Diffuse reflectance spectroscopy: Systemic and microvascular oxygen saturation is linearly correlated and hypoxia leads to increased spatial heterogeneity of microvascular saturation

Rapid low-cost hyperspectral imaging system for quantitative assessment of infantile hemangioma

Hemangioma, the predominant benign tumor occurring in infancy, exhibits a wide range of prognoses and associated outcomes. The accurate determination of prognosis through noninvasive imaging modalities holds essential importance in enabling effective personalized treatment strategies and minimizing unnecessary surgical interventions for individual patients. The present study focuses on advancing the personalized prognosis of hemangioma by leveraging noninvasive optical sensing technologies by the development of a novel rapid hyperspectral sensor (image collection in 5 s, lateral resolution of 10 μm) that is capable of quantifying hemoglobin oxygenation and vascularization dynamics during the course of tumor evolution. We have developed a quantitative parameter for hemangioma assessment, that demonstrated agreement with the clinician's conclusion in 90% among all cases during clinical studies on six patients, who visited clinician from two to four times. The presented methodology has potential to be implemented as a supportive tool for accurate hemangioma diagnostics in clinics.

Ocular surface microcirculation is better preserved with pulsatile versus continuous flow during cardiopulmonary bypass-An experimental pilot

BACKGROUND

Non-pulsatile cardiopulmonary bypass (CPB) may induce microvascular dysregulation. In piglets, we compared ocular surface microcirculation during pulsatile versus continuous flow (CF) bypass.

METHODS

Ocular surface microcirculation in small tissue volumes (~0.1 mm³ ) at limbus (high metabolic rate) and bulbar conjunctiva (low metabolic rate) was examined in a porcine model using computer assisted video microscopy and diffuse reflectance spectroscopy, before and after 3 and 6 h of pulsatile (n = 5 piglets) or CF (n = 3 piglets) CPB. Functional capillary density, capillary flow velocity and microvascular oxygen saturation were quantified.

RESULTS

At limbus, velocities improved with pulsatility (p < 0.01) and deteriorated with CF (p < 0.01). In bulbar conjunctiva, velocities were severely reduced with CF (p < 0.01), accompanied by an increase in capillary density (p < 0.01). Microvascular oxygen saturation decreased in both groups.

CONCLUSION

Ocular surface capillary densities and flow patterns are better preserved with pulsatile versus CF during 6 h of CPB in sleeping piglets.

Skin trauma rapidly induces thermoregulatory plexus hyperemia, while an increased nutritive papillary capillary function can be detected after 24 h

OBJECTIVE

Clinical assessments and laser Doppler perfusion measurements (LDPM) of skin microcirculation have limited value, as they fail to capture events regulated by local metabolic needs at a papillary capillary level. This study aimed to examine the ability of computer-assisted video microscopy (CAVM) and diffuse reflectance spectroscopy (DRS) to assess skin nutritive perfusion-compared to LDPM.

METHODS

Healthy volunteers (n = 10) were examined after (≈1 and ≈24 h) an incision (5 × 1 mm) on the forearm, at 0.1 mm (only with CAVM), 2-3 mm, and 30 mm from the trauma.

RESULTS

No changes were detected by CAVM after ≈1 h. After ≈24 h, 0-1 mm from the trauma, both CAVM parameters were increased: functional capillary density (capillary crossings/mm, 11.8 ± 1.4 vs. 7.3 ± 1.2, p < .01) and capillary flow velocities (CFV, %capillaries with brisk flow, 10 ± 6.8 vs. 1 ± 1, p < .01). At a distance of 2-3 mm, only CFV was increased (6.2 ± 6.1 vs. 1 ± 1, p < .05). DRS and LDPM measurements increased 2-3 mm from the trauma line in relation to baseline after both ≈1 and ≈24 h, that is, with DRS (%microvascular oxygen saturation): 45.8 ± 7.4% (baseline), 70.0 ± 12.5% (≈1 h), and 73.1 ± 10.4% (≈24 h), p < .01 and with LDPM (a.u.): 7.2 ± 2.5 (baseline), 28.3 ± 18.7 (≈1 h), and 45.9 ± 16.3 (≈24 h), p < .01.

CONCLUSIONS

≈24 h after skin trauma, an increased function of the nutritive papillary capillaries can be detected by CAVM.

