Radiography (x-ray)

• Introduction
• Parts of X-ray machine
• Views of X-ray
• Parameters
• X-ray absorption and object density
• Mechanism

Introduction

X-rays are electromagnetic waves produced in x-ray tube. Healthcare persons should call it as films, images or radiographs, but not x-ray. Direction of X-ray beam determines radiographic views include AP, PA, Oblique and Lateral.

Parts of x-ray machine

1. Operating console

   It provides controls for radiology technician to adjust machine before taking x-ray.

2. High frequency generator

   It powers the x-ray tube for generating x-ray.

3. X-ray tube

   It is vacuum diode which consists cathode and anode. Electron passes from cathode to anode produces electromagnetic wave of x-ray. This x-ray beam passes into the body and then to the cassette.

4. Radiographic cassette

   It is placed in one side of the body and x-ray tube is position another side of the body, like in the image. Cassette holds x-ray film. It receives x-ray waves that were not absorbed by the body parts.

Views of x-ray

• PA view

  X-ray beam travels from posterior to anterior as it traverses anatomic site. Example, chest x-ray PA view – x-ray tube is placed posterior side of the chest and cassette is placed in front of the chest.

  
• AP view

  X-ray beam passes through anatomic site from anterior to posterior. Portable X-ray machines use AP view. It is commonly used when the patient cant shifted to radiology department. Example, AP view of chest x-ray – The tube is in front of the chest and the cassette is placed in back side of the chest.

  
• Lateral view

  X-ray beam travels from side to side. In this method, the x-ray tube will be on one side and the cassette will be on another side.

  

Parameters

• Tube potential (kVp)

  Power and strength of x-ray beam (quality of x-ray).

• Tube intensity (Ma)

  Number of photons generated in x-ray beam (quantity of x-ray)

• Exposurre time (S)

  Time duration for preset x-ray beam.

• Focus to detector distance (Cm)

X-ray absorption and object density

X-Ray absorption is directly proportion with density of object. When object’s density increases, X-ray absorption will increase results in white appearance in the x-ray film.

There are black, grey and white colors in x-ray film and these are determined by objects density. Following are the density and color of object in the film,

• Air – black
• Fat – black (slightly less black than the air)
• Bone – white
• Metal – white
• Calcium – white
• Organs, muscles, tissues – shades of grey.

Mechanism

X-ray beam passed through the anatomic structure, some of rays absorbed in the structures (will not reach the x-ray cassette) will appear white and non-absorbed rays reach the cassette will appear as black in color. In simple words, x-ray film turns black when x-ray interacts with the film and stays white when x-ray absorbed by the body part.

1. Carol A. Boles, MD, William E. Erkonen, MD et al., Radiology - the basics and fundamentals of imaging., fourth edition.
2. Sutton D., textbook of radiology.
3. Michael Y.M. chen et al., Basic radiology., second edition.

Creator Details

Name	:	Deva senathipathi
Qualifications	:	Physiotherapist