Application of Scanning Acoustic Microscopy for Detection of Dental Caries Lesion

Introduction: A scanning acoustic microscope (SAM) is an apparatus for imaging acoustic properties. This apparatus can non-invasively and rapidly evaluate the hardness of materials in the elastic region. This device shows great potential for the diagnosis of dental caries in the clinical setting. However, since the tissue elastic modulus measured using a SAM is a property of the elastic region and the Knoop hardness is a property of the plastic region, the hardness properties differ completely. Therefore, we investigated whether the acoustic impedance measured using a SAM is related to the Knoop hardness, which is used as the standard for removal of carious dentin. Method: Polished sections were prepared from 20 extracted carious wisdom teeth. The acoustic impedance and Knoop hardness were measured for each section. In addition to comparing carious and healthy dentin in SAM images, we evaluated the difference between the carious and healthy dentin in terms of the acoustic impedance and Knoop hardness. We also evaluated the correlation between the Knoop hardness and acoustic impedance. Results: The SAM images were visualized as two-dimensional color images based on the acoustic impedance values. The mean acoustic impedance of carious dentin was significantly lower than that of healthy dentin, showing a similar trend as Knoop hardness. A strong correlation was observed between the two. Discussion: The acoustic impedance values obtained through acoustic microscopy differed significantly between carious and sound dentin. Both types of dentins were visualized using two-dimensional color images. A strong correlation was observed between the acoustic impedance value, which indicates the hardness of the elastic region, and the Knoop hardness, which indicates the hardness of the plastic region. The results of the present study indicate that acoustic impedance accurately reflects the hardness of dentin.

Non-invasive and low-artifact in vivo brain imaging by using a scanning acoustic-photoacoustic dual mode microscopy

Photoacoustic imaging is a potential candidate for in vivo brain imaging,whereas,its imaging performance could be degraded by inhomogeneous multi-layered media,consisted of scalp and skull.In this work,we propose a low-artifact photoacoustic microscopy(LAPAM)scheme,which combines conventional acoustic-resolution photoacoustic microscopy with scanning acoustic microscopy to suppress the reflection artifacts induced by multi-layers.Based on similar propagation characteristics of photoacoustic signals and ultrasonic echoes,the ultrasonic echoes can be employed as the filters to suppress the reflection artifacts to obtain low-artifact photoacoustic images.Phantom experiment is used to validate the effectiveness of this method.Furthermore,LAPAM is applied for in-vivo imaging mouse brain without removing the scalp and the skull.Experimental results show that the proposed method successfully achieves the low-artifact brain image,which demonstrates the practical applicability of LAPAM.This work might improve the photoacoustic imaging quality in many biomedical applications which involve tissues with complex acoustic properties,such as brain imaging through scalp and skull.

Scanning Electron Acoustic Microscopy of GaInAsSb by Metalorganic Chemical Vapor Deposition

Scanning electron acoustic microscopy (SEAM) is a new technique for imasing and characterization ofthermal, elastic and pyroelectric property variations on a microscale resolution. The signal generation mechanisms and the application of scanning electron acoustic microscopy in GalnAsSb alloy grown by MOCVD wereinvestigated. Defects below the surface of GalnAsSb alloy were found by SEAM images and cathodelumi-nescence. The results show that electronacoustic imaging has its own features over secondary electron imag-ing.

IC Surface Corrosion Inspection by C-Mode Scanning Acoustic Microscopy

C-mode scanning acoustical microscopy, C-SAM, is widely used in plastic package evaluations and for failure analysis. It permits to detect subsurface delaminations, cracks and pores （air bubbles） for different microelectronics packages. In this study, abnormality was observed in C-SAM daily test, the images showed no delaminations but inhomogeneities on the IC surface. Corrosion was found by optical microscope and scanning electron microscope after decapsulation. It can be revealed as the acoustic impedance is different between corrosion and normal area. The presence of inhomogeneities and discontinuities along ultrasonic waves＇ propagation paths inside the matter causes modifications in the amplitude and polarity of ultrasonic waves. However, C-SAM＇s capability in detecting IC surface corrosion has not been presented. The capability will be illustrated and the inspection mechanism will be discussed in this paper.

300MHZ scanning laser acoustic microscope

The knife-edge and harmonic technique in the Scanning Laser Acoustic Microscope is studied in this paper. The operating frequency of the SLAM can be increased from 100MHz to 300MHz by using the harmonic technique. The acoustic images of some samples are obtained on our SLAM at 300MHz.

THE MEASUREMENT OF PLASTIC DEFORMATION AND CRACK GROWTH IN CRACKED SPECIMENS BY SAM

In this paper,scanning acoustic microscope(SAM) was used to obtain some characteristic photographs which explain the mesoscopic information of several cracked specimens.New results on subsurface information of steel,nickel and aluminium were presented.Plastic deformation and crack initiation were observed and analysed.The length of crack propagation was measured.SAM is particularly suited to the study of many mesoscopic phenomena in material science because it can image mesoscopic subsurface feature without sectioning.It is revealed that SAM has a bright future in the field of mesomechanics.