Radiology Final

General Radiology Principles

Computed Tomography (CT)

• Hyperdense Lesions on CT:
  • Metallic clips
  • Intravenous contrast
  • Acute hemorrhage
  • Calcifications
  • Note: Lipoma is hypodense.

• CT is the best modality for detecting calcification.

• CT uses ionizing radiation.

Magnetic Resonance Imaging (MRI)

• MRI Properties:
  • Does NOT use ionizing radiation.
  • MRI contrast (Gadolinium) is relatively safe.
  • Takes more time to perform than CT.
  • Contraindicated with ferromagnetic substances (e.g., certain implants, pacemakers - check compatibility).

• MRI Uses & Sequences:
  • DWI (Diffusion Weighted Imaging): Gold standard for acute infarct (shows hyperintensity).
  • T1 + Contrast (Gadolinium): Excellent for intra-axial tumors and assessing enhancement.
  • MRV (MR Venography): Best for diagnosing cavernous sinus thrombosis.
  • FLAIR: Good for periventricular white matter disease; NOT specifically for calcification.
  • STIR: A fat suppression sequence (T2 based).

• MRI vs CT:
  • MRI generally less sensitive than CT for acute hemorrhage (CT is faster and better).
  • CT is better for detecting calcification and acute bone trauma.
  • MRI contraindicated for definite localization of intraorbital metallic foreign bodies (CT preferred).

Contrast Media

• Iodinated Contrast (CT/Angio):
  • Relative Contraindications: Asthma, Atopy (general allergies), specific food/penicillin allergies.
  • Strong Contraindication: Previous severe contrast allergy.
  • Preparation for at-risk patients (e.g., asthma): Oral prednisolone.

• Gadolinium Contrast (MRI):
  • Relatively safe compared to iodinated contrast.
  • Contraindicated in severe renal failure (e.g., Grade III or dialysis) due to risk of NSF.
  • Generally contraindicated in the first trimester of pregnancy.

Ultrasound (US)

• Properties:
  • No ionizing radiation.
  • Can visualize vessels (with Doppler).
  • Operator dependent.
  • Less accurate in obese patients.

• Optimal Conditions: Thin patient, children, full bladder (for pelvic US).

• Suboptimal Conditions: Obese patient, recent endoscopy (air artifact), excessive bowel gas.

Radiographic Density & Attenuation

• Highest Attenuation (most radiopaque/white): Metal, Bone, Contrast.

• Intermediate Attenuation: Soft tissues, water/fluid.

• Low Attenuation (most radiolucent/black): Fat, Air.

• Lung parenchyma: Has low attenuation and high penetration due to air content.

Chest X-ray Interpretation

Technique & Views

• Standard Views: PA (Posterior-Anterior) and Lateral.

• PA View: Taken on full inspiration. Standard distance (1.8m or 6ft) minimizes heart magnification.

• AP View (Anterior-Posterior): Often portable, exaggerates heart size. Supine position alters fluid/air appearances.

• Lateral View: Helps localize lesions, view retrosternal/retrocardiac spaces. Left hemidiaphragm often obscured anteriorly by the heart.

Anatomy & Signs

• Hilum: Contains pulmonary arteries/veins, bronchi, lymph nodes. Left hilum is normally slightly higher than the right. Prominent hila can indicate adenopathy or pulmonary hypertension.

• Heart Borders:
  • Right border = Right Atrium (adjacent to Middle Lobe).
  • Left border = Left Ventricle / Left Atrial Appendage (adjacent to Lingula/Upper Lobe).

• Silhouette Sign: Loss of a normal interface (border) indicates pathology in the adjacent lung.
  • Right heart border loss = RML pathology.
  • Left heart border loss = Lingula (LUL) pathology.
  • Diaphragm loss = Lower lobe pathology.

• Air Bronchogram: Visible air-filled bronchi surrounded by consolidated lung (e.g., pneumonia, edema). CT is more sensitive for detection. Not normally visible in peripheral lung.

