In this study, using DTT, we analyzed the status of the left AF in chronic stroke patients with aphasia and investigated relations between AQ and DTT findings of the left AF. Our results can be summarized as follows: 1) AQ showed moderate positive correlation with voxel number of the left AF. However, it did not show correlation with FA and ADC values of the left AF. 2) AQ differed according to the discontinuation or non-construction of the left AF; specifically, poorer AQ scores were observed for patients who showed discontinuation of integrity or non-construction of the left AF on DTT, compared with patients who did not show those findings. FA value represents the degree of directionality of microstructures (e.g., axons, myelin, and microtubules), and ADC value indicates the magnitude of water diffusion [
14,
32]. The opposite correlation of FA (
r = 0.275) and ADC (
r = -0.286) with AQ appear to be attributed to these characteristics of FA and ADC values [
14,
32]. In contrast, the voxel number indicates the volume of the remaining AF [
33,
34]. Therefore, our results appear to indicate that the voxel number of the left AF reflected language function of patients, irrespective of directionality and diffusivity of the AF. On the other hand, discontinuation or non-construction of the left AF was an important factor for language function in these patients. Non-reconstruction of the left AF in the type A group appears to indicate severe degeneration of the left AF following severe injury of the left AF at stroke onset.
Following introduction of DTI, several studies reported on the relationship of AF finding on DTI and language function in stroke patients with aphasia [
15,
16,
18,
19,
23]. In 2008, Breier et al reported FA values on DTT of the left AF and superior longitudinal fasciculus scanned at chronic stage (1-72 months), showed correlation with repeatability of language in 20 stroke patients with aphasia [
15]. In 2009, Hosomi et al reported on comparison of the asymmetry of FA value and fiber number between the right and left AF on DTT taken within two days from onset in 13 patients with left middle cerebral artery infarcts. Significant loss of fiber number of the left AF, compared with the right AF, was observed in the group of patients with aphasia, irrespective of change of FA value at discharge (13-52 days after onset) [
16]. In 2010, Zhang et al reported on a decrease in FA value and fiber number of the left AF in 10 patients with conduction aphasia [
18]. Using DTT, they also observed injuries of the left AF in these patients. Subsequently, Marchina et al [2010], who estimated the volume of three language-related neural tracts (the AF, extreme capsule, and uncinate fasciculus, which were affected by a stroke lesion), found that lesion loads of the AF were predictive of language function in terms of rate, informativeness, efficacy of speech, and naming ability in 23 chronic stroke patients with aphasia [
19]. A recent study by Kim et al [2012] reported that the integrity of the left AF was an important factor in prediction of prognosis of language function in stroke patients with aphasia [
23]. Therefore, our results coincided with findings from the previous studies described above, showing correlation of language function of stroke patients with aphasia with the volume of the remaining left AF and preservation of integrity of the left AF was found to be important for language function in stroke patients [
16,
19,
23]. However, our result showing that FA value of the left AF did not show correlation with language function was not completely consistent with results of previous studies reporting controversial results [
15,
18]. We believe that this discordance might be attributed to the characteristics of FA value, which represents the degree of directionality of the AF [
14,
32].