[en] New technologies, especially photo-sensors, are enabling detectors for positron emission tomography to operate in large magnetic field, to be compact and to achieve excellent timing, energy and position resolutions including depth of interaction. However, the complexity and cost of such detectors are constantly increasing. Using wavelength shifting bars in a planar geometry promises to provide excellent three-dimensional position resolution with good energy and timing resolutions at a small fraction of the cost of comparable detector. Two detector configurations are being investigated using 3×3 mm² wavelength shifting bars to collect the light from either monolithic or pixelated LYSO crystals. Promising performances have been achieved.