In vivo biomicroscopy of the skin with high-resolution magnetic resonance imaging and high frequency ultrasound

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.

Using 3D differential forms to characterize a pigmented lesion in vivo

BACKGROUND/PURPOSE

After the formulation of ABCD rules, many new feature extraction methods are emerging to describe the asymmetry, border irregularity, color variation and diameter of malignant melanoma. In this paper, a new research direction orthogonal to ABCD rules that characterizes 3D local disruption of skin surfaces to realize automatic recognition of melanoma is described.

METHODS

This paper examines 3D differential forms of skin surfaces to characterize the local geometrical properties of melanoma. Firstly, 3D data of skin surfaces are obtained using a photometric stereo device. Then differential forms of lesion surfaces are determined to describe the geometrical texture patterns involved. Using only these geometrical features, a simple least-squared error-based linear classifier can be constructed to realize the classification of malignant melanomas and benign lesions.

RESULTS

As with the 3D data of 35 melanoma and 66 benign lesion samples collected from local pigmented lesion clinics, the optimal sensitivity and specificity of the constructed linear classifier are 71.4% and 86.4%, respectively. The total area enclosed by the corresponding receiver operating characteristics curve is 0.823.

CONCLUSION

This study indicates that differential forms obtained from 3D data are very promising in characterizing melanoma. Combining these features with other skin features such as border irregularity and color variation might further improve the accuracy and reliability of the automatic diagnosis of melanoma.

In vivo high-resolution magnetic resonance skin imaging at 1.5 T and 3 T

As a noninvasive modality, MR is attractive for in vivo skin imaging. Its unique soft tissue contrast makes it an ideal imaging modality to study the skin water content and to resolve the different skin layers. In this work, the challenges of in vivo high-resolution skin imaging are addressed. Three 3D Cartesian sequences are customized to achieve high-resolution imaging and their respective performance is evaluated. The balanced steady-state free precession (bSSFP) and gradient echo (GRE) sequences are fast but can be sensitive to off-resonance artifacts. The fast large-angle spin echo (FLASE) sequence provides a sharp depiction of the hypodermis structures but results in more specific absorption rate (SAR). The effect of increasing the field strength is assessed. As compared to 1.5 T, signal-to-noise ratio at 3 T slightly increases in the hypodermis and almost doubles in the dermis. The need for fat/water separation is acknowledged and a solution using an interleaved three-point Dixon method and an iterative reconstruction is shown to be effective. The effects of motion are analyzed and two techniques to prevent motion and correct for it are evaluated. Images with 117 x 117 x 500 microm(3) resolution are obtained in imaging times under 6 min.

Use of ultrasound biomicroscopy to image human ovaries in vitro

OBJECTIVES

To test the hypothesis that ultrasound biomicroscopy is an effective tool for imaging human ovaries in vitro.

METHODS

This was a prospective, observational study of 11 women (mean age, 48.9 +/- 2.3 years; range, 40-65 years) undergoing unilateral or bilateral oophorectomy. Ovaries were obtained in the operating room and imaged in a cooled saline bath using conventional two-dimensional (2D) ultrasound. Follicles identified using conventional 2D ultrasound were then imaged in a cooled saline bath using ultrasound biomicroscopy. Ovaries were then placed in 10% neutral-buffered formaldehyde and transported to the Pathology Department for histological evaluation. Digital images of individually identified ovarian follicles using conventional ultrasound, ultrasound biomicroscopy and histology were obtained (n = 22). Thicknesses of the follicle wall, granulosa layer and theca interna layer were measured using standardized techniques.

RESULTS

The imaging sensitivity, defined as the smallest follicle visualized, was greater using ultrasound biomicroscopy (0.33 +/- 0.07 mm) than it was using conventional ultrasound (1.5 +/- 0.21 mm; P < 0.0001). The mean follicle wall thickness was greater using conventional ultrasound (0.675 +/- 0.039 mm) compared with ultrasound biomicroscopy (0.254 +/- 0.017 mm), which in turn, was greater than that measured by histology (0.160 +/- 0.009 mm) (P < 0.0001). The mean granulosa and theca layer thickness measurements, respectively, were greater using ultrasound biomicroscopy (0.067 +/- 0.004 mm; 0.186 +/- 0.014 mm) compared with histology (0.034 +/- 0.002 mm; 0.126 +/- 0.008 mm) (P < or = 0.001). Protrusions from the follicle wall into the antrum, believed to represent cumulus-oocyte complexes, were visualized in five of 22 follicles using ultrasound biomicroscopy.

CONCLUSIONS

The ultrasound biomicroscope was an effective tool to image human ovaries in vitro. Ultrasound biomicroscopy provided greater sensitivity and resolution for imaging ovarian follicles compared with conventional 2D ultrasonographic techniques.

