Prognostic value of collateral perfusion estimation by arterial spin labeling for acute anterior circulation ischemic stroke.

PURPOSE: This study aimed to verify the value of arterial spin labeling (ASL) collateral perfusion estimation for predicting functional outcomes in acute anterior circulation ischemic stroke. METHODS: This secondary analysis of an ongoing prospective observational study included data from participants with acute ischemic stroke due to steno-occlusion of the internal carotid artery and/or the middle cerebral artery within 8 h of symptom onset. We compared the collateral map, which is a 5-phase collateral imaging derived from dynamic contrast-enhanced magnetic resonance angiography, and ASL to validate the ASL collateral perfusion estimation. Multiple logistic regression analyses were conducted to identify independent predictors of favorable functional outcomes. RESULTS: One hundred forty-eight participants (68 ± 13 years, 96 men) were evaluated. The ASL collateral perfusion grade was positively correlated with the collateral perfusion grade of the collateral map (P < .001). Younger age (OR = 0.53, 95% CI = 0.36-0.78, P = .002), lower baseline NIHSS score (OR = 0.85, 95% CI = 0.78-0.92, P < .001), intermediate ASL collateral perfusion grade (OR = 4.02, 95% CI = 1.43-11.26, P = .008), good ASL collateral perfusion grade (OR = 26.37, 95% CI = 1.06-655.01, P = .046), and successful reperfusion (OR = 5.84, 95% CI = 2.08-16.42, P < .001) were independently associated with favorable functional outcomes. CONCLUSION: ASL collateral perfusion estimation provides prognostic information, which can be helpful in guiding management decisions.

Subtle Cognitive Deficits Are Associated with Amyloid-ß Positivity, but Not Severity of Self-Reported Decline: Results from the CoSCo Study.

INTRODUCTION: Subjective cognitive decline (SCD) can be considered as the preclinical manifestation of Alzheimer's disease (AD). The National Institute on Aging and the Alzheimer's Association criteria for preclinical AD proposed that subtle cognitive changes appear along with AD biomarkers in the late stage of preclinical AD. The objective of this study was to explore whether subtle cognitive impairment (SCI) in individuals with SCD is associated with brain amyloid-ß (Aß) status and SCD severity. METHODS: One hundred twenty individuals with SCD (mean age: 70.87 ± 6.10 years) were included in this study. SCI was defined as performance ≤ -1.0 SD on at least two neuropsychological tests. Participants underwent an amyloid positron emission tomography, which was assessed visually and quantitatively using standardized uptake value ratio (SUVR). The severity of SCD was assessed using two self-reported questionnaires: the SCD questionnaire based on the SCD-plus features and the Korean-Everyday Cognition (K-ECog) scale. RESULTS: SCD individuals with SCI (n = 25) had more Aß positivity than the SCD only group (n = 95) (44% vs. 15.79%; p = 0.002). In addition, the SCI group had a higher global SUVR than the SCD only group (p = 0.048). For self-reported questionnaires, there were no differences in SCD questionnaire total scores and K-ECog global and cognitive domain-specific scores between two groups. CONCLUSIONS: In SCD individuals, SCI was associated with higher Aß positivity, but not with the severity of self-reported cognitive decline, compared to the SCD only group. These results suggest that the recognition of objectively defined subtle cognitive deficits may contribute to the early identification of AD in SCD.

Collateral and permeability imaging derived from dynamic contrast material-enhanced MR angiography in prediction of PH 2 hemorrhagic transformation after acute ischemic stroke: a pilot study.

