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NUCLEAR
MEDICINE Radioactivity Assignment
PHYSICAL SCIENCE
NUCLEAR
MEDICINE Radioactivity Assignment
PHYSICAL SCIENCE
Radioactivity Assignment Nuclear Medicine
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Nuclear medicine is a branch of medicine which is generally used to both treat and diagnoses illnesses
and diseases in a safe/painless way. Nuclear medicine procedures allow the determination of medical
information which may otherwise be unavailable, require surgery or more expensive tests. The use of
nuclear medicine generally can make identifications of illnesses or abnormalities extremely early in
the progression of the illness- long before other practices could identify it. The factor of early
detection allows a disease/illness to be treated earlier, posing a higher chance of recovery (What Is
Nuclear Medicine? 2017).
Nuclear medicine is used for two primary purposes: diagnosis and therapy (ACR, 2017).
Diagnosis is generally referred to as imaging, and is only used to diagnose and establish what the
illness the patient is affected by is. Therapy is used to treat a patient from illnesses, again using
radioactive materials to accomplish said goal.
Nuclear medicine imaging uses minute amounts of radioactive materials, referred to as radiotracers,
and they are typically injected into the bloodstream, inhaled or swallowed. (ACR, 2017)
The radiotracer uses small amounts of radioactive dye to highlight concerning areas (such as cancer
cells or infection). Pictures can then be taken of the areas for closer analysis and treatment. ("Nuclear
Medicine Scans" 2017) The radiotracer is introduced to the body either through injection, inhalation
or consumption. The dye travels through the body, gathering in the area of the body which is under
examination. When the dye is eventually collected in a tumour or organ, it makes energy in the form
of gamma rays. In order to identify the gamma rays, a scanner or camera captures images based off
the gamma ray output. Nuclear medicine scan pictures can detail the function as well as the structure
of tissues and organs in the body. (ACR, 2017). The radioactive material present in the body will
decay over time, posing no risk to the patient.
As with any branch of medicine, there are many smaller sectors and ways to perform nuclear
medicine. Each type of testing has a different purpose, some working better on different types of
organs or illnesses to identify the issue.
Bone or Joint Scans:
Bone or join scan are utilised to find out if there are any abnormalities within the bones or joints. As
per usual, a small amount of radioactive material is injected into the vein, which are then taken up by
the skeletal system. Pictures are captured 2-3 hours’ post injection. ("Full Body Bone Scan | Nuclear
Medicine | Services & Treatments (Copy) | Premier Radiology" 2017)
Gallium Scan:
Gallium scans are used to identify infections or tumour. Small amounts of radioactive gallium are
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injected into the patient. Pictures are captured using a specialised camera. Dependent on the patients’
medical history, imaging will generally be at either 24, 48, or 72 hours’ post injection of the
radioactive material. (Gallium Scan: Medlineplus Medical Encyclopedia". 2017. Medlineplus.Gov.
https://medlineplus.gov/ency/article/003450.htm.) Gallium scans generally use gallium-67, an isotope
of gallium, which is commonly found in multiple salts like citrate and nitrate. The gallium-67
generally releases a spectrum of gamma rays (93, 185, 288, 394 KeV energy), and has a half-life of
approximately 78 hours. This type of scan has recently been largely replaced by 18-F FDG PET/CT
imaging which has earlier scans, better image quality and SUV quantification. (Venkatesh 2017)
Gallium-67 Citrate is used for the scans, and has a chemical structure of:
The radioactive decay equation for Gallium-67 is:
67
31𝐺𝑎∗ →
67
31𝐺𝑎 +
0
0𝛾 + 𝑒𝑛𝑒𝑟𝑔𝑦
Radioactivity Assignment Nuclear Medicine
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The above photo shows the electron capture decay of Ga-67, which occurs in the body throughout
gallium scans. The isotope slowly decays into Zn-67 which is stable, unlike the radioactive Ga-67.
A gallium scan is shown above.
