A mathematical model for velocity-selective arterial spin labeling.

PURPOSE: To present a theoretical framework that rigorously defines and analyzes key concepts and quantities for velocity selective arterial spin labeling (VSASL). THEORY AND METHODS: An expression for the VSASL arterial delivery function is derived based on (1) labeling and saturation profiles as a function of velocity and (2) physiologically plausible approximations of changes in acceleration and velocity across the vascular system. The dependence of labeling efficiency on the amplitude and effective bolus width of the arterial delivery function is defined. Factors that affect the effective bolus width are examined, and timing requirements to minimize quantitation errors are derived. RESULTS: The model predicts that a flow-dependent negative bias in the effective bolus width can occur when velocity selective inversion (VSI) is used for the labeling module and velocity selective saturation (VSS) is used for the vascular crushing module. The bias can be minimized by choosing a nominal labeling cutoff velocity that is lower than the nominal cutoff velocity of the vascular crushing module. CONCLUSION: The elements of the model are specified in a general fashion such that future advances can be readily integrated. The model can facilitate further efforts to understand and characterize the performance of VSASL and provide critical theoretical insights that can be used to design future experiments and develop novel VSASL approaches.

Canine Descemet Stripping Endothelial Keratoplasty with a Tissue Insertion Device: Technique and Long-Term Outcome.

Introduction. We describe a case of canine Descemet's stripping endothelial keratoplasty (DSEK) using an open-source canine tissue delivery device. Case Presentation. We follow the four-year outcomes of a 1.5-year-old Tibetan Terrier who presented with difficulty seeing, diffuse corneal edema, and central corneal thickness of 1400 microns in the left eye. To perform DSEK, a polycarbonate carrier and insertion device was designed for canine corneas that measure up to 15 mm in diameter. The tissue was loaded into the inserter prior to surgery with the endothelium facing inwards and the stroma facing the cartridge wall. From the cartridge, the graft was pulled into the eye using microforceps and an anterior chamber maintainer. We assessed preoperative endothelial cell count, postoperative corneal clearance, and graft adhesion. The donor was a two-year-old Airedale Terrier who died one day prior to surgery, with endothelial cell density of 3149 cells/mm2. One week after DSEK, the cornea began to clear, and pachymetry of the donor and graft total was 1410 microns. This improved to 800 microns at 4 months and continued improving in its clarity at the last postoperative visit 4 years after surgery. Discussion. We demonstrate the feasibility of conducting canine endothelial keratoplasty with a specially designed tissue delivery device and the potential of long-term corneal clearance after DSEK in canine eyes.

WITHDRAWN: I feel your pain: Higher empathy is associated with higher posterior default mode network activity.

The authors discovered an error in the primary analysis and have withdrawn the results from this version of the investigation.

Greater accelerometer-measured physical activity is associated with better cognition and cerebrovascular health in older adults.

OBJECTIVES: Physical activity (PA) may help maintain brain structure and function in aging. Since the intensity of PA needed to effect cognition and cerebrovascular health remains unknown, we examined associations between PA and cognition, regional white matter hyperintensities (WMH), and regional cerebral blood flow (CBF) in older adults. METHOD: Forty-three older adults without cognitive impairment underwent magnetic resonance imaging (MRI) and comprehensive neuropsychological assessment. Waist-worn accelerometers objectively measured PA for approximately one week. RESULTS: Higher time spent in moderate to vigorous PA (MVPA) was uniquely associated with better memory and executive functioning after adjusting for all light PA. Higher MVPA was also uniquely associated with lower frontal WMH volume although the finding was no longer significant after additionally adjusting for age and accelerometer wear time. MVPA was not associated with CBF. Higher time spent in all light PA was uniquely associated with higher CBF but not with cognitive performance or WMH volume. CONCLUSIONS: Engaging in PA may be beneficial for cerebrovascular health, and MVPA in particular may help preserve memory and executive function in otherwise cognitively healthy older adults. There may be differential effects of engaging in lighter PA and MVPA on MRI markers of cerebrovascular health although this needs to be confirmed in future studies with larger samples. Future randomized controlled trials that increase PA are needed to elucidate cause-effect associations between PA and cerebrovascular health.

