Comparison of high frequency ultrasound and optical coherence tomography as modalities for high resolution and non invasive skin imaging

Ultra-High-Frequency Ultrasound: A Modern Diagnostic Technique for Studying Melanoma

The development of new ultra-high-frequency devices with a resolution of 30 μm makes it possible to use ultrasound in the study of new small anatomical units and to apply this tool to new fields of pathology. Cutaneous melanoma is a severe skin disease with an incidence of approximately 160 000 new cases each year and 48 000 deaths. In this paper, we evaluate the role of HFUS in the diagnosis of cutaneous melanoma, describe the sonographic appearance of skin layers in the pre-excision phase as well as of lesion features, and correlate the characteristics with pathological examination.

Clinical Application of Ultra-High-Frequency Ultrasound

Musculoskeletal ultrasound involves the study of many superficial targets, especially in the hands, wrists, and feet. Many of these areas are within the first 3 cm of the skin surface and are ideal targets for ultra-high-frequency ultrasound. The high spatial resolution and the superb image quality achievable allow foreseeing a wider use of this novel technique, which has the potential to bring innovation to diagnostic imaging.

Ultra-high-frequency ultrasound monitoring of melanomas arising in congenital melanocytic nevi: a case series

The aims of our study were to evaluate with ultra-high-frequency ultrasound (UHFUS) the ultrasound features of congenital melanocytic nevi (CMNs) and malignant melanomas (MMs) arising in CMNs and the correlation between ultrasonographic thickness and histological thickness in MMs. We evaluated 10 patients with small-medium CMNs and 10 patients with MMs arising in small-medium CMNs. We collected patient's data, clinical and dermoscopic features. The UHFUS was performed using a 70 MHz frequency probe to study the ecostructure, shape and vascularization. Breslow thickness was compared with ultrasonographic thickness. In the MMs group the following dermoscopic features were described: hyperpigmentation (n = 9), regression area (n = 6), whitish-blue veil (n = 5), thickened network (n = 5), irregular globules (n = 3), inverse network (n = 2) and striae (n = 1). Hyperpigmentation (n = n = 9), thickened network (n = 7), irregular globules (n = 5), regression area (n = 5), striae (n = 1) and whitish-blue veil (n = 1) were found in the CMNs group. The multicomponent pattern was present in both MMs (n = 4) and in CMNs (n = 5). Moreover, the parameters indicative of suspected malignancy were variously combined in the two groups, without showing significant differences in the statistical analysis; with the exception of the blue veil that correlated with the diagnosis of MM. Ultrasonoghaphic vascularization was an ever-present parameter in MMs (100%), with high intensity of intratumoral signal, as opposed to CMNs. We also found a statistically significant correlation between ultrasound thickness and Breslow thickness. In the future, this technique could implement the diagnostic preoperative phase of MMs arising in CMNs in combination with standard clinical-dermatoscopic evaluation.

Optical coherence tomography-based non-invasive evaluation of premalignant lesions in SKH-1 mice

Non-invasively diagnosis of actinic keratoses (AK) is important for preventing cutaneous squamous cell carcinoma (cSCC). Optical coherence tomography (OCT) can be used to detect the cross-sectional skin micromorphology with sufficient resolution and imaging depth. It has the capability to reveal the changes in skin microstructure during the development of AK. Therefore, OCT can serve as a tool for diagnosing AK. This study explores the feasibility of OCT in evaluating the structural changes in mouse skin at the different stages following exposure to ultraviolet radiation. The performance of OCT is compared with histology, the gold standard in this context. The imaging results demonstrate that a wave-shaped irregular dermo-epidermal junction (DEJ), as well as the continuous thickening of the epidermis, are useful diagnostic parameters for diagnosing AK. Histological examinations confirm these observations. These findings emphasize the need for effective skin protection or medical treatment once changes in the DEJ and epidermis are detected. OCT shows strong potential for non-invasive evaluation of such changes and AK development, and can be used for the prevention of cSCC without the necessity of taking biopsies.

Therapy of infected wounds: overcoming clinical challenges by advanced drug delivery systems

In recent years, the incidence of infected wounds is steadily increasing, and so is the clinical as well as economic interest in effective therapies. These combine reduction of pathogen load in the wound with general wound management to facilitate the healing process. The success of current therapies is challenged by harsh conditions in the wound microenvironment, chronicity, and biofilm formation, thus impeding adequate concentrations of active antimicrobials at the site of infection. Inadequate dosing accuracy of systemically and topically applied antibiotics is prone to promote development of antibiotic resistance, while in the case of antiseptics, cytotoxicity is a major problem. Advanced drug delivery systems have the potential to enable the tailor-made application of antimicrobials to the side of action, resulting in an effective treatment with negligible side effects. This review provides a comprehensive overview of the current state of treatment options for the therapy of infected wounds. In this context, a special focus is set on delivery systems for antimicrobials ranging from semi-solid and liquid formulations over wound dressings to more advanced carriers such as nano-sized particulate systems, vesicular systems, electrospun fibers, and microneedles, which are discussed regarding their potential for effective therapy of wound infections. Further, established and novel models and analytical techniques for preclinical testing are introduced and a future perspective is provided.

The Application of Ultra-High-Frequency Ultrasound in Dermatology and Wound Management

The management of lower extremity wounds is frequently performed by means of clinical examination, representing a challenge for the clinician due to the various conditions that can potentially enter differential diagnosis. Several diagnostic techniques are available in the dermatologist’s arsenal as a support to diagnosis confirmation, including dermoscopy and ultrasonography. Recently, a novel ultrasonographic technique involving the use of ultra-high ultrasound frequencies has entered the scene, and appears a promising tool in the diagnostic workup of skin ulcerative lesions. The focus of this review is to discuss the potential role of ultra-high-frequency ultrasonography in the diagnostic workup of wounds in the light of the current applications of the technique.

Ultra-High Frequency Ultrasound, A Promising Diagnostic Technique: Review of the Literature and Single-Center Experience

OBJECTIVES

Ultra-high frequency ultrasonography (UHFUS) is a recently introduced diagnostic technique which finds several applications in diverse clinical fields. The range of frequencies between 30 and 100 MHz allows for high spatial resolution imaging of superficial structures, making this technique suitable for the imaging of skin, blood vessels, musculoskeletal anatomy, oral mucosa, and small parts. However, the current clinical applications of UHFUS have never been analyzed in a consistent multidisciplinary manner. The aim of this study is to revise and discuss the current applications of UHFUS in different aspects of research and clinical practice, as well as to provide some examples of the current work-in-progress carried out in our center.

