Free-breathing non-contrast MR angiography

1. A system comprising:

a chassis defining a bore;

a main magnet to generate a polarizing magnetic field within the bore;

a gradient system to apply a gradient magnetic field to the polarizing magnetic field;

a radio frequency system to apply an excitation pulse to patient tissue disposed within the bore and to receive signals from the patient tissue; and

a computing system to receive the signals from the radio frequency system, the computing system to execute program code to:

control the gradient system and the radio frequency system to acquire a predetermined number of three-dimensional sub-frames from the patient tissue using a T1-weighted radial sampling sequence and while contrast agent is not present in the patient tissue;

reconstruct a first three-dimensional image from a first-acquired one of the predetermined number of three-dimensional sub-frames;

reconstruct a plurality of three-dimensional images from respective sequentially-acquired subsets of the predetermined number of three-dimensional sub-frames, where each sequentially-acquired subset includes the first-acquired one of the predetermined number of three-dimensional sub-frames;

determine one of the plurality of three-dimensional images reconstructed from respective sequentially-acquired subsets of the predetermined number of three-dimensional sub-frames in which a blood-related signal strength is most similar to a blood-related signal strength in the first three-dimensional image reconstructed from the first-acquired one of the predetermined number of three-dimensional sub-frames; and

subtract the determined one of the plurality of the three-dimensional images from the first three-dimensional image to generate a second three-dimensional image.

2. A system according to claim 1 , where the T1-weighted radial sampling sequence includes acquisition of radial samples, and where an angle between successive radial samples is 111.25°.

3. A system according to claim 2 , the computing system to execute program code to:

determine, after control of the gradient system and the radio frequency system to acquire the predetermined number of three-dimensional sub-frames, whether the patient tissue has reached a steady state; and

if it is determined that the patient tissue has not reached a steady state, control the gradient system and the radio frequency system to acquire another three-dimensional sub-frame from the patient tissue using a T1-weighted radial sampling sequence while contrast agent is not present in the patient tissue,

wherein the plurality of three-dimensional images are reconstructed from respective subsets of the predetermined number of three-dimensional sub-frames and the another three-dimensional sub-frame.

4. A system according to claim 1 , where the T1-weighted radial sampling sequence includes acquisition of radial samples, and where an angle between successive radial samples is ΔΦ=180°/n total , where n total is the total number of radial samples.

5. A system according to claim 1 , the computing system to execute program code to:

determine, after control of the gradient system and the radio frequency system to acquire the predetermined number of three-dimensional sub-frames, whether the patient tissue has reached a steady state; and

if it is determined that the patient tissue has not reached a steady state, control the gradient system and the radio frequency system to acquire another three-dimensional sub-frame from the patient tissue using a T1-weighted radial sampling sequence while contrast agent is not present in the patient tissue,

wherein the plurality of three-dimensional images are reconstructed from respective subsets of the predetermined number of three-dimensional sub-frames and the another three-dimensional sub-frame.

6. A system according to claim 1 , wherein acquisition of the predetermined number of three-dimensional sub-frames from the patient tissue occurs while the patient is free breathing.

7. A computer-implemented method for a system comprising a main magnet to generate a polarizing magnetic field, a gradient system to apply a gradient magnetic field to the polarizing magnetic field, and a radio frequency system to apply an excitation pulse to patient tissue disposed within the polarizing magnetic field and to receive signals from the patient tissue, the method comprising:

controlling the gradient system and the radio frequency system to acquire a predetermined number of three-dimensional sub-frames from the patient tissue using a T1-weighted radial sampling sequence and while contrast agent is not present in the patient tissue;

reconstructing a first three-dimensional image from a first-acquired one of the predetermined number of three-dimensional sub-frames;

reconstructing a plurality of three-dimensional images from respective sequentially-acquired subsets of the predetermined number of three-dimensional sub-frames, where each sequentially-acquired subset includes the first-acquired one of the predetermined number of three-dimensional sub-frames;

determining one of the plurality of three-dimensional images reconstructed from respective sequentially-acquired subsets of the predetermined number of three-dimensional sub-frames in which a blood-related signal strength is most similar to a blood-related signal strength in the first three-dimensional image reconstructed from the first-acquired one of the predetermined number of three-dimensional sub-frames; and

subtracting the determined one of the plurality of the three-dimensional images from the first three-dimensional image to generate a second three-dimensional image.

8. A method according to claim 7 , where the T1-weighted radial sampling sequence includes acquisition of radial samples, and where an angle between successive radial samples is 111.25°.

