Week 1 - Medical Imaging

X-rays

A form of electromagnetic radiation. Projections that pass through a patient.

Rays are emitted from a projector and received by a detector.

Colours on an X-ray

The rays emitted pass through most material, however is absorbed by dense material such as bone.

• Rays that are blocked from passing through and absorbed create regions that turn white on an x-ray.

How is an x-ray taken?

A minimum of 2 perpendicular projections should be taken during an X-ray, so the bone is properly perceived.

• If an object is close to the projector the x-ray becomes fuzzy and large due to divergence.

• The patient should be placed close to the detector and far from the projector to ensure a clear image is formed.

X-ray examples

Axial - from top to bottom (head to toes)

X-rays Pros & Cons

Ultrasound

Uses a transducer to emit high-frequency sound waves through patients.

Ultrasound colours

Soundwaves are reflected back based on the density of tissues.

The denser a tissue, the more soundwaves are reflected, hence the whiter the colour on the ultrasound.

Ultrasound pros & cons

MRIs (Magnetic Resonance Imaging)

A extremely powerful magnet is used to resonate with hydrogen atoms in the human body.

• This resonance emits a radio frequency that the MRI’s receiver picks up and is able to map

MRI colours

The image colours are determined by the presence of hydrogen in tissues (e.g water or H₂O present)

• More water present, whiter image

• Less water present, darker image

Hence rigid tissue like bone is not detected

MRI pros & cons