MATERIALS AND METHODS

A literature search was performed in order to retrieve articles reporting the applications of UHFUS both in research and in clinical settings. Inclusion criteria were the use of frequencies above 30 MHz and study design conducted in vivo on human subjects.

RESULTS

In total 66 articles were retrieved. The majority of the articles focused on dermatological and vascular applications, although musculoskeletal and intraoral applications are emerging fields of use. We also describe our experience in the use of UHFUS as a valuable diagnostic support in the fields of dermatology, rheumatology, oral medicine, and musculoskeletal anatomy.

CONCLUSION

Ultra-high frequency ultrasonography application involves an increasing number of medical fields. The high spatial resolution and the superb image quality achievable allow to foresee a wider use of this novel technique, which has the potential to bring innovation in diagnostic imaging.

Optical coherence tomography imaging of oral mucosa bullous diseases: a preliminary study

OBJECTIVES

Optical coherence tomography (OCT) is a non-invasive technique based on optical imaging with a micrometre resolution. The purpose of this study is to investigate the potential role of OCT in evaluating oral mucosa bullous diseases.

METHODS

two patients with bullous pemphigoid (BP) and one patient with pemphigus vulgaris (PV) were examined and images of their oral lesions were performed using OCT.

RESULTS

In OCT images, the BP blister has a clearly different morphology from the PV one compared to the blistering level.

CONCLUSION

This exploratory study suggests that the OCT is able to distinguish epithelial and subepithelial layer in vivo images of healthy oral mucosa from those with bullous diseases, assisting the clinicians in differential diagnosis.The presented data are in accordance with the scientific literature, although a wider pool of cases is needed to increase statistical power. Histological examination and immunofluorescence methods remain the gold standard for the diagnosis of oral bullous diseases. In this context, the OCT can provide the clinician with a valuable aid both as an additional diagnostic tool and in the follow up of the disease.

Measurement of Oral Epithelial Thickness by Optical Coherence Tomography

Optical coherence tomography (OCT) is a real-time, in-situ, non-invasive imaging device that is able to perform a cross-sectional evaluation of tissue microstructure based on the specific intensity of back-scattered and reflected light. The aim of the present study was to define normal values of epithelial thickness within the oral cavity. OCT measurements of epithelial thickness were performed in 28 healthy patients at six different locations within the oral cavity. Image analysis was performed using Image J 1.52 software. The healthy epithelium has a mean thickness of 335.59 ± 150.73 µm. According to its location within the oral cavity, the epithelium showed highest values in the region of the buccal mucosa (659.79 µm) and the thinnest one was observed in the mouth’s floor (100.07 µm). OCT has been shown to be useful for the evaluation of oral mucosa in vivo and in real time. Our study provides reference values for the epithelial thickness of multiple sites within the oral cavity. Knowledge of the thickness values of healthy mucosa is, therefore, of fundamental importance.

The effect of melanin on in vivo optical coherence tomography of the skin in a multiethnic cohort

BACKGROUND

Noninvasive real-time assessment of living tissue is quickly becoming invaluable for bolstering histologic and dermatoscopic measures of cutaneous conditions. While many skin researchers have explored the utility of noninvasive imaging in inflammatory and malignant skin conditions, there is yet to be a definitive and direct assessment of the effects of melanin on the quality of optical coherence tomography (OCT) imaging and its accuracy in multiethnic patient populations. We conducted a study to evaluate the effects of melanin on the quality of in vivo OCT imaging.

METHODS

Volunteers of all Fitzpatrick skin types were imaged once in five skin regions. Images were analyzed for quality, defined quantitatively as depreciation of light as it passes through the depth of skin, and qualitatively as depth and contrast ranked by blinded clinicians.

RESULTS

Our analysis of sixteen subjects shows that there is a significant difference in quantitative OCT image quality between light (Fitzpatrick I-III) and dark (IV-VI) skin types for both epidermal (p 0.0328) and dermal levels (p 0.0021). However, there was no significant difference in qualitative blinded rater measures of image clarity (p 0.11) or perceived depth (p 0.13).

CONCLUSION

Based on our definition of image quality, our study shows that OCT images taken from darker skin types have slightly lower quality than those taken from lighter skin. However, because blinded rater assessment showed no differences in clarity or perceived depth, we conclude that OCT may be used without hesitation for manual visualization of skin and its appendages in all Fitzpatrick skin types. Further studies are required to more extensively characterize the effects of melanin on OCT imaging. Lasers Surg. Med. 51:407-411, 2019. © 2019 Wiley Periodicals, Inc.

Non-invasive imaging in dermatology and the unique potential of raster-scan optoacoustic mesoscopy

In recent years, several non‐invasive imaging methods have been introduced to facilitate diagnostics and therapy monitoring in dermatology. The microscopic imaging methods are restricted in their penetration depth, while the mesoscopic methods probe deeper but provide only morphological, not functional, information. ‘Raster‐scan optoacoustic mesoscopy’ (RSOM), an emerging new imaging technique, combines deep penetration with contrast based on light absorption, which provides morphological, molecular and functional information. Here, we compare the capabilities and limitations of currently available dermatological imaging methods and highlight the principles and unique abilities of RSOM. We illustrate the clinical potential of RSOM, in particular for non‐invasive diagnosis and monitoring of inflammatory and oncological skin diseases.

Optical coherence tomography for diagnosing skin cancer in adults

BACKGROUND

Early accurate detection of all skin cancer types is essential to guide appropriate management and to improve morbidity and survival. Melanoma and squamous cell carcinoma (SCC) are high-risk skin cancers, which have the potential to metastasise and ultimately lead to death, whereas basal cell carcinoma (BCC) is usually localised, with potential to infiltrate and damage surrounding tissue. Anxiety around missing early cases needs to be balanced against inappropriate referral and unnecessary excision of benign lesions. Optical coherence tomography (OCT) is a microscopic imaging technique, which magnifies the surface of a skin lesion using near-infrared light. Used in conjunction with clinical or dermoscopic examination of suspected skin cancer, or both, OCT may offer additional diagnostic information compared to other technologies.

