NUCLEAR MEDICINE Review ppt for Radiologic Technologist

NUCLEAR
MEDICINE
By: Mark Jayson P. Gutierrez, RRT, MAEd
RTII, UP – Philippine General Hospital
Faculty, Emilio Aguinaldo College-Manila

If we confess our sins, He is faithful
and just and will forgive us our
sins and purify us from all
unrighteousness.
- 1 John 1:9
Thought for the Day

 It is a branch of medicine that deals with the use
of radioactive substance in diagnosis or
treatment of diseases.
What Is Nuclear Medicine?

 The history of nuclear medicine is rich with
contributions from gifted scientists across
different disciplines in physics, chemistry,
engineering, and medicine.
 The multidisciplinary nature of Nuclear Medicine
makes it difficult for medical historians to
determine the birthdate of Nuclear Medicine.
History

 This can probably be best placed between
the discovery of artificial radioactivity in 1934
and the production of radionuclides by Oak
Ridge National Laboratory for medicine
related use, in 1946.
 Many historians consider the discovery of
artificially produced radioisotopes by Frederic
Joliot-Curie and Irene Joliot-Curie in 1934 as
the most significant milestone in Nuclear
Medicine.

 is the smallest quantity of an element that
retains all the chemical properties of that
element.
 The atom is made of two basic parts; the nucleus
(nuclear portion) and the orbital electrons (extra
nuclear portion).
 There are three (3) principal types of subatomic
particles that compose an atom – protons,
neutrons, and electrons.
The Atom

NUCLEAR MEDICINE Review ppt for Radiologic Technologist

 Found within the nucleus of an atom and are
symbolized by letter p or p+.
 They provide positive charge to the nucleus.
 Has a mass of 1.673 x 10 -27
kg or 1.00783 amu.
 Total number of protons equals atomic number
(Z) of an element.
 Discovered by E. Goldstein in 1886.
Protons

 Neutral particles within the nucleus of the atom.
 Slightly heavier than protons.
 No electric charge.
 Mass of 1.675 x 10 -27
kg or 1.0090 amu.
 Symbolized by the letter n.
 Discovered by J. Chadwick in 1932.
Neutrons

 Smallest of the subatomic particles and are
found in the extra nuclear portion of the atom.
 Are called negatrons and are given the symbol е
or e‑.
 Has a small mass of 9.1 x 10 -31
kg or 0.00055
amu.
 Discovered by J. J. Thompson in 1897.
Electrons

 The nucleus is composed of two types of these
particles- protons and neutrons; hence protons and
neutrons are called nucleons, which gives the atom
most of its mass.

 The nuclear diameter is of the order of 5x10 -15
m,
and composed of protons and neutrons.
 A proton can be converted to a neutron, and vice-
versa.
Nuclear Structure

 Nuclides – Any atomic species characterized by
the atomic mass number (A), protons (Z), and
number of neutron (N).
 Parent Nuclide – the original nuclide that
undergoes radioactive decay.
 Daughter Nuclide – the more stable nuclide
which results from radioactive decay.

 Is the emission of particle or energy to attain
stability.
 It decays by spitting out : Mass (alpha particle),
Charge (Beta particle), Energy (Gamma Rays).
Radioactivity

Its nucleus may be unstable because it has either:
Too many protons
Too many neutrons
Too many neutrons and protons
There are three reasons/conditions why
substance might be radioactive

-The process by which they emit high energy particles or
rays from their nucleus.
Those that involve nuclear transformation:
oNegative Beta Decay
oPositive Beta Decay
oElectron Capture
oAlpha Decay
Those that does not involve nuclear transformation:
oGamma Decay
Radioactive decay

-describes the rate of radioactive decay and the quantity
of the material present at any given time.
 The Radioactive Decay Law is exponential in nature,
and is expressed mathematically as:
A = Aoe-λt
WHERE:
A = activity at time (t)
Ao = Initial Activity
λ = decay constant per unit time
e = base of logarithm
Radioactive Decay Law

SAMPLE PROBLEM:
1. A radioactive material has an activity of 50mCi,
what would be its activity after 3 days if this
radioactive material has a half-life of 8 hrs?
2. The half-life of Ni-63 is 100 yrs. If you had 100g
of Ni-63, how much would be left over 500 yrs?

 Physical Half-life is the time required so that
activity of radionuclide is reduced to 50%.
 Biological Half-life is the time required for the
body to eliminate half of an administered dosage
of any substance by regular process of
deliberation.
 Effective Half-life is the time required for a
radioactive elimination in the body to be
diminished by 50% as a result of the combined
action of the Radioactive Decay and Biological
Elimination.

