Exploration of the two-photon excitation spectrum of fluorescent dyes at wavelengths below the range of the Ti:Sapphire laser

We have studied the wavelength dependence of the two-photon excitation efficiency for a number of common UV excitable fluorescent dyes; the nuclear stains DAPI, Hoechst and SYTOX Green, chitin- and cellulose-staining dye Calcofluor White and Alexa Fluor 350, in the visible and near-infrared wavelength range (540-800 nm). For several of the dyes, we observe a substantial increase in the fluorescence emission intensity for shorter excitation wavelengths than the 680 nm which is the shortest wavelength usually available for two-photon microscopy. We also find that although the rate of photo-bleaching increases at shorter wavelengths, it is still possible to acquire many images with higher fluorescence intensity. This is particularly useful for applications where the aim is to image the structure, rather than monitoring changes in emission intensity over extended periods of time. We measure the excitation spectrum when the dyes are used to stain biological specimens to get a more accurate representation of the spectrum of the dye in a cell environment as compared to solution-based measurements.

A simple but precise method for quantitative measurement of the quality of the laser focus in a scanning optical microscope

We report a method for characterizing the focussing laser beam exiting the objective in a laser scanning microscope. This method provides the size of the optical focus, the divergence of the beam, the ellipticity and the astigmatism. We use a microscopic‐scale knife edge in the form of a simple transmission electron microscopy grid attached to a glass microscope slide, and a light‐collecting optical fibre and photodiode underneath the specimen. By scanning the laser spot from a reflective to a transmitting part of the grid, a beam profile in the form of an error function can be obtained and by repeating this with the knife edge at different axial positions relative to the beam waist, the divergence and astigmatism of the postobjective laser beam can be obtained. The measured divergence can be used to quantify how much of the full numerical aperture of the lens is used in practice. We present data of the beam radius, beam divergence, ellipticity and astigmatism obtained with low (0.15, 0.7) and high (1.3) numerical aperture lenses and lasers commonly used in confocal and multiphoton laser scanning microscopy. Our knife‐edge method has several advantages over alternative knife‐edge methods used in microscopy including that the knife edge is easy to prepare, that the beam can be characterized also directly under a cover slip, as necessary to reduce spherical aberrations for objectives designed to be used with a cover slip, and it is suitable for use with commercial laser scanning microscopes where access to the laser beam can be limited.

Increased signals from short-wavelength-excited fluorescent molecules using sub-Ti:Sapphire wavelengths

We report the use of an all-solid-state ultrashort pulsed source specifically for two-photon microscopy at wavelengths shorter than those of the conventional Ti:Sapphire laser. Our approach involves sum-frequency mixing of the output from an optical parametric oscillator (λ= 1400-1640 nm) synchronously pumped by a Yb-doped fibre laser (λ= 1064 nm), with the residual pump radiation. This generated an fs-pulsed output tunable in the red spectral region (λ= 620-636 nm, ~150 mW, 405 fs, 80 MHz, M(2) ~ 1.3). We demonstrate the performance of our ultrashort pulsed system using fluorescently labelled and autofluorescent tissue, and compare with conventional Ti:Sapphire excitation. We observe a more than 3-fold increase in fluorescence signal intensity using our visible laser source in comparison with the Ti:Sapphire laser for two-photon excitation at equal illumination peak powers of 1.16 kW or less.

A compact instrument for adjusting laser beams to be accurately coincident and coaxial and its use in biomedical imaging using wave-mixed laser sources

Biomedical imaging applications that involve nonlinear optical processes such as sum-frequency generation (SFG) and four-wave mixing require that the pulses are synchronized in time and the beams are coaxial to better than 400 μrad. For this reason, folding mirrors are normally used to extend the beam path over a few meters so that detectors can be put into the beams to check their overlap at the start of a long path and also at the end of it. We have made a portable instrument with a footprint of only 22 cm × 11 cm × 16 cm that uses a short focal length lens and a telephoto combination for viewing the near-field and far-field simultaneously. Our instrument is simple to build and use, and we show its application in coherent anti-Stokes Raman scattering microscopy and SFG-based two-photon fluorescence microscopy.

