Emerging memory technologies for neuromorphic computing.

In this paper, we reviewed the recent trends on neuromorphic computing using emerging memory technologies. Two representative learning algorithms used to implement a hardware-based neural network are described as a bio-inspired learning algorithm and software-based learning algorithm, in particular back-propagation. The requirements of the synaptic device to apply each algorithm were analyzed. Then, we reviewed the research trends of synaptic devices to implement an artificial neural network.

Neuron Circuit Based on a Split-gate Transistor with Nonvolatile Memory for Homeostatic Functions of Biological Neurons.

To mimic the homeostatic functionality of biological neurons, a split-gate field-effect transistor (S-G FET) with a charge trap layer is proposed within a neuron circuit. By adjusting the number of charges trapped in the Si3N4 layer, the threshold voltage (Vth) of the S-G FET changes. To prevent degradation of the gate dielectric due to program/erase pulses, the gates for read operation and Vth control were separated through the fin structure. A circuit that modulates the width and amplitude of the pulse was constructed to generate a Program/Erase pulse for the S-G FET as the output pulse of the neuron circuit. By adjusting the Vth of the neuron circuit, the firing rate can be lowered by increasing the Vth of the neuron circuit with a high firing rate. To verify the performance of the neural network based on S-G FET, a simulation of online unsupervised learning and classification in a 2-layer SNN is performed. The results show that the recognition rate was improved by 8% by increasing the threshold of the neuron circuit fired.

Analysis on RF parameters of nanoscale tunneling field-effect transistor based on InAs/InGaAs/InP heterojunctions.

Tunneling field-effect transistors (TFETs) based on the quantum mechanical band-to-band tunneling (BTBT) have advantages such as low off-current and subthreshold swing (S) below 60 mV/dec at room temperature. For these reasons, TFETs are considered as promising devices for low standby power (LSTP) applications. On the other hand, silicon (Si)-based TFETs have a drawback in low on-state current (lon) drivability. In this work, we suggest a gate-all-around (GAA) TFET based on compound semiconductors to improve device performances. The proposed device materials consist of InAs (source), InGaAs (channel), and InP (drain). According to the composition (x) of Ga in In1-xGa(x)As layer of the channel region, simulated devices have been investigated in terms of both direct-current (DC) and RF parameters including tunneling rate, transconductance (g(m)), gate capacitance (Cg), intrinsic delay time (tau), cut-off frequency (fT) and maximum oscillation frequency (f(max)). In this study, the obtained maximum values of tau, fT, and f(max) for GAA InAs/In0.9Ga0.1As/InP heterojunction TFET were 21.2 fs, 7 THz, and 18 THz, respectively.

Efficient Hybrid Training Method for Neuromorphic Hardware Using Analog Nonvolatile Memory.

Neuromorphic hardware using nonvolatile analog synaptic devices provides promising advantages of reducing energy and time consumption for performing large-scale vector-matrix multiplication (VMM) operations. However, the reported training methods for neuromorphic hardware have appreciably shown reduced accuracy due to the nonideal nature of analog devices, and use conductance tuning protocols that require substantial cost for training. Here, we propose a novel hybrid training method that efficiently trains the neuromorphic hardware using nonvolatile analog memory cells, and experimentally demonstrate the high performance of the method using the fabricated hardware. Our training method does not rely on the conductance tuning protocol to reflect weight updates to analog synaptic devices, which significantly reduces online training costs. When the proposed method is applied, the accuracy of the hardware-based neural network approaches to that of the software-based neural network after only one-epoch training, even if the fabricated synaptic array is trained for only the first synaptic layer. Also, the proposed hybrid training method can be efficiently applied to low-power neuromorphic hardware, including various types of synaptic devices whose weight update characteristics are extremely nonlinear. This successful demonstration of the proposed method in the fabricated hardware shows that neuromorphic hardware using nonvolatile analog memory cells becomes a more promising platform for future artificial intelligence.

Reconfigurable neuromorphic computing block through integration of flash synapse arrays and super-steep neurons.

Neuromorphic computing (NC) architecture inspired by biological nervous systems has been actively studied to overcome the limitations of conventional von Neumann architectures. In this work, we propose a reconfigurable NC block using a flash-type synapse array, emerging positive feedback (PF) neuron devices, and CMOS peripheral circuits, and integrate them on the same substrate to experimentally demonstrate the operations of the proposed NC block. Conductance modulation in the flash memory enables the NC block to be easily calibrated for output signals. In addition, the proposed NC block uses a reduced number of devices for analog-to-digital conversions due to the super-steep switching characteristics of the PF neuron device, substantially reducing the area overhead of NC block. Our NC block shows high energy efficiency (37.9 TOPS/W) with high accuracy for CIFAR-10 image classification (91.80%), outperforming prior works. This work shows the high engineering potential of integrating synapses and neurons in terms of system efficiency and high performance.

