Diagnostic methods in medicine

Diagnostic methods in medicine

1. Radionuclides

   • Used to diagnose/detect growth
   • Must have a short half life
     • So it doesn't stay in patients body for long and will soon decay away.
     • Only a small amount is needed to form an image
     • Not too short
       • Transport issues
         • It would decay away before it even reached the patient
       • So it is made in the hospital
         • Radioisotope kept in metastable state
         • Another radioisotope is kept to produce the tracer
   • Must not be alpha or beta
     • They are least penetrating and most ionising
     • Must be gamma
       • Must be converted into radiopharmaceutical
         • A.K.A tracers
           • E.g. Iodine 123
             • For function of the thyroid gland and kidneys

2. Gamma Camera

   • Detects gamma photons from inside a patient
   • has collimator
     • Scinitillator
       • Photomultiplier tubes
         • 3. Photomultiplier tubes produce an electric pulse for each photon of light they receive
       • Made of sodium iodide
       • 2. Gamma photons hit this and produce flashes of visible light
         • Only about 10% of gamma photon energy converted to light
         • 4. Incident gamma photon strikes scintillator, a light photon releases a single electron by the photocathode and by the photoelectric effect.
           • 5. Electron then accelerated and releases 2 or 3 secondary electrons on impact
             • 6. 4 and 5 repeated until avalanche of electrons, electrical pulse is given at last electrode
               • 7. Electrical signals by photomultiplier analysed by computer and image formed
     • 1. Gamma photons pass upwards through collimator
       • This cuts out any gamma rays travelling at an angle
   • Used for bone scans

3. PET scanning

   • A beta plus emitter put into patient
     • Emits positron
       • Annihilates with electron
         • Emits 2 perpendicular gamma rays
           • They hit detectors
             • time taken to hit measured and position found
               • Image formed by computer

4. MRI scans

   • Uses Precession
     • It's the rotation or gyration action
       • Acting 90 degrees to any other force acting on the object
     • On nuclei
     • The magnetic axis rotates around the direction of the external field
     • Presssion has larmor frequency
       • w(0) = gyometric ratio and magnetic flux density of the magnetic field
         • To find requency make w() = 2pi f and rearrange
           • f = gymoetricratio x magnetic flux density/ 2pi
   • Atoms put into a magnetic field, causes them to line up
     • Some line up the other way
       • They are in a high energy state
         • Aim is to get every nuclei into this state
           • Radio frequency pulse used
             • To bring atoms to resonance
             • Switched on an off
               • Brings them into their higher energy state and back
                 • energy emitted is measured in form of radio frequency waves
                   • rate of relaxation is also measured
                     • Follows exponential decay
                     • Have 2 relaxation times
                       • T(1) Spin lattice relaxation time
                         • Energy of spinning nuclei transferred to surrounding lattice of nearby atoms
                       • T(2) Spin-spin relaxation time
                         • Energy transferred to other spinning nuclei
                       • Cancerous tissues have intermediate relaxation times
                       • Fatty tissues have millisecond times
                       • Water and watery tissues have several seconds
   • Have an RF receiving and emitting coils
   • Have longitudal gradient coil
     • Magnetic field varies across patients body
       • Only small part of body measured then
         • Has superconducting magnet and patient lying on the bed
   • Have computer
   • No isonising radiation = no hazards
     • No moving mechanisms just magnetic fields
       • Patient feels nothing
         • Better soft tissues scan then CAT
           • 3D images made
             • Any metallic objects like pacemakers are affected
               • People with Pacemakers cannot undergo mri scan