X-ray examination: what it is, what it is for, how it works

Bumps, falls or accidents, in general, require an x-ray examination, if only to confirm that there was no fracture. The exam is part of routine care in hospitals, clinics and emergency rooms.

What are X-rays?

X-rays are a part of the electromagnetic spectrum  at a frequency that we are not able to see with our eyes. They are used in X-ray imaging exams, done to examine internal parts of the body without having to make cuts or perforations.

The main exams done with X-rays are radiography  and computed tomography .

To understand how the X-ray scan works, we first need to understand a little about light and the electromagnetic spectrum.

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation, which is basically formed by light.

The light is a strange thing. It is made up of energy particles called photons , but it behaves like a wave. Do you know when we throw a stone into the water and several ripples spread everywhere from the point where the stone entered the water? It’s like that.

Waves, however, need a way  to exist. The waves in the water only exist because they are in the water. The sound is nothing more than waves that are transported through the air.

Light, however, is a particle and a wave. It, in a way, is the medium itself and therefore can be transported through the vacuum of space, coming from the sun to the earth, for example.

Why can’t we see X-rays?

The only thing that allows us to see  are our eyes, which receive the photons and send this information to the brain, which interprets them in the proper way so that we can form visual images. Everything we see is just waves that our eyes receive.

However, human eyes are not able to receive any light. To do this, it must be at the correct wavelength .

The wavelength is the distance between each repetition of waves. In the case of the stone that we throw in the lake, it is the space between each of the waves, which in this case is quite large.

Our eyes are able to identify a very specific spectrum of light, with a wavelength between 380 and 740 nanometers . Each nanometer is one millionth of a millimeter. Any photon with a wavelength greater or less than that is outside the visible spectrum of light .

All the colors we can see are in this spectrum, with violet between 380nm and 440nm and red between 625nm and 740nm.

Ultraviolet rays, for example, are between 10 and 380 nanometers, so we are not able to see them, but they are there, as well as the infrared, which starts from 740nm and goes up to 1 millimeter.

X-rays have an even shorter wavelength than UV rays. The shortest wavelength X-rays are only 0.01 nanometers, while the largest X-rays reach 10 nanometers, far from the spectrum that our eyes can capture. X-rays pass through our eyes without being noticed, and that’s why we don’t see them.

How does the X-ray scan work?

Now that you know that X-rays are a type of light radiation, just like light, but in another wavelength, it is easier to understand how it is able to show us things that are inside our body.

Because of the wavelength of the X-rays, most of them pass through our body. However, bones absorb radiation. For an X-ray examination, the part of the body that will be examined is positioned between the X-ray source and a clean photographic plate.

X-rays pass through the body and make the photographic sheet black, but when the bone is hit by X-rays, it absorbs the radiation and in the sheet, that part remains white.

The photons that pass through the bones leave few marks on the leaf, while in places where there was no interruption of the rays, or there was little, the leaf is dark.

Thus, it is possible to get a detailed and clear image of the bones, in addition to being able to have some information about other parts of the body based on the image and the amount of X-rays it was able to pass through.

What is the x-ray for?

The x-ray exam is basically for health professionals to assess the integrity of the bones. But X-rays are used for a variety of purposes, even outside of healthcare. Some of its uses include:

Imaging exams

Imaging exams are one of the most common and famous uses of X-rays. They cross the body and mark the photographic plate. Each part of the body has a different density and allows different amounts of X-rays to pass, so it is possible to identify different structures.

Fractures can be visualized with ease. Tumors can be identified. In the lungs, it is possible to diagnose pneumonia and tuberculosis using X-rays. In addition, objects lodged in the body, such as firearm bullets or pieces of iron, can be located.

Caries can be easily diagnosed using X-rays, as well as identifying unborn teeth, such as wisdom teeth.

The osteoporosis can also be diagnosed by X-rays, as the less dense bones allow more X-rays pass through the body in places that normally would not leave.

Through the use of contrast chemicals, X-rays allow you to identify certain structures such as blood vessels and muscles.

Finally, computed tomography uses several X-ray images to obtain detailed images of various planes of the entire body.

Metal detector

X-rays are widely used in airports to detect weapons, bombs or any object that is not allowed inside an airplane. It is possible to use it to detect metals, which appear clearly in the image even without the need to open bags and suitcases.

The identification of objects inside the bags speeds up magazines and increases security on airplanes. The system can also be used in many other places such as events, hotels, trains or companies.