Effects of Sub-threshold Transcutaneous Auricular Vagus Nerve Stimulation on Cingulate Cortex and Insula Resting-state Functional Connectivity.

Transcutaneous auricular vagus nerve stimulation (taVNS), a non-invasive alternative to vagus nerve stimulation (VNS) with implantable devices, has shown promise in treating disorders such as depression, migraine, and insomnia. Studies of these disorders with resting-state functional magnetic resonance imaging (MRI) (rsfMRI) have found sustained changes in resting-state functional connectivity (rsFC) in patients treated with low frequency (1-20 Hz) taVNS. A recent study has reported reductions in pain scores in patients with rheumatoid arthritis after a 12-week treatment of high-frequency (20 kHz) sub-threshold taVNS. However, no studies to date have examined the effects of high-frequency sub-threshold taVNS on rsFC. The objective of this study was to determine whether high-frequency sub-threshold taVNS induces changes in rsFC using seed regions from the cingulate cortex and insula, brain regions that play a key role in interoception and processing of pain. With a single-blind placebo-controlled repeated measures experimental design, rsfMRI scans were acquired before and after 15 min of either sub-threshold taVNS treatment or a sham control. Significant taVNS-related changes in functional connections to the cingulate cortex were detected between the anterior cingulate cortex and right superior temporal gyrus and between the midcingulate cortex and right inferior parietal lobule. In addition, significant changes in functional connections to the insula were detected between the posterior insula and right precuneus and between the anterior insula and right cuneus gyrus. These results suggest that high-frequency sub-threshold taVNS can lead to sustained effects on the rsFC of brain regions involved in interoception and processing of pain in a cohort of healthy subjects. This study lays the foundation for future rsfMRI studies of high-frequency sub-threshold taVNS in clinical populations.

A Surgical Kit for Stem Cell-Derived Retinal Pigment Epithelium Transplants: Collection, Transportation, and Subretinal Delivery.

Transplantation of stem cell-derived retinal pigment epithelium (RPE) cells is a promising potential therapy for currently incurable retinal degenerative diseases like advanced dry age-related macular degeneration. In this study, we designed a set of clinically applicable devices for subretinal implantation of RPE grafts, towards the overarching goal of establishing enabling technologies for cell-based therapeutic approaches to regenerate RPE cells. This RPE transplant kit includes a custom-designed trephine for the production of RPE transplants, a carrier for storage and transportation, and a surgical device for subretinal delivery of RPE transplants. Cell viability assay confirmed biocompatibility of the transplant carrier and high preservation of RPE transplants upon storage and transportation. The transplant surgical device combines foldable technology that minimizes incision size, controlled delivery speed, no fluid reflux, curved translucent tip, usability of loading and in vivo reloading, and ergonomic handle. Furthermore, the complementary design of the transplant carrier and the delivery device resulted in proper grasping, loading, and orientation of the RPE transplants into the delivery device. Proof-of-concept transplantation studies in a porcine model demonstrated no damage or structural change in RPE transplants during surgical manipulation and subretinal deployment. Post-operative assessment confirmed that RPE transplants were delivered precisely, with no damage to the host retina or choroid, and no significant structural change to the RPE transplants. Our novel surgical kit provides a comprehensive set of tools encompassing RPE graft manufacturing to surgical implantation rendering key enabling technologies for pre-clinical and clinical phases of stem cell-derived RPE regenerative therapies.

Effects of sub-threshold transcutaneous auricular vagus nerve stimulation on cerebral blood flow.

