Dear Yolanda, You do not need an app for BBL because the outcome , unfortunately, is quite predictable. The fat does not last beyond 6 - 12 months, as I have seen on many patients who came to my surgery center for butt implants surgery after their disappointment from the fat injection to the butts by other surgeons. Fat injection to the butts is physilogically illogical, because you can't expect injected fat to survive without good circulation. Many patient do the procedure multiple times, but the results are similar. Think about it, if large fat injection would have been consistent and reliable, breast implants would have disappeared from the matket. The reality is that last year, breast implants surgery was the number one cosmetic surgery performed in the US. Your best option is butt implants surgery. They do not disappear and when done correctly, they give you a very attractive and natural result. Consult only with board certified plastic surgeons who do lots of butt implants surgery in an accredited surgery center for your safety. Not all results are the same , because there are different techniques and different implants shapes and softness. Check the before and after pictures to make sure that they are numerous, consistent and you like them. Check also the reviews for positive patients experience. Best of luck, Dr Widder