The effect of retrograde autologous priming on intraoperative blood product transfusion in coronary artery bypass grafting.

INTRODUCTION: Retrograde autologous priming (RAP) of the cardiopulmonary bypass (CPB) circuit could reduce the degree of haemodilution associated with priming with acellular solutions. However, there is no strong evidence to prove that the practice of RAP reduced intraoperative packed red cell (PRC) or blood product transfusion. OBJECTIVE: To evaluate the effect of RAP on intraoperative PRC usage in coronary artery bypass grafting (CABG). METHODS: This study is a prospective, observational study on patients who underwent first-time, isolated CABG using CPB between April 2012 and July 2012. Two groups of patients were identified: 1. Non-RAP group (n=128) and 2. RAP group (n=73). The primary outcome for the study was the amount of PRC and blood product usage between the induction of anaesthesia and the cessation of CPB. RESULTS: Use of PRC and blood products in the operating room was comparable in both groups. Univariate logistic regression showed that RAP was not an independent predictor of PRC or blood product transfusion (p=0.43). Multivariate logistic regression showed that CPB time, preoperative haemoglobin (Hb) levels and creatinine clearance were independent predictors of blood product transfusion. CONCLUSION: Practising RAP with mean volumes of 300 ml does not necessarily reduce PRC and other blood product transfusion requirements during CABG. In our practice, RAP was performed, aiming at displacing CPB circuit prime volume with which the perfusionist felt comfortable and dictated by haemodynamic parameters prior to commencing CPB. We presume this is the case in many units around the world. This practice, in our opinion, is not enough to achieve the benefits of RAP, if any, in the form of a reduction of packed red cell transfusion requirements. The true advantages of RAP in cardiac surgery need to be studied in a prospective, randomized, controlled trial.

In vivo MRI-based 3D mechanical stress-strain profiles of carotid plaques with juxtaluminal plaque haemorrhage: an exploratory study for the mechanism of subsequent cerebrovascular events.

OBJECTIVES: Atherosclerotic plaque features, such as fibrous cap erosion, ulceration and rupture and presence of haemorrhage in carotid plaque are two important characteristics associated with subsequent cerebrovascular events and juxtaluminal haemorrhage/thrombus (JLH/T) indicates these two high-risk characteristics. This study aims to investigate the association between JLH/T and subsequent events in patients suffering from transient ischaemic attack (TIA). Three-dimensional mechanical analysis was employed to represent the critical mechanical stress (P-CStress) and stretch (P-CStretch) within the plaque. METHODS: Fifty TIA patients with mild-to-moderate carotid stenosis (30-69%) underwent high-resolution magnetic resonance imaging (MRI) within 72 h of the acute event and eight were excluded from the analysis due to various reasons. A total of 21 patients were found to have JLH/T in the carotid plaque and 21 did not (N-JLH/T). During a 2-year follow-up period, 11 (52.4%) patients in the JLH/T group experienced recurrent events and none in the N-JLH/T group. Three-dimensional plaque structure was reconstructed based on the in vivo MRI for the mechanical analysis. RESULTS: P-CStress of both groups was comparable (N-JLH/T: 174.45 ± 63.96 kPa vs. JLH/T: 212.60 ± 89.54 kPa; p = 0.120), but P-CStretch of JLH/T was significantly bigger than that of N-JLH/T (N-JLH/T: 1.21 ± 0.08 vs. JLH/T: 2.10 ± 0.53; p < 0.0001). Moreover, there were much bigger variations in stress and stretch of the JLH/T group during one cardiac cycle than in those of N-JLH/T group. CONCLUSIONS: In vivo MRI-depicted JLH/T might be a high risk factor initiating recurrent events, as big deformation appearing around the rupture site might prevent healing and tear the haemorrhage/thrombus away from the host structure and prompt further thrombo-embolic events.

High-resolution magnetic resonance imaging-based biomechanical stress analysis of carotid atheroma: a comparison of single transient ischaemic attack, recurrent transient ischaemic attacks, non-disabling stroke and asymptomatic patient groups.

