Cardiovascular magnetic resonance at 3.0T: Current state of the art

Background

The assessment of arterial stiffness is increasingly used for evaluating patients with different cardiovascular diseases as the mechanical properties of major arteries are often altered. Aortic stiffness can be noninvasively estimated by measuring pulse wave velocity (PWV). Several methods have been proposed for measuring PWV using velocity-encoded cardiovascular magnetic resonance (CMR), including transit-time (TT), flow-area (QA), and cross-correlation (XC) methods. However, assessment and comparison of these techniques at high field strength has not yet been performed. In this work, the TT, QA, and XC techniques were clinically tested at 3 Tesla and compared to each other.

Methods

Fifty cardiovascular patients and six volunteers were scanned to acquire the necessary images. The six volunteer scans were performed twice to test inter-scan reproducibility. Patient images were analyzed using the TT, XC, and QA methods to determine PWV. Two observers analyzed the images to determine inter-observer and intra-observer variabilities. The PWV measurements by the three methods were compared to each other to test inter-method variability. To illustrate the importance of PWV using CMR, the degree of aortic stiffness was assessed using PWV and related to LV dysfunction in five patients with diastolic heart failure patients and five matched volunteers.

Results

The inter-observer and intra-observer variability results showed no bias between the different techniques. The TT and XC results were more reproducible than the QA; the mean (SD) inter-observer/intra-observer PWV differences were -0.12(1.3)/-0.04(0.4) for TT, 0.2(1.3)/0.09(0.9) for XC, and 0.6(1.6)/0.2(1.4) m/s for QA methods, respectively. The correlation coefficients (r) for the inter-observer/intra-observer comparisons were 0.94/0.99, 0.88/0.94, and 0.83/0.92 for the TT, XC, and QA methods, respectively. The inter-scan reproducibility results showed low variability between the repeated scans (mean (SD) PWV difference = -0.02(0.4) m/s and r = 0.96). The inter-method variability results showed strong correlation between the TT and XC measurements, but less correlation with QA: r = 0.95, 0.87, and 0.89, and mean (SD) PWV differences = -0.12(1.0), 0.8(1.7), and 0.65(1.6) m/s for TT-XC, TT-QA, and XC-QA, respectively. Finally, in the group of diastolic heart failure patient, PWV was significantly higher (6.3 ± 1.9 m/s) than in volunteers (3.5 ± 1.4 m/s), and the degree of LV diastolic dysfunction showed good correlation with aortic PWV.

Conclusions

In conclusion, while each of the studied methods has its own advantages and disadvantages, at high field strength, the TT and XC methods result in closer and more reproducible aortic PWV measurements, and the associated image processing requires less user interaction, than in the QA method. The choice of the analysis technique depends on the vessel segment geometry and available image quality.     

Static jaw collimation settings to minimize radiation dose to normal brain tissue during stereotactic radiosurgery

At the University of Arkansas for Medical Sciences (UAMS) intracranial stereotactic radiosurgery (SRS) is performed by using a linear accelerator with an add-on micromultileaf collimator (mMLC). In our clinical setting, static jaws are automatically adapted to the furthest edge of the mMLC-defined segments with 2-mm (X jaw) and 5-mm (Y jaw) margin and the same jaw values are applied for all beam angles in the treatment planning system. This additional field gap between the static jaws and the mMLC allows additional radiation dose to normal brain tissue. Because a radiosurgery procedure consists of a single high dose to the planning target volume (PTV), reduction of unnecessary dose to normal brain tissue near the PTV is important, particularly for pediatric patients whose brains are still developing or when a critical organ, such as the optic chiasm, is near the PTV. The purpose of this study was to minimize dose to normal brain tissue by allowing minimal static jaw margin around the mMLC-defined fields and different static jaw values for each beam angle or arc. Dose output factors were measured with various static jaw margins and the results were compared with calculated doses in the treatment planning system. Ten patient plans were randomly selected and recalculated with zero static jaw margins without changing other parameters. Changes of PTV coverage, mean dose to predefined normal brain tissue volume adjacent to PTV, and monitor units were compared. It was found that the dose output percentage difference varied from 4.9–1.3% for the maximum static jaw opening vs. static jaw with zero margins. The mean dose to normal brain tissue at risk adjacent to the PTV was reduced by an average of 1.9%, with negligible PTV coverage loss. This dose reduction strategy may be meaningful in terms of late effects of radiation, particularly in pediatric patients. This study generated clinical knowledge and tools to consistently minimize dose to normal brain tissue.     

