Differential regional textural attributes of tongue in normal and acidity patients in the light of traditional Chinese medicine.

INTRODUCTION: In Traditional Chinese Medicine (TCM), tongue diagnosis plays an important role. Besides shape, colour and textural attributes of tongue regions have significance due to their association with different organs (viz. heart, lung, kidney-bladder, liver-gallbladder and stomach-spleen) in health and disease. Although numerous quantitative methods have been proposed to reduce inter and intra observer variability in tongue diagnosis, almost all of them considered only global colour/textural features i.e. from entire body of tongue. In this exploratory work, regional colour and texture information of tongue have been analysed for 16 healthy subjects (NOM) and 18 patients suffering from chronic acidity and indigestion (ACD).

METHODS: Tongue boundaries are marked manually in each image and the tongue body is automatically partitioned into five regions linked with said internal organs. Rough assessments of region boundaries are obtained from literature. The boundaries are fine-tuned according to experts' advice. Several first and second order statistical features based on grey scale intensities and a∗ values of LAB colour space (indicative of redness) have been extracted from five different regions of tongue images. Intragroup analysis using Wilcoxon signed rank test compared different regions within individual study groups. Additionally, intergroup analysis, using Wilcoxon rank sum test, compared tongues of NOM with ACD for each region separately. p values were adjusted using the Benjamini-Hochberg false discovery rate procedure with q = 0.05.

RESULTS: Intragroup analysis reveals a∗ values are statistically different (p ≤ 0.05) between stomach-spleen and liver-gallbladder regions for ACD while no significant change of a∗ are noted between these regions of normal tongue. It was found from intergroup analysis that correlation (one of the second order texture features extracted from grey scale images) of heart region has significantly decreased while correlation of kidney, liver-gallbladder and stomach-spleen regions significantly increased from NOM to ACD.

CONCLUSION: This exploratory study sheds light on importance of inclusion of regional textural analysis of tongue in quantitative studies and can be applied to automated tongue diagnosis for other diseases.