Theme 1 : Symposium Flashcards
Ionising radiation waves (3)
X-rays
Gamma rays
U/V light
What is the relationship between X-ray absorption and tissue?
Absorption proportional to density of tissue
State and Elaborate the 3 X-ray interactions
Transmitted- pass through unaffected/with a lower energy
Absorbed- transfer all energy to matter and not pass through the patient to the film
Scattered- diverted with or without energy loss
What are the strengths of radiography?
- Great spatial resolution- especially bone
- Cheap & available
- Easy interpretation
What are the weaknesses of radiography?
- Projectional
- Ionising radiation
- Very limited soft tissue visualisation
Explain and state the 2 types of resolutions in radiography
Contrast – differentiate between structures of different intensities
Spatial – ability to differentiate between 2 neighbouring structures
What are the weaknesses of computed tomography (CT)?
- Ionising radiation
- Limited soft tissue contrast – differentiation is difficult
What are the strengths of computed tomography (CT) ?
- Cross-sectional
- Spatial resolution
- Widely available
Non Ionising radiation (2)
Ultrasound and MRI
What are ultrasounds based on?
production and detection of echoes when probe is on patient
What are echoes?
Reflection of beam(s) and occurs at the interface between 2 materials
Attenuation
the amplitude and intensity of ultrasound waves - decreases as they travel through tissue
What are the interactions of ultrasounds?
Interactions the same as x rays + refraction
The More dense the tissue in ultrasounds…
= higher attenuation coefficient (dB/cm at 1MHz)
What are the strengths of ultrasounds?
- Non-ionising radiation
- Multiplanar
- Dynamic
- Doppler
What are the weaknesses of ultrasounds?
- Operator-dependent
- Can’t see through bone or gas
What are the strengths of Magnetic Resonance Imaging (MRI)?
- Non-ionising & Multiplanar
- Exquisite soft tissue contrast
- Reproducible & non-operator dependent
What are the weaknesses of Magnetic Resonance Imaging (MRI)?
- Limited availability - slow
- Magnetic field
- Some patients/equipment not suitable – checklist before MRI scan : Pacemaker,
- Intracranial aneurysm, clips will effect the MRI scan and therefore not suitable
- Expensive shielding
- Can be difficult to appreciate calcification or gas
State and elaborate the 3 conventional planes of MRI scans
- Axial (transverse) ‘bird’s eye view’ – back towards, front outwards
- Coronal (frontal) – patient facing towards you
- Sagittal (lateral) – front left back right
CT in chest drain insertion, what is it used for and how does the need travel to get to the target?
CT is used to guide lung biopsy
Needle travels through air to get to target
Ultrasound in chest drain insertion, what is it used for and how does the need travel to get to the target?
used to drain pleural effusions
Needle travels through fluid to get to target
Which aspect of the rib would you put your needle?
Inferior aspect of the space, top or bottom of the rib to avoid neurovascular bundle
