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Biological Imaging

Biological Imaging
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Have you ever wondered how we get detailed images of cells, like what you might find in biology textbooks? Or how doctors and researchers identify structures and activities in the body? Or how images of viruses and bacteria are captured, like those you might see in the news?

These detailed images were made possible by various biological imaging techniques.

  • First, we will define biological imaging and discuss the techniques involved in biological imaging.
  • Then, we will go through the different types of biological imaging and their importance in research and biomedical applications.

What is the Definition of Biological Imaging?

Let's start by stating the definition of biological imaging.

Biological imaging refers to a wide range of tools and techniques that are used in biological and health sciences to generate visual representations of different organ systems, diseases, cellular structures, and even molecular events.

What are Biological Imaging Techniques?

There are many types of biological imaging techniques. These can range from techniques used in hospitals for imaging bones and internal organs that are deep inside the body to other imaging techniques for viewing cells and viruses that are too small to be visible to the naked eye.

While we may be more familiar with techniques used in the biomedical field, the advancements in biological imaging have been helpful in understanding biological structure and function at subcellular levels.

There is a wide range of techniques available depending on what the researchers or scientists want to examine and analyze.

What are the Different Types of Biological Imaging Techniques?

There are different types of biological imaging techniques used in research. One of these is microscopy, or the use of microscopes.

Microscopes are instruments that produce enlarged images of small objects.

Researchers can use microscopes to examine and analyze internal and external structures of cells and microorganisms. Microscopes vary in their mechanisms and functions:

  • Light microscopes employ visible light to magnify small objects.

  • Electron microscopes use an electron beam to illuminate small objects. There are two main types of electron microscopes (Fig. 1):

    • Transmission electron microscopes are used to view the internal structure of thin slices of specimen.

    • Scanning electron microscopes can show the surface of a specimen in great detail.

  • Fluorescent microscopes involve the use of fluorescent dye to illuminate specific parts of the sample so that only those parts are seen in the microscope.

  • Confocal microscopes show only one point of the sample at a time, preventing parts from becoming out of focus which can happen with regular fluorescent microscopy.

If you ever wondered how researchers learned the structure of the virus SARS CoV-2 that is responsible for COVID-19, it was through the help of cryo-electron microscopy. Cryo-electron microscopy is a broad term used to describe the process of imaging radiation-sensitive specimens using a transmission electron microscope under cryogenic conditions (meaning, really low temperatures).

Other biological imaging techniques in research include: mass spectrometry imaging, bioluminescence imaging, and calcium imaging. Whereas microscopy generally provides larger and more detailed images of specimens, these other imaging techniques provide a different set of information.

Mass spectrometry imaging is a technique that visualizes the spatial distribution of molecules--such as lipids, peptides, and proteins--in a sample. This can be used to analyze the chemical characteristics of a biological specimen.

Bioluminescence imaging detects visible light produced by living organisms (called bioluminescence), enabling researchers to study biological processes in vivo (while the specimen under study is still alive). This procedure is becoming increasingly popular because it does not require the loss of life for the organism and it enables researchers to monitor changes in the same individual.

Calcium imaging detects changes in calcium ion (Ca2+) levels. It is typically used to study activities in neurons (or nerve cells). This technique can be used to image a wide range of specimens, from tissue to whole organisms.

What are Examples of Biological Imaging Techniques used in the Biomedical Field?

You might be more familiar with biological imaging used in the biomedical sciences. In the following sections, we will discuss examples of common biological imaging techniques that are widely used especially in the biomedical field.

X-ray

The x-ray is one of the earliest and most widely used biological imaging techniques. If you ever had a bone injury, had braces for your teeth, or had an annual physical exam, chances are, you’ve had an X-ray procedure.

X-rays are a type of electromagnetic radiation that have higher energy compared to visible light and can pass through most objects.

When x-rays travel through the body, they are absorbed by tissues in varying amounts depending on the radiological density of the tissues.

For example, bones contain calcium which readily absorbs x-rays, making them appear whiter than other tissues on radiographs, or images produced via x-ray. On the other hand, x-rays easily pass through less radiologically dense tissues like fat and air-filled cavities like the lungs, making them appear gray on a radiograph (Fig. 2).

