This PDF file contains the editorial “Guest Editorial: Special Section on Near Infrared Spectroscopy and Imaging of Tissues” for JBO Vol. 1 Issue 04

Adult near infrared spectroscopy (NIRS) is a potential method for noninvasively assessing changes in cerebral oxygenation. Unlike neonatal NIRS, access of light to the adult brain requires penetration through thick extracranial tissues, and hence detection of changes in cerebral chromophore concentration can only be achieved by using NIRS in the reflectance mode. This adds variables that are difficult to control. They include the effects of a different intraoptode distance, intersubject anatomical variation, and the influence of a pathological extra- to intracranial collateral blood supply. Although studies showing movements of oxyhemoglobin concentration following specific cerebral stimuli have been published, the separation of changes occurring in the extracranial and intracranial compartments remains a challenge. Experience with NIRS in the three adult clinical scenarios of carotid endarterectomy, head injury, and carbon dioxide stress testing is presented. The influence of extracranial contamination is demonstrated, as are the methods adopted to help control for extracranial blood flow changes. Provisional experience with spatially resolved spectroscopy (SRS) technology is also discussed.

Despite dramatic advances in the survival rate amongst infants undergoing cardiac surgery for congenital heart disease, the incidence of brain injury suffered by survivors remains unacceptably high. This is largely due to our limited understanding of the complex changes in cerebral oxygen utilization and supply occurring during the intraoperative period as a result of hypothermia, neuroactive drugs, and profound circulatory changes. Current techniques for monitoring the adequacy of cerebral oxygen supply and utilization during hypothermic cardiac surgery are inadequate to address this complex problem and consequently to identify the infant at risk for such brain injury. Furthermore, this inability to detect imminent hypoxic-ischemic brain injury is likely to become all the more conspicuous as new neuroprotective strategies, capable of salvaging ‘‘insulted’’ neuronal tissue from cell death, enter the clinical arena. Near infrared spectroscopy is a relatively new, noninvasive, and portable technique capable of interrogating the oxygenation and hemodynamics of tissue in vivo. These characteristics of the technique have generated enormous interest amongst clinicians in the ability of near infrared spectroscopy to elucidate the mechanisms of intraoperative brain injury and ultimately to identify infants at risk for such injury. This paper reviews the experience with this technique to date during infant cardiac surgery.

Our understanding of human brain function can clearly benefit from neurophysiological techniques capable of providing dynamic maps of activity. A series of studies is reviewed indicating that noninvasive nearinfrared optical imaging methods can provide a unique combination of spatial and temporal resolution that could be used to derive dynamic maps of human brain activity. The noninvasive NIR optical data reviewed are based on the frequency-domain time-resolved measurement of photon migration parameters (intensity and delay) through brain tissue. These measurements are taken through the intact surface of the head. With these methods, two distinct components of the optical response can be identified: the ‘‘slow optical signal’’ (2–10 s latency), presumably due to hemodynamic and metabolic changes, and the ‘‘fast optical signal’’ (or event-related optical response) occurring as early as 50 to 100 ms from stimulation, and probably due to neuronal activation.

We examined local changes of cerebral oxygenation in response to visual stimuli by means of near infrared spectroscopy. A sharply outlined colored moving stimulus which is expected to evoke a broad activation of the striate and prestriate cortex was presented to sixteen healthy subjects. Six of these subjects were also exposed to a colored stationary and a gray stationary stimulus. In two subjects the colored moving stimulus was tested against the colored stationary with an optode position presumably over area V5/MT. As a control condition, subjects performed a simple finger opposition task. Since the calcarine fissure varies greatly with respect to bony landmarks, optodes were positioned individually according to 3-D reconstructed magnetic resonance imaging (MRI). Concentration changes in oxyhemoglobin ([oxy-Hb]) and deoxyhemoglobin ([deoxy-Hb]) were continuously monitored with a temporal resolution of 1 s, using an NIRO 500 (Hamamatsu Photonics, KK, Japan). In response to the visual stimulus, the grand average across all sixteen subjects resulted in a significant increase in [oxy-Hb] of 0.3360.09 arbitrary units (mean6S.E.M.) mirrored by a significant decrease in [deoxy-Hb] of −0.1860.02 arbitrary units, while the motor control condition elicited no significant changes in any parameters. When the near infrared spectroscopy probes were positioned over area V5/MT, the drop of [deoxy-Hb] associated with the moving stimulus was significantly more pronounced than with the stationary stimulus in both subjects examined. No significant differences between the visual stimuli were observed at the optode position close to the calcarine fissure. The oxygenation changes observed in this study are consistent with the pattern we have reported for motor activation. They are in line with physiological considerations and functional MRI studies relying on blood oxygenation level-dependent contrast.

