Positron Emission Tomography Magnetic Resonance Imaging & Positron Emission Tomography AUBREY OVERSON

OUTLINE COMPARISON PET SCAN ~positron emission ~making of isotopes ~detector MRI ~A bit of physics of the system ~image reconstruction COMPARISON

Positron Emission Tomography Simultaneously & collinear produces two photons with energy 511 KeV (mec2) travel nearly 180º back to back this is measured by a coincidence detector

11C=20.34min; 13N=9.96 min; 15O=2.05 min; 18F =110min; CYCLOTRON Also has better radionuclides with a low atomic numbers (11C, 13N, 15O, 18F) which have a higher affinity of the human body as well as relatively short half lives… 11C=20.34min; 13N=9.96 min; 15O=2.05 min; 18F =110min;

collimator crystal  photomultiplier  coincidence circuit Scintillation Camera collimator crystal  photomultiplier  coincidence circuit

IMAGE RECONSTRUCTION 2D projection  3D Image Filtered Back-projection (FBP). MRI contrast works by altering the local magnetic field in the tissue being examined. Normal and abnormal tissue will respond differently to this slight alteration, giving us differing signals. These varied signals are transferred to the images, allowing us to visualize many different types of tissue abnormalities and disease processes better than we could without the contrast. http://www.seas.gwu.edu/~gogo/movies/homer3d.mov

Magnetic Resonance Imaging (MRI) Larmor Frequency

More MRI details When the RF pulse is turned off, the hydrogen protons begin return to their natural alignment within the magnetic field and release their excess stored energy. When they do this, they give off a signal that the coil now picks up and sends to the computer system. What the system receives is mathematical data that is converted, through the use of a Fourier transform, into a picture that we can put on film. That is the "imaging" part of MRI.

COMPARISONS PET MRI 500 machines in US Very common Metabolic processes Advantage of false color More sensitivity and resolution than SPECT or CT $2000-4000 dollars per scan MRI Very common does not use ionizing radiation is a comfort to many patients, ability to image in any plane. It gives images of brain tumors, abscesses, swelling, bleeding, nerve damage, and other disorders that increase the fluid content of tissues.