Image modalities differ in storage requirements depending on

• A. Both a and b
• B. The number of integrations with other systems
• C. The contrast and spatial resolution needed
• D. Whether data expansion techniques are used

Answer: (C)

Storage needs for medical images are driven by how much data each image holds. That amount is determined by spatial sampling (the number of pixels and slices or frames) and by how many gray levels the image stores (the bit depth, or contrast resolution). When you increase either the spatial resolution (more pixels per image, more slices or frames) or the number of gray levels (higher bit depth), the file size grows because more information must be stored for every pixel.

Other factors like how many systems the data must interact with or the use of compression techniques influence overall storage in practice, but the intrinsic data size of an image modality is set mainly by the detail required (spatial resolution) and the level of contrast/detail captured (contrast resolution).