Nuclear Medicine - Overview, radiation

What is special about radionuclide imaging (RNI)/Nuclear Medicine

The patient is the radioactive source

What is given to the patient before treatment

Pt is injected/ingests/inhales a radioactive isotope combined with a Pharmacological agent - radiopharmaceutical. Pt then becomes the source of radiation

How is the imaging then taken

Taken using Gamma Cameras/Detectors that detect the radioactivity that is being released from the pts body as gamma ray positrons or other radiation particles

What can the imaging be fused with and why

Can be fused with CT images to form detailed images showing function and anatomy of a system, organ or whole body

What is a nuclide

A species of atom with specific atomic number and neutron number and in a defined nuclear state

What is a nuclide normally assumed at

Ground state

What does “m” signify in nuclides

metastable states, e.g. TC^99m

What are isotopes

A group of nuclides with the same proton number but different neutron and electron numbers, e.g. Iodine-131, Iodine-123

What are nuclei of isotopes usually

Normally in a stable state but some exist for limited time in an excited state where radiation is emitted to de-excite to ground state

What is the de-excitation called

Decay

What happens at decay

Particle or energy is released, i.e. radiation

What are the 4 forms of radiation

α - biggest particle (like a helium atom)

β - smaller particle (like an electron)

γ / X-ray - high energy wave

Neutron - most powerful/penetrating, from nuclear fission, nuclear power plants, etc. not used medically (uranium)

What Z and A does technetium (Tc) have

Z = 43

A = 99

Therefore Technetium-99m

Why is Tc important and what is it like

It is the most frequently used radioisotope in nuclear medicine, a gamma emitter having a half-life of 6.04 hours and a primary photon energy of 140keV

What is absorbed in an alumina filled column in a generator

⁹⁹Mo

What is molybdenum prepared as

Ammonium molybdate (Nh₄)⁺(MoO₄)^-

What does ⁹⁹Mo decay to

Daughter ^99mTc as pertechnetate ion (TcO₄)^-

What does saline do in the generator

Chloride ions exchange with (TcO₄)^- but not (MoO₄)^-

What does sodium pertechnetate result in

Na⁺(⁹⁹Tc^mO₄)^-

What is the relationship between ^99mTc and ⁹⁹Mo in terms of decay

Amount of ^99mTc increases as ⁹⁹Mo decays

What is reached at the end of the process in the generator

Transient equilibrium

What are the 7 features of a generator

• Compact outer casing

• Alumina column encased in lead

• Generator supplied with sterile evacuated vials

• NaCl 0.9%w/v

• Required sterility filters

• Required sterile needles

• Sealed

5 features of Tc^99m (ideal radionuclide)

• Half life of 6 hours

• Photon energy 140KeV

• Gamma emitter

• Originates from molybdenum (parent)

• Tc^99m generators are portable and brought to hospital departments each week

What is a pharmaceutical

A chemical compound/substance mixed with/bound to the radioactive isotope which will be taken up by the body so the area of interest is visualised

Gamma camera components: multihole collimator

Filters the energy emitted from the pt removing unwanted scattered photons

Gamma camera components: large sodium iodine (TI) crystal

Transforms energy to flashes of light (scintillations)

Gamma camera components: light guide

picks up the light signal and guides it to photomultiplier tubes

Gamma camera components: photomultiplier tubes

the light signal is amplified and turned into electrical signal

Gamma camera components: associated electronic circuits

Reads electrical signal and plot the outbound data and form an image

How long can a pt be radioactive after RNI with Tc99m gamma radiation

24 hours

How long can a pt be radioactive after RNI with F18-FDG (PET/CT) beta and gamma radiation

6 hours

What are the best methods of radiation protection and what one is insufficient

Time and distance. Shielding won’t be sufficient at the distance we need to be from the pt

What are the 5 important radiation safety guidelines for the pt and public

• Carefully mixed (labelled radiopharmaceutical and measured doses)

• Hydrating and using the bathroom frequently

• Keep distance from other injected pts in waiting areas

• Following aftercare instructions (hydration, distance, breastfeeding cessation)

• Following pt prep instructions (stopping certain medications, fasting in some cases)