Vertebral Column Localization, Labeling, and Segmentation - Spinal Imaging and Image Analysis - page 190

The essential structures within the vertebral column that have been attracting
researchers for localization, labeling, and segmentation are the intervertebral discs,
the vertebrae and the Dural Sac.
The lumbar vertebrae are the

five vertebrae between the rib cage and the pelvis

which are designated as L1 L5, starting at the top. The intervertebral discs are

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fibrocartilaginous cushions which are named upon the vertebral bodies that sand-
wich a particular disc, e.g., the disc in between L1 and L2 is named L1-L2. In
clinical practice, the radiologist reports the diagnosis at each disc level and at each
vertebra level. Hence, the

first requirement of any lumbar Computer Aided Diag-
nosis (CAD) system is to localize and label the lumbar discs and vertebrae as shown
in Fig. 1 [ 5 ]. Speci cally, localization refers to providing centroids or bounding

boxes for each of the lumbar discs, and labeling refers to identifying each localized
disc as one of the six lumbar discs (T12-L1, L1-L2, L2-L3, L3-L4, L4-L5, L5-S1).
While some researchers have discussed methods to provide a point within each
lumbar disc [ 5 , 76 ], there are also methods [ 32 ] that provide a bounding box around
every visible disc in clinical lumbar MRIs as illustrated in Fig. 2 .
Another important tissue structure in the lumbar spine is the Dural Sac. It is the
membranous sac that encases the spinal cord within the bony structure of the

Fig. 2 This figure illustrates the results of an automatic lumbar disc localization method [ 32 ]
which detects all the visible discs in a lumbar MRI. In case more than six discs are detected, the
lower most six discs are identified as the lumbar discs. The red boxes are the bounding boxes
provided for each of the visible discs in the clinical MRI. The red stars show the automatic disc
centers, while the green stars show the true centers