Magnetic Resonance Imaging (MRI) Physics, Sequences, and Safety — WACS Viva & Clinical Scenarios (Radiological Physics, Equipment, and Radiation Safety)

Exam-style magnetic resonance imaging (mri) physics, sequences, and safety viva scenarios with examiner probes and model answers for Radiology candidates.

Scenarios covered

• SCENARIO 1: A 32-year-old male is undergoing MRI of the brain for suspected demyelinating disease. Detail the physical mechanisms of T1 relaxation (spin-lattice) and T2 relaxation (spin-spin), explain the influence of magnetic field strength (1.5 Tesla versus 3.0 Tesla) on these relaxation parameters, and define the pulse sequence timing parameters required to generate T1-weighted, T2-weighted, and proton density-weighted spin-echo images.
• SCENARIO 2: Explain the physical principles of spatial encoding in two-dimensional Fourier transform magnetic resonance imaging. Outline the sequential roles of the slice-selection gradient, phase-encoding gradient, and frequency-encoding gradient during a spin-echo sequence, and describe how raw data filling in k-space determines image resolution, field of view, and acquisition time.
• SCENARIO 3: A patient with acute ischemic stroke is evaluated with diffusion-weighted magnetic resonance imaging (DWI). Explain the biophysical basis of diffusion imaging, including the application of Stejskal-Tanner pulsed gradient pairs, the derivation and calculation of the Apparent Diffusion Coefficient (ADC), and the physical differentiation between true restricted diffusion and T2 shine-through.
• SCENARIO 4: Compare and contrast conventional spin-echo (SE), fast spin-echo/turbo spin-echo (FSE/TSE), inversion recovery sequences (STIR and FLAIR), and gradient-echo (GRE) pulse sequences in terms of radiofrequency excitation angles, rephasing mechanisms, image contrast generation, specific absorption rate (SAR) deposition, and sensitivity to magnetic susceptibility.
• SCENARIO 5: Describe the American College of Radiology and College-recognized four-zone MR safety framework (Zones I through IV). Detail the physical and biophysical hazards associated with the static magnetic field, time-varying gradient magnetic fields, and radiofrequency (RF) fields, including specific absorption rate (SAR) limits, acoustic noise, peripheral nerve stimulation, and protocol management during an acute helium quench.