Radiology - Image is Everything Flashcards
Intro to role of clinical imaging
What is imaging?
Tests done by doctors to see things that can’t been seen or felt from outside
What 3 types of X-ray are there?
Plain radiography, contrast studies (eg barium enema, arthrography) and computed tomography (CT)
What are X-rays?
Electromagnetic radiation produced by an electrical source that passes through body tissue (degree of dependency on the tissue density)
In X-ray what heats the filament cathode and what happens?
Electric current heats the cathode leading to electrons being emitted and striking the anode
What happens to newly generated X-rays?
Exit the window in casing and a beam is collimated. The X-rays penetrate the patient and scatter
What % of X-rays reach the film?
Only 1% of X-rays contribute to the image
What are the problems with an X-ray sensitive screen and film?
Over and under exposure are common (need to redo scan) and films may go missing
What is PACS?
Picture Archiving Communications Systems
What are the benefits of PACS?
Easier storage, access and retrieval of digital images (x-ray, CT etc)
How does density affect passing of X-rays?
Denser the tissue, fewer x-rays pass. Air lets all X-rays pass. Soft tissue lets some x-rays pass whilst cortical bone lets no x-rays through
What colour is the film where x-rays hit?
Black
What are the 3 main x-ray strengths?
Good at showing things surrounded by (black) air (eg lung cancer), good at showing things surrounded by (white) bone (fractures) and showing things that destroy (white) bone (eg bone cancer)
What are x-rays’ main weaknesses?
To be visible on x-ray an abnormality must have a differing density to its surrounding tissue
How do contrast studies work?
Liquids containing dense elements (eg barium or iodine) can block x-rays so by putting these in spaces between tissue the tissue outlines become visible
What are the dangers of x-ray?
The radiation can damage cell DNA leading to mutations which can cause cell death or turn it cancerous. (risk is related to the x-ray dose)
How does CT overcome the density issue of radiographs?
They are more able to distinguish between differing tissue density and often used to show soft tissue pathology. It has a superior contrast resolution in comparison to a radiograph.
Why are radiographs not sufficient to diagnose illness?
With radiographs the x-rays only come from one direction and so in the image, all structures between the x-ray source and the film are superimposed (ie it is hard to make out what is what let alone determine abnormalities)
How does CT overcome the superimposition issue of radiographs?
In a CT the x-rays are fired from all around the body and the processed by a computer (which gives a set of cross-sectional pictures) = no superimposition
What are the problems with CT?
Gives larges doses of ionising radiation AND soft tissues of very similar density cannot be distinguished (pelvic organs, muscles and tendons, joint cartilage and ligaments, some areas of the brain) AND it cannot resolve bone marrow disease
How does ultrasound and MRI solve the issues of x-ray?
neither use ionising radiation, both can show pelvic muscle and muscles and tendons. MRI can show joints, bone marrow disease and all areas of the brain. US is quick and easy, safe and doesn’t require a £1.5million scanner.
In US what converts electrical energy to acoustic energy?
piezoelectric crystals
Where are piezoelectric crystals housed?
In a transducer which has an electrical supply
What does the transducer in US produce?
Pulses of sound waves
What is used to help sound transmission into the body in US?
The skin being coated with jelly
How do different body tissues differ in acoustic properties?
Some transmit sound whilst others tend to reflect it
What is the role of the transducer in US?
Alternately transmits sound pulses and then listens for reflected sound returning. The returning acoustic energy is converted into an electrical impulse and fed into a computer
How does the computer ‘know’ where sound comes from in US?
By the time taken for it to return to the transducer. (it uses this to create a cross-sectional picture of soft tissue invisible to x-ray)
What is the diagnostic advantage to US?
It is done in real time, with the sonographer able to get a complete survey, and the diagnosis can be made during the scan
What 5 things make a good ultrasound exam?
Tissues that allow good transmission, lots of sound that reaches the target and returns to the transducer, tissues which have different acoustic properties, a well trained/experienced sonographer and modern equipment .
What 4 things help sound reach the target and return to the transducer?
Good skin/transducer contact, superficial structures, slim patients and correct transducer selection
What 5 things make a poor ultrasound exam?
Tissues that prevent sound transmission (eg gas/bone), sound can’t reach target or return to the transducer, tissues with identical acoustic properties, an incompetent operator and antique equipment
Why is US useful in imaging musculoskeletal soft tissue structures?
It has high spatial resolution.
How do different states affect US?
Body fluids readily transmit US whereas solid structures reflect US
Are abnormal tissue fluid collections well shown or badly shown? Why?
Well shown, as the surrounding tissues reflect more sound and so contrast with the black fluid.
Name 4 examples of abnormal tissues fluid collections
Pleural effusion, ascites, abcess, cysts
Why are US commonly used to identify soft tissue tumours?
Soft tissues with different acoustic properties are well differentiated.
What is the issue with US in relation to bone?
Bone blocks US so it can’t see the brain (skull), spinal canal, inside joints or assess bone marrow
What is the issue with US in relation to gas?
Gas blocks US so ‘windy’ patients are difficult to assess and structures containing gas, eg lungs and bowel, can’t be assessed.
Why are fat patients difficult to assess in US?
There is more body tissue for the waves from the transducer to travel through.
What does an MRI scanner create?
A strong magnetic field which is maximal inside the bore (tube of the scanner)
What is the magnetic field in the scanner in comparison to earth’s?
Earth’s is 0.0001 Tesla, the clinical field’s can reach 3T
In MRI what does the magnetic field result from?
Electrical current passed through coiled metal wire surrounding the bore.
What does the magnetic field in MRI rely on?
Superconductivity of current which occurs at low temperatures
What maintains the low temperatures required for MRI?
Liquid helium
How does the scanner produce the magnetic field in MRI?
It produces a burst of radio signal (RF pulse) which energises the body’s protons
After the production of RF pulses in MRI what happens?
The scanner waits and listens for a return signal, which is produced by the body’s protons.
What is the amount of signal produced by the body’s protons dependent on?
The molecular environment of the protons
What does the computer do with signals received in MRI?
Some ‘amazingly complex’ calculations and creates an image
What are 4 main issues with the MRI scanners?
Frostbite and thermal burns, deafness, disturbance of surgical and non-surgical ferrous materials and missile injuries
What ferrous materials can be disturbed in an MRI scanner?
Pacemakers, heart valves and mobile ferrous material eg shrapnel or intra-ocular foreign body (such as material ending up in the eye after an accident)
What 2 things can be done to help prevent patient injury?
Request card safety questionnaire and the removal of all ferrous metal (dental plates, earrings, belly button studs, belts, keys etc)
How can staff stay safe?
Security keypad lock at MRI suite entrance, all staff are vetted before entry to MRI suite is allowed, only approved staff (incl. cleaners, engineers and anaesthetists) are allowed entry and all staff must remove watches, credit cards and metal keys etc before entering
What are the 3 main strengths of the MRI scanner?
A sensitive way to assess acute muscle and tendon tears (especially in deep tissue), it provides excellent detail of spinal canal disease and allows the interior of joints to be imaged (can see ligament/cartilage injuries)
What are the 5 major weaknesses of MRI?
Expensive, can harm some patients, some patients find it too claustrophobic, time consuming (restless, in pain, unstable patients can’t be scanned) and MRI is poor at showing the detail of the lungs
What are some of the roles of imaging?
To help make or confirm a diagnosis, help narrow a differential diagnosis, to stage a known disease (eg cancer), to monitor effects of treatment and follow up on a known disease, aid intervention/deliver treatment
