Wed. Aug 21st, 2019

X-RAY MACHINE

medicaltechexpert

INTRODUCTION

X-rays were discovered by the German physicist Rontgen in November 1895, X-ray are electromagnetic waves of short wavelength in the range of 10A° to 0.02A° . It is used to visualize the internal anatomy of the human body .X-ray are the first electrical instrument used in the medical domains. X-ray can be used for both Diagnostic & therapeutic purpose.

BASIS OF DIAGNOSTIC RADIOLOGY

The main property of X-ray , which make them suitable for the purpose of medical diagnosis, are

  • Capability to penetrate matter
  • X-ray Can be observed depending upon the density through which they pass
  • Ability to produce luminescence (emit light ) and its effect on photographic emulsions.

DEFINITION / PRINCIPLE OF X-RAY

X-ray are produce whenever electrons collide at very high speed with matter and are thus suddenly stopped. X-ray are emitted when the fast moving electrods strike a target of high atomic weight

NATURE PROPERTIES OF X-RAY

  • Xray are electromagnetic radiations
  • It has shorter wavelength and in medical diagnostic region has the wavelength of the order  of 10-6 to 10ˉ10  m
  • They propagate with a speed of  3*10m/s
  • They are unaffected by electric and magnetic field
  • Electromagnetic radiation consist of photons and their interaction with matter causes energy exchange
E = hv = hc/λ

h- planks constant, c -velocity of photons, v -frequency of radiation , λ -wavelength

  • The wavelength of X-rays, directly depends on the voltage which is necessary for the production of radiation

PROPERTIES  OF X-RAYS

  • X rays are able to penetrate  several materials because of its shorter wavelength and extremely high energy
  • X-rays are observed when passing through matter
  • x-ray produce secondary radiation in all matter through, which day pass
  • secondary radiation is composed of
  • scattered radiation
  • characteristics radiation
  • Electrons

 x-ray produce ionization in gases.

It influences electric properties of liquids and solid

 x-ray produce fluorescence in certain material to help them emit light

 x ray affect photographic film

 They exhibit the phenomenon of reflection , refraction, interference, diffraction and polarization

 They are unaffected by electric and magnetic fields

 They have destructive effect on living tissue it is harmful to skin for longer  exposures

 X-ray  travels in straight line with velocity of light

X-RAY MACHINE/ X-RAY EQUIPMENT

Basic components of a Diagnostic x-ray machines are

  • power supply arrangement
  •  x ray  tube
  • Aluminium  filter
  • Collimator
  • bucky diaphragm
  • Lead shield

 The various components  in the machine are used to      

  1. Improve the quality of the image
  2. Increase the contrast between different tissues
  3. Improve  size resolution
  4. Minimise the dose of X-Rays.
block diagram of x-ray machine

Power Supply Arrangement:(X-ray machine subsystem)

      There are two parts of the circuit.

A) For producing high voltage and it is applied to the tubes anode and cathode and comprises a high voltage step-up transformer

It is followed by rectification

Current through the tube is measured by an mA meter.

Kv selector switch is to select differen anode voltage.

The voltage is measured with the help of a kV meter.

The time of exposure of X-rays and the duration f the application of Kv is controlled by exposure switch.

Main supply voltage (230v) variations can be compensated using a voltage compensator.

Second part of the circuit

B) Control of heating X-ray tube filament:

Filament is heated with 6-12v of AC supply and at a current of 3-5 amperes.As the tube current (mA) depends upon the filament temperature,the filament temperature control is attached to a mA selector.

  • High voltage generation:

Voltages in the range of 30-200 Kv are required for the production of X-rays for diagnostic purposes.These are generated by high voltage transformer.A high ratio step up transformer is used.Primary winding & secondary winding will be in the ratio of 1:500 respctively.

  • Self –rectified circuit(one pulse):

It is used in mobile and dental X-ray units.The maximum tube current for these mchine is about 100 Kv.

  • Full wave rectification X-ray circuit (two pulse):

It is used in medium and high capacity X-ray units.Most commonly used for diagnostic X-ray examination.

  • Three phase power for X-ray Generation:

It results in steady power to the X-ray tube instead of pulsating power.It reduces voltage ripple.It  increases the efficiency of X-ray production.

  • High frequency generators:

For producing high voltages,high frequency generators are used in modern X-ray machines.High frequencies varies from 500Hz-20kHz.It results in lower ripple in the output which increases its efficiency.

  • High tension cable:

A typical cable capacitance of high voltage cable is 130-230Pf/m.In high tension cable ,energy is delivered to the tube during non conducting period.

  • X-ray tube:

X-ray tube is an evacuated glass tube.X-ray tube is a vacuum diode consists of a cathode and an anode.Cathode block contains the filament which is a wounded helix of tungsten wire.Anode is the target which is made up of tungsten.Node is of two types-stationary anode and rotating anode type.Cooling arrangement is made for carrying the heat away from the tube.

Block diagram of x-ray subsystem

Aluminium Filters:

It absorbs lower X-ray frequencies.Thus the negative effects produced by low frequency is reduced and thereby increases the mage contrast.It confine the X-rays to the region of interest along with the collimator.

Collimator:

It is placed between Aluminium filter and the patient.Necessary shaping of X-ray beam can be done.Lamp and reflecting mirror adjustments make the medical attendant visible where the X-rays are striking on the patient.So that the beam can be positioned.

Bucky Grid:

Used to reduce scattered radiation.It is placed between the patient and film cassette.Used to improve the sharpness of the image.Various componenets of X-ray machine ar used to improve the quality of image.

  • Density or darkness
  • High contrast
  • sharpness

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