Imaging Flashcards
What is clinical imaging?
All the tests that doctors use to see things inside the body that they can’t see or feel from the outside
How are x-rays produced?
1) Electromagnetic radiation is produced by an electric source and directed at the patient
2) The waves pass through a tissues differentially depending on its density
3) Soft tissues lets some x-rays pass through, while cortical bone lets no x-rays pass through
4) X-ray film is blackened when hit by x-rays, so a picture is produced depending on what the x-rays have had to pass through
What are the strengths of x-rays?
1) Show things surrounded by black air e.g. lung cancer
2) Show things surrounded by white bone e.g. fractures
3) Show things that destroy white bone e.g. bone cancer
What are the limitation of x-rays?
1) To be visible on a simple x-ray, an abnormality must be of very different density to the tissue that surrounds it
2) A lot of pathology, especially that affecting soft tissue is of similar density to its surroundings and so isn’t shown on simple x-rays
3) X-rays are only fired from one direction and so they produce an image where all structures between the source and film are superimposed
What is meant by a contrast study?
An imaging procedure in which liquids containing dense element such as barium and iodine are injected to enhance x-rays, by making tissue outline visible
What are the benefits of using CT?
1) Better at distinguishing between tissues of similar density and often used to show soft tissue pathology
2) Superior contrast resolution compared to a radiograph
3) X-rays are fired from all around the body and processed by a computer to produce cross-sectional images with no superimposition
What are the limitations of using CT?
1) Give large doses of ionising radiation
2) Can’t distinguish between soft tissues of very similar density
3) Cannot resolve bone marrow disease
How are ultrasound images produced?
1) A transducer containing piezoelectric crystals sends out a beam of sound waves into the body
2) The sound waves are reflected back into the transducer by boundaries between tissues
3) The echoes generate electrical signals which are sent to the US scanner
4) Using the speed and sound of the echo’s return, the scanner calculates the distant from the transducer to the tissue boundary
5) These distances are used to generate 2D images of tissues and organs.
What are the benefits of taking an ultrasound?
1) High spatial resolution so useful in imaging MSK and soft tissue structures
2) Abnormal fluid collections are clearly shown
3) Quick, cheap, easy for patients
4) Completely safe
What are the limitations of ultrasound scanning?
1) US waves are blocked by bone, so can’t be used to look at the brain, spinal canal, inside joints or assess bone marrow
2) Gas blocks US, so windy patients and gas containing structures (lung and bowel) can’t be assessed
3) Patients with high BMI are very difficult to assess
Why is MRI safety important?
The following problems have been described:
- Frostbite and thermal burns
- Deafness
- Disturbance of surgical and non-surgical ferrous material
- Missile injuries
What are the clinical uses of MRI?
1) Medical diagnosis
2) To stage a known disease to inform treatment
3) To monitor the effects of a treatment and follow up a known disease
4) To aid intervention/deliver treatment e.g. image guided procedures
What is the significance of having piezoelectric crystals in an ultrasound transducer?
They are able to produce sound waves from an electric field and an electric field from sound waves.
What is the significance of the gel used in an ultrasound scan?
It keep air pockets from forming between the transducer and the skin which would block US waves from passing into the body.
What are the strengths of MRI?
1) Provide detail of spinal canal and brain
2) Allow interior of joints to be imaged
3) Allow assessment of acute muscle and tendon tears especially in deep tissues
