Kasia Harasiewicz

ADVANCES IN ULTRASOUND BIOMICROSCOPY

The visualisation of living tissues at microscopic resolution is attracting attention in several fields. In medicine, the goals are to image healthy and diseased tissue with the aim of providing information previously only available from biopsy samples. In basic biology, the goal may be to image biological models of human disease or to conduct longitudinal studies of small-animal development. High-frequency ultrasonic imaging (ultrasound biomicroscopy) offers unique advantages for these applications. In this paper, the development of ultrasound biomicroscopy is reviewed. Aspects of transducer development, systems design and tissue properties are presented to provide a foundation for medical and biological applications. The majority of applications appear to be developing in the 40-60-MHz frequency range, where resolution on the order of 50 microm can be achieved. Doppler processing in this frequency range is beginning to emerge and some examples of current achievements will be highlighted. The current state of the art is reviewed for medical applications in ophthalmology, intravascular ultrasound, dermatology, and cartilage imaging. Ultrasound biomicroscopic studies of mouse embryonic development and tumour biology are presented. Speculation on the continuing evolution of ultrasound biomicroscopy will be discussed.

Ultrasound biomicroscopy of anterior segment structures in normal and glaucomatous eyes.

We developed a new method of imaging the anterior segment of the eye using high-frequency ultrasound that allows structural details of the angle, iris, ciliary body, zonule, and posterior chamber to be visualized and measured at microscopic resolution in living patients. We applied the term ultrasound biomicroscopy to this technique, which we used to image anterior segment structures in a series of nine normal subjects. We provide a system of definition for anterior segment measurements that will allow reproducible measurements to be performed in the future. Measurements in normal subjects provide a foundation for future studies of specific glaucoma types and facilitate comparison of normal and glaucomatous eyes. Images in several specific types of glaucoma were obtained to exemplify the potential of this technique.

A NEW ULTRASOUND INSTRUMENT FOR IN VIVO MICROIMAGING OF MICE

We report here on the design and evaluation of the first high-frequency ultrasound (US) imaging system specifically designed for microimaging of the mouse. High-frequency US or US biomicroscopy (UBM) has the advantage of low cost, rapid imaging speed, portability and high resolution. In combination with the ability to provide functional information on blood flow, UBM provides a powerful method for the investigation of development and disease models. The new UBM imaging system is demonstrated for mouse development from day 5.5 of embryogenesis through to the adult mouse. At a frequency of 40 MHz, the resolution voxel of the new mouse scanner measures 57 microm x 57 microm x 40 microm. Duplex Doppler provides blood velocity sensitivity to the mm per s range, consistent with flow in the microcirculation, and can readily detect blood flow in the embryonic mouse heart, aorta, liver and placenta. Noninvasive UBM assessment of development shows striking similarity to invasive atlases of mouse anatomy. The most detailed noninvasive in vivo images of mouse embryonic development achieved using any imaging method are presented.

Principles and applications of ultrasound backscatter microscopy

The development of ultrasound backscatter microscopy (UBM) is described together with initial clinical and biological applications. UBM is essentially an extension of the powerful B-mode backscatter methods developed for clinical imaging in the 3-10-MHz frequency range. The development of new high sensitivity transducers in the 40-100-MHz range now permits visualization of tissue structures with resolution approaching 20 mu m and a maximum penetration of approximately 4 mm. The performance characteristics and trade-offs of these new polymer and ceramic devices are reviewed, and the implementation of high-frequency imaging systems is described. Initial clinical applications of UBM include ophthalmic, skin, and intravascular imaging. Examples of images and progress in these areas are presented. The biological application of UBM is illustrated by studies of drug uptake in living tumor spheroids. Significant increases in backscatter levels resulting from drugs targeting oxic and hypoxic cell populations are demonstrated.<<ETX>>

A 40-100 MHz B-SCAN ULTRASOUND BACKSCATTER MICROSCOPE FOR SKIN IMAGING

There is a growing interest in high resolution, subsurface imaging of cutaneous tissues using higher frequency ultrasound, and several commercial systems have been developed recently which operate at 20 MHz. Some of the possible applications of higher frequency skin imaging include tumour staging, boundary definition, and studies of the response of tumours to therapy, investigations of inflammatory skin conditions such as psoriasis and eczema, and basic studies of skin aging, sun damage and the effects of irritants. Investigation of these areas is quite new, and the role of ultrasound skin imaging is continuing to evolve. Lateral resolution in the 20 MHz imaging systems ranges from 200 to 300 microns, which limits imaging applications to cutaneous structures which are relatively large in size. In this paper, a real-time ultrasound backscatter microscope (UBM) for skin imaging is described which operates in the 40-100 MHz range, providing axial resolution between 17 and 30 microns and lateral resolution between 33 and 94 microns. This improvement in resolution over current skin ultrasound systems should prove useful in determining the margins of small skin lesions, and in obtaining more precise, in vivo skin thickness measurements to characterize nonmalignant skin disease. Example images of normal skin, seborrhoeic keratosis and malignant melanoma illustrate the imaging potential of this system.

A history of medical and biological imaging with polyvinylidene fluoride (PVDF) transducers

Polyvinylidene fluoride (PVDF) is a ferroelectric polymer with unique properties suitable for use in a wide range of medical and biological imaging applications. Most notable among these is its low acoustic impedance, which matches that of the body reasonably well, and its flexible mechanical properties. This paper traces the exploitation of PVDF as a transducer material from its early beginnings for thyroid and breast imaging to its current well-established applications in ultrasound biomicroscopy. Although PVDFs electromechanical properties fall short of composite ceramic materials in the traditional diagnostic frequency range, it has significant advantages in the 25-to 100-MHz range. Design criteria for high frequency transducers are reviewed, and examples of relevant medical and biological images are used to illustrate the excellent image quality obtained with this remarkable material.