OBJECTIVES

To determine the diagnostic accuracy of OCT for the detection of cutaneous invasive melanoma and atypical intraepidermal melanocytic variants, basal cell carcinoma (BCC), or cutaneous squamous cell carcinoma (cSCC) in adults.

SEARCH METHODS

We undertook a comprehensive search of the following databases from inception up to August 2016: Cochrane Central Register of Controlled Trials; MEDLINE; Embase; CINAHL; CPCI; Zetoc; Science Citation Index; US National Institutes of Health Ongoing Trials Register; NIHR Clinical Research Network Portfolio Database; and the World Health Organization International Clinical Trials Registry Platform. We studied reference lists and published systematic review articles.

SELECTION CRITERIA

We included studies of any design evaluating OCT in adults with lesions suspicious for invasive melanoma and atypical intraepidermal melanocytic variants, BCC or cSCC, compared with a reference standard of histological confirmation or clinical follow-up.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data using a standardised data extraction and quality assessment form (based on QUADAS-2). Our unit of analysis was lesions. Where possible, we estimated summary sensitivities and specificities using the bivariate hierarchical model.

MAIN RESULTS

We included five studies with 529 cutaneous lesions (282 malignant lesions) providing nine datasets for OCT, two for visual inspection alone, and two for visual inspection plus dermoscopy. Studies were of moderate to unclear quality, using data-driven thresholds for test positivity and giving poor accounts of reference standard interpretation and blinding. Studies may not have been representative of populations eligible for OCT in practice, for example due to high disease prevalence in study populations, and may not have reflected how OCT is used in practice, for example by using previously acquired OCT images.It was not possible to make summary statements regarding accuracy of detection of melanoma or of cSCC because of the paucity of studies, small sample sizes, and for melanoma differences in the OCT technologies used (high-definition versus conventional resolution OCT), and differences in the degree of testing performed prior to OCT (i.e. visual inspection alone or visual inspection plus dermoscopy).Pooled data from two studies using conventional swept-source OCT alongside visual inspection and dermoscopy for the detection of BCC estimated the sensitivity of OCT as 95% (95% confidence interval (CI) 91% to 97%) and specificity of 77% (95% CI 69% to 83%).When applied to a hypothetical population of 1000 lesions at the mean observed BCC prevalence of 60%, OCT would miss 31 BCCs (91 fewer than would be missed by visual inspection alone and 53 fewer than would be missed by visual inspection plus dermoscopy), and OCT would lead to 93 false-positive results for BCC (a reduction in unnecessary excisions of 159 compared to using visual inspection alone and of 87 compared to visual inspection plus dermoscopy).

AUTHORS' CONCLUSIONS

Insufficient data are available on the use of OCT for the detection of melanoma or cSCC. Initial data suggest conventional OCT may have a role for the diagnosis of BCC in clinically challenging lesions, with our meta-analysis showing a higher sensitivity and higher specificity when compared to visual inspection plus dermoscopy. However, the small number of studies and varying methodological quality means implications to guide practice cannot currently be drawn.Appropriately designed prospective comparative studies are required, given the paucity of data comparing OCT with dermoscopy and other similar diagnostic aids such as reflectance confocal microscopy.

High-Frequency Ultrasound Imaging for Examination of Early Dental Caries

The extent of dental tissue destruction during the treatment of white spot lesions (WSLs) increases with the severity of the lesion. If the depth and shape of WSLs can be predicted with a noninvasive diagnostic method before dental caries treatment, more conservative interventions can be planned. Given the superiority of high-frequency ultrasound (HFUS) imaging in observing the internal structures of the body, the present study aimed to verify the possibility of HFUS imaging to examine the depth and shape of WSLs. We prepared tooth samples and developed a biomicroscopic system with a HFUS transducer to obtain images of normal and WSL regions. HFUS images were compared with conventional ultrasound images and micro-computed tomography images. HFUS distinctly differentiated demineralization within WSL and normal regions. WSL depth calculated in the micro-computed tomography image was similar to that in HFUS. This study revealed that HFUS imaging has the potential to detect early dental caries and offer information on the invasion depth of early dental caries quantitatively.

3D bioprinting of skin tissue: From pre-processing to final product evaluation

Bioprinted skin tissue has the potential for aiding drug screening, formulation development, clinical transplantation, chemical and cosmetic testing, as well as basic research. Limitations of conventional skin tissue engineering approaches have driven the development of biomimetic skin equivalent via 3D bioprinting. A key hope for bioprinting skin is the improved tissue authenticity over conventional skin equivalent construction, enabling the precise localization of multiple cell types and appendages within a construct. The printing of skin faces challenges broadly associated with general 3D bioprinting, including the selection of cell types and biomaterials, and additionally requires in vitro culture formats that allow for growth at an air-liquid interface. This paper provides a thorough review of current 3D bioprinting technologies used to engineer human skin constructs and presents the overall pipelines of designing a biomimetic artificial skin via 3D bioprinting from the design phase (i.e. pre-processing phase) through the tissue maturation phase (i.e. post-processing) and into final product evaluation for drug screening, development, and drug delivery applications.

Ultrahigh-speed line-scan SD-OCT for four-dimensional in vivo imaging of small animal models

We report an ultrahigh-speed and high-resolution line-scan spectral-domain optical coherence tomography (SD-OCT) system that integrates a number of mechanisms for improving image quality. The illumination uniformity is significantly improved by the use of a Powell lens; Phase stepping and differential reconstruction are combined to suppress autocorrelation artifacts; Nonlocal means (NLM) is employed to enhance the signal to noise ratio while minimizing motion artifacts. The system is capable of acquiring cross-sectional images at more than 3,500 B-scans per second with sensitivities between 70dB and 90dB. The high B-scan rate enables image post-processing with nonlocal means, an advanced noise reduction algorithm that affords enhanced morphological details and reduced motion artifacts. The achieved axial and lateral resolutions are 2.0 and 6.2 microns, respectively. We have used this system to acquire four-dimensional (three-dimensional space and one-dimensional time) imaging data from live chicken embryos at up to 40 volumes per second. Dynamic cardiac tissue deformation and blood flow could be clearly visualized at high temporal and spatial resolutions, providing valuable information for understanding the mechanical and fluid dynamic properties of the developing cardiac system.

