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Ray ImagingRay Imaging

Inject a pharmaceutical labelled with a Inject a pharmaceutical labelled with a radioactive nuclideradioactive nuclide

Detect where Detect where -rays are coming from-rays are coming from Local concentration in patient indicates Local concentration in patient indicates

problems or otherwiseproblems or otherwise

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SCANNING

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

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RadiopharmaceuticalRadiopharmaceutical Choice of isotope for labelling:Choice of isotope for labelling:

Half life a few hoursProduces photon of a few hundred keVEasily attached to pharmaceuticalsCan be delivered to hospital in a form to last

several days

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Technetium 99Technetium 99 Most commonly used isotope Most commonly used isotope

Decays from excited to ground state by rayParent isotope is Molybdenum 99Half life about 6 hours

42429999

42429999MoMo TcTcmm

42429999 TcTc TcTc ++ (140keV)(140keV)mm

42429999

Half life 2.7 days

Half life 6.01 hours

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The CowThe CowInputneedle

Output needle

lead shield

Chromatographic

Adsorbent

Radionuclide Radionuclide GeneratorGenerator

Radionuclide Radionuclide GeneratorGenerator

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Att coef 0.16 1/cm

Undisturbedcm (%)1 85.25 44.910 20.215 9.120 4.1

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Gamma CameraGamma Camera

Consists of:Consists of:Light GuideCollimatorScintillatorArray of photomultipliersComputer

Position of scintillations can be foundPosition of scintillations can be found Distribution of radioactivity imagedDistribution of radioactivity imaged

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Gamma CameraGamma Camera

Output pulse shapesOutput pulse shapes

PhotomultipliertubesPhotomultipliertubes

Light guideLight guide

NaI(Tl)CrystalNaI(Tl)Crystal

CollimatorCollimator

LeadShieldLeadShield

photon

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AnalysisAnalysis Pulse are passed through a pulse height Pulse are passed through a pulse height

analyser analyser Allow only right energy pulsesLow energy pulses may come from other

scattering processes Position of each event calculated from Position of each event calculated from

relative energy at each photomultiplierrelative energy at each photomultiplier

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NaI (Tl)

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CollimatorCollimator Collimator restricts Collimator restricts

direction from which direction from which photons reach the photons reach the camera.camera.

Made of lead with Made of lead with holes.holes.

Bigger, shorter holes Bigger, shorter holes means more photons, means more photons, but more blurringbut more blurring

Visa versa.Visa versa.Radioactive Source

Collimator

Detector

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CollimatorCollimator Collimator restricts Collimator restricts

direction from which direction from which photons reach the photons reach the camera.camera.

Close to the Close to the collimator the umbra collimator the umbra region determines the region determines the resolution. resolution.

At distance the At distance the penumbra region penumbra region dominates.dominates.

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CollimatorCollimator Collimator restricts Collimator restricts

direction from which direction from which photons reach the photons reach the camera.camera.

Made of lead with Made of lead with holes.holes.

High gamma energies High gamma energies can penetrate the lead can penetrate the lead septa leading to septa leading to detoriation in detoriation in resolution.resolution.

Radioactive Source

Collimator

Detector

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Diagnostics and therapy, Diagnostics and therapy, 99m99mTc and Tc and 153153SmSm

Diagnostics and therapy, Diagnostics and therapy, 99m99mTc and Tc and 153153SmSm

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Lung metastases (SPECT/CT)Lung metastases (SPECT/CT)Lung metastases (SPECT/CT)Lung metastases (SPECT/CT)