A fixture for securing a sonography transducer in place against a test surface of a phantom has a cap having a cap surface, wherein the cap is formed to seat against an edge of the phantom and to maintain spacing between the cap surface and the test surface. One or more cutouts in the cap surface are dimensioned to accept the sonography transducer. One or more flexible supports within or adjacent the one or more cutouts are configured to stabilize at least one side of the transducer within the cutout.