Level 1 contains a list of body systems ex: cardiovascular Level 2 contains type of view ex: Xray, standard Level 3 contains list of organs ex: ventricle Level 4 is the details page.
It's not easy to give an answer to a non specific question. But I try to give some thoughts.
- Is there a reason why all levels look differently (level 1 entries in a list, level 2 in a grid, level 3 only text?
- Is there a reason why the label are below the icons (i suppose the black dots are icons)? This uses a lot of space and a user would have to scroll quit a lot to get to the desired entry
- Level 3: the links seem very close together which makes it difficult to tap on them.
- How does it behave. What I mean, what is the transition from one level to the other?
- how to I come back from level 3 to 2 or 1?
As said, your question is extremely broad, but these are the first things that popped in to my mind, looking at your mockups. If you do need more specific answers you should probably ask more specific questions about your design.