Type Ic Endoleak after LifeStream Balloon-Expandable Stent Graft and Zenith Iliac Branch Device Placement

Considering the recent advancements in endovascular management of aortoiliac aneurysms, the use of an iliac branch device (IBD) to preserve pelvic blood flow and reduce complications caused by embolization of the internal iliac artery (IIA) is recommended by various guidelines. Although the outcomes reported following IBD placement are mainly positive and durable, IBD-specific complications such as a type Ic endoleak and associated reintervention may occur. Moreover, only one IBD device and one type of balloon-expandable bridging stent graft for IIA are currently available on the domestic market. Here we present two cases of type Ic endoleak following IBD placement. In both cases, IIA diameter was slightly larger than the basic instructions for use. Notably, the initial procedures were considered successful; however, type Ic endoleaks were detected on 1-month follow-up imaging. This finding emphasizes the need for a precise preoperative evaluation, intraoperative manipulation, and postoperative follow-up.

Right Gastroepiploic Artery Transposition for a Common Hepatic Artery and Proper Hepatic Artery Aneurysm Repair

Although hepatic artery aneurysms (HAAs) are uncommon, they are associated with risk of rupture. HAAs >2 cm in diameter require endovascular or open surgical repairs. For HAAs involving the proper hepatic artery or gastroduodenal artery, which is a collateral artery from the superior mesenteric artery, hepatic arterial reconstruction is especially important to avoid ischemic liver injury. In this study, right gastroepiploic artery transposition was performed in a 53-year-old man after a 4 cm common hepatic artery and proper hepatic artery aneurysm was identified. The patient was discharged without any complications on postoperative day 8.

Clinical Outcomes of Internal Iliac Artery Interruption during Endovascular Aneurysm Repair

Purpose@#This study aimed to investigate the clinical outcomes of internal iliac artery (IIA) interruption during endovascular aneurysm repair (EVAR) and to identify the risk factors for ischemic complications. @*Materials and Methods@#Endovascular treatment was performed in 316 patients with aneurysms or pseudoaneurysms of the abdominal aorta or iliac arteries between March 2006 and January 2022. Medical records and radiological imaging studies were retrospectively reviewed. The incidences of buttock claudication, ischemic colitis, and spinal cord ischemia after IIA interruption were investigated as clinical outcomes. Binary logistic regression analysis were performed to identify the risk factors. @*Results@#IIA embolization was performed in 78 patients. Among the 42 patients who underwent IIA flow preservation procedures, the one-month computed tomography detected early failure in five patients. The origin of the IIA was covered with an endograft in ten patients who did not undergo embolization. Eventually, interruption of the IIA by EVAR was observed in 93 patients. Considering preoperative IIA occlusion, there was a total of six patients who did not have at least one IIA patency. Buttock claudication occurred in 32.6% of the patients, and none of the patients had ischemic colitis or spinal cord ischemia. In multivariable analysis, age ≤80 years and isolated iliac artery aneurysm were associated with the development of postoperative buttock claudication. @*Conclusion@#The most common complication after IIA interruption is buttock claudication; however, critical complications such as ischemic colitis or spinal cord ischemia are rare, even in bilateral IIA occlusion. Adjunctive procedures to preserve bilateral IIA perfusion should be adopted selectively.

Below-Knee Prosthetic Bypass Is a Viable Option for Limb Salvage in Patients with Extensive Femoropopliteal Occlusive Disease

