Medical detectors and medical imaging devices are provided. In one aspect, a medical detector includes: a photoelectric conversion device, a first crystal array layer disposed over the photoelectric conversion device, and a second crystal array layer disposed over the first crystal layer. The first crystal array layer includes a plurality of first scintillation crystals arranged in a first crystal array, and a first coupling medium being filled between every adjacent two of the first scintillation crystals. The second crystal array layer includes a plurality of second scintillation crystals arranged in a second crystal array, and a second coupling medium being filled between every adjacent two of the second scintillation crystals. A light transmittance of the second coupling medium is different from a light transmittance of the first coupling medium.