Review of machine learning for optical imaging of burn wound severity assessment

Significance

Over the past decade, machine learning (ML) algorithms have rapidly become much more widespread for numerous biomedical applications, including the diagnosis and categorization of disease and injury.

Aim

Here, we seek to characterize the recent growth of ML techniques that use imaging data to classify burn wound severity and report on the accuracies of different approaches.

Approach

To this end, we present a comprehensive literature review of preclinical and clinical studies using ML techniques to classify the severity of burn wounds.

Results

The majority of these reports used digital color photographs as input data to the classification algorithms, but recently there has been an increasing prevalence of the use of ML approaches using input data from more advanced optical imaging modalities (e.g., multispectral and hyperspectral imaging, optical coherence tomography), in addition to multimodal techniques. The classification accuracy of the different methods is reported; it typically ranges from ∼ 70 % to 90% relative to the current gold standard of clinical judgment.

Conclusions

The field would benefit from systematic analysis of the effects of different input data modalities, training/testing sets, and ML classifiers on the reported accuracy. Despite this current limitation, ML-based algorithms show significant promise for assisting in objectively classifying burn wound severity.

Motion-resistant three-wavelength spatial frequency domain imaging system with ambient light suppression using an 8-tap CMOS image sensor

Significance

We present a motion-resistant three-wavelength spatial frequency domain imaging (SFDI) system with ambient light suppression using an 8-tap complementary metal-oxide semiconductor (CMOS) image sensor (CIS) developed at Shizuoka University. The system addresses limitations in conventional SFDI systems, enabling reliable measurements in challenging imaging scenarios that are closer to real-world conditions.

Aim

Our study demonstrates a three-wavelength SFDI system based on an 8-tap CIS. We demonstrate and evaluate the system's capability of mitigating motion artifacts and ambient light bias through tissue phantom reflectance experiments and in vivo volar forearm experiments.

Approach

We incorporated the Hilbert transform to reduce the required number of projected patterns per wavelength from three to two per spatial frequency. The 8-tap image sensor has eight charge storage diodes per pixel; therefore, simultaneous image acquisition of eight images based on multi-exposure is possible. Taking advantage of this feature, the sensor simultaneously acquires images for planar illumination, sinusoidal pattern projection at three wavelengths, and ambient light. The ambient light bias is eliminated by subtracting the ambient light image from the others. Motion artifacts are suppressed by reducing the exposure and projection time for each pattern while maintaining sufficient signal levels by repeating the exposure. The system is compared to a conventional SFDI system in tissue phantom experiments and then in vivo measurements of human volar forearms.

Results

The 8-tap image sensor-based SFDI system achieved an acquisition rate of 9.4 frame sets per second, with three repeated exposures during each accumulation period. The diffuse reflectance maps of three different tissue phantoms using the conventional SFDI system and the 8-tap image sensor-based SFDI system showed good agreement except for high scattering phantoms. For the in vivo volar forearm measurements, our system successfully measured total hemoglobin concentration, tissue oxygen saturation, and reduced scattering coefficient maps of the subject during motion (16.5 cm/s) and under ambient light (28.9 lx), exhibiting fewer motion artifacts compared with the conventional SFDI.

Conclusions

We demonstrated the potential for motion-resistant three-wavelength SFDI system with ambient light suppression using an 8-tap CIS.

Quantitative hemodynamic imaging: a method to correct the effects of optical properties on laser speckle imaging

Significance

Studying cerebral hemodynamics may provide diagnostic information on neurological conditions. Wide-field imaging techniques, such as laser speckle imaging (LSI) and optical intrinsic signal imaging, are commonly used to study cerebral hemodynamics. However, they often do not account appropriately for the optical properties of the brain that can vary among subjects and even during a single measurement. Here, we describe the combination of LSI and spatial-frequency domain imaging (SFDI) into a wide-field quantitative hemodynamic imaging (QHI) system that can correct the effects of optical properties on LSI measurements to achieve a quantitative measurement of cerebral blood flow (CBF).

Aim

We describe the design, fabrication, and testing of QHI.

Approach

The QHI hardware combines LSI and SFDI with spatial and temporal synchronization. We characterized system sensitivity, accuracy, and precision with tissue-mimicking phantoms. With SFDI optical property measurements, we describe a method derived from dynamic light scattering to obtain absolute CBF values from LSI and SFDI measurements. We illustrate the potential benefits of absolute CBF measurements in resting-state and dynamic experiments.

Results

QHI achieved a 50-Hz raw acquisition frame rate with a 10 × 10    mm field of view and flow sensitivity up to ∼ 4    mm / s . The extracted SFDI optical properties agreed well with a commercial system (R 2 ≥ 0.98 ). The system showed high stability with low coefficients of variations over multiple sessions within the same day (< 1 % ) and over multiple days (< 4 % ). When optical properties were considered, the in-vivo hypercapnia gas challenge showed a slight difference in CBF (- 1.5 % to 0.5% difference). The in-vivo resting-state experiment showed a change in CBF ranking for nine out of 13 animals when the correction method was applied to LSI CBF measurements.

Conclusions

We developed a wide-field QHI system to account for the confounding effects of optical properties on CBF LSI measurements using the information obtained from SFDI.

Current and Emerging Imaging Techniques for Neurofibromatosis Type 1-Associated Cutaneous Neurofibromas

A consistent set of measurement techniques must be applied to reliably and reproducibly evaluate the efficacy of treatments for cutaneous neurofibromas (cNFs) in people with neurofibromatosis type 1 (NF1). cNFs are neurocutaneous tumors that are the most common tumor in people with NF1 and represent an area of unmet clinical need. This review presents the available data regarding approaches in use or development to identify, measure, and track cNFs, including calipers, digital imaging, and high-frequency ultrasound sonography. We also describe emerging technologies such as spatial frequency domain imaging and the application of imaging modalities such as optical coherence tomography that may enable the detection of early cNFs and prevention of tumor-associated morbidity.

