Comparing laser speckle contrast imaging and indocyanine green angiography for assessment of parathyroid perfusion.

Accurate intraoperative assessment of parathyroid blood flow is crucial to preserve function postoperatively. Indocyanine green (ICG) angiography has been successfully employed, however its conventional application has limitations. A label-free method overcomes these limitations, and laser speckle contrast imaging (LSCI) is one such method that can accurately detect and quantify differences in parathyroid perfusion. In this study, twenty-one patients undergoing thyroidectomy or parathyroidectomy were recruited to compare LSCI and ICG fluorescence intraoperatively. An experimental imaging device was used to image a total of 37 parathyroid glands. Scores of 0, 1 or 2 were assigned for ICG fluorescence by three observers based on perceived intensity: 0 for little to no fluorescence, 1 for moderate or patchy fluorescence, and 2 for strong fluorescence. Speckle contrast values were grouped according to these scores. Analyses of variance were performed to detect significant differences between groups. Lastly, ICG fluorescence intensity was calculated for each parathyroid gland and compared with speckle contrast in a linear regression. Results showed significant differences in speckle contrast between groups such that parathyroids with ICG score 0 had higher speckle contrast than those assigned ICG score 1, which in turn had higher speckle contrast than those assigned ICG score 2. This was further supported by a correlation coefficient of -0.81 between mean-normalized ICG fluorescence intensity and speckle contrast. This suggests that ICG angiography and LSCI detect similar differences in blood flow to parathyroid glands. Laser speckle contrast imaging shows promise as a label-free alternative that overcomes current limitations of ICG angiography for parathyroid assessment.

Assessing Intraoperative Laser Speckle Contrast Imaging of Parathyroid Glands in Relation to Total Thyroidectomy Patient Outcomes.

Background: Accurate assessment of parathyroid gland vascularity is important during thyroidectomy to preserve the function of parathyroid glands and to prevent postoperative hypocalcemia. Laser speckle contrast imaging (LSCI) has been shown to be accurate in detecting differences in parathyroid vascularity. In this surgeon-blinded prognostic study, we evaluate the relationship between intraoperative LSCI measurements and postoperative outcomes of total thyroidectomy patients. Methods: Seventy-two thyroidectomy patients were included in this study. After thyroid resection, an LSCI device was used to image all parathyroid glands identified, and a speckle contrast value was calculated for each. An average value was calculated for each patient, and the data were grouped according to whether the patient had normal (16-77 pg/mL) or low levels of parathyroid hormone (PTH) measured on postoperative day 1 (POD1). The aim of this study was to establish a speckle contrast threshold for classifying a parathyroid gland as adequately perfused and to determine how many such glands are required for normal postoperative parathyroid function. Results: A speckle contrast limit of 0.186 separated the normoparathyroid and hypoparathyroid groups with 87.5% sensitivity and 84.4% specificity: 7 of 8 patients with low PTH on POD1 had an average parathyroid speckle contrast above this limit, while 54 of 64 patients with normal postoperative PTH had an average parathyroid speckle contrast below this limit. Taking this value as the threshold for adequate parathyroid perfusion, it was determined that only one vascularized gland was needed for normal postoperative parathyroid function: 64 of 69 patients (92.8%) with at least one vascularized gland (determined by LSCI) had normal postoperative PTH, while all 3 patients (100%) with no vascularized glands had low postoperative PTH. Overall, the rates of temporary and permanent hypoparathyroidism in this study were 8.3% and 1.4%, respectively. Conclusions: LSCI is a promising technique for assessing parathyroid gland vascularity. It has the potential to help reduce the incidence of hypocalcemia after thyroidectomy by providing surgeons with additional information during surgery to aid in the preservation of parathyroid function.

Comparing intraoperative parathyroid identification based on surgeon experience versus near infrared autofluorescence detection - A surgeon-blinded multi-centric study.

BACKGROUND: Near infrared autofluorescence (NIRAF) detection has previously demonstrated significant potential for real-time parathyroid gland identification. However, the performance of a NIRAF detection device - PTeye® - remains to be evaluated relative to a surgeon's own ability to identify parathyroid glands. METHODS: Patients eligible for thyroidectomy and/or parathyroidectomy were enrolled under 6 endocrine surgeons at 3 high-volume institutions. Participating surgeons were categorized based on years of experience. All surgeons were blinded to output of PTeye® when identifying tissues. The surgeon's performance for parathyroid discrimination was then compared with PTeye®. Histology served as gold standard for excised specimens, while expert surgeon's opinion was used to validate in-situ tissues. RESULTS: PTeye® achieved 92.7% accuracy across 167 patients recruited. Junior surgeons (<5 years of experience) were found to have lower confidence in parathyroid identification and higher tissue misclassification rate per specimen when compared to PTeye® and senior surgeons (>10 years of experience). CONCLUSIONS: NIRAF detection with PTeye® can be a valuable intraoperative adjunct technology to aid in parathyroid identification for surgeons.

