Pet scanning.pptx

What is pet scan, it's principle, components of pet, pet working , cases of pet , pet clinical applications PET/CT, Disadvantages and accuracy.#PETSCAN

1. PET scanning by- Vaishnavi Kalbandhe

2. Topics : PET- Introduction History Types Components of PET scanner Principle of PET How do PET scan work Clinical applications Disadvantages Accuracy

3. PET- Introduction POSITRON EMISSION TOMOGRAPHY. Positron emission tomography is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes and in other physiological activities including blood flow, regional chemical composition and absorption. PET scan uses a mildly radioactive drug to show up areas of your body where cells are more active than normal. It is used to diagnose some conditions including cancer.

4. History: In 1975 the firstly commercial PET scanner was introduced. 70s and 80s PET was mainly used for research. 1990s being used in clinics regularly.

5. What exactly PET scan is ! It is nuclear 3-D imaging test that uses a radioactive substance called a tracer to look for disease in the body. Shows how organs and tissues are working at a molecular and cellular level. Scan is non- invasive, but does involve exposure to ionizing radiation. Best known for its role in detecting cancer imaging.

6. Types: PET f-18 FDG scan Cardiac PET scan PET/ CT Scan

7. Main system components: Scanner gantry Detector Septa Coincidence circuit Table Computer cyclotron

8. Detector: Comprised of an 8 X 8 scintillation, inorganic crystals which emits light photons after the interaction of photons. 4 photomultiplier tubes (PMTs) arranged in a circular pattern around the patient. Bismuth germinate oxide(BGO), gadolinium oxyorthoslilicate detectors(LSO) are three materials that can be used to form the detectors for PET. There are four rings of detectors in PET.

9. Scintillator - A material that fluoresces when struck by a charged particle or high energy proton. These are materials that are able to convert high energy radiation such as X-rays or gamma rays to a near visible or visible light. They are widely used as detectors.

10. Septa: Lead or tungsten circular shield mounted between the detector rings. Limits scattered radiation from the object reaching the detector (scattered out the transverse plane) In typical PET system, the imaging planes are separated by a lead or tungsten septa to disallow the detection of photons in one imaging plane being in coincidence with photons detected in other imaging planes.

11. Coincidence circuit: Specific electronic circuits “coincidence” circuit pick up gamma pairs due to the two gamma rays emitted during the positron annihilation almost simultaneously. This coincidence is a very strong signature that distinguishes from other photons. Coincidence detection is the simultaneous detection of two or more photons in different detectors.

12. Cyclotron: A cyclotron is a particle accelerator that produces the radioactive component of the tracer used in PET scanning. A machine used to produce radioisotopes (radioactive chemical elements) which are used to synthesize the radiopharmaceuticals. The most frequently used radioisotopes in PET are – Carbon- 11 Nitrogen- 13 Oxygen-15 Fluorine- 18 18 FDG (Fluorodeoxyglucose) is the most widely used PET tracer.

13. Table During a positron emission tomography (PET) scan, you lie on a narrow table that slides into a doughnut shaped hole. The bed is capable of moving in and out of the scanner to measure the distribution of PET pharmaceuticals throughout the body, and it adjusts to a very low position for easy patient access.

14. Computer A computer analyzes the gamma rays and uses the information to create an image map of the organ and tissue being studied.

15. Principle of PET: Positron emission- Positron emission occurs when the isotope decays and a proton decays to a neutron, a positron and a neutrino. After travelling a short distance (3-5 mm), the positron emitted encounters an electron from the surrounding environment. The two particles combine and “annihilate” each other, resulting in the emission of two gamma rays in opposite directions of 0.511 MeV each. Proton- present inside the nucleus and its mass is equal to mass of one hydrogen atom. Positron- a subatomic particle with the same mass as an electron and numerically equal but positively charged.

16. Annihilation- Being completely destroyed or obliterated. “annihilation is the process that occurs when a subatomic particle collide with its respective antiparticle to produce other particles, such as electron colliding with a positron to produce two photons. Gamma rays called annihilation photons are created when positron collide with electrons near the decay event. The scanner then detects the annihilation photons, which arrive at the detectors in coincidence at 180 degrees apart from one another.

17. Principle of PET: Emission detection As positron annihilation occurs, the detector detects the isotope location and concentration. The resultant light photons are converted into electrical signals that are registered by the system electronics almost instantly. The reconstruction software then takes the coincidence events measured at all angular and linear positions to reconstruct an image.

