Imaging Performance of a Handheld Ultrasound System With Real-Time Computer-Aided Detection of Lumbar Spine Anatomy: A Feasibility Study

Mohamed Tiouririne, Adam J Dixon, F William Mauldin Jr, David Scalzo, Arun Krishnaraj, Mohamed Tiouririne, Adam J Dixon, F William Mauldin Jr, David Scalzo, Arun Krishnaraj

Abstract

Objectives: The aim of this study was to evaluate the imaging performance of a handheld ultrasound system and the accuracy of an automated lumbar spine computer-aided detection (CAD) algorithm in the spines of human subjects.

Materials and methods: This study was approved by the institutional review board of the University of Virginia. The authors designed a handheld ultrasound system with enhanced bone image quality and fully automated CAD of lumbar spine anatomy. The imaging performance was evaluated by imaging the lumbar spines of 68 volunteers with body mass index between 18.5 and 48 kg/m. The accuracy, sensitivity, and specificity of the lumbar spine CAD algorithm were assessed by comparing the algorithm's results to ground-truth segmentations of neuraxial anatomy provided by radiologists.

Results: The lumbar spine CAD algorithm detected the epidural space with a sensitivity of 94.2% (95% confidence interval [CI], 85.1%-98.1%) and a specificity of 85.5% (95% CI, 81.7%-88.6%) and measured its depth with an error of approximately ±0.5 cm compared with measurements obtained manually from the 2-dimensional ultrasound images. The spine midline was detected with a sensitivity of 93.9% (95% CI, 85.8%-97.7%) and specificity of 91.3% (95% CI, 83.6%-96.9%), and its lateral position within the ultrasound image was measured with an error of approximately ±0.3 cm. The bone enhancement imaging mode produced images with 5.1- to 10-fold enhanced bone contrast when compared with a comparable handheld ultrasound imaging system.

Conclusions: The results of this study demonstrate the feasibility of CAD for assisting with real-time interpretation of ultrasound images of the lumbar spine at the bedside.

Conflict of interest statement

Conflicts of Interest

M.T. is a shareholder of ADial Pharmaceuticals. A.J.D. is an employee of Rivanna Medical. F.W.M. is a shareholder of Rivanna Medical and has pending patents PCT/US2011/022984, PCT/US2012/034945, PCT/US2013/045576, US/61/662,481, PCT/US14/18732, PCT/US14/18732, and PCT/US13/77917 that are of relevance to this work. D.S. disclosed no relevant relationships. A.K. disclosed no relevant relationships.

Figures

Figure 1
Figure 1
Demonstration of lumbar scanning technique with (A) Accuro and (B) V-Scan handheld ultrasound systems. (C) Schematic of the ultrasound beam intersecting the lumbar spine in the transverse plane.
Figure 2
Figure 2
Summary of image analysis performed on spinous process cross-sections of the lumbar spine. (A) Schematic of ultrasound beam intersecting a spinous process cross-section. (B) Image acquired by Accuro of a spinous process cross-section (with bone enhancement). (C) Radiologist measurements on the spinous process image: the blue circle denotes location of the spinous process tip, the green circles denote location of the articular processes, the white line is the spine midline. (D) Schematic of CAD results on the same image: the blue, green, and red dots are bright bone points identified by the algorithm, a cross-section of the 3D spine model is superimposed on the image to show the registration result, and the dashed white line is the spine midline. In both (C) and (D), dSP is depth to spinous process tip and dAP is depth to articular processes. (E) Graphics rendered to the Accuro screen by the CAD algorithm to indicate that the image contains a spinous process. Also shown are depth and midline indicators, along with a birds eye view of the 3D spine model. The blue number is the depth to the spinous process tip and the orange number is the depth to the epidural space (in cm).
Figure 3
Figure 3
Summary of image analysis performed on epidural space cross-sections of the lumbar spine. (A) Schematic of ultrasound beam intersecting an epidural space cross-section. (B) Image acquired by Accuro of an epidural space cross-section (with bone enhancement). (C) Radiologist measurements on the epidural space image: the green circles denote location of the articular processes, the orange ellipse denotes the location of the posterior surface of the vertebral body, and the white line is the spine midline. (D) Schematic of CAD results on the same image: the orange, green, and red dots are bright bone points identified by the algorithm, a cross-section of the 3D spine model is superimposed on the image to show the registration result, and the dashed white line is the spine midline. dVB is depth to spinous process tip, dAP is depth to articular processes, and dES is the depth to the epidural space. (E) Graphics rendered to the Accuro screen by the CAD algorithm to indicate that the image contains an epidural space. Also shown are depth and midline indicators, along with a birds eye view of the 3D spine model. The orange number is the depth to the epidural space (in cm).
Figure 4
Figure 4
Intermediate processing results of the bone enhancement method. (A) Raw, unprocessed B-mode image. (B) The shadow image, S(i,j), computed as described in the methods section. (C) Intermediate image computed by dividing the raw image (A) by the shadow image, S(i,j), and scaling by a sigmoid to increase bone contrast. (D) The final image with enhanced bone signals and suppressed tissue signals.
Figure 5
Figure 5
Representative images of a spinous process cross section (left) and an epidural space cross section (right) as acquired by the V-Scan (A,B) and Accuro (C,D) in a subject with BMI of 44 kg/m2. Labelled landmarks are spinous process tip (SP), articular processes (AP), vertebral body (VB), and erector spinae muscle (ESM).
Figure 6
Figure 6
Relationship between epidural depths measured in the ultrasound images by radiologists and subject BMI. The equation for the line of best fit is: depth (cm) = 2.82 + 0.072×BMI. The correlation between epidural depth and BMI is: Pearson’s r = 0.68, 95% CI: 0.54 – 0.79).
Figure 7
Figure 7
(A) Depth to the epidural space measured by the lumbar spine CAD algorithm versus depth to the epidural space measured by radiologists. (B) Bland-Altman analysis of epidural depths as measured by the lumbar spine CAD algorithm and radiologists. The difference between the depths measured by radiologists (RAD) and the depths measured by the CAD algorithm (CAD) are plotted against the average of the two measures (RAD+CAD)/2. The horizontal dashed lines represent the average difference (0.1 cm) and the 95% CI. μ: mean, σ: standard deviation.
Figure 8
Figure 8
(A) Midline location measured by the lumbar spine CAD algorithm versus midline location measured by radiologists. (B) Bland-Altman analysis of midline locations as measured by the lumbar spine CAD algorithm and radiologists. The difference between the midline locations measured by radiologists (RAD) and the midline locations measured by the CAD algorithm (CAD) are plotted against the average of the two measures (RAD+CAD)/2. The horizontal dashed lines represent the mean difference (−0.1 cm) and the 95% CI. μ: mean, σ: standard deviation.

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