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Støylen, intro 3010

Nuclear imaging

Asbjørn Støylen, dr. Med. ISB, DMF

NTNU

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Nuclear imaging •  The term is pre MR

– Nuclear refers to radioactivity (as in nuclear bomb)

– Utilises ionizing radiation (as X-ray) – Radiation source is introduced into the

patient •  Ingestion •  Injection •  Inhalation

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Basic principle:

•  A gamma ray emitting isotope is introduced into the body

•  It concentrates in the desired organ due to the chemical characteristics of the compound containing the isotope

•  Radiation from that organ is detected by a gamma camera

•  The organ is imaged by emission, not absorption

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Whole body bone scan

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Wavelength not so different

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NB: Gamma radiation: •  Ionising radiation

–  As X-ray

•  Has biological effects –  Precutions: –  Radiation dose

•  X-ray and nuclear imaging is to be avoided: –  In pregnancy (first 3 months absolutely) –  For women in fertile part of cycle

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Isotopes •  Remain in the body after the picture is

acquired •  Eliminated by

–  Excretion (urine / bile) –  Radioactive decay

•  Means longer radiation exposure time –  And patients remain radioactive

•  In general higher radiation dose than X-ray

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Nuclear imaging versus X-ray

•  X-ray –  External ionizing

radiation –  Transmission

•  Attenuation images of organs with contrast

–  Anatomical imaging –  Tomographic

reconstruction possible

•  Nuclear –  Internal ionizing

radiation –  Emission

•  Emission images of organs with isotope

–  Functional imaging –  Tomographic

reconstruction possible

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Nuclear imaging

•  Basic (planar) imaging •  SPECT (Single Photon Emission Computer

Tomography •  PET (Positron Emission Tomography)

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Gamma camera

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Gamma camera

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Isotopes for Basic and SPECT:

•  Isotopes –  99Technetium –  123Iodine –  111Indium –  67Gallium –  (201Thallium)

•  T1/2 –  6 hours –  13 hours –  2.8 days –  3.26 days –  3.04 days

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Radiotracers •  Isotopes are used as:

–  Free isotope (e.g 99Tc; thyroid, 67Ga; inflammation)

–  Chemical compounds (e.g. 99Tc-pyrophosphate; bone

–  Labelled proteins (e.g 99Tc-albumin; blood pool)

–  Labelled cells ( 111In leucocytes; inflammation) •  The biochemical properties of the

compound, not the radioactive element, is the basis for organ specificity

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Planar images

Kidney and bladder Thyroid

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Lung ventilation

•  Principle: –  Inghalation of

radioactive diust that is taken up in lung tissue

•  Areas that are not ventilated (collapsed or plugged segments) not visible

Normal ventilation

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Lung perfusion: •  Principle: radiotracer that is injected int blood, but are too large to pass through capillary bed

•  Areas with blocked perfusion (blod clot in artery) are not visualised

•  Problem: collapsed areas have low perfusion

Upper left segment not visible

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Combined ventilation and perfusion

Normal ventilation Abnormal perfusion: Blood clot stopping blood supply to lung

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Renography - time curves:

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Heart function (MUGA)

•  Right and left ventricle

•  End systolic radioactivity (volume)

•  End diastolic radioactivity (volume)

Blood pool imaging

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SPECT scanning:

•  Rotating camera •  Basic scanning from multiple angles •  Reconstruction to 3D volume •  Presentation as

–  multiple slices –  3D figures –  Planar plots

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SPECT scanning:

Only 180° necessary, acquisition time 15 – 30 minutes

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Gives a tomographic picture

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SPECT is used for

•  Bone scan (99Tc) •  Brain scan (99Tc) •  Heart perfusion scan (99Tc) •  Tumour scan (123I) •  Inflammation scan (111In –

leucocytes)

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Bone scan:

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Brain scan:

Image data are grey scale. Colours are only for display (Codes level of activity)

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Heart perfusion scan

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PET scan: •  Positron Emission Tomography •  Postitron emitting isotopes

–  18Fluorine T1/2= 110 min (Fluorodeoxyglucose)

–  13Nitrogen T1/2= 10 min (Ammonia (NH3 – in water)

–  11Carbon T1/2= 20 min –  15Oxygen T1/2= 2 min –  82Rubidium T1/2= 75 sec

•  Due to short half life they need to be produced on site in a cyclotron (Except 82Rb, can be generated separately)

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Principle: •  Positrons emmitted by isotope •  Travels a very short distance before

they are annihilated by an electron •  The mutual annihilation prduce to

gamma photons with opposite directions

•  The two gamma rays can be detected by a ring of detectors.

•  By multiple emissions, the intensity of gamma emission can be mapped

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PET scan:

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Indications: •  Cancer – main indications

– The most sensitive method for tumour detection today

•  Functional brain imaging – Can locate area of function (f.i. Speech –

before brain surgery) •  Heart – little use (Viability: shows

preserved metabolism)

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Tomography

•  PET is a true tomographic method •  Can be combined with other

tomographic imaging methods: –  PET-CT –  PET-MR

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PET CT

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Pazhenkottil A P et al. Heart 2010;96:2050-2050

©2010 by BMJ Publishing Group Ltd and British Cardiovascular Society

Combined CT / PET / SPECT

•  Combined CT exercise SPECT

•  Combined anatomical and functional imaging

•  NB RADIATION