Purpose@#This study aimed to (1) evaluate the outcomes of below-knee prosthetic bypass (BKPB) in the absence of the great saphenous vein, and (2) identify risk factors associated with these outcomes. @*Materials and Methods@#This study included 37 consecutive patients who underwent BKPB with or without distal modification between 2010 and 2022. We further assessed the following treatment outcomes: primary patency (PP), secondary patency (SP), limb salvage (LS), and amputation-free survival (AFS) rates. The risk factors for PP were also examined. @*Results@#Most patients (n=31) were male. In 32 (86.5%) patients, BKPBs were performed for chronic limb-threatening ischemia. At the time of initial admission, two (5.4%) early deaths and three (8.1%) major amputations were noted. At 1 year after BKPB, the overall PP, SP, LS, and AFS rates were 78%, 85%, 85%, and 70%, respectively; at 3 years, they were 58%, 70%, 80%, and 52%, respectively; and at 5 years, they were 35%, 58%, 62%, and 29%, respectively. Notably, PP was significantly lower in limbs with ≤1 patent tibial arteries than in limbs with ≥2 patent artery (hazard ratio [HR], 3.80; 95% confidence interval [CI], 1.14-12.69 for overall; and HR, 12.97; 95% CI, 2.15-78.08 for distal anastomosis to below-knee popliteal artery). However, the PP was unaffected by the distal modification. @*Conclusion@#BKPB is a viable option for LS in patients with extensive femoropopliteal disease. Tibial runoff was significantly correlated with patency; therefore, decision-making for BKPB and follow-up must involve careful evaluation of the outflow arteries.

Medial Arterial Calcification and the Risk of Amputation of Diabetic Foot Ulcer in Patients With Diabetic Kidney Disease

We assessed the risk factors for major amputation of diabetic foot ulcers (DFUs) in patients with diabetic kidney disease (DKD) stages 3b–5. For DFU assessment, in addition to DFU location and presence of infection, ischemia, and neuropathy, vascular calcification was assessed using the medial arterial calcification (MAC) score. Of 210 patients, 26 (12.4%) underwent major amputations. Only the location and extension of DFU, represented by Texas grade differed between the minor and major amputation groups. However, after adjusting for covariates, ulcer location of mid- or hindfoot (vs. forefoot, odds ratio [OR] = 3.27), Texas grades 2 or 3 (vs. grade 0, OR = 5.78), and severe MAC (vs. no MAC, OR = 4.46) was an independent risk factor for major amputation (all P < 0.05). The current use of antiplatelets was a possible protective factor for major amputations (OR = 0.37, P = 0.055). In conclusion, DFU with severe MAC is associated with major amputation in patients with DKD.

A Split-Gate Positive Feedback Device With an Integrate-and-Fire Capability for a High-Density Low-Power Neuron Circuit.

Hardware-based spiking neural networks (SNNs) to mimic biological neurons have been reported. However, conventional neuron circuits in SNNs have a large area and high power consumption. In this work, a split-gate floating-body positive feedback (PF) device with a charge trapping capability is proposed as a new neuron device that imitates the integrate-and-fire function. Because of the PF characteristic, the subthreshold swing (SS) of the device is less than 0.04 mV/dec. The super-steep SS of the device leads to a low energy consumption of ∼0.25 pJ/spike for a neuron circuit (PF neuron) with the PF device, which is ∼100 times smaller than that of a conventional neuron circuit. The charge storage properties of the device mimic the integrate function of biological neurons without a large membrane capacitor, reducing the PF neuron area by about 17 times compared to that of a conventional neuron. We demonstrate the successful operation of a dense multiple PF neuron system with reset and lateral inhibition using a common self-controller in a neuron layer through simulation. With the multiple PF neuron system and the synapse array, on-line unsupervised pattern learning and recognition are successfully performed to demonstrate the feasibility of our PF device in a neural network.

Deep Vein Thrombosis after COVID-19 mRNA Vaccination in a Young Man with Inferior Vena Cava Anomaly Leading to Recurrent Deep Vein Thrombosis

Severe side effects of adenoviral-vectored-DNA COVID-19 vaccines such as thrombosis have been reported. Herein, we report a case of sudden massive deep vein thrombosis (DVT) in a young man with inferior vena cava anomaly 20 hours after the second dose of the mRNA vaccine for COVID-19. There was recurrence of iliofemoral DVT after one year, despite complete resolution and administration of prophylactic anticoagulants. We suggest that the sudden episode was triggered by the vaccine rather than the venous anomaly, which can be associated with recurrence due to inadequate venous return through the small and tortuous infrarenal veins or increased venous pressure and stasis. There are no standard guidelines for the management of DVT following mRNA vaccination. However, we highlight the importance of initial workups, regular follow-ups, and standard treatment options, including the continuous administration of prophylactic anticoagulants which should be considered to prevent recurrence.

