Radiology 1: Intro to Clinical Imaging Flashcards
Give some benefits of digital x-ray recording over manual
- Post exposure manipulation reduced the need for repeated exposures
- Films won’t go missing
- Films easily shared with relevant people (national database)
Describe the production of an x-ray image
x-rays are produced
The beam passes through the patient
The intensity of the x-rays incident of the is recorded
Describe the relationship between tissue density and x-ray transmission
The denser the tissue, the fewer x-rays are transmitted
The less dense the tissue, the more x-rays are transmitted
Describe the effect incident x-rays have on the x-ray film
Incident x-rays turn the x-ray film black
More x-rays –> More black
Less x-rays –> Lighter
Describe the proportion x-rays that are transmitted through:
Air, soft tissue, cortical bone
Air - all x-rays (nearly)
Soft tissue - some
Cortical bone - none
Describe the strengths of x-rays, and give an example of its use
They show denser objects surrounded by air very well
e.g.
Tumours or fluid in the lungs
They show less dense areas surrounded by very dense areas well
e.g.
A bone fracture, bone cancer
Describe a the major weakness of an x-ray image
Give an application of this weakness
To be visible and distinguishable on an x-ray image the structures must be of significantly different density
e.g. soft tissues are imaged very poorly
Describe what is meant by a contrast study
Where a liquid containing dense elements is applied between tissues, or inside tissues allowing them to become visible to x-rays
Give 2 examples of contrast studies
Enemas and arthrograms
Describe the danger of x-rays to the patient and operators
The radiation can damage cell DNA causing mutations, leading to cell death or cancer
How can the risk to patients from x-rays be minimised?
By minimising the dose
Make sure the benefit outweigh the risk
Describe how a CT image is taken
Same as an x-ray image, except that x-rays are fired from all around the body
Describe another weakness of an x-ray image
As the x-rays come from 1 direction structure are superimposed
Describe the main benefit of CT over x-ray images
CT images do not have superimposition as x-ray images do
Of CT and x-rays which has a greater contrast resolution
CT
Describe the sort of view provided by a CT scan
Cross-sectional
What is the main negative of a CT scan over an x-ray
CT scans give far greater doses of ionising radiation
Give a weakness of CT scans
Can’t distinguish between soft tissues of very similar densities
e.g.pelvic organs, muscles & tendons
In an US (Ultrasound) scan what produces the pulses of sound waves
The transducer
Why is jelly applied to the skin for US scans
To assist with the transmission of sound into the body
How does an ultrasound scan work?
The transducer emits pulses of sound
The returning sound is detected and fed to a computer
How is the US image produced?
The time taken for the sound to return to the transducer is used to build a cross-sectional image
What type of tissue does US image best
Soft tissues
What are the ideal conditions for a US scan?
Lots of sound reaches and returns from the tissue:
good skin contact, little fat (slim patient), the viewed structure is superficial
Tissues with different acoustic properties are being viewed
What is a US scan good for viewing?
Solid structures surrounded by fluid
Tendons and muscles
Abnormal fluid collections
Tissues with different acoustic properties (e.g. soft tissue tumours)
Describe the weaknesses of US scans
- They can see past bone as it reflects the sound back
e. g. can’t see the brain, or bone marrow - Fat patients are harder to image
- Gas blocks US, gas containing structure can’t be assessed
e. g. can’t see lungs or bowel
How does a MRI scan work?
The scanner produces radio waves that effect the body’s protons
The scanner then detects a signal from the protons
From this an image is produced
Describe why an MRI scan can be dangerous
It is loud
Its magnetism can move certain metals causing:
- Projectiles
- Damage to internal tissue from internal metals (e.g. shrapnel)
How long do MRI scans take?
A long time (25-60mins)
Describe the strengths of MRI scans
Very good at imaging the brain
Can accurately asses muscle and tendon tears
(especially in deep tissue where US is less accurate)
Great detail of spinal canal disease
Great for imaging the interior of joints
Describe the weaknesses of MRI scans
Expensive
Potentially dangerous
Takes a long time (bad for those who need monitoring or are unstable)
Some find it claustrophobic
Describe the roles of clinical imaging
Help make/confirm differential diagnosis
To stage a diseases progression
To monitor treatments effectiveness
Name a region that MRI images poorly
The lungs
What is an image guided procedure?
A procedure where the surgeon is guided by imaging
