X-Ray, CT and PET Scan Flashcards Preview

CLINICAL PATHOLOGY > X-Ray, CT and PET Scan > Flashcards

Flashcards in X-Ray, CT and PET Scan Deck (48)
Loading flashcards...

What is ionising radiation? 

Ionising radiation is radiation that causes ionisation (esentially takes or add electrons off and become charged particles) when it interacts with matter 



Why do we use ionising radiation? 

Ionising radiation is used as they can penetrate through the body through different mediums/tissue) and be captured on our imaging detectors 


What are the two ways ionising radiation can act? 

  • Indirect action (radiation will break up water and produce free radicals) 
  • Direct action (directly impact DNA inside a cell) 


Describe the indirect action of ionising radiation 

  • Majority of our body is water 
  • Ionising radiation can break up water and result in the production of free radicals and hydrogen peroxide 
    • H• OH• HO2• H2O2
  • Free radicals are highly reactive and break down DNA 


Describe the direct action of ionising radiation 

Direct impact of the DNA inside our cells 


Direct effect of radiation damage 

  • Threshold effect (very high level of radiation exposure/ doses needed, beyond the threshold level, in order to see those effects) 
    • E.g Erythema and hair loss 


What are the indirect effects of radiation damage? 

  • Indirect effects can increase risk of the cancer induction 
  • Risk of genetic change in subsequent population 
  • Effect is proportional to radiation dose, no threshold 
    • All radiation has risk (the higher the radiation the higher the risk that radiation will cause cancer) 


What are positrons? 

Posotively charged electrons which interact with matter to create gamma rays 


How are positrons formed? 

They are emitted following the radioactive decay of an unstable nucleus 


What are positrons used in 

PET scanning (Positron Emission Tomography) 


What are gamma rays 

Are a type of penetrating electromagnetic radiation emitted following the radioactive decay of an unstable nucleus 


What are gamma rays used in? 

Gamma camera imaging e.g SPECT


What are X-rays? 

Spectrum of electcomagnetic radiation 


How are X-rays produced? 

They are produced artificially in an X-ray tube 


What are X-rays used in? 

X-ray imagine 

CT and radiographs 


What does X-ray attenuation mean? 

As the high-energy photons pass through material, their energy is decreasing

Essentially there is a reduction in the intensity of an X-ray beam as it traverses matter 


What factors affect attenuation? 

Attenuation increases with 

  • Higher atomic number 
  • Higher density 


What is used for transmission imaging and what is used for emission imaging? 

Transmission Imaging → X-Ray 

Emission Imaging → Gamma Rays 


What is transmission imaging? 

  • A patient will lie between an X-ray tube and detector 
  • Radiation will be directed through the patient 
  • A transmission map is collected (attenuation map) 
    • Maps all the tissues that either block the signal or not


  • Good at showing structure, especially between tissues of different densities or atomic number  


Describe emission imaging? 

  • Radiation is administered to the patient in the form of a tracer (radioactive material injected) 
  • Patient will emit radiation (e.g gamma rays)
  • These will be detected outside the patient 


What is an X-Ray tube composed of? 

  • Filament, Target (anode), tube (evacuated), Voltage difference between two terminals (filament and target) to accelarate electrons


How does an X-ray work? How are the X-rays produced? 

  1. A current will flow through a heating circuit which will cause electrons to be fired from the filament to the target (anode) 
  2. The electrons will accelerate through the voltage and hit the target (anode) 
  3. Upon hitting the target (metal tungsten), those electrons will produce a beam of X-rays 


How do we have the abillity to control X-rays? 

  • Operators can control the X-rays by changing the voltage setting 
    • X-rays are only produced when the tube is in action (can be switched on/off) 
  • High voltage and current can be used to control the amount and energy of X-rays produced 


What is the effect of X-ray on bone? 

Bone has a high atomic number and high density so therefore blocks most of the X-ray signal (high attenuation) hence appears white 

Soft tissue has a lower atomic number and lower density so therefore allows more X-rays through = blacker appearance 


Explain some uses of X-rays

  • Fractures 
  • Dental radiology 
  • Chest X-ray (look for pulmonary embolisms)
  • Mammography = X-ray of breast tissue 
    • Uses a compression plate to reduce breast thickness. Thinner breast tissue = better resolution 
    • Used to detect benign micro-calcifications, tumours 


What is fluoroscopy? 

Real-time X-ray 

A method of viewing the X-ray directly in real time (moving images of the interior of an object). e.g pumping of the heart, motion of swallowing 

Can be used for coronary angiographies to identify areas of stenosis and occlusion 


How does fluoroscopy work? 

  1. A catheter will be fed inside an artery for example and radio opaque dye is injected 
  2. This will show blood flow inside vessels 
  3. A radiologist will inject dye with a high atomic number int the patient and can be seen more visually using X-rays 


What are the limitations of planar X-ray? 

  • Cannot distinguish between overlying tissues 
    • E.g skull and below 
  • Tissues other than those being observed can reduce contrast in the image
  • Historically partially solved by moving the film cassette and X-ray relative to the patient to blur out overlying tissues called 'tomography'
  • Superseded by Computed Axial Tomography (now abbreviated to CT) 


Why does CT supersede X-ray? 

The CT scan is an X-ray image, but you can decipher all different tissues within the image 


What are the key elements of a CT scanner? 

  • X-ray tube 
  • Detectors (transmission image) 
  • Aperture/ Bore (where patient sits) 
  • Fan beam (rotates around the patient) 
  1. Patient will go into the CT scanner 
  2. When positioned the X-ray tube will rotate around the patient in order to derive slices through the patient while the patient bed slowly moves through the gantry 
  3. Has the abillity to show us 3D slices 

Decks in CLINICAL PATHOLOGY Class (52):