Ultrafast lasers, which generate optical pulses in the picosecond and femtosecond range, have progressed over the past decade from complicated and specialized laboratory systems to compact, reliable instruments. Semiconductor lasers for optical pumping and fast optical saturable absorbers, based on either semiconductor devices or the optical nonlinear Kerr effect, have dramatically improved these lasers and opened up new frontiers for applications with extremely short temporal resolution (much smaller than 10 fs), extremely high peak optical intensities (greater than 10 TW/cm2) and extremely fast pulse repetition rates (greater than 100 GHz).

Recent developments in compact ultrafast lasers

There have been three basic approaches to optical tomography since the early 1980s: diffraction tomography, diffuse optical tomography and optical coherence tomography (OCT). Optical techniques are of particular importance in the medical field, because these techniques promise to be safe and cheap and, in addition, offer a therapeutic potential. Advances in OCT technology have made it possible to apply OCT in a wide variety of applications but medical applications are still dominating. Specific advantages of OCT are its high depth and transversal resolution, the fact, that its depth resolution is decoupled from transverse resolution, high probing depth in scattering media, contact-free and non-invasive operation, and the possibility to create various function dependent image contrasting methods. This report presents the principles of OCT and the state of important OCT applications. OCT synthesises cross-sectional images from a series of laterally adjacent depth-scans. At present OCT is used in three different fields of optical imaging, in macroscopic imaging of structures which can be seen by the naked eye or using weak magnifications, in microscopic imaging using magnifications up to the classical limit of microscopic resolution and in endoscopic imaging, using low and medium magnification. First, OCT techniques, like the reflectometry technique and the dual beam technique were based on time-domain low coherence interferometry depth-scans. Later, Fourier-domain techniques have been developed and led to new imaging schemes. Recently developed parallel OCT schemes eliminate the need for lateral scanning and, therefore, dramatically increase the imaging rate. These schemes use CCD cameras and CMOS detector arrays as photodetectors. Video-rate three-dimensional OCT pictures have been obtained. Modifying interference microscopy techniques has led to high-resolution optical coherence microscopy that achieved sub-micrometre resolution. This report is concluded with a short presentation of important OCT applications. Ophthalmology is, due to the transparent ocular structures, still the main field of OCT application. The first commercial instrument too has been introduced for ophthalmic diagnostics (Carl Zeiss Meditec AG). Advances in using near-infrared light, however, opened the path for OCT imaging in strongly scattering tissues. Today, optical in vivo biopsy is one of the most challenging fields of OCT application. High resolution, high penetration depth, and its potential for functional imaging attribute to OCT an optical biopsy quality, which can be used to assess tissue and cell function and morphology in situ. OCT can already clarify the relevant architectural tissue morphology. For many diseases, however, including cancer in its early stages, higher resolution is necessary. New broad-bandwidth light sources, like photonic crystal fibres and superfluorescent fibre sources, and new contrasting techniques, give access to new sample properties and unmatched sensitivity and resolution.

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Optical coherence tomography - principles and applications

Although optical absorption is strongly associated with the physiological status of biological tissue, existing high-resolution optical imaging modalities, including confocal microscopy, two-photon microscopy and optical coherence tomography, do not sense optical absorption directly. Furthermore, optical scattering prevents these methods from imaging deeper than ~1 mm below the tissue surface. Here we report functional photoacoustic microscopy (fPAM), which provides multiwavelength imaging of optical absorption and permits high spatial resolution beyond this depth limit with a ratio of maximum imaging depth to depth resolution greater than 100. Reflection mode, rather than orthogonal or transmission mode, is adopted because it is applicable to more anatomical sites than the others. fPAM is demonstrated with in vivo imaging of angiogenesis, melanoma, hemoglobin oxygen saturation (sO_2) of single vessels in animals and total hemoglobin concentration in humans.

Functional photoacoustic microscopy for high-resolution and noninvasive in vivo imaging

Optical microscopy has been a fundamental tool of biological discovery for more than three centuries, but its in vivo tissue imaging ability has been restricted by light scattering to superficial investigations, even when confocal or multiphoton methods are used. Recent advances in optical and optoacoustic (photoacoustic) imaging now allow imaging at depths and resolutions unprecedented for optical methods. These abilities are increasingly important to understand the dynamic interactions of cellular processes at different systems levels, a major challenge of postgenome biology. This Review discusses promising photonic methods that have the ability to visualize cellular and subcellular components in tissues across different penetration scales. The methods are classified into microscopic, mesoscopic and macroscopic approaches, according to the tissue depth at which they operate. Key characteristics associated with different imaging implementations are described and the potential of these technologies in biological applications is discussed.

Going deeper than microscopy: the optical imaging frontier in biology

The study group.

http://www.vincenzoparisi.it/pdf/Ripandelli%20et%20al.%20Ophthalmology%202003.pdf

Cataract surgery as a risk factor for retinal detachment in very highly myopic eyes.

http://www.vincenzoparisi.it/pdf/Cop_Ophtalmology_2005.pdf

Prevalence of asymptomatic macular holes in highly myopic eyes.

Purpose:To review prevalence, long-term progression, and prognosis of vitreoretinal interface modifications in pathologic myopia with posterior staphyloma and investigate foveal sensitivity and fixation stability.Methods:Retrospective single-institution series of 214 eyes (116 patients) with patholo

/pdf/macular-vitreoretinal-interface-abnormalities-in-highly-3vltn2zhhx.pdf

MACULAR VITREORETINAL INTERFACE ABNORMALITIES IN HIGHLY MYOPIC EYES WITH POSTERIOR STAPHYLOMA: 5-Year Follow-up

Purpose:To illustrate a noninvasive method to analyze the retinal capillary lumen caliber in patients with Type 1 diabetes.Methods:Adaptive optics imaging of the retinal capillaries were acquired in two parafoveal regions of interest in eyes with nonproliferative diabetic retinopathy and unaffected

Analysis of retinal capillaries in patients with type 1 diabetes and nonproliferative diabetic retinopathy using adaptive optics imaging.

Purpose:To evaluate the parafoveal cone density in patients with Type 1 diabetes mellitus (DM1).Methods:Adaptive optics retinal images of the photoreceptor mosaic were acquired from 11 DM1 patients (study group) and 11 age-matched healthy subjects (control group). Cone density was analyzed, along th

Mario Stirpe

Papers

Cataract surgery as a risk factor for retinal detachment in very highly myopic eyes.

Prevalence of asymptomatic macular holes in highly myopic eyes.

MACULAR VITREORETINAL INTERFACE ABNORMALITIES IN HIGHLY MYOPIC EYES WITH POSTERIOR STAPHYLOMA: 5-Year Follow-up

Analysis of retinal capillaries in patients with type 1 diabetes and nonproliferative diabetic retinopathy using adaptive optics imaging.

Adaptive optics imaging of parafoveal cones in type 1 diabetes