NUCLEAR MEDICINE MIDTERMS

Positron Emission Tomography (P.E.T)  can exist forever, but when a positron emits
electron, the two particles annihilates into a flash
Outline energy
 Intro  Theorist Paul Dirac, predicted positron and other
 What is P.E.T particles in 1928
 History of a Positron  Positron can come from different number of
 What is a Positron sources, but for PET they are produced by nuclear
 How does P.E.T works decay.
 Benefits/Uses  when the positron and electron meets, they
 Things to consider/limitations annihilate, converting all their mass into energy
 Summary  Nuclear decay is basically when unstable nuclei are
produced in a cyclotron by bombarding the target
What is PET material with protons, and as a result a neutron is
 PET is a noninvasive, diagnostic imaging released.
technique for measuring the metabolic activity of  nuclear decay also called radioactive decay occurs
cells in the human body. when the nucleus of an atom is unstable and
 allows doctor to check for diseases continuously emits energy in the form of radiation.
 uses special dye, radiopharmaceutical containing the result is that the nucleus changes into one or
radioactive tracers that can be swallowed, more elements. daughter nuclei have a lower mass
inhaled or injected or more stable or lower energy than the parent
 organs and tissues absorbs the tracer nucleus
 outpatient procedure  nd or rd occurs in a series of sub sequential
 It was developed in the mid 1970s and it was the reactions until a stable nucleus is reach
first scanning method to give functional  3 types of nuclear decay: Alpha decay, Beta decay,
information about the brain. in combination with Electron capture.
ct or mri, malignancies.  18-O + proton => 18-F + neutron
 brain physiology to brain functions  In PET the target material is chosen so that the
 pet scanners, early 1960s product of the bombardment decays to a more
 ct scanners, early 1970s stable state isotope by emitting a positron, for
instance 18-F has too many protons, so one of
these protons decays into a neutron emitting in the
A little history about the positron process a positron an a neutrino.
 Existence first postulated(without action) in 1928  proton (+1 charge) => neutron (0 charge) +
by Paul Dirac positron (+1 charge) + neutrino (0 charge)
 First observed in 1932 by Carl D. Anderson, who  After decay, we’re left with 18-O
gave the positron its name. He also suggested to  when a fluorine 18 decay, achived half-life, it will
rename the electron to “negatron” but he was be transformed into oxygen 18
unsuccessful. cloud chamber
 both dirac and Anderson receive noble prices What happens after the positron is obtained?
 angelo morosso, responsible for the idea that  Left over energy from the nuclear decay process is
brain function is related to blood flow. invalidated shared between the positron and the departing
by Charles Roy and Charles Sherrington, 1890s neutrino. Kinetic energy.
concluded that blood flow will be directed to a  Because of conservation of energy and momentum
stimulated portion of the brain according to its the positron is forced to stay and thus become
function. autoradiography is used along with gas useful.
radiotracer in 1948, beginning of brain imaging.  Positron begins its activity in colliding with other
 allows visualization of blood flow, metabolism, particles and gradually losing its kinetic energy and
and neuroreceptors because of the positron thus slowing down.
energy  the chemical form or physical state of the
 In the 1950s American doctors got the idea that bombarded nuclei vary depending on the target
they could use these gamma-photons to produce and subsequent usage of the pet radionuclei. this
images of the interior of the human body, which allows the production of the pet radionuclei and
were more accurate than x-ray images. gaseous, solid, and solution
 the first pet camera was completed inJanuary
1974 by Michael Phelp’s and the first whole-body PET radionuclides
system for human and animal studies was  Fluorine-18= 109.8 mins
finished in December of that year or 1974  Carbon-11= 20.4 mins
 Nitrogen-13= 10 mins
What is a Positron?  Oxygen-15=2.0 mins
 A Positron is an anti-matter electron, it is identical  Copper-64= 12.7 hours
in mass but has an opposite charge of +1.  Gallium-68=68 mins
 Rubidium-82= 75 seconds