Comparative study of presurgical skin infiltration depth measurements of melanocytic lesions with OCT and high frequency ultrasound

A reliable, fast, and non-invasive determination of melanoma thickness in vivo is highly desirable for clinical dermatology as it may facilitate the identification of surgical melanoma margins, determine if a sentinel node biopsy should be performed or not, and reduce the number of surgical interventions for patients. In this work, optical coherence tomography (OCT) and high frequency ultrasound (HFUS) are evaluated for quantitative in vivo preoperative assessment of the skin infiltration depth of melanocytic tissue. Both methods allow non-invasive imaging of skin at similar axial resolution. Comparison with the Breslow lesion thickness obtained from histopathology revealed that OCT is slightly more precise in terms of thickness determination while HFUS has better contrast. The latter does not require image post-processing, as necessary for the OCT images. The findings of our pilot study suggest that non-invasive OCT and HFUS are able to determine the infiltration depth of lesions like melanocytic nevi or melanomas preoperatively and in vivo with a precision comparable to invasive histopathology measurements on skin biopsies. In future, to further strengthen our findings a statistically significant study comprising a larger amount of data is required which will be conducted in an extended clinical study in the next step. Comparison of optical coherence tomography and high frequency ultrasound B-Scans and a H&E stained histology of a melanocytic nevus.

Ultrasonographic staging of cutaneous malignant tumors: an ultrasonographic depth index

The objective of this paper is to assess the role of conventional and high-frequency ultrasound in the evaluation of the depth of cutaneous skin cancer. The study was performed on 46 subjects, divided into 3 categories, according to their skin pathology [basal cell carcinoma (BCC), 18 subjects; superficial spreading melanoma (SSM), 8 subjects; nodular melanoma (NM), 20 subjects]. Conventional and high-frequency ultrasonographic measurements were performed in order to assess the thickness of the tumors and the vascularization degree. We compared the mean values of the tumoral thickness obtained by using ultrasound (ultrasonographic depth index) with the histological depth index, obtained after performing histological sections stained with hematoxylin-eosin, and specific monoclonal antibodies in case of pigmented tumors. We established a correlation index between the histological and ultrasonographic values of the tumoral thickness. We found a strong correlation between the ultrasonographic index (measured by high-frequency sonography) and the histological index for nodular BCC (correlation of 98.4 %), NM subjects (correlation of 98.4 %), and SSM subjects (correlation of 99.4 %). An increase of the blood supply was noticed in nodular lesions only. Ultrasonography allows a very accurate assessment of skin cancer. The ultrasonographic depth index can be considered an objective, non-invasive marker for cutaneous tumors, comparable to the histological one, with a very good sensitivity (98-99 %).

Visualization of epidermal and dermal alteration in papulonodular mucinosis by multiphoton microscopy

Papulonodular mucinosis (PM) is a cutaneous clue to the presence and activity of silent lupus erythematosus (LE), but the exact pathogenesis is still under secret. Moreover, the currently available treatments for PM are not satisfactory. To demonstrate the possibility of multiphoton microscopy (MPM) to trace the pathological state of PM and evaluate the treatment efficacy, epidermal and dermal alteration in skin lesion with PM before and after treatment was examined using MPM. Microstructure of epidermis as well as content and distribution of collagen and elastin in dermis were quantified to characterize the pathological states of PM. The results showed significant morphological difference between skin lesion before and after treatment, indicating the possibility of MPM to assess the therapeutic efficacy. With the advancement on MPM miniaturization and enhancement of contrast and depth of imaging, the MPM technique can be applied in in vivo tracking PM formation and progression, and leading the better understanding the PM pathogenesis and mechanism of response to any treatment, helping to establish novel effective therapies for PM.

New diagnostic aids for melanoma

Detection of melanoma at an early stage is crucial to improving survival rates in melanoma. Accurate diagnosis by current techniques including dermatoscopy remains difficult, and new tools are needed to improve our diagnostic abilities. This article discusses recent advances in diagnostic techniques including confocal scanning laser microscopy, MelaFind, SIAscopy, and noninvasive genomic detection, as well as other future possibilities to aid in diagnosing melanoma. Advantages and barriers to implementation of the various technologies are also discussed.

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.

[Ultrasound microscopy in the upper aerodigestive tract. Initial clinical experiences]

PURPOSE

Initial clinical experiences with ultrasound microscopy in the upper aerodigestive tract are described.

MATERIALS AND METHODS

In the present pilot study, 20 healthy probands and 10 patients with lesions of the oral cavity, pharynx and larynx undergoing surgery were examined using a new prototype of an ultrasound microscope.

RESULTS

A total of 24 normal and six pathological findings of the upper aerodigestive tract were assessed. These included normal mucosa of the floor of the mouth, the inner cheek, the palate and the vocal fold. In addition, invasive carcinoma of the floor of the mouth, the aryepiglottic fold and the vocal fold was found. Furthermore, a papilloma of the palatal arch and two epiglottic cysts were examined.

CONCLUSION

Our results demonstrate that ultrasound microscopy is also viable in hollow organs. Pathological lesions differed clearly from normal mucosa. However, to recognize the regular pattern of different lesions of the upper aerodigestive tract, further investigations need to be carried out with a larger number of patients.

Advances and short comings in the early diagnosis of melanoma

Malignant melanoma kills more people each year than any other skin cancer, with approximately 8000 lives lost and a cost of over 3 billion dollars annually in the US alone. Tumor depth is the most important prognostic factor in melanoma. Thus, early detection has the potential to diagnose melanoma when lesions are thinner, and to improve survival in primary melanomas. In this review, we discuss the implications, barriers, and advantages of melanoma screening, and describe the currently employed methods of detection, newly available modalities, and current areas of research. We also discuss the efficacy, advantages and disadvantages, and clinical practicality of each, and suggest various means of combining different methodologies as well as tailoring various strategies to individual patient needs.

Measurement of melanoma thickness--comparison of two methods: ultrasound versus morphology

OBJECTIVE

The aim of our study was to investigate the association between non-invasive ultrasound examination and morphologic test results in the measurement of cutaneous melanoma thickness influencing surgical treatment strategy.