Assessing multimodal optical imaging of perfusion in burn wounds

A critical need exists for early, accurate diagnosis of burn wound severity to help identify the course of treatment and outcome of the wound. Laser speckle imaging (LSI) is a promising blood perfusion imaging approach, but it does not account for changes in tissue optical properties that can occur with burn wounds, which are highly dynamic environments. Here, we studied optical property dynamics following burn injury and debridement and the associated impact on interpretation of LSI measurements of skin perfusion. We used spatial frequency domain imaging (SFDI) measurements of tissue optical properties to study the impact of burn-induced changes in these properties on LSI measurements. An established preclinical porcine model of burn injury was used (n = 8). SFDI and LSI data were collected from burn wounds of varying severity. SFDI measurements demonstrate that optical properties change in response to burn injury in a porcine model. We then apply theoretical modeling to demonstrate that the measured range of optical property changes can affect the interpretation of LSI measurements of blood flow, but this effect is minimal for most of the measured data. Collectively, our results indicate that, even with a dynamic burn wound environment, blood-flow measurements with LSI can serve as an appropriate strategy for accurate assessment of burn severity.

Quantifying the confounding effect of pigmentation on measured skin tissue optical properties: a comparison of colorimetry with spatial frequency domain imaging

SIGNIFICANCE

Spatial frequency domain imaging (SFDI) is a wide-field diffuse optical imaging technique for separately quantifying tissue reduced scattering (μs  '  ) and absorption (μa) coefficients at multiple wavelengths, providing wide potential utility for clinical applications such as burn wound characterization and cancer detection. However, measured μs  '   and μa can be confounded by absorption from melanin in patients with highly pigmented skin. This issue arises because epidermal melanin is highly absorbing for visible wavelengths and standard homogeneous light-tissue interaction models do not properly account for this complexity. Tristimulus colorimetry (which quantifies pigmentation using the L  *   "lightness" parameter) can provide a point of comparison between μa, μs  '  , and skin pigmentation.

AIM

We systematically compare SFDI and colorimetry parameters to quantify confounding effects of pigmentation on measured skin μs  '   and μa. We assess the correlation between SFDI and colorimetry parameters as a function of wavelength.

APPROACH

μs  '   and μa from the palm and ventral forearm were measured for 15 healthy subjects with a wide range of skin pigmentation levels (Fitzpatrick types I to VI) using a Reflect RS® (Modulim, Inc., Irvine, California) SFDI instrument (eight wavelengths, 471 to 851 nm). L  *   was measured using a Chroma Meter CR-400 (Konica Minolta Sensing, Inc., Tokyo). Linear correlation coefficients were calculated between L  *   and μs  '   and between L  *   and μa at all wavelengths.

RESULTS

For the ventral forearm, strong linear correlations between measured L  *   and μs  '   values were observed at shorter wavelengths (R  >  0.92 at ≤659  nm), where absorption from melanin confounded the measured μs  '  . These correlations were weaker for the palm (R  <  0.59 at ≤659  nm), which has less melanin than the forearm. Similar relationships were observed between L  *   and μa.

CONCLUSIONS

We quantified the effects of epidermal melanin on skin μs  '   and μa measured with SFDI. This information may help characterize and correct pigmentation-related inaccuracies in SFDI skin measurements.

Spatial frequency domain imager based on a compact multiaperture camera: testing and feasibility for noninvasive burn severity assessment

SIGNIFICANCE

Spatial frequency domain imaging (SFDI) is a wide-field imaging technique that provides quantitative maps of tissue optical properties. We describe a compact SFDI imager that employs a multispectral compound-eye camera. This design enables simultaneous image acquisition at multiple wavelengths. Such a device has potential for application for quantitative evaluation of superficial tissues by nonspecialists in low-resource settings.

AIM

The aim of this work was to develop a compact SFDI imager for widefield imaging of in-vivo tissue optical properties and verify its ability to measure optical properties of tissue-simulating phantoms and in a preclinical model of burn wounds.

APPROACH

This compound-eye imager was constructed using a CMOS sensor subdivided into multiple regions, each having a bandpass filter and objective lens. The ability of the instrument to image optical properties was compared with (1) a commercial SFDI imager and (2) a laboratory-based system. Initial validation of ability to accurately characterize optical properties was performed using a tissue-simulating optical phantom. It was then applied to an established murine model of thermal contact burn severity. In-vivo measurements of the optical properties of rat skin were performed before and after the application of burns. Histology was used to verify burn severity.

RESULTS

Measurements of the tissue-simulating phantom optical properties made using the compound-eye imager agree with measurements made using the two comparison SFDI devices. For the murine burn model, the burns showed a decrease in the reduced scattering coefficient at all measurement wavelengths compared with preburn measurements at the same locations. This is consistent with previously reported changes in scattering that occur in full-thickness burns.

CONCLUSION

We demonstrate the potential for SFDI to be translated into compact form factor using a compound-eye camera that is capable of obtaining multiple wavelengths channels simultaneously.

Characterizing reduced scattering coefficient of normal human skin across different anatomic locations and Fitzpatrick skin types using spatial frequency domain imaging

SIGNIFICANCE

Spatial frequency domain imaging (SFDI), a noncontact wide-field imaging technique using patterned illumination with multiple wavelengths, has been used to quantitatively measure structural and functional parameters of in vivo tissue. Using SFDI in a porcine model, we previously found that scattering changes in skin could potentially be used to noninvasively assess burn severity and monitor wound healing. Translating these findings to human subjects necessitates a better understanding of the variation in "baseline" human skin scattering properties across skin types and anatomical locations.

AIM

Using SFDI, we aim to characterize the variation in the reduced scattering coefficient (μs') for skin across a range of pigmentation and anatomic sites (including common burn locations) for normal human subjects. These measurements are expected to characterize baseline human skin properties to inform our use of SFDI for clinical burn severity and wound healing assessments.

APPROACH

SFDI was used to measure μs' in the visible- and near-infrared regime (471 to 851 nm) in 15 subjects at 10 anatomical locations. Subjects varied in age, gender, and Fitzpatrick skin type.

RESULTS

For all anatomical locations, the coefficient of variation in measured μs' decreased with increasing wavelength. High intersubject variation in μs' at visible wavelengths coincided with large values of the melanin extinction coefficient at those wavelengths. At 851 nm, where intersubject variation in μs' was smallest for all anatomical locations and absorption from melanin is minimal, significant intrasubject differences in μs' were observed at the different anatomical locations.

