Er:YAG laser brain surgery with vascular specific coagulation

BACKGROUND AND OBJECTIVE

Erbium:yttrium-aluminum-garnet (Er:YAG) laser ablation can effectively resect water-bearing tissues. Application of Er:YAG resection in neurosurgery is complicated by unpredictable bleeding in surgical field. Recently, an integrated theranostic system combining a dual-wavelength laser surgery system using a thulium (Tm) fiber-laser for coagulation and Er:YAG for resection, combined with optical coherence tomography (OCT) guidance was demonstrated for the in vivo resection of tumor tissue. However, lateral thermal spread in the range of 100 seconds of micrometers is common due to lack of vascular specificity using a Tm fiber-laser for coagulation. In this study, a vascular specific ytterbium (Yb) fiber-laser is utilized for enhanced photocoagulation during in vivo neurosurgery improving the precision of Er:YAG tissue resection with minimal lateral thermal spread.

METHODS

Mice underwent stereotactic laser surgery with the proposed Yb/Er:YAG dual wavelength vascular specific neurosurgery in vivo. An OCT system (wavelength range 1310 ± 70 nm) and OCT derived angiography  images were used to record cortical images to confirm the coagulation of blood vessels and guide subsequent Er:YAG resection steps. After the laser surgery, mice were killed, and histological analysis was carried out using hematoxylin and eosin staining and Nissl staining to compare the lateral thermal spread with our previously reported Tm/Er:YAG neurosurgery where a continuous wave  Tm fiber-laser was used for coagulation.

RESULTS

Coagulation scheme using a Yb fiber-laser allowed stoppage of blood flow in disparately sized blood vessels encountered in the mice brain. Histological analysis of murine brain slices post Yb/Er:YAG laser surgery yielded lower thermal spread compared with Tm/Er:YAG laser surgery, maximizing the efficiency in both hemostasis (blood flow stoppage) and maximizing tissue ablation efficiency with minimal residual thermal damage zone.

CONCLUSION

In this study, a vascular specific coagulation scheme with Yb/Er:YAG dual-wavelength surgery is presented for neurosurgery. Additionally, Yb/Er:YAG study results are compared with that of a tissue coagulation approach in Tm/Er:YAG surgery previously reported to highlight improved coagulation, reduced nonspecific thermal damage and limited lateral thermal spread. Experimental results suggest that the developed dual-wavelength laser system can effectively resect neural tissues with high localization, minimal lateral thermal spread at the micrometer level while maintaining a bloodless surgical field.

Data automated bag breathing unit for COVID-19 ventilator shortages

BACKGROUND

The COVID-19 pandemic has caused a global mechanical ventilator shortage for treatment of severe acute respiratory failure. Development of novel breathing devices has been proposed as a low cost, rapid solution when full-featured ventilators are unavailable. Here we report the design, bench testing and preclinical results for an 'Automated Bag Breathing Unit' (ABBU). Output parameters were validated with mechanical test lungs followed by animal model testing.

RESULTS

The ABBU design uses a programmable motor-driven wheel assembled for adult resuscitation bag-valve compression. ABBU can control tidal volume (200-800 ml), respiratory rate (10-40 bpm), inspiratory time (0.5-1.5 s), assist pressure sensing (- 1 to - 20 cm H2O), manual PEEP valve (0-20 cm H2O). All set values are displayed on an LCD screen. Bench testing with lung simulators (Michigan 1600, SmartLung 2000) yielded consistent tidal volume delivery at compliances of 20, 40 and 70 (mL/cm H2O). The delivered fraction of inspired oxygen (FiO2) decreased with increasing minute ventilation (VE), from 98 to 47% when VE was increased from 4 to 16 L/min using a fixed oxygen flow source of 5 L/min. ABBU was tested in Berkshire pigs (n = 6, weight of 50.8 ± 2.6 kg) utilizing normal lung model and saline lavage induced lung injury. Arterial blood gases were measured following changes in tidal volume (200-800 ml), respiratory rate (10-40 bpm), and PEEP (5-20 cm H2O) at baseline and after lung lavage. Physiological levels of PaCO2 (≤ 40 mm Hg [5.3 kPa]) were achieved in all animals at baseline and following lavage injury. PaO2 increased in lavage injured lungs in response to incremental PEEP (5-20 cm H2O) (p < 0.01). At fixed low oxygen flow rates (5 L/min), delivered FiO2 decreased with increased VE.

