A Mathematical Analysis of Clustering-Free Local SAR Compression Algorithms for MRI Safety in Parallel Transmission

Parallel transmission (pTX) is a versatile solution to enable UHF MRI of the human body, where radiofrequency (RF) field inhomogeneity appears very challenging. Today, state of the art monitoring of the local SAR in pTX consists in evaluating the RF power deposition on specific SAR matrices called Virtual Observation Points (VOPs). It essentially relies on accurate electromagnetic simulations able to return the local SAR distribution inside the body in response to any applied pTX RF waveform. In order to reduce the number of SAR matrices to a value compatible with real time SAR monitoring ( << 103) , a VOP set is obtained by partitioning the SAR model into clusters, and associating a so- called dominant SAR matrix to every cluster. More recently, a clustering-free compression method was proposed, allowing for a significant reduction in the number of SAR matrices. The concept and derivation however assumed static RF shims and their extension to dynamic pTX is not straightforward, thereby casting doubt on the strict validity of the compression approach for these more complicated RF waveforms. In this work, we provide the mathematical framework to tackle this problem and find a rigorous justification of this criterion in the light of convex optimization theory. Our analysis led us to a variant of the clustering-free compression approach exploiting convex optimization. This new compression algorithm offers computational gains for large SAR models and for high-channel count pTX RF coils.

Hepaticojejunostomy for bile duct injury: state of the art

BACKGROUND

Hepaticojejunostomy (HJ) is the gold standard procedure for the reconstruction of the bile duct in many benign and malignant situations. One of the major situation is the bile duct injury (BDI) after cholecystectomy, either for early or late repair. This procedure presents some specificities associated to a debated management of BDI.

PURPOSE

This article provides a state-of-the-art of the hepaticojejunostomy procedure focusing on bile duct injury including its indications and outcomes CONCLUSION: Performed at the right moment and respecting the technical rules, HJ provides a restoration of the biliary patency in the long term of 80 to 90%. It is the main surgical technique to repair BDI. Complications and failure of this procedure can be difficult to manage. That is why the primary repair requires an appropriate multidisciplinary approach associated with an expert high quality surgical technique.

Perioperative antibiotherapy should replace prophylactic antibiotics in patients undergoing pancreaticoduodenectomy preceded by preoperative biliary drainage

BACKGROUND AND OBJECTIVES

Pancreaticoduodenectomy (PD) remains a morbid surgery. Preoperative biliary drainage (PBD) is often necessary before surgery but is associated with biliary contamination. We compared the postoperative complications of patients undergoing PBD who received the usual prophylactic antibiotics (PAs) or systematic antibiotherapy (ABT).

METHODS

All patients who underwent surgery between 2008 and 2017 were included. Systematic perioperative ABT with piperacillin + tazobactam (ABT group) was implemented in 2014 as the standard of care for PBD. Patients treated in the period before such implementation, during which standard cefazolin was given, served as the controls (PAs group). The primary outcomes were postoperative complications.

RESULTS

We included 122 patients with PBD who underwent surgery. There were no demographic differences between the two groups. Perioperative ABT was associated with a reduction in deep abdominal abscesses (36% vs 10%, P = .0008), respiratory tract infections (15% vs 3%; P = .02), bacteremia (41% vs 6%; P < .0001), and a shorter length of hospital stay (17 [13-27] vs 13 [10-14] days; P < .0001). ABT was a protective factor against the development of deep abdominal abscesses (odds ratio [OR] = 0.16; P = .001) whereas smoking (OR = 3.9) and pancreatic fistula (OR = 19.1) were risk factors.

CONCLUSION

Systematic perioperative ABT in patients undergoing PD preceded by PBD may reduce deep surgical infections and the length of hospital stay.

Multidisciplinary meetings specific to hepatocellular carcinoma: How to proceed?

The French "cancer plan" has created a framework for good practice in the course of care for cancer patients. Decisions must be made in a multidisciplinary team meeting (MDM) and an individualized care plan (ICP) is to be established for each patient. Hepatocellular carcinoma (HCC) is a common cancer with complex treatments that warrant a dedicated meeting. Cancer coordination centers (3C) ensure the organization and the functioning of MDMs. Multidisciplinary, standardized and systematic assessment of HCC patients allows for personalized management and orients them toward treatment that is either curative (transplantation, surgical resection, ablathermy) or palliative (chemoembolization, radiotherapy, systemic treatment, supportive care). MDMs bring together all the professionals treating the disease, and who are tasked with producing an enforceable document effective that justifies decisions and is often an essential step towardinclusion of patients in a clinical trial. It must be carried out according to a systematic schema in an approach applied from initial diagnosis to treatment outset and throughout the treatment. Numerous advances in HCC treatments have rendered their management complex, with the possibility of liver transplantation, twhose access is regulated by the Biomedicine Agency requiring the submission of MDM reports. MDMs must meet specific quality criteria to ensure effective management based on general guidelines and yet specifically tailored to each patient.