X-ray technology has been the foundation of many biological imaging techniques used until today. X-rays can be used to produce images of internal organs, bones, and other structures in the body. Some x-ray detectors produce images on photographic film, while others produce images digitally.

CT Scan

Computed Tomography or CT scan builds on the technology of the X-ray. A CT scan uses multiple beams of X-rays with the aid of computer technology to produce complex images of structures inside the body.

A CT machine projects x-ray beams from different angles while a computer converts these into multiple cross-sectional images that can be viewed individually or stacked as a three-dimensional model of the body part being studied. CT scans are typically used to look at bone fractures, tumors, and heart diseases. They can also be used to guide biopsies.

MRI

Magnetic Resonance Imaging or MRI differs from x-rays and CT scan. While the latter use potentially harmful ionizing radiation, MRI uses magnetic and radio waves to produce an image.

Inside an MRI machine are powerful magnets that pass radiofrequency currents for the imaging procedure.

The combination of magnetic and radio waves with the help of a computer creates a three-dimensional detailed image of internal organs and its structures. MRIs are best used to examine the non-bony parts of the body, including soft tissues, muscles, ligaments, and nerves.

Ultrasound

Ultrasound (or sonography) uses very high-frequency sound waves to generate images. Ultrasound scanners contain probes called transducers that emit high frequency sound waves and detect those that are reflected back.

Sound waves are reflected by boundaries between tissues that are in the path of the beam. The speed of sound and the time it takes for the echoes to return indicate the distance between the transducer and the boundary. The scanner calculates for this distance and uses them to generate a two-dimensional image called a sonogram (Fig. 3).

Since ultrasound only uses sound waves and not ionizing radiation like X-rays, it is generally regarded as a low-risk procedure. This is why ultrasound is used when viewing and assessing the development of babies in pregnant mothers.

PET Scan

Positron Emission Tomography or PET scan uses an injectable or ingestible radioactive tracer that cells can absorb and convert to energy.

Radioactive tracers are retained in tissues with a lot of cell activity. For this reason, a PET scan can show how tissues and organs are functioning in real time. Likewise, it can show abnormal cellular metabolism and identify malfunctioning organs.

For example, since cancer cells typically use a lot of energy, radioactive tracers would collect in cancerous tissue and show up as bright spots on the scan. On the other hand, damaged tissues that are less active will show up as dark spots on the scan. The PET scan is widely used to detect metabolic diseases such as cancer, brain disorders, and coronary diseases


What is the Importance of Biological Imaging?

Advancements in the biological imaging field have led to more non-invasive procedures. These advancements made disease diagnosis and treatment not only safer and accessible, but also more accurate and timely for patients.

Beyond the diagnosis and treatment of individual patients, the widespread clinical information obtained through biological imaging has revolutionized our understanding of mechanisms, causes, and treatments of various diseases.

Aside from medical applications, the importance of biological imaging in the basic sciences is unprecedented. Today, because of biological imaging techniques, we are able to visualize biological structures of various organisms, from bacteria to humans. We can also better understand the different biological processes that govern our body and the planet.

Biological Imaging - Key takeaways

  • Biological imaging refers to a wide range of tools and techniques that generate visual representations of different organ systems, diseases, cellular structures, and even molecular events.
  • Microscopes produce enlarged images of small objects. They are typically used to study cells and microorganisms.
  • Other imaging techniques like mass spectrometry imaging, bioluminescence imaging, and calcium imaging can be used to show other information such as chemical composition and cellular activity.
  • The biomedical field uses several non-invasive biological imaging techniques to study, diagnose, and treat diseases.
  • Biological imaging techniques include x-rays, MRI, CT scan, ultrasound, and PET scan.