Common Pathologies

• Atelectasis/Collapse: Loss of lung volume.
  • Signs: Opacification, fissure displacement, hilar displacement, volume loss, mediastinal shift (towards collapse).
  • RUL Collapse: Elevates right hilum and minor fissure.
  • LUL Collapse: Opacity obscuring left heart border, elevates left hilum.

• Pneumonia: Consolidation (opacity). Lobar pneumonia respects fissures.
  • RML pneumonia silhouettes right heart border.
  • LLL pneumonia silhouettes left hemidiaphragm.

• Pleural Effusion: Fluid in pleural space.
  • Signs: Blunting of costophrenic angles, meniscus sign, opacification. Supine: layers posteriorly, causing diffuse increased density.

• Pneumothorax: Air in pleural space.
  • Signs: Visible pleural line, absent lung markings peripherally.
  • Tension Pneumothorax: Mediastinal shift away from pneumothorax, ipsilateral hemidiaphragm depression. A medical emergency.
  • Supine: Air collects anteriorly, may be subtle (deep sulcus sign). CT is most sensitive for small pneumothorax.

• Pulmonary Embolism (PE): Spiral CT Angiography is the imaging modality of choice. CXR often normal or shows non-specific signs (atelectasis, small effusion).

• Lung Nodules: CXR insensitive for nodules <5mm. Peripheral calcified nodule usually benign. Signs favouring malignancy include size >8-10mm, irregular/spiculated border, growth.

• Pneumoperitoneum: Free air under diaphragm on erect CXR. Best modality is often standing upright CXR/abdomen X-ray. Most common cause: perforated viscus (e.g., peptic ulcer).

Brain CT & MRI

Hemorrhage

• Acute Hemorrhage: Hyperdense (bright) on non-contrast CT.

• Epidural Hematoma (EDH):
  • Biconvex (lens) shape.
  • Often associated with skull fracture (temporal bone common).
  • Does NOT cross sutures. Arterial source common (middle meningeal artery).

• Subdural Hematoma (SDH):
  • Crescent shape.
  • Crosses sutures, but not dural reflections (falx, tentorium). Venous source common.
  • Density varies with age: Acute = hyperdense, Subacute = isodense, Chronic = hypodense. Common in elderly and infants.

• Intraventricular Hemorrhage: Blood within ventricles. Associated with poor prognosis.

Ischemia / Infarct

• Acute Infarct: MRI with DWI is the most sensitive modality, shows restricted diffusion (hyperintense) within minutes to hours.

• CT may be normal initially, later shows hypodensity in a vascular territory.

Edema

• Cytotoxic Edema: Intracellular swelling (e.g., acute ischemia). Causes restricted diffusion on DWI.

• Vasogenic Edema: Extracellular fluid leakage (e.g., around tumors, inflammation). Appears as hypodensity on CT / T2 hyperintensity on MRI, often respecting white matter tracts.

• Diffuse Brain Edema Signs on CT:
  • Effacement of sulci and basal cisterns.
  • Small ventricles.
  • Loss of grey-white matter differentiation.
  • Diffuse brain hypodensity.

Tumors

• Intra-axial Tumors: Arise within brain parenchyma. Often enhance with T1+Contrast MRI.

• Extra-axial Tumors: Arise from meninges, nerves, etc. (outside brain).
  • Meningioma: Commonest extra-axial tumor, broad dural attachment (dural tail), usually enhances avidly.

• Failure to enhance makes intra-axial tumor less likely but does not exclude it.

Other

• Calcification: CT is the best modality. Common sites: pineal gland, choroid plexus, falx, basal ganglia (age-related/pathologic).

• Cavernous Sinus Thrombosis: MRV (MR Venography) is the investigation of choice.

• Normal Hyperdensities on CT: Acute blood, IV contrast, calcification (physiologic/pathologic), bone. Pituitary gland is normally isodense.

