MantisBT - ITK
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IDProjectCategoryView StatusDate SubmittedLast Update
0010421ITKpublic2010-03-15 12:152010-11-07 01:36
Reporterfbudin 
Assigned Toxiaoxiao 
PrioritynormalSeverityminorReproducibilityalways
StatusassignedResolutionopen 
PlatformOSOS Version
Product VersionITK-3-16 
Target VersionFixed in Version 
Resolution Date
Sprint
Sprint Status
Summary0010421: Computation of the FA with itkDiffusionTensor3D returns NaN
DescriptionIn some cases, FA should be 0 but 3.0 * isp - trace * trace is negative instead of being equal to 0 (very small value). This appends on my computer if I use doubles (if I use floats it works properly).

The current code is:
 const RealValueType isp = this->GetInnerScalarProduct();

  if( isp > 0.0 )
    {
    const RealValueType trace = this->GetTrace();
    const RealValueType anisotropy = 3.0 * isp - trace * trace;
    const RealValueType fractionalAnisotropy =
        static_cast< RealValueType >( vcl_sqrt(anisotropy / ( 2.0 * isp ) ) );
    return fractionalAnisotropy;
    }
It does not check that anisotropy is positive. In some cases, it ends up being negative and the function returns NaN.
Steps To Reproduce
Additional InformationIf anisotropy is negative, it should probably be set to 0.
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Issue History
Date ModifiedUsernameFieldChange
2010-03-15 12:15fbudinNew Issue
2010-03-15 17:05Luis IbanezStatusnew => assigned
2010-03-15 17:05Luis IbanezAssigned To => Luis Ibanez
2010-11-07 01:36Luis IbanezAssigned ToLuis Ibanez => xiaoxiao

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