References

  1. “Microscope | Types, Parts, History, Diagram, and Facts.” Encyclopedia Britannica, www.britannica.com/technology/microscope. Accessed 21 Sept. 2022.
  2. S. Milne, Jacqueline L., et al. “Cryo-Electron Microscopy: A Primer for the Non-Microscopist - PMC.” PubMed Central (PMC), 17 Dec. 2012, www.ncbi.nlm.nih.gov/pmc/articles/PMC3537914.
  3. “How Does a Confocal Microscope Work?” How Does a Confocal Microscope Work?, www.physics.emory.edu/faculty/weeks//confocal. Accessed 21 Sept. 2022.
  4. “X-Rays.” X-Rays, www.nibib.nih.gov/science-education/science-topics/x-rays. Accessed 21 Sept. 2022.
  5. “Advances in Biomedical Imaging - PubMed.” PubMed, 7 Feb. 2001, pubmed.ncbi.nlm.nih.gov/11176859.
  6. “What Is Electron Microscopy? - UMASS Medical School.” UMass Chan Medical School, 2 Nov. 2013, www.umassmed.edu/cemf/whatisem.
  7. Buchberger, Amanda Rae, et al. “Mass Spectrometry Imaging: A Review of Emerging Advancements and Future Insights - PMC.” PubMed Central (PMC), 13 Dec. 2017, www.ncbi.nlm.nih.gov/pmc/articles/PMC5959842.
  8. Sadikot, Ruxana T., and Timothy S. Blackwell. “Bioluminescence Imaging - PMC.” PubMed Central (PMC), www.ncbi.nlm.nih.gov/pmc/articles/PMC2713342. Accessed 21 Sept. 2022.
  9. Robbins, Miranda, et al. “Calcium Imaging Analysis – How Far Have We Come? - PMC.” PubMed Central (PMC), 26 Aug. 2021, www.ncbi.nlm.nih.gov/pmc/articles/PMC8406438.
  10. “Ultrasound.” National Institute of Biomedical Imaging and Bioengineering, www.nibib.nih.gov/science-education/science-topics/ultrasound. Accessed 21 Sept. 2022.
  11. Weissleder, Ralph, and Matthias Nahrendorf. “Advancing Biomedical Imaging.” Proceedings of the National Academy of Sciences of the United States of America, edited by Mark Davis, vol. 112, no. 47, Nov. 2015, pp. 14424–28. https://doi.org/10.1073/pnas.1508524112.

Frequently Asked Questions about Biological Imaging

Biological imaging technology encompasses a wide range of tools and techniques that generate visual representations of different organ systems, diseases, cellular structures, and even molecular events.

Biological imaging is important in the biomedical field as it provides clinical information used to study, diagnose, and treat diseases. Biological imaging also enables us to visualize cells, microorganisms, and even viruses. It also deepens our understanding of various biological processes that govern our body and the planet. 

5 examples of biological imaging techniques are: x-rays, MRI, CT scan, ultrasound, and PET scan.

There are many types of biological imaging techniques. One of these is microscopy. Microscopy enables us to view enlarged images of small objects. Other imaging techniques can show not just the structure, but also the activity of living cells. These include mass spectrometry imaging, bioluminescence imaging, and calcium imaging.

In the biomedical field, various imaging techniques are used to study, diagnose, and treat diseases. These include x-rays, MRI, CT scan, ultrasound, and PET scan.

Final Biological Imaging Quiz

Biological Imaging Quiz - Teste dein Wissen

Question

What does PET in PET scan stand for?

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Answer

Positron emission tomography

Show question

Question

What is a PET scan?

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Answer

A PET scan is an imaging test that uses radioactive tracers to examine blood flow, metabolism, and chemical composition in specific body tissues or organs. 

Show question

Question

What do you call the radioactive substance injected into or swallowed/inhaled by  a patient undergoing a PET scan?

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Answer

Tracer

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Question

______ refers to the life-sustaining chemical reactions that take place in living cells that either consume or produce energy.

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Answer

Metabolism

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Question

What happens to the tracer after it is administered to the patient?

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Answer

After some time, the tracer would be distributed throughout the body and retained in bodily tissues with a lot of cell activity.

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Question

The tracer releases _____ in the organ or tissue under study.

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Answer

Positrons

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Question

What do we mean by "hot spots" in a PET scan?

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Answer

Hot spots are bright patches on a PET scan, indicating higher levels of activity.

