Lecture 15: medical imaging Flashcards
How does an x-ray work?
Photons produce x-rays. Some of these x-rays pass through a patient and that gets detected.
Image comes from the attenuated x-rays and that depends on material density and the energy of the beam.
Match the density shades to the materials…
- Black, dark grey, grey, light grey, white.
- soft tissue, metal, bone, air, fat
Black = air Dark grey = fat Grey = soft tissue Light grey = bone White = metal
After you take an x-ray you have to interpret it in order to see if there is a problem. What factors would you examine?
View (PA/AP/lateral) Obvious abnormalities quality of image comparison to past scans date/time/patient name ABCDE (chest: air, breathing, circulation, disability, everything else) ABDO (abdomen: air, bowel, densities, organs) MSK= fractures, bone abnormalities
For what reasons would you use an x-ray in a hospital?
View any abnormalities in the:
- chest: infection, chest pain, cancer, post procedures
- abdomen: pain, obstructions, perforation, tumours
- MSK: trauma, pain, deformities, oedema, dislocation, fractures
Compare the pros and cons of using an x-ray.
+quick to use
+cheap
+portable
+simple
- radiation exposure (low)
- only see 1 plane
- can’t see all pathology
- poor soft tissue imaging
How does fluoroscopy work?
Photons create x-rays.
These x-rays directed at patient in pulses or continuously. They are then detected based on material density and the energy beams.
The pulses/continuous beams allow a x-ray-like video to be created.
Contrast can be used to enhance images.
For what clinical reasons would you use fluoroscopy?
Vascular/angiography
GI
GU
MSK
Compare the pros and cons of fluoroscopy.
+ can see in live motion
+quick
- higher radiation dose
- radiation exposed to clinician as well
- one plane
- can’t see all pathology
- poor soft tissue imaging
How does a CT scan work?
X-rays (produced by photons) are projected from 1 side of rotating gantry (ring) and detectors on the opposite side. Patient moves through gantry and axial images produced based on x-ray attenuation.
When using computed tomography, what materials would produce lighter and darker shades?
What is the HU value based off?
Lighter= more attenuating= +ve HU = more dense materials (bone, metal)
Darker= less attenuating= -ve HU= less dense materials (air, soft tissue, fat, blood)
HU value is based off passing x-rays through water (which is 0HU).
What are the clinical uses of a CT?
Diagnosis
Further investigations
Management
Monitoring conditions
Pro and cons of using a CT.
+quick
+good spatial resolution
+can scan most body parts well
- radiation exposure (=1yr background radiation)
- lower contrast resolution
- image affected by artefact
- overused?
- contrast reactions (allergies, irritation)
- requires breath holding
What is ultrasound?
Use of soundwaves to produce an image based on how long it takes for echoes to return. More reflection (hyperechoic) = white Less reflection (hypoechoic) = black
Describe the process of performing an ultrasound.
- Transducer emits ultrasound waves towards the tissues
- Waves echo off the tissue.
- Based on the density and distance of structures, the reflection times will differ.
- A black and white image will be produced due to the reflected echoes being recorded.
Describe the use and aim of an ultrasound.
Most commonly used to view fetuses or any internal body structures to find/exclude a source of disease.
The use of ultrasound is quick and doesn’t involve any radiation so it is safer to use.
