Ultrasonic microscanning

Ultrasound capsule endoscopy: sounding out the future

Video capsule endoscopy (VCE) has been of immense benefit in the diagnosis and management of gastrointestinal (GI) disorders since its introduction in 2001. However, it suffers from a number of well recognized deficiencies. Amongst these is the limited capability of white light imaging, which is restricted to analysis of the mucosal surface. Current capsule endoscopes are dependent on visual manifestation of disease and limited in regards to transmural imaging and detection of deeper pathology. Ultrasound capsule endoscopy (USCE) has the potential to overcome surface only imaging and provide transmural scans of the GI tract. The integration of high frequency microultrasound (µUS) into capsule endoscopy would allow high resolution transmural images and provide a means of both qualitative and quantitative assessment of the bowel wall. Quantitative ultrasound (QUS) can provide data in an objective and measurable manner, potentially reducing lengthy interpretation times by incorporation into an automated diagnostic process. The research described here is focused on the development of USCE and other complementary diagnostic and therapeutic modalities. Presently investigations have entered a preclinical phase with laboratory investigations running concurrently.

Design and testing of prototype handheld scanning probes for optical coherence tomography

Three simple and low-cost configurations of handheld scanning probes for optical coherence tomography have been developed. Their design and testing for dentistry applications are presented. The first two configurations were built exclusively from available off-the-shelf optomechanical components, which, to the best of our knowledge, are the first designs of this type. The third configuration includes these components in an optimized and ergonomic probe. All the designs are presented in detail to allow for their duplication in any laboratory with a minimum effort, for applications that range from educational to high-end clinical investigations. Requirements that have to be fulfilled to achieve configurations which are reliable, ergonomic-for clinical environments, and easy to build are presented. While a range of applications is possible for the prototypes developed, in this study the handheld probes are tested ex vivo with a spectral domain optical coherence tomography system built in-house, for dental constructs. A previous testing with a swept source optical coherence tomography system has also been performed both in vivo and ex vivo for ear, nose, and throat-in a medical environment. The applications use the capability of optical coherence tomography to achieve real-time, high-resolution, non-contact, and non-destructive interferometric investigations with micrometer resolutions and millimeter penetration depth inside the sample. In this study, testing the quality of the material of one of the most used types of dental prosthesis, metalo-ceramic is thus demonstrated.

Statistical analysis of high frequency ultrasonic backscattered signals from basal cell carcinomas

A statistical approach was implemented in the study of histologic characteristics from ex vivo basal cell carcinomas, based on the properties of backscattered acoustic waves, for the purpose of evaluating the method as a diagnostic tool. The study was developed using an ultrasound biomicroscope working at a frequency of 45 MHz. The parameters examined were signal-to-noise ratio (SNR), and shape parameters from the Weibull (b(W)) and generalized gamma (c(GG) and υ(GG)) probability density functions. Twenty-seven carcinomatous skin samples were obtained from volunteer patients and classified into two groups (BCC1 and BCC2) based on the distribution patterns of their tumor nests; also, seven non-tumoral samples were used for comparative purposes. Significant differences between groups were obtained for all studied parameters. The successful differentiation between some tissue groups suggests its potential use for carcinoma characterization.

Microsystem technologies for medical applications

Medical technologies are evolving at a very rapid pace. Portable communication devices and other handheld electronics are influencing our expectations of future medical tools. The advanced medical technologies of our future will not necessarily be large expensive systems. They are just as likely to be small and disposable. This paper reviews how microsystems are already impacting health care as commercial products or in clinical development. Example systems for point-of-care testing (POCT), patient monitoring tools, systemic drug delivery, local drug delivery, and surgical tools are described. These technologies are moving care from hospitals to outpatient settings, physicians' offices, community health centers, nursing homes, and the patients' homes. Microsystems that are rapidly adopted fulfill significant medical needs and are compatible with existing clinical practice.