BACKGROUND: Vulnerable carotid plaques are associated with cerebrovascular ischaemic events. High-resolution magnetic resonance (MR) imaging not only allows the morphological assessment of such plaques, but also provides geometrical data, which can be used for biomechanical stress analysis. We assess its utility to assess the plaque stress profiles of symptomatic (transient ischaemic attack (TIA) and non-disabling stroke) and asymptomatic patients. METHODS: A total of 70 consecutive patients with confirmed underlying carotid artery disease underwent carotid MR imaging of their carotid artery in a 1.5-T MR system using a standard carotid atheroma imaging protocol. MR images were manually segmented for different plaque components and used for biomechanical stress analysis. The maximum critical stress (M-CStress) for various clinical groups was determined and compared. RESULTS: M-CStress of symptomatic plaques (n = 45) was significantly higher than for asymptomatic plaques (n = 25) (median (interquartile range (IQR): 275 kPa (190-390) vs. 165 kPa (120-200), p = 0.0001)). Within the symptomatic group, no M-CStress differences were present between the TIA (n = 30) and stroke (n = 15) patients (260 kPa (190-370) vs. 295 kPa (200-510), p = 0.31). Within the TIA patient cohort, those who had presented with recurrent TIAs (n = 6) had significantly higher stresses than patients who had suffered a single episode (n = 24) (425 kPa (285-580) vs. 250 kPa (180-310), p = 0.001). CONCLUSIONS: Symptomatic carotid plaques, particularly those associated with recurrent TIAs, have high biomechanical stresses. As there is pre-existing evidence to suggest that high biomechanical stresses are associated with plaque vulnerability, MR-imaging-based stress analysis has the potential to identify high-risk patients with vulnerable plaques.

Ultrasmall superparamagnetic iron oxide-enhanced magnetic resonance imaging of abdominal aortic aneurysms--a feasibility study.

OBJECTIVES: Abdominal aortic aneurysms (AAAs), being predominantly atherosclerotic in nature, have underlying inflammatory activity. As it is well established that ultrasmall superparamagnetic iron oxide (USPIO) particles accumulate in the macrophages within atheromatous lesions, USPIO-enhanced magnetic resonance (MR) imaging can be potentially effective in the quantification of the associated inflammatory processes. METHODS: A total of 14 patients underwent USPIO-enhanced MR imaging using a 1.5T-MR system. Quantitative T(2)* and T(2) relaxation time data were acquired before and 36 h after UPSIO infusion at identical AAA locations. The pre- and post-USPIO-infusion relaxation times (T(2)(∗) and T(2)) were quantified and the correlation between pre- and post-USPIO infusion T(2)* and T(2) values was investigated. RESULTS: There was a significant difference between pre- and post-infusion T(2)* and T(2) values (both respective p-values = 0.005). A significant correlation between T(2)* and T(2) values post-USPIO infusion was observed (r = 0.90, p < 0.001), which indicates USPIO uptake by the aortic wall. CONCLUSIONS: Aortic wall inflammation using USPIO-enhanced MR imaging is feasible. Use of quantitative T(2) and T(2)* pulse sequences provides a quantitative method for assessing USPIO uptake by the aortic wall.

Abdominal aortic aneurysm surgery in renal, cardiac and hepatic transplant recipients.

With advancements in transplantation and improved long-term allograft survival, the once rare clinical scenario of an abdominal aortic aneurysm (AAA) in a patient with a functioning allograft has become much more frequent. In transplant recipients, AAA repair has the potential to cause irreversible ischaemic injury to the transplanted organ. Different case series and case reports have mentioned a variety of techniques to offer protection to the transplanted organs during aneurysm repair such as cold perfusion, shunting, temporary surgical bypass and extracorporeal circuits etc. Critical review of these adjuncts seems to suggest that that they do not give any better results than just using a "clamp and go" approach. Endovascular aneurysm repair (EVAR) may offer some advantages for transplant patients who have suitable anatomy for endovascular stent deployment. In addition to these surgical techniques, various aspects of medical management for renal, cardiac and hepatic transplant recipients undergoing AAA repair are discussed.

Association between biomechanical structural stresses of atherosclerotic carotid plaques and subsequent ischaemic cerebrovascular events--a longitudinal in vivo magnetic resonance imaging-based finite element study.