METHODS

Our prospective clinical study has been conducted in the Clinic of Plastic and Reconstructive Surgery of Kaunas University of Medicine Hospital (KUMH) since January 2004 until October 2008. A total of 100 patients with a clear clinical diagnosis of stage I-II cutaneous melanoma were enrolled in this study. Melanoma depth was measured using a linear 14-MHz frequency ultrasound sensor (Toshiba Xario XG). Surgically removed fragments of skin-subcutaneous tissue were fixated using 10% formalin solution in the operating theatre, and sent to KUMH Clinic of Pathological Anatomy. The most informative sections were analysed for tumour thickness, according to Breslow, as well as tumour type, vascular and lymphatic invasion and dissemination. A comparative data analysis of melanoma thickness measured by ultrasound (T) preoperatively and histologically estimated cutaneous melanoma (CM) thickness according to Breslow (pT) using the Bland-Altman method was performed.

RESULTS

Higher mean difference of melanoma thickness (60 μm) between T and pT measurements was found when tumour thickness matched pT1 and pT2 categories. In cases of CM depth exceeding 2mm, mean difference of measurements between CM thickness determined by ultrasound and histological examination was lower (30 μm). Data regression analysis showed that correlation between T and pT measurements was lower when CM was thinner (1-2 mm) (Pearson's correlation coefficient, r: 0.283). In cases of thicker melanoma (>2 mm), strong and statistically significant (p<0.0001) correlation (r: 0.869) was observed.

CONCLUSIONS

Correlation between melanoma thickness measured using a linear 14-MHz frequency ultrasound sensor and histologically estimated melanoma thickness according to Breslow was lower if melanoma was thinner (1-2 mm). However, in cases of thicker melanoma (>2 mm), very strong correlation between measurements was observed.

Characteristics of scar margin dynamic with time based on multiphoton microscopy

Scar margins dynamic with time were quantitatively characterized using multiphoton microscopy (MPM). 2D large-area and 3D focused images of elastin and collagen at scar margins were obtained to extract quantitative parameters. An obvious boundary was observed at the scar margin, showing altered morphological patterns of elastin and collagen on both sides. Content alteration of elastin and collagen between the two sides of boundary were defined to characterize scar margins from different individuals. The statistical results from 15 normal scar samples strongly demonstrated that content alteration degree of elastin and collagen had decreasing tendency with the increase of patient age or scar duration, consistent with the fact of normal scars regressing spontaneously over time. It indicated that alteration degree can potentially serve as quantitative indicators to examine wound healing and scar progression over time. With the advent of clinical portable multiphoton endoscopes, the MPM technique can be applied in tracking scar formation and progression in vivo by examination of scar margin.

Ultrasonic microscanning

A detailed review is given of the application of high-frequency ultrasound (HFUS) at frequencies of 20 MHz and above for high-resolution, cross-sectional imaging of biological soft tissue. The state of the art of HFUS imaging systems is discussed with respect to the underlying engineering concepts, system designs, and available transducer technology. Furthermore, the dependency of the spatial resolution on the system's parameters is analysed. Skin imaging, eye imaging, small animal imaging for preclinical research, and intravascular ultrasound in coronary arteries for arteriosclerotic disease diagnostics are presented as examples for the application of HFUS imaging in medical diagnostics. It is shown that, in the frame of the indicated applications, ultrasound in the frequency range 20-100MHz gives a good compromise between the contrary demands for a good spatial resolution and a sufficiently large penetration depth of ultrasound waves into the tissue. Scanning schemes for the imaging of tissue morphology are considered, including spatial compounding as a multidirectional imaging technique.

Biomechanical properties of in vivo human skin from dynamic optical coherence elastography

Dynamic optical coherence elastography is used to determine in vivo skin biomechanical properties based on mechanical surface wave propagation. Quantitative Young's moduli are measured on human skin from different sites, orientations, and frequencies. Skin thicknesses, including measurements from different layers, are also measured simultaneously. Experimental results show significant differences among measurements from different skin sites, between directions parallel and orthogonal to Langer's lines, and under different skin hydration states. Results also suggest surface waves with different driving frequencies represent skin biomechanical properties from different layers in depth. With features such as micrometer-scale resolution, noninvasive imaging, and real-time processing from the optical coherence tomography technology, this optical measurement technique has great potential for measuring skin biomechanical properties in dermatology.

Effects of a topically applied wound ointment on epidermal wound healing studied by in vivo fluorescence laser scanning microscopy analysis

Epidermal wound healing is a complex and dynamic regenerative process necessary to reestablish skin integrity. Fluorescence confocal laser scanning microscopy (FLSM) is a noninvasive imaging technique that has previously been used for evaluation of inflammatory and neoplastic skin disorders in vivo and at high resolution. We employed FLSM to investigate the evolution of epidermal wound healing noninvasively over time and in vivo. Two suction blisters were induced on the volar forearms of the study participants, followed by removal of the epidermis. To study the impact of wound ointment on the process of reepithelization, test sites were divided into two groups, of which one test site was left untreated as a negative control. FLSM was used for serial/consecutive evaluations up to 8 days. FLSM was able to visualize the development of thin keratinocyte layers developing near the wound edge and around hair follicles until the entire epidermis has been reestablished. Wounds treated with the wound ointment were found to heal significantly faster than untreated wounds. This technique allows monitoring of the kinetics of wound healing noninvasively and over time, while offering new insights into the potential effects of topically applied drugs on the process of tissue repair.

Monitoring of cell death in epithelial cells using high frequency ultrasound spectroscopy

Spectral and wavelet analyses were performed on ultrasound radiofrequency (RF) data collected from centrifuged cell samples containing HEp-2 cells after induction of apoptosis by exposure to camptothecin. Samples were imaged at several time points after drug exposure using high-frequency ultrasound in the range from 10-60 MHz. A 20-MHz transducer with a f-number of 2.35 and a 40-MHz transducer with a f-number of 3 were used for collecting the RF data. Normalized power spectra were computed from the backscattered ultrasound signals within a region-of-interest (ROI) for further analysis. Spectral slopes, integrated backscatter coefficients (IBCs) and wavelet parameters were estimated as a function of treatment time to monitor acoustic property changes during apoptosis. Changes in spectral parameters were detected starting six hours after treatment and coincided with changes in corresponding histology. Throughout the course of chemotherapy, variation in estimates of the spectral slope of up to 35% were observed. During the treatment, IBCs increased by 400% compared with estimates obtained from the control samples. Changes in spectral parameters are hypothesized to be linked to structural cell changes during apoptosis. In addition, the sensitivity of a wavelet-based analysis to the ultrasonic assessment of cellular changes was investigated. Results of the wavelet analysis showed variations similar to the spectral parameters. Where values of the spectral slope decreased, estimates of the scaling factors increased. Because wavelet analysis preserves the signal-time localization, its application will be potentially beneficial for assessing treatment responses in vivo. The current study contributes toward the development of a non-invasive method for monitoring apoptosis as a measure of the success of chemotherapeutic treatment of cancer.