CONCLUSIONS

Our study is the first report of wide-field mapping of human skin scattering properties across multiple skin types and anatomical locations using SFDI. Measured μs' values varied notably between skin types at wavelengths where absorption from melanin was prominent. Additionally, μs' varied considerably across different anatomical locations at 851 nm, where the confounding effects from melanin absorption are minimized.

Spatial Frequency Domain Imaging (SFDI) of clinical burns: A case report

While visual assessment by a clinician is the standard of care for burn severity evaluations, new technologies at various stages of development are attempting to add objectivity to this practice by quantifying burn severity. Assessment accuracy generally improves after the burn injury has progressed, but early assessments that correctly identify superficial partial and deep partial burns have the potential to lead to more prompt treatments and shorter recovery times. To date, Spatial Frequency Domain Imaging (SFDI) has only been used in animal models of burns, but has shown the potential to categorize burns accurately at earlier time points. Here we examine the potential for SFDI to assess burn severity in clinical patients. We also utilize Laser Speckle Imaging (LSI), an FDA cleared non-invasive imaging technology that typically measures blood perfusion in order to evaluate burns in clinical patients. We present a case series of two patients, both with partial thickness burns of varying severity. Partial thickness burns are often difficult for clinicians to categorize based on visual appearance alone. SFDI and LSI were both performed on each patient at approximately 24 and 72 h after their respective burn incidents. Each technique was able to render spatially resolved information that enabled improved assessment accuracy for each burn. This represents the first publication of SFDI applied to clinical burn patients after being successfully utilized in animal models, and highlights the potential for SFDI as a feasible tool for the timely categorization of burn severity.

Spatial frequency domain imaging: a quantitative, noninvasive tool for in vivo monitoring of burn wound and skin graft healing

There is a need for noninvasive, quantitative methods to characterize wound healing in the context of longitudinal investigations related to regenerative medicine. Such tools have the potential to inform the assessment of wound status and healing progression and aid the development of new treatments. We employed spatial frequency domain imaging (SFDI) to characterize the changes in optical properties of tissue during wound healing progression in a porcine model of split-thickness skin grafts and also in a model of burn wound healing with no graft intervention. Changes in the reduced scattering coefficient measured using SFDI correlated with structural changes reported by histology of biopsies taken concurrently. SFDI was able to measure spatial inhomogeneity in the wounds and predicted heterogeneous healing. In addition, we were able to visualize differences in healing rate, depending on whether a wound was debrided and grafted, versus not debrided and left to heal without intervention apart from topical burn wound care. Changes in the concentration of oxy- and deoxyhemoglobin were also quantified, giving insight into hemodynamic changes during healing.

Hyperspectral imaging in the spatial frequency domain with a supercontinuum source

We introduce a method for quantitative hyperspectral optical imaging in the spatial frequency domain (hs-SFDI) to image tissue absorption (μa) and reduced scattering (μs') parameters over a broad spectral range. The hs-SFDI utilizes principles of spatial scanning of the spectrally dispersed output of a supercontinuum laser that is sinusoidally projected onto the tissue using a digital micromirror device. A scientific complementary metal-oxide-semiconductor camera is used for capturing images that are demodulated and analyzed using SFDI computational models. The hs-SFDI performance is validated using tissue-simulating phantoms over a range of μa and μs' values. Quantitative hs-SFDI images are obtained from an ex-vivo beef sample to spatially resolve concentrations of oxy-, deoxy-, and met-hemoglobin, as well as water and fat fractions. Our results demonstrate that the hs-SFDI can quantitatively image tissue optical properties with 1000 spectral bins in the 580- to 950-nm range over a wide, scalable field of view. With an average accuracy of 6.7% and 12.3% in μa and μs', respectively, compared to conventional methods, hs-SFDI offers a promising approach for quantitative hyperspectral tissue optical imaging.

Burn wound classification model using spatial frequency-domain imaging and machine learning

Accurate assessment of burn severity is critical for wound care and the course of treatment. Delays in classification translate to delays in burn management, increasing the risk of scarring and infection. To this end, numerous imaging techniques have been used to examine tissue properties to infer burn severity. Spatial frequency-domain imaging (SFDI) has also been used to characterize burns based on the relationships between histologic observations and changes in tissue properties. Recently, machine learning has been used to classify burns by combining optical features from multispectral or hyperspectral imaging. Rather than employ models of light propagation to deduce tissue optical properties, we investigated the feasibility of using SFDI reflectance data at multiple spatial frequencies, with a support vector machine (SVM) classifier, to predict severity in a porcine model of graded burns. Calibrated reflectance images were collected using SFDI at eight wavelengths (471 to 851 nm) and five spatial frequencies (0 to 0.2  mm  -  1). Three models were built from subsets of this initial dataset. The first subset included data taken at all wavelengths with the planar (0  mm  -  1) spatial frequency, the second comprised data at all wavelengths and spatial frequencies, and the third used all collected data at values relative to unburned tissue. These data subsets were used to train and test cubic SVM models, and compared against burn status 28 days after injury. Model accuracy was established through leave-one-out cross-validation testing. The model based on images obtained at all wavelengths and spatial frequencies predicted burn severity at 24 h with 92.5% accuracy. The model composed of all values relative to unburned skin was 94.4% accurate. By comparison, the model that employed only planar illumination was 88.8% accurate. This investigation suggests that the combination of SFDI with machine learning has potential for accurately predicting burn severity.

Impact of hemoglobin breakdown products in the spectral analysis of burn wounds using spatial frequency domain spectroscopy

Burn wounds and wound healing invoke several biological processes that may complicate the interpretation of spectral imaging data. Through analysis of spatial frequency domain spectroscopy data (450 to 1000 nm) obtained from longitudinal investigations using a graded porcine burn wound healing model, we have identified features in the absorption spectrum that appear to suggest the presence of hemoglobin breakdown products, e.g., methemoglobin. Our results show that the calculated concentrations of methemoglobin directly correlate with burn severity, 24 h after the injury. In addition, tissue parameters such as oxygenation (StO2) and water fraction may be underestimated by 20% and 78%, respectively, if methemoglobin is not included in the spectral analysis.