Quantitative In Vivo Monitoring of Hypoxia and Vascularization of Patient-Derived Murine Xenografts of Mantle Cell Lymphoma Using Photoacoustic and Ultrasound Imaging

Tumor oxygenation and vascularization are important parameters that determine the aggressiveness of the tumor and its resistance to cancer therapies. We introduce dual-modality ultrasound and photoacoustic imaging (US-PAI) for the direct, non-invasive real-time in vivo evaluation of oxygenation and vascularization of patient-derived xenografts (PDXs) of B-cell mantle cell lymphomas. The different optical properties of oxyhemoglobin and deoxyhemoglobin make it possible to determine oxygen saturation (sO₂) in tissues using PAI. High-frequency color Doppler imaging enables the visualization of blood flow with high resolution. Tumor oxygenation and vascularization were studied in vivo during the growth of three different subcutaneously implanted patient-derived xenograft (PDX) lymphomas (VFN-M1, VFN-M2 and VFN-M5 R1). Similar values of sO₂ (sO₂ Vital), determined from US-PAI volumetric analysis, were obtained in small and large VFN-M1 tumors ranging from 37.9 ± 2.2 to 40.5 ± 6.0 sO₂ Vital (%) and 37.5 ± 4.0 to 35.7 ± 4.6 sO₂ Vital (%) for small and large VFN-M2 PDXs. In contrast, the higher sO₂ Vital values ranging from 57.1 ± 4.8 to 40.8 ± 5.7 sO₂ Vital (%) (small to large) of VFN-M5 R1 tumors corresponds with the higher aggressiveness of that PDX model. The different tumor percentage vascularization (assessed as micro-vessel areas) of VFN-M1, VFN-M2 and VFN-M5 R1 obtained by color Doppler (2.8 ± 0.1%, 3.8 ± 0.8% and 10.3 ± 2.7%) in large-stage tumors clearly corresponds with their diverse growth and aggressiveness. The data obtained by color Doppler were validated by histology. In conclusion, US-PAI rapidly and accurately provided relevant and reproducible information on tissue oxygenation in PDX tumors in real time without the need for a contrast agent.

Quantification of ocular surface microcirculation by computer assisted video microscopy and diffuse reflectance spectroscopy

In piglets we tested the applicability of digital video microscopy and diffuse reflectance spectroscopy for non-invasive assessments of limbal and bulbar conjunctival microcirculation. A priori we postulated that the metabolic rate is higher in limbal as compared to bulbar conjunctiva, and that this difference is reflected in microvascular structure or function between the two locations. Two study sites, Oslo University Hospital (OUH), Norway and Cleveland Clinic (CC), USA, used the same video microscopy and spectroscopy techniques to record limbal and bulbar microcirculation in sleeping piglets. Recordings were analyzed with custom-made software to quantify functional capillary density, capillary flow velocity and microvascular oxygen saturation in measuring volumes of approximately 0.1 mm³. The functional capillary density was higher in limbus than in bulbar conjunctiva at both study sites (OUH: 18.1 ± 2.9 versus 12.2 ± 2.9 crossings per mm line, p < 0.01; CC: 11.3 ± 3.0 versus 7.1 ± 2.8 crossings per mm line, p < 0.01). Median categorial capillary blood flow velocity was higher in bulbar as compared with limbal recordings (CC: 3 (1-3) versus 1 (0-3), p < 0.01). Conjunctival microvascular oxygen saturation was 88 ± 5.9% in OUH versus 94 ± 7.5% in CC piglets. Non-invasive digital video microscopy and diffuse reflectance spectroscopy can be used to obtain data from conjunctival microcirculation in piglets. Limbal conjunctival microcirculation has a larger capacity for oxygen delivery as compared with bulbar conjunctiva.

Reduction of the influence of film thickness on diffuse reflectance spectroscopy measurement of the tongue

Diffuse reflectance spectroscopy of the tongue contains rich physiological and biochemical information of human status. As it involves contact measurement of the tongue, preventing cross infection during measurement is an important problem to be solved. The use of sterile isolation films is a convenient and efficient way. However, these films can affect the spectral measurement results at the same time. In this paper, to study the influence of films on spectral analysis, a new modeling strategy with good robustness is proposed. The model is established by the use of spectra obtained with different thicknesses of films; thus it is insensitive to the film thickness. The experiment was conducted by gathering spectra of 35 volunteers' tongue using films of different thicknesses. First, the partial least squares method was used to reveal the relationship between the spectral data and the thickness of films. Second, the support vector machine established a classification model between the spectral data and subjects to study the influence of the film. The results showed that the model established by the new modeling strategy could minimize the error caused by variation of the film thickness.