High-resolution imaging diagnosis and staging of bladder cancer: comparison between optical coherence tomography and high-frequency ultrasound

A comparative study between 1.3-microm optical coherence tomography (OCT) and 40-MHz high-frequency ultrasound (HFUS) is presented to enhance imaging of bladder cancers ex vivo. A standard rat bladder cancer model in which transitional cell carcinoma (TCC) was induced by intravesical instillation of AY-27 cells was followed independently with both OCT and HFUS, and the image identifications were compared to histological confirmations. Results indicate that both OCT and HFUS were able to delineate the morphology of rat bladder [e.g., the urothelium (low backscattering/echo) and the underlying lamina propria and muscularis (high backscattering/echo]. OCT differentiated inflammatory lesions (e.g., edema, infiltrates and vasodilatation in lamina propria, hyperplasia) and TCC based on characterization of urothelial thickening and enhanced backscattering or heterogeneity (e.g., papillary features), which HFUS failed due to insufficient image resolution and contrast. On the other hand, HFUS was able to stage large T2 tumors that OCT failed due to limited imaging depth. The results suggest that multimodality cystoscopy combining OCT and HFUS may have the potential to enhance the diagnosis and staging of bladder cancers and to guide tumor resection, in which both high resolution (approximately 10 microm) and enhanced penetration (> 3mm) are desirable.

Nail thickness measurements using optical coherence tomography and 20-MHz ultrasonography

BACKGROUND

Nail diseases are often troubling to the patient and may present a diagnostic challenge to the dermatologist. Biopsies from the nail may be required although often perceived uncomfortable by the patient and potentially scarring. Noninvasive technologies are therefore of particular interest in the study of nails. Optical coherence tomography (OCT) is an optical imaging modality which may provide improved data.

OBJECTIVES

This study evaluates nail morphology and thickness in OCT images in comparison with high-frequency ultrasound (HFUS) imaging of the nail.

METHODS

Ten healthy volunteers were recruited for imaging and nail measurements; OCT and HFUS images were compared qualitatively. Nail thickness measurements with four different techniques were compared: ultrasound, OCT, polarization-sensitive (PS) OCT and callipers. The OCT system was developed at Risoe National Laboratory, Denmark. A commercially available 20-MHz ultrasound system (Dermascan; Cortex Technology, Hadsund, Denmark) was used.

RESULTS

In standard OCT the nail plate appeared as a layered structure containing a varying number of horizontal homogeneous bands of varying intensity and thickness. PS-OCT images of the nail plate also showed a layered structure. The refractive index of the nail was 1.47 +/- 0.09. OCT and PS-OCT had low coefficients of variation, 6.31 and 6.53, respectively, compared with other methods: HFUS 12.70 and callipers 14.03.

CONCLUSION

PS-OCT has to our knowledge not been applied to OCT analysis of the nail, and offers some advantages in separation of the nail bed from the nail plate.

Characterization of benign and malignant melanocytic skin lesions using optical coherence tomography in vivo

BACKGROUND

Although optical coherence tomography (OCT) is a promising noninvasive imaging technique for the micromorphology of the skin, OCT has not been studied systematically in skin cancer such as malignant melanoma (MM).

OBJECTIVE

We sought to visualize and characterize melanocytic skin lesions (MSL) by using OCT in vivo, compare OCT features of benign nevi (BN) and MM, and histologically validate the OCT findings.

METHODS

In all, 75 patients with 92 MSL, including 52 BN and 40 MM, were included in this study. MSL were investigated by OCT in vivo and consecutive histology. We compared the OCT images with the corresponding histologic slices of BN and MM. To ascertain accuracy of correlation between OCT images and histologic sections, the excised lesions were tattooed according to the level of OCT scanning. For every MSL, serial histologic slices were prepared.

RESULTS

MM often showed a marked architectural disarray (P = .036) and rarely displayed a clear dermoepidermal border (P = .0031) when compared with BN. OCT of MM infrequently demonstrated a dermoepidermal junction zone with finger-shaped elongated rete ridges as typically seen in BN (P = .011). Compared with BN, the papillary and superficial reticular dermis in MM frequently displayed a more diffuse or patchy reflectivity with loss of the typical bright horizontal linear structures (P = .022). However, more or less large vertical, icicle-shaped structures were the most striking OCT feature of MM, which were not observed in BN (P < .001).

LIMITATIONS

The diagnostic performance of OCT in the diagnosis of MSL could not be fully determined. Sensitivity and specificity studies also including other skin tumors have not been performed.

CONCLUSION

In this study, distinct OCT features of MSL could be correlated to histopathologic findings. With regard to the micromorphologic features visualized by OCT, we detected significant differences between BN and MM. These OCT features might serve as useful discriminating parameters of MSL.

Preoperative Ultrasonic Assessment of Thin Melanocytic Skin Lesions Using a 100-MHz Ultrasound Transducer: A Comparative Study

BACKGROUND

It has been shown that tumor thickness (TT) of melanocytic skin lesions (MSL) of less than 1 mm vertical thickness assessed by 20 MHz are often incorrectly evaluated.

OBJECTIVE

We aimed to evaluate the accuracy of 100-MHz ultrasound for the determination of TT of thin MSL, compared with conventional 20-MHz ultrasound and histologic findings.

METHODS

Thirty-seven patients with 50 suspicious MSL, including tumor diameter up to 1 cm and maximum vertical TT of less than 1 mm, were recruited. The agreement between the histologically and ultrasographically measured TT was analyzed using Bland and Altman plots.

RESULTS

Compared to histology, 20-MHz ultrasound (33.9 microm) as well as 100-MHz (16 microm) resulted in overestimation of TT that was twofold higher for 20-MHz ultrasound. The latter also revealed wider 95% limits of agreement (4.9 to 63 microm) than 100-MHz ultrasound (3.5 to 28.7 microm).

