Part 1Condition - Brain TumorSelected Medical Technologies - PET and MRI PET (Positron Emission Tomography) scanning creates 3D images of the body. To do this, it uses radioactive tracers, which are usually administered to the patient by injection. Tracers consist of carrier molecules closely bonded to a radioactive atom, called an isotope. The carrier molecule can interact with and bind to specific proteins or sugars in the body. The carrier molecule that will be used depends on what the doctor is looking for. If the doctor suspects a brain tumor, he or she may use radiotracers whose background activity in normal brain tissue is lower than that of FDG (Fluoro Deoxy Glucose), a modified form of glucose. The isotope produces small particles called positrons, which interact with surrounding electrons. This interaction results in the annihilation of the two particles, releasing two photons which move away in opposite directions (Fig. 2). The PET scanner's gamma ray detectors measure these photons and use this information to create an image of the area being scanned. (Fig. 1, 3) MRI or magnetic resonance imaging uses multiple magnetic fields, each to physically align the hydrogen atoms which are abundant in the human body since we are made up of approximately 70% water. Without MRI, the natural state of these atoms is constantly rotating randomly (Fig. 4), but with MRI, all atoms align in the direction of the field. The machine then applies a specific radio frequency (RF) pulse to the hydrogen atom, causing all the atoms to align toward the north or south (Figs. 5, 6). The system directs this impulse to the area being examined, in this case the brain, causing the atoms to spin in a different direction again...... middle of paper ...... Gould, R. and Edmonds , M. (2014). HowStuffWorks "What else happens during an MRI?" [online] HowStuffWorks. Available at: http://science.howstuffworks.com/mri4.htm [Accessed May 4. 2014].wiseGEEK, (2014). What is the difference between an MRI and a PET scan? [online] Available at: http://www.wisegeek.com/what-is-the-difference-between-an-mri-and-pet-scan.htm [Accessed May 4. 2014].Figure 1 http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucmed.html Figure 2 http://physiology-physics.blogspot.com.au/2008/12/pet-scan- particle-physics-and.html Figure 3 http://science.howstuffworks.com/nuclear-medicine1.htm Figure 4-8 http://science.howstuffworks.com/mri3.htm Figure 9 http://medicalphysicsweb.org /cws/article/research/43526 Figure 10 http://stonybrookmedicine.edu/imaging/pet-mri Figure 11http://www.naturalnews.com/032136_radiation_exposure_chart.html