# Spinal Cord Segmentation in Ultrasound Medical Imagery
###### Abstract  
In this paper, we study and evaluate the task of semantic segmentation of the spinal cord in ultrasound medical imagery. This task is useful for neurosurgeons to analyze the spinal cord movement during and after the laminectomy surgical operation. Laminectomy is performed on patients that suffer from an abnormal pressure made on the spinal cord. The surgeon operates by cutting the bones of the laminae and the intervening ligaments to relieve this pressure. During the surgery, ultrasound waves can pass through the laminectomy area to give real-time exploitable images of the spinal cord. The surgeon uses them to confirm spinal cord decompression or, occasionally, to assess a tumor adjacent to the spinal cord. The Freely pulsating spinal cord is a sign of adequate decompression. To evaluate the semantic segmentation approaches chosen in this study, we constructed two datasets using images collected from 10 different patients performing the laminectomy surgery. We found that the best solution for this task is Fully Convolutional DenseNets if the spinal cord is already in the train set. If the spinal cord does not exist in the train set, U-Net is the best. We also studied the effect of integrating inside both models some deep learning components like Atrous Spatial Pyramid Pooling (ASFP) and Depthwise Separable Convolution (DSC). We added a post-processing step and detailed the configurations to set for both models. ultrasound; deep learning; laminectomy; spinal cord; spinal cord pulsation; Convolutional Neural Networks (CNN); Densenet; semantic segmentation; medical image segmentation +
Footnote †: journal: Medical Image  
0000-0001-9599-4000-0000-0000-0000-0000-0000-area of ultrasound imagery analysis [1; 4; 5; 6; 7]. This gives physicians the ability to get more information for image-guided intervention and surgery. One of the most tackled tasks in medical imaging analysis is the semantic segmentation of body organs and tissues [4]. This procedure makes a partitioning of the input image into separate regions. Every region has a particular clinical relevance [4]. On the other hand, Ultrasound imaging is challenging regards to the application of semantic segmentation algorithms. In fact, it is operator dependent and presents relatively fewer details compared to other modalities like Computerized Tomography scans (CT scan) or Magnetic Resonance Imaging (MRI) [4]. Furthermore, medically used ultra-sonographic waves do not pass through bones [5; 6; 7]. Even in the absence of bones, the depth penetration of the ultrasound waves depends on the acoustic impedance of the body organs. This makes an unclear representation of the organ boundaries [4]. The Spine is also called vertebral column, spinal column, or backbone. It is composed of several bones named vertebrae [2; 3]. The basic functions of the spine are to protect the spinal cord and to maintain the body alignment. The spinal cord is a part of the central nervous system containing major nerve tracts [2; 3]. It connects the brain to nerves throughout the body and helps to regulate body functions. The spinal cord descends out of the brain at the base of the skull through the spinal column until it ends at the second lumbar vertebrae. It is enclosed and protected inside the bones of the spinal column. It is approximately about 45 cm (18 inches) long with a varying width from 13 mm (0.5 inch) in the cervical and lumbar regions to 6.4 (0.25 inch) in the thoracic area [2]. Figure 1 shows a description of the human vertebrae from the anterior and the right lateral view. Figure 2 demonstrated the location of the spinal cord inside the spinal canal of the vertebral column. We could realize the location of the lamina on the back part of the verteba and behind the spinal cord. Figure 1: Human vertebral column. The laminectomy is a surgical operation performed by neurosurgeons and orthopedic surgeons to relieve compression on the spinal cord. This pressure may engender mild to severe back pain or difficulty in walking or in controlling limb functions.