Default [Q][XP] Nandroid backup/kernel backup

is the boot.img in nandroid backup same as kernel. what i am really saying is can i use the boot.img in nandroid as a backup of my stock kernel.

device:
- Xperia P LT22i
- Rooted with Locked Bootloader
- Stock Jelly Bean 4.1.2 ROM and Kernel (3.0.8+)


just so you know i did search before i posted but no luck.