1. VIII.0 Medical Exposures in Nuclear Medicine.
Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources
VIII.0 Medical Exposures in Nuclear Medicine.
Learning objectives: To get a general overview of the nuclear medicine practice including some diagnostic methods and therapy
Activity: Lecture
Duration: 1 h
Materials and equipment needed: Computer and computer projector
1. Overview

2. WHAT IS NUCLEAR MEDICINE?
Diagnosis and therapy with
unsealed sources
Clinical problem
Radiopharmaceutical Instrumentation
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3. What is nuclear medicine (cont)?
Most radiopharmaceuticals used in nuclear medicine procedures can be detected externally using special detectors. e.g. gamma cameras, PET scanners.
Cameras work in conjunction with computers to form images that provide data and information about the organ or area of body being imaged.
The radiation dose received from a diagnostic nuclear medicine procedure is comparable to that received from some diagnostic x-ray examinations.
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4. What is nuclear medicine (cont)?
There are nearly 100 different nuclear medicine imaging procedures in use today, including:-.
diagnosis and treatment of hyperthyroidism;
cardiac stress tests to analyze heart function;
bone scans for metastatic growths;
lung scans for blood clots;
kidney, liver and gall bladder procedures to diagnose abnormal function or blockages.
Some examples will be presented below
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5. Objectives of Nuclear Medicine
For diagnostic procedures, the objective is to:-
obtain clinical data regarding the distribution of radiopharmaceuticals that reflect a combination of blood flow, capillary permeability and tissue extraction, and
record images of the activity distribution to determine organ function (e.g., determine cerebral blood flow, ventricular function, thyroid uptake).
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6. Diagnostic Nuclear Medicine
Request of examination
Prescribed activity
Preparation of radiopharmaceutical
Administration
Examination
Evaluation and reporting
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7. Prescribed activity
The prescribed activity of a radiopharmaceutical is that activity documented in a written directive or in the diagnostic clinical procedures manual, in accordance with the direction of the authorized user.
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8. Objectives of Nuclear Medicine
For therapeutic procedures, the objective is to:-
administer a prescribed absorbed dose to the target tissue to obtain the desired effect (e.g. reduce tumor size).
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9. Nuclear Medicine Therapy
Request of examination
Prescribed absorbed dose
Determine biokinetic data
Prepare radiopharmaceutical and activity
Administer the treatment
Patient follow up
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10. Prescribed dose
The prescribed dose is that absorbed dose that is aimed to give the desired therapeutic effect on the irradiated organ or tissue. The absorbed dose should, for each individual patient, be prescribed by the medical practioner.
The corresponding activity to be administered should be calculated for each patient and be based on known or estimated biokinetic data.
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11. Instrumentation in nuclear medicine
Activity meter
Sample counters
Single- and multi-probe systems
Gammacamera
Positron camera (PET)
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12. Activity meter (dose calibrator)
The instrument measures the quantity of radioactive material in the prepared radiopharmaceutical prior to administration to the patient.
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13. Activity meter (dose calibrator)
The instrument comprises:
a cylindrically shaped, gas filled sealed chamber with a well;
high voltage supply applied to electrodes;
specific energy settings for different radionuclides;
an activity readout (e.g. in MBq, GBq, etc).
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14. Sample counters Scintillation Well Counters are used:-
mainly to count blood and urine samples.
to count wipe test samples to identify if radioactive contamination exists in the area surveyed.
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15. Probe system
Scintillation detector mainly used for counting during thyroid uptake studies.
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16. Gamma camera
Siemens
Used to measure the spatial and temporal distribution of a radiopharmaceutical
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17. Gamma camera (principle of operation)
Position X
Position Y
Energy Z
PHA
PM-tubes
Scintillation
Detector
Collimator
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18. Gamma camera (static aquisition)
Collect a certain number of events to build up the image
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19. Gamma camera (dynamic acquisition)
Define region of interest
Generate time- activity curve
Collect events at a certain frame rate
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20. Gamma camera (tomographic acquisition) (SPECT)
Collect events at different angles
Reconstruct data
Present the result as transversal, coronal, sagittal or oblique slices
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21. PET - Scanning
Positron Emission Tomography (PET) is used to study physiologic and biochemical processes within the body
Processes studied include blood flow, oxygen, glucose and fatty acid metabolism, amino acid transport, pH and neuroreceptor densities.
