Browse Prior Art Database

Publication Date: 2016-Feb-18
Document File: 3 page(s) / 270K

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The Prior Art Database

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Multi-information image overlay for MR-based radiotherapy dose calculation presentation

    This document relates to the field of MR-only based radiotherapy planning (RTP). The procedure requires estimating electron density (ED) from the MR image instead of from a CT image as is the case in current state-of-the-art CT-based RTP. The ED is then used to guide the RTP process. While MR-derived ED is not as accurate as CT-derived ED, its accuracy has been shown sufficient for RTP calculations, as the reduction of ED data spatial resolution before using them as input to RTP calculations smoothes out the inaccuracies.

    From current oncology workflows, oncology clinicians are used to seeing a high- resolution planning CT image for visual inspection and sign-off for treatment planning. This may be a problem in MR-only based radiotherapy planning as presenting full-resolution ED images may reveal their inaccuracies, and may lead to the clinician rejecting the image even though the inaccuracies are not relevant for dose planning. On the other hand, presenting the simplified ED image would only show relevant data which accurately map to the dose plan, but may also not be acceptable to the clinician due to their perceived lack of detail.

    This document discloses a system that displays the ED image in user-selectable areas to allow simultaneous and spatially co-registered viewing of both full-resolution and reduced- resolution image data.

    Creating estimated electron density maps from MR images is a problem for which only approximate solutions exist. Such ED maps are needed e.g. for integrated PET/MR systems, where an attenuation map needs to be estimated for the attenuation correction of the PET images. They are also needed for radiation therapy planning based on MR, where electron density maps are required for the computation of the radiation dose during treatment simulation. However, due to the physics of the image acquisition, MR intensities do not uniquely correspond to electron density. Hence those maps cannot be derived from the MR image by a simple lookup operation, as is commonly done when estimating these maps from CT images.


    A popular approach is bulk density assignment to a number of pre-defined tissue classes, compare [1]. Other approaches include modelling CT value dependency from multi-dimensional MR information, compare [2]. However, none of these approaches guarantees artifact-free density maps.

Present work

    For MR-based radiotherapy planning (RT), the electron density distribution (ED) is computed on a CT-like image generated from the MR-image, called MRCAT ('MR-Calculated Attenuation'). However, the MRCAT image may lead to an inaccurate ED, e.g. due to image artifacts from the MR acquisition or from the image processing. As the ED is used as an input to RT, these inaccuracies may subsequently lead to a radiation dose distribution different from one computed based on CT images.

    However, in the current w...