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 NUCLEAR MEDICINE MIDTERMS
 radionuclides have the same chemical and What are some of the uses for PET
physical as their stable counterparts, Pet offers a  Patients with conditions affecting the brain,
unique platform for in vivo imaging studies of detects the size, shape, and function of the brain. a
complex. as a result, pet radionuclides has found brain’s pet scan allows doctor a view not only the
widespread use in cardiology, oncology, structures of the brain but how it functions as well.
neurology application. pet drugs have attracted check if the patient has cancer, if it spread, and
interest as potential to use to accelerate and diagnosing dimensia including alzheimer’s disease.
reduce the cost of therapeutic drug discovery differentiate disease.
efforts.  Heart, heart scan, non invasive nuclear test, uses
tracer to produce picture of the heart. use cardiac
Annihilation of a positron and electron pet scan to diagnose cad, coronary artery disease.
 The positron will encounter an electron and usually damage to the heart attack. Show healthy
completely annihilate each other resulting in and damaged heart function. help find out fuel
converting all their masses into energy. This is the benefit from a pci like angioplasty and stenty.
result of two photons, or gamma rays. coronary bypass surgey.
 electron, positron, and gamma annihilation is the  Certain types of Cancer, diagnose and identify new
process in which a positron collides with an or recurrent cancer. cell can be detected with the
electron resulting in the annihilation of both help of pet scanners
particles.  Alzheimer’s disease, use radioactive tracers to
 electrons are beta minus particles and positrons highlight amyloid proteins in te brain, mark of ad.
are beta plus particles. equal mass but opposite allows ad earlier. amyloid plaques
charges  Some neurological disorders
 positrons are the anti-matter of an electron
produced by beta plus decay
 Because of conservation of energy and Patients with brain disorders
momentum, each photon has energy of 511keV  PET scans of the brain are used to evaluate patients
and head in an almost 180 degrees from each who have memory disorders of an undetermined
other. cause, suspected or proven brain tumors or seizure
 511keV is the approximately amount of energy disorders that are not responsive to medical
created when an electron or positron are therapy and are therefore candidates for surgery.
converted into energy according to Einstein  provide 2 and 3 dimensional pictures of the brain
equation—e=mc2, where e is the energy, m is the activity by measuring radioactive isotopes that are
2
particle mass, and c , speed of light. 511kev ideal injected into the blood stream. use to detect or
rest state annihilation value. highlight tumor and diseases tissue measuring
tissue metabolism. tissue, blood flow, evaluate
patient who have seizure disorder that do not
correspond to the medical therapy, and memory
disorder.
 follow up to a ct or mri scan

(a)Normal brain
(b)Image of the brain of a 9 year old female with a history
of seizures poorly controlled by medication. PET imaging
How do we detect photons (gamma rays)? identifies the area (indicated by the arrow) of the brain
 PET detects these photons with a PET camera responsible for the seizures. Through surgical removal of
which allows to determine where they came this area of the brain, the patient is rendered "seizure-free".
from, where the nucleus was when it decayed,
and also knowing where the nucleus goes in the a b
body.
 pet works using a scanning device, machine with
a large hole at the center to detect photons or
the subatomic particles emitted by a radionuclide
to the organ or tissue being examined. results in
the emission of gamma rays, aform of energy
which is stuck up in the pet scanner, gamma ray d
etector, when the scanner detects a matching to interpret pet scan, it is important to know that
pair of gamma rays, asoftware program appearance of a normala nd abanormal brain
determines the point of region and creates a 3d commonly used radiotracer inbrain is the fdg,
image fluorodeoxyglucose, most prominent on the gray matter,

Heart Conditions
 PET scans of the heart are used to determine blood
flow to the heart muscle and help evaluate signs of
coronary artery disease. PET scans of the heart can
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 NUCLEAR MEDICINE MIDTERMS
also be used to determine if areas of the heart (a) (b)
that show decreased function are alive rather
than scarred as a result of a prior heart attack,
called a myocardial infarction. Combined with a
myocardial perfusion study, PET scans allow
differentiation of nonfunctioning heart muscle
from heart muscle that would benefit from a
procedure, such as coronary bypass for instance.
 pet scn reveals the size, s hape, position, and Alzheimer’s disease
some function of the heart. use with other  With Alzheimer’s disease there is no gross
procedures with pet, ecg and cardiac stress structural abnormality, but PET is able to show a
testing. diagnose heart problem on poor herat biochemical change.
blood flow.
(a) Image of heart which has had a myocardial Neurological disorders
infarction (heart attack). The arrow points to  Positron emission tomography (PET) imaging has
areas that have been damaged by the attack, recently been shown to aid in the diagnosis of
indicating "dead" myocardial tissue. Therefore, particular neurological syndromes associated with
the patient will not benefit from heart surgery, cancer.
but may have other forms of treatment  Before their cancer is even diagnosed, patients can
prescribed. develop problems with the brain, spinal cord or
myocardial infarction can be measured in 3d by mapping nerves, though the cancer has not spread to the
the distribution of radiopharmaceutical at stress anad nervous system. Called "paraneoplastic
rest. absolute concentration should be megabecquerel neurological disorders," these neurological
per ml. collected suually 2-10 minutes depending on problems occur as the body's immune system
theisotope begins to fight the cancer cells, but accidentally
(b)Normal heart attacks the brain or nerves as well. These problems
a b are uncommon, difficult to diagnose, and usually
appear in patients whose primary cancer is
extremely difficult to find. Abnormal antibodies in
the blood or spinal fluid are often associated with
these disorders, though they cannot help identify
the primary tumor.

How does it work?