PURPOSE: To evaluate the role of collateral and permeability imaging derived from dynamic contrast material-enhanced magnetic resonance angiography to predict PH 2 hemorrhagic transformation in acute ischemic stroke. METHODS: The secondary analysis of a published data from participants with acute ischemic stroke. The multiphase collateral map and permeability imaging were generated by using dynamic signals from dynamic contrast material-enhanced magnetic resonance angiography obtained at admission. To identify independent predictors of PH 2 hemorrhagic transformation, age, sex, risk factors, baseline National Institutes of Health Stoke Scale (NIHSS) score, baseline DWI lesion volume, collateral-perfusion status, mode of treatment, and successful early reperfusion were evaluated with multiple logistic regression analyses and the significance of permeability imaging in prediction of PH 2 hemorrhagic transformation was evaluated by subgroup analysis. RESULTS: In 115 participants, including 70 males (mean (SD) age, 69 (12) years), PH 2 hemorrhagic transformation occurred in 6 participants with very poor collateral-perfusion status (MAC 0). MAC 0 (OR, 0.06; 95% CI, 0.01, 0.74; P = .03) was independently associated with PH 2 hemorrhagic transformation. In 22 participants with MAC 0, the permeable signal on Kep permeability imaging was the only significant characteristic associated with PH 2 hemorrhagic transformation (P = .009). The specificity of Kep permeability imaging was 93.8% (95% confidence interval: 69.8, 99.8) in predicting PH 2 hemorrhagic transformation. CONCLUSION: Individual-based prediction of PH 2 hemorrhagic transformation in patients with acute ischemic stroke may be possible with multiphase collateral map and permeability imaging derived from dynamic contrast material-enhanced magnetic resonance angiography.

Multiphase MR Angiography Collateral Map: Functional Outcome after Acute Anterior Circulation Ischemic Stroke.

Background Collateral circulation determines tissue fate and affects treatment result in acute ischemic stroke. A precise method for collateral estimation in an optimal imaging protocol is necessary to make an appropriate treatment decision for acute ischemic stroke. Purpose To verify the value of multiphase collateral imaging data sets (MR angiography collateral map) derived from dynamic contrast material-enhanced MR angiography for predicting functional outcomes after acute ischemic stroke. Materials and Methods This secondary analysis of an ongoing prospective observational study included data from participants with acute ischemic stroke due to occlusion or stenosis of the unilateral internal carotid artery and/or M1 segment of the middle cerebral artery who were evaluated within 8 hours of symptom onset. Data were obtained from March 2016 through August 2018. The collateral grading based on the MR angiography collateral map was estimated by using six-scale MR acute ischemic stroke collateral (MAC) scores. To identify independent predictors of favorable functional outcomes, age, sex, risk factors, baseline National Institutes of Health Stroke Scale (NIHSS) score, baseline diffusion-weighted imaging (DWI) lesion volume, site of steno-occlusion, collateral grade, mode of treatment, and early reperfusion were evaluated with multiple logistic regression analyses. Results One hundred fifty-four participants (mean age ± standard deviation, 69 years ± 13; 99 men) were evaluated. Younger age (odds ratio [OR], 0.45; 95% confidence interval [CI]: 0.29, 0.70; P < .001), lower baseline NIHSS score (OR, 0.85; 95% CI: 0.78, 0.94; P < .001), MAC score of 3 (OR, 27; 95% CI: 4.0, 179; P < .001), MAC score of 4 (OR, 17; 95% CI: 2.1, 134; P = .007), MAC score of 5 (OR, 27; 95% CI: 2.5, 306; P = .007), and successful early reperfusion (OR, 7.5; 95% CI: 2.6, 22; P < .001) were independently associated with favorable functional outcomes in multivariable analysis. There was a linear negative association between collateral perfusion grades and functional outcomes (P < .001). Conclusion An MR angiography collateral map was clinically reliable for collateral estimation in patients with acute ischemic stroke. This map provided patient-specific pacing information for ischemic progression. © RSNA, 2020.

Self- and informant-reported cognitive functioning and awareness in subjective cognitive decline, mild cognitive impairment, and very mild Alzheimer disease.

