Common Factors of X Rays

Common Factors of X Rays | Chapter – 7

X rays called x radiation, are known for their properties like no mass and no charge. 

X rays are classified based on their energy level, shown by the voltage between electrodes. In this article, we are going to discuss common factors of x rays, where we discuss radiographic density, quality, artifacts, and so on. 

Soft X Rays

Soft x rays have low-energy photons and longer wavelengths and the energy of soft x rays is below than 5 KeV.

Soft x rays have very less penetrating power, so these are easily absorbed by low-density tissues such as soft tissues, or liquid, so soft x rays are used to capture soft tissues like mammography, or dental x rays.  

soft x rays

Properties of Soft X Rays

Here are the different properties of soft x rays are the following:

  1. The  Frequency range of soft x rays is between 30 to 3000 PHz.
  2. The wavelength range of soft  rays is 10 to 0.1 mm
  3. The level of photon energy is low in soft x rays.
  4. Soft x rays are used in most applications, such as mammography.

So, soft x rays have a specific range of energy in x ray spectrum and are widely used in medical imaging for studying and visualizing different structures and abnormalities. 

Hard X Rays

Hard x rays have high-energy photos, above 5-10 KeV, and can easily penetrate high-density tissues like bones or metals and are not easily absorbed by lower-density tissues.

Hard x rays are used in x rays and computed tomography. 

Along with this, hard x rays are used for industrial purposes, for testing purposes of different metals or objects, and also used in security and at airports for scanning cargo and baggage inspection. 

hard x rays

Properties of Hard X Rays

Hard x rays also have their unique properties like soft x rays following:

  1. The Frequency range of hard x rays is between 3 to 300 EHz.
  2. The wavelength of hard x rays is between 100 to 1 pm.
  3. The photon energy level is higher in hard x rays i.e.-, above 5 to 10 keV.
  4. The main application of hard x rays is used to image inside of objects such as medical radiography, airport security, to determine crystal structures, etc.

So, hard x rays have high energy photons and are used in medical imaging and also for different purposes. 

Difference between Soft and Hard X Rays

Soft and hard x rays have their unique characters and functions, a few of them are here:

The main difference between soft and hard x rays is that, have different ranges of frequencies; as harder x rays are greater than soft x rays.  

The second difference is hard x rays have higher energy and Soft X-rays will have lower energy.

The third difference is hard x rays as they have shorter wavelengths whereas soft x rays have longer wavelengths.

Here, these three differences are enough to differentiate between soft and hard x rays. 

Absorption of X Rays

The absorption of x rays is the interaction of x rays with different matters, through the process known as photoelectric absorption and Compton scattering. 

X ray penetration is one of the x ray properties and x rays can pass mostly body tissues or densities and penetrate the body based on their frequency and wavelength. Here, x ray absorption contributes to x ray image formation. 

We see different shades on the x ray images due to the different levels of x ray absorption and the level of x ray absorption depends upon the atomic structure, energy level of rays, and density of the materials.  

absorption of x rays

Here, the binding energy of the material is much less than the x ray, so the game of absorption takes place. 

High-energy x ray photons can penetrate high-density substances, such as bones or metals, and vice versa and the level of x ray absorption directly contributes to the image contrast, and here different level of absorption properties appears as a dark and bright area on the x ray image. 

Along with iodinated contrast agents are also used to enhance the x ray absorption and image visibilites and diagnosis. 

Why is X Ray Absorption Important?

When we diagnosed the x ray image for different abnormalities, we saw that different body parts were seen in different shades of grey. These shades make the image bright or dark, based on the level of x ray absorption. Heavy tissue densities can’t allow x rays to pass easily and vice versa, contributing to x ray image contrast. 

Hence, x ray absorption shows different levels of x ray contrast and is used in image diagnosis, helping in identifying pathologies. And also used in scientific research and much more. 

Radiographic Density

The radiographic density is the level of darkness or lightness of the x ray image, we also call it a “radiograph”.

The radiographic density is also called radiodensity. 

When the exposure is taken, the amount of x ray photos emitted also influences the density of the x ray image, which may be overexposed or underexposed. 

radiographic density

The level of x ray attenuation directly depends on the density of the targeted body area, if the higher the density, the more x ray attenuated, or vice versa. 

The x ray image has different density ranges shown as back, white, and grey. 

Five X Ray Densities

When the x ray images are taken, five x ray densities come in the role of making the x ray image readable easily. 

Low density body area is seen in black on the x ray image and the high-density body area is seen in white on the x ray film, because of the different densities of the body parts, captured in the x ray. 

Here are 5 most common x ray densities, are following:

From these five x ray densities, four x ray densities are natural and the rest are metal. 


The air is seen back on the x-ray image because air is a radiolucent substance. Such as lungs.


