How can the sensations of the meditation object (attention to the breath) be made more noticeable?

While practicing sitting vipassana meditation, using the felt sensations of the abdomen rising and falling with each breath as the meditation object, there is the frequent flood of mental images arising and passing away. The mental images seem much stronger, i.e. more noticeable, than the felt sensations of the meditation object. Is there a mind or mindfulness technique to make the felt sensations more noticeable, thus improving concentration on the chosen meditation object?