magnetic resonance imaging & positron emission tomography aubrey overson
TRANSCRIPT
Magnetic Resonance Imaging
&Positron Emission
Tomography
AUBREY OVERSON
OUTLINE
MRI
~A bit of physics of the system~image
reconstruction
PET SCAN
~positron emission
~making of isotopes~detector
COMPARISON
Positron Emission Tomography
Simultaneously & collinear•produces two photonswith energy 511 KeV (mec2)•travel nearly 180º back to back•this is measured by a coincidence detector
enp
enOnFpO 181818
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;
Scintillation Camera
collimator crystal photomultiplier coincidence circuit
IMAGE RECONSTRUCTION
2D projection 3D Image
Filtered Back-projection (FBP).
http://www.seas.gwu.edu/~gogo/movies/homer3d.mov
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.
Magnetic Resonance Imaging(MRI)
Larmor Frequency
field magnetic Static
ratio icgyromagnet
frequency pressesion
0
0
B
B
More MRI detailsWhen 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
PET500 machines in USMetabolic processes Advantage of false colorMore sensitivity and
resolution than SPECT or CT
$2000-4000 dollars per scan
MRIVery commondoes 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.