Medical images have typically much larger dynamic range than what could be displayed, therefore intensity window/level operation is performed automatically when loading a volume. The intensity window may be incorrect for extraordinary image content (e.g., there is a small but very bright region in the image). You can adjust window/level by left-mouse click-and-drag up/down/left-right; or using Volumes module). If you share an image then we can see if we can make the automatic window/level algorithm more robust.