。
I have to go get an X-ray tomorrow.
Literal
Tomorrow X-ray photography [object-を] receive [purpose-に] go-must.
レントゲン撮影 is 'X-ray photography' — レントゲン from the German physicist's name, 撮影 meaning 'photography/filming.' 受けに行く uses purpose に — 'go in order to receive.' ~なければならない expresses obligation.