BACKGROUND: High-resolution magnetic resonance (MR) imaging has been used for MR imaging-based structural stress analysis of atherosclerotic plaques. The biomechanical stress profile of stable plaques has been observed to differ from that of unstable plaques; however, the role that structural stresses play in determining plaque vulnerability remains speculative. METHODS: A total of 61 patients with previous history of symptomatic carotid artery disease underwent carotid plaque MR imaging. Plaque components of the index artery such as fibrous tissue, lipid content and plaque haemorrhage (PH) were delineated and used for finite element analysis-based maximum structural stress (M-C Stress) quantification. These patients were followed up for 2 years. The clinical end point was occurrence of an ischaemic cerebrovascular event. The association of the time to the clinical end point with plaque morphology and M-C Stress was analysed. RESULTS: During a median follow-up duration of 514 days, 20% of patients (n = 12) experienced an ischaemic event in the territory of the index carotid artery. Cox regression analysis indicated that M-C Stress (hazard ratio (HR): 12.98 (95% confidence interval (CI): 1.32-26.67, p = 0.02), fibrous cap (FC) disruption (HR: 7.39 (95% CI: 1.61-33.82), p = 0.009) and PH (HR: 5.85 (95% CI: 1.27-26.77), p = 0.02) are associated with the development of subsequent cerebrovascular events. Plaques associated with future events had higher M-C Stress than those which had remained asymptomatic (median (interquartile range, IQR): 330 kPa (229-494) vs. 254 kPa (166-290), p = 0.04). CONCLUSIONS: High biomechanical structural stresses, in addition to FC rupture and PH, are associated with subsequent cerebrovascular events.

An emergency EVAR service reduces mortality in ruptured abdominal aortic aneurysms.

OBJECTIVES: The aim of this study was to compare all in-hospital mortality for ruptured abdominal aortic aneurysms (rAAAs) before and after the establishment of an emergency EVAR (eEVAR) service. DESIGN AND METHODS: An eEVAR service was established in January 2006, since when all patients presenting with rAAAs have been considered for endovascular repair. Data for all rAAAs presenting between January 2006 and December 2007 was prospectively collected (Group 1). This patient group was compared to those presenting with rAAA between January 2003 and December 2005 when eEVAR was not offered at our institution (Group 2). These records had also been collected prospectively and submitted to the National Vascular Database (NVD). RESULTS: A total of 50 rAAAs (17 eEVAR, 29 open repairs, 4 palliated) presented after the introduction of eEVAR (Group 1) and 71 in the historical Group 2 of which 54 underwent open repair and 17 were palliated. The total in-hospital mortality was significantly lower in Group 1 20% (eEVAR (n=1), 6%: Open (n=5), 17%: palliated (n=4), 100%) when compared to Group 2 54% (Open (n=21), 39%: palliated (n=17), 100%) (p=0.000001). Furthermore similar significant differences were seen in 30-day operative mortalities between the two groups 13% in Group 1 versus 39% in Group 2 (p=0.0003). In addition the proportion of patients who were palliated has significantly decreased (8% Group 1 versus 24% Group 2, p=0.01). CONCLUSIONS: The establishment of an eEVAR service has significantly reduced in-hospital mortality for patients presenting with ruptured abdominal aortic aneurysms.

The development of a VBHOM-based outcome model for lower limb amputation performed for critical ischaemia.

BACKGROUND: VBHOM (Vascular Biochemistry and Haematology Outcome Models) adopts the approach of using a minimum data set to model outcome and has been previously shown to be feasible after index arterial operations. This study attempts to model mortality following lower limb amputation for critical limb ischaemia using the VBHOM concept. METHODS: A binary logistic regression model of risk of mortality was built using National Vascular Database items that contained the complete data required by the model from 269 admissions for lower limb amputation. The subset of NVD data items used were urea, creatinine, sodium, potassium, haemoglobin, white cell count, age on and mode of admission. This model was applied prospectively to a test set of data (n=269), which were not part of the original training set to develop the predictor equation. RESULTS: Outcome following lower limb amputation could be described accurately using the same model. The overall mean predicted risk of mortality was 32%, predicting 86 deaths. Actual number of deaths was 86 (chi(2)=8.05, 8 d.f., p=0.429; no evidence of lack of fit). The model demonstrated adequate discrimination (c-index=0.704). CONCLUSIONS: VBHOM provides a single unified model that allows good prediction of surgical mortality in this high risk group of individuals. It uses a small, simple and objective clinical data set that may also simplify comparative audit within vascular surgery.

Temporal dependence of in vivo USPIO-enhanced MRI signal changes in human carotid atheromatous plaques.