Solid tissue simulating phantoms having absorption at 970 nm for diffuse optics

Tissue simulating phantoms can provide a valuable platform for quantitative evaluation of the performance of diffuse optical devices. While solid phantoms have been developed for applications related to characterizing exogenous fluorescence and intrinsic chromophores such as hemoglobin and melanin, we report the development of a poly(dimethylsiloxane) (PDMS) tissue phantom that mimics the spectral characteristics of tissue water. We have developed these phantoms to mimic different water fractions in tissue, with the purpose of testing new devices within the context of clinical applications such as burn wound triage. Compared to liquid phantoms, cured PDMS phantoms are easier to transport and use and have a longer usable life than gelatin-based phantoms. As silicone is hydrophobic, 9606 dye was used to mimic the optical absorption feature of water in the vicinity of 970 nm. Scattering properties are determined by adding titanium dioxide, which yields a wavelength-dependent scattering coefficient similar to that observed in tissue in the near-infrared. Phantom properties were characterized and validated using the techniques of inverse adding-doubling and spatial frequency domain imaging. Results presented here demonstrate that we can fabricate solid phantoms that can be used to simulate different water fractions

Quantitative long-term measurements of burns in a rat model using Spatial Frequency Domain Imaging (SFDI) and Laser Speckle Imaging (LSI)

BACKGROUND AND OJECTIVES

The current standard for diagnosis of burn severity and subsequent wound healing is through clinical examination, which is highly subjective. Several new technologies are shifting focus to burn care in an attempt to help quantify not only burn depth but also the progress of healing. While accurate early assessment of partial thickness burns is critical for dictating the course of treatment, the ability to quantitatively monitor wound status over time is critical for understanding treatment efficacy. SFDI and LSI are both non-invasive imaging modalities that have been shown to have great diagnostic value for burn severity, but have yet to be tested over the course of wound healing.

METHODS

In this study, a hairless rat model (n = 6, 300-450 g) was used with a four pronged comb to create four identical partial thickness burns (superficial n = 3 and deep n = 3) that were used to monitor wound healing over a 28 days period. Weekly biopsies were taken for histological analysis to verify wound progression. Both SFDI and LSI were performed weekly to track the evolution of hemodynamic (blood flow and oxygen saturation) and structural (reduced scattering coefficient) properties for the burns.

RESULTS

LSI showed significant changes in blood flow from baseline to 220% in superficial and 165% in deep burns by day 7. In superficial burns, blood flow returned to baseline levels by day 28, but not for deep burns where blood flow remained elevated. Smaller increases in blood flow were also observed in the surrounding tissue over the same time period. Oxygen saturation values measured with SFDI showed a progressive increase from baseline values of 66-74% in superficial burns and 72% in deep burns by day 28. Additionally, SFDI showed significant decreases in the reduced scattering coefficient shortly after the burns were created. The scattering coefficient progressively decreased in the wound area, but returned towards baseline conditions at the end of the 28 days period. Scattering changes in the surrounding tissue remained constant despite the presence of hemodynamic changes.

CONCLUSIONS

Here, we show that LSI and SFDI are capable of monitoring changes in hemodynamic and scattering properties in burn wounds over a 28 days period. These results highlight the potential insights that can be gained by using non-invasive imaging technologies to study wound healing. Further development of these technologies could be revolutionary for wound monitoring and studying the efficacy of different treatments. Lasers Surg. Med. 49:293-304, 2017. © 2017 Wiley Periodicals, Inc.

Fluorescence lifetime spectroscopy of tissue autofluorescence in normal and diseased colon measured ex vivo using a fiber-optic probe

We present an ex vivo study of temporally and spectrally resolved autofluorescence in a total of 47 endoscopic excision biopsy/resection specimens from colon, using pulsed excitation laser sources operating at wavelengths of 375 nm and 435 nm. A paired analysis of normal and neoplastic (adenomatous polyp) tissue specimens obtained from the same patient yielded a significant difference in the mean spectrally averaged autofluorescence lifetime -570 ± 740 ps (p = 0.021, n = 12). We also investigated the fluorescence signature of non-neoplastic polyps (n = 6) and inflammatory bowel disease (n = 4) compared to normal tissue in a small number of specimens.

Multi-site optical excitation using ChR2 and micro-LED array

Studying neuronal processes such as synaptic summation, dendritic physiology and neural network dynamics requires complex spatiotemporal control over neuronal activities. The recent development of neural photosensitization tools, such as channelrhodopsin-2 (ChR2), offers new opportunities for non-invasive, flexible and cell-specific neuronal stimulation. Previously, complex spatiotemporal control of photosensitized neurons has been limited by the lack of appropriate optical devices which can provide 2D stimulation with sufficient irradiance. Here we present a simple and powerful solution that is based on an array of high-power micro light-emitting diodes (micro-LEDs) that can generate arbitrary optical excitation patterns on a neuronal sample with micrometre and millisecond resolution. We first describe the design and fabrication of the system and characterize its capabilities. We then demonstrate its capacity to elicit precise electrophysiological responses in cultured and slice neurons expressing ChR2.

Multi-site optical excitation using ChR2 and micro-LED array

Studying neuronal processes such as synaptic summation, dendritic physiology and neural network dynamics requires complex spatiotemporal control over neuronal activities. The recent development of neural photosensitization tools, such as channelrhodopsin-2 (ChR2), offers new opportunities for non-invasive, flexible and cell-specific neuronal stimulation. Previously, complex spatiotemporal control of photosensitized neurons has been limited by the lack of appropriate optical devices which can provide 2D stimulation with sufficient irradiance. Here we present a simple and powerful solution that is based on an array of high-power micro light-emitting diodes (micro-LEDs) that can generate arbitrary optical excitation patterns on a neuronal sample with micrometre and millisecond resolution. We first describe the design and fabrication of the system and characterize its capabilities. We then demonstrate its capacity to elicit precise electrophysiological responses in cultured and slice neurons expressing ChR2.