Note: Most gamma rays are emitted almost
immediately (<10-12
second) after the primary decay
process, whether it be alpha decay, negatron decay,
positron decay, or electron capture. When the
intermediate excited state last longer than 10-9
second, the term “metastable” is used.

 Isotopes
 Isobars
 Isotones
 Isomers
Nuclear Families

 The discovery of radioactivity made it necessary to
develop apparatus, first for detecting nuclear
radiations and later for measuring their intensity and
energy.
 The amount and type of radioactivity being
administered to patient must be measured and
documented, and the areas in which people work
must be monitored to ensure safety to both health
care personnel and patients.
 A detection system can be considered to consist of
two parts, a detector and a measuring apparatus.

There are two main categories of detectors:
 GAS FILLED DETECTORS - Those that depend on
ionization in which ionization is translated into
electric current or impulses.
 SCINTILLATION DETECTORS - those that depend on
excitation.
Types of Detectors

 Radiation is sensed by detecting the ionization of gas
molecules produced by deposition of energy during
radiation’s passage through the gas-filled detectors.
 One important approach to radiation detection is the
use of an ionization chamber. The generic design
concept is a gas-filled chamber with positive and
negative electrodes, placed either at opposite sides
of the chamber. A potential difference is created
between two electrodes, but no current flows in the
absence of exposure of the chamber to radiation.
Gas – Filled Detectors

 The interaction of ionizing radiation with the gas in
the chamber creates positive and negative ions,
which move to the electrodes and produced
electrical current.
PRINCIPLE:
When ionizing radiation produces ion pairs in the
gas, the resulting free electrons are attracted to the
anode and the positively charged gas molecule ions
are attracted to the cathode, (an ion pair is positively
charged gas molecule ion and the free electron that
came from it). This bulk movement of charge
produces an electrical signal from the detector.
Commonly used gases: Helium, Neon, Argon, and
Hydrogen.

3 Types Of Gas-filled
Detectors

Basic Ionization Chamber
The voltage difference between the electrodes are
calibrated to be just high enough to “harvest” all of the
ions from the sensitive volume of the chamber, but not
high enough that the ions in the chamber are
accelerated to the point of creating additional
secondary ionizations.
As a result of this voltage calibration strategy, the
current produced in any single event is very small and
not measurable with any accuracy. Rather, the
ionization chamber is used to measure the total
current resulting from multiple events over a certain
integration time in a given radiation detection setting.

Radiation survey meters such as the cutie-pie, some
pocket dosimeters and radionuclide dose calibrator
are all examples of specialized basic ionization.
The amount of energy converted to electrical current
per unit of radioactivity is unique for each
radionuclide, and radionuclide dose calibrators must
be calibrated for the radionuclide to be measured.

Proportional Counters
The main difference between a proportional
counter and basic ionization chamber is greater
applied voltage between electrodes in the
former.
The higher voltage results in secondary
ionization in the sensitive volume of the
chamber. The term gas amplification describes
this phenomenon.
Gas amplification can result in increased
ionization by a factor of 1,000-1,000,000.

The resulting current pulse is large enough to
be measured individually and is proportional to
the energy originally deposited in the gas
chamber.
The name of the device is based on the
proportionality of total ionization to the total
energy of the ionizing radiation.
Proportional chambers do not have wide
application in clinical nuclear medicine. They
are used in research to detect alpha and beta
particles.
One characteristic of proportional counters that
makes them particularly useful is their ability to
distinguish between alpha and beta radiation.

Geiger - Muller Counter
The voltage is increased even higher than in the
proportional chamber application.
The effect is that nearly all the molecules of the gas
are ionized, liberating a large number of electrons.
This results in a large electron pulse and detection of
single event but not their energy.

The detector may not be capable of responding to a
second event if the filling gas has not been restored
to its initial condition. Therefore, a quenching agent is
added to the filling gas of the Geiger counter to
enable the chamber to return to its original condition;
subsequent ionizing events can then be detected.
The minimum time between ionizations that can be
detected is known as the dead time or resolving time.

Geiger counter is used for contamination control in
nuclear medicine laboratories. They are not
particularly useful as dosimeters because they are
difficult to calibrate for varying condition of radiation.
Survey meter is one of the example of GM counter.

 When ionizing particles pass through certain crystals,
flashes of light or scintillation is emitted.
 The amount of light emitted is proportional to the
amount of energy absorbed by the material.
 This type of detector is the most commonly used
detector in nuclear medicine.
Scintillation Detectors

 This detector can be used to measure the energy
distribution of particles in addition to counting
them.
 Has a very high sensitivity to gamma rays and to
small amounts of activity.
 Considered to be the most useful type of nuclear
– indicator detector.
 Due to its high sensitivity, it is particularly used
for detecting low levels of activity.
 They should be calibrated with the nuclide of
interest.