Impact of concurrent amiodarone treatment on the tolerability and efficacy of carvedilol in patients with chronic heart failure

OBJECTIVE

To assess the safety and efficacy of carvedilol when administered to heart failure patients already receiving amiodarone.

DESIGN

Retrospective analysis of the clinical outcome of 230 patients treated with carvedilol for chronic heart failure, stratified according to whether they were already receiving amiodarone (amiodarone group, 80 patients) or not (non-amiodarone group, 130 patients) at baseline.

SETTING

Heart failure clinic at a university affiliated public teaching hospital.

MAIN OUTCOME MEASURES

Incidence of adverse events; changes in functional status and echocardiographic dimensions at three months.

RESULTS

Adverse reactions to carvedilol occurred in 33 (41%) of the amiodarone group and 43 (29%) of the non-amiodarone group (p = 0.049). Carvedilol was discontinued in 21 (26%) of the amiodarone group and 37 (25%) of the non-amiodarone group (NS). The clinical outcome at three months did not differ significantly between the two groups; 31 (39%) of the amiodarone group improved their New York Heart Association status, 28 (35%) were unchanged, and 21 (26%) deteriorated compared with 67 (45%), 51 (34%), and 32 (21%), respectively, for the non-amiodarone group (NS). Both groups had highly significant decreases in heart rate and left ventricular end systolic dimension, and a significant increase in left ventricular ejection fraction after three months of carvedilol treatment, with no significant differences between the groups.

CONCLUSIONS

The beneficial effects of carvedilol on left ventricular remodelling, systolic function, and symptomatic status are not affected by concurrent treatment with amiodarone. Adverse reactions necessitating cessation of carvedilol are no more frequent in patients receiving amiodarone.

Tolerability and efficacy of carvedilol in patients with New York Heart Association class IV heart failure

OBJECTIVES

The purpose of this study was to assess the tolerability and efficacy of carvedilol in patients with New York Heart Association (NYHA) functional class IV symptoms.

BACKGROUND

Carvedilol, a nonselective beta-adrenergic blocking drug with alpha-adrenergic blocking and antioxidant properties, has been shown to improve left ventricular function and clinical outcome in patients with mild to moderate chronic heart failure.

METHODS

We retrospectively analyzed the outcomes of 230 patients with heart failure treated with carvedilol who were stratified according to baseline functional class: 63 patients were NYHA class IV and 167 were NYHA class I, II or III. Carvedilol was commenced at 3.125 mg b.i.d. and titrated to 25 mg b.i.d. as tolerated. Patients with class IV symptoms were older (p = 0.03), had lower left ventricular fractional shortening (p < 0.001), had lower six-min walk distance (p < 0.001) and were receiving more heart failure medications at baseline compared with less symptomatic patients.

RESULTS

Nonfatal adverse events while taking carvedilol occurred more frequently in class IV patients (43% vs. 24%, p < 0.0001), and more often resulted in permanent withdrawal of the drug (25% vs. 13%, p < 0.01). Thirty-seven (59%) patients who were NYHA class IV at baseline had improved by one or more functional class at 3 months, 8 (13%) were unchanged and 18 (29%) had deteriorated or died. Among the less symptomatic group, 62 (37%) patients had improved their NYHA status at 3 months, 73 (44%) were unchanged and 32 (19%) had deteriorated or died. The differences in symptomatic outcome at three months between the two groups were statistically significant (p = 0.001, chi-square analysis). Both groups demonstrated similar significant improvements in left ventricular dimensions and systolic function.

CONCLUSIONS

Patients with chronic NYHA class IV heart failure are more likely to develop adverse events during initiation and dose titration when compared with less symptomatic patients but are more likely to show symptomatic improvement in the long term. We conclude that carvedilol is a useful adjunctive therapy for patients with NYHA class IV heart failure; however, they require close observation during initiation and titration of the drug.