understand that a tracer is a substance containing radioactive nuclei that can be introduced into the body and is then absorbed by the tissue being studied

Production and Use of X‑Rays

1. How X‑Rays are Made

Imagine a high‑speed camera that takes a picture of the inside of a body.

The “camera” is a vacuum tube where electrons are shot at a metal target (usually tungsten).

When the fast electrons hit the target, they suddenly slow down and release energy as electromagnetic radiation – the X‑rays.

  1. Electron source: A heated filament emits electrons (thermionic emission).

  2. Acceleration: A high voltage (kV) pulls the electrons toward the target.

  3. “Braking radiation” – electrons decelerate in the target and emit X‑rays.

  4. When electrons knock out inner‑shell electrons, outer electrons drop down, emitting X‑rays with specific energies.

2. Controlling the X‑Ray Beam

The intensity and energy of the X‑ray beam are adjusted by:

  • Voltage (kV) – higher voltage → higher energy photons.

  • Current (mA) – higher current → more photons.

  • Exposure time – longer time → more photons.

These parameters are chosen to give enough detail while keeping the dose to the patient as low as possible.

3. Using X‑Rays in Medicine

X‑rays pass through the body and are absorbed by tissues with different densities.

Dense tissues (bone) absorb more and appear white; soft tissues absorb less and appear grey; air appears black.

This contrast lets doctors see fractures, tumors, and other abnormalities.

4. Tracers: Radioactive Substances in the Body

A tracer is a substance that contains radioactive nuclei.

It can be introduced into the body (e.g., by injection, inhalation, or ingestion) and will be taken up by specific tissues.

Analogy: Think of a tracer as a glow‑in‑the‑dark sticker that you stick on a particular part of a toy.

When you shine a black‑light, only that sticker lights up, letting you see exactly where it is.

5. Common Tracers and Their Uses

TracerRadioisotopeTarget TissueTypical Scan
Fluorodeoxyglucose (FDG)\$^{18}\$F (fluorine)Active tissues (e.g., cancer cells)PET scan
Technetium‑99m (Tc‑99m)\$^{99m}\$TcBones, heart, lungsSPECT scan
Iodine‑131 (I‑131)\$^{131}\$IThyroid glandDiagnostic scan, therapy

6. Safety and Dose Management

The dose of radiation is measured in millisieverts (mSv).

A typical chest X‑ray is about 0.1 mSv, while a CT scan can be up to 10 mSv.

Rule of thumb: The ALARA principle (As Low As Reasonably Achievable) guides all imaging – use the lowest dose that still gives a useful image.

7. Key Take‑Away

  • X‑rays are produced by accelerating electrons onto a metal target.

  • They are used to create images that show differences in tissue density.

  • A tracer is a radioactive substance that homes in on specific tissues, allowing us to “see” where it goes.

  • Safety is paramount: doses are kept as low as possible while still providing useful diagnostic information.

Remember: Think of X‑rays as a light that can pass through the body and of tracers as tiny glowing markers that show us where certain cells or organs are working. 🚀