System classification exercise: “X-ray, MRI, and ultrasound systems in hospitals are examples of analog systems.” Determine whether this description applies, considering modern mixed-signal design.

Introduction / Context:
Modern medical imaging systems integrate analog front ends with extensive digital processing. Labeling them as purely analog overlooks the role of digitization, reconstruction algorithms, storage, and display pipelines that are central to image quality and workflow.

Given Data / Assumptions:

• These systems sense analog physical phenomena (X-ray intensity, acoustic echoes, NMR signals).
• Signals are conditioned by analog circuits (gain, filtering) and then digitized.
• Digital back ends perform heavy processing, control, and visualization.

Concept / Approach:
Such equipment is best described as mixed-signal: analog front ends capture and condition signals; high-resolution ADCs digitize them; digital subsystems perform reconstruction (FFT, beamforming, filtered back-projection) and image post-processing. Control, calibration, storage, and user interfaces are primarily digital.

Step-by-Step Solution:

Verification / Alternative check:
Block diagrams from vendors show analog front-end ICs followed by ADCs and powerful DSP/FPGA/CPU stages, confirming the mixed-signal characterization.

Why Other Options Are Wrong:

• Applies (purely analog): Ignores digital conversion and processing pipelines.
• Only MRI / only when film is used: Partial or outdated; even film-era systems had control electronics and modern systems are highly digital.
• Cannot be evaluated: The architecture pattern is industry standard.

Common Pitfalls:
Equating analog sensing with an entirely analog system; overlooking ADC/DSP roles fundamental to modern imaging quality and features.

Final Answer:
Does not apply (they are mixed-signal systems)