INTRODUCTION: Ultrasmall superparamagnetic iron oxide (USPIO)-enhanced MRI has been shown to be a useful modality to image activated macrophages in vivo, which are principally responsible for plaque inflammation. This study determined the optimum imaging time-window to detect maximal signal change post-USPIO infusion using T1-weighted (T1w), T2*-weighted (T2*w) and quantitative T2* (qT2*) imaging. METHODS: Six patients with an asymptomatic carotid stenosis underwent high resolution T1w, T2*w and qT2* MR imaging of their carotid arteries at 1.5 T. Imaging was performed before and at 24, 36, 48, 72 and 96 h after USPIO (Sinerem, Guerbet, France) infusion. Each slice showing atherosclerotic plaque was manually segmented into quadrants and signal changes in each quadrant were fitted to an exponential power function to model the optimum time for post-infusion imaging. RESULTS: The power function determining the mean time to convergence for all patients was 46, 41 and 39 h for the T1w, T2*w and qT2* sequences, respectively. When modelling each patient individually, 90% of the maximum signal intensity change was observed at 36 h for three, four and six patients on T1w, T2*w and qT2*, respectively. The rates of signal change decrease after this period but signal change was still evident up to 96 h. CONCLUSION: This study showed that a suitable imaging window for T1w, T2*w and qT2* signal changes post-USPIO infusion was between 36 and 48 h. Logistically, this would be convenient in bringing patients back for one post-contrast MRI, but validation is required in a larger cohort of patients.

Invasive and non-invasive modalities of imaging carotid stenosis.

Despite recent therapeutic advances, acute ischemic complications of atherosclerosis remain the primary cause of morbidity and mortality in Western countries, with carotid atherosclerotic disease one of the major preventable causes of stroke. As the impact of this disease challenges our healthcare systems, we are becoming aware that factors influencing this disease are more complex than previously realized. In current clinical practice, risk stratification relies primarily on evaluation of the degree of luminal stenosis and patient symptomatology. Adequate investigation and optimal imaging are important factors that affect the quality of a carotid endarterectomy (CEA) service and are fundamental to patient selection. Digital subtraction angiography is still perceived as the most accurate imaging modality for carotid stenosis and historically has been the cornerstone of most of the major CEA trials but concerns regarding potential neurological complications have generated substantial interest in non-invasive modalities, such as contrast-enhanced magnetic resonance angiography. The purpose of this review is to give an overview to the vascular specialist of the current imaging modalities in clinical practice to identify patients with carotid stenosis. Advantages and disadvantages of each technique are outlined. Finally, limitations of assessing luminal stenosis in general are discussed. This article will not cover imaging of carotid atheroma morphology, function and other emerging imaging modalities of assessing plaque risk, which look beyond simple luminal measurements.

Five day antibiotic prophylaxis for major lower limb amputation reduces wound infection rates and the length of in-hospital stay.

OBJECTIVE: To compare wound infection, revision rates and hospital stay after major lower limb amputation between patients receiving 24 hours versus 5 days of prophylactic antibiotics. METHODS: The outcomes of a consecutive series of 40 major lower limb amputations in patients receiving a short 24-hour course of combined prophylactic antibiotics (flucloxacillin/vancomycin + gentamicin/ciproxin + metronidazole) were retrospectively analysed. Following this a further consecutive group of 40 major lower limb amputations were studied prospectively following the institution of a 5-day combined regime using the same antibiotics. RESULTS: The 2 groups of patients were similar in terms of demographics, vascular risk factors and level of amputation. The 5-day antibiotic regime led to a significant reduction in wound infection rates (5% vs. 22.5%, P=0.023) and a reduced length of hospital stay (22 vs. 34 days, P=0.001). Revision rates were lower (2.5% vs. 10%) but did not reach statistical significance (P=0.36). More patients in the prospective 5-day antibiotic series were operated on by the vascular trainee. (77.5% vs. 55% P=0.033). CONCLUSIONS: This data supports the use of a prolonged 5-day course of combined antibiotics after major lower limb amputation. This appears to reduce stump infection rates leading to shorter in-hospital stay.

Internal iliac artery branch graft for common iliac artery aneurysm following previous open abdominal aortic aneurysm repair.