Near infrared spectroscopy (NIRS) is a noninvasive and real-time method for monitoring oxy-[HbO2] and deoxyhemoglobin [Hb] in tissue, and is suitable for intraoperative monitoring. In this study, NIRS monitoring was performed on 10 patients during carotid cross-clamping. The data were analyzed with a theoretical cerebral hemoglobin model developed to identify an ischemic pattern using NIRS parameters. Temporal profiles of changes in [HbO2] and [Hb] were divided into three phases: initial (immediately after clamping), second (during clamping), and last phase (immediately after clamp release). In the initial phase, [HbO2] decreased and [Hb] increased in all the cases. In the second phase, recovery patterns of [HbO2] were classified into three groups: complete (3 patients), incomplete (3 patients), and no recovery (2 patients). In the last phase, the [HbO2] increased and [Hb] decreased. Relative changes in [HbO2] and [Hb] measured by NIRS were correlated with changes in blood flow of the internal carotid artery (ICA)measured by a magnetic flowmeter and stump pressure of the internal carotid arteries. The degree of [HbO2] decrease in the initial phase was significantly correlated with ICA blood flow before clamping (r=0.90, p<0.05). Three of the 4 patients with ICA stump pressure over 50 mmHg showed a complete recovery pattern in the second phase, while all 4 patients with ICA stump pressure under 50 mmHg showed an incomplete recovery or no recovery pattern with NIRS. These results suggest that NIRS is useful in evaluating changes in cerebral blood flow and the extent of hemodynamic reserve during carotid cross-clamping.

Near infrared spectrophotometry (NIRS) is a noninvasive method for measuring oxygenated and deoxygenated hemoglobin in the neonatal brain. Using oxygen as a tracer, it is possible to calculate cerebral blood flow (cbf) and hemoglobin concentration (cHbc), which corresponds to cerebral blood volume, by inducing small changes in arterial oxygen saturation (SaO2). Variability of tcpO2 is considered to be associated with severe retinopathy of prematurity (ROP). A preliminary analysis without control found a 51% incidence of ROP in infants subjected to NIRS measurements whereas among infants who were not exposed to oxygen changes, only 29% developed ROP (stages 1 to 4, p50.008). A controlled study (retrospective cohort study) with matched pairs was performed. Thirty-nine premature newborns who had received NIRS recordings were matched with 39 out of 172 infants who had not received NIRS. Using this controlled study design there was no difference in the incidence and severity of ROP between the two groups. The conclusions are that: (1) Small changes in oxygen saturation of 3 to 10% to measure cbf and cHbc did not increase the incidence or the degree of severity of ROP. (2) A controlled study design is important. Analyses of uncontrolled data would have led to the conclusion that oxygen changes as used with NIRS increase the risk of ROP.

