Dear Colleagues, The National Library of Medicine (NLM) at the National Institutes of Health (NIH) recently met to review the Journal of Biomedical Optics. NLM uses an advisory committee composed of experts in the field of biomedicine and biomedical research to consider journals for indexing.

The infrared and Raman spectroscopy of bone and teeth tissues are reviewed. Characteristic spectra are obtained for both the mineral and protein components of these tissues. Vibrational spectroscopy is used to study the mineralization process, to define the chemical structure changes accompanying bone diseases, and to characterize interactions between prosthetic implants and tissues. Microspectroscopy allows acquisition of spatially resolved spectra, with micron scale resolution. Recently developed imaging modalities allow tissue imaging with chemical composition contrast.

We have measured the local blood flow (BF) and oxygen consumption (OC) in the human calf muscle using near-infrared spectroscopy during venous occlusion. Venous occlusion was achieved by inflating a pneumatic cuff around the thigh of the subject. We have investigated the influence of the inflation time and cuff pressure on the recovered values of BF and OC. We have found that if the cuff pressure is increased from a threshold pressure (~30 mmHg) to a critical pressure (~45 mmHg) in less than about 6 s, one measures the same values of BF and OC independent of the total inflation time and final cuff pressure. We also report nine-pixel spatial maps of BF and OC to show that this technique can lead to spatially resolved measurements of blood flow and oxygen consumption in tissues.

The possibility of optical oximetry of the blood in the fetal brain measured across the maternal abdomen just prior to birth is under investigation. Such measurements could detect fetal distress prior to birth and aid in the clinical decision regarding Cesarean section. This paper uses a perturbation method to model photon transport through an 8-cm-diam fetal brain located at a constant 2.5 cm below a curved maternal abdominal surface with an air/tissue boundary. In the simulation, a near-infrared light source delivers light to the abdomen and a detector is positioned up to 10 cm from the source along the arc of the abdominal surface. The light transport [W/cm2 fluence rate per W incident power] collected at the 10 cm position is Tm =2.2x10-6 cm?2 if the fetal brain has the same optical properties as the mother and Tf=1.0x10-6 cm?2 for an optically perturbing fetal brain with typical brain optical properties. The perturbation P=(Tf -Tm)/Tm is ?53% due to the fetal brain. The model illustrates the challenge and feasibility of transabdominal oximetry of the fetal brain.

Using full-spectrum near infrared spectroscopy (fsNIRS), we measured changes in oxy- and deoxyhemoglobin (HbO2 and Hb), total hemoglobin (T-Hb) concentration, and hemoglobin oxygen saturation (SbO2) in the brain tissue of seven neonates immediately following birth. It was found that HbO2 rose rapidly within 2–3 min after birth. During the same time, there was a transient increase in T-Hb concentration, after which it decreased together with Hb. SbO2 increased rapidly after birth, from 18% at 1.5 min to about 55% at 5–6 min, followed by a gradual increase of about 10%. Oxygenation in the brain occurred much sooner in three subjects given oxygen for a short time immediately after birth than in those who did not receive oxygen. This preliminary study indicated that dynamic changes occur in cerebral circulation and oxygenation as part of the physiological changes taking place soon after birth.

Near infrared spectroscopic topography (NIRS) is widely recognized as a noninvasive method to measure the regional cerebral blood volume (rCBV) dynamics coupled with neuronal activities. We analyzed the rCBV change in the early phase of epileptic seizures in 12 consecutive patients with medically intractable epilepsy. Seizure was induced by bemegride injection. We used eight-channel NIRS in nine cases and 24 channel in three cases. In all of the cases, rCBV increased rapidly after the seizure onset on the focus side. The increased rCBV was observed for about 30–60 s. The NIRS method can be applied to monitor the rCBV change continuously during seizures. Therefore, this method may be combined with ictal SPECT as one of the most reliable noninvasive methods of focus diagnosis.

Numerical modeling was used for the theoretical analysis of the propagation of optical radiation in the tissues of the human head, generated by a single source placed on the surface of the scalp. Of special interest and importance is the propagation of radiation within the layer of cerebrospinal fluid contained in the subarachnoid space (SAS), which is the only low absorption/high transmittance medium whose width can vary rapidly. Qualitative and quantitative assessment of changes in propagation of radiation within the SAS could become a source of information on changes in the geometry of this anatomical compartment playing a crucial role in cranio-spinal physiology and pathology. Essential for the idea of the possible noninvasive assessment of changes in width of the SAS by an optical method is the dependence of intensity of radiation reaching a photodetector located at a certain distance from the source on changes in the width of this fluid layer, which acts like a biological optical waveguide. Monte Carlo modeling and numerical analysis confirmed the feasibility of assessing changes in the width of the subarachnoid space optically. Presented here are details of the Monte Carlo simulation of light propagation in the tissues of human head and the results of such simulation as a function of the width of the subarachnoid space, calculated for different distances between the source and detector and for a few selected values of bone thickness. Results of numerical modeling were then compared with those of experiments on a mechanical-optical model.

