31. Diagnostic applications of isotopes.

Question 1

On what basis is the distribution of istopes obtained? Name some diagnostic applications.

Answer 1

The distribution of isotopes can be detected by diagnostic equipments based on scintillation:

• scintillation counter

1. Gamma camera (Anger camera)
2. SPECT (single photon emission commuted tomography)
3. PET (positron emission photography)

Question 2

Explain the structure and function of a gamma camera refering to the picture below

Answer 2

Gamma camera:

1. γ-photons from isotope pass through collimator plates
2. Compton-scattering + photoelectric effect in the NaI scintillation crystal → scintillations
3. PMTs: low intensity scintillations to electric pulses (e^- avalanche)
4. computer: reconstructs 2D image of the isotope distribution → map of radioactive isotope

Question 3

Explain what static examinations are

Answer 3

Static examination:

one detection in order to visualize spatial distribution of the radioactive isotope at a certain point of time

Question 4

Explain what dynamic examinations are

Answer 4

Dynamic examination:

2+ detections in order visualize how spatial distribution of the radioactive isotope changes in time

→ isotope accumulation curve can be obtained

Question 5

What are the phases in the isotope accumulation curve? Refer to the diagram

Answer 5

Isotope accumulation curve:

after isotope injection:

1. lag phase: time until the appearance of the activity (T₀) → characterizes the transport capacity to the organ
2. clearance: slope of the curve between T and T_max characterizes the organ → uptake rate of the radioactive isotope
3. elimination: decreasing part of the curve → T_eff which characterizes the decay of the labeled substance and its elimination from the target organ

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→ area under curve gives mean isotope content of the organ during that period

Question 6

Explain the function of a SPECT

Answer 6

SPECT (=single photon emitting computer tomography):

1. γ radiating isotope added to the body
2. gamma camera detection done in several different directions (overall data collection in 360°)
3. computer directs movement of the detector, stores the data, calculates and reconstructs the cross-sectional image of the body (3D)

Question 7

Explain the function of a PET refering to the picture below

Answer 7

PET (= positron emitting tomography):

1. positron emitting isotope added to the body (e.g. in sugar solution)
2. γ-photons as a result of annihilation detected (β⁺ + e^- = 2γ)
3. detected by 2 scintillation detectors along the ring simultaneously (within a few ns)
4. computer calculate final image → 3D cross section

→ information about distribution of radioactive isotopes → activity (metabolism) measured

Question 8

What is scintigraphy?

Answer 8

Scintigraphy:

form of diagnostic test used in nuclear medicine, wherein radioisotopes (= radiopharmacons) are taken internally, and the emitted radiation is captured by gamma cameras to form 2D images

⇔ in contrast, SPECT and PET form 3D images

Question 9

What are radiopharmacons?

Answer 9

Radiopharmacons:

**chemical agents **or drugs having **radioactivity **

**→ **preparations labeled with radioisotopes for diagnostic or therapeutic purposes