Soil tomography

From the X-rays it is possible to analyze the chemical composition of the soil. Each chemical element absorbs, reflects or allows the crossing of X-rays in different amounts and through these data it is possible to know how much of each is in the soil.

This is useful for agriculture, geography and several other areas that can benefit from information about the chemical composition of the land.

DNA research

The famous image that represents DNA is iconic and was discovered through the use of X-rays, which allowed an accurate image about the DNA molecule. Using X-ray waves, it was possible to observe the method as they refract in the molecular crystals that make up the double helix, thus obtaining important information about the structure.

Without X-rays, several discoveries in the DNA field would not be possible.


Radiation therapy is used to treat cancer , aiming to destroy cancer cells that may be in the body of a patient with radiation. It can be made from radioisotopes (such as cobalt-60 or cesium-137), which emit gamma rays, or from kilovoltage equipment, which emit X-rays.

In this case, the radiation is applied from several different angles, seeking to reduce the exposure of healthy tissue as much as possible.

What is the head x-ray for?

The x-ray examination of the head or skull serves to detect possible injuries or bone changes, resulting from illness or trauma. The entire skull region is evaluated, comprising the mandible and face.

It may be necessary to perform the examination when the person has undergone facial reconstructions or placement of bone prostheses.

How is the X-ray exam done?

In health, X-ray examinations are done in several ways, but invariably X-rays are produced and sent accurately to the location that you want to examine or treat.

In the machine, a vacuum glass tube has a pair of electrodes. One is a filament similar to those inside a fluorescent lamp. This filament is heated with electricity and releases electrons.

The other electrode is a tungsten disc , a very dense metal with a high melting point (tungsten melts at 3422 ºC, being the second material with the highest melting point, behind only carbon). This disc has a positive charge and when electrons are released from the filament, tungsten attracts them.

The impact of these electrons on the disk causes tungsten to release energy in the form of X-ray photons, which are launched everywhere.

The glass tube where all this is found is surrounded by materials that prevent X-rays from passing, such as lead. Only a small opening allows the waves to come out. This opening is directed at the patient, who is positioned according to the exam being performed.

On the other side of the patient, a camera records X-rays, which pass through different amounts of materials in the body. Bones are dense, so less X-rays pass through them, while muscles allow more photons to pass. Their image turns out to be less clear in the image, while the bones appear clearly.

What types of x-rays?

There are several types of X-ray exams. Among them are:


Radiography is the simplest of X-ray examinations. On one side is the machine and, on the other, a plate that records X-rays. On the plate is placed the part of the body that will be examined, which may be an arm, a leg, chest, head, whatever.

There is a tendency to substitute radiographic film for digital radiographs.

Computed tomography

Computed tomography is composed of several radiographs. The region of the body to be examined receives X-rays and passes the images to the computer, which unites them all and forms a detailed and high-resolution image of the body.


The mammography is performed using X-ray is basically a detailed breast radiography, seeking to find tumors that may be there.


Angiographies seek to examine blood vessels, organs and the heart. In order to perform this examination, a contrast agent is inserted into the patient’s body , which is a liquid that absorbs X-rays.

As muscles and blood vessels are not very apparent on ordinary radiography, contrast is necessary to make it possible to make an adequate observation of these tissues, which appear clearly after the application of the liquid.


Fluoroscopy uses a constant source of X-rays so that the exam shows a moving image instead of a static one.

It can be used for swallowing exams, which analyze the patient’s swallowing mechanism, or in surgeries where the study of body fluids is necessary, such as in the surgery to install a pacemaker, where barium is added to the bloodstream. and monitored through fluoroscopy to find out if the device is working correctly.

Most common X-ray locations

Some locations are often examined using X-rays. They are as follows:

Chest X-ray

Complaints of shortness of breath or difficulty in breathing are often examined using a chest X-ray. With it, we seek to find infections, problems in the lungs or ribs, in addition to any other problem that may be causing the breathing difficulty.

X-ray of the kidneys

Symptoms of pain in the abdomen may cause the doctor to order an x-ray of the kidneys, which may have stones that appear on the exam, as well as tumors.

X-ray of the mouth

The X-ray examination clearly shows cavities, for example, or wisdom teeth, in addition to structures that cannot be seen with the naked eye because they are inside the gums.

X-rays of fractures

X-rays are used on fractures to examine the extent of the damage and confirm the condition. When there is only suspicion, it serves for confirmation, but even if you are sure that a bone is broken, information on how many parts the bone has broken and what other injuries there are in it is important for the doctor.

