Iterative method for reducing errors in navigator echo MR imaging

A method for constructing an MR image of an object disposed to experience periodic motion, said method comprising the steps of:

• operating an MR system to acquire a reference navigator echo associated with said object when said object is at a specified reference position;
• applying an MR sequence to said object to acquire a set of MR image data when said object is selectively displaced from said reference position, said data set including an acquired navigator echo having a specified field of view;
• truncating said acquired navigator echo by means of a selectively positioned truncation window;
• calculating a difference between linear phase shifts respectively associated with said truncated acquired navigator echo and said reference navigator echo;
• displacing said truncation window by an amount representing said linear phase shift difference;
• iteratively repeating said truncating, difference calculation, and truncation window displacement steps a specified number of times to provide a final phase shift difference or spatial displacement value;
• employing said final phase shift difference value to determine the displacement of said object from said specified reference position when said MR data set is acquired;
• and
• accepting said MR data set for use in constructing an image of said object only if said determined displacement lies within a particular displacement window with respect to said reference position.

Apparatus for constructing an MR image of an object disposed to experience periodic motion, said apparatus comprising:

• a set of MR components operable to acquire a reference navigator echo associated with said object when said object is at a specified reference position, and further operable to acquire a set of MR image data when said object is selectively displaced from said reference position, said data set including an acquired navigator echo having a specified field of view;
• a processor for truncating said acquired navigator echo, for calculating a difference between linear phase shifts respectively associated with said truncated acquired navigator echo and said reference navigator echo, and for displacing a truncation window associated with said truncated acquired navigator echo by an amount representing said linear phase shift difference;
• and
• said processor is further disposed to iteratively repeat said truncating, said difference calculation, and said truncation window displacement operations a specified number of times, in order to determine the displacement of said object from said specified reference position when said MR data set is acquired.