Cancer Patients  Before the examination begins, a radioactive
 Used to determine if there are new or advancing substance is produced in a machine called a
cancers by analysis of biochemical changes. cyclotron and attached, or tagged, to a natural
 unlike computed tomography, or mri that shows body compound, most commonly glucose, but
anatomical detail, pet shows physiological sometimes water or ammonia. Once this substance
phenomena. offers substantial advantage over is administered to the patient, the radioactivity
anatomical imaging modalities in the oncology localizes in the appropriate areas of the body and is
department detected by the PET scanner.
 distinguish benign and malignant lesions with ct  Different colors or degrees of brightness on a PET
scan a nd mri while ct scan and mri cannot. image represent different levels of tissue or organ
 It is used to examine the effects of cancer therapy function. For example, because healthy tissue uses
by characterizing biochemical changes in the glucose for energy, it accumulates some of the
cancer. PET scans can be performed on the whole tagged glucose, which will show up on the PET
body. images. However, cancerous tissue, which uses
 labeling of small biological important molecule more glucose than normal tissue, will accumulate
such as aminoacids, water and molecule more of the substance and appear brighter than
 physiological maps normal tissue on the PET images.
 critical, lung cancer, lymphoma, melanoma, head
and neck cancer

(a) Image showing malignant breast mass that was not

revealed by conventional imaging techniques such as CT,
MRI, and mammogram.
(b) Image of same patient with enlarged left axillary
lymph nodes (indicated by arrows), which through biopsy
were found to be metastatic (spread from another
location). The whole body scan reveals a mass in the left
breast (indicated by arrow), that was malignant and
subsequently removed.
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 NUCLEAR MEDICINE MIDTERMS
Labeling  Some patients, specifically those with heart
 Chemical compounds we'd like to follow through disease, may undergo a stress test in which PET
the body are labeled with radioactive atoms that scans are obtained while they are at rest and again
decay by emitting positrons. Labeling is a process after undergoing the administration of a
of attaching some kind of identifying tag to the pharmaceutical to alter the blood flow to the heart.
compound you want to follow which will later let  Usually, there are no restrictions on daily routine
you identify where the compound has gone. In after the test, although you should drink plenty of
PET the compounds that can be labeled are fluids to flush the radioactive substance from your
limited only by the imagination of the body.
investigators and the physical half-life of the
positron emitting label. One of the big advantages
of PET is that the atoms which can be labeled
(turned into positron emitters) are the same
atoms which naturally comprise the organic
molecules utilized in the body. These atoms
include oxygen, carbon and nitrogen to name a
few. Since these atoms occur naturally in organic
compounds, replacing the naturally occurring
atoms in a compound with a labeled atom leaves
you a compound that is chemically and
biologically identical to the original (so it will What are the benefits vs. risks?
behave in a manner identical to its unlabeled  Because PET allows study of body function, it can
sibling) and that is traceable. In addition to help physicians detect alterations in biochemical
naturally occurring compounds such as processes that suggest disease before changes in
neurotransmitters, sugars, etc., it is also possible anatomy are apparent with other imaging tests,
to label synthesized compounds (such as drugs) such as CT or MRI.
and follow them as well.  Because the radioactivity is very short-lived, your
radiation exposure is low. The substance amount is
Tracers so small that it does not affect the normal
 A second important attribute of PET is that it can processes of the body.
follow labeled compounds in trace quantities.  PET imaging has been shown to improve detection
This means that the labeled compounds can be of a variety of cancers, and earlier tests have
introduced into the body without affecting the suggested this technique may be useful in
normal processes of the body. For example, identifying small tumors in patients with
labeling a pound of sugar and ingesting that sugar paraneoplastic neurological disorders.
would be a good example of a non-trace quantity  The radioactive substance may expose radiation to
of labeled compound. At these quantities, blood the fetus in patients who are pregnant or the
chemistry would be altered (e.g. insulin produced infants of women who are breast-feeding. The risk
in response to rising blood sugar levels). Often to the fetus or infant should be considered in
you want to follow the time course of a relation to the potential information gain from the
compound in the body by introducing trace result of the PET examination. If you are pregnant,
quantities of a compound that will behave the you should inform the PET imaging staff before the
same as the unlabeled compound without examination is performed.
altering the ongoing physiological state of
chemical processes of the body. PET is sensitive Things to consider You will remain still for a long time.
enough to detect trace amounts of labeled  Claustrophobic persons may feel some anxiety.
compound and so is well suited to this kind of  Even though you may feel the desire to feel
investigation. something due to the radioactivity, you will be
disappointed, unless they mistakenly inject you
How is it performed? plutonium gas.
 A nurse or technologist will take you into a special
injection room, where the radioactive substance Limitations
is administered as an intravenous injection  PET can give false results if a patient's chemical
(although in some cases, it will be given through balances are not normal. Specifically, test results of
an existing intravenous line or inhaled as a gas). It diabetic patients or patients who have eaten within
will then take approximately 30 to 90 minutes for a few hours prior to the examination can be
the substance to travel through your body and adversely affected because of blood sugar or blood
accumulate in the tissue under study. During this insulin levels.
time, you will be asked to rest quietly and avoid  Also, because the radioactive substance decays
significant movement or talking, which may alter quickly and is effective for a short period of time, it
the localization of the administered substance. must be produced in a laboratory near the PET
After that time, scanning begins. This may take 30 scanner. It is important to be on time for the
to 45 minutes. appointment and to receive the radioactive
substance at the scheduled time. PET must be done
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 NUCLEAR MEDICINE MIDTERMS
by a radiologist who has specialized in nuclear
medicine and has substantial experience with
PET. Most large medical centers now have PET
services available to their patients. Medicare and
insurance companies cover many of the
applications of PET, and coverage continues to
increase.
 Finally, the value of a PET scan is enhanced when
it is part of a larger diagnostic work-up. This often
entails comparison of the PET scan with other
imaging studies, such as CT or MRI.

