Computed Tomography (CT) Principles, Instrumentation, and Artifacts — WACS Viva & Clinical Scenarios (Radiological Physics, Equipment, and Radiation Safety)

Exam-style computed tomography (ct) principles, instrumentation, and artifacts viva scenarios with examiner probes and model answers for Radiology candidates.

Scenarios covered

• SCENARIO 1: Explain the mathematical and physical principles governing image reconstruction in modern multi-detector row computed tomography (MDCT), comparing analytical Filtered Back Projection (FBP) with Statistical and Model-Based Iterative Reconstruction (IR) algorithms in terms of noise handling, low-contrast resolution, and radiation dose reduction.
• SCENARIO 2: Define the pitch factor in helical (spiral) multi-detector computed tomography. Analyze the physical and clinical consequences of varying the pitch between values less than 1.0 and greater than 1.0 on table displacement, total beam collimation, slice sensitivity profile (SSP), longitudinal spatial resolution, and effective patient dose.
• SCENARIO 3: Describe the physical mechanisms underlying beam hardening, photon starvation, metal streak artifacts, and partial volume averaging in computed tomography. For each artifact, specify the corresponding scanner-based, acquisition-based, and post-processing mitigation strategies.
• SCENARIO 4: Detail the instrumentation and functional role of the major gantry hardware components in modern multi-detector CT systems, with specific emphasis on high-heat-capacity X-ray tubes, bow-tie filtration, pre-patient and post-patient collimation, solid-state scintillation detector arrays, and slip-ring technology.
• SCENARIO 5: Define the standard radiation dosimetry metrics in computed tomography: CTDI100, weighted CTDI (CTDIw), volume CTDI (CTDIvol), Dose Length Product (DLP), and Size-Specific Dose Estimates (SSDE). Explain the operational mechanics of angular (x-y axis) and longitudinal (z-axis) automatic tube current modulation (ATCM) in dose optimization.