Transcutaneous auricular vagus nerve stimulation (taVNS) has shown promise as a non-invasive alternative to vagus nerve stimulation (VNS) with implantable devices, which has been used to treat drug-resistant epilepsy and treatment-resistant depression. Prior work has used functional MRI to investigate the brain response to taVNS, and more recent work has also demonstrated potential therapeutic effects of high-frequency sub-threshold taVNS in rheumatoid arthritis. However, no studies to date have measured the effects of high-frequency sub-threshold taVNS on cerebral blood flow (CBF). The objective of this study was to determine whether high-frequency (20 kHz) sub-threshold taVNS induces significant changes in CBF, a promising metric for the assessment of the sustained effects of taVNS. Arterial spin labeling (ASL) MRI scans were performed on 20 healthy subjects in a single-blind placebo-controlled repeated measures experimental design. The ASL scans were performed before and after 15 min of either sub-threshold taVNS treatment or a sham control. taVNS induced significant changes in CBF in the superior posterior cerebellum that were largely localized to bilateral Crus I and Crus II. Post hoc analyses showed that the changes were driven by a treatment-related decrease in CBF. Fifteen minutes of high-frequency sub-threshold taVNS can induce sustained CBF decreases in the bilateral posterior cerebellum in a cohort of healthy subjects. This study lays the foundation for future studies in clinical populations, and also supports the use of ASL measures of CBF for the assessment of the sustained effects of taVNS.

Large-scale phenotypic drug screen identifies neuroprotectants in zebrafish and mouse models of retinitis pigmentosa.

Retinitis pigmentosa (RP) and associated inherited retinal diseases (IRDs) are caused by rod photoreceptor degeneration, necessitating therapeutics promoting rod photoreceptor survival. To address this, we tested compounds for neuroprotective effects in multiple zebrafish and mouse RP models, reasoning drugs effective across species and/or independent of disease mutation may translate better clinically. We first performed a large-scale phenotypic drug screen for compounds promoting rod cell survival in a larval zebrafish model of inducible RP. We tested 2934 compounds, mostly human-approved drugs, across six concentrations, resulting in 113 compounds being identified as hits. Secondary tests of 42 high-priority hits confirmed eleven lead candidates. Leads were then evaluated in a series of mouse RP models in an effort to identify compounds effective across species and RP models, that is, potential pan-disease therapeutics. Nine of 11 leads exhibited neuroprotective effects in mouse primary photoreceptor cultures, and three promoted photoreceptor survival in mouse rd1 retinal explants. Both shared and complementary mechanisms of action were implicated across leads. Shared target tests implicated parp1-dependent cell death in our zebrafish RP model. Complementation tests revealed enhanced and additive/synergistic neuroprotective effects of paired drug combinations in mouse photoreceptor cultures and zebrafish, respectively. These results highlight the value of cross-species/multi-model phenotypic drug discovery and suggest combinatorial drug therapies may provide enhanced therapeutic benefits for RP patients.

Photoreceptors are the cells responsible for vision. They are part of the retina: the light-sensing tissue at the back of the eye. They come in two types: rods and cones. Rods specialise in night vision, while cones specialise in daytime colour vision. The death of these cells can cause a disease, called retinitis pigmentosa, that leads to vision loss. Symptoms often start in childhood with a gradual loss of night vision. Later on, loss of cone photoreceptors can lead to total blindness. Unfortunately, there are no treatments available that protect photoreceptor cells from dying. Research has identified drugs that can protect photoreceptors in animal models, but these drugs have failed in humans. The classic way to look for new treatments is to find drugs that target molecules implicated in a disease, and then test them to see if they are effective. Unfortunately, many drugs identified in this way fail in later stages of testing, either because they are ineffective, or because they have unacceptable side effects. One way to reverse this trend is to first test whether a drug is effective at curing a disease in animals, and later determining what it does at a molecular level. This could reveal whether drugs can protect photoreceptors before research to discover their molecular targets begins. Tests like this across different species could maximise the chances of finding a drug that works in humans, because if a drug works in several species, it is more likely to have shared target molecules across species. Applying this reasoning, Zhang et al. tested around 3,000 drug candidates for treating retinitis pigmentosa in a strain of zebrafish that undergoes photoreceptor degeneration similar to the human disease. Most of these drug candidates already have approval for use in humans, meaning that if they were found to be effective for treating retinitis pigmentosa, they could be fast-tracked for use in people. Zhang et al. found three compounds that helped photoreceptors survive both in zebrafish and in retinas grown in the laboratory derived from a mouse strain with degeneration similar to retinitis pigmentosa. Tests to find out how these three compounds worked at the molecular level revealed that they interfered with a protein that can trigger cell death. The tests also found other promising compounds, many of which offered increased protection when combined in pairs. Worldwide there are between 1.5 and 2.5 million people with retinitis pigmentosa. With this disease, loss of vision happens slowly, so identifying drugs that could slow or stop the process could help many people. These results suggest that placing animal testing earlier in the drug discovery process could complement traditional target-based methods. The compounds identified here, and the information about how they work, could expand potential treatment research. The next step in this research is to test whether the drugs identified by Zhang et al. protect mammals other than mice from the degeneration seen in retinitis pigmentosa.