CONCLUSION

Analysis of agreement clearly demonstrated that the performance of 100-MHz ultrasound is superior to conventional 20-MHz ultrasound, even though a relatively small positive bias was observed in 100-MHz ultrasound, indicating a systematic error. We consider 100-MHz ultrasound a useful tool for the noninvasive determination of TT of thin MSL in vivo.

Validation of optical coherence tomographyin vivousing cryostat histology

We aimed to validate for the first time optical coherence tomography (OCT) measurements of epidermal thickness (ET) using cryopreparation for histology. OCT assessments of ET were performed on healthy skin using the algorithms as follows: first, peak-to-valley analysis of the A-scan (ET-OCT-V), second, line-traced image analysis of the B-scan (ET-OCT-IA). Histology was performed using cryostat sections which were also evaluated using the image analysis (ET-Histo). We selected 114 samples, including B-scans and corresponding histology, for method comparison between ET-OCT-IA and ET-Histo. Forty-two A-scans were available for method comparison between ET-OCT-V and ET-Histo. Bland and Altman plots revealed a marked bias with wide 95% limits of agreement for ET-OCT-V versus ET-Histo. Comparison of ET-OCT-IA versus ET-Histo revealed only a slight bias and narrow 95% limits of agreement. A-scan analysis for ET determination is linked to significant limitations and lacks agreement with histology. By contrast, we observed satisfactory agreement between ET-OCT-IA and ET-Histo indicating that both methods can be utilized interchangeably. OCT using the line-traced image analysis of the B-scan appears to be a valid and relatively practicable method for the determination of ET in vivo. Furthermore, the comparisons with the in vivo OCT profiles demonstrate that cryostat sectioning provides a better preservation of relative and absolute dimensions of skin layers than paraffin embedding.

Epidermal thickness assessed by optical coherence tomography and routine histology: preliminary results of method comparison

BACKGROUND

Optical coherence tomography (OCT) is a promising non-invasive imaging technique for studying the epidermis and upper dermis in vivo. As proposed previously by Welzel et al. (J Am Acad Dermatol 1997; 37: 958-963), distance measurements between the entrance peak and the second peak of the A-scan seem to correspond to epidermal thickness (ET). However, there is a lack of systematic studies comparing OCT with histology.

METHODS

Sixteen healthy subjects were included in this pilot study. OCT assessments were conducted on the upper back. To determine ET by OCT, the distance between the entrance peak and the second peak of the A-scan was calculated (ET-OCT). After OCT measurement a 4 mm punch biopsy was taken on each subject from the same site previously assessed. The maximum thickness of the epidermis (ET-Histo) was determined microscopically using routine histological slices (formalin-paraffin technique, haematoxylin-eosin staining). Correlation and agreement between the two methods were assessed by means of the Pearson correlation procedure and Bland-Altman plots, respectively.

RESULTS

ET-Histo was 79.4 +/- 21.9 microm, including a stratum corneum thickness of 20 +/- 12.1 microm. OCT measurements resulted in an ET of 106 +/- 15.4 microm. No correlation between ET-Histo and ET-OCT was observed (r = 0.29, P = 0.27). There was a considerable lack of agreement between histology and OCT measurements as expressed in a high bias of 26.63 microm [95% confidence interval (CI) 14.49-38.77]. Furthermore, the lower 95% limits of agreement were -18.03 microm (95% CI -37.11 to 1.05) and the upper 95% limits of agreement were 71.28 microm (95% CI 52.2-90.36) indicating that ET-OCT may be 71.28 microm above or 18.03 microm below ET-Histo.

CONCLUSIONS

Our preliminary data suggest that the above-described OCT algorithm is probably not a valid measure for the evaluation of ET. The second peak of the A-scan seems not to correspond to the dermo-epidermal junction zone, but rather to fibrous structures in the upper dermis. Nevertheless, further systematic comparison studies between OCT and histology are warranted, using different OCT algorithms for ET determination and cryopreparation, which has a higher reliability than the formalin-paraffin technique.

In vivo optical coherence tomography of basal cell carcinoma

BACKGROUND

Optical coherence tomography (OCT) is a promising non-invasive imaging technique that has not systematically been studied in skin cancer such as basal cell carcinoma (BCC).

OBJECTIVE

We aimed, first, to describe the in vivo histologic features of BCC by using OCT, and second, to find out whether it is possible to differentiate BCC subtypes by means of OCT.

METHODS

Prior to the excision, the BCCs (n=43) as well as adjacent non-lesional skin sites were assessed by OCT in vivo. The lesional area of interest was marked prior to OCT and tattooed after excision, respectively, in order to enable topographical concordance between the cross-sectional OCT images and the histologic sections.

RESULTS

Compared to non-lesional skin, a loss of normal skin architecture and disarrangement of the epidermis and upper dermis was observed in the OCT images of BCCs. Features that were frequently identified by OCT and correlated with histology included large plug-like signal-intense structures, honeycomb-like signal-free structures, and prominent signal free cavities in the upper dermis. With regard to the aforementioned OCT features, no statistically significant (P<0.05) difference was found between nodular, multifocal superficial, and infiltrative BCCs, respectively.

CONCLUSIONS

OCT is capable to visualize altered skin architecture and histopathological correlates of BCC. However, there is not at this time sufficient data supporting the clinical use of OCT for the differentiation of BCC subtypes.

In vivo data of epidermal thickness evaluated by optical coherence tomography: effects of age, gender, skin type, and anatomic site

BACKGROUND

The knowledge of epidermal thickness (ET) is of great significance in many areas of medical and biological research.

OBJECTIVES

We aimed to assess optical coherence tomography (OCT) in terms of precision, and to investigate the influence of several constitutional factors, such as age, gender, skin type, and anatomic site, on the mean ET using OCT in vivo.

METHODS

Eighty-three subjects were studied using OCT in vivo. Intra- and inter-day repeatability measurements were performed. The mean ET was assessed in six different body sites of young (20-40 years old) and old (60-80 years old) Caucasians, respectively. An ethnic group was included into the study.

