Polyethylene Wear

Automatice PolyEthylene Wear Automatice PolyEthylene Wear

Measurement

報告人: 廖振焜 報告人: 廖振焜

指導教授:傅楸善教授

Polyethylene Wear

• An important prognostic factor of total hip arthroplasty

• If we measure it serially we could find theIf we measure it serially, we could find the trend of wearing direction, and wearing

volume of different materials volume of different materials.

Manual Method

• Livermore’s method is a well established method

• Find the thinnest polyethylene and thenFind the thinnest polyethylene and then measure it.

d i b

• Inter- and intra-observer error

• Livermore J, Ilstrup D, Morrey B. Effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg Am. 1990;72:518-28.

p y y p g ;

Computerized Methods

Hardinge K, Porter ML, Jones PR, Hukins DW, Taylor CJ. Measurement of hip prostheses using image analysis. The maxima hip technique. J Bone Joint Surg Br.

1991;73:724-8.

Shaver SM, Brown TD, Hillis SL, Callaghan JJ. Digital edge-detection measurement of polyethylene wear after total hip arthroplasty. J Bone Joint Surg Am. 1997;79:690-700.

Martell JM, Berdia S. Determination of polyethylene wear in total hip replacements with use of digital radiographs. J Bone Joint Surg Am. 1997;79:1635-41.

Computerized Methods

• All of them required manual intervention.

• We propose to develop a method without manual intervention

manual intervention.

– Development of simulator

l f i

– Development of automatic PE wear meter

Why Do We Use Simulator?

• To verify the accuracy of new methods.

• To simulate every control condition.

• To reduce noise in early development of

• To reduce noise in early development of new methods.

How Does Our Simulator Work?

• Line tracing method

Wh i O GL Di X?

• Why not using OpenGL or DirectX?

– Reflection vs. Transparency

Ab i l

• Absorption law

– Beer-Lambert law

P i ^kb

– Penetration = e^-kbc

– k: molar absorbability – b: path length

– c: concentration

X l di ib i

• X-rays energy: normal distribution

– Hard to implement

How Does Our Simulator Work?

• It is hard to implement by absorption law.

• Absorption example

• Lookup table method

• Lookup table method

Automatic PE Wear Meter

• Find head-neck junction by cross-correlation.

– P(x,y) correlate to Q(x,y)

– Cross-correlation = Σ(P(x,y)-p)(Q(x,y)-q) – p: mean of P(x,y)

– q: mean of Q(x,y)

– Find region of maximum cross-correlation value – Cost about 20 seconds.

Automatic PE Wear Meter

• Project 200 lines from indicated place to upper right side with about 135 degrees span.p

• Detect edges with vector edge detector.

Automatic PE Wear Meter

– Find center from the 200 detected edges.

– f(x,y): Σ((x-xi)²+(y-yi)²-D)² – D: 1/nΣ(x-xi)( ) (y y )²+(y-yi)²

– Find minimum of f(x,y)

Automatic PE Wear Meter

• Check acetabulum centers by “Hill- Climbing Search”.

Automatic PE Wear Meter

• Project 240 lines from the new center with

270 d Th l l ft t i

270 degrees span. The lower left part is excluded.

• Find head edges with the same vector edge detector.

• Find the head center

• Check head centers by “Hill Climbing

• Check head centers by Hill-Climbing Search”

Material and Methods

• Simulated 64 X-rays

– 2 different anteversions – 2 different inclinations2 different inclinations

– 4 different upper wearings 4 diff t di l i

– 4 different medial wearings

• Compare results with simulated parameters

Material and Methods

• 88 total hip arthroplasty X-rays

– First 88 total hip arthroplasy X-rays in En Chu Kong hospital g p

– Digitalized by Sony S70 digital camera No exclusion criteria

– No exclusion criteria

Result

• 64 simulated X-rays:

– 61 excellent detections

– Error of medial wear is -0.023±0.176mmError of medial wear is 0.023±0.176mm – Error of upper wear is -0.152± 0.315mm

Result

• 3 wrong detections

Result

• Program measurable: 53.4% (47/88)

A i 64 8% (57/88)

– Accept minor error: 64.8% (57/88)

• Livermore’s method measurable: 23.9%

(21/88)

• With aid: 78 4% (69/88)

• With aid: 78.4% (69/88)

Result

Measurable

＼ Our Program

Livermore’s Method

Livermore’s Method with

＼

Unmeasurable

Our Program Method without Aid

Method with Aid

Our Program 8 24

Livermore’s Livermore s

Method without Aid

27 49

Livermore’s Method with

Aid

2 0

Aid

Measurable

＼ Unmeasurable

Program Livermore’s Method With Aid

Program^g 88 ²⁴

Livermore’s Method 27 49

With Aid 2 0

Measurable

＼ Unmeasurable

Program Livermore’s Method With Aid

Program^g 8 2424

Livermore’s Method 27 49

With Aid 2 0

Measurable

＼ Unmeasurable

Program Livermore’s Method With Aid

Program 8 24

Livermore’s Method 27 ⁴⁹

With Aid 2 0

Measurable

＼ Unmeasurable

Program Livermore’s Method With Aid

Program 8 24

Livermore’s Method 27 49

With Aid 2 ⁰

Discussion

• Reasons of misdetections

L k

– Low kv

– Screw noise Bone noise – Bone noise

• Precision error of simulated X-rays

Quantization error – Quantization error

• Distorsions

X fil i – X-ray filming – Digitizing

Conclusions

• We designed a program which can

automatically measure polyethylene wear.

We have tested it on simulated X-rays and y the result is encouraging. Clinical validation is needed in future work

is needed in future work.

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