Viability of preloaded Descemet membrane endothelial keratoplasty grafts with 96-hour shipment.

OBJECTIVE: To assess feasibility and compare the effects of 96-hour shipment of Descemet membrane endothelial keratoplasty (DMEK) grafts as a scroll or a tri-fold on cell viability. METHODS AND ANALYSIS: DMEK grafts were prepared at the Rocky Mountain Lions Eye Bank. Twenty pre-stripped DMEK grafts, paired from 10 donors, were either tri-folded in an endothelium-in configuration using microforceps and loaded into a plastic Treyetech cartridge, or suctioned in a scrolled endothelium-out configuration into a modified Jones Tube. Grafts were shipped via FedEx to a secondary location and back for 48 hours each way, resulting in a total shipping time of 96 hours. After shipping, grafts were removed from inserters onto glass slides and unfolded using viscoelastic with endothelium facing upwards. Calcein-AM stained grafts were imaged with a fluorescent microscope and endothelial cell loss (ECL) was measured using trainable segmentation in Fiji by a masked grader. RESULTS: A total of 20 grafts were shipped for 96 hours, split between preloaded tri-folded (n=10) and preloaded scrolled (n=10) tissues. No significant difference in ECL was observed across groups after prolonged shipping (14.8% vs 13.7% ECL respectively, p=0.68). CONCLUSION: For preloaded DMEK after 96 hours, both scrolled and tri-folded tissue demonstrated clinically acceptable levels of ECL. The data suggest a wider window of time for endothelial cell viability and is promising for the prospect of international shipment of preloaded grafts.

Defining Hypoperfusion in Chronic Aphasia: An Individualized Thresholding Approach.

Within the aphasia literature, it is common to link location of lesioned brain tissue to specific patterns of language impairment. This has provided valuable insight into the relationship between brain structure and function, but it does not capture important underlying alterations in function of regions that remain structurally intact. Research has demonstrated that in the chronic stage of aphasia, variable patterns of reduced cerebral blood flow (CBF; hypoperfusion) in structurally intact regions of the brain contribute to persisting language impairments. However, one consistent issue in this literature is a lack of clear consensus on how to define hypoperfusion, which may lead to over- or underestimation of tissue functionality. In the current study, we conducted an exploratory analysis in six individuals with chronic aphasia (>1 year post-onset) using perfusion imaging to (1) suggest a new, individualized metric for defining hypoperfusion; (2) identify the extent of hypoperfused tissue in perilesional bands; and (3) explore the relationship between hypoperfusion and language impairment. Results indicated that our individualized metric for defining hypoperfusion provided greater precision when identifying functionally impaired tissue and its effects on language function in chronic aphasia. These results have important implications for intervention approaches that target intact (or impaired) brain tissue.

Association of Federal Regulations in the United States and Canada With Potential Corneal Donation by Men Who Have Sex With Men.

