PET vs. SPECT scan | Dr. Paulien Moyaert

Summary

This video explains the differences between PET (Positron Emission Tomography) and SPECT (Single-Photon Emission Computed Tomography), both crucial imaging techniques in nuclear medicine. PET uses positron-emitting radioisotopes like fluorine-18 to detect cancer early by showing metabolic activity, while SPECT uses gamma-emitting radioisotopes like technetium to assess bone activity. PET and SPECT scans reveal how organs function and can detect biochemical changes before structural changes occur, making them valuable in diagnosing diseases such as cancer. The video also touches on how radiotracers work and their applications.

Takeaways

• 📚 PET and SPECT are imaging techniques in nuclear medicine that show organ function rather than just physical structure.
• 🔍 These scans can detect early disease stages by observing biochemical processes before anatomical changes occur.
• 🏥 They are particularly useful in oncology, with PET able to identify cancer earlier than CT scans.
• 📈 PET stands for positron emission tomography and uses positron-emitting radioisotopes, like fluorine-18.
• 🌟 SPECT stands for single-photon emission tomography and uses gamma-emitting radioisotopes, such as Technetium.
• 🔖 Radioisotopes are attached to tracers to create radiotracers, which are used to study specific bodily processes.
• 🍬 Fluorodeoxyglucose (FDG), made with fluorine-18, is used to diagnose cancer due to its uptake by high metabolic activity areas like cancer cells.
• 🦴 Technetium is often linked with methylene diphosphonate for bone scans, detecting fractures, infections, and tumors.
• 🛰️ Radiotracers emit gamma rays upon decay, which are detected by cameras to form images.
• 🤝 PET uses a ring of detectors to record gamma rays from positron-electron annihilation, creating detailed images.
• 🔄 SPECT uses rotating detectors to capture information from single gamma ray photons emitted by the radiotracers.

Q & A

What are the main differences between PET and SPECT imaging techniques?

PET (positron emission tomography) uses positron-emitting radioisotopes, most commonly fluorine-18, while SPECT (single-photon emission tomography) uses gamma-emitting radioisotopes, most commonly Technetium. PET is known for identifying cancer earlier than CT scans, whereas SPECT is often used for bone scans.

How do PET and SPECT scans differ in terms of the radioactive tracers they use?

PET scans use radioisotopes like fluorine-18, which emits positrons that annihilate upon meeting electrons, producing two gamma rays. SPECT scans use radioisotopes like Technetium, which emits a single gamma ray photon.

What is the role of tracers in PET and SPECT imaging?

Tracers are compounds attached to radioactive isotopes to create radiotracers. They act like GPS tags, directing the radioisotope to specific areas within the body for imaging. For instance, fluorine-18 can be attached to glucose to form FDG, which is used for cancer detection.

How does the body process FDG in PET imaging?

FDG (fluorodeoxyglucose) is a glucose analog that, when injected into the body, is mistaken for normal glucose by cells. It is absorbed and accumulates in areas of high metabolic activity, such as cancer cells, due to their increased glucose consumption.

What is the significance of PET and SPECT in detecting diseases at early stages?

PET and SPECT scans are valuable for detecting changes in the body's biochemical processes at the earliest disease stages, often before any anatomical changes are visible with other imaging techniques like X-rays, CT, or MRI.

How do PET and SPECT scanners detect gamma rays emitted by radiotracers?

PET scanners use hundreds of detectors in rings around the patient to record gamma rays that interact simultaneously with a pair of detectors. SPECT scanners use two large rectangular detectors that rotate around the patient to capture information.

What is the process that occurs when a positron encounters an electron in PET imaging?

When a positron emitted by a radioisotope in PET imaging encounters an electron in the body, both particles annihilate, releasing energy in the form of two gamma rays that travel in opposite directions.

How does the PET scanner form an image from the gamma rays?

The PET scanner uses the simultaneous detection of gamma rays by pairs of detectors to trace back to the point of annihilation. A computer then uses this data to form a detailed image of the body's metabolic activity.

What is the typical setup of a PET scanner?

A typical PET scanner consists of hundreds of detectors arranged in rings around the patient. These detectors are used to capture the gamma rays emitted by the radiotracers.

How does Technetium differ in its imaging process compared to Fluorine-18?

Technetium, used in SPECT imaging, emits only a single gamma ray photon, unlike Fluorine-18 in PET imaging, which emits two gamma rays upon positron-electron annihilation. This difference affects how the scanners capture and form images.

What is the purpose of attaching Technetium to methylene diphosphonate in SPECT imaging?

Technetium attached to methylene diphosphonate is used in bone scans because this bone-seeking tracer accumulates in areas of increased bone activity, such as fractures, infections, and tumors.