ABR IR/DR cheat sheet

Absolute contraindication to iodinated contrast: prior anaphylactoid reaction to contrast is a relative contraindication; untreated pheochromocytoma and thyrotoxicosis are relative; metformin does not require withholding in patients with normal renal function per current ACR guidance.

Contrast-induced nephropathy risk rises with eGFR <30 mL/min/1.73 m2; use lowest volume of low- or iso-osmolar contrast and premedicate only for prior allergic-type reactions, not for renal protection alone.

Percutaneous transhepatic cholangiography (PTC) and biliary drainage: correct coagulopathy (INR >1.5 and platelets <50,000 are typical thresholds for correction) and give antibiotics before biliary intervention.

TIPS: pressure gradient goal is <12 mmHg (ideally ≤8-10 mmHg) to reduce variceal rebleeding; post-procedure encephalopathy occurs in roughly 20-30% and is managed with lactulose.

Uterine artery embolization: primary endpoint is reduction of fibroid-related bleeding and bulk symptoms; ovarian failure and nontarget embolization are recognized complications; fertility is not absolutely contraindicated.

Radioembolization (Y-90): perform pretreatment planning angiography with technetium-99m MAA lung shunt study; lung shunt fraction >20% (or >30% with certain dose models) contraindicates treatment due to radiation pneumonitis risk.

Sclerotherapy and embolization of pulmonary arteriovenous malformations: feed artery embolization is preferred; coils or vascular plugs are used; small PAVMs may be observed if asymptomatic and <2-3 mm feeding artery.

Central venous access: for internal jugular approach, the vein lies lateral to the carotid artery; ultrasound guidance reduces arterial puncture and pneumothorax; confirm tip at cavoatrial junction on post-procedure imaging.

Biopsy of a solitary pulmonary nodule: coaxial technique permits multiple passes; pneumothorax risk is highest with small, deep lesions and with emphysema; post-biopsy expiratory chest radiograph is standard.

LI-RADS: LR-5 requires arterial phase hyperenhancement plus washout and/or capsule and/or threshold growth in a lesion ≥10 mm in a cirrhotic liver or at-risk patient; LR-M is used for lesions with features of malignancy but not HCC-specific.

Bosniak classification: category I is simple cyst (no follow-up), II is benign (no follow-up), IIF requires follow-up imaging, III is indeterminate (surgery or close follow-up), IV is malignant (surgery).

Adrenal incidentaloma: lesions with Hounsfield units ≤10 on unenhanced CT are lipid-rich adenomas; >10 HU requires washout study or chemical-shift MRI; >4 cm or heterogeneous lesions warrant further evaluation.

Thyroid nodule ultrasound: ACR TI-RADS assigns points for composition, echogenicity, shape, margin, and echogenic foci; FNA thresholds are based on total points and nodule size (e.g., ≥2.5 cm for TR4, ≥1.5 cm for TR5).

Pulmonary embolism on CTPA: acute PE shows central filling defect with acute angles; chronic PE shows eccentric, web-like, or calcified defects with obtuse angles and vessel narrowing.

Chest radiograph silhouette sign: loss of the right heart border indicates right middle lobe disease; loss of the left heart border indicates lingula; loss of the diaphragm indicates lower lobe disease.

Fat-containing renal mass on CT or MRI suggests angiomyolipoma; if the mass is large or symptomatic, consider hemorrhage risk; lipid-poor AML can mimic renal cell carcinoma.

Ovarian torsion on ultrasound: enlarged edematous ovary with peripherally displaced follicles and absent or decreased arterial/venous flow; Doppler may be normal in early or intermittent torsion.

Bone age and skeletal maturity: in children, the Salter-Harris classification describes physeal fractures (I through V); type I may be radiographically occult and require clinical correlation or MRI.