V. Kananen

Ultrasonic transport of particles into articular cartilage and subchondral bone

Osteoarthritis (OA) is a debilitating musculoskeletal disease without a cure. Delivery of therapeutic compounds is a problem and localized drug therapy could enable new treatment strategies. In this study high-intensity ultrasound was used to deliver micro- and nano-particles (MNPS) into three bovine osteochondral samples: (1) control (C) that was exposed to the particles without sonication, (2) UST-1 that was sonicated prior to immersion in a MNPS and (3) UST-2 that was sonicated in the presence of MNPS. Following treatment samples were cut into 2.9 ± 0.3 mm sections and digital images were obtained by light microscopy. In the sonicated samples (UST-1 and UST-2) MNPS penetrated into articular cartilage and subchondral bone. No MNPS penetration was observed in C. The proposed technique could potentially be used for local drug treatment of OA.

Discriminating pores from inclusions in rolled steel by ultrasonic echo analysis

The quality of steel is degraded by inclusions and pores which form during production. When exposed to external stress, large inclusions initiate cracks that weaken the mechanical strength of steel components. In this study, an ultrasonic immersion pulse-echo setup, which is currently used for quality control, was employed for signal-based inclusion and pore discrimination. The results from the used wavelet and short-time Fourier transform methods were verified with optical microscopy and scanning electron microscopy. The ultrasonic method was tested on 22 rolled bearing steel 100Cr6 samples featuring a total of 24 inclusions and 16 pores. Based on the differences in the echo peak frequency, it was possible to discriminate all pores from inclusions with the wavelet transform method. Sulfide and oxide inclusions also featured differences within the 9–14 MHz frequency range. The developed ultrasonic method was found to be capable of discriminating inclusions from pores in rolled bearing steel 100Cr6.

Ultrasonic damage assessment of articular cartilage for ultrasonic drug delivery

Osteoarthritis (OA) is a common musculoskeletal disease. There are drug therapies under development, but no localized way to transfer drugs into articular cartilage (AC). Previously we showed that 20 kHz high intensity ultrasound (HIU) can deliver micro- and nano-particles into AC [1]. However, at low frequencies, cavitation may occur. Our hypothesis is that 20 MHz ultrasound pulse-echo can be used to track changes in ultrasound reflection from AC during HIU. Here we tested the feasibility of this approach for characterizing cavitation-related damage. We observed that the relative decrease in mean surface reflection coefficient at 15, 20 and 25 MHz were -40.9 +/- 7.9 %, -53.4 +/- 12.0 % and -61.1 +/- 7.1 %, respectively, during a 5-minute HIU exposure. Frequencies above 16 MHz were the most sensitive to changes induced by HIU in both samples. We propose that the change resulted from cavitation-related cratering of the AC surface and exposure of AC tissue with lower collagen content. In conclusion, the acoustic reflection coefficient of the AC surface could be a sensitive parameter to estimate damage in the AC surface during HIU exposure.

Ultrasonic inclusion and pore classification in rolled and unrolled steel samples

The feasibility of an ultrasonic method to discriminate inclusions and pores (foreign bodies, FBs) in rolled and unrolled steel samples was studied. A 10 MHz point-focused transducer was used to scan immersed steel samples in pulse-echo mode to detect FBs. The differences in RF-echo amplitude and frequency content allowed discriminating inclusions from pores in the steel samples. Optical microscopy and scanning electron microscopy served as reference methods on cut samples to verify the classification after the ultrasonic measurement. The FB classification method was tested on 24 inclusions and 16 pores from rolled samples. All FBs were correctly classified indicating that this method is feasible for FB classification in rolled steel samples. In the unrolled samples, differences in calcium-aluminate (CaAl) inclusion and pore spectra at 16 MHz should allow CaAl discrimination from pores.

P1E-3 Ultrasonic QNDE Instrument for Quantitative Inclusion and Pore Characterization of Steel Billets

Steel fabrication suffers from inclusions and pores that are formed into steel during production. Ultrasonic characterization of unrolled steel bars is challenging due to low signal-to-noise ratio (SNR). Signal processing provides methods to characterize granular steel samples. We are developing a 9.5 MHz instrument for quantitative inclusion (manganese-sulphur) and pore characterization in immersed steel billets. The instrument is capable of quantitative foreign body classification. MnS inclusions and soft inclusions (pores) can be segregated. After the samples were characterized ultrasonically, inclusions were cut out and a scanning electron microscope (SEM) was used to validate the results. The instrumentation will allow nondestructive waste product content estimation for each waste material separately. It improves the steel fabrication quality control by giving detailed information of the inner structure and therefore allowing more precise fabrication process control.

Estimating the size of a scatterer by transmitted signal delay

Using delay in the time-of-flight (TOF) of an ultrasonic signal to estimate the lateral size of a scatterer was evaluated. A rolled steel sample featuring a 2 mm diameter side-drilled hole (SDH) was immersed in water. The maximum delay produced by the SDH was estimated from through transmission signals. To estimate SDH size the measured delay was compared to theoretical delays with straight path assumption. The size estimate agreed with the real size. This result can find relevance by enabling a simple method for scatterer size estimation.

GHz ultrasonics with arbitrary code excitation

Recently we developed a high frequency coded signal ultrasound microscope based on quadrature modulation [1, 2]. The device allowed pulse-echo operation at 300 MHz, however, local oscillator crosstalk reduced the SNR of pulse compression. To achieve GHz-range operation we present an improved design with new RF-components. The new design improved SNR by 16 dB compared to [2]. We also investigated the use of a dual-band chirp to further reduce the local oscillator interference. We successfully tested the device with a GHz ultrasound transducer in 0.9-1.1 GHz band using an arbitrary TX code. This achievement is a first step towards bringing the advantages of coded excitation into GHz ultrasound microscopy.

Quantitative Ultrasonics for Inclusion and Pore Characterization of Steel Billets

We present ultrasonic quantitative inclusion and pore characterization in bearing steel 100Cr6. A 9.5MHz focused transducer (14cm focal length, 6.3MHz bandwidth) scanned across the top surface of immersed 22*12*6cm3 production samples (8pcs). Automatic pre‐processing was employed to detect inclusions in samples. Recorded RF‐data were analyzed. Continuous wavelet transform and cross‐correlation were applied to measured and registered RF‐signals from known (verified by SEM) inclusions and pores. This allowed characterizing the echoes by shape from wavelet coefficients (WC) and cross‐correlation coefficients: the echo is a superposition of the reflection from the inclusion front and back surface, whereas pores exhibit no back surface echo due to their large acoustic impedance mismatch. Fourier transform allows characterizing echo RF‐signals by frequency content. Dissimilarities ‐signal phase and WCs‐ in echo characteristics between different inclusion and pore classes allows quantitative inclusion and pore c...

P4G-4 Airborne Ultrasonic Confocal Instrument for Parametric Imaging of Complex Samples

A 680 kHz confocal airborne ultrasonic instrument was built for quantitative material characterization based on parametric imaging. This instrument allows characterization of fragile or moist sensitive samples. Few such instruments are commercially available. The instrument performs simultaneous attenuation and time-of-flight measurements in linear reflection and transmission modes. Sample surface topography is measured in reflection mode and local sample thickness is calculated using the inter-transducer distance. Results for a Pinus Sylvestris test sample are presented. The speed of sound, attenuation, and modulus of elasticity can be mapped locally (local density was measured with X-ray in transmission mode). No repeatable nonlinear sample characteristics were achieved for this sample.