OBJECTIVES: The present study examined self-reports and informant reports of cognitive function and discrepancies between the two reporting methods in healthy controls (HC), subjective cognitive decline (SCD), mild cognitive impairment (MCI), and very mild Alzheimer disease (AD) using three questionnaires. METHODS: The study included a total of 300 individuals (mean age: 74.4 ± 5.7 y), including 130 HC, 70 SCD, 51 MCI, and 49 very mild AD patients. Self-ratings and informant ratings of cognitive function were assessed using the Korean Dementia Screening Questionnaire-Cognition (KDSQ-C), AD8, and Subjective Memory Complaints Questionnaire (SMCQ). Awareness of cognitive functioning was measured on the basis of the discrepancy scores between self-reports and informant reports. RESULTS: Group comparisons on questionnaire scores adjusting for age, education, and depressive symptoms showed that self-reports were lowest in HC than other groups, with no differences between SCD and MCI groups. Informant reports were lower in SCD than in MCI, while discrepancy scores were higher in SCD than in MCI (P < .001 for KDSQ-C and SMCQ; P = .076 for AD8). There were no differences in self-reports, informant reports, and discrepancy scores between MCI and AD groups. CONCLUSIONS: These results support the usefulness of informant-reported cognitive functioning to classify MCI among elderly with subjective cognitive complaints. In addition, discrepancies between self-reports and informant reports demonstrate that overestimation and underestimation of cognitive function may serve as a clinical indicator of SCD and MCI across the cognitive continuum, respectively.

Design and simulation of novel laparoscopic renal denervation system: a feasibility study.

PURPOSE: In this study, we propose a novel laparoscopy-based renal denervation (RDN) system for treating patients with resistant hypertension. In this feasibility study, we investigated whether our proposed surgical instrument can ablate renal nerves from outside of the renal artery safely and effectively and can overcome the depth-related limitations of the previous catheter-based system with less damage to the arterial walls. METHOD: We designed a looped bipolar electrosurgical instrument to be used with laparoscopy-based RDN system. The tip of instrument wraps around the renal artery and delivers the radio-frequency (RF) energy. We evaluated the thermal distribution via simulation study on a numerical model designed using histological data and validated the results by the in vitro study. Finally, to show the effectiveness of this system, we compared the performance of our system with that of catheter-based RDN system through simulations. RESULTS: Simulation results were within the 95% confidence intervals of the in vitro experimental results. The validated results demonstrated that the proposed laparoscopy-based RDN system produces an effective thermal distribution for the removal of renal sympathetic nerves without damaging the arterial wall and addresses the depth limitation of catheter-based RDN system. CONCLUSIONS: We developed a novel laparoscope-based electrosurgical RDN method for hypertension treatment. The feasibility of our system was confirmed through a simulation study as well as in vitro experiments. Our proposed method could be an effective treatment for resistant hypertension as well as central nervous system diseases.

Hippocampal and entorhinal structures in subjective memory impairment: a combined MRI volumetric and DTI study.

BACKGROUND: Subjective memory impairment (SMI) is common among older adults. Increasing evidence suggests that SMI is a risk factor for future cognitive decline, as well as for mild cognitive impairment and dementia. Medial temporal lobe structures, including the hippocampus and entorhinal cortex, are affected in the early stages of Alzheimer's disease. The current study examined the gray matter (GM) volume and microstructural changes of hippocampal and entorhinal regions in individuals with SMI, compared with elderly control participants without memory complaints. METHODS: A total of 45 participants (mean age: 70.31 ± 6.07 years) took part in the study, including 18 participants with SMI and 27 elderly controls without memory complaints. We compared the GM volume and diffusion tensor imaging (DTI) measures in the hippocampal and entorhinal regions between SMI and control groups. RESULTS: Individuals with SMI had lower entorhinal cortical volumes than control participants, but no differences in hippocampal volume were found between groups. In addition, SMI patients exhibited DTI changes (lower fractional anisotropy (FA) and higher mean diffusivity in SMI) in the hippocampal body and entorhinal white matter compared with controls. Combining entorhinal cortical volume and FA in the hippocampal body improved the accuracy of classification between SMI and control groups. CONCLUSIONS: These findings suggest that the entorhinal region exhibits macrostructural as well as microstructural changes in individuals with SMI, whereas the hippocampus exhibits only microstructural alterations.

