Ultrasound biomicroscopic imaging of the effects of YAG laser cycloablation in postmortem eyes and living patients

Real-time imaging of transscleral diode laser cyclophotocoagulation by optical coherence tomography

PURPOSE

To present optical coherence tomography (OCT) for real-time imaging of cyclophotocoagulation effects.

METHODS

In a pilot study, real-time transscleral OCT images were generated during diode laser cyclophotocoagulation in four eyes of four patients suffering from uncontrolled glaucoma using a specially designed contact applicator containing the OCT fiber, a focussing fiber optic and the fiber of the diode laser.

RESULTS

When the contact system was used, two layers could be differentiated: a superficial thick hyperreflective complex representing conjunctiva, Tenon's capsule, episclera and sclera, and a thinner hyporeflective layer representing the ciliary body. During cyclophotocoagulation, real-time OCT showed a clear and sudden thickening of the ciliary body in the treated area.

CONCLUSION

This new OCT device represents a first step towards visual, real-time imaging of cyclophotocoagulation. After further adaptation of the delivery system, further trials are needed to correlate OCT findings with aqueous production and intraocular pressure.

Acoustic modulation and photon-phonon scattering in optical coherence tomography

Acousto-optic interactions allow the measurement of nonoptical material properties with high-resolution optical methods. We modulated a sample with ultrasound while simultaneously imaging with a traditional optical coherence tomography (OCT) system. The measured acousto-optic signal then depends on the mechanical response of the tissue to the applied modulation. The acquired acoustically enhanced OCT signals are consistent with established acousto-optic theory and provide enhanced contrast to OCT images.

ACP Best Practice No 164: Necropsy techniques in ophthalmic pathology

Much important information can be obtained at necropsy by the pathological examination of the eye and its adnexal structures in adults and children. This information may be related to the cause of death (for example, violent shaking trauma in physical child abuse), or may pertain to disease processes affecting the eye, the orbit, and surrounding structures outside the orbit. This article reviews the technical methods used to remove the following: the vitreous (for example, for biochemistry); the eye itself (anterior approach); the eye and orbital contents (posterior approach); the eye, orbit and orbital walls; and the eye, orbital walls, and surrounding structures. The removal of the eye and adnexal ocular structures must be recognised as a "culturally sensitive" issue, which must be approached cautiously. It should only be undertaken for sound scientific reasons, with the fully informed consent of the relatives and/or the coroner (or equivalent authority), and with properly agreed procedures for the eventual retention or disposal of the ocular tissues. For this reason, this article reviews not only the scientific indications and methods for the removal of such tissues, but also the legal and ethical issues that must underpin this pathology "best practice".

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 PVDF's 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.

Evaluation of laser sclerostomy fistulas using ultrasound biomicroscopy

BACKGROUND

Laser sclerostomy is a relatively new technique in glaucoma surgery. Clinical examination, particularly of the intrascleral part of laser sclerostomy fistulas, is difficult. We performed ultrasound biomicroscopy (UBM) in order to determine, if it were possible to visualize fistulas. Moreover, it was the aim to investigate whether this imaging technique could provide additional information on fistula morphology.

PATIENTS AND METHODS

Ten eyes of eight patients with chronic open angle glaucoma who had undergone erbium-YAG laser sclerostomy ab externo were examined using a UBM-probe with a 20 MHz transducer providing spatial resolution of approximately 80 microm.

RESULTS

Radial scanning allowed visualization of the sclerostomy fistula in nine of ten eyes. The different functional state of sclerostomy fistulas correlated well to UBM findings. It was possible to image differences in the morphology of occluded and patent fistulas and to visualize the filtering pathway in functioning blebs.

CONCLUSIONS

Ultrasound biomicroscopy allows imaging of laser sclerostomy fistulas. UBM and clinical findings correlated well in the majority of the patients we examined. The technique supplements clinical examination and in some cases may provide additional information.

High-frequency ultrasound properties of multicellular spheroids during heating

High-frequency ultrasound monitoring is a possible method for real-time imaging of thermal therapy in tissues at microscopic resolution. The objective of this work was to measure changes in the ultrasound properties of V79 spheroids (grown from Chinese Hamster lung fibroblasts) exposed to heating. Spheroids are clonal aggregates of cells that provide a useful model for investigating the ultrasound properties of cells in the absence of connective tissue. Relative echo signal power and attenuation coefficients were measured over the frequency range 30 MHz to 70 MHz, from spheroids heated from 37 degrees C to 50 degrees C or 60 degrees C. Echo signal power from the viable rim decreased during the first 5 min by a factor of 1.08 before the spheroid reached 50 degrees C. For the next 25 min, echo signal power rose to a factor of 1.27 above the initial level, after which it remained relatively constant over the remainder of the 50 degrees C heating period. At 60 degrees C, echo signal from the viable rim remained relatively constant, although it appeared to have possibly decreased slightly over the duration of the heating period. Echo signal power from the necrotic core fell to a factor of 1.4 and 1.54 below the initial level at 50 degrees C and 60 degrees C, respectively. First-order chemical rate analysis applied to the echo signal power results in the viable rim at 50 degrees C revealed a rate constant for the 5-15-min heating interval. Interpretation of the echo signal power results in terms of histological stains indicates that the rise in echo signal power at 50 degrees C was due to a loss of cell cohesion, and the possible drop in echo signal power at 60 degrees C was due to spheroid coagulation. Attenuation coefficients decreased by up to 1.54 dB mm-1 over a 30-min period at 60 degrees C. The appearance of a real-time ultrasound image of lesion formation in cells is discussed.

Ultrasound properties of liver tissue during heating

The objective of this work was to determine changes in the ultrasound properties of heated tissues, with potential application to monitoring of minimally invasive thermal therapy (MITT). Changes in backscatter coefficients and frequency-dependent attenuation coefficients were measured over the frequency range 2.5 MHz to 5 MHz from heated samples of store-bought fresh bovine liver, which was used as a tissue model. Individual liver samples were heated from 37 degrees C to either 50 degrees C, 55 degrees C, 60 degrees C, 65 degrees C or 70 degrees C by warm water. The backscatter coefficient increased during the first 3 min by a factor of 1.09 and 1.11 before the tissue reached 50 degrees C and 55 degrees C, respectively. A decrease in backscatter coefficient followed at 50 degrees C by a factor of 1.12 below the initial level and, at 55 degrees C, the backscatter coefficient dropped below the initial level by a factor of 1.19. The backscatter coefficient decreased within the first 2 min by a factor of 1.22 before the tissue reached 60 degrees C, then increased gradually to a factor of 1.05 below the initial level. At 65 degrees C and 70 degrees C, the changes in backscatter coefficient were highly variable, which may have been due to production of gas microbubbles in the heated tissues. The ultrasound attenuation coefficient increased by as much as 1.48 dB cm-1 over a 30-min period at 70 degrees C. First-order rate parameters derived from the attenuation results revealed one rate process at 50 degrees C and 55 degrees C and two rate processes at 60 degrees C, 65 degrees C and 70 degrees C. An activation energy of 1.00 x 10(4) cal mol-1 was derived from the second rate constants at 60 degrees C, 65 degrees C and 70 degrees C, which indicates that changes in attenuation may be due to protein denaturation. In conclusion, ultrasound image monitoring of thermal therapy treatment in liver may be feasible; however, the backscatter coefficient changes during heating are small and are of the same order as the variation in these changes from point to point in the tissue.