In some embodiments of the present invention, apparatus is provided, including a capsule 50, configured to be swallowed by a subject 54 and to pass through a GI tract 72 of the subject 54, the capsule including a capsule housing 61, at least one radiation source 60, configured to emit radiation, a rotatable collimator 63 configured to rotate with respect to the housing 61 and to collimate the radiation emitted by the radiation source 60, at least one photon detector 62, configured to detect photons generated responsively to the emitted radiation, the apparatus including a control unit 52 configured to analyze data regarding the photons in order to generate information useful for identifying a clinically-relevant feature of the GI tract 72 of the subject 54. Additional embodiments are also described.