Importance: Federal policy in the United States prohibits corneal donation by men who have had sex with another man (MSM) in the preceding 5 years, whereas Canada enforces a 12-month ban. The potential consequences of these policies on corneal donations should be evaluated. Objective: To estimate the number of potential corneal donations associated with MSM deferral policies in the United States and Canada. Design, Setting, and Participants: A nonvalidated telephone survey study was conducted of all 65 eye banks in the United States and Canada to investigate how many potential corneal donors were disqualified in 2018 because of federal MSM restrictions. Published demographic data were also used to arrive at a separate estimate. Survey data were gathered from May 2019 to February 2020. Main Outcomes and Measures: Eye banks were asked if they keep records of referrals disqualified specifically because of the federal MSM restrictions and, if so, how many referrals they disqualified in 2018 owing to MSM status. Results: Fifty-four of 65 eye banks (83%) responded to the survey, with 30 eye banks reporting they do not keep specific records of MSM deferrals. The remaining 24 eye banks reported disqualifying 360 referrals in 2018 because of MSM status, equating to 720 corneas. The 24 eye banks accounted for 46.2% of corneal donations in the United States and Canada in 2018, yielding an estimate of approximately 1558 corneas rejected that year because of MSM status. A separate estimate using published MSM demographic data indicates that up to 3217 potential corneal donations may have been disqualified in 2018 because of these federal policies. Conclusions and Relevance: Findings suggest that between 1558 and 3217 corneal donations were disqualified in 2018 because of federal regulations prohibiting corneal donation by men who have had sex with another man in the preceding 5 years in the United States or 1 year in Canada. With modern virologic testing that is reliable within days of HIV exposure and given the global shortage of corneal tissue, these policies should be reevaluated using current scientific evidence to increase the availability of vision-restoring surgery worldwide.

Preloading Trifolded Grafts for Descemet Membrane Endothelial Keratoplasty Affects Scroll Formation.

PURPOSE: The trifolded, endothelium-in approach to Descemet membrane endothelial keratoplasty (DMEK) facilitates tissue insertion into the anterior chamber. We hypothesized that preloading the trifolded donor grafts in a cartridge for 48 hours before insertion would induce biomechanical changes that decrease their scrolling tendency compared with those loaded immediately before insertion. METHODS: Ten Descemet membrane donor grafts, peeled and cut to 8.0 mm, were prepared by a single eye bank technician. Each graft was trifolded and pulled into a DMEK cartridge and stored for 48 hours. They were then pulled with microforceps into a petri dish filled with balanced salt solution. A video was recorded of the graft becoming a scroll over a 2-minute period. Each graft, serving as its own control, was then trifolded, pulled into the cartridge, and the process repeated. Images from 1, 5, 10, 60, and 120 seconds were extracted from video recording of the procedures. Scroll width was analyzed by graders masked to group assignment. A paired t test was used to determine differences in scroll width at each time point between the 48-hour and instant trifolding conditions. RESULTS: All grafts scrolled after removal from the cartridge into balanced salt solution. We measured a significant difference at all time points 1 through 120 seconds (4.02 preloaded vs. 2.91-mm instant trifold, P = 0.035). CONCLUSIONS: Preloading DMEK grafts in a trifolded configuration for 48 hours reduces the scrolling tendency of Descemet membrane for at least 2 minutes.

Aspiration of Tri-folded, Endothelium-In Grafts for Descemet Membrane Endothelial Keratoplasty.

