X-rays & ECGs

X-rays & ECGs

1. X-rays

   • Using X-Rays
     • Fluoroscopy
       • Used to show if Organs are working
         • E.g To detect blocked blood vessels movement gastrointestinal tract
       • Process
         • Placing a paitent between a X-ray source and fluorescent screen
           • Different amounts of X-rays are absorbed
             • The intensity when it reaches the screen depends on what is has passed through and how much has been absorbed
               • The X-rays hit the screen and fluoresces (gives off light)
                 • Image seen is due to the different intensites of the X-rays
                   • The higher the intensity from the source the brighter the screen
                     • Image intensifiers are used so a smaller dosage of X-rays can be given
                       • Contrast Mediums are given to improve contrast by 'enhancing' the soft tissue
     • CAT scans
       • Computerised axial tomography makes a '2-d slice' of the body
         • Can also make '3-d slices' of the body
       • X-ray beam rotates around the body
         • Picked up by detectors
           • Computer makes a high-quality image based on the No. of absorbed X-rays
             • Useful when diagnosing less obvious problems
       • Often used to diagnose cancers
     • Risks and Benefits
       • No need for surgery
       • Radiation dose is equivalent to 10 years of backround radiation
         • Not recomended for pregnant women or children
   • A type of Ionising Radiation
     • Medical uses of Radiation
   • X-ray machines
     • Evacuated Tube with 2 Electrodes
       • - Electrode (Cathode) acts as the filiment
         • This is heated, giving energy to the Electrons
           • Once the Electrons have enough energy they 'boil off'
             • This is called 'Thermionic Emission'
               • Thermionic emission is releasing electrons from a surface
             • The Electrons accelerate towards the anode (+) by a potential difference
               • These Electron beams are used to make X-rays
                 • When the Electrons collide with a metal target (anode)
                   • Some of the kinetic energy is converted into X-rays
     • If temp increases, the number of electrons emitted increases
   • Kinetic energy calculations
     • I = n x q
       • I = current in amps (a)
       • N = No. of particles flowing per sec
       • q = Charge on each particle (colombs C)
     • K.E = 1⁄2 × mass × velocity2
       • mass in kg velocity in m/s
     • K.E = Electronic Charge x accelarating potential difference
       • Electronic Charge = e Accelerating potential difference = V
       • K.E = 1⁄2 × mass × velocity2 = e x V
         • All sides equal
     • Electronic Charge = 1.6 x 10(-16)

2. ECGs

   • Electrocardiographs
   • Shows graph of heart electrical signals
   • Electrocardiogram
   • Graph of heart electrical signals
     • P = Contraction of Atria
     • QRS = Contraction of Ventricles
       • Also relaxation of Atria
     • T = Relaxation of Ventricles
     • Frequency f = 1/ time s
   • Triggered by potential difference between the inside & outside of cell
     • Changes from -70mV to +40mV
       • Increase is called 'action potential'
         • Action potential passes down the length of the cell making the heart contract

3. Pulse Oximetry

   • Uses light to check the % of Oxygen in the blood
   • A transmitter emits two beams of light (Red & Infrared)
     • Photo (light) detector on opposite side detects light
       • The relative absorption of light by Oxyhaemoglobin (HbO) adn reduced haemoglobin is processed by a device
         • Device works out how much Oxygen is in the blood

4. Pacemaker

   • Naturally a group of cells on the wall of the right atrium which controls heartbeat.
   • Sometimes heart cannot produce necessary signals
     • Isn't fast enough Pulses irregularly Other problems
     • A device used to regulate heatbeat
       • Fitted with minor surgery but needs batteries to be powered
         • Modern pacemakers can be programmed externally
           • Can measure breathing and temp and adjust heart rate to match the activity

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