Gastrointestinal System (GIS) Radiology

Contrast Studies

• Barium:
  • Contraindicated in suspected perforation.
  • Excellent mucosal detail. Water insoluble.
  • Used for swallows, meals, follow-throughs, enemas.

• Water-Soluble Contrast:
  • Used if perforation is suspected.
  • Low osmolality agents preferred. Less mucosal detail than barium.

Specific Conditions

• Pneumoperitoneum: Free intraperitoneal air. Most common cause: perforated peptic ulcer. Best seen on erect CXR or left lateral decubitus abdomen X-ray.

• Bowel Obstruction: Dilated loops of bowel proximal to obstruction, collapsed distally.

• Crohn's Disease: Skip lesions, often affects terminal ileum (string sign), transmural inflammation, fistulas, abscesses. Strictures are common.

• Ulcerative Colitis: Continuous mucosal inflammation starting in rectum. Loss of haustra (lead pipe colon). Strictures are uncommon. Increased cancer risk. No skip lesions.

• Sigmoid Volvulus: Twisting of sigmoid colon. Coffee bean sign on AXR. Apex points to RUQ.

• Liver Hemangioma: Most common benign liver tumor. Typically hyperechoic on US and T2 hyperintense on MRI.

• Diverticulosis/Diverticulitis: Outpouchings (diverticulosis). Inflammation = diverticulitis, often LLQ pain. Complications: abscess, perforation, fistula (esp. colo-vesical).

• Gallstones: Ultrasound is the primary imaging modality. Stones appear as echogenic foci with posterior acoustic shadowing.

• Diaphragmatic Hernia: Bochdalek (posterior) more common on left. Morgagni (anterior) more common on right.

• Pancreatitis: CT may show enlarged pancreas, peripancreatic inflammation (hypodense fluid/stranding), necrosis (non-enhancing areas).

Renal Imaging

• Ultrasound: Initial investigation for hydronephrosis, renal masses, size.

• CT: Best for stones (non-contrast), masses (contrast-enhanced), trauma.

• Nuclear Renography: Assesses function and drainage.
  • DTPA: Measures GFR (filtration). Low extraction.
  • MAG3: Measures effective renal plasma flow (secretion). High extraction. Preferred for assessing obstruction.
  • DMSA: Binds to cortex. Best for detecting scars and assessing differential renal function.

Mammography

BI-RADS Classification

• BI-RADS 0: Incomplete assessment, needs further imaging.

• BI-RADS 1: Negative.

• BI-RADS 2: Benign finding(s). (e.g., stable mass >2yrs, typical benign calcifications, simple cyst, fat-containing lesion).

• BI-RADS 3: Probably Benign (<2% risk of malignancy). Needs short-interval follow-up (usually 6 months).

• BI-RADS 4: Suspicious abnormality. Needs biopsy (4a=low, 4b=moderate, 4c=high suspicion).

• BI-RADS 5: Highly suggestive of malignancy (>95% risk). Needs biopsy.

• BI-RADS 6: Known biopsy-proven malignancy.

Benign Features

• Mass Shape/Margin: Round, oval, well-circumscribed/defined margins.

• Calcifications:
  • Coarse / "Popcorn" (degenerating fibroadenoma).
  • Large rod-like (secretory disease).
  • Round/Punctate.
  • "Eggshell" / Rim (cyst, fat necrosis).
  • Lucent-centered.

• Associated Features: Fat containing (lipoma, hamartoma, galactocele, oil cyst). Simple cyst on US. Stable appearance over time.

Malignant Features

• Mass Shape/Margin: Irregular shape, spiculated margins, indistinct/obscured margins, microlobulated margins.

• Calcifications:
  • Fine linear / Fine linear branching (most suspicious).
  • Pleomorphic (varying shapes/sizes), clustered.
  • Amorphous, clustered.