9. A method according to claim 8 , further comprising:

determining, after controlling the gradient system and the radio frequency system to acquire the predetermined number of three-dimensional sub-frames, whether the patient tissue has reached a steady state; and

if it is determined that the patient tissue has not reached a steady state, controlling the gradient system and the radio frequency system to acquire another three-dimensional sub-frame from the patient tissue using a T1-weighted radial sampling sequence while contrast agent is not present in the patient tissue,

wherein the plurality of three-dimensional images are reconstructed from respective subsets of the predetermined number of three-dimensional sub-frames and the another three-dimensional sub-frame.

10. A method according to claim 7 , where the T1-weighted radial sampling sequence includes acquisition of radial samples, and where an angle between successive radial samples is ΔΦ=180°/n total , where n total is the total number of radial samples.

11. A method according to claim 7 , further comprising:

determining, after controlling the gradient system and the radio frequency system to acquire the predetermined number of three-dimensional sub-frames, whether the patient tissue has reached a steady state; and

if it is determined that the patient tissue has not reached a steady state, controlling the gradient system and the radio frequency system to acquire another three-dimensional sub-frame from the patient tissue using a T1-weighted radial sampling sequence while contrast agent is not present in the patient tissue,

wherein the plurality of three-dimensional images are reconstructed from respective subsets of the predetermined number of three-dimensional sub-frames and the another three-dimensional sub-frame.

12. A method according to claim 7 , wherein acquisition of the predetermined number of three-dimensional sub-frames from the patient tissue occurs while the patient is free breathing.

13. A non-transitory computer-readable medium storing program code, the program code executable by a computer system to cause the computer system to:

control a gradient system and a radio frequency system to acquire a predetermined number of three-dimensional sub-frames from patient tissue using a T1-weighted radial sampling sequence while contrast agent is not present in the patient tissue;

reconstruct a first three-dimensional image from a first-acquired one of the predetermined number of three-dimensional sub-frames;

reconstruct a plurality of three-dimensional images from respective sequentially-acquired subsets of the predetermined number of three-dimensional sub-frames, where each sequentially-acquired subset includes the first-acquired one of the predetermined number of three-dimensional sub-frames;

determine one of the plurality of three-dimensional images reconstructed from respective sequentially-acquired subsets of the predetermined number of three-dimensional sub-frames in which a blood-related signal strength is most similar to a blood-related signal strength in the first three-dimensional image reconstructed from the first-acquired one of the predetermined number of three-dimensional sub-frames; and

subtract the determined one of the plurality of the three-dimensional images from the first three-dimensional image to generate a second three-dimensional image.

14. A medium according to claim 13 , where the T1-weighted radial sampling sequence includes acquisition of radial samples, and where an angle between successive radial samples is 111.25°.

15. A medium according to claim 14 , the program code executable by a computer system to cause the computer system to:

determine, after controlling the gradient system and the radio frequency system to acquire the predetermined number of three-dimensional sub-frames, whether the patient tissue has reached a steady state; and

if it is determined that the patient tissue has not reached a steady state, controlling the gradient system and the radio frequency system to acquire another three-dimensional sub-frame from the patient tissue using a T1-weighted radial sampling sequence while contrast agent is not present in the patient tissue,

wherein the plurality of three-dimensional images are reconstructed from respective subsets of the predetermined number of three-dimensional sub-frames and the another three-dimensional sub-frame.

16. A medium according to claim 13 , where the T1-weighted radial sampling sequence includes acquisition of radial samples, and where an angle between successive radial samples is ΔΦ=180°/n total , where n total is the total number of radial samples.

17. A medium according to claim 13 , the program code executable by a computer system to cause the computer system to:

determine, after controlling the gradient system and the radio frequency system to acquire the predetermined number of three-dimensional sub-frames, whether the patient tissue has reached a steady state; and

if it is determined that the patient tissue has not reached a steady state, controlling the gradient system and the radio frequency system to acquire another three-dimensional sub-frame from the patient tissue using a T1-weighted radial sampling sequence while contrast agent is not present in the patient tissue,

wherein the plurality of three-dimensional images are reconstructed from respective subsets of the predetermined number of three-dimensional sub-frames and the another three-dimensional sub-frame.

18. A medium according to claim 13 , wherein acquisition of the predetermined number of three-dimensional sub-frames of the patient tissue using a T1-weighted radial sampling sequence occurs while the patient is free breathing.