High-Resolution MRI of Basal Cell Carcinomas of the Face Using a Microscopy Coil

OBJECTIVE

The objective of this article is to evaluate the diagnostic accuracy of high-resolution MRI using a microscopy surface coil to stage basal cell carcinomas of the face.

CONCLUSION

High-resolution MRI using a microscopy surface coil is a promising method to determine the extension of basaliomas of the facial region and to exclude infiltration of bone by the tumor.

Advances in MR imaging of the skin

MR imaging of the skin is challenging because of the small size of the structures to be visualized. By increasing the gradient amplitude and/or duration, skin layers can be visualized with a voxel size of the order of 20 microm, clearly the smallest obtained for in vivo images in a whole-body imager. Currently, the gradient strength of most commercial systems enables acquisition of such a small voxel size, and the main difficulty has thus become to achieve sufficient detection sensitivity. The signal-to-noise ratio (SNR) can be increased either by increasing the magnetic field strength or by minimizing noise with small coils; cooling copper coils or superconducting coils can enhance the SNR by a factor of 3 or more. MR imaging, because of the large number of parameters it is able to measure, can provide more than the microscopic architecture of the skin: physical parameters such as relaxation times, magnetization transfer or diffusion, and chemical parameters such as the water and fat contents or phosphorus metabolism. In spite of the amount of information they have provided to date, MR imaging and spectroscopy have had limited clinical applications, mainly because cutaneous pathologies are easily accessible to the naked eye and surgery. However, MR technologies indeed represent powerful research tools to study normal and diseased skin.

Three-dimensional reconstruction of basal cell carcinomas

BACKGROUND

Basal cell carcinoma (BCC) is the most common type of skin cancer. One of the main problems with BCC is the risk of local recurrence of the tumor after treatment. This is mainly due to its irregular outgrowths, which cannot be detected clinically.

OBJECTIVE

To better understand the tumor morphology and growth pattern of BCC, we tried to develop a method that provides a precise three-dimensional model of the tumor.

METHODS

Because Mohs surgery provides the best overview of the tumor and the tumor margins (both lateral and in depth), the reconstruction was based on slides from Mohs surgery. After digitization and processing of the slides, the tumor was then surrounded by a Mohs surgeon on a computer screen. These selections (lines) were used for a three-dimensional reconstruction of the tumor using MedSurf3D software.

RESULTS

This method allows three-dimensional reconstruction of any given BCC. The MedSurf3D software enables visualization of a three-dimensional model of the tissue, which is removed during the surgical procedure.

CONCLUSIONS

Three-dimensional reconstruction is a fascinating tool that might improve our understanding of the behavior, growth pattern, and tumor morphology of BCCs. This technique might also be useful in other fields of cutaneous oncology, such as the calculation of the tumor volume of melanomas.

Investigating sun-damaged skin and actinic keratosis with optical coherence tomography: a pilot study

Actinic Keratosis (AK) arises from sun-damaged skin and is the first clinical manifestation in the multistep process of skin carcinogenesis to invasive squamous cell carcinoma. Thus, it is an ideal target for chemopreventive efforts. Noninvasive measures of AK severity are needed to assess the efficacy of chemoprevention agents. We performed a pilot study on 20 participants to investigate the OCT appearance of sun-protected skin of the upper inner arm as well as sun-damaged skin and early AKs of the dorsal forearms, and to determine if features or quantitative measures in Optical Coherence Tomography (OCT) images could be used to reliably differentiate between these categories. OCT images of upper inner arm (normal appearing skin) showed skin layers and features (stratum corneum, epidermis, dermis, blood vessels) seen in previous studies; additionally in this participant group the subcutaneous fat layer was usually identified. Sun-damaged skin was characterized by increased signal in the epidermis and rapid attenuation of light. AKs were diverse in appearance but frequently characterized by high surface reflection, the presence of a low-signal band in the stratum corneum, and heterogeneous appearance in the epidermis/dermis. Significant differences were found between skin categories using measures of stratum corneum and epidermal/dermal depths and intensities. The presence of a dark band in the stratum corneum was 79% sensitive and 100% specific for AK. This study indicates that OCT holds promise as a useful technique for identifying and characterizing AKs and monitoring their response to chemoprevention agents.

Changing paradigms in dermatology: new ways to examine the skin using noninvasive imaging methods

Detailed visualization of the skin in the practice of dermatology is key to a comprehensive examination and accurate diagnosis. Advancements in digital dermoscopy, microscopy, imaging and photography have formed an impressive arsenal with which dermatologists can offer state-of-the-art patient care while streamlining their clinical practice and improving their academic and research capacities. Many types of advanced imaging are used in the biologic sciences at the bench; however, our paper reviews the clinical, noninvasive in vivo human applications of these emerging technologies. Our experiences with these instruments reinforce such reviews.