 It is invented by Hal Anger in the late 1950’s.
 It is the most commonly used imaging instruments in
Nuclear Medicine.
 The complete camera system consists of:
Collimator
Crystal Sodium Iodide
Photomultiplier tube
Pulse height analyzer
Scaler/Timer
Cathode Ray Tube (CRT)
ANGER SCINTILLATION CAMERA
(GAMMA CAMERA)

 The basic function of the gamma camera is to
provide an image of the radionuclide injected to
the patient. The radionuclide emits gamma rays,
which can escape from the body and thus can be
detected by gamma camera.

 Shielding device used to limit the angle of entry
of radiation.
 Determine to a large extent the final image
quality obtained from the gamma camera and
are therefore one of the most important part of
the gamma camera.
Collimator

 Converging Collimator – holes are not parallel
but are angled to converge to a focal point,
providing some magnification.
 Diverging Collimator – opposite of converging
collimator, holes are angled opposite direction in
converging collimator which make the image
smaller.
Types of Collimator

Parallel Hole Collimator – is the most commonly used
collimator. It consist of a large number of small hole,
separated by the lead septa, which are parallel to each
other, and usually perpendicular to the crystal.

Pinhole Collimator – thick conical collimators with a single
2-5 mm hole in the bottom center. As a source is moved
away from the surface of a pinhole collimator, the camera
image gets smaller.

 NaI (Tl) crystals are hydroscopic, thus they absorbed
moisture from air, so they have to be sealed with
aluminum can with a glass window.
 Its purpose is to convert gamma rays to light
photons as the gamma rays interact with the crystal
and loose energy.
 The numbers of light photons produced in the
crystals are proportional to the energy of the gamma
ray.
Crystal

 Whenever possible, cover the crystal with a collimator or
other protective cover to avoid something dropping on
or biting the crystal. Even a quite small impact can break
the crystal.
 Avoid large temperature fluctuations in the gamma
camera room and ensure the collimator is attached to
the camera detector head whenever possible to insulate
the crystal from temperature fluctuations. Also avoid
the sun shining directly on the detector and crystal.
 Avoid contamination of the crystal.
Precautions to avoid damage to the crystals:

 By means of the light pipe and reflector, a large
fraction of light is transmitted to the photocathode of
the PMT, wherein it converts the light from the crystal
into an electrical pulse which contain series of
dynodes.
Photomultiplier Tube (PMT)

 For every 7-10 light photons, which reach the
cathode, one electron is ejected by photoelectric
effect. The electron produced are accelerated
towards the first dynode, 3-4 electrons are
released, which in turn accelerated towards D2,
where again 3-4 further electrons are released
and so on for all the dynodes. Thus, for each
dynode, the number of electrons is multiplied by
a factor of 3-4.

 Is an electronic device used to determine which
portion of the detected spectrum is used to create
images.
 The PHA can be set to allow only selected energies to
be counted, and reduce the number of Compton
scatter photons in the image.
 The PHA allows the operator either to set the upper
and lower energy limits or to set a peak energy level
and associated window.
Pulse Height Analyzer (PHA)

 The window, measured by percent, determines
the acceptable range of energies around the
peak for subsequent counting.
 Wide windows accept more photons and
produce images in a shorter time but include
more photons that degrade image quality.

Responsible for counting the number of detected
gamma ray which falls inside the PHA window.
Scaler and Timer

Scintigraphy
 Appearances of the kidney on bone scintigraphy. Bone scintigraphy in a breast cancer patient
with bone metastases scan and normal renal parenchymal uptake.

Appearances of the kidney on bone scintigraphy. Bone scintigraphy in a malignant lymphoma patient
with bone metastases scan and intense renal parenchymal uptake.

POSITRON EMISSION
TOMOGRAPHY
PET is form of tomography made possible by the
unique fate of positrons. When positrons undergo
annihilation by combining the negatively charged
electron, two 511-keV gamma rays are given off in
opposite directions 180 degrees apart.
Commonly used radionuclide: Fluorine-18 with a half-
life of 110 minutes.

A PET scan uses radiation, or nuclear
medicine imaging, to produce 3-
dimensional, color images of the
functional processes within the human
body.
The machine detects pairs of gamma
rays which are emitted indirectly by a
tracer (positron-emitting
radionuclide) which is placed in the
body on a biologically active
molecule.

Modern machines often use a CT X-ray scan which is
performed on the patient at the same time in the
same machine.

