P3-Topic 2 X-rays & ECG's

P3-Topic 2 X-rays & ECG's

1. X-rays are electromagnetic waves with very short wavelengths

   • We can use them to produce images of the bones and organs within the human body
   • They have very high frequencies and are highly ionising

2. Using X - Rays

   • Inverse Square Law: Area increases with square distance so intensity decreases with the square
   • In a CAT scanner an X-ray source is used to produce a three dimensional image of the intrenal structure of a patient
   • Fluoroscopes use x-ray images on a screen. These allow doctors to see a real time image of a patients internal condition

3. ECG's & Pulse Oximetry

   • The heart beats is cused by nodes which send action potentials that cause the heart to contract
     • An action potential is an electrical signal that contracts the heart muscles
       • Action potentials can be detected on the surface on the skin because we are made out of ions and so we conduct electriciy
         • The three main electrical potentials are:
           • P wave – de-polarisation of the atria (upper heart chambers)
           • QRS wave – de-polarisation of the ventricles (lower, larger heart chambers)
           • T wave – re-polarisation of the ventricles
     • A pace maker is used to monitor the heart and detect irregular heart beats.
       • If an irregular heart b eat is detected, the pacemaker produces electrical signals to correct the heartbeat
     • F = 1/T
       • F = frequency (hertz, Hz ) and T = time period (seconds, s)
   • A pulse oximeter works by detecting a change in the red and infrared light
     • They are attached to fingers because the detectors are fairly close and fingers are relitively thin
     • There are 2 light sources. One is visible light and the other is infrared
       • 2 LED's are needed in a pulse oximeter because one is absorbing LED light and the other is absorbing the infrared

4. X-Ray Machines

   • An X-ray machine consists of an evacuated tube that contains 2 electodes
     • The tube is evacuated so that electrons do not collide with other particles
     • The negative electrode (cathode) is a wire filament.
       • When it is heated to a certain point the cathode emits a beam of electrons in a particular direction. This is called THERMONIONIC EMISSION
     • The other is a positive electrode (anode).
       • When there is a large potential difference between the anode and the cathode, the electons are excelerated towards the anode
         • There will also be more electrons which will make more x-rays

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