Medical Tracers

How do doctors look inside our bodies when we are scanned by a machine? This has to do with the radioactivity of so-called medical tracers. Some radioactive substance is inserted into our body, and as a result, the radiation emitted by the substance is visible from outside our body by special equipment. Doctors can then base their diagnosis on where they see radioactivity inside our bodies. You can learn the basics of medical tracers by reading this article.

Medical Tracers Medical Tracers

Create learning materials about Medical Tracers with our free learning app!

  • Instand access to millions of learning materials
  • Flashcards, notes, mock-exams and more
  • Everything you need to ace your exams
Create a free account
Table of contents

    Definition of medical tracers

    A medical tracer is a chemical compound containing a radioactive isotope that is used by doctors to see inside bodies by detecting radiation it emits.

    So exactly how do doctors use medical tracers to diagnose us?

    Diagnosis with medical tracers

    Radioactive tracers are used to produce images of areas of the body during tests. Different parts of our bodies absorb different biochemical substances. By "attaching" a radioactive isotope to such a substance, we create a medical tracer, and we can observe how our body processes the medical tracer by looking at the radiation coming from it.

    This is why the radioactive substance is called a (medical) tracer: it traces the path that the non-radioactive version of the substance takes within a body.

    If this radiation is beta (β) or gamma (γ) radiation, then it can travel through a decent thickness of tissue (as opposed to alpha (α) radiation, the particles of which are too large to be able to travel much more than0.1 mmthrough tissue). Thus, if the medical tracer contains radioactive isotopes that emit beta or gamma radiation, and it is absorbed by an organ, then we can see this organ by observing the radiation coming from the organ.

    The equipment that is used to detect gamma radiation is a specialized camera that is made to capture the gamma spectrum instead of the visible spectrum of light. To detect other types of radiation, so-called scintillation counters are used: these machines catch radiation particles inside a chamber that causes them to emit light. This process is called scintillation and we can use regular (but sensitive) cameras to detect this light.

    If someone is suspected to have a dangerously swollen kidney, then we can find the biochemical agent that is absorbed by kidneys, and attach a radioactive isotope to it such that the substance emits beta or gamma radiation: it is now a medical tracer. In practice, the isotope technetium-99m is often used in medical tracers for kidney scans. We then inject the medical tracer into the person's body and wait a bit until the kidneys have absorbed most of it. We can now point beta or gamma radiation detection devices toward our patient, effectively see their kidneys, and either diagnose them with a swollen kidney or not.

    Isotopes in medical tracers

    Let's see what we require from a radioactive isotope that is used in a medical tracer.

    1. The radiation emitted must be able to travel from the inside of a patient's body to a radiation detector outside the body.
    2. The radiation must be able to be detected by the detector.
    3. The radiation emitted must not be of such high energy that it damages the patient's body.
    4. The radiation must be there long enough to be able to use it for a diagnosis, but short enough for the patient to only be exposed to the radiation for not much longer than necessary.
    5. The isotope itself must not damage the patient's body in any other way than its radioactivity.

    This means that the radioactive isotope inside the medical tracer must have the following characteristics.

    1. The isotope emits beta or gamma radiation.
    2. The energy per radiation particle must not be too low.
    3. If the isotope emits gamma radiation, it must be of a low enough frequency as to not damage the patient's body.
    4. The half-life of the isotope must be on the scale of minutes to days, and preferably a few hours.
    5. The isotope must not be toxic.

    Examples of medical tracers

    Medical Tracers PET scan brain StudySmarterA PET scan showing radioactivity in the brain.

    The image above shows radiation levels inside someone's head after being injected with a medical tracer. The brighter the color in the image is, the higher the radiation level is in that place, and thus the higher the concentration of the medical tracer is. This gives doctors information about the health of the patient's head.

    Examples of isotopes used in medical tracers

    Different radioisotopes can be used in medical tracers. For the interested reader, we have collected some examples of radioactive isotopes that can be used in medical tracers.

    Technetium-99

    A variant of technetium-99 that is in an excited state (technetium-99m) is the most widely used medical radioactive isotope because it has a lot of good properties. It emits low-frequency gamma radiation in the process of going to its lower energy level, has a half-life of 6 hours, and it is not toxic, so it checks all the boxes of being used in a good medical tracer.

    Gallium-68

    Gallium-68 emits beta radiation, has a half-life of 68 minutes, and it is not toxic, so this is also a good medical tracer. This isotope is mostly used for detecting some variants of cancer.

    Fluorine-18

    Fluorine-18 emits beta radiation, has a half-life of 110 minutes, and it is not toxic. It is widely used in PET scans to let us observe brains, hearts, thyroid glands, and bones among other things.

    Rubidium-82

    Rubidium is an alkali metal that has characteristics that are very similar to those of potassium. Therefore, the beta decay of rubidium-82 can be used to trace the movement of potassium: it can take the place of potassium in many biological processes. It has a half-life of only just over one minute, so the diagnosis should be done quickly, but the patient will only experience serious radiation levels for a few minutes.

    Example of the use of a medical tracer

    Let's look at an example of the process of using a medical tracer.

    It is known that a dead or damaged heart muscle cell does not retain potassium very well, while healthy heart muscle cells do. To find out if someone's heart is (partially) damaged, we can use a medical tracer as in the following step-by-step procedure.

