Tomography Explained: CT, MRI, Ultrasound & Cross-Sectional Imaging

What Is Tomography?

Tomography (from Greek tomos = slice, graphein = to write) refers to any imaging technique that produces cross-sectional "slices" of the body, eliminating superimposition of structures.

Major Modalities

1. Computed Tomography (CT / CAT Scan)

• Physics: Rotating X-ray tube + detectors → computer reconstruction.
• Strengths: Speed, bone detail, lung tissue, acute hemorrhage, trauma.
• Radiation: Yes (ionizing).

2. Magnetic Resonance Imaging (MRI)

• Physics: Strong magnetic field + radiofrequency pulses → hydrogen proton signals.
• Strengths: Soft tissue contrast (brain, spine, joints, ligaments), no radiation.
• Limitations: Longer scan, cost, contraindications (certain implants, claustrophobia).

3. Ultrasound (Sonography)

• Physics: High-frequency sound waves → real-time images.
• Strengths: Real-time, portable, no radiation, Doppler flow, OB/GYN, guided procedures.
• Limitations: Operator-dependent, poor bone/air penetration.

4. Nuclear Medicine (SPECT/PET)

• Physics: Radioactive tracers → gamma camera (SPECT) or coincidence detection (PET).
• Strengths: Physiologic/metabolic info (cancer staging, cardiac perfusion, brain function).

Key Principle

All tomographic modalities acquire data from multiple angles/projections and use mathematical reconstruction algorithms to generate slices. This distinguishes them from planar radiography (standard X-ray).

Clinical Use

Tomography enables diagnosis of cancer, stroke, trauma, infection, vascular disease, and congenital anomalies—often guiding biopsy, surgery, or radiation planning.