Simulated Radiograph of Total Hip Arthroplasty for Verifying Measuri

ng InstrumentChen-Kun Liaw1,3 Rong-Sen Yang2 Sheng-Mou Hou2 Chiou-Shann Fuh3 T

ai-Yin Wu4

En Chu Kong Hospital, Taipei Hsian, Taiwan1

National Taiwan University Hospital, Taipei, Taiwan2

National Taiwan University, Computer Science and Information Engineering3

Taipei City Hospital4 Abstract [Background] Orientation of acetabulum and wearing parameters are important pr

ognostic factors after total hip arthroplasty. Various methods are proposed to measure them. All these methods need a standardized radiograph to verify their accuracy. In the past, mechanical devices are used. The disadvantages are expensiveness and operation error. We developed a program to do the same job. With this program, every parameter can be manipulated, and the results are reproducible without operation error.

 

[Methods] With Windows plateform and Borland C++ builder tool, we developed the simulator. Ray tracing method is used to estimate the thickness of metal which the X-ray bean passed through. Then the photo-density is calculated by interpolation of look up tables. Parameters that we can manipulate include thickness, cup size, head size, inclination, anatomic anteversion, radiographic anteversion, and operative anteversion.

 

[Results] With this program, we simulated 45 X-rays with different inclinations and anteversions. These simulated radiographs are printed in papers as teaching materials for practicing measurement of anteversions and wearings. The quality is as good as real X-rays, in which the real orientations and wearing are hard to estimate. We also use these simulated X-rays as source of automatic wearing measurement program. The result shows that the errors are within one millimeter.

 

[Conclusions] Mechanical simulation is straightforward but expensive, with inevitable operation error. Computer simulated radiograph could be a standard to estimate accuracy of a new method and also serving as a training material for residents.

Introduction Many parameters can (should) be measured.

a. Orientations:

Anteversion:

Lewinnek method

Liaw method

Widmer method

Fabeck method

Inclination

b. Wearing: Upper, Medial, Posterior

Manual methodLivermore method

…

Computerized method

Hardinge methodShaver methodLiaw method

Verification of these methods is important!!

Mechanical SimulationAdvantages:

1. Easy to persuade people to use.

Disadvantages

1. Expensive

2. Precision?

3. Digitalization

Our Solution•Building our own software

•Cost down

•Digitalization•Bias elimination

•Batch processing can automatically produce many simulated X-rays.

Our Algorithm•Ray tracing

–See X-ray as many X-ray lines

–Trace every X-ray line

–Calculate the total thickness of metal it passes.

–Convert thickness to gray-scale pixel

SIC03-P012