High-frequency ultrasound imaging of the intervertebral disc

In vitro investigation of the detailed structure of the intervertebral disc has been reliant upon microdissection and histological techniques. However, these techniques are laborious and destructive; the latter aspect is important because it precludes repetitive testing of the disc during in vitro experimentation. The aim of the present study was to investigate the potential of using scanning acoustic microscopy (SAM) to image the detailed structure of the intact disc. A mechanically scanned 46-MHz transducer operating in pulse-echo mode was used to obtain images of porcine coccygeal and lumbar discs; scanned regions-of-interest (ROIs) were marked using permanent dye and small surface cuts, respectively. SAM images were compared with corresponding images obtained using conventional histological techniques. The annulus fibrosus was characterised by alternate light and dark bands; the former represent the boundary between adjacent lamellae. Lamellar discontinuities and pathologic abnormalities were observed in specimens. SAM is a novel, nondestructive method for detailed visualisation of the internal structure of the disc in vitro.