CONCLUSIONS

ABBU provides oxygenation and ventilation across a range of parameter settings that may potentially provide a low-cost solution to ventilator shortages. A clinical trial is necessary to establish safety and efficacy in adult patients with diverse etiologies of respiratory failure.

Differentiation of Brain Tumor Microvasculature From Normal Vessels Using Optical Coherence Angiography

BACKGROUND AND OBJECTIVES

Despite rapid advances and discoveries in medical imaging, monitoring therapeutic efficacy for malignant gliomas and monitoring tumor vasculature remains problematic. The purpose of this study is to utilize optical coherence angiography for vasculature characterization inside and surrounding brain tumors in a murine xenograft brain tumor model. Features included in our analysis include fractional blood volume, vessel tortuosity, diameter, orientation, and directionality.

STUDY DESIGN/MATERIALS AND METHODS

In this study, five tumorous mice models at 4 weeks of age were imaged. Human glioblastoma cells were injected into the brain and allowed to grow for 4 weeks and then imaged using optical coherence tomography.

RESULTS

Results suggest that blood vessels outside the tumor contain a greater fractional blood volume as compared with vessels inside the tumor. Vessels inside the tumor are more tortuous as compared with those outside the tumor. Results indicate that vessels near the tumor margin are directed inward towards the tumor while normal vessels show a more random orientation.

CONCLUSION

Quantification of vascular microenvironments in brain gliomas can provide functional vascular parameters to aid various diagnostic and therapeutic studies. © 2021 Wiley Periodicals LLC.

Laser brain cancer surgery in a xenograft model guided by optical coherence tomography

Higher precision surgical devices are needed for tumor resections near critical brain structures. The goal of this study is to demonstrate feasibility of a system capable of precise and bloodless tumor ablation. An image-guided laser surgical system is presented for excision of brain tumors in vivo in a murine xenograft model. The system combines optical coherence tomography (OCT) guidance with surgical lasers for high-precision tumor ablation (Er:YAG) and microcirculation coagulation (Thulium (Tm) fiber laser).

Methods: A fluorescent human glioblastoma cell line was injected into mice and allowed to grow four weeks. Craniotomies were performed and tumors were imaged with confocal fluorescence microscopy. The mice were subsequently OCT imaged prior, during and after laser coagulation and/or ablation. The prior OCT images were used to compute three-dimensional tumor margin and angiography images, which guided the coagulation and ablation steps. Histology of the treated regions was then compared to post-treatment OCT images.

Results: Tumor sizing based on OCT margin detection matched histology to within experimental error. Although fluorescence microscopy imaging showed the tumors were collocated with OCT imaging, margin assessment using confocal microscopy failed to see the extent of the tumor beyond ~ 250 µm in depth, as verified by OCT and histology. The two-laser approach to surgery utilizing Tm wavelength for coagulation and Er:YAG for ablation yielded bloodless resection of tumor regions with minimal residual damage as seen in histology.

Conclusion: Precise and bloodless tumor resection under OCT image guidance is demonstrated in the murine xenograft brain cancer model. Tumor margins and vasculature are accurately made visible without need for exogenous contrast agents.

In situ process monitoring in selective laser sintering using optical coherence tomography

Selective laser sintering (SLS) is an efficient process in additive manufacturing that enables rapid part production from computer-based designs. However, SLS is limited by its notable lack of in-situ process monitoring when compared to other manufacturing processes. We report the incorporation of optical coherence tomography into an SLS system in detail and demonstrate access to surface and sub-surface features. Video frame rate cross-sectional imaging reveals areas of sintering uniformity and areas of excessive heat error with high temporal resolution. We propose a set of image processing techniques for SLS process monitoring with OCT and report the limitations and obstacles for further OCT integration with SLS systems.

Optical coherence tomography image-guided smart laser knife for surgery

BACKGROUND AND OBJECTIVE

Surgical oncology can benefit from specialized tools that enhance imaging and enable precise cutting and removal of tissue without damage to adjacent structures. The combination of high-resolution, fast optical coherence tomography (OCT) co-aligned with a nanosecond pulsed thulium (Tm) laser offers advantages over conventional surgical laser systems. Tm lasers provide superior beam quality, high volumetric tissue removal rates with minimal residual thermal footprint in tissue, enabling a reduction in unwanted damage to delicate adjacent sub-surface structures such as nerves or micro-vessels. We investigated such a combined Tm/OCT system with co-aligned imaging and cutting beams-a configuration we call a "smart laser knife."