Cranio-brain computed tomography

Computed tomography of the skull and brain is a common test that looks for damage to the skull or brain, which may have been caused by trauma or stroke.

When should it be done?

The X-ray examination should be done when there is a suspicion of a problem inside the body that cannot be diagnosed by simple observation. This includes countless different conditions, such as cancer, fractures, cysts, objects lodged inside the body, twists, calculations and many others.

Radiography is an extremely versatile test, allowing the confirmation or elimination of suspicions with a low-invasive test with remarkable accuracy.

Among the diseases that can be diagnosed by X-rays are:

  • Fractures;
  • Bone cancer;
  • Breast cancer;
  • Tumors in general;
  • Blockages of blood vessels;
  • Pneumonia and other lung problems;
  • Digestive blocks;
  • Osteoporosis;
  • Wisdom tooth growth;
  • Swallowed objects;
  • Teeth decay;
  • Osteomyelitis;
  • Kidney stones;
  • Gallstones;
  • Arthritis.


Contraindications for X-ray examinations are few and specific. Especially when there is no need to use contrast, hardly anything can stop someone from taking the test.


Yes, pregnant women can take X-rays, as long as they inform the doctor of the pregnancy. Normally the tests do not emit enough radiation to have any effect on the baby’s development, but several of them in a short time can cause problems.

Pregnant women should also avoid CT scans. The amount of radiation from this test is still small, but it is considerably greater than that of a simple radiograph and can cause problems in the development of the fetus, especially in early pregnancy.

The test, however, can be indicated anyway, when the benefits outweigh the risks, which are not usually many.

Amounts of X-rays already made

It is recommended that no more than 5 radiographic examinations are performed per year. Although the amount of radiation in one of them is very low, the repetition can be problematic and increase the risks of the exam.

Renal failure and hypothyroidism

The contrast used frequently for X-rays can worsen kidney failure in patients who already suffer from the condition and is not indicated. The same applies to hypothyroidism .

Pre-examination and post-examination care

Some exams involving X-rays require prior preparation.


When there is a need to use contrast (a liquid that is used to facilitate the visualization of certain parts of the body) and the patient has some allergy to the substance, prior administration of antiallergics may be necessary.


In cases of X-ray examinations involving the abdomen, fasting may be necessary to prevent food from appearing in the image, hindering the identification of the organs.

Remove metals

Watches, earrings, rings, necklaces and any other type of metal can interfere with X-ray and computed tomography images, so they must be removed. If you have an implant, it is important to tell your doctor.

Doing the exams with the metals is not a big problem, but they appear clearly in the image and depending on how they are positioned, they can interfere with the exam, hiding something that would appear if the metal was not there.

How to interpret the results

The results can be read by the radiologist and depend a lot on what you are looking for. A fracture is usually clearly visible on an X-ray examination as the bones appear clearly, but this is not the only diagnosis that the technique allows.

CT scans can diagnose tumors and other injuries, and your doctor will know what to look for in them based on your knowledge of the human body.

For the images to be developed, it takes around 10 to 15 minutes. In addition, the doctor’s report may add some waiting time, as it depends a lot on what is being analyzed.

What can affect the results?

The lack of clarity in some tests can affect the result. Organs and blood vessels allow many X-rays to pass through, so they can be difficult to see on examination. To solve this problem, it is common to use a contrast .

Contrast is a liquid that does not allow X-rays to pass through so easily. It is placed in the body, in the bloodstream or in the organ to be examined, which allows the examination to present an organ or vessel that would normally be clearly invisible.

In addition, the amount of X-rays can also affect the results. It is possible to regulate the amount of X-rays that come out of the X-ray machine. This influences the appearance of each organ in the image and this amount is modified depending on which organ is being examined.


At first, X-ray examinations are perfectly safe. They are based on radiation, but are usually in an extremely small amount and for a short time. But it is important to note that frequent and prolonged exposure to X-rays can cause cell damage, leading to burns or cancer.

That is why radiologists use lead aprons during radiographs. This protects them from radiation, which has no harmful effect on the patient, as he is there for a short examination. However, for the professional, who stays in the radiography room for hours and on several days of the week, protection is necessary.


The price of an X-ray exam is varied, as it depends on the region being examined. A skull radiography, for example, according to the Intermunicipal Health Consortium of Western Paraná, costs R $ 24.00.

