Storage and Learning Phase Transitions in the Random-Features Hopfield Model.

The Hopfield model is a paradigmatic model of neural networks that has been analyzed for many decades in the statistical physics, neuroscience, and machine learning communities. Inspired by the manifold hypothesis in machine learning, we propose and investigate a generalization of the standard setting that we name random-features Hopfield model. Here, P binary patterns of length N are generated by applying to Gaussian vectors sampled in a latent space of dimension D a random projection followed by a nonlinearity. Using the replica method from statistical physics, we derive the phase diagram of the model in the limit P,N,D→∞ with fixed ratios α=P/N and α_{D}=D/N. Besides the usual retrieval phase, where the patterns can be dynamically recovered from some initial corruption, we uncover a new phase where the features characterizing the projection can be recovered instead. We call this phenomena the learning phase transition, as the features are not explicitly given to the model but rather are inferred from the patterns in an unsupervised fashion.

Long-term efficacy of endovascular treatment of isolated iliac artery aneurysms.

PURPOSE: The aim of this study was to evaluate the efficacy of endovascular treatment of isolated iliac artery aneurysms (IIAA) and compare our data with those reported in the literature. MATERIALS AND METHODS: From May 2005 to December 2010, 32 patients (31 men and one woman; mean age 73±12 years) with a total of 40 IIAAs underwent endovascular treatment at our institute. We evaluated technical success, long-term patency, early and late complications and overall mortality. RESULTS: At a median follow-up of 36 months, we achieved a technical success of 100%, a primary patency of 95% and a secondary patency of 100%, with complete exclusion of the aneurysm in 84.6% of cases. In 12.8% of cases, there was a reduction in aneurysm sac volume, with an incidence of type II endoleak of 12.8%. Overall survival at 1, 2, 3, and 6 years was 96.8%, 84.2%, 66.6% and 64%, respectively. CONCLUSIONS: Our study documents the effectiveness of endovascular treatment of iliac aneurysms, which has become the first-choice treatment at our institute. This finding is consistent with the most recent literature and confirms the safety and long-term patency of stent-graft placement.

Endovascular treatment of transplanted renal artery stenosis with PTA/stenting.

PURPOSE: We evaluated the effectiveness of endovascular treatment with percutaneous transluminal balloon angioplasty (PTA)/stenting of transplanted renal artery stenosis (TRAS). MATERIALS AND METHODS: Between January 2005 and December 2010, 17 patients (4 women, 13 men; mean age 60.9 years) with TRAS underwent PTA/stenting. The parameters analysed were: technical success, pre- and post-treatment serum creatinine (SCr) and blood pressure (BP), average number of antihypertensive drugs administered before and after treatment and vessel patency on colour Doppler ultrasound (CDUS) at 1, 3, 6 and 12 months and once a year thereafter. RESULTS: Technical success was 100%. During a mean follow-up of 28.3±18.7 months, there was a statistically significant reduction in SCr and BP values. In 18 % of cases, moderate (<60%) restenosis was observed on CDUS without renal failure and not requiring new treatment. There was a reduction in antihypertensive drugs from an average of 3.5±0.5 to 1.5±0.5. CONCLUSIONS: Consistent with the literature data, our experience shows that endovascular treatment with PTA/stenting is a safe and effective option for managing TRAS and can thus be considered the method of choice.

[Endovascular treatment of abdominal aortic aneurysms: 6 years of experience at a single centre]. / Trattamento endovascolare di aneurismi dell'aorta addominale: esperienza monocentrica di sei anni.

PURPOSE: We sought to assess the effectiveness of endovascular abdominal aortic aneurysm (AAA) repair (EVAR) through a retrospective review of 6 years' experience at a single centre. MATERIALS AND METHODS: From April 2005 to August 2011, 222 patients affected by abdominal aortic aneurysms underwent EVAR. We evaluated primary technical success, postprocedural mortality, intraprocedural and postprocedural complications with contrast-enhanced computed tomography (CT) and contrast-enhanced ultrasound (US) follow-up at 1, 6 and 12 months and annually thereafter. RESULTS: The procedures were elective in 75.7% and urgent due to symptomatic or ruptured aneurysm in 24.3%. Technical success was 98.6%; three patients (1.4%) required conversion to open surgery. Postoperative mortality rate was 24% for urgent and 2.3% for elective procedures. During a mean follow-up period of 29.6 months, no cases of stent-graft migration were observed; the overall incidence of endoleaks was 27% (60/222) and comprised four type I (1.8%) and one type III (0.45%), all treated by stent-graft extension, and 55 type 2 (24.8%), eight of which (14.5%) were treated by percutaneous injection of thrombin. In 10/222 cases (4.5%), thrombotic occlusion of the iliac extension was detected, which was successfully treated by transcatheter intra-arterial thrombolysis. One patient developed stent-graft infection requiring surgical explantation. Average hospital stay was 4 days, and average time in intensive care was 2 days. CONCLUSIONS: Consistent with the literature data, our study confirms the safety and long-term efficacy of EVAR for treating AAA.

Comparison of cryoplasty and conventional angioplasty for treating stenotic-occlusive lesions of the femoropopliteal arteries in diabetic patients: immediate, mid-term and long-term results.

PURPOSE: The authors compared the immediate, mid-term and long-term effectiveness of cryoplasty and conventional angioplasty for treating stenotic-occlusive lesions of the femoropopliteal arteries in diabetic patients. MATERIALS AND METHODS: From October 2006 to November 2009, 48 patients with non-insulin-dependent diabetes mellitus (DM) and an indication for percutaneous revascularisation of the femoropopliteal arteries were randomly assigned to treatment with angioplasty or cryoplasty. The following parameters were analysed and compared between the two groups: immediate technical success (residual stenosis <30%) and distal run-off as assessed on postprocedural angiography, and degree of restenosis and distal run-off at 6 and 12 months, as assessed with either colour Doppler ultrasound (CDUS) or digital subtraction angiography (DSA). RESULTS: Treatment with angioplasty revealed a significant superiority in procedural technical success (p=0.04), a significant reduction in the degree of restenosis at 6 months (p=0.02) and a significant increase in the distal run-off at 6 (p=0.005) and 12 (p=0.01) months. CONCLUSIONS: Conventional angioplasty is more effective than cryoplasty for treating stenotic-occlusive lesions of the femoropopliteal arteries in diabetic patients and provides better immediate, mid-term and long-term results.