Demystifying PET-CT for Final MBBS
Where Anatomy meets Physiology. Master the physics, understand the tracers, and nail your clinical scenarios.
Start Learning ↓1. The Core Concept
PET (Positron Emission Tomography) provides functional imaging (metabolism, receptors), while CT (Computed Tomography) provides precise anatomical landmarks. Together, they create a functional-anatomical map.
Interactive Fusion Simulation
Computed Tomography (CT)
Shows excellent anatomical detail based on tissue density (Hounsfield Units). However, it cannot differentiate between a benign fibrous mass and an active malignant tumor if they look identical anatomically.
- ✔ High spatial resolution
- ✔ Exact localization of structures
- ✖ Poor functional data
2. Basic Physics: Annihilation
Unlike standard X-rays, PET uses unstable isotopes that emit a Positron (antimatter electron). When antimatter meets matter, energy is created.
Step 1: Decay
The tracer (e.g., F-18) decays and emits a Positron (β+).
Step 2: Annihilation
The positron travels ~1mm, hits an electron (e-). Their mass turns into pure energy.
Step 3: Coincidence Detection
Two 511 keV gamma rays shoot out exactly 180° apart. The scanner detects them simultaneously.
3. The Radiotracers
Different molecules target different pathophysiological processes. Click a tracer to learn its mechanism, or view the chart comparing their physical properties.
18F-FDG
MetabolismMechanism (The "Trap")
FDG is an analog of glucose. It enters cells via GLUT transporters and is phosphorylated by Hexokinase. Because it lacks a 2'-hydroxyl group, it cannot continue in glycolysis and is trapped inside the cell.
Primary Indications
Oncology (Staging, Restaging most solid tumors like Lung, Lymphoma), Infection/Inflammation, Myocardial viability.
MBBS High-Yield Pearl:
"Tumors exhibit the Warburg Effect (aerobic glycolysis), consuming huge amounts of glucose. Brain and heart normally take up FDG, making assessment there tricky."
Radioisotope Physical Half-lives
Determines how quickly the tracer must be used after production (Cyclotron vs. Generator).
4. Clinical Scenarios (Test Yourself)
Apply your knowledge. Which tracer is most appropriate for the following clinical presentations?
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