The CT scan of the cervical spine with contrast can be around R $ 188.00 while one of the thoracic aorta costs R $ 400.00. It all depends on the region to be examined, whether contrast is needed, among other things.

How was the X-ray discovered?

The X-ray was discovered in 1895 by the German physicist Wilhelm Conrad Röntgen from the Crookes tube experiment.

The Crookes tube creates X-rays, sending electrons from an energized cathode into an anode, creating light. William Crookes (creator of the Crookes tube) did not know this, but Wilhelm Conrad Röntgen, when carrying out the experiment, detected the X-rays on a piece of paper covered with barium platinocyanide, a chemical compound that reacts to ultraviolet, violet or blue radiation glowing green.

Barium platinocyanide also reacts with X-rays and thus, Röntgen discovered their existence. The physicist realized that certain materials that normally block visible light did not prevent X-rays from reaching the barium platinocyanide photographic plate.

He then asked his wife, Anna Bertha Ludwig, to put her hand between the Crookes tube and the platinum-cyanide paper and the result was the first radiograph in history, where the woman’s bones could be seen in the resulting image, which you can see see below:

The first radiograph in history was the hand of Röntgen’s wife, with her ring. The first radiographs had a white background and a black image (the opposite of today) because of the material used in the film, which at the time was different from the one currently used.

Common questions

X-rays are bad?

X-ray examinations emit radiation, but the amount is too small to cause any damage to the human body. Repeating the exams in a short time, however, can cause problems.

What is the radiation dose?

The dose of ionizing radiation in the human body is measured in sieverts  (Sv) . In the case of X-ray exams, we will deal with the milisievert  (mSv) , which is one thousandth of Sv. Each 1000mSv is equivalent to 1Sv.

Basically, everything emits an extremely low amount of radiation. Eating a banana , for example, makes your body absorb approximately 0.0001 mSv.

The world average of naturally absorbed radiation (through food, cosmic radiation, gamma rays) is 2.4mSv / year, varying from place to place on the planet.

An arm X-ray emits approximately 0.001mSv. A dental computed tomography reaches 0.15 mSv. A mammogram can emit up to 0.4 mSv.

Each exam has a different amount of radiation, but all of them emit little, one of the highest being the whole body computed tomography, which can reach, in some cases, 10 mSv.

What is the radiation limit of my body?

For safety, the basic guidelines for radiation protection indicate that the general public should not be exposed to more than 3.4mSv per year while professionals dealing with radiation should not absorb more than 20mSv annually.

However, there are places on the planet where natural radiation reaches up to 10mSv. And this is not a problem.

Radiation only affects the body at doses much larger than that. It is necessary to absorb 50mSv to 100mSv for blood changes to appear. Radiation intoxication only appears after 500mSv, when nausea can manifest. It is from there that it starts to get dangerous.

Whole 1Sv (ie 1000mSv) can cause bleeding. From 4Sv onwards, death within 2 months becomes possible if there is no treatment for radiation poisoning.

After 10Sv, death occurs between 1 and 2 weeks due to the destruction of the internal intestinal wall, in addition to other parts of the body such as the bone marrow. With exposure to 20Sv, death occurs in a few minutes or hours.

But an X-ray exam is nowhere near  1 full Sv. To achieve the required dose of radiation for blood damage, at least 5 full body CT scans would be needed in a short period of time.


As much as the radiation doses are low, professionals who deal with it can be constantly exposed.

It is recommended that they are not exposed to more than 20 mSv per year, but the greater the exposure and the longer it is, the greater the risk of developing cancer. Therefore, the use of lead equipment, which blocks radiation, is recommended for these people.

Can the X-ray room become radioactive?

No . Radiography devices have electromagnetic radiation, which stops being produced the moment the electricity stops being sent to the device. This type of radiation is like light and as its source stops producing it, the radiation disappears, unlike radiotherapy devices, which use radioactive material.

The same applies to any metal that can be used. Metals do not absorb radiation from radiography devices.

Can pregnant women take X-rays?

There are no contraindications for pregnant women. It is advisable to inform the doctor of pregnancy so that he can choose what is best, but the small amount of radiation should not affect the baby’s development.

Is it safe for children?

As for the fetus and adults, children are safe by performing X-ray examinations.

You have learned that X-ray exams are varied, useful and safe, bringing several advantages to medical diagnoses in a non-invasive way, in addition to other everyday utilities.