International Conference on Recent Advances and Future Trends in Information Technology (iRAFIT2012) Proceedings published in International Journal of Computer Applications® (IJCA) 6 Cobb Angle Quantification for Scoliosis Using Image Processing Techniques Raka Kundu A.K.C.S.I.T, University of Calcutta, Kolkata-700009. R&D, N.I.O.H,Kolkata-700090 Prasanna Lenka, Ratnesh Kumar R&D,N.I.O.H,Kolkata-90 Amlan Chakrabarti A.K.C.S.I.T, University of Calcutta, Kolkata-700009 ABSTRACT Measurement of Cobb angle is the standard technique used for scoliosis assessment. The challenging task in computerized method lies in totally automating the method of curvature measurement from digital X-ray images. In this paper we presented a method which automatically measures the Cobb angle from radiographs after selection of the end vertebrae of the curve. The image processing methods used shows an appreciable measurement of scoliosis curvature in digital X- ray image, reducing user intervention. The proposed method detects the inclination of the vertebra by identifying the lines of the endplate from edge image, helping in calculating the Cobb angle in the direction of the endplates automatically. An intra-observer and inter-observer assessment was performed over the radiographs using the manual and the proposed digital method. A level of improvement for Cobb angle measurement is achieved in the proposed computerized image processing technique in terms of estimating the vertebral slope and limiting user intervention. General Terms Biomedical Image Processing. Keywords Image Processing, Digital X-ray image, Scoliosis, Cobb angle. 1. INTRODUCTION Scoliosis [1] is a three dimensional deformity that causes abnormal curve of the spine. It involves lateral curvature accompanied with vertebral rotation of the spine. Scoliosis is of several types based on the cause and age of the curve development. About 2% of female and 0.5% of male population can be affected by scoliosis. Adolesant idiopathic scoliosis is the most common form of scoliosis. Depending on condition and severity of the curve and chances of getting the curve worse, the treatment of scoliosis involves observation, bracing and surgery. The deformity of spine may be characterized by measurement of lateral curvature from anterior-posterior radiograph images. The standard in orthopedics for quantifying the degree of scoliosis is the measurement of Cobb’s angle from radiographs. This measurement helps in understanding the stage of deformity, monitoring curve progression and management of scoliosis. Cobb angle below 25 degree is kept under observation with routine measurements. Cobb angle between 25-40 degree and that is still growing, a brace treatment is recommended. Bracing is not required for people who have finished growing the curve. A surgery is usually suggested for curvature having Cobb angle greater than 45 degree. The Cobb angle measurement technique consists of selection of the end vertebrae which tilt more severely toward the concavity of the curve. Lines are drawn one from the upper endplate of the superior vertebrae and the other from the lower endplate of the inferior vertebrae of the curve. The angle (θ) formed by intersection of the two lines is considered to be the Cobb angle [Figure 1] which represents the measurement of lateral curvature. The normal measurement errors for Cobb angle magnitude quantification are due to selection of different end vertebrae and in estimation of the slope of the end vertebrae. Same selected end vertebrae may result in Cobb angle degree variation due to improper estimation of the vertebral slope. Manual method which includes drawing lines through endplates of vertebrae with use of pencil, scale and protractor on X-ray plate is less preferable as the lines may not run across right corners of the endplates leading to variation in Cobb angle quantification. Technological improvement has increased the use of digital X-ray image for clinical purpose. To improve the reliability and accuracy of Cobb angle quantification method, several algorithms have been developed till date. In 2002 Chockalingam et al. [2] proposed a computer assisted Cobb angle measurement method which produces eight lines over the region of interest (ROI), resulting in eight equal segments. The observer needed to mark two points on each line where the line intersected the vertebra edge. The program then determined midpoint of each line and formed the spinal midline connecting these midpoints. The Cobb angle was quantified based on this midline. In 2007 a reliability assessment of Cobb angle was performed by Gstoettner et al. [3] for manual versus digital measurement tool. The Incoview software was used for this purpose where lines were drawn over the upper and lower endplates of the extreme vertebrae of the curve and the program measured the Cobb angle automatically. In 2008 Allen et al. [4] used an automatic Cobb angle measurement method which was based on active shape model and it also needed training set. In 2010 Tanure et al. [5] performed a reliability assessment of Cobb angle using manual and digital method. The digital method consisted marking the endplates of the superior and inferior vertebrae of the curve with the mouse. One dot on each extremity of each endplate was needed and the remaining steps of Cobb angle measurement were done automatically. In 2009 Zhang et al. [6] developed a new technique of computerized Cobb angle measurement method. The method needed contrast and brightness adjustment with ROI selection. Canny edge detection, fuzzy Hough transform were used to find the lines over the endplates of the vertebrae. The Cobb angle was calculated according to direction of these lines. Figure 1: Representation of Cobb angle (θ = θ1+θ2)