Introduction
Tissue acoustic properties, such as sound speed, attenuation, and impedance, are closely associated with its mechanical characteristics. Acoustic microscopy, which employs high-frequency ultrasound ranging from several tens of MHz to several GHz, enables the quantitative evaluation of these acoustic properties. Understanding the acoustic properties of biological tissues may offer new insights into disease pathology. Furthermore, because clinical ultrasound images depend on tissue acoustic properties, understanding them could improve the interpretation of echogenic patterns and contribute to developing new diagnostic approaches. Although acoustic microscopy has been applied to cardiovascular and cutaneous tissues in medical research, studies focusing on the liver, particularly hepatic tumours, remain limited.
Aims & Methods
This study aimed to quantify sound speed in hepatocellular carcinoma (HCC)—the most common primary liver tumour—and to examine its relationship with histopathological features. Histopathological classification followed World Health Organization criteria, including histological grade (well, moderately, and poorly differentiated) and histological growth pattern (trabecular, pseudoglandular, and solid). Tissue sound speed was measured using a scanning acoustic microscope (AMS-50SI; Honda Electronics Co., Ltd.) with an 80 MHz transducer. Regions of interest were identified on haematoxylin and eosin-stained slides. Serial 10 μm-thick sections were prepared from formalin-fixed, paraffin-embedded tissue blocks and rehydrated for measurement. Differences in sound speed among histological categories were compared, and statistical analysis was conducted to assess significance. A p-value of < 0.05 was considered significant. This study was approved by the institutional review board, and written informed consent was obtained.
Results
Tissue sound speed was measured at 66 sites from 51 patients. Histological grading identified 22 well, 41 moderately, and 3 poorly differentiated cases. Median sound speeds were 1584.0 m/s, 1595.9 m/s, and 1550.1 m/s, respectively. Poorly differentiated HCC showed significantly lower sound speed than the other grades (p = 0.021). Growth patterns included 50 trabecular, 10 pseudoglandular, and 6 solid cases, with median sound speeds of 1595.9 m/s, 1586.0 m/s, and 1563.6 m/s, respectively. The trabecular pattern tended to exhibit higher sound speed than the solid pattern (p = 0.063). Tissues with abundant fat or glycogen (n = 16) had significantly lower sound speeds than those without (p = 0.002). After excluding these cases, which could act as potential confounding factors, sound speed in poorly differentiated HCC remained significantly lower (p = 0.016), and higher values in the trabecular pattern persisted. Additionally, the pseudoglandular pattern showed greater variability in sound speed than the trabecular pattern.
Conclusion
Variations in acoustic properties among histological subtypes of HCC may contribute to developing novel quantitative assessments in ultrasound imaging and pathological diagnosis.
Disclosure
Kazuto Kobayashi, a co-author, has reported a relationship with Honda Electronics Co., Ltd. that includes: employment.