An on-site cyclotron is required to produce the very short half life PET radiopharmaceuticals.
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22. PET-scanner principle
Detector
Detector
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23. PET-SCANNER
M Dahlbom, UCLA
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24. Radionuclides Radionuclide Halflife Particle energy (mean)
C min 0.39 MeV
N min MeV
O min MeV
F min MeV
Cu min 1.3 MeV
Ga min 0.83 MeV
Rb min 1.5 MeV
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25. PET in oncology
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26. BONE SCAN Normal Pathologic
Bone uptake of Tc99m MDP reflects bone metabolism and blood flow, and allows functional analysis of bone turnover
The ability to image bone metabolism alterations enables detection of lesions such as
Bone metastasis
Benign or malignant bone tumors
Bone trauma
Intravenous injection of MBq Tc99m MDP . Whole body scanning h after injection
Normal
Pathologic
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27. LUNG SCAN
An embolization of the pulmonary capillary bed yields an image reflecting the lung blood perfusion (Tc99m MAA).
Ventilation studies (Tc99m -aerosols) reflect the regional and segmental ventilation.
Diagnosis of pulmonary emboli.
Intravenous injection (perfusion) of 100 MBq Tc99m MAA. Inhalation of 100MBq Tc99m aerosol (ventilation). Immediate scanning.
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28. ROI:s (region of interest) Renogram
Kidney function
Dynamic renal scintigraphy reflects renal blood perfusion, uptake and excretion. The acquisition yields a series of images. By calculating count rate in a defined ROI, a renogram is created, providing quantitative data. Different radiopharmaceuticals, such as Tc99m-MAG3, Tc99m-DTPA and I123-Hippuran, are used for renal clearance and function assessment. Administered activity MBq.
ROI:s (region of interest) Renogram
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29. Myocardial perfusion
Accumulation of Tl201, Tc99m MIBI or Tetrofosmin in the myocard depends on blood flow and cellular metabolism, hence, reflects regional perfusion and viability of the cardiac muscle.
The evaluation of a patient suspected or known for C.A.D. is based on image interpretation or quantitative analysis from reconstructed tomographic slices, which also yields regional perfusion information.
The examination is performed under maximum stress condition and after rest.
Injected activity 1000 MBq Tc99m or 100 MBq Tl201. Tomographic study.
Stress
Rest
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30. ECG-gated myocardial perfusion
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31. Nuclear medicine images
Nuclear imaging detects functional properties of the human tissue. Anatomical information is found with conventional X-rays, CT or MR
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32. CURRENT METHODS-THERAPY
Radiopharmaceutical For treatment of Route of Maximum
administration activity
I iodide Thyrotoxicosis Oral GBq
I iodide Carcinoma of thyroid Oral GBq
I MIBG Malignancy IV GBq
P phosphate Polycythaemia vera IV or oral MBq
Sr chloride Bone metastases IV MBq
Y colloid Arthritic conditions Intra-articular MBq
malignant effusions Intra-cavitary GBq
Er colloid Arthritic conditions Intra-articular MBq
Re colloid Arthritic conditions Intra-articular MBq
Sm EDTMP Bone metastases IV GBq
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33. I-131 therapy The absorbed dose to be delivered should be determined
from uptake measurements, effective half-life of the radio-
pharmaceutical and the size of the thyroid.
The radiopharmaceutical is administered p.o.
Hyperthyroidism
Cured after Hypothyroidism
3-4 months 1 year after <7 years after >7 years
85% % % %
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34. Radiosynovectomy
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35. PAIN PALLIATION Intravenous injection of a radiopharmaceutical which
includes e.g. Sr-89 or
Sm-153
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36. Nuclear medicine - unclear medicine?
No! Nuclear medicine is an efficient
diagnostic and therapeutic tool and
is justified from a medical point of view.
Do we need radiation protection then?
YES!
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