The aim of this study was to clarify the influence of subcutaneous adipose tissue (AT) thickness on nearinfrared (NIR) optical density and the penetration depth of light in muscle tissue in vivo. The thickness of adipose tissue in the leg was measured using ultrasonography in 12 young subjects. Optical densities (OD) at 775, 807, and 827 nm were measured when the distance between the light source and the detector was increased from 20 to 100 mm in 10 mm steps. Ultrasonography showed that AT thickness ranged from 4 to 10 mm. The OD increased with increasing distance between the light source and the detector in all subjects. At the same distance between the light source and the detector (30 mm), the OD values correlated negatively with AT thickness (r 5 20.79, −0.82, and −0.79 at 775, 807, and 827 nm, respectively). Ultrasonography also showed that only the extensor hallucis longus muscle (EHL), which is under the extensor digitrum longus muscle (EDL), was activated during the flexion of the big toe. In order to evaluate the penetration depth of NIR light, the depth of EHL was measured and the OD observed before and during flexion. When the distance between the light source and detector was set at 30 mm, the OD values before exercise ranged from 0.36 to 3.18 at 775 nm, from 0.19 to 2.43 at 807 nm, and from 0.15 to 1.60 at 827 nm. Changes in OD during exercise were detectable for all subjects, and the EHLs of the subjects were located 10.0 to 20.2 mm under the detector. However, when the light source-detector distance was set at 20 mm, changes in OD during exercise were detectable for only 2 subjects, whose AT thicknesses were 4.0 or 5.0 mm, and the EHLs of the subjects were 10.0 or 11.7 mm deep. At a distance of 40 mm, 9 out of 12 subjects showed changes in OD, and their AT thicknesses and EHL locations ranged from 6.4 to 10.0 mm and from 11.4 to 20.4 mm deep, respectively...

Time-resolved and spectroscopic in vivo measurements were performed to determine the optical properties of the female breast in transmission. The time-resolved measurements were carried out at different positions on the female breast with a Ti:sapphire laser (800 nm) using a synchroscan streak camera. A diffusion model was used to calculate the absorption coefficient mA and the reduced scattering coefficient. In addition, spectroscopic in vivo measurements of more than 100 patients were performed in a wavelength range between 650 and 1000 nm. A variety of pathological alterations could be characterized by measuring patients of different ages, different breast sizes, and at varying locations on the breast. The results indicate that besides the pure detection of the amount of blood in the neovascular network, the volume concentrations of water and fat seem to be of particular importance for discrimination. In order to quantify this observation, an analytical model was developed that takes the volume percentages of fat and water, the concentration and oxygenation of hemoglobin, and the relevant optical parameters into account. Experiments were carried out with volunteers and patients in a clinical environment: Typical observations are presented and analyzed statistically.

A method has been developed for the rapid and direct identification of a single point mutation in a DNA sequence using fluorescence resonance energy transfer (FRET). The probe was a 16-base oligomer with 58-bound x-rhodamine and 38-bound fluorescein (R*16*F); the two dyes acted as a donor/acceptor pair for FRET, resulting in a dramatic difference in the fluorescence emission of the R*16*F in a duplex structure (hybridized to a complementary strand) and as a single strand (melted). This difference was used to obtain the melting temperature (Tm), by spectroscopically following the transition from double to single strand, for the probe hybridized to three different strands: the 16-base complement, the 16-base complement containing a single base mismatch, and the 16-base complementary sequence in the phage DNA M13mp18(+). The Tms thus determined for the perfectly base-paired duplexes, with R*16*F hybridized to the 16-mer complement and to M13, differed by 2°C, whereas the Tm obtained for R*16*F hybridized to the mismatched 16-mer complement was 10°C lower than that for the perfect duplex. The sharpness of the transition and the ease of detection allow single base mismatches to be reliably detected in nano- and subnanomolar concentrations in less than 1 h following hybridization.

Significant narrowing of both the spectral and temporal profiles of emission radiation from optically pumped dyes was observed in discrete and continuously disordered media such as dilute colloidal dye solutions and densely packed forms of sandy powders and animal tissue treated with rhodamine 640 dye solution. The narrowing of the spectral and temporal response is attributed to laser action arising from feedback of the emission radiation from the surrounding scattering walls into the photoexcited dye regions of the animal and sandy colloidal disordered media.

Pulsed radiation generated by powerful neodymium glass lasers was used to treat 272 cases of stage I skin melanomas; 250 patients (91.9%) patients were treated 5 years ago or earlier. Local recurrences of melanoma were detected in 2 (0.7%) cases within 1 to 8 years of followup. Regional metastases developed in 45 (16.5 63.3%) cases and distant ones in 12 (4.461.6%); 1 (0.4%) female patient presented with a transport metastasis. In patients treated 5 years ago or earlier, regional metastases occurred in 16.263.8% cases, distant ones in 4.461.6%, and transport ones in 0.4%. Five-year survival was registered in 84.562.8% of patients. Powerful pulsed laser radiation is effective in treating flat and slightly elevated skin melanomas that are up to 4.5 cm thick and that are characterized by levels I to IV of invasion.

