Indications for x-ray
- Trauma (# or disloc.)
- Infective processes (pneumonia etc.)
- Skeletal survey (malignancies or disorders of bine growth)
- Follow-up after treatment
Advantages (x-rays)
- Easily accessible
- Quick
- Doesn’t require specialized ax
- Inexpensive
- Bed side
Disadvantages (x-rays)
- 2 dimensional image or 3 dimensional structure (overlapping of structures)
- Ionising radiation (risk of malignancy)
- Caution in pregnant pts (fetus is susceptible to ionizing radiation - risk of malignancy)
Conventional Radiography (x-rays)
- X-rays are a form of energy
- Electromagnetic spectrum
- 2 dimen of 3 dimen structure.
Ultrasound
- Shooting beam of high frequency sound into a soft tissue
- Sound returns to same probe which sent it
- Various tissues bounce signal back creating the image
- Sound wave can’t travel well in the air therefore gel is used to reduce air btw probe & pt - reduces reflect & acoustic impedance for clear pic
Ultrasound
- Curved probes: lower frequency & penetrated deeper
- Linear probes: higher frequency & superficial structures
Indications (ultra.)
- Solid & fluid-containing structures/organs
- Not for air containing structures like bone, cardiac or pelvic or abdominal organs
Advantages (ultra)
- Portable and cheap
- No ionising radiation (children or pregnant pts)
- Real time imaging
- User-dependent
- Doppler studies
CT scan
- X -ray tube that spins fast around pt with a row of receptors on the other side of the patient also spinning on the same axis
- Attenuation of the X-ray beam is constantly recorded at various angles around the patient.
- 3D images: multi planar rendering & volume rendering
CT (advantages
- Quick
- Gold standard for trauma & lung
- Good for calcification & staging malignancy
Disadvantages (CT)
- High dose of ionising radiation
- Not bedside
- Motion artefacts
- Caution pregnancy & paediatric
- No contrast medium in renal failure
Contrast vs non-contrast
• Non- contrast: bleeds, stones
• Contrast: infections, malignancies, vascular pathology (dural venous sinus thrombosis etc )
• CT angiograms: aneurysms, dissections, injuries
MRI
• Align all the Hydrogen (Free Proton) atoms
• Radiowaves interact with spinning H+
• Protons flip back into their original direction, and give off radio waves
• “Coils” detect these radio waves.
• Characteristics of the tissues determine signal retrieved
MRI (advantages)
• Best soft tissue resolution
• Brain, spinal cord and MSK
• No radiation
• Contrast (gadolinium) – not iodine based, more renal friendly
MRI (disadvantages)
• Very expensive
• Long procedure (30 mins – 1 hour)
• Not easily accessible
• Cannot be done in emergency situations
• Expert interpretation
Bone scan
• Nuclear medicine
• Poor anatomical differentiation
• Radioactive substance
• ‘Hot spots’ – cancer, inflammation, infection
• Radiation emitted from the patient