A fluorescence lifetime imaging scanning confocal endomicroscope

We describe a fluorescence lifetime imaging endomicroscope employing a fibre bundle probe and time correlated single photon counting. Preliminary images of stained pollen grains, eGFP-labelled cells exhibiting Förster resonant energy transfer and tissue autofluorescence are presented.

A compact, multidimensional spectrofluorometer exploiting supercontinuum generation

We report a novel, compact and automated multidimensional spectrofluorometer that exploits a fibre-laser-pumped ultrafast supercontinuum source to provide resolution with respect to intensity, excitation and emission wavelength, decay time and polarisation. This instrument has been applied to study the photophysics of the phase-sensitive membrane probe di-4-ANEPPDHQ and to characterise protein-protein interactions via Förster resonance energy transfer. It can be applied to in situ measurements via a fibre-optic probe in medical and other contexts and is demonstrated here to provide a comprehensive characterisation of tissue autofluorescence.

Improved sectioning in a slit scanning confocal microscope

We describe a simple implementation of a slit scanning confocal microscope to obtain an axial resolution better than that of a point-scanning confocal microscope. Under slit illumination, images of a fluorescent object are captured using an array detector instead of a line detector so that out-of-focus light is recorded and then subtracted from the adjacent images. Axial resolution after background subtraction is 2.2 times better than the slit confocal resolution, and out-of-focus image suppression is calculated to attenuate with defocus faster by 1 order of magnitude than in the point confocal case.

High speed optically sectioned fluorescence lifetime imaging permits study of live cell signaling events

We present a time domain optically sectioned fluorescence lifetime imaging (FLIM) microscope developed for high-speed live cell imaging. This single photon excited system combines wide field parallel pixel detection with confocal sectioning utilizing spinning Nipkow disc microscopy. It can acquire fluorescence lifetime images of live cells at up to 10 frames per second (fps), permitting high-speed FLIM of cell dynamics and protein interactions with potential for high throughput cell imaging and screening applications. We demonstrate the application of this FLIM microscope to real-time monitoring of changes in lipid order in cell membranes following cholesterol depletion using cyclodextrin and to the activation of the small GTP-ase Ras in live cells using FRET.

Optical sectioning microscopes with no moving parts using a micro-stripe array light emitting diode

We describe an optical sectioning microscopy system with no moving parts based on a micro-structured stripe-array light emitting diode (LED). By projecting arbitrary line or grid patterns onto the object, we are able to implement a variety of optical sectioning microscopy techniques such as grid-projection structured illumination and line scanning confocal microscopy, switching from one imaging technique to another without modifying the microscope setup. The micro-structured LED and driver are detailed and depth discrimination capabilities are measured and calculated.

Near- to mid-infrared picosecond optical parametric oscillator based on periodically poled RbTiOAsO(4)

We describe a Ti:sapphire-pumped picosecond optical parametric oscillator based on periodically poled RbTiOAsO(4) that is broadly tunable in the near to mid infrared. A 4.5-mm single-grating crystal at room temperature in combination with pump wavelength tuning provided access to a continuous-tuning range from 3.35 to 5microm , and a pump power threshold of 90 mW was measured. Average mid-infrared output powers in excess of 100 mW and total output powers of 400 mW in ~1-ps pulses were obtained at 33% extraction efficiency.

Ultralow-pump-threshold, femtosecond Cr(3+):LiSrAlF(6)laser pumped by a single narrow-stripe AlGaInP laser diode

We report what we believe to be the first demonstration of a Kerr-lens mode-locked Cr(3+):LiSrAlF(6)laser that is pumped by a single narrow-stripe AlGaInP laser diode with a diffraction-limited output beam. A novel low-loss three-mirror laser cavity design is described in which strong, localized Kerr lensing was exploited such that 75-fs-duration pulses were obtained for only 36mW of incident pump power. This pump power was maintained for 18h by just three AA batteries as the electrical power source. We have shown that mode locking can be sustained for pump powers as low as 22mW.

Quantum-well intermixing for the control of second-order nonlinear effects in AlGaAs multiple-quantum-well waveguides

We present experimental evidence to demonstrate the feasibility of a promising new quasi-phase-matching technique in AlGaAs multiple-quantum-well waveguides. Non-phase-matched second-harmonic-generation measurements indicate that, for sub-half-bandgap excitation near 1.5 microm , quantum-well intermixing by impurity-free vacancy disordering results in a reduction of the nonlinear susceptibility chi((2))(zxy) (~340 pm/V) by 17%. Relatively low intermixed waveguide losses, and the high spatial resolution of the impurity-free vacancy disordering process, suggest that periodic intermixing along the direction of propagation should lead to useful frequency-conversion efficiencies.

Bright solitary pulses in AlGaAs waveguides at half the band gap

We show that bright temporal solitonlike pulses can propagate in AlGaAs waveguides excited in the half-bandgap spectral regime. The use of an antiresonant reflecting optical waveguide permits the dispersion of the waveguide to be controlled so that a mode with anomalous dispersion can propagate.

Detection of bacteraemia by the continuously monitoring BacT/Alert system

AIMS

To analyse a continuously monitoring blood culture system with respect to the time to detection of various groups of organisms, their clinical importance, and the relative efficacy of the aerobic and anaerobic bottles.

METHODS

Four thousand blood cultures were monitored and the information relating to the positive cultures was noted and analysed.

RESULTS

Four hundred and seventy seven blood cultures were detected as positive, 81% (387/477) of which were detected within 48 hours. The most pathogenic organisms were detected in the shortest period, less pathogenic later and those generally regarded as contaminants last. Clinically important isolates were also detected earlier. Many positive blood cultures were detected in only one bottle of the set, even those regarded as clinically important.

CONCLUSIONS

The management of continuously monitoring blood culture systems could be improved by considering time to detection trends. Clinicians should be aware of the relatively rapid detection of clinically important, positive blood cultures in relation to patient treatment.

Self-mode-locked NaCl:OH(-) color-center laser

We have demonstrated self-mode locking of an NaCl:OH,(-) color-center laser by exploiting the Kerr effect in a rod of high-nonlinearity glass placed within the laser cavity. The mode-locking process was initiated by a regenerative acousto-optic modulation, and sub-100-fs pulses were produced at wavelengths of ~1575 nm.