• Associated Features: Architectural distortion, asymmetric density, skin thickening/retraction, suspicious axillary lymph nodes (loss of fatty hilum, rounded, dense). Notch and lobar edge signs.

Specific Lesions / Scenarios

• Fibroadenoma: Common benign tumor, often oval, well-defined, may have popcorn calcification.

• Fat Necrosis: Can occur post-trauma/surgery. May present as oil cyst (lucent with eggshell calcification) or mimic malignancy.

• Cyst: Well-defined, round/oval. Appears as anechoic lesion with posterior acoustic enhancement on US. May have eggshell calcification if old.

• Imaging in Young Women (<30-35): Ultrasound is the preferred initial imaging modality for a palpable lump.

Musculoskeletal (MSK) Radiology

Bone Lesions - General Features

• Benign Signs: Well-defined margin, narrow zone of transition, sclerotic rim, geographic bone destruction, no cortical destruction, no aggressive periosteal reaction.

• Malignant Signs: Ill-defined margin, wide zone of transition, permeative or moth-eaten bone destruction, cortical destruction, aggressive periosteal reaction (Codman's triangle, sunburst, lamellated), soft tissue extension.

Specific Bone Lesions

• Benign:
  • Non-ossifying fibroma (NOF): Eccentric, metaphyseal, lytic, sclerotic border, bubbly appearance. Common in children/adolescents.
  • Enchondroma: Intramedullary cartilage tumor, often in hands/feet. May have calcification.
  • Giant Cell Tumor (GCT): Epiphyseal, lytic, geographic, abuts articular surface, usually no sclerotic rim. Can be locally aggressive.

• Malignant:
  • Osteosarcoma: Metaphyseal, destructive, produces osteoid (bone matrix), aggressive periosteal reaction. Most common primary malignant bone tumor in adolescents.
  • Ewing Sarcoma: Diaphyseal, permeative destruction, lamellated ("onion skin") periosteal reaction. Affects children/young adults. Mimics osteomyelitis.
  • Multiple Myeloma: Punched-out lytic lesions, diffuse osteopenia. Commonest primary malignant bone tumor in adults >40.
  • Metastases: Most common malignant bone tumor overall. Can be lytic, blastic, or mixed.

Arthritis

• Osteoarthritis (OA): Degenerative. Non-uniform joint space narrowing, osteophytes, subchondral sclerosis, subchondral cysts. Affects weight-bearing joints, DIPs, PIPs.

• Inflammatory Arthritis (e.g., Rheumatoid Arthritis): Uniform joint space narrowing, marginal erosions, periarticular osteopenia, soft tissue swelling. Affects small joints (MCPs, PIPs, wrists).

• Seronegative Spondyloarthropathies (e.g., Ankylosing Spondylitis): Affects axial skeleton (sacroiliac joints, spine). Sacroiliitis (erosions, sclerosis, fusion). Syndesmophytes (leading to bamboo spine). Enthesitis. Shiny corner sign, dagger sign, trolley track sign are specific features.

• Gout: Deposition of urate crystals. Punched-out erosions with sclerotic borders and overhanging edges. Tophi (soft tissue masses). Joint space preserved until late.

• Septic Arthritis: Joint infection. Rapid joint destruction, effusion. Usually monoarticular.

Metabolic Bone Disease

• Hyperparathyroidism: Subperiosteal bone resorption (classic sign, esp. radial aspect of phalanges), salt-and-pepper skull, brown tumors, Rugger Jersey spine.

• Osteomalacia: Defective mineralization. Decreased bone density, Looser zones (pseudofractures).

Bone Scan

• "Super Scan": Diffusely increased skeletal uptake with absent/faint kidney visualization. Seen in widespread metastatic disease, severe hyperparathyroidism, osteomalacia.

• Three-Phase Bone Scan: Useful for evaluating osteomyelitis and complex regional pain syndrome.

