[Mristudio-users] Anatomical localization and ROI statistics

[Ardalan Vossoughi]

Dear
my understanding is reliability precision and consistency are the same
concepts and it indicates if the Target is hit and not necessarily in the
bulls eye
validity or accuracy on the other side indicates if the bulls eye is hit
reliability is necessary but not sufficient conditions for validity
this way as Doctor Mori mentioned biases reduce validity; this is
regardless of precision which is under the influence of variability,ie
decreased precision or reliability with increased variability
Regards
AV
 On Mar 3, 2013 7:55 AM, "susumu mori" <susumu at mri.jhu.edu> wrote:

> Hi Shaimaa,
>
>
> Q2. If  I draw ROI in specific location eg. Left cerebral peduncle and get
>> a ROI statistics, and if I repeat the same step in each patient manually eg
>> in left cerebral peduncle too, if I compare the results among subjects,
>>  will the results be reliable?
>>
>
> For brain image analysis, manual delineation of structures is considered
> as the gold standard. It is recognized as ACCURATE.
> However, it is known as low PRECISION.
>
> Accuracy is also called bias and precision is related to variability or
> reproducibility.
>
> I don't know the definition of "reliability", though (somebody can explain
> it?).
>
> For example, if you have a rifle and shoot at a bull's eye. You expect
> your shots are scattered around the center. The amount of the scattering is
> precision (variability or reproducibility). It tells how good you are.
>
> On the other hand, if your rifle's scope is misaligned, you see the center
> of your scattered shots is not aligned to the center of the bull's eye.
> This is accuracy (bias).
>
> If you use automated analysis (e.g. voxel-based analysis or automated
> segmentation), you get 100% precision (do 10 times and get 10 identical
> answers). However the accuracy is unknown. Therefore, people compare the
> automated analysis results with manual delineation to measure the accuracy.
> People want to use automated methods because manual delineation has low
> precision. There is a bit of circular logic here and there is no single
> method that is the best.
>
> So, your approach is perfectly fine. In Fig. 1A of the attached paper,
> there is a description about different ROI placement approaches. Each has
> pros and cons. Hope this will help you understanding the art of ROI.
>
> Susumu
>
>
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