Acute skin trauma induces hyperemia, but superficial papillary nutritive perfusion remains unchanged

OBJECTIVES

Superficial skin papillary capillaries with blood supply from a superficial vascular plexus and regulated by local metabolic needs supply oxygen and nutrients for epithelial cell proliferation. A deep vascular plexus regulated by autonomous nerves serves body thermoregulation. In healthy volunteers, we assessed circulatory effects of a standardized skin trauma by CAVM, DRS, and LDPM to assess the measuring depth of the three techniques and to describe the acute trauma effects on nutritive and thermoregulatory perfusion.

METHODS

Volunteers (n=12) were examined at baseline and after induction of a 5.0 mm×1.0 mm incision on the forearm; 30 minutes after the trauma induction, data were collected at 0-1, 2-3 and 30 mm distances.

RESULTS

LDPM showed hyperemia at 2-3 mm distance (35.8±15.2 a.u.), but not at 30 mm distance (7.4±2.5 a.u.) compared to baseline (8.8±1.8 a.u.). The DRS saturation increased at 2-3 mm (71.2±4.8%), but not at 30 mm (49.8±7.9%) compared to baseline (45.8±7.4%). Capillary density and flow velocities were unaffected at all distances.

CONCLUSIONS

The results indicate that skin nutritive papillary capillary function can be assessed by CAVM and DRS, but not with LDPM because of its dependence of the deep plexus perfusion.

Intraoperative measurement of bowel oxygen saturation using a multispectral imaging laparoscope

Intraoperative monitoring of tissue oxygen saturation (StO2 ) has potentially important applications in procedures such as organ transplantation or colorectal surgery, where successful reperfusion affects the viability and integrity of repaired tissues. In this paper a liquid crystal tuneable filter-based multispectral imaging (MSI) laparoscope is described. Motion-induced image misalignments are reduced, using feature-based registration, before regression of the tissue reflectance spectra to calculate relative quantities of oxy- and deoxyhaemoglobin. The laparoscope was validated in vivo, during porcine abdominal surgery, by making parallel MSI and blood gas measurements of the small bowel vasculature. Ischaemic conditions were induced by local occlusion of the mesenteric arcade and monitored using the system. The MSI laparoscope was capable of measuring StO2 over a wide range (30-100%) with a temporal error of ± 7.5%. The imager showed sensitivity to spatial changes in StO2 during dynamic local occlusions, as well as tracking the recovery of tissues post-occlusion.

Sepsis is associated with altered cerebral microcirculation and tissue hypoxia in experimental peritonitis

OBJECTIVE

Alterations in cerebral microvascular blood flow may develop during sepsis, but the consequences of these abnormalities on tissue oxygenation and metabolism are not well defined. We studied the evolution of microvascular blood flow, brain oxygen tension (PbO2), and metabolism in a clinically relevant animal model of septic shock.

DESIGN

Prospective randomized animal study.

SETTING

University hospital research laboratory.

SUBJECTS

Fifteen invasively monitored and mechanically ventilated female sheep.

INTERVENTIONS

The sheep were randomized to fecal peritonitis (n = 10) or a sham procedure (n = 5), and craniectomies were performed to enable evaluation of cerebral microvascular blood flow, PbO2, and metabolism. The microvascular network of the left frontal cortex was evaluated (at baseline, 6, 12, and 18 hr) using sidestream dark-field videomicroscopy. Using an off-line semiquantitative method, functional capillary density and the proportion of small perfused vessels were calculated. PbO2 was measured hourly by a parenchymal Clark electrode, and cerebral metabolism was assessed by the lactate/pyruvate ratio using brain microdialysis; both these systems were placed in the right frontal cortex.

MEASUREMENT AND MAIN RESULTS

In septic animals, cerebral functional capillary density (from 3.1 ± 0.5 to 1.9 ± 0.4 n/mm, p < 0.001) and proportion of small perfused vessels (from 98% ± 2% to 84% ± 7%, p = 0.004) decreased over the 18-hour study period. Concomitantly, PbO2 decreased (61 ± 5 to 41 ± 7 mm Hg, p < 0.001) and lactate/pyruvate ratio increased (23 ± 5 to 36 ± 19, p < 0.001). At 18 hours, when shock was present, animals with a mean arterial pressure less than 65 mm Hg (n = 6) had similar functional capillary density, proportion of small perfused vessels, and PbO2 values but significantly higher lactate/pyruvate ratio (46 ± 18 vs 20 ± 4, p = 0.009) compared with animals with an mean arterial pressure of 65-70 mm Hg (n = 4).

CONCLUSIONS

Impaired cerebral microcirculation during sepsis is associated with progressive impairment in PbO2 and brain metabolism. Development of severe hypotension was responsible for a further increase in anaerobic metabolism. These alterations may play an important role in the pathogenesis of brain dysfunction during sepsis.

