An imager 40 comprising: a scintillator 42 to convert photons of one wavelength to a longer wavelength； a reflector arrangement comprising non-planar reflective portions； and at least one detector positioned to image at least a portion of scintillator 42 via the reflector-arrangement. Scintillator 42 may convert X-rays to visible light. The reflector-arrangement may comprises a curved mirror. Imager 40 may comprise first and second detectors 46a,46b, where: a first and second reflective portion of the reflector-arrangement respectively reflect converted photons from a first and second section of scintillator 42 in first and second directions to first and second fields of view, with detectors 46a,46b positioned to detect respective converted photons in the first and second fields of view, so imaging the scintillator’s 42 first and second sections. The first and second reflective portions may be respective first and second planar mirrors facing away from one another. Also an imager comprising a scintillator and a plurality of detectors moveable to position each detector in turn in an imaging position to directly image the scintillator. Also an imager comprising a curved scintillator and a detector positioned to image at least a portion of the scintillator. Also a radiotherapy device comprising an imager.
