Pattern is another name for Precision Aerobatics. It come in two flavors: AMA style pattern (National Society of Radio Controlled Aerobatics) and IMAC (International Miniature Aerobatic Club). There are several differences between the two types. IMAC rules require scale-like aircraft and AMA pattern requires a plane specifically made to fly RC aerobatic maneuvers. Different maneuver sequences are used in each style. AMA style pattern has been around for 30 or more years, while IMAC is somewhat newer.

Except for the planes there really isn't and difference between IMAC and NSRCA. TEh same maneuvers are performend. How they are judged are different and what manuevers are allowed in which classes is different, but if you need to do a loop or roll in NSRCA then you will do the same thing in IMAC.

Take a look at the RC aerobatics guide. http://www.modelaircraft.org/comp/05...c-aero2005.pdf
Page 1 -88 is for pattern, page 88 to 111 is for IMAC.