A Technique to Detect Extrapulmonary Tuberculosis via Superparamagnetic Nanoprobes

Take Mycobacterium bovis  BCG, an attenuated tuberculosis-causing bacteria, and intradermally inject it into a mouse.

An inflammatory response against the bacteria forms a granuloma comprising bacteria, epithelioid macrophages, conventional macrophages, and lymphocytes.

Perform magnetic resonance imaging or MRI. The magnetic field aligns randomly oriented protons in the tissue in its direction.

Apply a radio frequency pulse perpendicular to the magnetic field. The protons absorb energy from the pulse and tilt away from the field.

When the pulse stops, protons emit the absorbed energy, termed free-induction decay or FID, and realign with the field.

Measure the FID signal to obtain an image. The decay duration is tissue-specific, and areas with a longer decay appear lighter.

Take superparamagnetic nanoprobes conjugated to Mycobacterium-specific polyclonal antibodies and inject intravenously.

The antibodies bind to multiple epitopes on the bacteria, labeling the granuloma.

The nanoprobes shorten the decay of neighboring protons to make the granuloma appear darker, confirming mycobacterial infection.