Biological Imaging

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.

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.

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.

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.

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

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.