shows absent or decreased flow, and the bell-clapper deformity predisposes to it.

Osteomyelitis on MRI shows marrow edema (low T1, high T2/STIR), and contrast enhancement helps distinguish it from reactive edema.

Salter-Harris classification: I through physis only, II through physis and metaphysis, III through physis and epiphysis, IV through all, V crush injury.

Anterior cruciate ligament tear shows discontinuity and abnormal signal on sagittal MRI; the secondary sign is a bone contusion at the lateral femoral condyle and posterior tibial plateau.

Rotator cuff tear is evaluated on coronal oblique and sagittal oblique MRI; full-thickness tears show fluid signal extending through the tendon.

Bone tumors: osteosarcoma shows aggressive periosteal reaction (Codman triangle, sunburst); Ewing sarcoma occurs in the diaphysis of long bones in children.

Gout shows juxta-articular erosions with overhanging edges and tophi; CPPD shows chondrocalcinosis and degenerative changes in atypical joints.

Meniscal tear is diagnosed on MRI by abnormal signal contacting the articular surface on two or more slices.

Dual-energy CT can detect bone marrow edema and monosodium urate crystals, useful in occult fractures and gout.

Acute ischemic stroke: CT is used to exclude hemorrhage; MRI diffusion-weighted imaging shows restricted diffusion within minutes and is the most sensitive sequence.

The ASPECTS score quantifies early ischemic changes on non-contrast CT; a score of 6 or lower indicates a large infarct core in the middle cerebral artery territory.

Intracerebral hemorrhage shows hyperdensity on non-contrast CT; the spot sign on CT angiography predicts hematoma expansion.

The Alberta Stroke Program recommends thrombectomy for large vessel occlusion within 6 to 24 hours when imaging selection criteria are met.

Brain abscess shows a thin, smooth enhancing rim with restricted diffusion centrally; glioblastoma shows a thick irregular rim without restricted central diffusion.

Cervical spine trauma is cleared by CT when there is no fracture, no neurologic deficit, and no high-risk mechanism; MRI is added for ligamentous injury or neurologic symptoms.

Spinal cord compression from metastatic disease shows epidural soft tissue; MRI with contrast is the modality of choice.

Head and neck squamous cell carcinoma is staged by tumor size, nodal necrosis, and extranodal extension; extranodal extension upstages to N3b.

BI-RADS categories: 0 incomplete, 1 negative, 2 benign, 3 probably benign (less than 2% malignancy, short-interval follow-up), 4 suspicious (biopsy), 5 highly suggestive of malignancy, 6 known biopsy-proven malignancy.

Screening mammography reduces mortality in women aged 50 to 74; guidelines differ on starting age and interval (annual versus biennial).

Dense breast tissue (BI-RADS c or d) lowers mammographic sensitivity and is an indication for supplemental ultrasound or MRI in some guidelines.

Microcalcification morphology: fine pleomorphic and linear branching patterns are suspicious; coarse and round patterns are typically benign.

MRI is the most sensitive modality for breast cancer; indications include high-risk screening, extent of disease, and occult primary with axillary metastasis.

Ultrasound features of malignancy include irregular shape, non-parallel orientation, spiculated margins, and posterior acoustic shadowing.

Male breast cancer most often presents as a subareolar mass; gynecomastia is flame-shaped and centered on the nipple.

Stereotactic biopsy is used for calcifications visible only on mammography; ultrasound-guided biopsy is preferred when the lesion is sonographically visible.

The pediatric chest radiograph shows a normal thymus as a sail sign or wave sign; it should not be mistaken for a mass.

Intussusception is diagnosed by ultrasound showing a target or pseudokidney sign; air or contrast enema is both diagnostic and therapeutic.

Hypertrophic pyloric stenosis shows an elongated pyloric canal greater than 14 mm and muscle thickness greater than 3 mm on ultrasound.

Necrotizing enterocolitis shows pneumatosis intestinalis, portal venous gas, and fixed bowel loops; it occurs predominantly in premature neonates.

Pediatric bone age is assessed with the Greulich and Pyle atlas; a left hand and wrist radiograph is standard.

Non-accidental trauma should be suspected with metaphyseal corner fractures, rib fractures in infants, and fractures of differing ages.

