Accelerating three‐dimensional molecular cardiovascular MR imaging using compressed sensing

Purpose:

To accelerate the acquisition of three‐dimensional (3D) high‐resolution cardiovascular molecular MRI by using Compressed Sensing (CS) reconstruction.

Materials and Methods:

Molecular MRI is an emerging technique for the early assessment of cardiovascular disease. This technique provides excellent soft tissue differentiation at a molecular and cellular level using target‐specific contrast agents (CAs). However, long scan times are required for 3D molecular MRI. Parallel imaging can be used to speed‐up these acquisitions, but hardware considerations limit the maximum acceleration factor. This limitation is important in small‐animal studies, where single‐coils are commonly used. Here we exploit the sparse nature of molecular MR images, which are characterized by localized and high‐contrast biological target‐enhancement, to accelerate data acquisition. CS was applied to detect: (a) venous thromboembolism and (b) coronary injury and aortic vessel wall in single‐ and multiple‐coils acquisitions, respectively.

Results:

Retrospective undersampling showed good overall image quality with accelerations up to four for thrombus and aortic images, and up to three for coronary artery images. For higher acceleration factors, features with high CA uptake were still well recovered while low affinity targets were less preserved with increased CS undersampling artifacts. Prospective undersampling was performed in an aortic image with acceleration of two, showing good contrast and well‐defined tissue boundaries in the contrast‐enhanced regions.

Conclusion:

We demonstrate the successful application of CS to preclinical molecular MR with target specific gadolinium‐based CAs using retrospective (accelerations up to four) and prospective (acceleration of two) undersampling. J. Magn. Reson. Imaging 2012; 36:1362–1371. © 2012 Wiley Periodicals, Inc.     

Key Performance Indicators in an Acute Surgical Unit: Have We Made an Impact?

Introduction

Timely access to acute surgery is a worldwide issue and New Zealand is similarly affected. Auckland City Hospital is one of the largest metropolitan public hospitals in New Zealand where more than 60?% of surgical admissions fit into the acute category. In January 2009, an Acute Surgical Unit (ASU) was set up to improve acute surgical flow. Key performance indicators (KPIs) were identified as valuable tools in evaluating ASU service performance. Our goals were to describe the current acute patient pathway, present the early trend of KPIs for the ASU?and determine whether an impact has been made on acute surgical patients.

Methods

A retrospective review of patients admitted with acute general surgical conditions from January 2008 (pre-ASU) to October 2010 was performed. Patient data were identified through hospital electronic records. KPIs assessed included: (1) time to assess referred patients from the emergency department (ED) and from GPs [where patient assessment occurs in the assessment and planning unit (APU)]; (2) preoperative length of stay (LOS[PO]); (3) length of stay of nonadmitted patients (LOS[NA]); (4) case volume “in?h” (0730–1730) versus “after?h”; and (5) readmission rate. Statistical analysis was performed?with one-way ANOVA, regression, and χ² tests.

Results

Results show a reduction of mean time from referral to assessment from 2.28 to 1.6?h in the ED (p?≤?0.001). Patients are seen in APU after GP referral sooner as well as the time from referral to assessment reducing from 2 to 1.76?h (p?<?0.001). The LOS[PO] has not changed significantly overall (34.58 vs. 34.88?h, p?=?not significant [NS]). However, there are encouraging signs in high-volume procedures, such as appendicectomy. The mean LOS[PO] for?appendicectomy was 7.81?h but is now?6.53?h (p?≤?0.005). The LOS[NA] has decreased from 15.23 to 9.48?h (p?<?0.005). Since the development of the ASU, the number of cases operated on “in?hours” is increasing with a corresponding decrease in “after?hours” operating.

Conclusions

Our?KPIs demonstrate an early positive trend of facilitating acute patient flow. There is minimal difference between pre- and post-ASU LOS[PO].The causes are likely multifactorial, including increased case volume displacing minor cases of lesser urgency, lack of operating staff,?and shortage of hospital beds in?winter months. This study supports the utility of?ASU in facilitating patient flow in a NZ metropolitan public hospital.     

Cycling-off modes during pressure support ventilation: Effects on breathing pattern,patient effort,and comfort

Purpose

Expiratory asynchrony during pressure support ventilation (PSV) has been recognized as a cause of patient discomfort, increased workload, and impaired weaning process. We evaluated breathing pattern, patient comfort, and patient effort during PSV comparing 2 flow termination criteria: fixed at 5% of peak inspiratory flow vs automatic, real-time, breath-by-breath adjustment within the range of 5% to 55%.

Materials and methods

Randomized crossover clinical trial. Sixteen awake patients, in the process of weaning, under PSV for more than 24 hours were subjected to 3 phases of PSV, each lasting 1 hour and using 1 of the 2 aforementioned termination criteria.

