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Optimized Alignment Phantom

IP.com Disclosure Number: IPCOM000187640D
Original Publication Date: 2009-Sep-25
Included in the Prior Art Database: 2009-Sep-25
Document File: 3 page(s) / 600K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

The combination of magnet resonance (MR) imaging scanners and positron emission tomography (PET) scanners can significantly increase the diagnostic value of the received images. For instance, the combination enables the physician to locate findings in the PET image based on the anatomical reference given by the MR image. In order to combine them in a way that the same volume is scanned, the scanners have to be precisely geometrically registered. Therefore the transformation matrix between the coordinate systems of the scanners has to be determined. Up to now, there is no state of the art MR-PET combination available as a product, though research is conducted in this field and first prototypes have been developed. Alignment phantoms have been proposed, which are composed of two spheres that are visible in the MR and PET imaging. The phantom is used together with transformation algorithms to execute the alignment of the coordinates from the MR and the PET insert. The main disadvantage of alignment spheres with combined visibility in both MR and PET is that the MR scan will have to deal with artifacts due to susceptibility differences between the satellites and the surrounding air as well as artifacts generated inside the filling. Figure 1 shows the magnetic field distortion of two alignment spheres filled with MR and PET visible material.

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Optimized Alignment Phantom

Idea: Ralf Ladebeck, DE-Erlangen; Chares Watson, Ph.D., USA-Knoxville (TN); Stefan Stocker, DE- Erlangen

The combination of magnet resonance (MR) imaging scanners and positron emission tomography (PET) scanners can significantly increase the diagnostic value of the received images. For instance, the combination enables the physician to locate findings in the PET image based on the anatomical reference given by the MR image. In order to combine them in a way that the same volume is scanned, the scanners have to be precisely geometrically registered. Therefore the transformation matrix between the coordinate systems of the scanners has to be determined.

Up to now, there is no state of the art MR-PET combination available as a product, though research is conducted in this field and first prototypes have been developed. Alignment phantoms have been proposed, which are composed of two spheres that are visible in the MR and PET imaging. The phantom is used together with transformation algorithms to execute the alignment of the coordinates from the MR and the PET insert. The main disadvantage of alignment spheres with combined visibility in both MR and PET is that the MR scan will have to deal with artifacts due to susceptibility differences between the satellites and the surrounding air as well as artifacts generated inside the filling. Figure 1 shows the magnetic field distortion of two alignment spheres filled with MR and PET visible material.

In order to create superior technical solution it is now proposed to separate the MR and the PET visible structure. The novel alignment phantom structure can for example be realized by using two or more spheres, or similar objects of two types, as shown in Figure 2 for spheres embedded in a cylindrical structure. One type can be activated with a positron emitting isotope like 68Ge (visible for PET scanners), whereas the other type contains a high mobile proton density (visible for MR scanners), for instance water.

These spheres are mounted in a fixed, known geometric relation to each other, thereby defining the distance between the corresponding coordinate points and their relative orientation. As an alternative, concentric spheres, or more generally, PET visible spheres contained within a MR visible background object (or vice versa) can be used.

One implementation could be that a PET visible sphere is used which is not visible in MR. This can be achieved by placing the radioactive material inside a material that does not contain protons or in a material that decreases the transversal relaxation time T2 to less than a few...