The Influence of Flush Methods on Transfemoral Catheter Cerebral Angiography: Continuous Flush versus Intermittent Flush.

PURPOSE: To evaluate the influence of different flush methods on transfemoral cerebral angiography (TFCA). MATERIALS AND METHODS: This single-blind randomized controlled trial included 50 patients who had undergone TFCA. Balanced block randomization was used to allocate participants into intermittent-flush (n = 25) and continuous-flush (n = 25) groups. Differences in procedure duration, amounts of contrast medium and heparinized saline used, heparin dose, blood loss, fluoroscopy time, radiation dose, and occurrence of new embolic signal (NES) on diffusion-weighted imaging (DWI) were compared between the two groups. RESULTS: The procedure duration was shorter in the continuous-flush group (mean 26.5 min ± 3.7) than in the intermittent-flush group (mean 29.6 min ± 2.8) (P = .004). Amounts of injected contrast medium (mean 20.2 mL ± 4.4 vs 57.1 mL ± 9.0), wasted heparinized saline (mean 19.8 mL ± 9.6 vs 92.3 mL ± 16.7), and aspirated blood (mean 4.7 mL ± 1.3 vs 13.2 mL ± 2.9) were lower in the continuous-flush group than in the intermittent-flush group (P < .001). The amount of injected (or infused) heparinized saline, heparin dose, fluoroscopy time, radiation dose, and occurrence of NES on DWI did not differ between the groups (P > .05). CONCLUSIONS: The use of continuous flushing during TFCA reduced the procedure time, amount of contrast medium needed, amount of wasted heparinized saline, and blood loss, but no difference in the occurrence of NES on DWI was noted between the groups.

Subjective memory complaints, depressive symptoms and instrumental activities of daily living in mild cognitive impairment.

BACKGROUND: The diagnostic relevance of subjective memory complaints (SMCs) in mild cognitive impairment (MCI) remains to be unresolved. The aim of this study is to determine clinical correlates of SMCs in MCI. Furthermore, we examined whether there are the differences due to different aspects of complaints (i.e. prospective memory (PM) versus retrospective memory (RM) complaints). METHODS: We examined the cross-sectional associations between SMCs and depressive symptoms, instrumental activities of daily living (IADL), and cognitive measures in sixty-six individuals with MCI (mean age: 65.7 ± 8.01 years). The criteria for MCI included SMCs, objective cognitive impairment, normal general cognitive function, largely intact functional activities, and absence of dementia. SMCs were assessed using the Prospective and Retrospective Memory Questionnaire (PRMQ), which contains 16 items describing everyday memory failure of both PM and RM. RESULTS: SMC severity (i.e. PRMQ total score) was associated with stronger depressive symptoms and worse IADL performance. SMCs were not related to cognitive measures. For PM and RM subscores, both depressive symptoms and IADL were related to the PRMQ-PM and -RM scores. The main contributors to these PM and RM scores were depressive symptoms and IADL impairment, respectively. CONCLUSIONS: This study suggests that SMCs are more associated with depressive symptoms and IADL problems than with cognitive performance in individuals with MCI. Furthermore, while PM and RM complaints are related to both depressive symptoms and IADL, the differences between these main contributors suggest that RM complaints based on IADL could be more associated with the organically driven pathological features of MCI.

High-speed thermoreflectance microscopy using charge-coupled device-based Fourier-domain filtering.

