BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates an inventive device.
FIG. 2 shows an examination image composed of voxels according to the prior art.
FIG. 3 shows an examination image generated with the inventive method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The device 1 shown in FIG. 1 for implementation and monitoring of ablations has schematically shown magnetic resonance system 2 that is of conventional design. The magnetic resonance system 2 has a magnet for generation of a static magnetic field, a radio-frequency system as well as a schematically shown computer system 3 for controlling the radio-frequency and gradient pulses, for image reconstruction and for evaluation and operation of the magnetic resonance system 2. A monitor 4 on which examination images can be displayed is connected to the computer system 3.
As is shown in FIG. 1, a patient 5 is located on a patient bed 6 inside the magnet. A device 7 for generation of high intensity focused ultrasound (HIFU) is used for treatment of a tumor. Non-invasive tumor ablations can be effected with the device 7.
During the procedure, examination images are generated at short intervals with the magnetic resonance system 2 so that the curve of the temperature and the achieved maximum temperature can be monitored in real time during the procedure. The corresponding examination images are provided by the computer system 3 and displayed on the monitor.
The geometry of the examination images composed of voxels is shown in FIGS. 2 and 3. FIG. 2 shows an examination image composed of voxels according to the prior art and FIG. 3 shows an examination image generated with the device and the method according to the invention. Only the relevant section that contains the HIFU focus is shown by the examination images.
The conventional examination image 8 shown in FIG. 2 contains cuboid voxels 9; the geometry of the ultrasound focus 10 is additionally shown. The ultrasound focus 10 has the shape of an ellipsoid; the length of the primary axes is typically 3 mm, 3 mm and 12 mm. Only this demarcated region is heated by means of HIFU; the temperature gradients are correspondingly very steep. Given such conventional examination images the information about the temperature is frequently shown in color, for example by a color representation of the edge lines of the voxels or via colored crosses or via other known means. The temperatures of individual voxels can likewise be shown over the course of time. As can be seen in FIG. 2, approximately 18 voxels are required for the coverage of the ultrasound focus 10. Due to the large number of the required voxels 9 the generation of the examination image in conventional ways is extremely time-critical.
For comparison, in FIG. 3 an examination image 11 is shown in which non-cuboid parallelpiped voxels 12 are used instead of cubic voxels. In the shown exemplary embodiment, the ratio of the edge lengths of a voxel is approximately 2.5:1. This nearly corresponds to the ratio of the two primary axes of the ultrasound focus 10 in the imaging plane. Due to the non-cuboid parallelpiped voxels 12, in the examination image 11 shown in FIG. 3, only approximately 6-9 voxels 12 per slice are required in order to cover the entire ultrasound focus 10.
In FIG. 3 a lower number of voxels 12 do in fact indicate a relatively precise temperature, since only the middle voxels contain no spatial temperature gradients. This disadvantage is overcompensated by a significantly better signal-to-noise ratio. Improvements of the signal-to-noise ratio by a factor of 4 as well as a severely reduced measurement duration can be achieved by the changed voxel geometry.
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
Patent Application
20080058634
