33. Medical applications of X-rays. X-ray imaging: radiography and radioscopy, conventional angiography, DSA, DEXA. Computed tomography. Hounsfield scale.

Principle of X-ray Diagnostics

• Fundamental Principle:
• X-rays are a form of electromagnetic radiation with high energy and short wavelength.
• They penetrate tissues with varying absorption depending on density, atomic number, and thickness.
• Dense tissues (e.g., bone) absorb more X-rays → appear white on film.
• Soft tissues absorb less → appear darker.
• X-ray Production:

• Produced in an X-ray tube by accelerating electrons toward a metal target (e.g., tungsten).
• X-rays arise via:
• Bremsstrahlung radiation (braking radiation).
• Characteristic radiation (electron transitions in the target atom).
• Lead Shielding:
• Used to protect patients and healthcare workers from unnecessary exposure.
• Lead is effective due to its high density and high atomic number.

X-ray Diagnostic Methods

1. Radiography

• Produces static 2D images.
• X-rays pass through the body → differential absorption captured on film or digital detector.
• Useful for: fractures, chest imaging, dental exams.

2. Fluoroscopy

• Provides real-time dynamic imaging.

• Continuous X-ray beam and fluorescent screen/detector allow visualization of moving structures.
• Applications: GI tract studies, catheter placement, angiography.

3. Computed Tomography (CT)

• Combines X-rays with computer processing for cross-sectional images.
• Steps:

1. Scanning phase: Multiple X-ray beams rotate around the body, acquiring images at different angles.
2. Reconstruction phase: Computer reconstructs the data into cross-sectional (tomographic) images.
3. Post-processing: Images can be displayed in digital or analog form.

• Advantages: detailed 3D visualization, high contrast resolution.