Imaging

Question 1

X-ray

Answer 1

– produced within the x-ray machine. No external radioactive material is involved.

X-ray beam:
– x-rays travel in straight lines and a beam of x-rays diverges from its source
– structures the beam hits first will be magnified in relation to those which are nearer the detector
– move further away to reduce magnification
– closer to study in more detail

Bone absorbs most the radiation and appears white. causing the least exposure to the digital screen
– air absorbs the least radiation, causing maximum exposure and appearing as black

useful for:
- chest
– abdomen
– skeletal system
– looking at fracture healing

– anteriorposterior (AP)
– lateral (chest x-ray just AP to reduce heart magnification)

Fluoroscopy:
– when continuous low power x-ray beam is passed through the patient to produce dynamic images as they are happening
—- GI tract, ateriography

Dangers of X-ray radiation:
– there is no safe dose limit
– some areas of the body are more at risk than others
—- GI radiation 20 times more likely to end up in fatal cancer than over the bone

x-rays may cause alteration of cellular division and other intracellular processes and are therefore potentially harmful to the human body
– radiation exposure to reproductive organs poses more risk
– children are more radiosensitive than adults
– irradiation to a foetus should be avoided wherever possible

Question 2

CT scan

Answer 2

Computerised tomography scan
– sometimes referred to as a CAT scan

• an x-ray and a computer create detailed images of the inside of the body
• can produce detailed images of many structures inside the body, including the internal organs, blood vessels and bones
• x-ray source rotates around the patient

Advantages:
– can be undertaken without any damage to metal implants
– bony structures imaged more clearly and more detailed
– rapid examination- very quick so valuable for really ill patients, less need to hold your breath
– lower costs than MRI
– CT scan is very quick compared to MRI

Disadvantages:
– uses x-radiation to produce images, ionising radiation is classed as a carcinogen, small risk as low dose
– less soft tissue detail than MRI scans

Question 3

MRI (magnetic resonance imaging)

Answer 3

Produces images of the body by utilising the magnetic properties of certain nuclei in the body

The high intensity magnetic field displaces the nuclei from their position, when they return the nuclei release energy

Useful for:
– brain and spinal imaging
– internal derangement of joints
– primary soft tissue and bone tumours
– acute and chronic soft tissue injuries to tendons, ligaments and muscles
– osteomyelitis and soft tissue infection

Advantages:
– no documented side effects of MRI imaging
– soft tissues pictured in more detail than a CT scan

Disadvantages:
– time taken for MRI much longer than CT
– higher cost than CT scan
– patient may need to hold breath for short periods during imaging
– patients with metal implants or certain medical devices are not able to undergo an MRI imagine because of magnetic field pulses

Question 4

Ultrasound

Answer 4

Utilises high frequency waves to produce images of soft tissue

Ultrasound waves are transmitted from the transducer into the soft tissues

A coupling gel is required on the skin surface to make good contact

Visualisation of soft tissues is dependant on the differences in acoustic impedance of tissues and organisation of the connective tissues

Uses:
– imaging of neonatal birth
– monitoring pregnancy, uterus and ovaries
– visualises liver, gall bladder, pancreas, kidneys etc
– assesses thyroid, testes and soft tissue lesions
– confirms pleural effusions and pleural masses
– identification of joint effusions and synovitis

Advantages:
– low cost compared to MRI
– high resolution soft tissue imagining, however poor imagine of bone
– good extra articular visualisation
– portable examination possible (MRI or CT scan are not portable)
– can easily compare the contralateral joint (MRI required additional costs)
– can image dynamically-move the body part during examination (MRI and CT scan you need to be still)

Disadvantages:
– limited intra articular visualisation
– cannot image through air filled spaces (whereas MRI can image through air)