Segmentation of the thoracolumbar fascia in ultrasound imaging: a deep learning approach

Abstract

Background: Only in recent years it has been demonstrated that the thoracolumbar fascia is involved in low back pain (LBP), thus highlighting its implications for treatments. Furthermore, an easily accessible and non-invasive way to investigate the fascia in real time is the ultrasound examination, which to be reliable as is, it must overcome the challenges related to the configuration of the machine and the experience of the operator. Therefore, the lack of a clear understanding of the fascial system combined with the penalty related to the setting of the ultrasound acquisition has generated a gap that makes its effective evaluation difficult during clinical routine. The aim of the present work is to fill this gap by investigating the effectiveness of using a deep learning approach to segment the thoracolumbar fascia from ultrasound imaging.

Methods: A total of 538 ultrasound images of the thoracolumbar fascia of LBP subjects were finally used to train and test a deep learning network. An additional test set (so-called Test set 2) was collected from another center, operator, machine manufacturer, patient cohort, and protocol to improve the generalizability of the study.

Results: A U-Net-based architecture was demonstrated to be able to segment these structures with a final training accuracy of 0.99 and a validation accuracy of 0.91. The accuracy of the prediction computed on a test set (87 images not included in the training set) reached the 0.94, with a mean intersection over union index of 0.82 and a Dice-score of 0.76. These latter metrics were outperformed by those in Test set 2. The validity of the predictions was also verified and confirmed by two expert clinicians.

Conclusions: Automatic identification of the thoracolumbar fascia has shown promising results to thoroughly investigate its alteration and target a personalized rehabilitation intervention based on each patient-specific scenario.

Keywords: Deep fascia; Deep learning; Low back pain; Segmentation; Thoracolumbar.

Fig. 1

Thoracolumbar fascia of a low back pain subject, from US imaging. Selection: (blue) a portion of TLF composed by different sublayers, (yellow) a portion of epimysial fascia of the erector spinae muscles. The proper gliding between TLF and epimysium ensures forces transmission

Fig. 2

(a) Image and (b) mask (labelled) as inputs for the network

Fig. 3

Training/Validation (a) accuracy and (b) loss from model

Fig. 4

Examples of TLF segmentation: (a) original images, (b) clinicians’ annotations VS (c) model outputs