Scatter Radiation

Scatter Radiation

INTRODUCTION

When a photon beam interacts with matter, some of its part get absorbed, some gets deflected to new direction and rest of it is transmitted to produce a radiographic image.

The part which is deflected from its original path to a new direction is known as scatter radiation.

The secondary radiation which makes no favorable contribution to the formation of image and produce an overall blackness on the film thus reducing the image contrast.

Scattered x-rays cannot be completely removed by the use of anti scatter grids or energy filters.

Scatter radiation is a result of either coherent scattering or the Compton effect Some scattering also occurs as a result of interaction between the x-ray beam and the tabletop and image receptor (IR), and any other matter that happens to be within the radiation field.

Sources of scatter radiation

• Patient him/herself
• Glass walls of x-ray tube
• Tabletop
• Cassette
• Back scatter from floor

Back scatter from wall

Characteristics of scatter radiation

• More oblique in nature
• Produced by matter in all directions
• Less energy than primary beam
• With increase in energy of primary radiation more scatter produced
• Amount of scatter depends on
• Volume of tissue
• Thickness of patient

KVp used

Effects of scatter radiation

Increase overall density of the film which is not useful in production of image thus produces fog Reduces contrast

• Reduce light transmitting ability of film/cassette

Result in formation of noise

Solution to Decrease of scatter radiation

• Beam limiting devices ( collimation)
• Filtration
• Radiographic grids
• Air gap technique

Compression in mammography

Beam Limiting devices

In addition to decreasing patient dose, beam limiting devices such as collimators reduce the amount of scatter radiation and thereby increasing image contrast.

Collimation refers to decreasing the size of the projected field to limit the x-ray beam field size to the anatomic area of interest only.

• Beam restriction serves two purposes:
• Limiting patient exposure

Reducing the amount of scatter radiation produced within the patient.

Compression technique in mammography

It reduces amount of scatter by diminishing the thickness of tissue through which x-rays pass through.

It displaces the adipose tissue sideways thus reducing the volume of the part to be x-rayed and lowers the kilovoltage to be used Advantages

• It acts as immobilizing device

Helps in the reduction of the scatter radiation thus improving the contrast.

Air gap technique

The air gap technique is a scatter reduction method that uses an increased object to image distance to reduce scatter reaching the image receptor.

This technique is used in lateral C- Spine and chest radiographs.

Since the patient is the source of scatter and the increased object to image receptor distance causes much of the scattered radiation to miss the image receptor.

This reduces scatter and improve the contrast of the image.

The major disadvantage of the air gap technique is the loss of sharpness which results from the increased object to image receptor distance.

Radiographic grids

It is a radiographic accessory which is designed to minimize the effect of scatter radiation reaching the film.

A radiographic grid is a device made of parallel radiopaque strips alternately separated with low-attenuation strips of Aluminum, Plastic and Wood. It is placed between the patient and the radiographic image receptor to remove scattered x-ray photons that emerge from the patient before they reach the film or other image receptor.

Improves image contrast significantly..

Filtration

This is the process of shaping the x-ray beam to increase the amount of useful photons and decrease the low energy photons.

When x-ray photons interact with the human body only the high energy photons penetrate the body, while low energy photons are absorbed in the body and contribute to scatter.

Filtration absorbs the low energy photons from the beam and hence increases the image contrast.

Other methods to decrease scatter

Optimizing Technical Parameters

• Secondary Protective Barriers and Apparel

Reduction of Repeat Examinations

Optimizing Technical Parameters

KVp Affects the penetrability of the beam Higher kVp, more photons go through patient to the Image receptor, less absorbed by patient, higher scatter and less contrast on image Lower the kVp, increase in dose absorbed by patient, less fog on film more contrast image Higher kVp and lower mA reduce the overall number of photons, decreasing scatter generation.

Secondary Protective Barriers and Apparel

Secondary protective barriers, such as lead-lined walls and ceilings, shield individuals from scattered and leakage radiation.

Protective apparel, including lead aprons, gloves, and thyroid shields, ensures the safety of personnel and patients during radiographic procedures. These measures are particularly important in high-scatter environments like fluoroscopy suites.

Scatter Radiation

To reduce scatter radiation during C-arm fluoroscopy, position the C-arm so that the x-ray tube is under the patient whenever possible.

Reduction of Repeat Examinations

Unnecessary repeats not only increase patient dose but also result in additional scatter.

Ensuring proper technique, patient positioning, and equipment calibration reduces the likelihood of retakes, contributing to lower overall scatter levels.