METHODS

A blow-off model that considers absorption coefficients and beam delivery systems was utilized to predict Tm cut depth, tissue removal rate and spatial distribution of residual thermal injury. Experiments were performed to verify the volumetric removal rate predicted by the model as a function of average power. A bench-top, combined Tm/OCT system was constructed using a 15W 1940 nm nanosecond pulsed Tm fiber laser (500 μJ pulse energy, 100 ns pulse duration, 30 kHz repetition rate) for removing tissue and a swept source laser (1310 ± 70 nm, 100 kHz sweep rate) for OCT imaging. Tissue phantoms were used to demonstrate precise surgery with blood vessel avoidance. Depth imaging informed cutting/removal of targeted tissue structures by the Tm laser was performed.

RESULTS

Laser cutting was accomplished around and above phantom blood vessels while avoiding damage to vessel walls. A tissue removal rate of 5.5 mm³ /sec was achieved experimentally, in comparison to the model prediction of approximately 6 mm³ /sec.

CONCLUSION

We describe a system that combines OCT and laser tissue modification with a Tm laser. Simulation results of the tissue removal rate using a simple model, as a function of average power, are in good agreement with experimental results using tissue phantoms. Lasers Surg. Med. 50:202-212, 2018. © 2017 Wiley Periodicals, Inc.

Dual-wavelength photothermal optical coherence tomography for imaging microvasculature blood oxygen saturation

A swept-source dual-wavelength photothermal (DWP) optical coherence tomography (OCT) system is demonstrated for quantitative imaging of microvasculature oxygen saturation. DWP-OCT is capable of recording three-dimensional images of tissue and depth-resolved phase variation in response to photothermal excitation. A 1,064-nm OCT probe and 770-nm and 800-nm photothermal excitation beams are combined in a single-mode optical fiber to measure microvasculature hemoglobin oxygen saturation (SO(2)) levels in phantom blood vessels with a range of blood flow speeds (0 to 17  mm/s). A 50-μm-diameter blood vessel phantom is imaged, and SO(2) levels are measured using DWP-OCT and compared with values provided by a commercial oximeter at various blood oxygen concentrations. The influences of blood flow speed and mechanisms of SNR phase degradation on the accuracy of SO(2) measurement are identified and investigated.

In vivo depth-resolved oxygen saturation by Dual-Wavelength Photothermal (DWP) OCT

Microvasculature hemoglobin oxygen saturation (SaO2) is important in the progression of various pathologies. Non-invasive depth-resolved measurement of SaO2 levels in tissue microvasculature has the potential to provide early biomarkers and a better understanding of the pathophysiological processes allowing improved diagnostics and prediction of disease progression. We report proof-of-concept in vivo depth-resolved measurement of SaO(2) levels in selected 30 µm diameter arterioles in the murine brain using Dual-Wavelength Photothermal (DWP) Optical Coherence Tomography (OCT) with 800 nm and 770 nm photothermal excitation wavelengths. Depth location of back-reflected light from a target arteriole was confirmed using Doppler and speckle contrast OCT images. SaO(2) measured in a murine arteriole with DWP-OCT is linearly correlated (R(2)=0.98) with systemic SaO(2) values recorded by a pulse-oximeter. DWP-OCT are steadily lower (10.1%) than systemic SaO(2) values except during pure oxygen breathing. DWP-OCT is insensitive to OCT intensity variations and is a candidate approach for in vivo depth-resolved quantitative imaging of microvascular SaO(2) levels.

Birefringence measurement of the retinal nerve fiber layer by swept source polarization sensitive optical coherence tomography

A Swept Source Polarization-Sensitive Optical Coherence Tomography (SS-PS-OCT) instrument has been designed, constructed, and verified to provide high sensitivity depth-resolved birefringence and phase retardation measurements of the retinal nerve fiber layer. The swept-source laser had a center wavelength of 1059 nm, a full-width-half-max spectral bandwidth of 58 nm and an A-line scan rate of 34 KHz. Power incident on the cornea was 440 µW and measured axial resolution was 17 µm in air. A multiple polarization state nonlinear fitting algorithm was used to measure retinal birefringence with low uncertainty. Maps of RNFL phase retardation in a subject measured with SS-PS-OCT compare well with those generated using a commercial scanning laser polarimetry instrument. Peak-to-valley variation of RNFL birefringence given here is less than values previously reported at 840nm.

