The invention relates to a system, a medical image acquisition system, and a method for imaging an interior of a turbid medium (25). The invention also relates to a marker (60) for use in the method for imaging an interior of a turbid medium (25). The system, the medical image acquisition system, and the method may be used for obtaining an image of an interior of a turbid medium (25) by: accommodation of a turbid medium (25) inside a receiving volume (20); irradiation of the receiving volume (20) with light from a light source; detection of light emanating from the receiving volume (20) as a result of irradiating the receiving volume (20) with light from the light source through the use of a photodetector unit. The detected light is then used to reconstruct an image of an interior of the turbid medium (25). According to the invention, the system, the medical acquisition system, and the method are adapted such that during a measurement the receiving volume (20) comprises at least one marker (60) comprising a predetermined concentration of a chosen fluorescent agent. The light source is arranged for generating excitation light that causes fluorescent emission in the marker (60) and the photodetector is arranged to detect light emanating from the receiving volume (20) as a result of irradiating the receiving volume (20) with excitation light. The use of a marker (60) according to the invention enables obtaining information relating to the geometry of the turbid medium (25). If the turbid medium (25) comprises an unknown concentration of a second fluorescent agent, and the light source and the photodetector unit are arranged for causing fluorescence in the second fluorescent agent and detecting the resulting fluorescence light, respectively, the use of a marker (60) according to the invention enables calibration of the signal resulting from this fluorescence light.