18. Image acquisition: The image acquisition is based on a external detection in coincidence of the emitted gamma rays. Valid annihilation event requires a coincidence within 12 nanoseconds between two detectors on opposite sides of the scanner. For accepted coincidences, lines of response connecting the coincidence detectors are drawn through the object and used in the image reconstruction.

19. Image Reconstruction: Images are created from the raw data collected as rays corresponding to each detected annihilation event. It is the process where actual PET image is formed from the raw data (sinograms) collected by the PET scanner. The detection of photon pairs by opposing crystals create one event (LOR). Millions of this event will be stored within sinograms and used to reconstruct the image. Basic principle of tomographic image reconstruction from projections of an object is common to CT. The goal of PET image reconstruction is to provide cross-sectional images of the radiotracer distribution in an object, using the coincidence events detected by the scanner.

20. Sinogram For each image ( in case of 3-Dimensional object to be imaged, each cross-sectional image or slice), the projection data may be compiled and displayed in an array called a sinogram. This acquisition and organization of raw data is the first step in image reconstruction.

21. Preparation before PET

22. How do PET scans work? A small of radioactive sugar molecule, 18 fluoro-2-deoxyglucose (FDG), is injected into the bloodstream (can also be inhaled as gas or swallowed in pill form). A PET scan is used to detect and generate images that indicate areas of high FDG uptake. Many cancers require more energy than normal cells, and the FDG tracer accumulates in this cells. This allows cancers to be seen on the PET images as hot spots.

23. FDG- 18 fluoro-2-deoxyglucose (FDG) It is a positron emitting radiotracer used in positron emission tomography (PET) to diagnose and monitor various conditions. FDG accumulates within malignant cells because of their high rate of glucose metabolism. Once injected with this agent, the patient is imaged on a whole body PET scanner to reveal malignant lesions which may have been overlooked or difficult to characterize by X-ray, CT or MRI.

24. Clinical Applications A PET scan is an effective way to help identify variety of conditions including cancer heart disease brain disorders Your doctor can use this information to help diagnose, monitor or treat your condition.

25. Cancer Cancer cells show up as bright spots on PET scans because they have a higher metabolic rate than do normal cells. PET scans may be useful in: Detecting cancer Revealing whether your cancer has spread Checking whether a cancer treatment is working Finding a cancer recurrence PET scans must be interpreted carefully because non-cancerous conditions can look like cancer and some cancers do not appear on PET scans. Many type of solid tumors can be detected by PET-CT and PET-MRI scans.

26. Prostate Cancer

27. Heart Diseased PET scans can reveal areas of decreased blood flow in the heart. This information can help you and your doctor decide, for example; whether you might benefit from a procedure to open clogged heart arteries (angioplasty) or coronary artery bypass surgery. Brain Disorders PET scans can be used to evaluate certain brain disorders such as tumors, Alzheimer's disease and seizures.

28. Cardiac PET scan images

29. CT vs. PET A CT scan shows detailed pictures of the organs and tissues inside your body.   A PET scan can find abnormal activity and it can be more sensitive than other imaging tests . It may also show changes to your body sooner. Doctors use PET-CT scans to provide more information about the cancer. PET scans show metabolic changes occurring at the cellular level in an organ or tissue. This is important because disease often begins at the cellular level. CT scans (and MRIs) can't reveal  problems at the cellular level . PET scans can detect very early changes in a patient's cells. CT scans are more accurate than PET scans , but PET scans can be used to diagnose cancer at an early stage. Both scans are painless and take about 30 minutes to complete. 

30. Risks For a PET scan radioactive drug will be injected into a vein. As the amount of radiation being exposed from the tracer is small, the negative effects from the radiation is low. But the tracer might; Expose your unborn baby to radiation if you are pregnant. Expose your child to radiation if you are breastfeeding. Cause an allergic reaction, although this is rare.

31. Disadvantages: PET scanning can give false results if chemical balances within the body are not normal. Specifically test results of diabetic patients or patients who have eaten within a few hours prior to the examination can be adversely affected because of altered blood sugar or blood insulin levels.

32. Noise The noise level in nuclear medicine imaging is generally too high compared to other imaging modalities. The major source of noise is the random distribution of photons per picture element detected by the gamma camera. A high noise level will reduce contrast and image quality. To reduce noise: Increase either examination time either patient exposure. Increase pixel size ( but not too much) Image processing such as background subtraction and digital filtering should be applied.

33. Accuracy: It is more accurate than any other tests in finding local and metastatic tumors. Although, PET cannot detect metastatic cells, it can detect clusters of tumors cells that metastasized or spread to other tissues or organs. We use PET scan to show whether a tumor is cancerous or not.

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