RESULTS

OCT proved to be a precise technique in terms of repeatability and reproducibility as expressed in low coefficients of variation. Comparison of young and old Caucasians demonstrated a significant decrease of ET with age in all anatomic sites investigated. ET assessed in males and females did not significantly differ, except for forehead skin which is significantly thinner in old females than in males. ET observed in Caucasians did not significantly differ from ET measured in ethnic individuals. Anatomic sites insignificantly influenced ET on an inter-individual level. However, differences of ET between body sites on an intra-individual level are significant.

CONCLUSIONS

This was the first systematic in vivo study on ET investigating several influencing parameters of the epidermal dimension in a reasonable study sample by means of OCT. The results presented here may serve as ET reference data in a variety of clinical and experimental matters.

Optical coherence tomography for the characterization of basal cell carcinoma in vivo: a pilot study

BACKGROUND

Optical coherence tomography combines principles of ultrasonography and optical interferometry to provide real-time cross-sectional images of subsurface microstructure of tissue in vivo.

OBJECTIVE

The purpose of this pilot study was to define and characterize basal cell carcinoma by using optical coherence tomography.

METHODS

Twenty-three patients with 49 lesions clinically suggestive of superficial basal cell carcinoma were recruited. Optical coherence tomography was used to characterize the features of the pearly papules in real time and in vivo. Shave biopsy and light microscopic images were compared with images from optical coherence tomography.

RESULTS

Basal cell carcinoma was identified in 27 patients; all 27 had optical coherence tomographic images for comparison. Seven images were uninterpretable, probably because of technical problems. Of the remainder, 20 sites matched the histologic features seen on light microscopy, with excellent correlation between optical coherence tomographic images and histopathologic features of superficial, nodular, micronodular and infiltrative basal cell carcinomas.

LIMITATIONS

This study was limited by the small number of patients examined. Also, as this study was not designed as an intent-to-diagnose study, the actual predictive value of optical coherence tomography technology remains unproven.

CONCLUSIONS

Optical coherence tomography technology has potential for the diagnosis and histopathologic characterization of basal cell cancer. Additional studies to determine any practical role for optical coherence tomography are indicated.

Automatic characterization and segmentation of human skin using three-dimensional optical coherence tomography

A set of fully automated algorithms that is specialized for analyzing a three-dimensional optical coherence tomography (OCT) volume of human skin is reported. The algorithm set first determines the skin surface of the OCT volume, and a depth-oriented algorithm provides the mean epidermal thickness, distribution map of the epidermis, and a segmented volume of the epidermis. Subsequently, an en face shadowgram is produced by an algorithm to visualize the infundibula in the skin with high contrast. The population and occupation ratio of the infundibula are provided by a histogram-based thresholding algorithm and a distance mapping algorithm. En face OCT slices at constant depths from the sample surface are extracted, and the histogram-based thresholding algorithm is again applied to these slices, yielding a three-dimensional segmented volume of the infundibula. The dermal attenuation coefficient is also calculated from the OCT volume in order to evaluate the skin texture. The algorithm set examines swept-source OCT volumes of the skins of several volunteers, and the results show the high stability, portability and reproducibility of the algorithm.

Swept source optical coherence tomography using an all-fiber 1300-nm ring laser source

The increased sensitivity of spectral domain optical coherence tomography (OCT) has driven the development of a new generation of technologies in OCT, including rapidly tunable, broad bandwidth swept laser sources and spectral domain OCT interferometer topologies. In this work, the operation of a turnkey 1300-nm swept laser source is demonstrated. This source has a fiber ring cavity with a semiconductor optical amplifier gain medium. Intracavity mode selection is achieved with an in-fiber tunable fiber Fabry-Perot filter. A novel optoelectronic technique that allows for even sampling of the swept source OCT signal in k space also is described. A differential swept source OCT system is presented, and images of in vivo human cornea and skin are presented. Lastly, the effects of analog-to-digital converter aliasing on image quality in swept source OCT are discussed.

Comparison of histometric data obtained by optical coherence tomography and routine histology

There is a lack of systematic investigations comparing optical coherence tomography (OCT) with histology. OCT assessments were performed on the upper back of 16 healthy subjects. Epidermis thickness (ET) was assessed using three methods: first, peak-to-valley analysis of the A-scan (ET-OCT-V); second, manual measurements in the OCT images (ET-OCT-M); third, light microscopic determination using routine histology (ET-Histo). The relationship between the different methods was assessed by means of the Pearson correlation procedure and Bland and Altman plots. We observed a strong correlation between ET-Histo (79.4+/-21.9 microm) and ET-OCT-V (79.2+/-15.5 microm, r=0.77) and ET-OCT-M (82.9+/-15.8 microm, r=0.75), respectively. Bland and Altman plots revealed a bias of -0.19 microm (95% limits of agreement: -27.94 microm to 27.56 microm) for ET-OCT-V versus ET-Histo and a bias of 3.44 microm (95% limits of agreement: -24.9 microm to 31.78 microm) for ET-OCT-M versus ET-Histo. Despite the strong correlation and low bias observed, the 95% limits of agreement demonstrated an unsatisfactory numerical agreement between the two OCT methods and routine histology indicating that these methods cannot be employed interchangeably. Regarding practicability, precision, and indication spectrum, ET-OCT-V and ET-OCT-M are of different clinical value.

Design and fabrication of a 40-MHz annular array transducer

This paper investigates the feasibility of fabricating a five-ring, focused annular array transducer operating at 40 MHz. The active piezoelectric material of the transducer was a 9-microm thick polyvinylidene fluoride (PVDF) film. One side of the PVDF was metallized with gold and forms the ground plane of the transducer. The array pattern of the transducer and electrical traces to each annulus were formed on a copper-clad polyimide film. The PVDF and polyimide were bonded with a thin layer of epoxy, pressed into a spherically curved shape, then back filled with epoxy. A five-ring transducer with equal area elements and 100-microm kerfs between annuli was fabricated and tested. The transducer had a total aperture of 6 mm and a geometric focus of 12 mm. The pulse/echo response from a quartz plate located at the geometric focus, two-way insertion loss (IL), complex impedance, electrical crosstalk, and lateral beamwidth all were measured for each annulus. The complex impedance data from each element were used to perform electrical matching, and the measurements were repeated. After impedance matching; fc approximately equal to 36 MHz and -6-dB bandwidths ranged from 31 to 39%. The ILs for the matched annuli ranged from -28 to -38 dB.