Dipolar weighted MR imaging in-vivo

A method of magnetic resonance imaging comprising:

• (a) applying a first RF pulse having a first phase to excite resonance in dipolar and Zeeman spin systems;
• (b) applying a second RF pulse having a second phase, the second phase being 90.degree. rotated in a first angular direction from the first phase;
• (c) applying a third RF pulse which causes the resonance excited in the dipolar spin system to refocus into a dipolar magnetic resonance echo, the third RF pulse having a third phase, the third phase being the same as the first phase;
• (d) phase encoding the resonance excited in the dipolar and Zeeman spin systems with a first phase encode gradient;
• (e) applying a read gradient during the dipolar magnetic resonance echo;
• (f) during the read gradient, sampling magnetic resonance signals with a digital receiver having a fourth phase, the fourth phase being 90.degree. in the first angular direction out of phase from the third phase, the first sampled magnetic resonance signals including dipolar and Zeeman spin system resonance signal components that are 90.degree. out of phase in one phase rotation direction;
• (g) repeating steps (a)-(f) with the first phase rotated 180.degree., the second phase 90.degree. out of phase in a second angular direction relative to the rotated first phase, the second angular direction being opposite to the first angular direction, the third phase being 180.degree. out of phase with the rotated first phase, and the receiver phase being 90.degree. out of phase to the third phase in the second angular direction such that in the second sampled magnetic resonance signals include the dipolar and Zeeman spin system magnetic resonance signal components that are substantially 90.degree. out of phase in an opposite phase rotation direction relative to the first sampled magnetic resonance signals;
• (h) combining the first and second sampled magnetic resonance signals such that the first and second sampled dipolar spin system magnetic resonance signal components combine and the first and second sampled Zeeman spin system magnetic resonance signal components tend to cancel;
• (i) repeating steps (a)-(h) for a plurality of phase encodings;
• (j) reconstructing the combined magnetic resonance signals into an image representation.

A magnetic resonance method comprising:

• exciting resonance in both a dipolar spin system and a Zeeman spin system;
• receiving and converting the magnetic resonance into an electrical resonance signal which includes dipolar and Zeeman spin system resonance components that are substantially 90.degree. out of phase in one direction of phase rotation;
• re-exciting magnetic resonance in the dipolar and Zeeman spin systems and converting the resultant resonance into a second electrical magnetic resonance signal which includes dipolar and Zeeman spin system resonance components which are substantially 90.degree. out of phase in an opposite direction of phase rotation;
• combining the first and second electrical resonance signals such that the dipolar components additively combine and the Zeeman spin system resonance components subtractively combine.

A magnetic resonance imaging apparatus comprising:

• a means for generating a static magnetic field through an examination region in which a portion of a subject having dipolar and Zeeman spin systems is disposed;
• a digital transmitter means for generating radio frequency signals for transmission into the examination region with a selectable phase;
• a digital receiver means for receiving and demodulating resonance signals received from the examination region with a selectable phase offset to generate an electrical magnetic resonance signal;
• a first buffer means and a second buffer means connected with the digital receiver means for receiving electrical resonance signals therefrom;
• a gradient magnetic field means for selectively generating magnetic field gradients across the examination region;
• a sequence control means (1) for controlling timing and phase of the digital transmitter means and the digital receiver means and for controlling timing of the gradient magnetic field means such that in a first repetition, magnetic resonance is excited in both the dipolar and Zeeman spin systems to produce a first magnetic resonance signal which has dipolar and Zeeman spin system components which are 90.degree. out of phase in a first direction of phase rotation, the first magnetic resonance signal being buffered in the first buffering means, and (2) for controlling the timing and phase of the digital transmitter and receiver and the timing of the gradient magnetic field means in a second repetition such that magnetic resonance is excited in the dipolar and Zeeman spin systems to produce a second magnetic resonance signal which has dipolar and Zeeman spin system resonance components which are 90.degree. out of phase in a second direction of phase rotation, the second direction of phase rotation being opposite to the first direction of phase rotation, the second magnetic resonance signal being buffered in the second buffering means;
• a combining means for combining the first and second magnetic resonance signals from the first and second buffer means such that the dipolar spin system resonance components combine and the Zeeman spin system resonance components cancel to produce a dipolar spin system weighted resonance signal;
• an image reconstruction means for reconstructing a plurality of the dipolar spin system weighted magnetic resonance signals into an electronic image representation;
• an image memory means for storing the electronic image representation.