Relevant information
 But PET imaging is not yet widely available, and
clear indicators of clinically meaningful outcomes
using PET are essential to warrant use with this
patient population.
 "Accurately defining the role of this technique for
these patients is critical," comments study author
Steven Allder, MD, of the department of
Neurology, Royal Hallamshire Hospital in
Sheffield, United Kingdom. Toward this end, Adler
and colleagues studied the use of PET imaging in
32 patients with suspected paraneoplastic
neurological disorders who had not yet been
diagnosed with cancer.
 With each patient, all relevant investigations had
been performed prior to PET imaging resulting in
no diagnostic conclusions. Each patient then
underwent PET imaging from neck to pelvis. All
patients were then prospectively followed-up,
with the results of all further investigation
collected. Final diagnosis was determined, and
the sensitivity and specificity of the results of the
initial PET scan were calculated.
 "This particular PET scanning in our patient
population successfully yielded a high proportion
of relevant lesions that were undetectable by
alternative diagnostic means," reports Allder.
Results of this study indicate that PET is an
appropriate, promising tool for patients with
undiagnosed paraneoplastic neurological
disorders.

Summary of P.E.T
 PET produces images of the body by detecting the
radiation emitted from radioactive substances.
These substances are injected into the body, and
are usually tagged with a radioactive atom (C-11,
Fl-18, O-15 or N-13) that has short decay time.
These radioactive atoms are formed by
bombarding normal chemicals with neutrons to
create short-lived radioactive isotopes. PET
detects the gamma rays given off at the site
where a positron emitted from the radioactive
substance collides with an electron in the tissue.
The results are evaluated by a trained expert.

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 NUCLEAR MEDICINE MIDTERMS
RADIOPHARMACEUTICS  Radiation refers to particles or waves coming
from the nucleus of the atom (radioisotope or
WHAT IS RADIOPHARMACY?
radionuclide) through which the atom attempts
 Radiopharmacy = Nuclear Pharmacy to attain a more stable configuration.
 Nuclear pharmacy is a specialty area of
pharmacy practice dedicated to the
compounding dispensing of and radioactive
materials for use in nuclear medicine
procedures."
 RADIONUCLIDES, ATOM THAT HAS UNSTABLE
NUCLEUS. GET RID OF EXCESS, GIVE OFF
ENERGY IN THE FORM OF RADIATION
 ELEMENTS W/ Z=83 AND ABOVE ARE
RADIOACTIVE

INTRODUCTION

 All substances are made of atoms.

 These have electrons (e) around the outside
(negatively charged), and a nucleus in the
middle.
 The nucleus consists of protons (positively
charged) and neutrons (neutral). TYPES OF RADIOACTIVITY: HOW TO PRODUCE A
 The atomic number of an atom is the number RADIOACTIVE NUCLIDE
of protons in its nucleus.
 The atomic mass is the number of protons + 1- Natural radioactivity: Nuclear reactions occur
neutrons in its nucleus. spontaneously
2- Artificial radioactivity: The property of
radioactivity produced by particle
bombardment or electromagnetic irradiation.
 A-Charged-particle reactions
 e.g. protons (¹₁H)
e.g. deuterons (²₁H)
e.g. alpha particles (4He)
 B-Photon-induced reactions
 The source of electromagnetic energy
 Isotopes of an atom have the same number of may be gamma- emitting radionuclide
protons, but a different number of neutrons. or high-voltage x-ray generator.
• Example:  C-Neutron-induced reactions
 Consider a carbon atom: It has  It is the most widely used method
6 protons and 6 neutrons - we  It is the bombardment of a
call it "carbon-12" because it nonradioactive target nucleus with a
has an atomic mass of 12 (6 source of thermal neutrons.
plus 6).
 One useful isotope of carbon is PRODUCTION OF RADIONUCLIDES:
"carbon-14", which has 6
1-Charged particle bombardment
protons and 8 neutrons.
 Radioisotopes, Radionuclides: unstable  Radionuclides may be produced by bombarding
isotopes which are distinguishable by target materials with charged particles in
radioactive transformation. particle accelarators such as cyclotrons.
 Radioactivity: the process in which an unstable  A cyclotron consists of:
isotope undergoes changes until a stable state o Two flat hollow objects called dees.
is reached and, in the transformation, emits o The dees are part of an electrical circuit.
energy in the form of radiation (alpha particles,  On the other side of the dees are large magnets
beta particles and gamma rays). that (drive) steer the injected charged particles

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 NUCLEAR MEDICINE MIDTERMS
(protons, deutrons, alpha and hélium) in a • Adsorbent Material: Alumina (aluminum oxide,
circular path Al₂O3)
 The charged particle follows a circular path until • Eluent: saline (0.9% NaCl)
the particle has sufficient energy that it passes • Eluate: (99m TcO4-¹)
out of the field and interact with the target
nucleus.