Spotlight article: thrombolysis in unstable angina: randomized double-blind trial of t-PA and placebo. Circulation 1992;85: 150-7. (Freeman MR, Langer A, Wilson RF, Morgan CD, Armstrong PW.)

This is a well-written and executed study that indicates that infusion of t-PA in patients with unstable angina does not decrease in-hospital cardiac events and, in fact, may worsen myocardial perfusion. The small sample size requires further study replication.

Acute congestive heart failure: pharmacologic intervention

Acute CHF is a highly unstable condition that requires immediate pharmacologic intervention. Mechanisms that are normally used to control the release of neurohormones are impaired in CHF. Therapeutic interventions produce hemodynamic and clinical benefits in part by restoring a balance of the neurohormonal system. This balance is achieved by interfering with actions of vasoconstriction and potentiating the effects of vasodilation and contractility. To maintain an optimal healing atmosphere, the patient's individualized needs for social support and spiritual beliefs must be considered. How the patient perceives his or her illness may also impact patient hemodynamics and outcomes.

Altered beta adrenergic receptor function in subjects with symptomatic mitral valve prolapse

Individuals with mitral valve prolapse (MVP) frequently show symptoms of a hyperadrenergic state. beta adrenergic receptor characteristics were compared in the lymphocytes of subjects with symptomatic MVP and control subjects during rest and exercise. At rest, the proportion of receptors binding agonist with high affinity, as determined from isoproterenol competition for (-)[125I]-iodopindolol binding sites, was greater in MVP subjects than in controls. With exercise, the proportion of high-affinity receptors in MVP subjects decreased to control levels. Isoproterenol stimulation of lymphocyte 3',5'-cyclic adenosine monophosphate (cyclic AMP) also was greater in MVP subjects than in controls at rest, but not during exercise. Plasma catecholamine concentrations in MVP subjects were normal during both rest and exercise. Unlike exercise, isoproterenol infusion elicited clinical manifestations of increased adrenergic responsiveness in MVP subjects. The beta receptor in exercised MVP subjects exhibited unusually high affinity agonist binding (i.e. a lower dissociation constant KH than in either the same subjects at rest or exercised controls) and also abnormal coupling to the stimulatory guanine nucleotide-binding regulatory protein (GS) of adenylate cyclase, as reflected by the inability of guanine nucleotide to convert the receptor to a low-affinity state. These findings suggest that functional alteration of the beta adrenergic receptor, in the absence of abnormal plasma catecholamine levels, might contribute to the hyperadrenergic state of MVP subjects at rest. However, desensitization of high affinity beta receptors or altered receptor-GS coupling might preserve normal adrenergic responsiveness during exercise.

Captopril in the treatment of chronic CHF

Captopril is an effective oral drug that helps break the cycle of CHF. Improvements in symptomatology, functional capacity and exercise tolerance are seen with long-term therapy. Captopril is an important addition to the present drug therapy of CHF.

Captopril in the treatment of chronic CHF

Captopril is an effective oral drug that helps break the cycle of CHF. Improvements in symptomatology, functional capacity and exercise tolerance are seen with long-term therapy. Captopril is an important addition to the present drug therapy of CHF.

Absolute bioavailability and dose proportionality of betaxolol in normal healthy subjects

The absolute bioavailability and dose proportionality of betaxolol [(+/-)-1-(p-[2-cyclopropylmethoxy)ethyl]phenoxy]-3- (isopropylamino)-2-propanol hydrochloride], a cardioselective beta-adrenergic antagonist effective in the treatment of angina and hypertension, was studied in 12 healthy male subjects using a four-way crossover Latin Square design. Each subject received a 10-mg iv dose administered by constant-rate infusion over a period of 30 min and three oral doses (10, 20, and 40 mg). Blood and urine were collected over a 48-h period and analyzed for betaxolol using gas-liquid chromatography with electron capture detection. Maximum concentrations occurred 3-4 h after the dose. The maximum mean (+/- SD) blood concentrations normalized to the 10-mg oral dose were 21.6 +/- 3.7, 21.1 +/- 3.7, and 22.5 +/- 4.0 micrograms/L following the 10-, 20-, and 40-mg doses, respectively. A significant lag time of 10-80 min was observed after oral doses but was not related to dose size. The terminal slope (ts), absolute bioavailability (F), and renal clearance (CLr) were likewise not affected to an important degree by dose (ts: 0.043 +/- 0.006, 0.044 +/- 0.005, 0.046 +/- 0.006 h-1; F: 0.88 +/- 0.08, 0.82 +/- 0.06, 0.84 +/- 0.07; CLr: 0.68 +/- 0.22, 0.69 +/- 0.19, 0.65 +/- 0.22 mL/min kg). Unlike many beta-adrenergic antagonists, betaxolol has a long half-life (13-20 h) and high and consistent bioavailability (70-90%), and its disposition is independent of the size of the administered dose.

Hemodynamic effects of a constant intravenous infusion of piroximone in patients with severe congestive heart failure

The hemodynamic effects and serum levels of piroximone (MDL 19,205), a new inotropic agent with vasodilating properties, were measured in 10 patients with chronic severe congestive failure during a constant 48-h infusion. The initial five patients (group A) received piroximone at 10 micrograms/kg/min; however, because a sustained increase in heart rate greater than or equal to 25% from baseline developed in two patients and an episode of paroxysmal supraventricular tachycardia developed in another, the last 5 patients (group B) received an 8 micrograms/kg/min infusion. Because the steady-state hemodynamic alterations of group A prior to the onset of tachyarrhythmias were similar to those of group B, these results were combined. A significant increase in cardiac output from 3.65 +/- 0.31 (SE) to 5.20 +/- 0.49 L/min and decrease in pulmonary capillary wedge pressure (27 +/- 2 to 20 +/- 2 mm Hg), right atrial pressure (18 +/- 2 to 11 +/- 2 mm Hg), and systemic vascular resistance (1811 +/- 172 to 1293 +/- 80 dynes.s.cm-5) occurred (all p less than 0.05) without a significant change in mean arterial pressure. The peak plasma piroximone level was lower in the eight patients who did not develop a sustained increase in heart rate greater than or equal to 25% above baseline (2.1 +/- 0.5 micrograms/ml; range 1.6-2.9 micrograms/ml) than in the two who did (5.0 and 5.8 micrograms/ml). The latter two patients had the highest serum creatinine levels in the study population.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic effects of prolonged intravenous therapy with enoximone in patients with severe congestive heart failure

