Ultrasonography

Ultrasound (USG) is a real-time imaging modality utilizing high-frequency sound waves to evaluate anatomical structures and physiological processes.

Basic Physics:
- Sound Waves: Ultrasound operates at frequencies >20 kHz, with medical USG typically using 1–20 MHz.
- Acoustic Impedance: Defined as the product of tissue density and sound velocity, influencing wave reflection and transmission.
- Attenuation: Caused by absorption, reflection, and scattering; higher frequencies provide better resolution but reduced penetration.
Transducers:
- Linear Probe (7–18 MHz): High-resolution imaging for superficial structures.
- Curvilinear Probe (2–6 MHz): Deeper penetration, used for abdominal and obstetric imaging.
- Phased Array Probe (2–5 MHz): Small footprint, ideal for cardiac and intercostal imaging.
- Endocavitary Probe (5–9 MHz): Used for transvaginal and transrectal examinations.
Modes of Ultrasound:
- B-Mode (Brightness Mode): Standard grayscale imaging.
- M-Mode (Motion Mode): Used in cardiac and fetal heart rate assessments.
- Doppler (Color, Spectral, Power): Evaluates blood flow dynamics and vascular pathology.
Artifacts in Ultrasound:
- Acoustic Shadowing: Hypoechoic region behind dense structures (e.g., stones, bones).
- Enhancement: Increased echogenicity behind fluid-filled structures.
- Reverberation & Comet Tail Artifacts: Commonly seen in air or metal interfaces.

A standardized method ensures thorough evaluation and reduces diagnostic errors.

Patient Preparation:
- Fasting for abdominal USG to reduce bowel gas interference.
- Hydration for better visualization of pelvic structures.
- Proper positioning and use of gel to optimize contact.
Scan Planes:
- Sagittal (Longitudinal): Head-to-foot direction.
- Transverse: Perpendicular to the sagittal plane.
- Oblique & Coronal Views: Essential for detailed anatomical assessment.
Image Optimization:
- Adjust gain, depth, time gain compensation (TGC), and focal zone for best clarity.
- Use Doppler settings correctly for vascular flow assessment.
Documentation:
- Label images with correct anatomical location.
- Compare with prior studies if available.
- Note normal variations and incidental findings.

USG is the primary modality for hepatobiliary and pancreatic imaging due to its real-time capability and lack of radiation exposure.

Liver:
- Evaluate size, echotexture, vasculature (portal/hepatic veins), and masses.
- Features of fatty liver (increased echogenicity), cirrhosis (nodular surface), and hepatocellular carcinoma (heterogeneous mass with vascularity).
Gallbladder and Biliary System:
- Identify gallstones (hyperechoic foci with shadowing), cholecystitis (thickened GB wall, pericholecystic fluid).
- Assess bile duct dilation (>6 mm CBD in adults suggests obstruction).
Pancreas:
- Evaluate for pancreatitis (hypoechoic swelling, peripancreatic fluid), tumors (hypoechoic mass with vascular invasion).
Spleen:
- Assess size, echotexture, and detect infarcts, splenomegaly, or accessory spleens.

USG plays a pivotal role in evaluating pregnancy, fetal well-being, and gynecological pathology.

Obstetric USG:
- First Trimester: Confirm viability, gestational age, yolk sac, and fetal pole.
- Second & Third Trimester: Evaluate fetal growth, amniotic fluid, placenta, and anomalies.
- Doppler in Obstetrics: Assess uteroplacental and fetal circulation (umbilical artery, middle cerebral artery).
Gynecological USG:
- Evaluate the uterus (size, endometrial thickness, fibroids, adenomyosis).
- Ovarian pathology: Functional cysts, polycystic ovaries, ovarian tumors.

Doppler USG assesses hemodynamics, vascular pathology, and perfusion abnormalities.

Carotid Doppler:
- Evaluate atherosclerotic plaques, stenosis, and occlusions.
- Identify turbulent flow patterns, peak systolic velocity (PSV), and end-diastolic velocity (EDV).
Venous Doppler:
- Rule out deep vein thrombosis (DVT) via compression, augmentation, and spectral analysis.
- Assess for chronic venous insufficiency (reflux in incompetent valves).
Abdominal Doppler:
- Hepatic, renal, and mesenteric artery evaluation.
- Detects portal hypertension (reversed flow in the portal vein, collateral circulation).
Peripheral Arterial Doppler:
- Identifies peripheral artery disease (PAD) based on triphasic, biphasic, or monophasic waveforms.

Advancements in ultrasound technology are enhancing diagnostic accuracy and clinical utility.

Elastography:
- Evaluates liver fibrosis and tumor stiffness using shear wave and strain imaging.
- Differentiates benign vs. malignant lesions in breast and thyroid.
Contrast-Enhanced Ultrasound (CEUS):
- Uses microbubble contrast agents to enhance vascular imaging.
- Useful in liver lesion characterization, renal masses, and cardiac imaging.
3D & 4D Ultrasound:
- Provides volumetric assessment in fetal imaging, gynecology, and vascular studies.
Fusion Imaging:
- Combines ultrasound with CT/MRI for interventional guidance.
AI in Ultrasound:
- Automated lesion detection, improved workflow, and quantification of imaging parameters.