Show question

Question

Heart tissue that has been damaged will be less active and will consume less sugar. As a result, on a PET scan it would be visible as a ____ area compared to normal heart tissue.

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Answer

darker

Show question

Question

Distinguish a CT scan from a PET scan.

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Answer

While the CT scan shows detailed cross-section images of the organs and tissues of the body, the PET scan shows the activities within these organs and tissues.

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Question

What is the purpose of a PET scan?

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Answer

A PET scan is typically performed to assess organs or tissues for the presence of diseases or other conditions.

Show question

Question

Does a patient need to worry about radiation exposure after a PET scan? Why or why not?

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Answer

A PET scan uses only a little amount of radiation, so there is no need to worry about radiation exposure; a PET scan typically exposes the patient to the same amount of radiation as a conventional CT scan. Moreover, the radiation does not stay in the patient's body for very long. 

Show question

Question

Describe how a PET scan works.

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Answer

A small amount of tracer is administered to a patient. After some time, the tracer would be distributed throughout the body and retained in bodily tissues with a lot of cell activity. The PET scanner has a special type of camera that detects positrons released by the tracer in the organ or tissue under study. 

A computer reconstructs the signals into three-dimensional images and displays them on a monitor. 



Show question

Question

Cancer cells typically consume a lot of sugar and appear as ______ on a PET scan. 

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Answer

bright patches

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The following are functions of a PET scan except for:

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Answer

Detecting how cancer is spreading from the original site to other parts of the body

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Question

What is a PET-CT scan?

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Answer

Some machines combine the PET scan with a CT scan, and these are called PET-CT. A PET-CT scan would provide more definitive information about the metabolic changes and their locations in the body.

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Question

What does CT in CT scan mean?

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Answer

Computed tomography

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Question

What is another name for the CT scan?

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Computed axial tomography or CAT scan

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Question

How is a CT scan different from a typical x-ray procedure?

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Answer

Whereas a typical X-ray procedure produces flat images, a CT scan produces highly detailed images that make it easier for the viewer to understand the volume and shape of the structures being examined. A CT scan also has the ability to produce images of bones, soft tissues, and blood vessels simultaneously. 

Show question

Question

A CT scan uses ____ to produce an image of the internal structure of a selected body part.

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Answer

x-rays

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Question

This substance may be administered to the patient before the test to help specific structures show up better on the images.

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Answer

Contrast dye

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Question

Why would a physician recommend a CT scan if a patient is suspected of having cancer?

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Answer

A CT scan can be recommended when a patient is suspected of cancer because it can help visualize the tumor and assess its size, location, and potential interaction with nearby tissues and organs.

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Question

Describe the typical CT scan procedure.

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Answer

The patient will lie down on a platform that will slowly pass through a central hole in the machine. An X-ray beam rotates around the patient's body, allowing multiple images to be taken from different angles. The machine sends signals to the computer, which creates separate images of the region of the body. A contrast dye may be injected into the patient before the test.


Show question

Question

The individual, two-dimensional images of the body part under study that are produced by a CT scan are called ___.

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Answer

Slices

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Question

How is a CT scan used to produce a three-dimensional model?

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A CT scan creates multiple images of the internal structure of a body part. These images can be stacked together to form a three-dimensional model of the body part. 

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Question

Why would a CT scan be performed alongside a PET scan?

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Answer

The CT scan provides anatomic pictures of the organs and structures, and the PET scan offers data about the metabolic pathways active in these tissues or cells. The PET/CT can give a more in-depth look at these structures than either test alone. 


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The density of the tissue is _____ to the attenuation of x-rays passing through it.

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proportional

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Lung and body fat tissues have low attenuation, so they appear as ____ patches on a CT scan. 

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Answer

dark

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Question

Muscle, liver, and bone are denser so these appear as ____  patches on CT.

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bright

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A ____ is a specialist who has had training in the use of imaging equipment and cross-sectional image interpretation.

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Answer

radiologist

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Question

How much radiation does a CT scan involve?