RADIOACTIVE DECAY:

• The rate of decay can be described by:

 N is the number of atoms at elapsed time t

2- Neutron bombardment  N0 is the number of atoms when t = 0
 λ is the disintegration constant characteristic of
 Radionuclides may be produced by each individual radionuclide.
bombarding target materials with neutrons
in nuclear reactors
 The majority of radiopharmaceuticals are  The intensity of radiation can be described by:
produced by this process

3- Radionuclide generator systems Radioactive Decay Law

 Principle:  The rate at which a particular decayprocess

o A long-lived parent radionuclide is occurs is proportional to the (N) number of
allowed to decay to its short-lived radioactive nuclei present
daughter radionuclide and the
latter is chemically separated in a
physiological solution.
 Example:
o technetium-99m, obtained from a
generator constructed of
molybdenum-99 absorbed to an
alumina column.
 e is the euler’s number or 2.718
 lambda, decay constant
 t is the time

RADIOACTIVE DECAY:

 Half-life - symbol t₁/2-the time taken for the

99Mo/99m Tc Generator: activity of a given amount of a radioactive
• Parent: 99Mo as molybdate (99 MoO2) substance to decay to half of its initial value.
• Half-life: 66 hr.  Total activity-symbol A-number of decays an
• Decays by ß- emission, gamma: 740, 780 keV. object undergoes per second.
• High affinity to alumina compared to 99m Tc.  Radionuclidic purity- is that percentage of the
• Daughter: 99m Tc as pertechnetate (99m TcO4- total radioactivity that is present in the form of
¹) the stated radionuclide

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 NUCLEAR MEDICINE MIDTERMS
MODE OF RADIOACTIVE DECAY:
 Since alpha particles cannot penetrate the dead
• Radioactive decay is the process in which an
layer of the skin, they do not present a hazard
unstable atomic nucleus spontaneously loses
from exposure external to the body. However,
energy by emitting ionizing particles and
due to the very large number of ionizations they
radiation.
produce in a very short distance, alpha emitters
 This decay, or loss of energy, results in an atom can present a serious hazard when they are in
of one type, called the parent nuclide
close proximity to cells and tissues such as the
transforming to an atom of a different type, lung. Special precautions are taken to ensure
named the daughter nuclide. that alpha emitters are not inhaled, ingested or
o When an unstable nucleus decays, It injected.
may give out:-
2- BETA PARTICLE DECAY:
1-ALPHA PARTICLE DECAY:
 Beta particles have a charge of minus 1. This
• Alpha particles are made of 2 protons and 2
means that beta particles are the same as an
neutrons.
electron. We can write them as B- e-, because
• We can write them as or , because
they're the same as an electron.
they’re the same as a helium nucleus.
 This means that when a nucleus emits a B-
• This means that when a nucleus emits an
particle: the atomic mass is unchanged the
alpha particle, its atomic number decreases
atomic number increases or decreases by 1.
by 2 and its atomic mass decreases by 4.
 They are fast, and light.
• Alpha particles are relatively slow and
 Beta particles have a medium penetrating
heavy.
power- they are stopped by a sheet of
• They have a low penetrating power you can
aluminium.
stop them with just a sheet of paper.
 Example of radiopharmaceutical emits B-
• Because they have a large charge, alpha
phosphorus-32
particles ionise other atoms strongly.
 Beta particles ionise atoms that they pass, but
• Alpha-decay occurs in very heavy elements,
not as strongly as alpha particles do.
for example, Uranium and Radiu
 beta particle is the same as an electron
 Beta particles are much less massive and less
 Americium 241
charged than alpha particles and interact less
 Californium 252
intensely with atoms in the materials they pass
 Radium 226
through, which gives them a longer range than
 Thorium 235
alpha particles.
 Uranium 235

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 NUCLEAR MEDICINE MIDTERMS
3- GAMMA RAY: RADIATION MEASUREMENT:

 Gamma rays are waves, not particles. This  (R) the roentgen for exposure: Is the amount of
means that they have no mass and no charge. y radiation that produces ionization of one
• in Gamma decay: electrostatic unit of either positive or negative
o atomic number unchanged charge per cubic centimeter of air at 0 °C and
o atomic mass unchanged. 760 mmHg.
• Gamma rays have a high penetrating power - it  (rad) radiation absorbed dose is a more
takes a thick sheet of metal such as lead to universal unit, it is a measure of the energy
reduce them. deposited in unit mass of any material by any
• Gamma rays do not directly ionise other atoms, type of radiation.
although they may cause atoms to emit other  (rem) has been developed to account for the
particles which will then cause ionisation. differences in effectiveness of different
• We don't find pure gamma sources - gamma radiations in causing biological damage.
rays are emitted alongside alpha or beta  Rem= rad x RBE
particles.  RBE is the relative biological effectiveness of
• Gamma ray: not a particle. it's a burst of energy the radiation.
 The basic unit for quantifying radioactivity (i.e.
describes the rate at which the nuclei decay).
 Curie (Ci): Curie (Ci), named for the famed
scientist Marie Curie
o Curie = 3.7 x 1010 atoms disintegrate
per second (dps)
o Millicurie (mC) = 3.7 x 107 dps
o Microcurie (uC) = 3.7 x 104 dps
 Becquerel (Bq): A unit of radioactivity. One
becquerel is equal to 1 disintegration per
second.