To demonstrate the use of a commercially available branch stent graft system, designed to preserve the internal iliac artery (IIA) in common iliac artery (CIA) aneurysms (CIAA) in two patients, who had undergone previous abdominal aortic aneurysm (AAA) surgery.

Efficacy of TNP on lower limb wounds: a meta-analysis.

This meta-analysis of the three RCTs that have compared topical negative pressure with conventional treatment in patients with lower limb ulcers found that it significantly reduced healing times and increased the number of healed wounds.

Comparison of risk-scoring methods in predicting the immediate outcome after elective open abdominal aortic aneurysm surgery.

BACKGROUND & OBJECTIVES: The aim of this study was to apply three simple risk - scoring systems to prospectively collected data on all elective open Abdominal Aortic Aneurysm (AAA) operations in the Cambridge Academic Vascular Unit over a 6 - year period (January 1998 to January 2004), to compare their predictive values and to evaluate their validity with respect to prediction of mortality and post-operative complications. METHODS: 204 patients underwent elective open infra-renal AAA repair. Data were prospectively collected and risk assessment scores were calculated for mortality and morbidity according to the Glasgow Aneurysm Score (GAS), VBHOM (Vascular Biochemistry and Haematology Outcome Models) and Estimation of Physiologic Ability and Surgical Stress (E-PASS). RESULTS: The mortality rate was 6.3% (13/204) and 59% (121/204) experienced a post-operative complication (30-day outcome). For GAS, VBHOM and E-PASS the receiver operating characteristics (ROC) curve analysis for prediction of in-hospital mortality showed area under the curve (AUC) of 0.84 (95% confidence interval [CI], 0.76 to 0.92; p<0.0001), 0.82 (95% CI, 0.68 to 0.95; p=0.0001) and 0.92 (95% CI, 0.87 to 0.97; p<0.0001) respectively. There were also significant correlations between post-operative complications and length of hospital stay and each of the three scores, but the correlation was substantially higher in the case of E-PASS. CONCLUSIONS: All three scoring systems accurately predicted the risk of mortality and morbidity in patients undergoing elective open AAA repair. Among these, E-PASS seemed to be the most accurate predictor in this patient population.

Cardioprotection by remote ischaemic preconditioning.

Perioperative myocardial infarction is a leading cause of morbidity and mortality after major non-cardiac surgery. Pharmacological agents such as beta-blockers may reduce the risk but are associated with side-effects and may be contra-indicated in some patients. Basic scientific experiments and preliminary clinical trials in humans suggest that remote ischaemic preconditioning (RIPC), where brief ischaemia in one tissue confers resistance to subsequent sustained ischaemic insults in another tissue, may provide a simple, cost-effective means of reducing the risk of perioperative myocardial ischaemia. The Medline and Pubmed databases were searched for articles concerning RIPC. The mechanism may be humoral, neural, or a combination of both, and involves adenosine, opioids, bradykinins, protein kinase C, and K-ATP channels, although the precise end-effector remains unclear. Small randomized trials in humans undergoing major surgery suggest that RIPC induced by brief lower limb ischaemia significantly reduces myocardial injury. It may also reduce other ischaemic complications of surgery and anaesthesia. Small studies provide some evidence that RIPC could reduce myocardial injury and other ischaemic complications of surgery. However, large-scale clinical trials to assess the effect of RIPC on mortality and morbidity are required before RIPC can be recommended for routine clinical use.

Weekend effect in non-elective abdominal aortic aneurysm repair.

BACKGROUND: The 'weekend effect' describes the phenomenon where patient outcomes appear worse for those admitted at the weekend. It has been used recently to justify significant changes in UK health policy. Recent evidence has suggested that the effect may be due to a combination of inadequate correction for confounding factors and inaccurate coding. The effects of these factors were investigated in patients with acute abdominal aortic aneurysm (AAA). METHODS: Patients undergoing non-elective AAA repair entered into the UK National Vascular Registry from January 2013 until December 2015 were included in a case-control study. The patients were divided according to whether they were treated during the week (Monday 08.00 hours to Friday 17.00 hours) or at the weekend. Data extracted included demographics, co-morbidities, preoperative medications and baseline blood test results, as well as outcomes. Coding issues were investigated by looking at patients treated for ruptured, symptomatic or asymptomatic AAA within the non-elective cohort. The primary outcome was in-hospital mortality. Secondary outcomes included length of inpatient stay, and cardiac, respiratory and renal complications. RESULTS: The mortality rate appeared to be higher at the weekend (odds ratio (OR) 1·69, 95 per cent c.i. 1·47 to 1·94; P < 0·001), but this effect disappeared when confounding factors and coding issues were corrected for (corrected OR for ruptured AAA 1·09, 0·92 to 1·29; P = 0·330). Differences in outcomes were similar for prolonged length of hospital stay (uncorrected OR 1·21, 95 per cent c.i. 1·06 to 1·37, P = 0·005; corrected OR for ruptured AAA 1·06, 0·91 to 1·10, P = 0·478), and morbidity outcomes. CONCLUSION: After appropriate correction for confounding factors and coding effects, there was no evidence of a significant weekend effect in the treatment of non-elective AAA in the UK.

