Illustration (a) in
The section A in illustration (b) is shown enlarged in illustration (c), whereby this section presents a metastasized tissue portion and a healthy tissue portion. As can be seen in illustration (c), the healthy tissue portion exhibits a number of macrophages 14 and iron particles 11 that are enclosed in the macrophages. Fewer iron particles 11 are contained in the tissue of the metastasis 23. The super-paramagnetic iron oxide particles alter the magnetic field and therewith the signal in the MR acquisition. These different magnetic fields lead to a different phase position of the nuclear spins in tissue with and without iron oxide particles. When the magnetic field change is ΔB, the phase given acquisition of a phase-sensitive acquisition sequence changes by Δφ=γΔBTE, whereby γ is the gyromagnetic ratio and TE is the echo time of the imaging sequence. If a pixel now contains tissue with and without iron particles, the total signal intensity is composed of
I
total
=I
background
+I
iron exp(i-γΔBTE)
This means that the phase in the healthy tissue changes relative to that in metastasized tissue. The signal difference between healthy tissue and metastasis tissue is oscillating.
In order to now make the phase difference optimally large between metastasis tissue and non-metastasized tissue, the echo time must be appropriately selected so that the iron oxide particle-comprising tissue can be differentiated relative to tissue that does not comprise iron oxide particles. An echo time between 35 and 50 ms can be exemplarily adopted.
Naturally, the echo time depends on the basic magnetic field strength and on other factors and must be adapted to the remaining circumstances of the examination.
The magnitude signal intensity of image points that exhibit iron oxide-containing particles is less than the signal intensity of tissue without iron oxide particles. In the present case the signal intensity of tissue with iron oxide particles can now be determined. This is the reference phase (φ0. The phase of the tissue of the acquired lymph nodes can now be compared with the reference phase. For example, the phase filter can then be selected such that all phase positions within a range around the reference angle are populated with a value between 0 and 1 while phase positions outside of a predetermined range receive the value 1 or greater than 1. Other embodiments of the phase filter are also possible. More precise information with regard to the phase filter can be found in U.S. Pat. No. 6,501,272. Overalls the phase filter must be selected such that the signal intensity reduction in the healthy tissue parts is reduced relative to tissue portions with metastases, upon the subsequent multiplication with the magnitude image.
The total signal information then results from multiplications of the original signal intensity magnitude image with the modified phase image in which the phase position was changed as mentioned above.
The steps that can be implemented for detection of slight changes of the lymph nodes are shown in summary in
In summary, the method described herein enables the detection of small metastases and very small lymph nodes by magnetic resonance tomography.
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.
Number | Date | Country | Kind |
---|---|---|---|
10 2006 026 723.0 | Jun 2006 | DE | national |