Physics
Core concepts
Master X-ray production (tube, kV, mA, focal spot) and image formation. Know CT physics: pitch, reconstruction, windowing, and dose metrics (CTDIvol, DLP). Understand MRI physics: T1/T2, proton density, sequences, and safety (ferromagnetic, gadolinium). Learn ultrasound physics: frequency, resolution, Doppler, and artefacts. Know radiation dose units (Gy, Sv, mGy) and the principles of optimisation. Understand contrast media (iodinated, gadolinium) and their risks.
Traps
- Pitch affects dose and image quality-know the relationship.
- T1 vs T2: fat is bright on T1; fluid is bright on T2.
- Gadolinium is contraindicated in severe renal impairment (NSF risk).
- Ultrasound artefacts (shadowing, enhancement, reverberation) can mimic pathology.
- Do not confuse kV (penetration) with mA (quantity).
Worked example / rule of thumb
A CT with a pitch of 1.5: higher pitch reduces dose but may affect image quality. Rule of thumb: kV controls penetration; mA controls quantity; pitch affects dose and coverage. For MRI safety, screen for ferromagnetic implants and renal function before gadolinium.
Key points
- kV vs mA: penetration vs quantity.
- Pitch affects dose and image quality.
- T1: fat bright; T2: fluid bright.
- Gadolinium risk in renal impairment.
- Recognise ultrasound artefacts.