Abstract
In this article, we present a graph-based method using a cubic template for volumetric segmentation of vertebrae in magnetic resonance imaging (MRI) acquisitions. The user can define the degree of deviation from a regular cube via a smoothness value Δ. The Cube-Cut algorithm generates a directed graph with two terminal nodes (s-t-network), where the nodes of the graph correspond to a cubic-shaped subset of the image’s voxels. The weightings of the graph’s terminal edges, which connect every node with a virtual source s or a virtual sink t, represent the affinity of a voxel to the vertebra (source) and to the background (sink). Furthermore, a set of infinite weighted and non-terminal edges implements the smoothness term. After graph construction, a minimal s-t-cut is calculated within polynomial computation time, which splits the nodes into two disjoint units. Subsequently, the segmentation result is determined out of the source-set. A quantitative evaluation of a C++ implementation of the algorithm resulted in an average Dice Similarity Coefficient (DSC) of 81.33% and a running time of less than a minute.
Highlights
Lumbar stenosis (LS), a narrowing of any part of the lumbar spinal canal with encroachment on the neural structures by surrounding bone and soft tissue [1,2] is the most frequent reason for surgery in patients over 65 years of age [1]
Similar to LS, degenerative spondylolisthesis primarily occurs in elderly patients, and a combination of MR imaging (MRI) and computer tomography (CT) is applied for preoperative evaluations in this case
The introduced method is the first one using a 3D-graph that is based on a cubic-shaped subset of nonequidistant image voxels as well as a smoothness-constraint in order to segment volumetric, cubic-like target-structures
Summary
Lumbar stenosis (LS), a narrowing of any part of the lumbar spinal canal with encroachment on the neural structures by surrounding bone and soft tissue [1,2] is the most frequent reason for surgery in patients over 65 years of age [1]. While MR imaging (MRI) is considered purposive for the visualization of the soft tissue, X-ray computer tomography (CT) is seen as the method of choice for preoperatively evaluating bone anatomy [3]. Similar to LS, degenerative spondylolisthesis primarily occurs in elderly patients, and a combination of MRI and CT is applied for preoperative evaluations in this case. A shift towards a more frequent application of MRI, even for morphological evaluations of the bone structure, would result in less radiation exposure [3], which is what motivates this work
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