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2  Ray Imaging u Inject a pharmaceutical labelled with a radioactive nuclide  Detect where  -rays are coming from u Local concentration in patient indicates problems or otherwise

3 SCANNING

4 The figure shows an image from a rectilinear scan showing cancer in the upper left lung using a 67 Ga citrate.

5 Radiopharmaceutical u Choice of isotope for labelling: êHalf life a few hours  Produces  photon of a few hundred keV êEasily attached to pharmaceuticals êCan be delivered to hospital in a form to last several days

6 Technetium 99 u Most commonly used isotope  Decays from excited to ground state by  ray êParent isotope is Molybdenum 99 êHalf life about 6 hours Mo Tc m   TcTc+(140keV) m  Half life 2.7 days Half life 6.01 hours

7 The Cow Input needle Output needle lead shield Chromatographic Adsorbent Radionuclide Generator

8 Att coef /cm

9 Gamma Camera u Consists of: êLight Guide êCollimator êScintillator êArray of photomultipliers êComputer u Position of scintillations can be found u Distribution of radioactivity imaged

10 Gamma Camera Output pulse shapes Photomultiplier tubes Light guide NaI(Tl) Crystal Collimator Lead Shield  photon

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14 Analysis u Pulse are passed through a pulse height analyser êAllow only right energy pulses êLow energy pulses may come from other scattering processes u Position of each event calculated from relative energy at each photomultiplier

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16 NaI (Tl)

17 Collimator u Collimator restricts direction from which photons reach the camera. u Made of lead with holes. u Bigger, shorter holes means more photons, but more blurring u Visa versa. Radioactive Source Collimator Detector

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19 Collimator u Collimator restricts direction from which photons reach the camera. u Close to the collimator the umbra region determines the resolution. u At distance the penumbra region dominates.

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22 Collimator u Collimator restricts direction from which photons reach the camera. u Made of lead with holes. u High gamma energies can penetrate the lead septa leading to detoriation in resolution. Radioactive Source Collimator Detector

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25 Diagnostics and therapy, 99m Tc and 153 Sm

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28 Lung metastases (SPECT/CT)