Interventional Radiology

Vascular Procedures

• Angiography: Imaging of blood vessels using contrast.
  • Digital Subtraction Angiography (DSA): Subtracts bone/soft tissue for better vessel visualization.
  • Femoral artery is the most common access site for systemic/aortic/cerebral angiography.
  • Femoral artery is lateral to the femoral vein.

• Angioplasty/Stenting: Opening narrowed/occluded vessels. Better results in stenosis vs occlusion, and in larger vs smaller vessels.

• Embolization: Blocking blood vessels (e.g., to treat bleeding, tumors, AVMs).

• IVC Filter: Placed in Inferior Vena Cava (usually infrarenal) to prevent pulmonary embolism.
  • Indications: Contraindication to anticoagulation, failure of anticoagulation, complication (bleeding) on anticoagulation.
  • Complication: Can cause IVC thrombosis.

Non-Vascular Procedures

• Biopsy: Image-guided (US or CT) tissue sampling.
  • US Guidance: Suitable for superficial/accessible lesions (liver, kidney, thyroid). General anesthesia often not required.
  • CT Guidance: Better for deep lesions (lung, retroperitoneum).
  • Pre-procedure checks: Consent, coagulation studies, patient fasting.

• Percutaneous Nephrostomy: Placing a drainage tube into the renal collecting system. Used to relieve obstruction.

Pathologies

• Deep Vein Thrombosis (DVT): Non-compressibility of the vein on ultrasound is the most sensitive sign.

• Arterial Occlusive Disease: Mostly due to atherosclerosis. Emboli often lodge at bifurcations (cardiac origin common). Thrombi form in situ.

• Abdominal Aortic Aneurysm (AAA): Aortic diameter >3cm. Most common location is infrarenal. Ultrasound is good for screening and size monitoring. Intimal flap indicates dissection, not just aneurysm. Rupture is major risk.

Nuclear Medicine

Radiopharmaceuticals & Principles

• Technetium-99m (99mTc): Workhorse isotope. Half-life 6 hours, energy 140 keV. Decays via isomeric transition. Produced from Molybdenum-99 generator.

• 18F-FDG: Glucose analog used for PET scanning. Uptake reflects metabolic activity. Most common PET tracer.

• Radiation Safety: Minimize dose (ALARA principle). Stochastic effects (cancer risk) possible even at low doses. <10 rad unlikely to cause acute effects.

Common Scans

• PET Scan (FDG):
  • Oncology: Staging, restaging, treatment response assessment, detecting recurrence. Important in lymphoma management (negative scan after chemo = good prognosis, follow-up).
  • Also used for infection/inflammation, cardiology, neurology.

• Myocardial Perfusion Imaging (MPI):
  • Uses tracers like Thallium-201 or Tc-99m agents (Sestamibi, Tetrofosmin).
  • Compares stress vs rest images to detect ischemia (reversible defect) or infarction (fixed defect).
  • Higher sensitivity than ECG stress test alone.
  • Assesses coronary flow reserve.
  • Note: Tc-99m HMPAO is a brain agent, not used for MPI.

• Bone Scan:
  • Uses Tc-99m labeled bisphosphonates (MDP/HDP).
  • Highly sensitive for detecting metastatic disease, osteomyelitis, fractures, arthritis.
  • Non-specific uptake patterns require clinical correlation.
  • Wrong indication: Primary lung/brain imaging (unless looking for skull/spine mets).

• Thyroid Scan:
  • Uses Iodine-123, I-131, or Tc-99m pertechnetate.
  • Evaluates thyroid function and morphology (nodules).
  • Increased uptake: Graves' disease.
  • Decreased uptake: Thyroiditis, recent iodine exposure (contrast).
  • Low uptake in hyperthyroidism suggests thyroiditis (treat symptoms, follow up).

• Renal Scan (Renography): (See GIS section). Assesses function, drainage, scars.