We present a Fourier-domain filtering method for charge-coupled device (CCD)-based thermoreflectance microscopy to improve the thermal imaging speed while maintaining high thermal sensitivity. The time-varying reflected light distribution from the surface of bias-modulated microresistor was recorded by a CCD camera in free-run mode and converted to the frequency domain using the fast Fourier transform (FFT) for all pixels of the CCD. After frequency peak filtering followed by inverse FFT, a thermoreflectance image was obtained. The imaging results of the proposed method were quantitatively compared with those of the conventional four-bucket method, showing that the Fourier-domain filtering method can provide thermal imaging 24-42 times faster than the four-bucket method, depending on the required thermal sensitivity.

Fast mapping of absorbing defects in optical materials by full-field photothermal reflectance microscopy.

We report a technique for rapidly mapping absorbing defects in optical materials, which act as laser-induced damage precursors, based on full-field photothermal reflectance microscopy. An intensity-modulated pump beam heats absorbing defects in the optical sample, creating localized, modulated refractive-index variations around the defects. A probe beam then illuminates the defect sites, and the measured amplitude of the reflectance variation is used to map the distribution of defects in the medium. Measurements show that this method offers a faster defect mapping speed of about 0.03 mm(2) per minute and a detectivity of a few tens of nanometers comparable to that of conventional scanning photothermal deflection microscopy.

Precise temperature mapping of GaN-based LEDs by quantitative infrared micro-thermography.

A method of measuring the precise temperature distribution of GaN-based light-emitting diodes (LEDs) by quantitative infrared micro-thermography is reported. To reduce the calibration error, the same measuring conditions were used for both calibration and thermal imaging; calibration was conducted on a highly emissive black-painted area on a dummy sapphire wafer loaded near the LED wafer on a thermoelectric cooler mount. We used infrared thermal radiation images of the black-painted area on the dummy wafer and an unbiased LED wafer at two different temperatures to determine the factors that degrade the accuracy of temperature measurement, i.e., the non-uniform response of the instrument, superimposed offset radiation, reflected radiation, and emissivity map of the LED surface. By correcting these factors from the measured infrared thermal radiation images of biased LEDs, we determined a precise absolute temperature image. Consequently, we could observe from where the local self-heat emerges and how it distributes on the emitting area of the LEDs. The experimental results demonstrated that highly localized self-heating and a remarkable temperature gradient, which are detrimental to LED performance and reliability, arise near the p-contact edge of the LED surface at high injection levels owing to the current crowding effect.

Microlensed dual-fiber probe for depth-resolved fluorescence measurements.

We propose and demonstrate a compact microlensed dual-fiber probe that has a good collection efficiency and a high depth-resolution ability for fluorescence measurements. The probe is formed with a conventional fusion splicer creating a common focusing lens on two fibers placed side by side. The collection efficiency of the fabricated probe was evaluated by measuring the fluorescence signal of a fresh ginkgo leaf. It was shown experimentally that the proposed probe could effectively collect the fluorescence signal with a six-fold increase compared to that of a general flat-tipped probe. The beam propagation method was used to design a probe with an optimized working distance and an improved resolving depth. It was found that the working distance depends mainly on the radius of curvature of the lens, whereas the resolving depth is determined by the core diameters of the illumination and collection fibers. The depth-resolved ability of probes with working distances of ~100 µm and 300 µm was validated by using a two-layer tissue phantom. The experimental results demonstrate that the microlensed dual-fiber probe has the potential to facilitate depth-resolved fluorescence detection of epithelial tissue.

Nonlinear endomicroscopy using a double-clad fiber coupler.

A double-clad fiber coupler is developed to be used in two-photon-excited fluorescence endomicroscopy to replace a dichroic mirror and separate the fluorescence signal from the excitation laser beam. With the double-clad fiber coupler, the endomicroscope becomes more compact, easier to be aligned, and more stable in alignment. The double-clad fiber coupler can transmit 62% of the excitation laser beam through the core. The fluorescence collection efficiency of the double-clad fiber coupler is 34%, which is, to the best of our knowledge, the highest fluorescence collection efficiency achieved by couplers used in two-photon-excited fluorescence endomicroscopes. As a result, the contrast of endomicroscopy imaging is enhanced.