Skin microcirculation in healthy term newborn infants--assessment of morphology, perfusion and oxygenation

Despite microcirculation's fundamental role, assessments of its function are limited. We explored the applicability of Computer Assisted Video Microscope (CAVM), Laser Doppler Perfusion Measurements (LDPM) and Diffuse Reflectance Spectroscopy (DRS) to study skin microvascular morphology, perfusion and oxygen saturation in twenty-five healthy newborns day 1-3 of life.

RESULTS

Day 1-3 (mean (SD)): Microvascular density (CAVM; number of microvessels crossing a grid of lines/mm line, c/mm): Chest: 11.3 (1.5), 11.0 (1.7), 10.7 (1.6). Hand: 13.2 (2.0), 13.2 (1.9), 12.4 (1.6). Capillary density was significantly higher in the hand than in the chest each day (p <  0.001). Perfusion (LDPM; arbitrary units): Chest: 109.1 (26.0), 101.4 (24.6), 100.8 (25.3). Hand: 58.9 (17.5), 54.3 (15.8), 46.9 (14.8). Perfusion was significantly higher in the chest than in the hand each day (p <  0.01). Microvascular oxygen saturation (DRS; %): Chest: 88.1 (5.2), 87.8 (10.0), 86.7 (9.0). Hand: 79.9 (15.2), 82.7 (11.8), 82.2 (12.1) (p <  0.05). Capillary flow velocities (CAVM) were similar in the chest and hand: 60-70% capillaries had "continuous high flow" and 30-40% "continuous low flow".Multimodal skin microvascular assessments with CAVM, LDPM and DRS are feasible with reproducible data in newborns. The hand has lower perfusion, higher capillary density and higher oxygen extraction than the chest.

PaO2 oscillations caused by cyclic alveolar recruitment can be monitored in pig buccal mucosa microcirculation

BACKGROUND

Cyclic alveolar recruitment and derecruitment play a role in the pathomechanism of acute lung injury and may lead to arterial partial pressure of oxygen (PaO(2) ) oscillations within the respiratory cycle. It remains unknown, however, if these PaO(2) oscillations are transmitted to the microcirculation. The present study investigates if PaO(2) oscillations can be detected in the pig buccal mucosa microcirculation.

METHODS

Respiratory failure was induced by surfactant depletion in seven pigs. PaO(2) oscillations caused by cyclic recruitment and derecruitment were measured in the thoracic aorta by fast fluorescence quenching of oxygen technology. Haemoglobin oxygen saturation, haemoglobin amount and blood flow in the buccal mucosa microcirculation were determined by combined fast white light spectrometry and laser Doppler flowmetry additionally to systolic arterial pressure. Measurements were performed during baseline conditions and during cyclic recruitment and derecruitment.

RESULTS

Measurements remained stable during baseline. Respiratory-dependent oscillations occurred in the systemic circulation [PaO(2) oscillations 92 (69-172) mmHg; systolic arterial pressure oscillations 33 (13-35) %] and were related to the respiratory rate (5.0 ± 0.2/min) as confirmed by Fourier analysis. Synchronised oscillations were detected to the pig buccal mucosa microcirculation [haemoglobin oxygen saturation oscillations 3.4 (2.7-4.9) %; haemoglobin amount oscillations 8.5 (2.3-13.3) %; blood flow oscillations 66 (18-87) %]. The delay between PaO(2) -\ and microcirculatory oxygen oscillations was 7.2 ± 2.8 s.

CONCLUSION

The present study suggests that PaO(2) oscillations caused by cyclic recruitment and derecruitment were transmitted to the buccal mucosa microcirculation. This non-invasive approach of measuring oxygen waves as a surrogate parameter of cyclic recruitment and derecruitment could be used to monitor PaO(2) oscillations at the bedside.

A wireless handheld probe with spectrally constrained evolution strategies for diffuse optical imaging of tissue

We present a low-cost, portable, wireless diffuse optical imaging device. The handheld device is fast, portable, and can be applied to a wide range of both static and dynamic imaging applications including breast cancer, functional brain imaging, and peripheral artery disease. The continuous-wave probe has four near-infrared wavelengths and uses digital detection techniques to perform measurements at 2.3 Hz. Using a multispectral evolution algorithm for chromophore reconstruction, we can measure absolute oxygenated and deoxygenated hemoglobin concentration as well as scattering in tissue. Performance of the device is demonstrated using a series of liquid phantoms comprised of Intralipid(®), ink, and dye.