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Date Submitted

Last Update

0010421

ITK

public

2010-03-15 12:15

2010-11-07 01:36

Reporter

fbudin

Assigned To

xiaoxiao

Priority

normal

Severity

minor

Reproducibility

always

Status

assigned

Resolution

open

Platform

OS Version

Product Version

ITK-3-16

Target Version

Fixed in Version

Summary

0010421: Computation of the FA with itkDiffusionTensor3D returns NaN

Description

In 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.

Additional Information

If anisotropy is negative, it should probably be set to 0.

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Issue History
Date Modified	Username	Field	Change
2010-03-15 12:15	fbudin	New Issue
2010-03-15 17:05	Luis Ibanez	Status	new => assigned
2010-03-15 17:05	Luis Ibanez	Assigned To	=> Luis Ibanez
2010-11-07 01:36	Luis Ibanez	Assigned To	Luis Ibanez => xiaoxiao