Which device has the lowest spatial resolution among these modalities?

• A. Gamma camera
• B. MRI and CT
• C. Ultrasonography
• D. Screen-Film Radiography

Answer: (A)

Spatial resolution is about how small a detail you can distinguish in an image. A gamma camera in nuclear medicine detects gamma rays from a radiotracer through a collimator, and that collimator is the main limiter of sharpness. The design that preserves photon counts (sensitivity) by allowing only certain photon paths also blur exact locations, so the resulting images have relatively coarse detail. The net effect is that fine anatomical structures aren’t resolved as clearly, giving the lowest spatial resolution among these modalities.

In comparison, CT and MRI create detailed anatomical maps with voxel sizes often well under a millimeter, providing much finer detail. Ultrasonography can achieve high spatial resolution close to the probe, especially with high-frequency transducers, and screen-film radiography delivers very high spatial resolution due to high-resolution detectors and imaging geometry.