Image analysis – Applications – Biomedical applications
Reexamination Certificate
1998-01-08
2001-02-20
Mancuso, Joseph (Department: 2723)
Image analysis
Applications
Biomedical applications
Reexamination Certificate
active
06192144
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an MR method for the image-assisted monitoring of the displacement of an object relative to a vascular system, in which a first MR data set is acquired which represents the course of the vascular system within a three-dimensional volume, after which the position of the object is continuously measured and reproduced in an MR angiogram derived from the first MR data set.
2. Description of Related Art
An MR method of this kind is known from Proceedings of 3rd SMR, 490, 1995. A comparatively long period of time (from 8 to 20 minutes) is required for the acquisition of an MR data set. Therefore, this MR data set is acquired before introduction of the object, for example a catheter, into the vascular system. After introduction of the catheter, the position of the object is continuously measured in real time and is reproduced in an MR angiogram derived from the first MR data set.
The known method meets its limits when the patient moves during the intervention. The real-time measured position of the object can then no longer be reproduced at the correct location in the angiogram, because the motion of the patient has not been taken up in the angiogram.
SUMMARY OF THE INVENTION
Therefore, it is an object of the invention to improve a method of the kind set forth in such a manner that the position of the object relative to the vascular system is also correctly reproduced in the case of motion of the patient.
This object is achieved according to the invention by executing the following steps:
a) acquisition of the MR data of a slice which belongs at least partly to the volume and is adapted to the position of the object, said acquisition taking place in the temporal vicinity of a measurement of the position of the object,
b) reconstruction of a slice image from this MR data,
c) reconstruction of an MR image of the same slice from the first data set or from a second MR data set which has been acquired in the temporal vicinity thereof and represents the three-dimensional volume,
d) determination of shifts, at least in the vicinity of the object, from the slice image and the MR image,
e) correction of the measured position and/or the MR angiogram in conformity with the shifts and subsequent reproduction of the position of the object in the angiogram,
f) repetition of the steps a) to e) for other positions of the object.
The invention is based on the consideration that, using the slice image acquired quasi in real time, the motion can be quantitatively determined by comparing this slice image with an MR image of the same slice which is derived from the first data set or from a second data set which has been acquired substantially simultaneously with the first data set. The motion-induced shift of the object between the acquisition of the first or the second MR data set on the one side and the acquisition of the MR data for the relevant slice image on the other side can be derived from this comparison. Therefore, the position thereof in the MR angiogram, or the MR angiogram itself, can be corrected so that the object is reproduced in the correct position relative to the vascular system, despite the motion.
When the sequences with which the first MR data set is acquired deviate substantially from the sequences with which the MR data for the individual slice images is acquired during the displacement of the object, structures in the slice image on the one hand and in an MR image derived from the first data set on the other hand could be reproduced with different contrast. In that case it would not be possible to determine the shift occurring between the acquisition of the first MR data set and the acquisition of the MR data for the slice image by comparison of the two images, so that the measured position of the object and/or the MR angiogram could no longer be corrected in conformity with the shift. In that case it is necessary to acquire a second MR data set in the temporal vicinity of the first data set. The comparability of the various images can be ensured by acquiring the second MR data set and the MR data for the various slices by means of similar excitation sequences.
A preferred version of the invention is characterized in that at least one microcoil is attached to the object in order to measure the position of the object, that a number of excitation sequences are generated for the acquisition of the MR data of the slice, the amplitude and/or direction of the magnetic gradient field active during the acquisition of the MR signal being varied from one sequence to another, and that the position of the object is derived from MR signals received by the microcoil in response to these sequences. The sequences generated according to this so-called projection reconstruction method enable at the same time the measurement of the position of the object by means of the microcoil connected thereto and the formation of an MR slice image by means of an additional receiving coil which picks up the MR signals then generated.
A device for carrying out the method according to the invention, including means for the acquisition of a first MR data set which represents the course of the vascular system within a three-dimensional volume and means for continuous measurement of the position of an object and its reproduction in an MR angiogram derived from the first MR data set is characterized in that it includes
a) means for measuring the MR data of a slice, belonging at least partly to the volume and adapted to the position of the object, in the temporal vicinity of a measurement of the position of the object,
b) means for reconstructing a slice image from this MR data,
c) means for reconstructing an MR image of the same slice from the first data set or from a second MR data set which has been acquired in the temporal vicinity thereof and represents the three-dimensional volume,
d) means for determining shifts, at least in a vicinity of the object, from the slice image and the MR image,
e) means for correcting the measured position and/or the MR angiogram in conformity with the shifts and subsequent reproduction of the position of the object in the angiogram.
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“Tracking and Monitoring the Effects of Interventional MR Instruments” G. McKinnon, Proceedings of 3rdSMR, p. 490.
M. Kouwenhoven et al, “Current MR Angiography Imaging Techniques, a Survey” In the Book “Vascular Diagnostics”, Edited by P. Lanser and J. Rosch, Springer Verlag, Heidelberg 1994, pp. 379-387.
Cooperrider F. E.
Mancuso Joseph
U.S. Philips Corporation
Vodopia John F.
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