Diagnostic ultrasound tooth imaging using fractional fourier transform

Abstract

Abstract-An ultrasound contact imaging method is proposed to measure the enamel thickness in human tooth. A delay-line transducer with a working frequency of 15 MHz is chosen to achieve a minimum resolvable distance of 400 µm in human enamel. To confirm the contact between the tooth and the transducer, a verification technique based on the phase shift upon reflection is used. Because of the high attenuation in human teeth, linear frequency modulated chirp excitation and pulse compression are exploited to increase the penetration depth and improve the signal-to-noise ratio. Preliminary measurements show that the enamel-dentin boundary creates numerous internal reflections, which cause the applied chirp signals to interfere arbitrarily. In this work, the fractional Fourier transform (FrFT) is employed for the first time in dental imaging to separate chirp signals overlapping in both time and frequency domains. The overlapped chirps are compressed using the FrFT and matched filter techniques. Micro-CT is used for validation of the ultrasound measurements for both techniques. For a human molar, thickness of the enamel layer is measured with an average error of 5.5% after compressing with the FrFT and 13.4% after compressing with the matched filter based on average speed of sound in human teeth.

In Vitro Enamel Thickness Measurements with Ultrasound

“…This also means that V marked areas might not necessarily have the same SOS present in T marked areas. Furthermore, anisotropy in teeth has been reported by several studies as a primary obstacle for the utilisation of diagnostic ultrasound in dentistry (Harput et al 2011;Huysmans and Thijssen 2000;Louwerse et al 2004;Slak et al 2011;Tagtekin et al 2005). …”

“…Tagtekin et al (2005) investigated ultrasound for monitoring occlusal enamel on worn molars in vitro and concluded that ultrasound was a promising tool for that task. Indeed, several studies have compared ultrasound measurements with histology, the gold standard in the field, but with mixed results (Harput et al 2011;Louwerse et al 2004;Slak et al 2011;Tagtekin et al 2005). One factor that may explain the variation between these studies is the assumed SOS in enamel.…”

Harmonic cancellation in switched mode Linear Frequency Modulated (LFM) excitation of ultrasound arrays

“…LFM signals and matched filtering techniques are commonly used in a wide range of applications to improve SNR of the received signals such as in [11] and [12]. An LFM signal can be expressed for time t as…”

Detection of restoration faults under fillings in human tooth using ultrasound

“…However, the usage of coded excitation in echodentography is not common except some recent studies [6], [7]. In this work, an LFM chirp is used as an excitation signal to improve the signal-to-noise ratio (SNR) and penetration depth.…”

“…The received ultrasound echoes from the tooth sample were saved by a Waverunner 64xi Oscilloscope (LeCroy Corp.) and signals were processed in Matlab (Mathworks Inc.). The contact mode imaging and the importance of glycerin couplant is explained in [7].…”