Calibration and Quality Assurance of Imaging Equipment

Calibration

Calibration compares the equipment's output against a known reference and adjusts it so the measurements fall within tolerance.

Equipment	Parameters calibrated
X-ray	kVp accuracy, mA/mAs linearity, exposure timer, HVL, output (dose) reproducibility, focal spot size
CT	CT number of water (0 HU), uniformity, noise, spatial resolution, slice thickness, CTDI dose
MRI	Magnetic field homogeneity, RF coil, gradient accuracy, SNR
Ultrasound	Depth and distance accuracy, dead zone, uniformity, resolution
Display and film	Monitor luminance, DICOM grayscale (GSDF)

Quality assurance (QA) programme

1. Acceptance testing confirms the new unit meets specifications.
2. Commissioning/baseline records reference values.
3. Constancy tests at daily, weekly, monthly and annual intervals using phantoms.
4. Corrective action if limits are exceeded.
5. Documentation of every test; audits.
6. Reject analysis and dose monitoring (DRLs) for patients.

Tools: phantoms (CT water phantom, ACR MRI phantom), dosimeters and ion chambers, kVp meters, test patterns.

Exam tip

Write the QA cycle, 3 tests for X-ray and CT, and mention phantoms.