Introduction to
Nuclear Medicine
What is Nuclear medicine?
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It is the use of radioactive materials in medicine.
It may be either diagnostic or therapeutic
In the therapeutic issue we must differentiate between
Brachytherapy (internal radiotherapy) sealed source
radiotherapy is a form of radiotherapy where a radiation source
is placed inside or next to the area requiring treatment.
Brachytherapy is commonly used as an effective treatment for
cervical, prostate, breast, and skin cancer
and Teletheraby (External beam radiotherapy). Kilovoltage
("superficial") X-rays are used for treating skin cancer and
superficial structures. Megavoltage ("deep") X-rays are used to
treat deep-seated tumors (e.g. bladder, bowel, prostate, lung, or
brain).
Nuclear Medicine Procedures
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Nuclear medicine procedures may be:
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diagnostic studies, which are tests of body function
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therapeutic procedures in which the radiation is used to treat
disease.
Radionuclide therapy is used in the treatment of both
benign disease (eg hyperthyroidism and arthritis) and
malignant disease (eg thyroid cancer, Suprarenal gland
tumors and hepatocellular carcinoma)
Nuclear Medicine Diagnoses What?
Radiopharmaceuticals
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The radioactive materials administered to patients are
known as radiopharmaceuticals.
These consist of :
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a chemical molecule which determines the behavior of the
radiopharmaceutical in the body
a radionuclide. The radiation emitted by the radionuclide
may be detected from outside the body by a radionuclide
imaging device (a gamma camera) or may be detected in a
sample of a body fluid (eg plasma or urine)
Radiopharmaceuticals
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Diagnostic radiopharmaceuticals must deliver the
minimum possible radiation dose to the patient while
still obtaining the required diagnostic information.
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Therapy radiopharmaceuticals must deliver the
maximum radiation dose to the diseased organ or
tumor, while minimizing the radiation dose to nontarget tissues such as the bone marrow.
The Ideal Radionuclide for
In-vivo Imaging
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It must emit photons in high abundance in energies
which can be efficiently detected by the gamma camera
(100 keV - 300 keV)
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It should not emit charged particles as these are
absorbed within a few millimetres of tissue. These can
not be detected outside of the body and greatly increase
the radiation dose to the patient.
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It should have a short half-life, again to keep the
radiation dose as low as possible.
The Ideal Radionuclide for
Therapy
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Must emit energetic charged particles. These are
usually beta particles but may be Auger electrons,
internal conversion electrons or even alpha particles.
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Low cost, available, safe.
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A fairly short half-life, typically several days.
Targeting the Right Tissue or
Organ
The metabolism of the radiopharmaceutical in the body
will depend on its chemical properties.
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Some are simple ions, such as 67Ga citrate and sodium
131Iodide
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Some are particles or aggregates of molecules labelled
with a radionuclide
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Some are radio-labelled blood cells (red cells or white
cells)
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The remainder are labelled complex molecules, such as
phosphonates, peptides and antibodies.
Clinical applications
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Bone scintigraphy: is a study of the skeletal system
that uses a form 99mTc injected intravenously absorbed
by the bone.
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Genitourinary studies: provides both an anatomic
and functional evaluation of the kidneys especially after
transplantation.
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Brain scan: evaluate various neurologic conditions as
Alzheimer and Parkinson disease.
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Thyroid uptake study: to evaluate functions of the
thyroid gland using sodium iodide 131I.
Radionuclides in Common Use
Four radionuclides account for the large majority of
clinical procedures. These are :
principal g energy 140 keV
 99mTc
T½ 6 hours
 131I
T½ 8 days
 67Ga
T½ 3.3 days principal g energies 93 keV,
184 keV and 296 keV
T½ 3 days x-ray emission at 70-80 keV
 201Tl
principal g energy 360 keV
Nuclear Medicine Team
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Nuclear medicine technologist: responsible for
handling, assessment, and administration of
radionuclides, patient safety, statistical analysis for
digitally processed images, decontaminate the area.
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Nuclear medicine physician: radiologist has received
training in the performance and interpretation of
nuclear medicine procedures.
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Medical nuclear physicist: received advanced training
in nuclear physics, computers, and radiation safety.
Responsible for preparing radioactive materials and
calibration and maintenance of imaging equipment.
Radionuclide Imaging and
Radiation Safety (1)
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Unlike Diagnostic Radiology and Radiotherapy,
Nuclear Medicine imaging devices do not emit
radiation.
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The technologist may take as many images as required
to provide the diagnosis without changing the radiation
exposure of the patient.
Radionuclide Imaging and
Radiation Safety (2)
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However, a malfunctioning gamma camera may result in errors
in diagnosis or an non-interpretive study so that the patient gets
no benefit from the radiation exposure arising from the
administered radiopharmaceutical.
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It is therefore essential that the principles of radionuclide
imaging are well understood, that the quality control procedures
are routinely performed and that the gamma camera is serviced
when required.
Advantages of Nuclear medicine
imaging
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Functional
Sensitive, quantitative.
Very safe.
Low radiation.
Screening & Follow up
Whole body evaluation without increased
radiation dose to the patient.
Very high specificity (no natural radioactivity
from the body).
Disadvantages of Nuclear medicine
imaging
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Not widely available.
Poor SNR.
Require NM instruments & radiopharmaceuticals.
Relatively higher cost than X-ray or US.
Radiation exposure to the patient.
Low spatial resolution (5-10mm).
Slow image acquisition.