Development of an imaging device for label-free parathyroid gland identification and vascularity assessment.

During thyroid surgeries, it is important for surgeons to accurately identify healthy parathyroid glands and assess their vascularity to preserve their function postoperatively, thus preventing hypoparathyroidism and hypocalcemia. Near infrared autofluorescence detection enables parathyroid identification, while laser speckle contrast imaging allows assessment of parathyroid vascularity. Here, we present an imaging system combining the two techniques to perform both functions, simultaneously and label-free. An algorithm to automate the segmentation of a parathyroid gland in the fluorescence image to determine its average speckle contrast is also presented, reducing a barrier to clinical translation. Results from imaging ex vivo tissue samples show that the algorithm is equivalent to manual segmentation. Intraoperative images from representative procedures are presented showing successful implementation of the device to identify and assess vascularity of healthy and diseased parathyroid glands.

Developing a Clinical Prototype to Guide Surgeons for Intraoperative Label-Free Identification of Parathyroid Glands in Real Time.

BACKGROUND: Patients undergoing thyroidectomy may have inadvertent damage or removal of the parathyroid gland(s) due to difficulty in real-time parathyroid identification. Near-infrared autofluorescence (NIRAF) has been demonstrated as a label-free modality for intraoperative parathyroid identification with high accuracy. This study presents the translation of that approach into a user-friendly clinical prototype for rapid intraoperative guidance in parathyroid identification. METHODS: A laboratory (lab)-built spectroscopy system that measures NIRAF in tissue was evaluated for identifying parathyroid glands in vivo across 162 patients undergoing thyroidectomy and/or parathyroidectomy. Based on these results, a clinical prototype called PTeye was designed with a user-friendly interface and subsequently investigated in 35 patients. The performance of the lab-built system and the clinical prototype were concurrently compared side by side by a single user with 20 patients in each group. The influence of (i) intrapatient and interpatient variability of NIRAF in thyroid and parathyroid glands and (ii) thyroid and parathyroid pathology on intraoperative parathyroid identification were investigated. The effect of blood on NIRAF intensity of parathyroid and thyroid was tested ex vivo with the PTeye system to assess if a hemorrhagic surgical field would affect parathyroid identification. Accuracy of both systems were determined by correlating the acquired data with either visual confirmation by a surgeon for unexcised parathyroid glands or histology reports for excised parathyroid glands. RESULTS: The overall accuracy of the lab-built system in guiding parathyroid identification was 92.5%, while the PTeye system achieved an accuracy of 96.1%. Unlike the lab-built system, the PTeye could guide parathyroid identification even as the operating room lights remained on and required only 25% of the laser power used by the lab-built setup. Parathyroid glands had elevated NIRAF intensity compared to thyroid and other neck tissues, regardless of thyroid or parathyroid pathology. Blood did not seem to affect tissue NIRAF measurements obtained with both systems. CONCLUSION: In this study, the clinical prototype PTeye demonstrated high accuracy for label-free intraoperative parathyroid identification. The intuitive interface of the PTeye that can guide in identifying parathyroid tissue in the presence of ambient room lights suggests that it is a reliable and easy-to-use tool for surgical personnel.

Non-Invasive Monitoring of Temporal and Spatial Blood Flow during Bone Graft Healing Using Diffuse Correlation Spectroscopy.

Vascular infiltration and associated alterations in microvascular blood flow are critical for complete bone graft healing. Therefore, real-time, longitudinal measurement of blood flow has the potential to successfully predict graft healing outcomes. Herein, we non-invasively measure longitudinal blood flow changes in bone autografts and allografts using diffuse correlation spectroscopy in a murine femoral segmental defect model. Blood flow was measured at several positions proximal and distal to the graft site before implantation and every week post-implantation for a total of 9 weeks (autograft n = 7 and allograft n = 10). Measurements of the ipsilateral leg with the graft were compared with those of the intact contralateral control leg. Both autografts and allografts exhibited an initial increase in blood flow followed by a gradual return to baseline levels. Blood flow elevation lasted up to 2 weeks in autografts, but this duration varied from 2 to 6 weeks in allografts depending on the spatial location of the measurement. Intact contralateral control leg blood flow remained at baseline levels throughout the 9 weeks in the autograft group; however, in the allograft group, blood flow followed a similar trend to the graft leg. Blood flow difference between the graft and contralateral legs (ΔrBF), a parameter defined to estimate graft-specific changes, was elevated at 1-2 weeks for the autograft group, and at 2-4 weeks for the allograft group at the proximal and the central locations. However, distal to the graft, the allograft group exhibited significantly greater ΔrBF than the autograft group at 3 weeks post-surgery (p < 0.05). These spatial and temporal differences in blood flow supports established trends of delayed healing in allografts versus autografts.