Liver Transplantation With Old Grafts: A Ten-Year Experience

BACKGROUND

The persistent scarcity of donors has prompted liver transplantation teams to find solutions for increasing graft availability. We report our experience of liver transplantations performed with grafts from older donors, specifically over 70 and 80 years old.

PATIENTS AND METHODS

We analyzed our prospectively maintained single-center database from January 1, 2005, to December 31, 2014, with 380 liver transplantations performed in 354 patients. Six groups were composed according to donor age: <40 (n = 84), 40 to 49 (n = 67), from 50 to 59 (n = 62), from 60 to 69 (n = 76), from 70 to 79 (n = 64), and ≥80 years (n = 27).

RESULTS

Donors <40 years of age had a lower body mass index, died more often from trauma, and more often had cardiac arrest and high transaminase levels. In contrast, older donors (≥70 years of age) died more often from stroke. Recipients of grafts from donors <50 years of age were more frequently infected by hepatitis C virus; recipients of oldest grafts more often had hepatocellular carcinoma. Cold ischemia time was the shortest in donors >80 years of age. Patient survival was not significantly different between the groups. In multivariate analysis, factors predicting graft loss were transaminase peak, retransplantation and cold ischemia time but not donor age.

CONCLUSIONS

Older donors >70 and >80 years of age could provide excellent liver grafts.

Azacitidine-induced pyoderma gangrenosum at injection sites in a patient with myelodysplastic syndrome

Pyoderma gangrenosum (pg) is a rare neutrophilic dermatosis characterized by painful necrotic ulceration affecting preferentially the lower extremities. Diagnosis is challenging, and a thorough workup (including biopsy) is required. In this case report, we describe a 67-year-old patient with a diagnosis of myelodysplastic syndrome (mds) who developed fever and pg two days after the first cycle of subcutaneous azacitidine (Vidaza; Celgene Corporation, Summit, NJ, USA). On physical examination, the patient had four erythematous plaques at sites of subcutaneous injections of azacitidine on the arms, as well as three other plaques in proximity. A skin biopsy demonstrated a dense neutrophilic interstitial infiltrate in the dermis. After the diagnosis of pg, prednisone 1 mg/kg was started and the fever subsided rapidly. This was followed by the resolution of the cutaneous lesions. Changing the route of administration of azacitidine from subcutaneous to intravenous and adding a daily dose of prednisone during the treatment allowed the patient to receive a total of 10 cycles of azacitidine. This is the second case reported in the literature. Because azacitidine is frequently used in mds and acute myeloid leukemia, clinicians should be aware of this rare cutaneous adverse event. Our approach can be used to avoid the recurrence of pg when continuing azacitidine treatment.

Procarbazine, lomustine and vincristine toxicity in low-grade gliomas

Background

Procarbazine, lomustine, and vincristine (pcv) significantly improve survival outcomes in lgg (low-grade gliomas). Administration of pcv to lgg patients increased tremendously over the past years as it went from 2 patients per year between 2005 and 2012 to 23 patients in 2015 only in our centre. However, serious hematological and non-hematological adverse events may occur. The purpose of this study was to evaluate the toxicity of pcv and its clinical relevance in our practice.

Methods

We retrospectively reviewed the charts of 57 patients with lgg who received pcv at the Centre hospitalier de l'Université de Montréal between 1 January 2005 and 27 July 2016.

Results

Procarbazine, lomustine, and vincristine were associated with severe hematological toxicity as clinically significant grade 3 anemia, neutropenia, and thrombocytopenia occurred in 7%, 10%, and 28% of patients, respectively. Other frequent adverse events such as the increase of liver enzymes, cutaneous rash, neurotoxicity, and vomiting occurred in 65%, 26%, 60%, and 40% of patients, respectively. Patients with prophylactic trimethoprim/sulfamethoxazole had more grade 3 hematological toxicity with pcv, especially anemia (p = 0.040) and thrombocytopenia (p = 0.003) but we found no increase in pcv toxicity in patients on concurrent anticonvulsants. Patients with grade 3 neutropenia had a significantly lower survival (median survival 44.0 months vs. 114.0 months, p = 0.001). Patients who were given pcv at diagnosis had more grade 3 anemia than those who received it at subsequent lines of treatment (p = 0.042).

Conclusion

Procarbazine, lomustine, and vincristine increase survival in lgg but were also associated with major hematologic, hepatic, neurologic, and cutaneous toxicity. Anti-Pneumocystis jiroveci pneumonia (pjp) prophylaxis, but not anticonvulsants, enhances hematologic toxicity.

Risk score to predict biliary leakage after elective liver resection

Background

Biliary leakage remains a major cause of morbidity after liver resection. Previous prognostic studies of posthepatectomy biliary leakage (PHBL) lacked power, population homogeneity, and model validation. The present study aimed to develop a risk score for predicting severe PHBL.

Methods

In this multicentre observational study, patients who underwent liver resection without hepaticojejunostomy in one of nine tertiary centres between 2012 and 2015 were randomly assigned to a development or validation cohort in a 2 : 1 ratio. A model predicting severe PHBL (International Study Group of Liver Surgery grade B/C) was developed and further validated.