PROPERTIES OF AN IDEAL DIAGNOSTIC RADIOISOTOPE:

 Types of Emission:
 Pure Gamma Emitter: (Alpha & Beta
Particles are unimageable & Deliver High
Radiation Dose.)
 Energy of Gamma Rays:
 Ideal: 100-250 keV e.g. 99m Tc, 123I, 111In
 Suboptimal:<100 keV e.g. 201TI

>250 keV e.g.67Ga &131I

 Photon Abundance:
 Should be high to minimize imaging time

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 NUCLEAR MEDICINE MIDTERMS
• Easy Availability: as complex as:
 Readily Available, Easily Produced &
1-the creation of a multi-component reagent kit N.B. Kit
Inexpensive: e.g. 11C, Vs, 99m Tc
• Target to Non target Ratio: for radiopharmaceutical preparation
 It should be high to: maximize the efficacy • means a sterile and pyrogen-free reaction vial
of diagnosis minimize the radiation dose to containing the nonradioactive chemicals [e.g.,
the patient complexing agent (ligand), reducing agent,
• Effective Half-life: stabilizer, or dispersing agent] that are required
 It should be short enough to minimize the to produce a specific radiopharmaceutical after
radiation dose to patients and long enough reaction with a radioactive component.
to perform the procedure. Ideally 1.5 times
the duration of the diagnostic procedure. 2- the synthesis of a radiolabeled compound via a multi-
 Example: For a Bone Scan which is a 4-h step preparation process.
procedure, 99m Tc-phosphate compounds
• The process of compounding
with an effective half-life of 6 h are the
radiopharmaceuticals must be under the
ideal radiopharmaceuticals.
supervision of recognized nuclear physician or a
• Patient Safety:
radiopharmacist.
 Should exhibit no toxicity to the patient.
• STABILITY OF COMPOUNDED PREPARATIONS
• Preparation and Quality Control: o All extemporaneously compounded
parenteral radiopharmaceutical
 Should be simple with little manipulation. preparations should be used no more than
 No complicated equipment 24 hours post compounding process unless
 No time consuming steps data are available to support longer
PREPARATION OF RADIOPHARMACEUTICAL storage.

1-Sterilization: RADIATION SHIELDING:

• Radiopharmaceutical preparations intended for • Adequate shielding must be used to protect Ionizing
parenteral administration are sterilized by a suitable laboratory personnel from radiation. Alpha and
beta radiations are readily shielded because of their
method.
• Terminal sterilization by autoclaving is limited range of penetration.
recommended for heat stable products • The alpha particles are mono-energetic and have a
• For heat labile products, the filtration method is range of a few centimeters in air.
recommended. • aluminum, glass, or transparent plastic materials,
are used to shield sources of beta radiation.
2- Addition of antimicrobial preservatives:  Gamma radiation is commonly shielded with lead
and tungsten.
• Radiopharmaceutical injections are commonly
supplied in multidose containers.
• The requirement of the general monograph for
parenteral preparations that such injections
should contain a suitable antimicrobial
preservative in a suitable concentration does
not necessarily apply to radiopharmaceutical
preparations.
• A reason for this exemption is that many
common antimicrobial preservatives (for
example, benzyl alcohol) are gradually
decomposed by the effect of radiation in
aqueous solutions.

3- Compounding:

• compounding can be as simple as: adding a

radioactive liquid to a commercially available
reagent kit

MISHELLE JENEVA M. QUIAMBAO

 NUCLEAR MEDICINE MIDTERMS
 Microbiological Control (sterility test)
and Bacterial Endotoxin Testing
 Labelling, The label on the outer
package should include:
 a statement that the product is
radioactive or the international
symbol for radioactivity
 the name of the
radiopharmaceutical preparation;
 the preparation is for diagnostic or
for therapeutic use;
 the route of administration;
 the total radioactivity present (for
example, in MBq per ml of the
solution)
RADIOPHARMACEUTICAL QUALITY CONTROL
 the expiry date
 Visual Inspection of Product  the batch (lot) number
 Visual inspection of the compounded  for solutions, the total volume;
radiopharmaceutical shall be conducted  any special storage requirements
to ensure the absence of foreign matter with respect to temperature and
and also to establish product identity by light;
confirming that  the name and concentration of any
 a liquid product is a solution, a colloid, added microbial preservative
or a suspension
APPLICATION OF RADIOPHARMACEUTICALS:
 a solid product has defined properties
that identify it. 1-Treatment of disease: (therapeutic
 Assessment of Radioactivity radiopharmaceuticals)
 The amount of radioactivity in each
compounded radiopharmaceutical  They are radiolabeled molecules designed to
should be verified and documented deliver therapeutic doses of ionizing radiation
prior to dispensing, using a proper to specific diseased sites.
standardized radionuclide (dose)  Chromic phosphate P32 for lung, ovarian,
calibrator. uterine, and prostate cancers
 Sodium iodide I 131 for thyroid cancer.
 Radionuclidic Purity can be determined with Samarium Sm 153 for cancerous bone tissue
the use of a suitable counting device  Sodium phosphate P 32 for cancerous bone
 The gamma-ray spectrum, should not tissue and other types of cancers
be significantly different from that of a  Strontium chloride Sr 89 for cancerous bone
standardized solution of the tissue
radionuclide.
2- As an aid in the diagnosis of disease (diagnostic
 Radiochemical purity radiopharmaceuticals)
 Radiochemical purity is assessed by a
variety of analytical techniques such as:  The radiopharmaceutical accumulated in an
 liquid chromatography paper organ of interest emit gamma radiation which
chromatography are used for imaging of the organs with the help
 thin-layer chromatography of an external imaging device called gamma
electrophoresis camera.
 the distribution of radioactivity on the  Radiopharmaceuticals used in tracer techniques
chromatogram is determined for measuring physiological parameters (e.g. 51
Cr-EDTA for measuring glomerular filtration
Radiopharmaceutical quality control: rate).
• Verification of Macroaggregate Particle  Radiopharmaceuticals for diagnostic imaging
Size and Number (e.g.99m TC-methylene diphosphonate (MDP)
 pH used in bone scanning

