QA

Question 1

Why do QA in MRI? What are the consequences of poor image quality? (3 marks)

Answer 1

Track changes in performance of the system.

Ensure that image quality is no degrading over time.

Poor IQ may lead to mis-diagnosis, repeated scanning, longer scan times.

Question 2

How can the following be measured and what can affect it in terms of issue with equipment:

• SNR
• Uniformity
• Ghosting
• Geometry
• Slice Thickness

Answer 2

• SNR -> measure by taking images and subtracting them to get the noise. Issues caused by problems with the RF coil calibration.
• Uniformity -> take an image of a uniform region and look at standard deviation across it. Issues caused by non-homogenous B-field so issues with the shim coils.
• Ghosting -> caused by phase encoding artefacts, seen by imaging a uniform circular region and seeing ringing artefacts. Caused by phase encoding problems with the RF phase generation.
• Geomtry -> image a phantom with gridlines in of known geomtry and measure the size of the grid and assess any visual distortion. Issues caused by issues with the field gradient amps.
• Slice thickness, image a slice with a diagonal line across it and determine the thickness from the geomtry. Issues caused by the gradient fields.

Question 3

What are the modern day challenges with MRI QA? (3 marks)

Answer 3

Multi-channel coils are commonly used and it is not easy to define SNR and uniformity for these. Due to the design they are inherently non-uniform.