Method for the determination of a spatial assignment or spatial distribution of magnetic particles

• US 9,651,637 B2
• Filed: 10/11/2016
• Issued: 05/16/2017
• Est. Priority Date: 10/15/2015
• Status: Active Grant

• Current Assignee: Bruker Biospin GMBH (Bruker Corporation)
• Original Assignee: Bruker Biospin GMBH (Bruker Corporation)
• Inventors: Weber, Alexander, Heinen, Ulrich
• Primary Examiner(s): Vargas, Dixomara
• Application Number:
  US15/290,482
• Publication Number:
  US 20170108560A1
• Time in Patent Office: 217 Days
• CPC Class Codes: A61B 5/0515 Magnetic particle imaging
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G01R 33/0029 Treating the measured signals, e.g. removing offset or noise
• CPC Class Codes: G01R 33/1276 of magnetic particles, e.g. imaging of magnetic nanoparticles G01R33/1269 takes precedence
• CPC Class Codes: G01R 33/5601 involving use of a contrast agent for contrast manipulation, e.g. a paramagnetic, super-paramagnetic, ferromagnetic or hyperpolarised contrast agent
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating
• CPC Class Codes: G06T 7/0012 Biomedical image inspection
• CPC Class Codes: G06T 7/62 of area, perimeter, diameter or volume

Abstract

A method related to Magnetic Particle Imaging (MPI) includes a signal processing step in which MPI time signals are acquired and successive acquisition cycles are completed within one scanning period. From the scanning period, an image acquisition period is selected for which a composite time signal is generated by concatenating measured values acquired in immediate succession. A corrected time signal is determined from the composite time signal by windowing, performing a Fourier transform, and reducing a number of frequency values by eliminating intermediate frequencies of the Fourier transform of the windowed, composite time signal. In a reconstruction step, a spatial assignment and/or distribution of the magnetic particles is computed, and in an outputting step, the results of the reconstruction and/or one or more parameters derived therefrom are stored and/or displayed.

Claims

1. A method of determining a spatial assignment and/or spatial distribution of magnetic particles in a specified analysis volume performed by a Magnetic Particle Imaging (MPI) measuring device, comprising:

in an acquisition step performed with a receiving device of the MPI measuring device, acquiring m MPI time signals with a total of m·

N measured values A_q, where q=0, . . . , m·

N−

1, completing m successive acquisition cycles within a scanning period, and in each of the acquisition cycles acquiring an MPI time signal of duration T₀ with N time-assigned measured values by repeatedly executing a specified measurement sequence, where m≧

1 and N≧

1;

in a signal processing step;

a) selecting one image acquisition period from the scanning period and, for the selected image acquisition period, generating a composite time signal z with signal values z_j, where j=0, . . . , n·

N−

1, by concatenating n·

N measured values acquired in immediate succession, where n≦

m, acquiring at a desired starting time of the image acquisition period a measured value A_r, with 0≦

r≦

(m−

n)·

N−

1, and assigning the measured value A_r to a start signal value z₀ so that z₀=A_r, and an image acquisition period of duration n·

T₀, is covered; and

b) determining a corrected time signal {tilde over (z)} from the composite time signal z, wherein the determining the corrected time signal {tilde over (z)} comprises windowing the composite time signal z to produce a windowed composite time signal, computing a Fourier transform of the windowed composite time signal to produce a windowed, Fourier-transformed, composite time signal having a number of frequency values, and reducing the number of frequency values by eliminating intermediate frequencies among the number of frequency values to produce a reduced frequency spectrum;

in a reconstruction step, computing the spatial assignment and/or the spatial distribution of the magnetic particles from either the reduced frequency spectrum or the corrected time signal {tilde over (z)}; and

in an outputting step, providing results of the reconstruction and/or at least one parameter derived from the reconstruction.

2. The method according to claim 1, wherein the windowing includes multiplying the signal values z_j of the composite time signal z with interpolation points w_j=w(t_j) of a window function w(t), wherein the interpolation points are correspondingly assigned in terms of time, and the window function w(t) as a function of time is selected so that the following applies at least by approximation:

3. The method according to claim 2, wherein:

the computing of the Fourier transform includes computing a discrete Fourier transform from the resulting composite time signal z′

to produce an extended frequency spectrum with N·

n frequency values F₀, F₁, . . . , F<sub>N*n−

1</sub>; and

the reducing includes generating from the extended frequency spectrum the reduced frequency spectrum with N frequency values f_k, where;

f_k=F_k*n for k=0, . . . , N−

1.

4. The method according to claim 3, wherein the corrected time signal {tilde over (z)} is computed by performing an inverse Fourier transform of the reduced frequency spectrum.

5. The method according to claim 2, wherein the computing of the Fourier transform and the reducing collectively include applying a matrix operator C′

to the resulting, composite time signal z′

, with {tilde over (z)}=F′

<sup>−

1</sup>RFz′

=C′

z′

, where

F is a Fourier matrix of dimension n·

N×

n·

N,

R is a matrix of dimension n·

N×

N with the coefficients r_ij=δ

<sub>(n·

i),j</sub> which eliminates the intermediate frequencies, and

F′

<sup>−

1</sup> is an inverse Fourier matrix of dimension N×

N.

6. The method according to claim 2, wherein the window function w(t) has a sideband suppression that is greater than a parasitic signal/noise ratio of the composite time signal z.

7. The method according to claim 2, wherein m=n.

8. The method according to claim 2, wherein n<

m.

9. The method according to claim 1, further comprising repeating the signal processing step, the reconstruction step, and the outputting step for each of different image acquisition periods that have respective durations that are equal to each other but respective starting times that differ from each other.

10. The method according to claim 9, wherein the starting times of the different image acquisition periods differ by integer multiples of T₀.

11. The method according to claim 1, wherein the windowing, the performing of the Fourier transform, and the reducing collectively include applying a matrix operator C to the composite time signal z, with {tilde over (z)}=F′

<sup>−

1</sup>RFWz=Cz, where

W is a diagonal matrix of dimension n·

N×

n·

N, whose diagonal elements are interpolation points w_j of a discretized window function w(t), which is chosen as a function of time such that the following applies at least by approximation;

12. The method according to claim 1, wherein the windowing includes multiplying the composite time signal z by a window function w(t) having a sideband suppression that is greater than a parasitic signal/noise ratio of the composite time signal z.

13. The method according to claim 1, wherein m=n.

14. The method according to claim 1, wherein n<

m.

15. The method according to claim 1, wherein the providing comprises storing and/or displaying the results of the reconstruction.