Fats are seen as lighter than the air, such as fat tissue. 

Soft Tissue/Water

Fluid fills cavities in the body seen as whiter than the fat tissues, as they have higher tissue in that area.


Human bones are very dense and very little x ray can pass through them and are seen white on the x-ray image. Such as calcification of bones, any blockage in the arteries, etc. 


Metal is seen as pure white on the x ray image as it is a radioopaque material. 

The metal is not presented in the body naturally, as we already mentioned, these may be implanted in the body or swallowed or pierced accidentally, such as foreign objects or iodinated contrast media.  

Abnormal X Ray Densities

If you’re a radiologist or radiographer general physician, you must know these five x ray densities, so that you can easily differentiate between normal x-ray densities and abnormal ones which helps you to diagnose the diseases easily and smoothly assist the patient in further evaluation. 

Radiographic Quality

Radiographic quality is a very important factor in medical imaging diagnosis, as it shows the clarity of the x ray image for better diagnostic purposes. 

Radiographic quality has many factors, such as image clarity, contrast, resolution, low noise, and desired exposure factors.

radiographic density

If any x ray image receptor takes more radiation on any specific area, then that area is overexposed and becomes darker in the final x ry image output or vice versa,i.e.- underexposed. 

X Ray Image Contrast

Contrast is a concept of the difference between radiographic densities and x ray image contrast helps radiologists to diagnose the abnormalities such as differentiate between anatomical radiology and pathological radiology. 

x ray image contrast

X ray image contrast is the result of different densities of the body tissues on the x ray image. Here, when this density difference is high, then the image is known as a high-contrast image.

X Ray Unsharpness

X ray unsharpness is a concept of loss of the spatial resolution of the x ray image and affects the image clarity.

x ray image unsharpness

Types of Unsharpness

There are many types of x ray unsharpness, but here are the main three:

Motion Unsharpness

Motion unsharpness is caused by the movement of the patient.

When x ray is taken and the patient moves a little, this will contribute to motion unsharpness. 

These patients’ movements may be voluntary or involuntary depending upon the action of the body parts underexposure. 

motion unsharpness

To reduce motion unsharpness, we must keep the patient immobilized or ask the patient to not move and stay still for a whole or hold the breath for a short time, if we focus on these, then we can easily conquer the motion unsharpness. 

Geometric Unsharpness

The geometric unsharpness is the concept of the geometry of the x ray beam in radiography.

The final focal spot in x ray decreases the geometric unsharpness, and radiographers get the best quality images, this can be captured if OFD (Object to Film Distance); 

If it is not possible to keep the patient’s body near to x ray source, then FFD goes beyond the normal range limit and accounts for image unsharpness. 

System Unsharpness

The system’s unsharpness is caused by the detector used in the x ray system because every detector has its features and characteristics, so they are also limited to some extent.

X Ray Image Quality

The x ray image quality results from x ray beam penetration power.

Mas and KvP are the two main factor that contributes to the x-ray image, here, mAs result in no electrons or photos, and KVP results in the speed of the x ray beam. So, Proper exposure is a metric that is followed to get better diagnostic images. 

x ray image quality

X ray image quality is influenced by contrast, spatial resolution, detector performance, focal spot size, noise, collimation, artifacts, etc. 

While getting better x ray images, radiographers must be aware of the ALARA Principle. 

Proper collimation reduces scattered radiation and enhances image quality. 

X Ray Noise

X ray noise is the random variation of the x ray photons on an x ray image and looks like salt and pepper distribution. 

That is because of the level of distribution of darker or lighter pixels. This may be high or low. 

x ray noise

X ray noise directly contributes to decreasing x ray image quality and results in poor diagnoses of any diseases or abnormalities. 

X ray image is affected by quantum noise, patients, low radiation dose, motion, and detector quality. 

X Ray Artifacts

X ray artifacts are unwanted shadows in an x ray images and are not accounted for in diagnosis and degrading x ray image quality.

The artifacts are outside of the patient’s body errors.

X ray artifacts may be a result of hardware failure, radiographer’s eros or software issues, or image processing errors. 

x ray attifacts

The most common causes of x ray image artifacts are improper x ray image handling, processing system errors, or patient movements. 

The few most common x ray artifacts are motion artifacts, detector erodes, image processor errors, or grid artifacts. 

Last Words 

In this article, we learned common factors of x rays like radiographic density, x ray image quality or x ray absorption, x ray artifacts, and so on. 


This article is for educational purposes only. The information provided is here, based on the author’s learning and experiences. 

Any external linking data isn’t our authority and can be changed by the official sources, so keep it in references, while studying. 

If you use this article, then proper attributions or mentions are mandatory. 

Leave a Comment

Your email address will not be published. Required fields are marked *