Combined fundamental and harmonic ultrasonic imaging at low MI or deeper depths

A method of harmonic ultrasonic imaging comprising:

• transmitting first ultrasonic waves into a subject which comprise a first fundamental frequency component exhibiting a first modulation characteristic and a second fundamental frequency component exhibiting a frequency in the vicinity of a nonlinear receive frequency;
• receiving echo signals in response to the first ultrasonic waves;
• transmitting second ultrasonic waves into a subject which comprise a fundamental frequency component at the first fundamental frequency exhibiting a second modulation characteristic;
• receiving echo signals in response to the second ultrasonic waves;
• combining the received echo signals by pulse inversion;
• and
• forming an image using the combined echo signals.

A method of harmonic ultrasonic imaging comprising:

• transmitting first ultrasonic waves into a subject which are of the form a sin ω1t+b sin ω2t;
• transmitting second ultrasonic waves into a subject which are substantially of the form a sin(ω1t+π);
• receiving echoes in response to the transmitted wave;
• combining the echoes by pulse inversion;
• and
• forming an image using the combined echoes, wherein ω2t≡nω1t and n≠1.

A method for ultrasonically imaging a target location at a depth within a subject comprising:

• transmitting ultrasonic waves to the target location which contain first and second fundamental frequency components;
• forming an image from harmonic frequency components of the first fundamental frequency when an ultrasonic contrast agent is present at the target location;
• and
• forming an image from fundamental frequency components of the second fundamental frequency when an ultrasonic contrast agent is absent at the target location.