PET scans can be used to diagnose a health
condition, as well as for finding out how an
existing condition is developing.
PET scans are often used to see how
effective an ongoing treatment is.

PET/CT Combined
PET/CT imaging
can identify both
the presence of
disease and its
precise location.

 The density and effective atomic number for NaI (TI)
crystals are not ideal for detecting the 511-keV
gamma rays used in PET imaging.
 Bismuth germinate oxide (BG0) is approximately
twice as dense with an effective Z of 74, compared
with an effective Z of 50 for NaI (TI). BG0 detectors
have been used extensively in PET imaging
applications for this reason.
 Other materials: LSO, GSO, and YSO
DETECTOR MATERIALS

RADIOPHARMACEUTICALS
 Is reserved for radioactive materials that have met
legal requirements for administration to the patients
or subjects.
 Portray the physiology, biochemistry or pathology of
a body system without causing any perturbation of
function.
 They are referred to as “radiotracers” because they
are given in subpharmacologic process in the body.

 Radiopharmaceuticals are a combination of a
RADIOACTIVE molecule that permits external
detection and a BIOLOGICALLY ACTIVE molecule or
drug that acts as a carrier and determines
localization and biodistribution.

DESIGN CHARACTERISTICS OF
RADIOPHARMACEUTICALS
 The radionuclide decay should result in gamma
emissions of suitable energy (100-300 keV is ideal for
gamma cameras) and sufficient abundance of
emission of external detection.
 It should not contain particulate radiation (beta
emissions), which increases patient’s radiation dose
without adding diagnostic information.

 Beta emissions are suitable for therapeutic
radiopharmaceuticals.
 The effective half-life should only be longer enough
for the intended application, usually a few hours.
 The specific activity should be high. (Tc-99m).
 The pharmaceutical component should be free of any
toxicity or secondary effects.

 Should be readily available or easily
compounded and should have a reasonable cost.
 The agent should rapidly and specifically localize
according to the intended application.

PRODUCTION OF RADIONUCLIDES
 The radionuclides most commonly used clinically are
artificially produced.
 Bombardment of medium atomic-weight nuclides
with low-energy neutrons in nuclear reactor results in
neutron-rich radionuclides that undergo beta-minus
decay.
 Proton bombardment of a wide variety of target
nuclides in cyclotrons or other special accelerators
produces proton-rich radionuclides that undergo
positron decay or electron capture.

Technitium – 99m
- is the most commonly used radionuclide because of the
following:
 Readily available.
 Favorable energy of its principal gamma photon
(140keV).
 Favorable dosimetry with lack of primary particulate
radiations.
 Ideal half-life (6 hours) for many clinical imaging studies.

RADIATION SAFETY PROCEDURES
 Wear laboratory coats in area where radioactive
materials are present.
 Wear disposable gloves when handling radioactive
materials.
 Monitor hands and body for radioactive
contamination before leaving the area.
 Use syringe and vial shields as necessary.

 Do not eat, drink, smoke, apply cosmetics, or store
food in any area where radioactive material is stored
or used.
 Wear personnel monitoring devices in areas with
radioactive materials.
 Never pipette by mouth.
 Dispose of radioactive waste in designated, labeled
and properly shielded receptacles located in a
secured area.

 Label containers, vials, syringes containing
radioactive materials. When not in use, place in
shielded containers or behind lead shielding in a
secure area.
 Store all sealed sources (floods, dose calibrator
sources) in shielded containers in a secured area.
 Before administering doses to patients, determine
and record activity.
 Know what steps to take and who to contact
(radiation safety officer) in the event of radiation
accident, improper operation of radiation safety
equipment, or theft/loss of licensed material.

PROCEDURE FOR RADIOACTIVE SPILL
• Notify all persons in the area that a spill has
occurred.
• Prevent the spread of contamination by isolating the
area and covering the spill (absorbent paper).
• If clothing is contaminated, remove and place in
plastic bag.
• If an individual is contaminated, rinse contaminated
region with lukewarm water and wash with soap.

 Notify the radiation safety officer.
 Wear gloves, disposable lab coats and booties to
clean up spill with absorbent paper.
 Put all contaminated absorbent paper in labeled
radioactive waste container.
 Check the area or contaminated individual with
appropriate radiation survey meter.

“Yet to all who received Him, to those who
believed in His name, He gave the right to
become children of God-children born not of
natural descent, nor of human decision or a
husband’s will, but born of God.”
- John 1: 12-13
Word of Encouragement

“If you give your BEST,
there would be NO
REGRETS”
- Mark Jayson P. Gutierrez

NUCLEAR MEDICINE Review ppt for Radiologic Technologist

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