UWE Bristol Engineering showcase 2015

Joshua Milton
Mechanical Engineering (MEng)
Project Supervisor
Melvyn Smith
Using Computer Vision to Calculate the Cobb Angle of a Scoliosis Patient
Currently, the NHS is experiencing budget cuts in many sectors. Due to the large amount of X-Rays taken each year,
any method to drastically reduce the number of X-Rays taken would ease the strain in many other sectors. Each X-
Ray costs the NHS on average £27, with this figure the total cost per year in the UK due to scoliosis X-rays can be
estimated at £103.842 million. The potential health risks of X-Rays are well known, the ionising radiation produced
causes cancerous cells to develop. This thesis explores the development of computer vision and tests to see if a
screening method can be used to replace X-Rays when calculating the Cobb angle of Scoliosis patient's.
Project Objectives
The main objective of the thesis is to propose
and test a screening method based on
computer vision techniques that can calculate
the Cobb angle of a patient suffering from
Scoliosis.
The Cobb Angle and its Calculation
In order to measure the Cobb angle a line must be
drawn parallel to the most tilted vertebra at the
top of the curve. Then a similar line is drawn at the
most tilted vertebra at the bottom of the curve.
For each parallel line a perpendicular line is drawn
from one end of the line towards the centre of the
curve so that the lines cross from each end of the
curve. The angle where the lines cross is the Cobb
angle.
The Cobb angle measurement is the gold standard
of scoliosis evaluation endorsed by Scoliosis
Research Society. It is used as the standard
measurement to quantify and track the
progression of scoliosis.
Methodology Study
The methodology study identifies the optimum
method of collecting data. Three methods have
been identified as potential ways of collecting the
raw data of the spine location and ultimately the
Cobb angle. The ASUS Xtion Pro Live depth camera
is the computer vision device used to collect the
data of the authors torso. The data produced by
each of the three methods is compared to a recent
X-Ray of the author. The X-Ray produced a cobb
angle of 33 degrees. The most accurate data
collection method was found to be the cross
sectional method. The is method uses the depth
data form the ASUS camera to produce several line
graphs looking at the cross section of the torso on
MATLAB. From the graphs the location of the spine
was recorded so the spine could be constructed in
Solidworks. Once the spine was reconstructed the
Cobb angle was calculated at 32.83 degrees
Optimum Distance Study
The optimum distance study identifies the
optimum distance for the torso of the patient to
be away from the camera. The cross sectional
method is used between the distance of 1000 -
1800mm at increments of 200mm. At each point
the Cobb angle determined is compared to that
found by the X-Ray. The Cobb angel found at
1000mm was found to be most accurate with an
error percentage of 0.51 %.
Variety of Cobb Angles Study
The final study aims at assessing the cross
sectional method used in the previous study with
different severities of Scoliosis. Three models are
manufactured with different Cobb angels using
chicken wire and paper mache. The cross sectional
method is used to determine the Cobb angle. All
three cases using the cross sectional method
produced an error percentage of under 2.5%.
Project Conclusion
The ASUS Xtion Live Pro was chosen as part of
a feasibility study to assess whether it can
perform to the standard of an X-Ray.
In the feasibility study it was found that a
cross sectional method that used MATLAB
and Solidworks had the potential to find the
Cobb angle with a low percentage error. This
data collection method was tested in two
more studies in order to assess the accuracy
of the technique with the distance from the
patient as a variable and then the severity of
the patient’s case as the variable.
The results were promising with an optimum
distance found at 1000mm and a low
percentage error of no more than 2.33% for
all the variety of scoliosis cases.
For the method to be seriously considered to
potentially replace X-Rays for calculating the
Cobb angle in Scoliosis patients a larger study
would need to be taken to produce more data
as the study only approached one human
torso and model torsos.