Anti-lymphocyte globulin therapy in aplastic anaemia--a university hospital experience.

Antilymphocyte globulin (ALG) was given every other day for 5 doses with platelet transfusions immediately following ALG administration in 6 patients with aplastic anaemia. Four patients responded and 3 durable remissions were achieved. One patient relapsed and further treatment with anti-thymocyte globulin and cyclosporin also failed. One patient died of Flavobacterium septicaemia 6 days after completion of ALG. Our data suggests that using an alternate day regimen, a response rate similar to a daily regimen can be obtained.

Remote preconditioning and major clinical complications following adult cardiovascular surgery: systematic review and meta-analysis.

BACKGROUND: A number of 'proof-of-concept' trials suggest that remote ischaemic preconditioning (RIPC) reduces surrogate markers of end-organ injury in patients undergoing major cardiovascular surgery. To date, few studies have involved hard clinical outcomes as primary end-points. METHODS: Randomised clinical trials of RIPC in major adult cardiovascular surgery were identified by a systematic review of electronic abstract databases, conference proceedings and article reference lists. Clinical end-points were extracted from trial reports. In addition, trial principal investigators provided unpublished clinical outcome data. RESULTS: In total, 23 trials of RIPC in 2200 patients undergoing major adult cardiovascular surgery were identified. RIPC did not have a significant effect on clinical end-points (death, peri-operative myocardial infarction (MI), renal failure, stroke, mesenteric ischaemia, hospital or critical care length of stay). CONCLUSION: Pooled data from pilot trials cannot confirm that RIPC has any significant effect on clinically relevant end-points. Heterogeneity in study inclusion and exclusion criteria and in the type of preconditioning stimulus limits the potential for extrapolation at present. An effort must be made to clarify the optimal preconditioning stimulus. Following this, large-scale trials in a range of patient populations are required to ascertain the role of this simple, cost-effective intervention in routine practice.

Signal-to-noise ratio increase in carotid atheroma MRI: a comparison of 1.5 and 3 T.

OBJECTIVES: This study reports quantitative comparisons of signal-to-noise ratio (SNR) at 1.5 and 3 T from images of carotid atheroma obtained using a multicontrast, cardiac-gated, blood-suppressed fast spin echo protocol. METHODS: 18 subjects, with carotid atherosclerosis (>30% stenosis) confirmed on ultrasound, were imaged on both 1.5 and 3 T systems using phased-array coils with matched hardware specifications. T(1) weighted (T(1)W), T(2) weighted (T(2)W) and proton density-weighted (PDW) images were acquired with identical scan times. Multiple slices were prescribed to encompass both the carotid bifurcation and the plaque. Image quality was quantified using the SNR and contrast-to-noise ratio (CNR). A phantom experiment was also performed to validate the SNR method and confirm the size of the improvement in SNR. Comparisons of the SNR values from the vessel wall with muscle and plaque/lumen CNR measurements were performed at a patient level. To account for the multiple comparisons a Bonferroni correction was applied. RESULTS: One subject was excluded from the protocol owing to image quality and protocol failure. The mean improvement in SNR in plaque was 1.9, 2.1 and 2.1 in T(1)W, T(2)W and PDW images, respectively. All plaque SNR improvements were statistically significant at the p<0.05 level. The phantom experiment reported an improvement in SNR of 2.4 for PDW images. CONCLUSIONS: Significant gains in SNR can be obtained for carotid atheroma imaging at 3 T compared with 1.5 T. There was also a trend towards increased CNR. However, this was not significant after the application of the Bonferroni correction.