The hemodynamic differences between bolus administration and constant intravenous infusion over a 48-h period with enoximone, a new positive inotropic/vasodilator agent, were evaluated. Twenty-four patients were studied, 15 patients in the bolus group (Group A) and nine patients in the constant infusion group (Group B). The overall hemodynamic results were similar in both groups. Cardiac output increased in Group A from 3.1 +/- 0.71 to 5.5 +/- 1.3 L/min and in Group B from 3.6 +/- 1.0 to 5.9 +/- 1.2 L/min. Significant decreases occurred in pulmonary capillary wedge pressure (30 +/- 7 to 20 +/- 8 mm Hg and 37 +/- 5 to 21 +/- 11 mm Hg) and systemic vascular resistance (2184 +/- 456 to 1300 +/- 305 dyn.s.cm-5 and 1752 +/- 415 to 1035 +/- 130 dyn.s.cm-5). Group A required repeat drug boluses every 3-5 h to maintain these hemodynamic effects. The terminal blood half-life of enoximone derived following the continuous infusion in Group B was 10.6 +/- 7.0 h. In conclusion, intravenous enoximone produces acute salutary hemodynamic effects in patients with severe congestive heart failure that can be sustained for at least 48 h by intermittent boluses or a continuous infusion.

Prognostic value of exercise-induced ventricular ectopic activity for mortality after acute myocardial infarction

To evaluate the importance of ventricular ectopic activity on the predischarge treadmill exercise test for predicting mortality in patients after acute myocardial infarction (AMI), 163 patients with uncomplicated AMI were studied using symptom limited low-level treadmill exercise testing and 24-hour ambulatory electrocardiographic monitoring before hospital discharge. All patients were followed for at least 2 years or until recurrent AMI, coronary artery bypass grafting or death. Seventeen patients (10%) died during the follow-up period, 15 patients (9%) had recurrent AMI and 45 patients (28%) underwent bypass surgery. Ventricular ectopic activity was the only single treadmill abnormality that predicted subsequent cardiac death; angina pectoris, electrocardiographic ST-segment depression and a hypotensive blood pressure response did not. The mortality rate in the 20 patients with exercise-induced ventricular ectopic activity was 25%, compared with 8% in those without (p less than 0.004). Furthermore, in this patient population, exercise-induced ventricular ectopic activity was a much better predictor of cardiac death than that detected by ambulatory monitoring. Thus, ventricular ectopic activity on the predischarge treadmill exercise test is an important risk factor for death after AMI.

Prognostic value of electrocardiographic exercise testing and noninvasive assessment of left ventricular ejection fraction soon after acute myocardial infarction

To determine the relative value of clinical findings, results of low-level treadmill electrocardiographic (ECG) exercise testing and left ventricular (LV) ejection fraction (EF) for predicting cardiac events in the year after an acute myocardial infarction (AMI), 72 patients who had had an uncomplicated AMI were studied with either radionuclide angiography or 2-dimensional echocardiography to assess LVEF and a low-level treadmill exercise test before hospital discharge. All patients were followed for 1 year. Nineteen patients (26%) had at least 1 cardiac event: coronary artery bypass grafting (11 patients), recurrent AMI (6 patients) or cardiac death (6 patients). Multiple logistic regression analysis revealed that total cardiac events were predicted by exercise ECG ST-segment depression or angina, prior AMI, ventricular ectopic activity during exercise and digoxin therapy (cumulative r = 0.58, p less than 0.001). Coronary artery bypass grafting was predicted by exercise ECG ST-segment depression or angina (r = 0.29, p = 0.01). Recurrent AMI was predicted by exercise ECG ST-segment depression or angina, prior AMI and ventricular ectopic activity during exercise (cumulative r = 0.49, p less than 0.001). Cardiac death was predicted by an LVEF of 40% or less (r = 0.38, p = 0.01). The presence of both an LVEF of 40% or less and ECG ST-segment depression on treadmill exercise testing defined a subgroup of patients with a high incidence of early cardiac death (33%).(ABSTRACT TRUNCATED AT 250 WORDS)

Determinants of systemic availability of oral hydralazine in heart failure

Short-term therapy with oral hydralazine can favorably affect abnormal hemodynamics in patients with congestive heart failure, but the range of dosage is large. To investigate whether this variability in effective dose is a result of altered systemic availability, we studied 10 patients with congestive heart failure. Bioavailability (F) was calculated as the ratio of the blood AUC for a single 75 mg oral dose to the AUC of a 0.3 mg/kg iv dose. Acetylation capability was determined by sulfamethazine metabolic clearance (CLsmz). The F value in six subjects with CLsmz greater than 100 ml/min was 9.9% +/- 6.0% (means +/- SD) and was lower than the value of 26.2% +/- 13.0% (P less than 0.05) in the four patients with CLsmz less than 60 ml/min. Thus acetylation ability is an important consideration during low-dose hydralazine therapy (less than or equal to 225 mg/day). The clearance of the single intravenous dose of hydralazine averaged 29.5 +/- 8.0 ml/min/kg, which is not different than that reported in populations without heart failure. After oral dosage titration to induce maximum hemodynamic changes, the dose-normalized hydralazine AUC rose from 53.5 +/- 50.5 to 247.2 +/- 213.4 min/L X 10(3). Thus large oral doses of hydralazine result in disproportionate increases in systemic availability compatible with saturation of the first-pass effect or systemic clearance. In the doses required for maximum hemodynamic effects in our patients (225 to 3000 mg/day), this saturation phenomenon was a prominent determinant of systemic availability.

