Nuclear Medicine Physics

Integrating detector

  • Integrating detector

    • Detects how much total energy hits it from whatever source, does not specify the source only how much actually hits it

    • Good for high dose rates

  • Photon counting

    • Not used much yet - the future

    • Each time a photon hits the detector it can detect if it is good energy or a shitty photon (ie from scatter) and can get rid of the bad photons to not include in the image

    • Good for lower dose rates

    • In nuc med this is the detectors we use

    • Gamma ray comes in, hits a NaI crystal then goes to a photomultiplier

      • Photomultiplier acts as a magnifier, increases photon and shit

      • Photoelectric effect is what must be the interaction in the detector

    • The most likely energy resolution of the NaI crystal with PMT imaging Tc99 is 10%

  • Better detectors have these traits

    • High density

    • High Z

    • Low afterglow

    • Hydrophobic

    • High energy resolution

  • Gamma camera

    • Give isotope to pt

    • Isotope gives of rays which hit detector, goes through collimator, then scintillator then PM tubes

  • Colllimators

    • localize the source

    • Basically a funnel that only lets photons through a small area

    • Difference between these is basically how long is the hole that allows photons in

      • Longer = less weird angle photons can get through

    • LEHS

      • Low energy (for lwoer energy gamma ray)

      • Low resolution

      • High sensitivity

    • LEHR

      • High resolution

      • Low sensitivity

    • HE

      • Higher energy collimators need to be thicker and means that the openings need to be smaller so you will have lower sensitivity and somewhat lower resolution

      • Low resolution

      • Low sensitivity

      • High energy

    • Low energy = <160 keV = tc99m

    • Med energy = < 300 = In-111 & Ga=67

    • High energy = > 300 keV = I-131

    • You can also have different orientations of the holes

      • Parallel hole = major one used

      • Converging = good for small areas of anatomy

      • Diverging = when you need really large view in a single image - think of it like a fisheye lens

      • Pinhole collimator = small object and it is superficial = thyroid diagnostic imaging

  • Typical pulse height analyzer energy window with is 20% & resolution is 10%

    • 20% window means you go to the peak and go 10% up and 10% down and everything between that is a photon that is accepted and everything outside of those values is rejected

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