The main processor and RAM are BGAs. i.MX plus what looks to be at least 16MB of SDRAM going by the package type.
Frankly, you can drive an LCD like that (~320x240 colour 16-bit, non-memory type) from an STM32F4 + 512K of SRAM, so I'm not sure why they bothered with an i.MX... seems a little overkill. My guess is they have a lot of code written for that, and the engineering cost being the main driver of the instrument cost, meant it worked out cheaper. I know they use i.MX in the DS1074Z, and I expect they're slowly moving away from Blackfins as they put more of the processing load in their scopes on FPGAs, or maybe the i.MX has good enough DSP anyway.