Introduction à la Médecine Nucléaire

Introduction to Nuclear Medicine

• Nuclear medicine is a branch of radiology focusing on either Magnetic Resonance Imaging (MRI) or scintigraphy.
• MRI uses hydrogen protons to create images.
• Scintigraphy utilizes radioactive elements that attach to body cells, allowing for detection of emitted radiation to reveal physiological function.

Principles of Nuclear Medicine Imaging

• Scintigraphy uses radiotracers (biological or not) specific to physiological functions or metabolic pathways.
• Radiotracers are typically administered intravenously or via inhalation.
• Detection occurs externally, pinpointing the tracer's location within the patient.
• Two key techniques include single-photon emission computed tomography (SPECT) and positron emission tomography (PET).
• PET imaging differs as the source of emission is internal to the patient.

Radiotracers

• Radiotracers, also called radiopharmaceuticals, consist of a carrier molecule linked to a radioactive marker.
• The carrier targets specific tissues or structures.
• The radioactive marker emits gamma rays, enabling location identification.
• Radiotracers are distinguished from stable isotopes by their radioactive emission of particles or radiation.

Detection Methods

• Gamma cameras rely on photons interacting with the detector to create images.
• Attenuation coefficient (μ) increases with atomic number (Z) and decreases with photon energy (E).
• Photomultiplier tubes convert light signals from the crystal into electrical signals proportional to the energy of the incident photon.
• Coincidence detection, in PET, is crucial as it identifies pairs of photons emitted during annihilation.

Imaging Modes in Nuclear Medicine

• Static imaging involves stationary detectors, capturing images at various points to showcase the distribution of the radiotracer in planes of the body.
• Dynamic imaging involves scanning over time, visualizing the progression of the process under investigation.
• Modern equipment employs sophisticated 3D imaging for more precise anatomical orientation, or hybrid modality combining nuclear and other imaging techniques.
• Example use: Radiotracer that is absorbed by the heart's ventricles during a cardiac pump cycle.