Radioactivity Assignment Nuclear Medicine
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Gastric Emptying:
Gastric emptying is used to evaluate the functioning of the stomach and digestive system. The patient
will either eat a scrambled egg and begin imaging immediately, taking 2 hours, or drink a glass of
water and then imaging will begin immediately for 60 minutes. ("Gastric Emptying Scan" 2017)
Oesophageal Reflux Study:
This test is used to find out if liquid material moves in a reverse direction from the stomach or the
oesophagus, also commonly known as reflux. In this case, a small amount of the radioactive liquid is
mixed with a drink the patient must consume. A binder is then placed on the abdomen to place
pressure on the stomach. Pictures are then captured. ("CT Risks A Hot Topic On Social Media |
Atlantic Medical Imaging" 2017)
Hepatobiliary Scan:
These scans are used to analyse gall bladder function, as well as the bile ducts. The patient is injected
with radiotracers, which are then taken up by bile-producing glands. Pictures are taken immediately
for a minimum of one hour, and possibly up to three hours. (“Hepatobiliary (HIDA) Scan | Nuclear
Medicine”, 2017)
Liver or Spleen Scan:
This test is mainly used to find out the size and function of the liver and spleen. A small amount of
radioactive material is injected into the vein. Pictures of the liver and spleen are taken. ("Liver-Spleen
Scan" 2017)
Meckel’s Scan:
This study is undertaken to discover if the patient has a Meckel’s diverticulum, a slight bulge in the
small intestine present from birth. This study is frequently performed on children. Pictures are
captured after the injection for a period of about 45 minutes. ("Test Preparation- Meckel's
Diverticulum Scan" 2017)
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Image: A Meckel’s scan result
MUGA Scan:
MUGA scans are used to judge the function of the heart, often performed on customers who will be
receiving chemotherapy. To perform this, the patient generally has a small amount of blood drawn,
which is taken and mixed with the radioisotope tracker. This mixture is consequently reinjected into
the patient and imaging begins approximately 10 minutes later. The test then takes about one hour.
("Multigated Acquisition Scan (MUGA)" 2017) The imaging takes photos of the heart with each
pump to find out how well the heart is functioning and how much blood pumps with each beat. It
generally only captures images of the lower chambers of the heart and reports abnormalities in the
size of the chambers (ventricles), as well as abnormalities in the movement of blood through the heart.
It is also taken before chemotherapy to find any pre-existing heart conditions. It is common for cancer
survivors who have had radiation therapy to the chest, spine or upper abdomen, as well as people who
have had a bone marrow/stem cell transplant or certain types of chemotherapy. ("MUGA Scan"
2017). Technetium-99m is generally used for this form of imaging (“Radionuclide
Angiogram/MUGA Scan”, 2017). Technetium-99m has a gamma decay equation of:
Radioactivity Assignment Nuclear Medicine
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𝑇𝑐99𝑚 → 𝑇𝑐99 +0
0𝛾
Renal Scan:
Renal scans are used to assess blood flow as well as the level at which kidneys are functioning in the
patients. A computer is used to graph the level of blood flow and function of the kidneys. Pictures are
collected for a period of 30 minutes. ("Renal Scan" 2017)
SPECT Brain Scan:
This test is unusual in comparison to the others as it’s a two-part test. The first part involves an
injection. An IV is placed into the patients arm and the medication will be administered through it,
taking around 30 minutes. The patient can leave between the two tests but must return around an hour
and a half later for the remainder of the testing (imaging). The imaging portion of the testing takes
about 45 minutes. ("SPECT Brain Imaging: Background, Indications, Contraindications" 2017)
SPECT Liver Scan (Red Blood Cell Scan of Liver):
This is often undertaken as a follow-up of a CT scan, MRI or Ultrasound to rule out a benign (dead)
liver tumour (haemangioma). This is also a two-part test. The first portion will take approx. 30
minutes. The technologist will again draw a small sample of blood, and then reinject it into the patient
after mixing it with the isotope. Again, the patient may leave but must return 1.5 hours afterwards for
imaging. The imaging will take around 45 minutes. ("Types Of Nuclear Medicine" 2017)
Radioactivity Assignment Nuclear Medicine
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Both SPECT scans are less commonly referred to as a single-photon emission computerised
tomography scans, and let a doctor analyse the function of internal organs (“Why its’s Done” –Mayo
Clinic”, 2017).
