Optical detection of peripheral nerves: an in vivo human study.

BACKGROUND AND OBJECTIVES: A critical challenge encountered in interventional pain medicine procedures is to accurately and efficiently identify transitions to peripheral nerve targets. Current methods, which include ultrasound guidance and nerve stimulation, are not perfect. In this pilot study, we investigated the feasibility of identifying tissue transitions encountered during insertions toward peripheral nerve targets using optical spectroscopy. METHODS: Using a custom needle stylet with integrated optical fibers, ultrasound-guided insertions toward peripheral nerves were performed in 20 patients, with the stylet positioned in the cannula of a 20-gauge stimulation needle. Six different peripheral nerves were represented in the study, with 1 insertion per patient. During each insertion, optical reflectance spectra were acquired with the needle tip in subcutaneous fat, skeletal muscle, and at the nerve target region. Differences in the spectra were quantified with 2 parameters that provide contrast for lipid and hemoglobin, respectively. RESULTS: The transition of the needle tip from subcutaneous fat to muscle was associated with lower lipid parameter values (P = 0.003) and higher hemoglobin parameter values (P = 0.023). The transition of the needle tip from the muscle to the nerve target region was associated with higher lipid parameter values (P = 0.008). CONCLUSIONS: The results indicate that the spectroscopic information provided by the needle stylet could potentially allow for reliable identification of transitions from subcutaneous fat to skeletal muscle and from the muscle to the nerve target region during peripheral nerve blocks.

Optical detection of vascular penetration during nerve blocks: an in vivo human study.

BACKGROUND AND OBJECTIVES: Complications resulting from vascular penetration during nerve blocks are rare but potentially devastating events that can occur despite meticulous technique. In this in vivo human pilot study, we investigated the potential for detecting vascular penetration with optical reflectance spectroscopy during blocks of the sympathetic chain and the communicating ramus at lumbar levels. METHODS: A custom-designed needle stylet with integrated optical fibers was used in combination with a commercial needle shaft. The needle stylet was connected to a console that delivered broadband light to tissue and spectrally resolved light that was scattered near the stylet tip. A total of 18 insertions were performed on 10 patients; testing for vascular penetration at the nerve target region was performed with aspiration and with radio-opaque contrast injections, visualized fluoroscopically. Optical absorption by hemoglobin was quantified with a blood parameter that was calculated from each spectrum. The blood parameter provided a measure of the difference between spectra acquired from the nerve target region and reference spectra acquired from blood extracted from a volunteer. RESULTS: In 2 insertions, vascular penetration was detected. Pronounced optical absorption by hemoglobin was observed to be associated with both of these events and absent in all other cases. The difference between the blood parameters obtained when vascular penetration was detected, and all other blood parameters were statistically significant (P = 0.006), with a diagnostic odds ratio of 35.4 (confidence interval, 2.21 to ∞). CONCLUSIONS: The results from this study suggest that optical spectroscopy has the potential to detect intravascular needle placement, which may in turn increase the safety of nerve blocks.

Needle stylet with integrated optical fibers for spectroscopic contrast during peripheral nerve blocks.

The effectiveness of peripheral nerve blocks is highly dependent on the accuracy at which the needle tip is navigated to the target injection site. Even when electrical stimulation is utilized in combination with ultrasound guidance, determining the proximity of the needle tip to the target region close to the nerve can be challenging. Optical reflectance spectroscopy could provide additional information about tissues that is complementary to these navigation methods. We demonstrate a novel needle stylet for acquiring spectra from tissue at the tip of a commercial 20-gauge needle. The stylet has integrated optical fibers that deliver broadband light to tissue and receive scattered light. Two spectrometers resolve the light that is received from tissue across the wavelength range of 500-1600 nm. In our pilot study, measurements are acquired from a postmortem dissection of the brachial plexus of a swine. Clear differences are observed between spectra acquired from nerves and those acquired from adjacent tissue structures. We conclude that spectra acquired with the stylet have the potential to increase the accuracy with which peripheral nerve blocks are performed.

Epidural needle with embedded optical fibers for spectroscopic differentiation of tissue: ex vivo feasibility study.

Epidural injection is commonly used to provide intraoperative anesthesia, postoperative and obstetric analgesia, and to treat acute radicular pain. Identification of the epidural space is typically carried out using the loss of resistance (LOR) technique, but the usefulness of this technique is limited by false LOR and the inability to reliably detect intravascular or subarachnoid needle placement. In this study, we present a novel epidural needle that allows for the acquisition of optical reflectance spectra from tissue close to the beveled surface. This needle has optical fibers embedded in the cannula that deliver and receive light. With two spectrometers, light received from tissue is resolved across the wavelength range of 500 to 1600 nm. To determine the feasibility of optical tissue differentiation, spectra were acquired from porcine tissues during a post mortem laminectomy. The spectra were processed with an algorithm that derives estimates of the hemoglobin and lipid concentrations. The results of this study suggest that the optical epidural needle has the potential to improve the accuracy of epidural space identification.

Optical detection of the brachial plexus for peripheral nerve blocks: an in vivo swine study.

BACKGROUND AND OBJECTIVES: Accurate identification of nerves is critical to ensure safe and effective delivery of regional anesthesia during peripheral nerve blocks. Nerve stimulation is commonly used, but it is not perfect. Even when nerve stimulation is performed in conjunction with ultrasound guidance, determining when the needle tip is at the nerve target region can be challenging. In this in vivo pilot study, we investigated whether close proximity to the brachial plexus and penetration of the axillary artery can be identified with optical reflectance spectroscopy, using a custom needle stylet with integrated optical fibers. METHODS: Ultrasound-guided insertions to place the needle tip near the brachial plexus at the axillary level were performed at multiple locations in 2 swine, with the stylet positioned in the cannula of a 20-gauge stimulation needle. During each insertion, optical reflectance spectra were acquired with the needle tip in skeletal muscle, at the surface of muscle fascia, and at the nerve target region; confirmation of the final needle position was provided by nerve stimulation. In addition, an insertion to the lumen of the axillary artery was performed in a third swine. Differences in the spectra were quantified with lipid and hemoglobin parameters that provide contrast for optical absorption by the respective chromophores. RESULTS: The transition of the needle tip from skeletal muscle to the nerve target region was associated with higher lipid parameter values (P < 0.001) and lower hemoglobin parameter values (P < 0.001). The transition of the needle tip from muscle fascia to the nerve target region was associated with higher lipid parameter values (P = 0.001). Intraluminal access of the axillary artery was associated with an elevated hemoglobin parameter. CONCLUSIONS: Spectroscopic information obtained with the optical needle is distinct from nerve stimulation and complementary to ultrasound imaging, and it could potentially allow for reliable identification of the injection site during peripheral nerve blocks.

High-resolution resonant and nonresonant fiber-scanning confocal microscope.

We present a novel, hand-held microscope probe for acquiring confocal images of biological tissue. This probe generates images by scanning a fiber-lens combination with a miniature electromagnetic actuator, which allows it to be operated in resonant and nonresonant scanning modes. In the resonant scanning mode, a circular field of view with a diameter of 190 µm and an angular frequency of 127 Hz can be achieved. In the nonresonant scanning mode, a maximum field of view with a width of 69 µm can be achieved. The measured transverse and axial resolutions are 0.60 and 7.4 µm, respectively. Images of biological tissue acquired in the resonant mode are presented, which demonstrate its potential for real-time tissue differentiation. With an outer diameter of 3 mm, the microscope probe could be utilized to visualize cellular microstructures in vivo across a broad range of minimally-invasive procedures.