1. A method for producing a series of image frames of a moving subject using a magnetic resonance imaging (MRI) system, the steps comprising:
a) acquiring MR signals to form an image data set for each image frame by performing a pulse sequence with the MRI system, the pulse sequence including:
a)i) a preparatory pulse sequence comprised of a non-selective RF inversion pulse that inverts spin magnetization throughout the field of view of the image frames and a selective RF inversion pulse that re-inverts spin magnetization in a pool of moving spins flowing into a region of interest within a field of view of each image frame; and
a)ii) a plurality of image data acquisition pulse sequences performed in sequence after the preparatory pulse sequence to acquire the MR signals for the image data set for each image frame as the inverted spin magnetization in the field of view of each image frame recovers;
b) reconstructing the image frames from the acquired image frame data sets; and
c) displaying in sequence the reconstructed image frames to depict the flowing spins having re-inverted spin magnetization as they flow throughout the region of interest.
2. The method as recited in claim 1 in which the moving subject is a beating heart and the pool of moving spins is blood flowing into the heart.
3. The method as recited in claim 2 in which the performance of step a) is initiated by a cardiac gating signal such that each acquired image frame depicts the beating heart at a selected cardiac phase.
4. The method as recited in claim 3 in which the data acquisition in step a) is segmented such that only a portion of each image frame data set is acquired in step a)ii) and step a)i) and a)ii) are repeated to acquire the remaining portion of each image frame data set.
5. The method as recited in claim 2 in which the image frame data sets are acquired over substantially two cardiac cycles.
6. The method as recited in claim 1 in which the image data acquisition pulse sequence is a balanced, steady-state free precession pulse sequence.
7. The method as recited in claim 1 in which steps a) through c) are repeated to produce image frames in near real time.
8. A method for producing a series of image frames of a moving subject using a magnetic resonance imaging (MRI) system, the steps comprising:
a) acquiring MR signals to form an image data set for each image frame by performing a pulse sequence with the MRI system, the pulse sequence including:
a)i) a preparatory pulse sequence comprised of a non-selective RF inversion pulse that inverts spin magnetization throughout the field of view of the image frames and a selective RF inversion pulse that re-inverts spin magnetization in a pool of moving spins flowing into a region of interest within a field of view of each image frame; and
a)ii) a plurality of image data acquisition pulse sequences performed in sequence after the preparatory pulse sequence to acquire the MR signals for the image data set for each image frame as the inverted spin magnetization in the field of view of each image frame recovers;
b) reconstructing the image frames from the acquired image frame data sets; and
c) displaying in sequence the reconstructed image frames to depict the flowing spins having re-inverted spin magnetization as they flow throughout the region of interest;
in which each image frame data set substantially under samples k-space.
9. A method for producing a series of image frames of a moving subject using a magnetic resonance imaging (MRI) system, the steps comprising:
a) acquiring MR signals to form an image data set for each image frame by performing a pulse sequence with the MRI system, the pulse sequence including:
a)i) a preparatory pulse sequence comprised of a non-selective RF inversion pulse that inverts spin magnetization throughout the field of view of the image frames and a selective RF inversion pulse that re-inverts spin magnetization in a pool of moving spins flowing into a region of interest within a field of view of each image frame; and
a)ii) a plurality of image data acquisition pulse sequences performed in sequence after the preparatory pulse sequence to acquire the MR signals for the image data set for each image frame as the inverted spin magnetization in the field of view of each image frame recovers;
b) reconstructing the image frames from the acquired image frame data sets; and
c) displaying in sequence the reconstructed image frames to depict the flowing spins having re-inverted spin magnetization as they flow throughout the region of interest;
in which the image frame reconstruction in step b) includes:
b)i) calculating the magnitude of the MR signal at each image frame pixel; and
b)ii) controlling the brightness of each image frame pixel using the magnitude calculated in step b)i).
10. The method as recited in claim 9 in which step b) further includes:
b)iii) calculating the phase of the MR signal at each image frame pixel; and
b)iv) altering the brightness of image frame pixels produced in step b)ii) using the phase calculated in step b)iii).
11. The method as recited in claim 10 in which step b) further includes:
b)v) producing a separate phase image for each image frame using the phase information produced in step b)iii).
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1-9. (canceled)
10. A method for determining an operating point of a compressor including at least one impeller, compressor blades attached to the at least one impeller, a housing and at least two sensors, the method comprising:
calculating a deflection of the compressor blades taking place;
determining an operating point and spacing of the compressor blades with respect to a surge limit, based on the calculating of the deflection, by measuring passage times of the compressor blades at a sensor;
determining a signal that is representative of a rotation speed and is associated with the compressor impeller;
determining, in a learning or adaptation mode, compressor blade-specific, state-induced and position-induced deviations from an ideal state using compressor blade-specific passage times that are measured and compared with ideal passage times; and
measuring, in a working mode, compressor blade-specific passage times; and
correcting, in the working mode, the compressor blade-specific passage times using the determined state-induced and position-induced deviations.
11. The method for reliably operating a compressor at the surge limit according to claim 10, wherein the compressor blade-specific, state-induced and position-induced deviations of the compressor blades are determined upon start-up of the compressor after alignment of the compressor blades.
12. The method for reliably operating a compressor at the surge limit according to claim 10, wherein the compressor blade-specific, state-induced and position-induced deviations are determined after a minimum rotational speed of the impeller is reached.
13. The method for reliably operating a compressor at the surge limit according to claim 10, wherein the compressor blade-specific, state-induced and position-induced deviations are stored as a spacing or as a factor, in the form of a time, a displacement or an angle.
14. The method for reliably operating a compressor at the surge limit according to claim 10, wherein the compressor blade-specific, state-induced and position-induced deviations are stored in an adaptation mode in a compressor adaptation model and read out in a working mode.
15. A device for determining an operating point of a compressor, the device comprising:
at least one compressor blade sensor;
at least one impeller sensor;
an apparatus for predefining a system time; and
at least one integrated storage map including a number of storage cells equating to a number of compressor blades to be monitored.
16. The device for determining the operating point of a compressor according to claim 15, further comprising an apparatus for synchronising the storage map with the rotation of the impeller such that the measured passage times are comparable with ideal passage times and can be corrected using the compressor blade-specific state-induced and position-induced deviations.
17. The device for determining the operating point of the compressor according to claim 15, further comprising an evaluation unit configured to establish an operating point of the compressor and accordingly the spacing with respect to a surge limit, the evaluation unit having at least one input, via which corrected passage times are supplied.
18. The device for determining the operating point of a compressor according to claim 15, further comprising a switch configured to be switched upon meeting of a condition in order to switch between a learning- and working mode and an adaptation mode.