Thyroid Scan and Uptake (Radionuclide Iodine Uptake):
This examination determines how well the thyroid gland is functioning by taking a measurement of
the uptake of iodine by the thyroid gland. Pictures of the thyroid gland are also taken during the
process of testing. The test is performed over two days. On the first day, the patient must consume a
radioactive iodine pill, and is asked to return in 6 hours for the first analysis of Iodine uptake, as well
as the first imaging process. On the second day, the patient is asked to return for a 24-hour uptake
measurement. At this point, the radiologist reviews the test and determines whether the thyroid gland
requires examination. At this point, there may be more images of the gland obtained post review of
the results and physical examination (ACR, 2017).
Nuclear medicine can also be used in a therapeutic method. Therapy is performed using unsealed
radioactive sources, and can treat ailments from illnesses of the thyroid, pain relief of bone metastasis
to treatment of cancer (Therapeutic Nuclear Medicine, 2017). Research into fresh
radiopharmaceuticals to treat different tumours and illnesses is always being consistently undertaken
(Research, SNMMI, 2017). Radiation therapy is one of the more prominent examples of therapeutic
nuclear medicine. It uses ionising radiation to kill cancerous cells, as well as to shrink the tumour. It
does this through damaging the cell’s DNA, which then stops the cells from performing mitosis- that
is, the process of growing and dividing. The most commonly used way of exposing the cells to
radiation is through external radiation therapy, which consists of a limited area of the body being
exposed to a beam of especially high-energy x-rays to the main tumour. However, targeted
radionuclide therapy is more commonly used as it is systematic treatment- much alike chemotherapy.
Targeted therapy using radiopharmaceuticals consists of radioactive compounds commonly used in
nuclear medicine for treatment, which primarily is used in cancer cells which migrated from primary
tumours to lymph nodes/secondary organs like bone marrow. The recently distributed tumour cells are
generally difficult to treat because there are intense changes in the number of targetable receptors in
each cell.
It uses molecules labelled with a radionuclide to deliver a lethal level of radiation to the
tumour/disease site. A distinctive feature to the radionuclides is that they can employ a ‘bystander’ or
‘crossfire’ effect (as shown below), which then can kill surrounding tumour cells even if they aren’t
fully developed- i.e., don’t have the tumour-associated antigen or receptors (Medicine, 2017).
Radioactivity Assignment Nuclear Medicine
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As shown above, the differences between external beam radiation therapy and targeted radionuclide
therapy are extreme, as the external beam therapy requires knowledge of locations of tumour, whereas
the radionuclide therapy only requires knowledge of the tumour biology, and can exterminate any
surrounding tumour as well as the known tumour itself (Advancing Nuclear Medicine Through
Innovation, 2007).
Radioactivity Assignment Nuclear Medicine
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Radionuclide Therapy:
The biological effect from the therapy is obtained by energy taken in from the radiation released from
the radionuclide. Contrary to how the nuclides used for the nuclear medicine imaging emit gamma
rays, which have high penetration levels, the radionuclides used for targeted radionuclide therapy
must release radiation with a short path length. There are three types of radiation that work for
targeted radionuclide therapy- beta particles, alpha particles (diagram below) and Auger electrons,
which can- respectively- irradiate tissue volumes with multicellular, cellular and subcellular
dimensions. Within these categories, there are various radionuclides in a variety of tissue ranges, half-
lives and chemistries, which presents a striking possibility of finding the perfect properties for a
targeted radionuclide to be utilised for each individual patient. Further development in this field is
pushed forward by the desire to move away from nonspecific noxious therapies regularly used in
oncology and forward to less toxic targeted treatments (Medicine 2017).