PMN-PT single crystal focusing transducer fabricated using a mechanical dimpling technique

A ∼5MHz focusing PMN-PT single crystal ultrasound transducer has been fabricated utilizing a mechanical dimpling technique, where the dimpled crystal wafer was used as an active element of the focusing transducer. For the dimpled focusing transducer, the effective electromechanical coupling coefficient was enhanced significantly from 0.42 to 0.56. The dimpled transducer also yields a -6dB bandwidth of 63.5% which is almost double the bandwidth of the plane transducer. An insertion loss of the dimpled transducer (-18.1dB) is much lower than that of the plane transducer. Finite element simulation also reveals specific focused beam from concave crystal surface. These promising results show that the dimpling technique can be used to develop high-resolution focusing single crystal transducers.

A high-frequency ultrasound imaging system combining limited-angle spatial compounding and model-based synthetic aperture focusing

High-frequency ultrasound (HFUS) imaging systems are routinely used for medical diagnostics (skin, eyes) and for medical research (small animal imaging). Although systems with array transducers are already commercially available, imaging systems with single-element transducers are still of interest and available as well, because this type of transducer is less complex, less expensive, and technically mature. Nevertheless, drawbacks exist, for example, the need for mechanical scanning units and the limited depth of field. In this paper, we present a high-frequency (20 MHz) ultrasound imaging system equipped with a spherically focused transducer. Limited-angle spatial compounding is utilized to improve the image contrast, to suppress speckle and noise, and to reduce imaging artifacts. To overcome the limitation in depth of field, the system uses a novel synthetic aperture focusing technique based on the correlation of the recorded echo signals with the simulated point spread function of the imaging system. This method results in lower side lobe levels and greater noise reduction compared with delay-and-sum focusing, which is demonstrated by wire phantom measurements. When used in combination with limited-angle spatial compounding, as presented in this paper, the resulting image quality is superior to conventional single-element HFUS imaging systems and to array systems. Examples of measurements on tissue phantoms and small animals (ex vivo) are presented and discussed in detail.

High-resolution ultrasonography assists the differential diagnosis of blue naevi and cutaneous metastases of melanoma

BACKGROUND

Metastases of cutaneous melanoma may simulate benign blue naevi clinically.

OBJECTIVES

To investigate the value of ultrasonography in the differential diagnosis of lesions that look similar clinically, i.e. blue naevi and cutaneous metastases of melanoma.

METHODS

Participants were invited for inclusion in the study if they had a cutaneous blue lesion clinically suggestive of a blue naevus or cutaneous metastasis of melanoma. After obtaining signed consent, the lesion was photographed and studied using dermoscopy and high-resolution ultrasonography before being removed for histological examination. Clinical, dermoscopic and ultrasonographic images were reviewed anonymously by four dermatologists to assign the diagnosis of blue naevus or metastasis of melanoma. The diagnostic performance of clinical examination, dermoscopy and sonography was assessed for the ability of each to differentiate between metastases of melanoma and blue naevi with reference to the histological diagnosis. Moreover, experts undertook a semeiological description of each ultrasonographic image according to seven items: location of the lesion, echogenicity, homogeneity, shape of the lesion, definition of margins, posterior acoustic shadow and increased posterior echogenicity.

RESULTS

  Twenty-eight patients were included with a total of 39 blue skin lesions, and 17 of the 28 patients had a previous history of melanoma. Interobserver agreement in the semeiological description of the sonographic images was good (κ≥0·6) for five of seven items. Sonography was more specific (94%) than clinical examination (77%) and dermoscopy (74%). The sonographic features contributing to the differential diagnosis were: location of the lesion (P=0·027), shape of the lesion (P<0·001), homogeneity (P=0·001) and increased posterior echogenicity (P=0·007).

CONCLUSIONS

Ultrasonography is a reproducible and specific tool that can assist the differential diagnosis between blue naevi and metastases of melanoma. A blue naevus is a homogeneous, hypoechoic, 'dish-shaped' lesion, located in the superficial dermis, whereas metastases of melanoma are 'potato-shaped', hypoechoic, heterogeneous lesions, located in the hypodermis.