Depth-resolved blood oxygen saturation measurement by dual-wavelength photothermal (DWP) optical coherence tomography

Non-invasive depth-resolved measurement of hemoglobin oxygen saturation (SaO(2)) levels in discrete blood vessels may have implications for diagnosis and treatment of various pathologies. We introduce a novel Dual-Wavelength Photothermal (DWP) Optical Coherence Tomography (OCT) for non-invasive depth-resolved measurement of SaO(2) levels in a blood vessel phantom. DWP OCT SaO(2) is linearly correlated with blood-gas SaO(2) measurements. We demonstrate 6.3% precision in SaO(2) levels measured a phantom blood vessel using DWP-OCT with 800 and 765 nm excitation wavelengths. Sources of uncertainty in SaO(2) levels measured with DWP-OCT are identified and characterized.

New spiropiperidines as potent and selective non-peptide tachykinin NK2 receptor antagonists

The synthesis of a series of 2-(5-fluoro-1H-indol-3-yl)ethyl spiropiperidines is described together with their tachykinin NK2 receptor affinities measured in a rat colon binding assay. Equivalent NK2 receptor binding affinity was observed for the spirooxazolidinone 3-benzyl-8-[2-(5-fluoro-1H-indol-3-yl)ethyl]-1-oxa-3,8-diazaspiro[4.5] decan-2-one (3a), the imidazolidinone 3-benzyl-8-[2-(5-fluoro-1H-indol-3-yl)ethyl]-1,3,8-triazaspiro[4.5 ] decan-2-one (3s), and the pyrrolidinone 2-benzyl-8-[2-(5-fluoro-1H-indol-3-yl)ethyl]-2,8-diazaspiro[4.5]decan -3 - one (3t). Substitution in the phenyl ring of compound 3a produced no significant enhancement in NK2 binding affinity. Replacement of the phenyl ring in 3a with other aromatic rings resulted in a significant loss in binding affinity. Compound 3a was shown to be a potent NK2 receptor antagonist in guinea pig trachea where it also demonstrated 1000-fold selectivity for NK2 receptors over NK1. In the anesthetized guinea pig, compound 3a administered by the intravenous or oral route displayed potent and long-lasting antagonist activity against NK2 receptor agonist induced bronchoconstriction.

Matrix metalloproteinase inhibitors containing a (carboxyalkyl)amino zinc ligand: modification of the P1 and P2' residues

Systematic modification of the presumed P1 side chain in a series of (carboxyalkyl)amino-based inhibitors of matrix metalloproteinases enabled identification of the 2-(1,3-dihydro-1,3-dioxo-2H-benz[f]isoindol-2-yl)ethyl group as a preferred substituent imparting potent inhibition of the enzymes collagenase and gelatinase. It was subsequently found that the P2'-P3' residues in this series could be replaced by small non-peptide residues, while maintaining inhibitory potency. The imide group in this series of compounds can undergo autocatalytic hydrolysis under neutral conditions.

Structure of the catalytic domain of fibroblast collagenase complexed with an inhibitor

Collagenase is a zinc-dependent endoproteinase and is a member of the matrix metalloproteinase (MMP) family of enzymes. The MMPs participate in connective tissue remodeling events and aberrant regulation has been associated with several pathologies. The 2.4 angstrom resolution structure of the inhibited enzyme revealed that, in addition to the catalytic zinc, there is a second zinc ion and a calcium ion which play a major role in stabilizing the tertiary structure of collagenase. Despite scant sequence homology, collagenase shares structural homology with two other endoproteinases, bacterial thermolysin and crayfish astacin. The detailed description of protein-inhibitor interactions present in the structure will aid in the design of compounds that selectively inhibit individual members of the MMP family. Such inhibitors will be useful in examining the function of MMPs in pathological processes.

Conformationally constrained tachykinin analogues: potent and highly selective neurokinin NK-2 receptor agonists

The design and synthesis of potent and selective neurokinin NK-2 receptor agonists 12 (GR64349) and 31 are described, together with structure-activity relationships for related analogues. Compound 12 (EC50 = 3.7 nM at NK-2 receptors in the rat colon; selectivity > 1000- and > 300-fold with respect to NK-1 and NK-3 receptors, respectively) was derived by incorporation of a Gly-Leu gamma-lactam conformational constraint into the C-terminal region of the neurokinin A octapeptide analogue [Lys3]-NKA(3-10). Compound 31 (EC50 = 15 nM in rat colon) contains a novel fused-bicyclic constraint at the corresponding site in the substance P hexapeptide analogue [Ava6]-SP(6-11).