PURPOSE: In Descemet membrane endothelial keratoplasty (DMEK), loading and positioning of tri-folded grafts into a cartridge is generally conducted with forceps or a hook, risking graft tear or trauma. We demonstrate the feasibility of loading tri-folded grafts into a cartridge with no touch to the endothelium required beyond the tri-folding process. METHODS: A corneoscleral rim with a prestripped DMEK graft is placed into a petri dish. After the graft is tri-folded with forceps and removed from its stromal attachment, the graft is gently wicked into the tip of a saline-filled Alcon B IOL cartridge connected to IV extension tubing and a 3 cc syringe, drawn into the cartridge by positioning it adjacent to the graft tip. The remainder of the graft is aspirated with the addition of saline. The cartridge orientation is reversed for graft injection. In this retrospective analysis, we analyzed surgical videos for preparation times, and assessed postoperative visual acuity, pachymetry, and endothelial cell density. RESULTS: Thirteen cases underwent this approach. Median preparation time from stain to cartridge eye contact was 8.5 minutes, and time from graft injection to final centration and bubbling was 2.9 minutes. Corneal thickness decreased from a median of 623 microns preoperatively to 566 µm at 1 month (P = 0.038). Visual acuity improved by 1 month by a median of 0.3 logarithm of the minimum angle of resolution (logMAR) (P = 0.016). Endothelial cell density decreased by 32.4% at 1 month compared with baseline. CONCLUSIONS: Endothelium-in DMEK grafts may be loaded into a plastic cartridge using a skill set similar to aspiration of a scroll.

Comparison of Tri-folded and Scroll-based Graft Viability in Preloaded Descemet Membrane Endothelial Keratoplasty.

PURPOSE: To compare corneal endothelial damage associated with 2 techniques for preloaded Descemet membrane endothelial keratoplasty (DMEK): a tri-folded graft stored in a plastic cartridge designed for DMEK and a scrolled graft stored in a modified Jones Tube, at the time of preparation and after shipping. METHODS: DMEK grafts were prepared at the Rocky Mountain Lions Eye Bank. The grafts were either tri-folded and loaded in a plastic cartridge or scrolled and loaded into a modified Jones Tube. In each group, the grafts were then either immediately removed from the cartridges or shipped for 48 hours. The grafts were then stained with Calcein AM and imaged using a fluorescent microscope. Endothelial cell loss (ECL) was determined using trainable segmentation in Fiji by 2 graders. At each time point, rates of ECL loss were compared across the 2 groups. To explore the role of donor characteristics, a multivariable regression model was produced to account for method (tri-folding vs. scroll), donor age, donor gender, death-to-preservation time, death-to-preparation time, and shipping. RESULTS: A total of 40 grafts were prepared, processed, imaged, and analyzed. No significant difference in cell loss was seen between groups at either time point alone. In the multivariate model, no significant increase in cell loss was associated with either tri-folding (3.7% less ECL; P = 0.051) or shipping (4.3% less ECL; P = 0.049). CONCLUSIONS: All techniques used resulted in clinically acceptable levels of ECL. Tri-folded tissue in a plastic cartridge did not result in ECL inferior to a scroll when prepared either immediately or preloaded for 48 hours.

Viability of Descemet Membrane Endothelial Keratoplasty Grafts Folded in the Eye Bank.

PURPOSE: Preloaded, trifolded grafts in Descemet membrane endothelial keratoplasty require transfer of the trifolding process from the corneal transplant surgeon to the eye bank technician. We sought to assess whether trifolding may be safely conducted by an eye bank technician with cell loss comparable to standard peeling and lifting. METHODS: A total of 10 grafts were stained, peeled, and transferred directly onto a bed of Calcein-AM and Amvisc Plus by an eye bank technician. Five grafts were removed and stained as a scroll, and 5 grafts were trifolded with the endothelium in before transfer. Photographs were acquired with an inverted fluorescence microscope, and image segmentation was performed. A t test was conducted to compare differences in endothelial cell loss across groups. RESULTS: Mean cell loss in the scroll group was 18.5% [95% confidence interval (CI): 15.2%-21.9%] compared with 7.6% of the trifolded group (95% CI: 1.7%-13.5%). A 2-tailed t test indicated decreased cell loss in the trifolded group (P = 0.013). CONCLUSIONS: Despite additional manipulation of the graft, trifolding of Descemet membrane and endothelium may be performed by an eye bank technician without significantly increased cell loss relative to graft preparation as a scroll.