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Anais do IHC'2001 - Departamento de Informática e Estatística - UFSC

Anais do IHC'2001 - Departamento de Informática e Estatística - UFSC

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298<br />

<strong>Anais</strong> <strong>do</strong> IHC’2001 - IV Workshop sobre Fatores Humanos em Sistemas Computacionais<br />

analysed. The measurement problem at this point could be solved in several ways, ranging<br />

from fully manual methods (the <strong>do</strong>ctor uses a ruler on the screen to measures the diameter)<br />

to fully automatic methods (the <strong>do</strong>ctor presses a button and the diameter is measured and<br />

displayed by the machine).<br />

The first type of solution is not really an option these days - we should be able to <strong>do</strong><br />

better than that with available digital image analysis technology. The last type of solution,<br />

however, is not a realistic option either, since fully automatic methods often fail to reliably<br />

isolate the head from the rest of the image, a precondition for measurement. In practice, we<br />

will find solutions where the <strong>do</strong>ctor and the machine interact to obtain a reliable<br />

measurement of the head's diameter.<br />

In the context of this example, user intervention can occur at several moments in<br />

the process, such as to initialise the method (the <strong>do</strong>ctor clicks one point insi<strong>de</strong> the baby's<br />

head), to check the accuracy of the result produced automatically (the head's contour found<br />

by the machine is drawn and the <strong>do</strong>ctor confirms its position before the diameter is<br />

estimated), or even to correct the segmentation result manually (the <strong>do</strong>ctor edits the contour<br />

produced by the machine before measurement is <strong>do</strong>ne).<br />

3. An early review of aspects related to interactive practices in the<br />

segmentation of medical images<br />

The interaction strategies a<strong>do</strong>pted by existent methods differ with respect to following<br />

three aspects have been discussed by Olabarriaga and Smeul<strong>de</strong>rs (2001):<br />

• The type of data input by the user during the segmentation process. The main types<br />

usually i<strong>de</strong>ntified are:<br />

a) setting parameter values in a continuous or discrete interval;<br />

b) pictorial input directly indicating positions on the image grid; and<br />

c) choosing among pre-<strong>de</strong>fined menu items or select among pre-computed segmented<br />

results.<br />

• The computational consequence of user input, i.e., how the input data are interpreted to<br />

feedback the computational part. In the simple case, the input data are directly used as<br />

parameters for the computational part. Indirection (that is, interpretation of user input)<br />

is mainly aimed at:<br />

a) achieving interaction simplicity, typically enabling the user to see only the grey<br />

image on the screen and to draw the object with a graphical tool; and<br />

b) reducing the amount of user interventions by means of an "intelligent" analysis of<br />

user actions and revision of the parameters for the computational part.<br />

• The goal of user intervention in the interactive process. We i<strong>de</strong>ntify five main purposes<br />

(also consi<strong>de</strong>red five different user roles, although the user may play more than one<br />

role in many situations):<br />

a) to judge (accept or reject) the result generated by the computational part;<br />

b) to correct the outcome directly using a graphic editor, eventually when and where<br />

the computational method fails;

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