Outcomes of Isolated Endarterectomy and Patch Angioplasty of the Common Femoral Artery According to Current Inclusion Criteria for Endovascular Treatment

Purpose@#This study aimed to evaluate the outcomes of isolated common femoral endarterectomy with patch angioplasty (IFEA) in the endovascular era. @*Materials and Methods@#In 2012-2022, 189 limbs underwent femoral endarterectomy with patch angioplasty. Of them, 45 IFEAs were included. We evaluated safety based on early complications; efficacy with primary patency (PP) and reintervention, above-ankle amputation, or stenosis (RAS)-free survival. We also evaluated lesion characteristics and outcomes according to the inclusion criteria (IC) of vascular mimetic implant-common femoral artery (VMI-CFA) stenting trial. @*Results@#Forty-one patients were male, and 30 IFEAs were required for claudication. No cases of early mortality occurred. Ten limbs (22%) developed localonvascular complications (hematoma, 3; lymphocele, 5; wound infection, 2), of which 8 resolved spontaneously. The overall PP and secondary patency rates were 100% at 1 year and 87% and 97% at 3 years, respectively. Twenty-one lesions (47%) did not meet the IC. The PP within the IC was 100% at 1 and 3 years, and the PP outside the IC was 100% at 1 year and 73% at 3 years (P=0.068). The overall RAS-free survival rates were 91% at 1 year and 81% at 3 years. All cases of RAS occurred in lesions outside the IC. The multivariate analysis showed that dialysis was associated with poor RAS-free survival (adjusted odds ratio, 8.56; 95% confidence interval, 1.9-35.5; P=0.005). @*Conclusion@#The recent VMI-CFA trial results should be interpreted with caution.IFEA is a low-risk and durable procedure; however, careful follow-up is warranted in patients undergoing dialysis.

Endovascular Repair of an Ilio-Iliac Arteriovenous Fistula with Pseudoaneurysm after Lumbar Disc Surgery: A Case Report

Aortoiliac vascular injury during lumbar disc surgery is potentially life-threatening, but occasionally presents with delayed-onset symptoms. This is a case report of a fistulized pseudoaneurysm presenting with claudication. A 73-year-old female presented with swelling of the left leg and short-distance claudication. Two months prior, she had undergone discectomy for the management of right foot drop caused by an L4-L5 herniated lumbar disc. The left ankle-brachial index was 0.71.Computed tomography angiography revealed a 31 mm×20 mm pseudoaneurysm of the left common iliac artery fistulized to the left common iliac vein. The patient was successfully treated with stent graft placement.

Endovascular Repair of an Ilio-Iliac Arteriovenous Fistula with Pseudoaneurysm after Lumbar Disc Surgery: A Case Report

Aortoiliac vascular injury during lumbar disc surgery is potentially life-threatening, but occasionally presents with delayed-onset symptoms. This is a case report of a fistulized pseudoaneurysm presenting with claudication. A 73-year-old female presented with swelling of the left leg and short-distance claudication. Two months prior, she had undergone discectomy for the management of right foot drop caused by an L4-L5 herniated lumbar disc. The left ankle-brachial index was 0.71.Computed tomography angiography revealed a 31 mm×20 mm pseudoaneurysm of the left common iliac artery fistulized to the left common iliac vein. The patient was successfully treated with stent graft placement.

Changes in the Normal Infrarenal Aortic Length and Tortuosity in Elderly People

Purpose@#To investigate the changes in the infrarenal aortic length and tortuosity in elderly patients. @*Materials and Methods@#We retrospectively reviewed the medical records andcomputed tomography (CT) scans of 857 patients who underwent surgery for colorectal cancer between August 2009 and July 2012. Among these patients, 48 patients who were aged ≥60 years, underwent follow-up CT at least 5 years after surgery, did not have aortic disease, and did not receive radiation therapy were enrolled. The aortic tortuosity index (ATI) was defined by dividing the distance along the central lumen line from the lowest renal artery to the aortic bifurcation (L1) by the straight-line distance from the lowest renal artery to the aortic bifurcation (L2). Aortic diameters were measured at the lowest renal artery level (D1) and 20 mm below (D2). A paired t-test and Wilcoxon signed-rank test were used to compare lengths and diameters between the initial and final CT scan. Spearman’s correlation analysis was performed to determine the correlations between time and the changes in L1 and ATI. @*Results@#The average follow-up period was 68 months. The mean changes in L1 and L2 were 0.69 mm and –0.59 mm, respectively, while the mean changes in D1 and D2 were 0.77 mm and 0.58 mm, respectively. The mean increase in ATI was 0.015. All findings were statistically significant. On Spearman’s correlation analysis, ΔL1 and ΔATI showed no correlation with follow-up duration. @*Conclusion@#The infrarenal aortic length and tortuosity of elderly patients increases at a slow rate over time.

Does Catheter-Directed Thrombolysis Prevent Postthrombotic Syndrome?