Results

Effective pressure support during automatic adjustment (AA) was 12.5 ± 3.2 cm H₂O vs 12.5 ± 3.9 cm H₂O (P = .9) with the fixed termination criterion, and external positive end-expiratory pressure was 6.2 ± 1.8 vs 6.8 ± 2 (P < .05). The effective termination criterion was higher during AA (31% [23-39] vs 12% [6-23]; P < .01), but without producing premature breath terminations. Pressure overshoots and alternative cycling-off were also decreased. Throughout the AA period, we observed a higher respiratory rate (24 ± 8 breaths/min vs 19 ± 6 breaths/min; P < .001), lower tidal volume (484 ± 88 mL vs 518 ± 102 mL; P < .001), and shorter inspiratory times (1.0 ± 0.3 seconds vs 1.3 ± 0.3 seconds; P < .001). Automatic adjustment was associated with lower airway occlusion pressure after 0.1 second (P0.1) (1.8 ± 0.9 cm H₂O vs 2.4 ± 1 cm H₂O; P < .01), lower pressure-time product to trigger the ventilator, and lower subjective discomfort (visual analog scale, 3.7 ± 1.3 vs 4.5 ± 1.2; P < .001).

Conclusions

When compared with a fixed termination criterion, the use of a variable, real-time–adjusted termination criterion improved some indices of patient-ventilator synchrony, producing better breathing pattern, less discomfort, and slightly lower patient effort during PSV.     

Association between tidal volume size,duration of ventilation,and sedation needs in patients without acute respiratory distress syndrome: an individual patient data meta-analysis

Purpose

Mechanical ventilation with lower tidal volumes (≤6 ml/kg of predicted body weight, PBW) could benefit patients without acute respiratory distress syndrome (ARDS). However, tidal volume reduction could be associated with increased patient discomfort and sedation needs, and consequent longer duration of ventilation. The aim of this individual patient data meta-analysis was to assess the associations between tidal volume size, duration of mechanical ventilation, and sedation needs in patients without ARDS.

Methods

Studies comparing ventilation with different tidal volume sizes in patients without ARDS were screened for inclusion. Corresponding authors were asked to provide individual participant data. Patients were assigned to three groups based on tidal volume size (≤6 ml/kg PBW, 6–10 ml/kg PBW, or ≥10 ml/kg PBW). Ventilator-free days, alive at day 28, and dose and duration of sedation (propofol and midazolam), analgesia (fentanyl and morphine), and neuromuscular blockade (NMB) were compared.

Results

Seven investigations (2,184 patients) were included in the analysis. The number of patients breathing without assistance by day 28 was higher in the group ventilated with tidal volume ≤6 ml/kg PBW compared to those ventilated with tidal volume ≥10 ml/kg PBW (93.1 vs. 88.6 %; p = 0.027, respectively). Only two investigations (187 patients) could be included in the meta-analysis of sedation needs. There were neither differences in the percentage of study days that patients received sedatives, opioids, or NMBA nor in the total dose of benzodiazepines, propofol, opioids, and NMBA.

Conclusions

This meta-analysis suggests that use of lower tidal volumes in patients without ARDS at the onset of mechanical ventilation could be associated with shorter duration of ventilation. Use of lower tidal volumes seems not to affect sedation or analgesia needs, but this must be confirmed in a robust, well-powered randomized controlled trial.     

Effects of alveolar recruitment maneuvers on clinical outcomes in patients with acute respiratory distress syndrome: a systematic review and meta-analysis

Purpose

To assess the effects of alveolar recruitment maneuvers (ARMs) on clinical outcomes in patients with acute respiratory distress syndrome (ARDS).

Methods

We conducted a search of the MEDLINE, EMBASE, LILACS, CINAHL, CENTRAL, Scopus, and Web of Science (from inception to July 2014) databases for all (i.e. no language restriction) randomized controlled trials (RCTs) evaluating the effects of ARMs versus no ARMs in adults with ARDS. Four teams of two reviewers independently assessed the eligibility of the studies identified during the search and appraised the risk of bias and extracted data from those which were assessed as meeting the inclusion criteria. Data were pooled using the random-effects model. Trial sequential analysis (TSA) was used to establish monitoring boundaries to limit global type I error due to repetitive testing for our primary outcome (in-hospital mortality). The GRADE system was used to rate the quality of evidence.

Results

Our database search identified ten RCTs (1,594 patients, 612 events) which satisfied the inclusion criteria. The meta-analysis assessing the effect of ARMs on in-hospital mortality showed a risk ratio (RR) of 0.84 [95 % confidence interval (CI) 0.74–0.95; I ² = 0 %], although the quality of evidence was considered to be low due to the risk of bias in the included trials and the indirectness of the evidence—that is, ARMs were usually conducted together with other ventilatory interventions which may affect the outcome of interest. There were no differences in the rates of barotrauma (RR 1.11; 95 % CI 0.78–1.57; I ² = 0 %) or need for rescue therapies (RR 0.76, 95 % CI 0.41–1.40; I ² = 56 %). Most trials found no difference between groups in terms of duration of mechanical ventilation and length of stay in the intensive care unit and hospital. The TSA showed that the available evidence for the effect of ARMs on in-hospital mortality is precise in the case of a type I error of 5 %, but it is not precise with a type I error of 1 %.

Conclusions

Although ARMs may decrease the mortality of patients with ARDS without increasing the risk for major adverse events, current evidence is not definitive. Large-scale ongoing trials addressing this question may provide data better applicable to clinical practice.