Ultrawideband photonic crystal fiber coupler for multiband optical imaging system.

We report a photonic crystal fiber (PCF) coupler having an ultrawide spectral bandwidth keeping single mode operation. The use of the PCF coupler in a fiber-based optical coherence tomography (OCT) system enables us to handle the wide spectral bands of various light sources, including superluminescent diodes (SLDs) at 1300 nm and 820 nm, Ti:sapphire lasers, and white-light sources. The multiband imaging performances of the PCF-based OCT system are demonstrated by obtaining dental images at 1300 nm and 820 nm with the same setup. In addition, we show that the PCF coupler could cover the spectrum over a one octave span and guide both the fundamental wave (1030 nm) and the second harmonic wave (515 nm) simultaneously.

Coexistence of Cerebral Microbleeds and Amyloid Pathology in Patients with Cognitive Complaints.

BACKGROUND AND PURPOSE: We investigated the prevalence of amyloid positivity and cerebral microbleeds (CMBs) in subjects with cognitive complaints with the aim of identifying differences in clinical parameters and cognitive function according to the pattern of coexistence. METHODS: We retrospectively enrolled 200 subjects with memory impairment and applied both standardized ¹8F-florbetaben PET and brain MRI, including susceptibility-weighted imaging. The amyloid burden was visually classified as positive or negative, and the number and location of CMBs were also analyzed visually. Descriptive analysis was performed for the prevalence of amyloid positivity and CMBs. The relationship between the coexisting pattern of those two findings and clinical parameters including the results of neuropsychiatric tests was analyzed. RESULTS: Positive amyloid PET scans were exhibited by 102 (51.5%) of the 200 patients, and 51 (25.5%) of them had CMBs, which were mostly located in lobar areas in the patients with positive amyloid scans. The patients with CMBs were older and had a higher burden of white-matter hyperintensities than the patients without CMBs. The patients with CMBs also performed worse in confrontation naming and frontal/executive function. When classified by topographical region, parietal CMBs (odds ratio=3.739, p=0.024) were significantly associated with amyloid positivity. CONCLUSIONS: The prevalence of CMBs was higher in patients with cognitive decline than in the general population. CMBs play distinctive roles in affecting clinical parameters and neuropsychological profiles according to the coexistence of amyloid pathology.

Are plasma homocysteine levels related to neurological severity and functional outcome after ischemic stroke in the Korean population?

Hyperhomocysteinemia is known to be an independent risk factor for arteriosclerosis. However, the prognosis of functional disability in cerebrovascular disease has not been well established. Therefore, we conducted this study to determine the prognostic significance of plasma homocysteine (Hcy) levels in Asian patients with functional disabilities after acute ischemic stroke. A total of 267 patients were examined within 24 h after symptom onset. Hcy was measured at admission. The correlations between plasma Hcy concentration and functional disability at 1-month, 3-months, 6-months, and 12-months after stroke onset were analyzed. In addition, the associations between each risk factor for stroke or neurological severity and plasma Hcy level were evaluated. The results of the present study showed that there was no significant correlation between Hcy level on admission and modified Rankin Scale score obtained at 1-month, 3-months, 6-months, and 12-months after stroke onset. There was also no association between plasma Hcy level and neurological severity after stroke or stroke subtype. This study showed that there is no association between Hcy levels and functional outcome after stroke. Therefore, we cautiously assert that plasma Hcy levels have no value as predictors of functional disability in Asian patients with stroke.

The relationship between low bone mineral density and Parkinson's disease in a Korean population.

