What are MRI and CT scanning, and how are they used to assess body composition?

Overview

MRI (magnetic resonance imaging) and CT (computed tomography) scanning are medical imaging technologies that can be used to assess body composition in addition to their more common clinical uses. Both are considered highly accurate reference methods for measuring body fat and muscle tissue.

Details

How they work

• CT scanning uses X-rays (ionizing radiation) to produce images of internal structures.
• MRI uses magnetic fields and radio waves — no radiation is involved.

What they measure

Both MRI and CT can provide accurate, valid, precise, and reliable measurements of:

• Subcutaneous fat — fat stored just beneath the skin
• Visceral fat — fat surrounding internal organs, which is more closely linked to disease risk
• Skeletal muscle volume and size
• Organ size (quantitative estimation)

How accurate are they?

MRI and CT results closely match measurements taken from cadaver studies, making them a gold standard reference for body composition research. However, both technologies still rely on mathematical reconstruction algorithms to define borders between tissue types (e.g., fat vs. muscle). Results are therefore best described as highly accurate estimations rather than absolute measurements.

Notes

• Visceral fat is considered a more clinically significant marker of metabolic and cardiovascular disease risk than subcutaneous fat alone. The ability of MRI and CT to distinguish visceral fat is one of their key advantages.
• Despite their accuracy, MRI and CT are often not practical for routine body composition assessment due to cost, equipment availability, radiation exposure (CT), and the need for clinical settings. Alternative tools such as 3D body scanning may serve a similar purpose in accessible, everyday fitness and wellness environments.

Applies to: General health technology assessment; relevant background for understanding body composition measurement standards across all Styku configurations.