MISHELLE JENEVA M. QUIAMBAO

 NUCLEAR MEDICINE MIDTERMS
NUCLEAR MEDICINE IMAGING
Nuclear Medicine
 Therapeutic and diagnostic use of radioactive
substances.

Radioactivity:
 Naturally occurring radioisotopes (radioactive
isotopes) discovered by Becquerel (1896)
 First artificial radioisotopes produced by the
Curies (1934) is Phosphorous 32

HISTORY NEUTRON, BETA EMISSION

PROTON, POSITRON OR ELECTRON CAPTURE
 1935-Hevesy Uses Phosphorous 32 for metabolic
studies with Geiger- DEFINITIONS
 Muller Counter  ISOTOPE: Nuclides of same atomic number Z but
 1949 - 1st radionuclide imaging by Cassen of different N (and A) - same element.
lodine 131 uptake in thyroid  NUCLIDE: Species of atom characterized by the
 gland (scintillator+PMT, scanner, collimator, 1/4" constitution of its nucleus (in particular N, Z)
spatial resolution) Truman P. Kohman
 1957 - Anger camera (planar imaging)  RADIONUCLIDE: Nuclide of measurable half time.
 1960-Kuhl & Edwards construct Mark IV scanner  RADIOACTIVE DECAY: The process by which an
 1977 - Kayes & Jaszczak develop SPECT unstable nucleus is transformed into a more stable
independently. daughter nucleus by emitting nuclear particles.
 1950-1st PET attempts
 1976 - First commercial PET (Phelps & Hoffman at
CT)

RADIONUCLIDE IMAGING
Characteristics
 The distribution of radioactive agent inside the
body is imaged.
 Projection and CT imaging methods.
 Imaging of functional or metabolic contrasts (not
anatomic)
o Brain perfusion, function
o Myocardia perfusion
o Tumor detection (metastasis)
No=initial quantity of the substance
N= the quantity still remained and not yet decayed
E= euler’s number, 2.71828
Lambda= the radioactive decay constant or disintegration
constant

Radionuclides in Clinical Use

 Most naturally occurring radioactive isotopes not
clinically useful (long T1/2 charged particle
emission)
 Artificial radioactive isotopes produced by
bombarding stable isotopes with high-energy
Nuclear Stability photons or charged particles
 The neutrons and protons which form the nucleus
of an atom are held together by a combination of
forces such as gravitational and electrostatic
forces. The protons tend to repel each other. This
means that, as bigger atoms are but together, it
becomes more difficult for the nucleus to be  Nuclear reactors (n), charged particle accelerators
stable as one collection of particles (Linacs, Cyclotrons)
 The nucleus of many atoms is not stable. Nuclei
with in favorable neutron/proton ratio will
disintegrate or decay into stable nuclei by
spontaneous emission of nuclear particles
MISHELLE JENEVA M. QUIAMBAO
 NUCLEAR MEDICINE MIDTERMS
Properties of 99m Tc: Anger Logic
 T₁/2 = 6 h  The Anger camera is a system for achieving a large
 radiates 140 keV gamma ray number of resolvable elements with a limited
 the short half time and absence of Beta emission number of detectors. It thus overcomes the
allows low radiation dose to patient. previous difficulty of having the resolution limited
 The 140 keV gamma radiation allows for 50% by the number of discrete detectors.
penetration of tissue at a thickness of 4.6 cm.  The principle is based on estimating the position of
Applications: a single event by measuring the contribution to a
 99m Tc-Sestamibi (myocardial perfusion, cancer) number of detectors.
 99m Tc-labeled hexamethyl-propyleneamine  Cameras of this general type have a single crystal
(brain perfusion) viewed by arrays of detectors with the detected
Other gamma emitters: outputs followed by a position computer to
 123 111 67 201
I, In, Ga, TI, Kr 81 m estimate the position of each event.
Imaging
 If the photons emanating from the radionuclide
have sufficient energy to escape from the human
body in significant numbers, images can be
generated that portray in vivo distribution of the
radiopharmaceutical.