There have been few studies concerning osteoporosis in patients with Parkinson's disease (PD), even though patients with PD have a high incidence of falls. Using a Korean population, we investigated the association between bone mineral density (BMD) and PD. A total of 107 patients with PD were compared with age-matched and sex-matched normal controls. Using the Hoehn & Yahr staging system, we classified the patients with PD into three subgroups. Parts II and III of the Unified Parkinson's Disease Rating Scale were administered to evaluate the relationship between the severity of PD and BMD. In conclusion, in the PD population we found that decreased BMD was related to the severity of immobility of patients, and that BMD changes were greater at the femoral neck than the spine area. Therefore, we assert that clinicians should consider administering screening tests to elderly patients with PD and provide appropriate primary or secondary prophylactic treatment for osteoporosis.

Different Cortical Thinning Patterns Depending on Their Prognosis in Individuals with Subjective Cognitive Decline.

BACKGROUND AND PURPOSE: Subjective cognitive decline (SCD) may be the first stage corresponding to subtle cognitive changes in patients with Alzheimer's disease (AD) spectrum disorders. We evaluated the differences in cortical thinning patterns among patients with SCD who progressed to mild cognitive impairment or dementia (pSCD), those who remained stable (sSCD), and healthy normal controls (NCs). METHODS: We retrospectively recruited SCD subjects (14 pSCD and 21 sSCD cases) and 29 NCs. Structural 3-dimensional-T1-weighted magnetic resonance imaging was performed using a single 1.5 Tesla scanner. Freesurfer software was used to map cortical thickness for group comparisons. RESULTS: Compared with NC group, the sSCD group showed diffuse cortical atrophy associated with bilateral fronto-parieto-temporal area. The pSCD group showed further characteristic cortical atrophy in AD-vulnerable regions including the inferior parieto-temporal and middle temporal areas. Cortical thinning in the bilateral medial frontal areas was observed in patients with sSCD and involved the right inferior temporal and left precentral areas in those with pSCD. CONCLUSIONS: Our study showed that SCD subjects exhibit different cortical thinning patterns depending on their prognosis.

See-Through Type 3D Head-Mounted Display-Based Surgical Microscope System for Microsurgery: A Feasibility Study.

BACKGROUND: The surgical microscope is used primarily for microsurgeries, which are more complicated than other surgical procedures and require delicate tasks for a long time. Therefore, during these surgical procedures, surgeons experience back and neck pain. To solve this problem, new technology, such as wearable displays, is required to help surgeons maintain comfortable postures and enjoy advanced functionality during microsurgery. OBJECTIVE: The objective of this study was to develop a surgical microscope system that would work with wearable devices. It would include a head-mounted display (HMD) that can offer 3D surgical images and allow a flexible and comfortable posture instead of fixed eyepieces of surgical microscope and can also provide peripheral visual field with its optical see-through function. METHODS: We designed and fabricated a surgical microscope system that incorporates a see-through type 3D HMD, and we developed an image processing software to provide better image quality. The usability of the proposed system was confirmed with preclinical examination. Seven ENT (ear, nose, and throat) surgical specialists and 8 residents performed a mock surgery-axillary lymph node dissection on a rat. They alternated between looking through the eyepieces of the surgical microscope and viewing a 3D HMD screen connected to the surgical microscope. We examined the success of the surgery and asked the specialists and residents to grade eye fatigue on a scale of 0 (none) to 6 (severe) and posture discomfort on a scale of 1 (none) to 5 (severe). Furthermore, a statistical comparison was performed using 2-tailed paired t test, and P=.00083 was considered significant. RESULTS: Although 3D HMD case showed a slightly better result regarding visual discomfort (P=.097), the average eye fatigue was not significantly different between eyepiece and 3D HMD cases (P=.79). However, the average posture discomfort, especially in neck and shoulder, was lower with 3D HMD display use than with eyepiece use (P=.00083). CONCLUSIONS: We developed a see-through type 3D HMD-based surgical microscope system and showed through preclinical testing that the system could help reduce posture discomfort. The proposed system, with its advanced functions, could be a promising new technique for microsurgery.