In some cases, mixed emitters are utilised to complete both imaging and therapy with the same
radionuclide (for example- the mixed beta/gamma emitter iodine-131). Iodine and its isotopes can
only be used for thyroid problems, as the thyroid cells are the only cells in the body that can absorb
iodine (De Jorgen and Nandurkar 2017). Iodine-131 is a highly reactive radioisotope, with an
extremely short half-life of 8.02 days. As it is highly reactive, it is frequently used in minute doses for
thyroid cancer therapies. Despite it being used in low doses for medical examinations, it is an ideal
tracer for use in humans. This is because only a few radioactive atoms need to be injected into the
bloodstream for the path of the iodine to be efficiently monitored. The atoms combine with molecules
which will then transform into thyroid gland hormones. From that point gamma ray scintigraphy
(imaging) then can monitor the thyroid activity and report any abnormalities. However, in recent
times, Iodine-131 use has decreased due to favour of an alternate isotope, Iodine-132. As mentioned
earlier, Iodine-131 is also commonly used for treatment of thyroid cancers. In these cases, stronger
doses of Iodine-131 are injected into the bloodstream in the same manner, and the subsequent beta
Radioactivity Assignment Nuclear Medicine
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particles, due to the trajectory of their released beta particles, guarantee that the radiation only affects
a moderately small part of the body ("Radioactivity : Iodine 131" 2017).
Iodine decays through a process of beta decay with the formula of:
131
53I →
131
54𝑋𝑒 +
0
−1𝑒
Iodine decays with a process of beta decay, and the emitted beta particles are emitted as well as
Xenon, which is then used to image and/or treat the medical issue.
Another common radioisotope used for medical imaging is technetium-99m, which is a metastable
radioactive tracer isotope. It has a gamma ray energy of around 140KeV, which is increasingly
convenient to use for detection of any issues with bodily functions. It has both an extremely short
physical and biological half-life, which means it is very quick to clear from the body following
imaging. It also only has gamma energy and is not accompanied by alpha/beta emission, which allows
for a more exact alignment of imaging detectors.
Isotope
Half-lives in days
TPhysical TBiological TEffective
99mTc 0.25 1 0.20
The above table shows the half-life of Technetium-99m.
As Technetium-99m is produced by bombarding molybdenum-98 with neutrons, the resultant
molybdenum-99 decays with a half-life of 66 hours into the metastable state of Tc.
𝑇𝑐99𝑚 → 𝑇𝑐99 +0
0𝛾
Radioactivity Assignment Nuclear Medicine
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This process allows production of Technetium-99m for medical purposes. Technetium-99m is strange
as it has a half-life of 6.03 hours for gamma emission. This is excessively long for an electromagnetic
decay circumstance. As it has such a long half-life leading to this decay, the state is called metastable,
hence the ‘99m’ designation ("Technetium-99M" 2017). The diagram below exemplifies the aspects
of the complex decay of Technetium-99m.
Radioactivity Assignment Nuclear Medicine
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Technetium-99m decays through beta decay from Molybdenum-99:
99
42𝑀𝑜 → 𝑇𝑐99𝑚+ -1e
It then goes through gamma decay to become Technicium-99.
𝑇𝑐99𝑚 → 𝑇𝑐99 +0
0𝛾
Technicium-99m is used in 35million procedures per year, and accounting for around 80% of all
nuclear medicine procedures worldwide- making it a very popular choice to use for diagnosis and
treatment ("Radioisotopes In Medicine" 2017).
Nuclear medicine is used frequently to provide diagnosis of any abnormalities before physical
symptoms are shown and visibly noticeable, meaning it becomes significantly easier for the patient to
receive successful treatment. It’s ability to allow for immediate, accurate diagnosis makes it
Radioactivity Assignment Nuclear Medicine
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irreplaceable, as well as the fact that it can detect diseases in extremely early stages. It also has an
ability to treat as well as diagnose.
However, there are always risks and negatives to any medical endeavour. The main risk is to the
health of infants, toddlers, elderly peoples and pregnant women. It is also an extremely expensive
process- as the machines which take the photos tend to be excessively expensive, making it hard for it
to be easily accessible as not every hospital/doctors surgery. However, with the huge advantages to
nuclear medicine, these risks are outweighed and it has since become a vital aspect of the medical
world.
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