Nuclear medical imaging may be divided into 3

categories: Detection of Gamma Radiation
1. Conventional or planar imaging  Scintillation detectors most commonly used
2. SPECT o Crystals: Nal(Ti), BGO(Bismuth Germanate),
3. PET CsF(Cesium Fluoride), BaF2
o Criteria: Stopping power, response time,
1. Conventional or Planar Imaging
efficiency, energy resolution
 The 3D distributed radiopharmaceutical is
 Ion collection detectors (ionization chambers) not
imaged onto a planar or 2D surface producing
used because of low efficiency, slow response
a projection image.
 Semiconductor detectors (diodes): very high
 STATIC
o used for studies in which the energy resolution, fast but small and high cost
distribution of the
radiopharmaceutical is effectively
static throughout the acquisition
o Example: Bone Scan
o Inject -> wait -> Image
o Organ size, shape and position
o Regions of increased or decreased
uptake
o Renal Scan, Bone Scan, Lung
Perfusion Scan
 DYNAMIC
o used for studies in which the distribution
of radiopharmaceutical changes rapidly
with time
o Inject -> image immediately -> acquire
series of frames over time
o Gallbladder emptying scan, gastric Applications
emptying scan  Thyroid imaging: The thyroid gland is situated in
 GATED the lower part of the neck at a depth of about 1
o used to study organs with regular cm. The purpose of thyroid is to secrete the
physiological motion hormone thyroxin which is carried in the blood
o Cardiac gated blood pool imaging stream and controls a number of body functions:
Scintillation Camera (Anger Camera) o stimulate metabolism
 Imaging of radionuclide distribution in 2D o influence growth
 Replaced "rectilinear scanner", faster, increased o control mental development
o store iodine
efficiency, dynamic imaging (uptake/washout)
 underactive thyroid:
Application in SPECT and PET o mental dullness,
 One large crystal (38-50 cm Dia) coupled to array o low temperature
of PMT o decrease in metabolism

MISHELLE JENEVA M. QUIAMBAO
 NUCLEAR MEDICINE MIDTERMS
 Imaging of thyroid can be useful for the following SPECT Artifacts
purposes:  Reconstruction methods similar to x-ray CT
1. To determine the amount of thyroid tissue left  X-ray attenuation: X-ray from source is attenuated
after surgery or radiotherapy for thyroid disease, by tissue ⇒ unknown concentration of tracer and
2. To detect thyroid metastases associated with unknown distribution of tissue absorption.
thyroid cancer, o Corrective measures:
3. To show the comparative function of different  Transmission measurement with
parts of the glands, external source to determine
4. To measure the size and position of the thyroid tissue absorption
prior to surgery or other treatments of the  Assume constant absorption and
disease. use geometric mean of two
 To obtain images, the patient is given an oral measurements 180° apart, which is
dose of 30μCi 1311 in the form of KI (potassium independent on d
iodide). The scan is taken 24hrs later.  Iterative reconstruction
 131 I emits y rays (336 keV). Positron Emission Tomography
 Use with positron emitters (beta-plus)
 Thyroid scan, spot lumps or inflammation,  Positron annihilates with electron of nearby atom
Investigate the cause of overactive thyroid ⇒ two gamma quanta each at 511keV leave under
 Radioactive iodine uptake test, thyroid is 180°
functioning properly  "Tagging" of radiation:
 Both, small amount of radionuclide, injected, o Windowing
orally, intravenously o Coincidence detection ("electronic
Single Photon Emission Computed Tomography (SPECT) collimation")
 If one or more gamma cameras are attached to a
computer-controlled gantry, which allows the
detectors to be rotated around a patient, multiple
views (or 2D projections) of the 3D pharmacutical
distribution can be acquired.
 First SPECT 1963 (Mark IV) used array of
detectors
o Rotation, Translation
o High count rates
o Many components
o Mostly single-slice
 Rotating camera:
o Multiple slices PET Detectors
o Multi-camera systems  Individual Coupling:
o Expensive, packing problematic, high count
rate
 Block Design:
o Digital encoding, longer dead time, more
economic, somewhat reduced resolution

MISHELLE JENEVA M. QUIAMBAO

 NUCLEAR MEDICINE MIDTERMS
PET resolution compared to MRI
 Modern PET= 2-3 mm resolution

CATEGORY MRI PET

About 5-10
30 -45 minutes
minutes per area
Time For Scan per area scanned
(about 45
(about 2-3 hours
minutes whole
for whole body)
body)
Less detailed but
Soft Tissue Higher details of
better for tumors
soft tissue
> 2cm
Bony Structures less detailed More detailed
Bone injuries,
Soft tissue, lung and chest
inflammation, imaging, cancer
Structures
cross section detection,
images showing
metabolic activity
Can change the
contrast of
images, superior Good for imaging
Advantages for detection of metabolic
tumors, no activity, shorter
radiation, few scan time
side effects to
contrast
Claustrophobia,
cannot use with
Uses ionizing
Disadvantage metal implants,
radiation, costly,
takes time and
availability
you have to be
still. Costly

MISHELLE JENEVA M. QUIAMBAO