Pattern Classification Methods for Analysis and Visualization of Brain Perfusion CT Maps - Computational Intelligence Paradigms in Advanced Pattern Classification - page 160

6 System Validation and Results

The DMD system was validated on set of 37 triplets of medical images acquired
from 30 different adult patients (man and woman) with suspicious of ischemia /
stroke. Each triplet was consisted of perfusion CBF and CBV map and “plain” CT
image (one of the image from perfusion treatment acquired before contrast arrival
became visible). The algorithm response was compared to image description done
to each case by radiologist.
The hypothesis to verify was if there are any lesions in perfusion map and if the
algorithm found correct position of them (if the algorithm gave a wrong answer
for any of those conditions the case was considered as “error”). Tests results were
summed up according to terminology presented in Table 4.

Table 4 Classification of test results according to presence / absence of errors (according
to [2])

Actual condition
Present Absent

T est result Positive True positive False positive

Negative False (invalid) negative True (accurate) negative

• True positive (TP) - approvement of hypothesis (presence / position of lesions),

algorithm results matched radiologist description.

• False positive (FP) - the error of rejecting a hypothesis (presence / position of

lesions) when it is actually true (algorithm did not find lesions or situated them
in wrong place).

• True negative (TN) - rejecting a hypothesis (presence of lesions) when perfu-

sion maps did not show lesions.

• False negative (FN) - the error of failing to reject a hypothesis (presence of le-

sions) when perfusion maps did not show lesions.

The obtained results are presented in tables. Table 5 contains results of full auto-
matic detection (without manual correction of position of symmetry axis). Table 6
contains results of semi automatic detection (with manual correction of position of
symmetry axis).

Table 5 Full automatic detection results (without correction of position of symmetry axis)

Actual condition
Present Absent

Test result Positive 11 21

Negative 14 28