N-acetylprocainamide kinetics during intravenous infusions and subsequent oral doses in patients with coronary artery disease and ventricular arrhythmias

The kinetics of N-acetylprocainamide (NAPA) were studied in 5 patients (all men, mean age = 62) with coronary artery disease and ventricular arrhythmias during loading infusions of 0.22-0.45 mg/kg/min, prolonged (19-48 hrs) intravenous infusions 2.5-5.2 mg/min, and in 4 of the patients, during subsequent oral doses 1.5-3 g every 8 hrs. Serum, concentrations of NAPA were determined by high-performance liquid chromatography. The individual concentration-time profiles could, with one exception, be described by a two-compartment, open, kinetic model with apparent first-order elimination. The kinetic variables were: initial distribution volume (Vc) 0.20 +/- 0.11 l/kg (mean +/- SD); steady-state distribution volume (Vss) 1.58 +/- 0.55 l/kg; distributional clearance (Cle) 133 +/- 23 ml/(kg X hr); absorption rate constant (Ka) 0.354 +/- 0.173 hr-1; and fraction of dose reaching systemic circulation (F) 1.00 +/- 0.14. The data for one patient who had received increasing oral dosages of 1.5, 2, 2.5 and 3 g every 8 hours resulted in systematic underprediction of observed concentrations at the two highest oral dosing rates. This suggests the possibility of some degree of nonlinearity or time-dependent change in the kinetic behavior of NAPA. Only low concentrations of procainamide, less than 1 mg/L, were found at the end of the infusions.

Long-term efficacy of high-dose diltiazem for chronic stable angina pectoris: 16-month serial studies with placebo controls

In order to assess the long-term efficacy of diltiazem for the treatment of angina pectoris, eight patients with chronic stable exertional angina who were previously entered into a 4-month randomized, double-blind placebo controlled study, were studied for an additional 12-months. The patients continued to take diltiazem, 360 mg/day, and underwent treadmill exercise testing after 10 and 16 months of therapy. A single-blind placebo week was introduced after 16 months and a treadmill test was performed at the end of this week. Diltiazem therapy continued to augment exercise duration until 0.1 mV of ECG ST depression at 10 and 16 months as compared to the final placebo period: 573 +/- 133 (SD) seconds at 10 months; 565 +/- 148 seconds at 16 months; vs 431 +/- 151 seconds at final placebo (both p less than 0.001). Also, the time to angina pectoris was prolonged on diltiazem by 181 seconds at 16 months (p less than 0.01) and the total duration of exercise was increased by 101 seconds (p less than 0.001) as compared to placebo. In addition, angina frequency decreased from 17 +/- 11 attacks/week on placebo to 0.6 +/- 0.6 attacks/week during diltiazem therapy at 16 months. Two of the eight patients noted mild pedal edema, but no other adverse effects were experienced. Thus diltiazem, 360 mg/day, can be an effective single agent for the long-term treatment of chronic stable angina pectoris.

Comparative predictive value of ST-segment depression or angina during early and repeat postinfarction exercise tests

To determine the relative value of electrocardiographic (ECG) ST-segment depression alone compared to angina alone for predicting multivessel coronary artery disease during early and repeat postinfarction exercise tests, we evaluated 93 postmyocardial infarction patients with modified treadmill exercise tests prior to hospital discharge (mean 14 +/- 2 days), and 36 of these 93 patients with repeat exercise tests at six weeks following infarction. It was concluded that angina alone or angina irrespective of the presence of ST-segment depression are better predictors of multivessel coronary artery disease than ECG ST-segment depression alone, and the persistence of ischemic abnormalities during repeat treadmill exercise tests following infarction is useful for confirming the presence of multivessel coronary artery disease.

Miscoding of hospital discharges as acute myocardial infarction: implications for surveillance programs aimed at elucidating trends in coronary artery disease

The current decline in coronary artery disease mortality (CAD) may be a result of a declining population risk or of a declining case-fatality rate. Information on incidence trends for myocardial infarction (MI) could be used to distinguish between these 2 possibilities. Hospital discharge codes for MI (ICDCM-410) could be used as a convenient proxy for incidence trends, provided that coding of hospital discharges is sufficiently accurate. To evaluate the accuracy of medical records coding of patients signed out with an acute MI code (ICDCM-410), we compared them to an independent cardiology surveillance study of all patients with acute MI admitted to a large county teaching hospital. Over a 12-month period, 110 patients were coded as ICDCM-410 by medical records, but only 67 of these were detected by cardiology surveillance. The charts of the 43 patients not detected by surveillance were reviewed. In none of the 43 was evidence of acute MI found. In 28 of the 43, the discharge summaries listed rule out MI or status post-MI readmitted for further diagnostic workup, but were miscoded as ICDCM-410. Twelve of the 43 patients had cardiac arrests but were coded as ICDCM-410, even though there was no evidence of MI. Therefore, erroneous coding of patients as acute MI (ICDCM-410) may conceal a true downward trend in the incidence of CAD.

Positive inotropic and vasodilator effects of MDL 17,043 in patients with reduced left ventricular performance

To assess the potential positive inotropic properties of the drug MDL 17,043, 10 patients were studied who had impaired left ventricular (LV) performance and who were undergoing diagnostic cardiac catheterization (LV ejection fraction 16 to 46%). MDL 17,043 was given in repeated i.v. doses of 0.5 mg/kg every 15 minutes until a maximal effect was observed or a total dose of 3 mg/kg was attained. Cardiac output increased from 3.5 +/- 1.0 to 5.3 +/- 0.7 liters/min (p less than 0.005); pulmonary artery wedge pressure decreased from 22 +/- 4 to 9 +/- 5 mm Hg (p less than 0.001); and total systemic resistance decreased from 2,335 +/- 1,147 to 1,310 +/- 365 dyne cm-5 (p less than 0.025). Also, maximal LV dP/dt increased from 1,011 +/- 301 to 1,243 +/- 330 mm Hg/s (p less than 0.001). No significant changes in heart rate, systemic blood pressure, routine blood chemistries, complete blood counts or platelet counts were observed. Thus, MDL 17,043 has hemodynamic effects consistent with positive inotropic and vasodilating properties in patients with reduced LV performance. Because this agent is effective orally, further evaluation in patients with overt congestive heart failure is warranted.