Time-resolved infrared (IR) radiometry was used to measure surface temperatures during pulsed Er:YSGG(l=2.79 mm) and Er:YAG (l=2.94 mm) laser irradiation of dental enamel. Scanning electron microscopy (SEM)was used to determine the melting and vaporization thresholds and to characterize other changes in thesurface morphology. The magnitude and temporal evolution of the surface temperature during multiplepulse irradiation of the tissue was dependent on the wavelength, fluence, and pre-exposure to laser pulses. Radiometry and SEM micrographs indicate that ablation is initiated at temperatures well below the melting and vaporization temperatures of the carbonated hydroxyapatite mineral component (1200 °C). Ablation occurred at lower surface temperatures and at lower fluences for Er:YAG than for Er:YSGG laser irradiation: 400 °C vs. 800 °C and above 7 J/cm2 vs. 18 J/cm2, respectively. However, the measured surface temperatures were higher at l=2.79 mm than at l=2.94 mm during low fluence irradiation (<7 J/cm2). Spatially dependent absorption in the enamel matrix is proposed to explain this apparent contradiction.

Seven laser instruments, delivering radiation at a selection of wavelengths in the range of 0.355 to 118 mm, were investigated for their ability to kill Escherichia coli as a lawn of the bacteria on nutrient agar culture plates. Easily the most effective was a 600-W CO2 laser operating at 10.6 mm, which produced 1.2- cm2 circular zones of sterilization at energy densities of around 8 J cm22 in a 30-msec exposure. Circular zones with an area of 0.7 cm2 were achieved with 200 W from a Nd:YAG laser delivering 8-ms, 10-J pulses of 1.06 mm radiation at 20 Hz. The exposure time, however, was 16 s and the energy density (1940 J cm22) was more than 240 times higher than with the CO2 laser. This difference is believed to be partly due to the much higher absorption of radiation at 10.6 mm than at 1.06 mm, by water in the bacterial cells and the surrounding medium (nutrient agar). Sterilization was observed after exposure to frequency-tripled Nd:YAG laser radiation at 355 nm (3.5 J cm22). Lasers that were totally ineffective in killing Escherichia coli (with their wavelength and maximum energy densities tested) were the far infrared laser (118 mm; 7.96 J cm22), the laser diode array (0.81 mm; 13,750 J cm22), and the argon ion laser (0.488 mm; 2210 J cm22). The speed at which laser sterilization can be achieved is particularly attractive to the medical and food industries.

Three-photon excitation of 2,5-bis(4-biphenyl) oxazole (BBO) was observed when it was excited with the fundamental output of a femtosecond Ti:sapphire laser above 820 nm. The emission spectrum of BBO was identical for one-, two-, and three-photon excitation at 320, 640, and 960 nm, respectively. In toluene and triacetin, the emission intensity of BBO depended on the square of the laser power for wavelengths below 820 nm and displayed a sharp transition to a cubic dependence at longer wavelengths. The spatial distribution of the emission of BBO with three-photon excitation was more strongly localized than for two-photon excitation of a coumarin fluorophore at the same wavelength. The same single exponential intensity decay was observed for one-, two-, and three-photon excitation. However, the frequency domain anisotropy decay with threephoton excitation at 960 nm revealed a larger time-zero anisotropy, larger differential polarized phase angle, and larger modulated anisotropy than is possible for two-photon excitation with colinear oscillators. In triacetin, the anisotropy is not constant for three-photon excitation at different wavelengths. Surprisingly, the fluorescence intensities for three-photon excitation were only about 100-fold less than for two-photon excitation. The increasing availability of Ti:sapphire lasers suggests that multiphoton excitation can become a common tool in fluorescence spectroscopy.