IMAGING

Question 1

TYPES OF IMAGING

Answer 1

• X-ray
• Computed Axial Tomography (CAT SCAN or CT)
• Magnetic Resonance Imaging (MRI)
• Ultrasound

Question 2

X-RAYS

Answer 2

• X-rays are produced within the x-ray machine
• No external radioactive material is involved
• Radiographers can change the current and voltage settings on the x-ray machine in order to manipulate the properties of the x-ray beam produced
• Different x-ray beam spectra are applied to different body parts
• The image is produced by x-rays passing through the patient to a digital screen below

Question 3

X-RAY BEAM

Answer 3

• X-rays travel in straight lines and a beam of x-rays diverges from its source
• Structured the beam hits first will be magnified in relation to those which are nearer the detector
• To reduce magnification the x-ray source can be moved further away from the subject
• Structures that need to be measured accurately should be placed closer to the detector

Question 4

WHAT ARE X-RAYS USEFUL FOR?

Answer 4

o Chest
o Abdomen
o Skeletal system
 Trauma
 Spine
 Joints
 Degenerative
 Metabolic
 Metastic
o Assessment of fracture healing

Question 5

HOW DO X-RAYS WORK?

Answer 5

• Bone absorbs most radiation, causing least exposure to the digital screen. Displayed as white on the image
• Air absorbs least radiation, causing maximum exposure, so the image appears black
• Between these 2 extremes, a large differential tissue absorption results in a grey scale image

Question 6

WHAT ARE THE 2 ANGLES X-RAYS ARE USUALLY TAKEN FROM?

Answer 6

Anteroposterior AP and lateral

Question 7

FLUROSCOPY/SCREENING

Answer 7

• Fluoroscopy is the term used when a continuous low power x-ray beam is passed through the patient to produce dynamic images on a television monitor
• Many different procedures, such as barium studies of the gastrointestinal tract, arteriography and interventional procedures are monitored and carried out with the aid of fluoroscopy

Question 8

DANGERS OF X-RADIATION

Answer 8

• There is no ‘safe dose limit’ pf radiation
• All doses of radiation carry some risk
• The greater the dose, the greater the risk

Question 9

X-RAY SAFETY

Answer 9

• Referrers for radiological investigations are required to provide sound clinical reasons to justify exposing patients to radiation
• Local rules of the x-ray department must be adhered to
• All x-rays may cause alteration of cellular division and other intracellular processes and are therefore potentially harmful to the human body
• For this reason all medical exposure to radiation should be justified in terms of risk to benefit ration

Question 10

CT SCAN

Answer 10

• A computerised tomography (CT) scan uses x-rays and a computer to create detailed images of the inside of the body
• They are sometimes referred to as CAT scans
• They can produce detailed images of many structures inside the body, including the internal organs, blood vessels and bones
• The x-ray source rotates around the patient

Question 11

ADVANTAGES OF CT SCANNING

Answer 11

• CT scan can be undertaken without any damage to metal implants
• Bony structures imaged more clearly and detailed
• Rapid examination technique, so valuable for ill patients, less need to hold your breath
• Lower cost than MRI scans
• CT is very quick compared to MRI

Question 12

DISADVANTAGES OF CT SCANNING

Answer 12

• Used 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 13

MRI

Answer 13

• Magnetic resonance scanning produces images of the body by utilising the magnetic properties of certain nuclei in the body
• The patient is positioned in the scanner surrounded by a large magnet
• The high intensity magnetic field displaces the nuclei from their position, when they return the nuclei releases energy
• Computer analysis processes the energy signals to a grey scale image
• Pathological tissue returns different signals compared to normal

Question 14

WHAT IS MRI USEFUL FOR?

Answer 14

• MRI is useful for brain and spinal imaging and internal derangement of joints
• Primary soft tissue and bone tumours
• Acute and chronic soft tissue injured to tendon, ligaments and muscle
• Osteomyelitis and soft tissue infection

Question 15

ADVANTAGES OF MRI

Answer 15

• No documented side effects of MRI
• Soft tissues pictured in more detail than CT

Question 16

DISADVANTAGES OF MRI

Answer 16

• Patients with metal implants and certain medical devices are not able to undergo MRI imaging because of magnetic field pulses
• Time taken for MRI is much linger than CT
• Higher cost than CT
• Pt may need to hold breath for short periods of time during imaging

Question 17

ULTRASOUND

Answer 17

• Ultrasound (US) utilises high frequency sound waves to produce images of soft tissue
• The US waves are transmitted from the US probe/transducer into the soft tissues
• A coupling gel is required on the skin surface to make good contact
• Visualisation of soft tissues is dependent on the differences in acoustic impedance of tissues and organisation of the connective tissues

Question 18

SOME USES FOR ULTRASOUND

Answer 18

• Imaging of neonatal brain (through anterior fontanelle)
• Confirms pleural effusions and pleural masses
• Visualises liver, gall bladder, pancreas, kidneys etc
• Useful in monitoring pregnancy; uterus and ovaries
• Assesses thyroid, testes and soft tissue lesions
• Identification of joint effusions and synovitis

Question 19

ADVANTAGES OF ULTRASOUND

Answer 19

• Low cost compared to MRI
• High resolution soft tissue imaging, but poor imaging of bone, sound waves do not pass through bone
• Good extra articular visualisation (same as MRI)
• Portable examination possible (MRI not portable)
• Can easily compare contralateral joint (MRI requires additional cost)
• Can image dynamically-move the body part during examination (not possible with MRI)

Question 20

DISADVANTAGES OF ULTRASOUND

Answer 20

• Limited intra articular visualisation
• Cannot image through air filled spaces (whereas MRI can image through air)