Highly potent and selective heptapeptide antagonists of the neurokinin NK-2 receptor

Incorporation of D-Pro9 into substance P related peptides is known to enhance neurokinin NK-2 receptor agonist potency and selectivity with respect to other neurokinin receptors. We now report that replacement of D-Trp9 by D-Pro9 in the nonselective neurokinin antagonist [Arg5,D-Trp7,9, Nle11]-SP(5-11) gave a partial agonist with NK-2 receptor selectivity. Further incorporation of Pro10 provided the weak but selective NK-2 antagonist Arg-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH2 (compound 4; NK-2 pKB = 5.9; NK-1 pKB = 4.7; NK-3 pKB less than 4.6). Addition of a suitable lipophilic N-terminal substituent (e.g. Boc, PhCO, cyclohexylcarbonyl) to this compound greatly enhanced NK-2 antagonist activity (compound 10, GR 83074; NK-2 pKB = 8.2), and combined with further optimization of the N-terminal amino acids, provided the extremely potent and selective NK-2 antagonist PhCO-Ala-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH2 (compound 34, GR 94800; NK-2 pKB = 9.6; NK-1 pKB = 6.4; NK-3 pKB = 6.0). Compounds of this class produced a potent inhibition of NK-2 agonist-induced bronchoconstriction in the anaesthetized guinea-pig.

New kappa-receptor agonists based upon a 2-[(alkylamino)methyl]piperidine nucleus

The syntheses of some 1-[(3,4-dichlorophenyl)acetyl]-2- [(alkylamino)methyl]piperidines and their activities as kappa-opioid receptor agonists are described. Selected structural modifications are made to the basic moiety and at the 2-, 3-, 4-, 5-, and 6-positions on the piperidine nucleus to enable structure-activity relationships to be delineated. As a result, some highly potent and selective kappa-receptor agonists have been identified. In particular, this has been achieved by introduction of oxygen-containing functionality into the 4-position of the piperidine nucleus or the 3-position of the pyrrolidinylmethyl side chain. Thus, 1-[(3,4-dichlorophenyl)acetyl]- 2-[[1-(3-oxopyrrolidinyl)]methyl]piperidine (10) possesses high activity in the rabbit vas deferens (LVD, kappa-specific tissue) (IC50 = 0.20 nM) and is a potent antinociceptive agent, as determined by the mouse acetylcholine-induced abdominal constriction test (MAC) (ED50 = 0.06 mg/kg, sc). The spirocyclic analogue 8-[(3,4-dichlorophenyl)acetyl]-7-(1-pyrrolidinylmethyl)-1,4-dio xa-8- azaspirol4.5]decane (39) showed exceptionally potent activity: LVD, IC50 = 0.10 nM; MAC, ED50 = 0.001 mg/kg, sc. Both 10 and 39 displayed high selectivity for kappa-opioid receptors over both mu- and delta-opioid receptor subtypes.

Synthesis, antinociceptive activity, and opioid receptor profiles of substituted trans-3-(decahydro- and octahydro-4a-isoquinolinyl)phenols

A series of trans-3-(6- and 7-substituted-decahydro-4a-isoquinolinyl)phenols and trans-3-(octahydro-4a-isoquinolinyl)phenols have been synthesized as potential opioid analgesics. Using a combination of in vitro and in vivo test systems, the receptor profiles of selected compounds have been assessed and in some instances distinguish between mu- and kappa-receptor agonists. In general, introduction of a 6-exocyclic methylene group into the trans-3-(decahydro-4a-isoquinolinyl)phenol system enhanced both antinociceptive activity and kappa-opioid receptor selectivity. For each series, analogues bearing an N-cyclopropylmethyl substituent exhibited greater kappa-receptor selectivity while N-methyl derivatives showed greater mu-receptor selectivity. The 7-substituted compounds (3b) were significantly less potent antinociceptive agents than their 6-substituted counterparts (3a), the octahydroisoquinoline analogues exhibiting intermediate activity. The axial 8-methyl-6-exocyclic methylene isoquinoline (20) is the most potent compound in the mouse abdominal constriction assay (ED50 = 0.05 mg/kg sc), whereas the equatorial 8-methyl isomer (16) was significantly less potent (ED50 = 3.3 mg/kg sc).