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Answer

A CT scan involves a tiny amount of radiation, which is within the limits of what is considered safe. Although the radiation exposure from CT is greater than that from regular x-ray treatments, the increase in cancer risk from a single CT scan is still minimal.

Show question

Question

How is a CT scan different from an MRI scan?

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Answer

A CT scan uses x-rays, so it involves the use of radiation. On the other hand, an MRI scan uses a powerful magnet to send radio waves to the patient's body, and it does not involve radiation.

Show question

Question

What is biological imaging?

Show answer

Answer

Biological imaging refers to a wide range of tools and techniques that are used in biological and health sciences to generate visual representations of different organ systems, diseases, cellular structures, and even molecular events.

Show question

Question

_____ use an electron beam to illuminate small objects, particularly the internal structure of thin slices of specimen.

Show answer

Answer

Transmission electron microscopes

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Question

What is the difference between light microscopes and electron microscopes?

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Answer

Light microscopes use visible light, while electron microscopes use an electron beam to illuminate the specimen.

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Question

_______ is a technique that visualizes the spatial distribution of molecules in a sample. 

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Answer

Mass spectrometry imaging

Show question

Question

An image produced by an x-ray is called a __________.

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Answer

radiograph

Show question

Question

How does an x-ray produce images of the body?

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Answer

X-rays are a type of electromagnetic radiation that have higher energy compared to visible light and can pass through most objects. When x-rays travel through the body, they are absorbed by tissues in varying amounts depending on the radiological density of the tissues. 

Show question

Question

CT scans use ___ and computer technology to produce complex images of structures inside the body. 

Show answer

Answer

x-ray beams

Show question

Question

____ uses magnetic and radio waves to produce an image. 

Show answer

Answer

MRI

Show question

Question

How are images produced using ultrasound?

Show answer

Answer

Ultrasound scanners contain probes called transducers that emit high frequency sound waves and detect those that are reflected back.  The speed of sound and the time it takes for the echoes to return indicate the distance between the transducer and the boundary. The scanner calculates for this distance and uses them to generate two-dimensional images.

Show question

Question

Why is ultrasound--and not PET scans, CT scans, or x-rays--used when viewing and assessing babies in pregnant mothers?

Show answer

Answer

PET scans use radioactive tracers that can be harmful for the baby. Likewise, CT scans and x-rays use radiation to produce images. Ultrasound differs from these procedures because it only uses sound waves, making it safer for the baby.

Show question

Question

____ uses an injectable radioactive tracer that cells can absorb and convert to energy.

Show answer

Answer

PET scan

Show question

Question

How is a PET scan used to detect cancer?

Show answer

Answer

Radioactive tracers are retained in tissues with a lot of cell activity. Given that cancer cells typically use a lot of energy, radioactive tracers collect in cancerous tissue and show up as bright spots on the scan.

Show question

Question

Why is biological imaging important?

Show answer

Answer

Biological imaging is important in the biomedical field as it provides clinical information used to study, diagnose, and treat diseases. Biological imaging also enables us to visualize cells, microorganisms, and even viruses. It also deepens our understanding of various biological processes that govern our body and the planet. 

Show question

Question

What is bioluminescence imaging? 

Show answer

Answer

Bioluminescence imaging detects visible light produced by living organisms, enabling researchers to study biological processes in vivo. This procedure does not require the loss of life for the specimen and it enables researchers to monitor changes in the same individual.

Show question

Question

What is calcium imaging typically used for?

Show answer

Answer

Calcium imaging detects changes in calcium ion (Ca2+) levels. It is typically used to study activities in neurons (or nerve cells). 

Show question

Question

_______ is a medical imaging technique that allows doctors to determine the extent of a patient's injury, illness, or tumor growth. 

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Answer

MRI or CT

Show question

Question

_______ uses a magnetic field coupled with computer-generated radio waves to create high quality visual images of the organs and tissues within the body.

Show answer

Answer

MRI

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Question

The MRI scan can be used to diagnose many types of cancers, concussions, broken bones, and other structural injuries that cause damage to your organs and tissues

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Answer

True

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Question

MRI cannot be used to diagnose disorders of the brain.

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Answer

False

Show question

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