    1. We combine rubidium-82 isotopes with an appropriate biological substance to create a medica tracer.
    2. We inject this contaminated substance into the patient.
    3. We wait for a few minutes. In general, the wait time depends on how easily the substance is absorbed and the half-life of the medical tracer.
    4. At this point, the radioactive rubidium-82 should have taken the place of some potassium atoms in the heart muscle cells.

    If we see radiation coming from heart tissue, we know that this tissue contains rubidium-82, so it contains potassium, which means that it is a healthy bit of heart tissue. If we do not see radiation coming from some part of the heart muscle tissue, we know that this part must be damaged or dead. Thus, we can diagnose our patient based on our radiation observations made possible by the medical tracer.

    Uses of radioactive tracers

    Radioactive isotopes can be used in tracers in other contexts as well, in which case they are called radioactive tracers. Below is a list of uses of radioactive tracers other than in medicine.

    Uses of radioactive tracers: Fracking

    Fracking is a process in which you create fractures in rock formations. You can inject these cracks with a radioactive tracer such that you can observe the profile of the fractures you created.

    Uses of radioactive tracers: Radiocarbon dating

    Medical Tracers A fossil of a mammoth in a museum StudySmarterRadiocarbon dating can determine how long ago this dinosaur died.

    The carbon of every living organism consists of the same percentage of carbon-14 isotopes, but once an organism dies, the carbon atom interchange with its environment stops. This means that the percentage of carbon-14 isotopes decreases slowly but steadily, because carbon-14 is radioactive, with a half-life of nearly 6000 years. Thus, by measuring the percentage of carbon-14 isotopes in an organism, we can figure out how long ago it died. In this process, you could regard the carbon-14 as a tracer that is naturally present in every organism, and not the precise location of the radioactive isotopes matters, but the quantity of the total radiation matters in "diagnosing" how long an organism has been deceased.

    Medical Tracers - Key takeaways

    • A medical tracer is a substance containing a radioactive isotope that is used by doctors to see inside bodies.
    • By "attaching" a radioactive isotope to a biochemical substance, we can observe that substance by looking at the radiation coming from it. If this substance is absorbed by an organ, then we can see this organ by observing the radiation coming from the organ.
    • Medical tracers must have the following characteristics.
      1. The isotope emits beta or gamma radiation.
      2. The energy per radiation particle must not be too low.
      3. If the isotope emits gamma radiation, it must be of a low enough frequency to not damage the patient's body.
      4. The half-life of the isotope must be on the scale of minutes to days, and preferably a few hours.
      5. The isotope must not be toxic.
    • The principle of seeing things using radioactive tracers is not limited to only medical applications.
    Frequently Asked Questions about Medical Tracers

    What are medical tracers?

    A medical tracer is a substance containing a radioactive isotope that is used by doctors to see inside bodies.

    What are tracers used for?

    Medical tracers are used to diagnose patients. In general, radioactive tracers are used to observe things that we can otherwise not observe because there is a visual obstruction in our way.

    What is an example of a radioactive tracer used in medicine?

    A good example of a radioactive isotope used in a medical tracer is technetium-99m. This excited state of the isotope technetium-99 emits low-energy gamma radiation and has a half-life of 6 hours, making it excellent for use in a medical tracer.

    How do medical tracers work?

    Medical tracers emit detectable radiation, so if part of the tracer is absorbed by an organ, we can see this organ through the radiation emitted by the tracer.

    What type of radiation is used in medical tracers?

    The radiation used in medical tracers is beta or gamma radiation, because those types of radiation can penetrate the multiple centimetres of tissue that are between the organ and the doctor.

    Discover learning materials with the free StudySmarter app

    Sign up for free
    1
    About StudySmarter

    StudySmarter is a globally recognized educational technology company, offering a holistic learning platform designed for students of all ages and educational levels. Our platform provides learning support for a wide range of subjects, including STEM, Social Sciences, and Languages and also helps students to successfully master various tests and exams worldwide, such as GCSE, A Level, SAT, ACT, Abitur, and more. We offer an extensive library of learning materials, including interactive flashcards, comprehensive textbook solutions, and detailed explanations. The cutting-edge technology and tools we provide help students create their own learning materials. StudySmarter’s content is not only expert-verified but also regularly updated to ensure accuracy and relevance.

    Learn more
    StudySmarter Editorial Team

    Team Physics Teachers

    • 9 minutes reading time
    • Checked by StudySmarter Editorial Team
    Save Explanation

    Study anywhere. Anytime.Across all devices.

    Sign-up for free

    Sign up to highlight and take notes. It’s 100% free.

    Join over 22 million students in learning with our StudySmarter App

    The first learning app that truly has everything you need to ace your exams in one place

    • Flashcards & Quizzes
    • AI Study Assistant
    • Study Planner
    • Mock-Exams
    • Smart Note-Taking
    Join over 22 million students in learning with our StudySmarter App

    Get unlimited access with a free StudySmarter account.

    • Instant access to millions of learning materials.
    • Flashcards, notes, mock-exams, AI tools and more.
    • Everything you need to ace your exams.
    Second Popup Banner