PURPOSE: The aim of this study is to identify risk factors of postthrombotic syndrome (PTS) and evaluate the efficacy of catheter-directed thrombolysis (CDT) for preventing the development of PTS in patients with lower extremity deep vein thrombosis (DVT). MATERIALS AND METHODS: From 2005 January to 2013 December, 139 limbs of 126 patients were included in this study who had the first episode of proximal DVT at the affected limb and who had visited our out-patient clinic. CDT was performed on 55 limbs (39.6%). We achieved complete recanalization in 39 limbs (70.9%) and partial recanalization (residual thrombus 0.05). CONCLUSION: We suggest that CDT is not effective in preventing PTS, while higher BMI and longer thrombotic burden are associated with the development of PTS in patients with DVT.

Pseudoaneurysm after Knee Arthroscopic Synovectomy in a Septic Arthritis Patient / 대한정형외과학회잡지

Arthroscopic synovectomy is a widely-used method to treat septic knee arthritis. To date, many authors have reported minimal complications related to arthroscopic treatment, especially vascular injuries. A three-dimensional computed tomography angiography revealed a pseudoaneurysm that arise from the popliteal artery near the arthroscopic site in septic arthritis patients with atherosclerosis and neurofibromatosis. A careful arthroscopic procedure via the posteromedial or posterolateral portal is recommended for the prevention of this complication. We, therefore, recommend close observation after arthroscopic procedure, despite the occurrence of complications; nonetheless, early diagnosis and treatment are important. We report a case of pseudoaneurysm of the popliteal artery with a complicating arthroscopic synovectomy in septic arthritis with literature review.

Cerebral monitoring during carotid endarterectomy by transcranial Doppler ultrasonography

PURPOSE: To evaluate the efficacy and safety of cerebral monitoring by transcranial Doppler ultrasonography (TCD) for the detection of cerebral ischemia during carotid endarterectomy (CEA). METHODS: From August 2004 to December 2013, 159 CEAs were performed in a tertiary hospital. All procedures were performed under general anesthesia. Intraoperative TCD was routinely used to detect cerebral ischemia. Of the 159 patients, 102 patients were included in this study, excluding 27 patients who had a poor transtemporal isonation window and 30 patients who used additional cerebral monitoring systems such as electroencephalography or somatosensory evoked potentials. When mean flow velocity in the ipsilateral middle cerebral artery decreased by >50% versus baseline during carotid clamping carotid shunting was selectively performed. The carotid shunt rate and incidence of perioperative (<30 days) stroke or death were investigated by reviewing medical records. RESULTS: Carotid shunting was performed in 31 of the 102 patients (30%). Perioperative stroke occurred in 2 patients (2%); a minor ischemic stroke caused by embolism in one and an intracerebral hemorrhage in the other. Perioperative death developed in the latter patient. CONCLUSION: TCD is a safe cerebral monitoring tool to detect cerebral ischemia during CEA. It can reduce use of carotid shunt.

Effect of Clinical Suspicion by Referral Physician and Early Outcomes in Patients with Acute Superior Mesenteric Artery Embolism

PURPOSE: To investigate the pattern of referral of patients with superior mesenteric artery embolism (SMAE) and its effect on outcomes, and to evaluate the risk factors for bowel infarction. MATERIALS AND METHODS: This retrospective study included 66 consecutive patients diagnosed with acute SMAE between January 2001 and June 2016. Appropriate diagnosis by the referring physician was defined if the referral letter indicated that acute mesenteric ischemia was suspected or had been diagnosed at the referral center. Surgical delay was defined as the interval between symptom onset and surgery for definitive treatment. RESULTS: Among 54 patients transferred from other centers, 26 patients (48.1%) were diagnosed appropriately by the referring physician. The rate of appropriate diagnosis was differed significantly by the use of computed tomography (CT) scan at referral center (25/35 with CT and 1/19 without CT, P=0.00). The surgical delay was significantly longer in patients without appropriate diagnosis compared with the patients with appropriate diagnosis (53.5±52.3 hours vs. 28.8±23.6 hours, P=0.04). Initially, 56 patients received surgical treatment with 31 underwent bowel resection due to infarction, 6 received conservative treatment, and the remaining 4 patients refused any treatment. The surgical delay, abdominal distension, tenderness, rebound tenderness, and level of C-reactive protein were associated with bowel infarction at initial operation. Overall in-hospital mortality was 32%. CONCLUSION: A high index of suspicion with appropriate diagnostic modality, such as CT scan is crucial in patients with SMAE for reducing surgical delay as a risk factor of bowel infarction.