Determination of haptic position of transsclerally fixated posterior chamber intraocular lenses by ultrasound biomicroscopy

ABSTRACT Transscleral fixation of posterior chamber intraocular lenses has become an increasingly popular procedure in eyes lacking adequate posterior capsular support. The assumption is generally made that these lenses are fixated in the ciliary sulcus. To test this assumption, 17 cases with transsclerally fixated posterior chamber intraocular lenses were examined with ultrasound biomicroscopy, a new method of producing subsurface images in living eyes at microscopic resolution. All lens haptics were easily visualized with this technique. Of 34 haptics in 17 patients, 13 were adequately located in the sulcus region, eight were located posterior to the ciliary processes, and 13 were located anterior to the sulcus region, accompanied by some degree of angle closure. Haptics with a more posterior scleral exit of the suture tended to be located more posteriorly. The cases in which the haptics were located anteriorly had scleral exit points from 1 mm to 2 mm from the limbus. The surgical placement of transsclerally fixated lenses is a blind procedure in most cases. Our series demonstrates the difficulty in reliably placing the haptics in the ciliary sulcus.

An ultrasound biomicroscopic analysis of angle-closure glaucoma secondary to ciliochoroidal effusion in IgA nephropathy.

Immunoglobulin A nephropathy is a common glomerulonephritis of unknown cause. Episcleritis, scleritis, anterior uveitis, and keratoconjunctivitis sicca have been associated with this disease. We diagnosed angle-closure glaucoma secondary to ciliochoroidal effusion in a patient with IgA nephropathy confirmed by biopsy. High-frequency ultrasound biomicroscopy was used to determine internal relationships of angle structures and to follow changes with treatment. Supraciliary effusion undetected by B-scan ultrasound and retinal examination was easily imaged by ultrasound biomicroscopy. Glaucoma mechanisms included forward rotation of the ciliary processes, which caused direct angle closure in a manner similar to plateau iris. Ultrasound biomicroscopy showed that cycloplegia improved this mechanism by retracting the ciliary processes, but angle closure secondary to forward iris bowing from pupil block remained. Iridectomy was performed and immediately opened the angle. Ultrasound biomicroscopy proved a useful method of defining mechanisms and a helpful guide to treatment in this type of glaucoma.

High frequency 40-MHz ultrasound. A possible noninvasive method for the assessment of the boundary of basal cell carcinomas.

BACKGROUND Ultrasound imaging systems operating close to 20 MHz in frequency have been used to image skin tumors. Ultrasound imaging at 20 MHz has been used to determine the boundaries of basal cell carcinomas (BCCs). An inherent shortcoming of imaging systems operating at these frequencies is their limited resolution. OBJECTIVE We investigated whether 40‐MHz ultrasound imaging could provide higher resolution compared with the lower frequency systems and thus be a superior, noninvasive method of assessing the boundaries of BCCs. METHODS Nine BCCs from six individuals were examined clinically and ultrasonographically, and then biopsied to confirm diagnosis. The depth of BCCs measured on histological sections was compared with the corresponding value obtained using ultrasound. For this study we required a nonsurgical, nondestructive means of treating BCCs that would allow repeated ultrasound imaging, and therefore topical 5‐fliiorouracil (5‐FU) was chosen. Following 5‐FU therapy a biopsy was obtained from the site of the treated BCC after ultrasound imaging had been performed. Clinical, ultrasonic and histopathologic evaluation of each BCC was carried out independently by different individuals. At the end of the study all the BCC sites were treated surgically be electrodesiccation and curettage or completely excised. RESULTS High resolution ultrasound images of BCCs were obtained with agreement between histology and ultrasound findings in all nine lesions prior to therapy and in eight of nine lesions posttherapy. There was a significant correlation between the depth of BCCs measured histologically and using ultrasound (P = 0.0004, r = 0.92). CONCLUSIONS This study suggests that 40‐MHz ultrasound may provide an estimate of the boundary of a BCC in vivo. High frequency 40‐MHz ultrasound imaging may be an adjunct to clinical and histologic evaluation but does not replace the need to obtain tissue for microscopic examination.

Does high-frequency (40-60 MHz) ultrasound imaging play a role in the clinical management of cutaneous melanoma?

The assessment of cutaneous melanoma in the clinical setting is often difficult, and important features such as depth and width remain unknown until the pathology report is received. Access to prognostic features such as vertical height before excisional biopsy would offer a basis for guidance in defining surgical margins and early planning of treatment options. Recently developed high-frequency ultrasound imaging in the 40− to 60-MHz range is a noninvasive method that provides in vivo information about cutaneous lesions. Imaging at these frequencies provides high-resolution data within the range of the epidermis and dermis (3–4 mm in depth). Ten cutaneous melanomas and seven pigmented lesions were assessed in this fashion. Vertical height was documented and compared to histopathological findings. High-frequency ultrasound imaging determination of vertical height correlated well with the standard measurement of Breslows thickness on histological sections only in midrange (1.0–3.0 mm) lesions. Inflammatory cells at the base of three melanomas provoked an overestimation of the depth measurement with ultrasonography. Thick keratin layers such as those found on the feet acted as a virtual block to the high-frequency scanner. The application of this new advance in noninvasive imaging technology to the clinical assessment of cutaneous melanoma provides interesting in vivo data but in its present state does not replace the need for the biopsy of pigmented lesions and histopathological diagnosis.