Results

A total of 2218 procedures were included. PHBL of any severity and severe PHBL occurred in 141 (6·4 per cent) and 92 (4·1 per cent) patients respectively. In the development cohort (1475 patients), multivariable analysis identified blood loss of at least 500 ml, liver remnant ischaemia time 45 min or more, anatomical resection including segment VIII, transection along the right aspect of the left intersectional plane, and associating liver partition and portal vein ligation for staged hepatectomy as predictors of severe PHBL. A risk score (ranging from 0 to 5) was built using the development cohort (area under the receiver operating characteristic curve (AUROC) 0·79, 95 per cent c.i. 0·74 to 0·85) and tested successfully in the validation cohort (AUROC 0·70, 0·60 to 0·80). A score of at least 3 predicted an increase in severe PHBL (19·4 versus 2·6 per cent in the development cohort, P &lt; 0·001; 15 versus 3·1 per cent in the validation cohort, P &lt; 0·001).

Conclusion

The present risk score reliably predicts severe PHBL. It represents a multi-institutionally validated prognostic tool that can be used to identify a subset of patients at high risk of severe PHBL after elective hepatectomy.

Surgery for rectal cancer after high-dose radiotherapy for prostate cancer: is sphincter preservation relevant?

AIM

The feasibility and outcome of sphincter-saving resection for rectal cancer were assessed in patients previously treated by high-dose radiotherapy for prostate cancer.

METHOD

Between 2000 and 2012, 1066 patients underwent rectal excision for rectal cancer. Of these, 236 were treated by conventional radiotherapy (45 Gy) and sphincter-saving resection (Group A) and 12 were treated by external-beam radiotherapy (EBRT) for prostate cancer (70 Gy) and sphincter-saving resection (Group B) of whom five had a metachronous and seven a synchronous cancer. The end-points were surgical morbidity, pelvic sepsis, reoperation and definitive stoma.

RESULTS

Tumour characteristics were similar in both groups. Surgical morbidity (67% vs 25%, P = 0.004), anastomotic leakage (50% vs 10%, P = 0.001, and reoperation (50% vs 17%, P = 0.011) were significantly higher in Group B. Multivariate analyses showed that EBRT for prostate cancer was the only independent factor for anastomotic leakage (OR = 5.12; 95% CI 1.45-18.08; P = 0.011) and definitive stoma (OR = 10.56; 95% CI 3.02-39.92; P < 0.001).

CONCLUSION

High-dose radiotherapy for prostate cancer increases morbidity from rectal surgery and the risk of a permanent stoma. This suggests that a delayed coloanal anastomosis or a Hartmann procedure should be proposed as an alternative to low anterior resection in this population.

Current induced domain wall motion in GaMnAs close to the Curie temperature

Domain wall dynamics produced by spin transfer torques is investigated in (Ga, Mn)As ferromagnetic semiconducting tracks with perpendicular anisotropy, close to the Curie temperature. The domain wall velocities are found to follow a linear flow regime which only slightly varies with temperature. Using the Döring inequality, boundaries of the spin polarization of the current are deduced. A comparison with the predictions of the mean field k·p theory leads to an estimation of the carrier density whose value is compatible with results published in the literature. The spin polarization of the current and the magnetization of the magnetic atoms present similar temperature variations. This leads to a weak temperature dependence of the spin drift velocity and thus of the domain wall velocity. A combined study of field- and current-driven motion and deformation of magnetic domains reveals a motion of domain walls in the steady state regime without transition to the precessional regime. The ratio between the non-adiabatic torque β and the Gilbert damping factor α is shown to remain close to unity.

Magnetization reversal in Pt/Co(0.5 nm)/Pt nano-platelets patterned by focused ion beam lithography

Arrays of ultrathin Pt/Co(0.5 nm)/Pt nano-platelets with lateral sizes ranging from 30 nm to 1 µm have been patterned by focused ion beam (FIB) lithography under a weak Ga(+) ion fluence. From polar magneto-optical Kerr microscopy it is demonstrated that nano-platelets are ferromagnetic with perpendicular anisotropy down to a size of 50 nm. The irradiation process creates a magnetically soft ring at the nano-platelet periphery in which domain nucleation is initiated at a low field. The magnetization reversal in nano-platelets can be interpreted using a confined droplet model. All of the results prove that ultimate FIB patterning is suitable for preparing discrete magnetic recording media or small magnetic memory elements and nano-devices.

Interplay of Peltier and Seebeck effects in nanoscale nonlocal spin valves

We have experimentally studied the role of thermoelectric effects in nanoscale nonlocal spin valve devices. A finite element thermoelectric model is developed to calculate the generated Seebeck voltages due to Peltier and Joule heating in the devices. By measuring the first, second, and third harmonic voltage response nonlocally, the model is experimentally examined. The results indicate that the combination of Peltier and Seebeck effects contributes significantly to the nonlocal baseline resistance. Moreover, we found that the second and third harmonic response signals can be attributed to Joule heating and temperature dependencies of both the Seebeck coefficient and resistivity.