Spectral imaging permits two-dimensional mapping of the backscattering properties of biological systems. Such mapping requires broadband illumination of the entire area of interest. However, imaging of turbid biological media under these conditions often involves mean photon path lengths that exceed the pixel size. Using a numerical Monte Carlo model, we have studied the effects of photon scattering in a hemoglobin-bearing model system. We find that photon migration and the resulting wavelength-dependent optical coupling between pixels can complicate the analysis of imaging spectroscopy data. In fact, the wavelength dependence of photon trajectories also alters the distribution of photon exit angles at the tissue surface. We therefore find that the finite optical field of view of an imaging spectrometer can affect the measured spectra in the absence of chromatic aberrations.

The optical performance of the eyes of nine vertebrate species was evaluated using optical system design techniques and schematic eye models. Essential features of eyes, including the modulation transfer function (MTF) and the MTF cutoff frequency are related to the numerical aperture of the eyes. Superior resolution for in vivo imaging of photoreceptors may be achieved by dilating the iris pupil of an eye, minimizing coherence, and using short wavelength illumination. The difference of lateral and axial resolution between a small and a large eye for imaging photoreceptors in vivo.

Single 130 fs laser pulses in the near-IR (800 nm) were used to create ophthalmoscopically viewed minimum visible lesions (MVLs) within the macular and paramacular regions in rhesus monkey eyes. MVL thresholds at 1 and 24 h are reported as the 50% probability for damage (ED50) together with their fiducial limits at the 95% confidence level. These measured thresholds are compared with previously reported thresholds for near-IR and visible wavelengths for both macular and paramacular areas. Threshold doses were lower at the 24 h reading than at the 1 h reading for both retinal regions and the ED50s for the macula were slightly lower than for the paramacula. We measured the 24 h MVL ED50 thresholds to be 0.35 and 0.55 µJ for the macular and paramacular areas, respectively. The combined data for both areas yielded a threshold of 0.45 µJ.

Invasive bile determination is very useful in the diagnosis of many gastric pathologies. At the moment, this measurement is performed with Bilitec 2000, an optical fiber sensor, that is based on absorption by bilirubin. Nevertheless, erroneous evaluations are possible, due to the different configurations which the bilirubin molecule can adopt. The optical behavior of human samples of pure bile and bile+gastric juice has been examined using an optical fiber spectrophotometer and two suitably modified Bilitec 2000 units. A protocol has been established for the treatment of biological fluids, in order to make it possible to study the behavior of their optical properties as a function of pH and concentration without causing any alteration in the samples. The analysis of pH dependence evidenced the presence of different calibration curves at different pH values: the selfaggregation of the bilirubin molecules observed in pure bile samples was almost totally absent in the gastric samples. Measurements carried out on Bilitec 2000 showed that the most appropriate wavelength for bilirubin detection in the stomach should be 470 nm.

The properties of polarized light emerging from turbid media in the exact backscattering direction are studied by modulating the incident light polarization state and isolating the synchronous signal with lock-in amplifier detection. The results are reported for polystyrene microsphere suspensions in distilled water, with and without glucose, and for both ex vivo and in vivo biological tissues. A new theoretical formulation based on Mueller calculus is developed to describe the observed behavior of the backscattered light in terms of two sample parameters: optical rotation and depolarization. This technique proved successful in modeling both phantom and tissue samples. Results showed the presence of a significant surviving polarization fraction in the backscattering direction even in extremely dense optical phantom media, an important finding that has not been observed at other detection angles. Substantial polarized light preservation in biological tissue samples is also demonstrated for this detection geometry. This illustrates the potential of using polarized light to investigate turbid biological materials in vivo in retroreflection geometry.

Comparative studies of oxygen consumption, changes of photosensitizer fluorescence, and photodestruction of erythrocytes, and photodestruction of oxygen transport protein hemoglobin were performed during photodynamic reaction in whole and hemolyzed blood with phthalocyanines, chlorines, porphyrins, and methylene blue photosensitizers in vitro and in selected cases in vivo. The present work deals with the investigation of blood oxygen saturation SO2 and photosensitizer fluorescence during and immediately after light irradiation in the photodynamic therapy process. It has been observed that SO2 behavior strongly correlates with the type of photosensitizer. The decrease of photosensitizer fluorescence (photobleaching) during light irradiation can be followed by the recovery of the photosensitizer fluorescence immediately after interruption of the irradiation within 6–8 min. The levels of photodestruction of erythrocytes in whole blood and photodestruction of hemoglobin in hemolyzed blood in combination with the above photosensitizers reveal the influence of photodynamic reactions upon the ability of blood to transport oxygen. Maximal photohemolysis activity has been found with chlorine p6 photosensitizers.

We describe a novel method and instrumental setup for regenerating antibodies immobilized on a fiberoptic probe of an immunosensor using ultrasonic irradiation with broadband imaging transducers. The instrumental setup and irradiation conditions for antibody regeneration using ultrasound are described. The results of the measurements with antibody against breast cancer antigen illustrate the effectiveness and potential of the regenerable immunosensor. A 65% removal of the antigens bound to the Mab immobilized on the fiber surface is attained after ultrasound regeneration.