A system and method for the treatment of mitral valve regurgitation by reshaping the mitral valve annulus using one or more plications of annular or adjacent tissue each fixed by a retainer is described. It is determined whether the specific information of the image forming apparatus is identical to that of the exchangeable part. The x-ray system also includes a field-generator controller configured to control a field to deflect at least one of the electron beams, wherein the electron beam, at the first energy level, impinges on the target at a first contact position and the electron beam, at the second energy level, impinges on the target at a second contact position. Electric current for welding is transmitted around the electrically insulative ring, through the electrically conductive portion of the rotation nut and into the electrically conductive part of the head tube assembly. The sheet further includes a first horizontal rib that extends in a third direction along the sheet substantially all the way between the third and fourth edges of the sheet, wherein the first horizontal rib protrudes in a fourth direction opposite said second direction.