Congenital diaphragmatic hernia presents with bowel loops in the chest and mediastinal shift; the left side is more common.

Medulloblastoma arises in the cerebellar vermis and shows restricted diffusion; pilocytic astrocytoma is cystic with an enhancing mural nodule.

FDG-PET/CT is used for staging and response assessment in lymphoma; Deauville score compares uptake with mediastinal blood pool and liver.

Bone scintigraphy with Tc-99m MDP detects osteoblastic metastases; it is less sensitive for purely lytic lesions such as multiple myeloma.

Myocardial perfusion imaging uses stress and rest SPECT; reversible defects indicate ischemia, fixed defects indicate infarction.

Thyroid uptake and scan with I-123 or Tc-99m pertechnetate distinguishes Graves disease (diffuse increased uptake) from subacute thyroiditis (low uptake).

Ventilation-perfusion scan is interpreted with the modified PIOPED criteria; a high-probability pattern shows multiple mismatched perfusion defects.

Radioiodine (I-131) therapy is used for differentiated thyroid cancer after thyroidectomy; it is contraindicated in pregnancy and lactation.

Sentinel lymph node mapping uses Tc-99m sulfur colloid or blue dye; it is standard for breast cancer and melanoma staging.

Lu-177 DOTATATE targets somatostatin receptors in neuroendocrine tumors; Ga-68 DOTATATE PET localizes them.

Uterine artery embolization treats symptomatic fibroids; complications include post-embolization syndrome and ovarian failure.

Transjugular intrahepatic portosystemic shunt (TIPS) reduces portal pressure in refractory variceal bleeding and ascites; hepatic encephalopathy is a major complication.

Percutaneous transhepatic cholangiography and biliary drainage are alternatives when endoscopic retrograde cholangiopancreatography fails.

Radiofrequency ablation is effective for hepatocellular carcinoma smaller than 3 cm and for selected metastases.

Aortic stent-grafting for abdominal aortic aneurysm requires adequate proximal and distal landing zones; endoleak is a common complication.

Angioplasty and stenting of renal artery stenosis are indicated for refractory hypertension or flash pulmonary edema, not for all stenoses.

IVC filter placement is indicated when anticoagulation is contraindicated in patients with venous thromboembolism; retrieval is attempted when no longer needed.

Chemoembolization (TACE) and radioembolization (Y-90) are locoregional therapies for intermediate-stage hepatocellular carcinoma.

Iodinated contrast media are classified by osmolality: high, low, and iso-osmolar; low- and iso-osmolar agents are preferred for most intravascular use.

Contrast-induced acute kidney injury risk is increased with pre-existing renal impairment, diabetes, and dehydration; prophylactic hydration is the main preventive measure.

Metformin should be withheld in patients with reduced renal function at the time of iodinated contrast administration per local protocols.

Gadolinium-based agents are contraindicated in severe renal impairment (eGFR below 30) for linear agents because of nephrogenic systemic fibrosis risk; macrocyclic agents are preferred.

Anaphylactoid reactions to contrast are treated with epinephrine, oxygen, fluids, and antihistamines; premedication with corticosteroids reduces recurrence.

Barium is contraindicated when perforation or obstruction is suspected; water-soluble iodinated contrast is used instead.

Ultrasound contrast agents are microbubbles that remain intravascular; they are used for lesion characterization and vascular studies.

Extravasation of iodinated contrast is managed with elevation, cold or warm compresses, and clinical monitoring; severe cases require surgical consultation.

The Joint Commission National Patient Safety Goals require two patient identifiers before any procedure or medication administration.

Time-out is performed immediately before a procedure with the full team present to confirm patient, site, procedure, and consent.

Radiation dose monitoring programs track CTDIvol and DLP per protocol and compare against diagnostic reference levels.

Root cause analysis is used for sentinel events; failure mode and effects analysis is proactive risk assessment.

The ACR accreditation program requires peer review, protocol review, and equipment quality control for modality accreditation.

Handoff communication should use structured tools such as SBAR to reduce omissions of critical information.

Just culture distinguishes human error from at-risk behavior and reckless behavior, guiding appropriate response.

Quality metrics in radiology include report turnaround time, critical result communication, and repeat rate.