Pyruvate improves cardiac electromechanical and metabolic recovery from cardiopulmonary arrest and resuscitation

Severe depletion of myocardial energy and antioxidant resources during cardiac arrest culminates in electromechanical dysfunction following recovery of spontaneous circulation (ROSC). A metabolic fuel and natural antioxidant, pyruvate augments myocardial energy and antioxidant redox states in parallel with its enhancement of contractile performance of stunned and oxidant-challenged hearts. This study tested whether pyruvate improves post-arrest cardiac function and metabolism. Beagles were subjected to 5 min cardiac arrest and 5 min open-chest cardiac compression (OCCC: 80 compressions min(-1); aortic pressure 60-70 mmHg), then epicardial dc countershocks (5-10 J) were applied to restore sinus rhythm. Pyruvate was infused i.v. throughout OCCC and the first 25 min ROSC to a steady-state arterial concentration of 3.6+/-0.2 mM. Control experiments received NaCl infusions. Phosphocreatine phosphorylation potential (approximately PCr) and glutathione/glutathione disulfide ratio (GSH/GSSG), measured in snap-frozen left ventricle, indexed energy and antioxidant redox states, respectively. In control experiments, left ventricular pressure development, dP/dt and carotid flow initially recovered upon defibrillation, but then fell 40-50% by 3 h ROSC. ST segment displacement in lead II ECG persisted throughout ROSC. Approximately PCr collapsed and GSH/GSSG fell 61% during arrest. Both variables recovered partially during OCCC and completely during ROSC. Pyruvate temporarily increased approximately PCr and GSH/GSSG during OCCC and the first 25 min ROSC and enhanced pressure development, dP/dt and carotid flow at 15-25 min ROSC. Contractile function stabilized and ECG normalized at 2-3 h ROSC, despite post-infusion pyruvate clearance and waning of its metabolic benefits. In conclusion, intravenous pyruvate therapy increases energy reserves and antioxidant defenses of resuscitated myocardium. These temporary metabolic improvements support post-arrest recovery of cardiac electromechanical performance.     

An epidemiological study of falls on integrated general medical wards

Reducing falls in hospital requires an environmental as well as a patient-orientated approach. We studied patient and ward characteristics relating to falls in an acute setting. In a prospective open observational study, we examined fall characteristics in two nuclear designed wards (A and B) and a longitudinal ward (C). We recorded 63 falls among 1609 patients. Ward C had the most falls (31 vs 18/14; p = 0.01), fall positive days (29 vs 15/10; p = 0.002) and fallers (27 vs 13/12; p = 0.001; OR 2.54, CI--1.41-4.57). Ward C had a higher cumulative risk of falls (p = 0.006) and fall positive days (p = 0.003). Choice of ward was a significant independent risk factor for falls (p = 0.01) when controlled for age, sex, and diagnostic variation between the wards. Most falls were intrinsic (A 66.7%, B 64.2%, C 61.3%, p = 0.45). A significantly higher proportion of falls on ward C occurred by the bed (p = 0.04). Significant differences exist between the wards, and fall reduction programmes should identify and compensate for adverse ward-related factors to increase the effectiveness of patient-targeted fall risk assessments.     

Flocculation of serum lipoproteins with cyclodextrins: application to assay of hyperlipidemic serum

We describe the complexation of isolated and native lipoproteins by natural macrocyclic polymers of glucose ("cyclodextrins"). Treatment of serum with cyclodextrin produces an immediate flocculation of the lipoproteins. The formation of cyclodextrin-lipoprotein complexes was evident on agarose electrophoresis gels. The concentration-dependent ability of alpha-cyclodextrin to precipitate chylomicrons and very-low-, low-, and high-density lipoproteins was used for clarifying lipemic serum. Results for normal and lipemic patients' specimens for some routinely measured analytes showed a good correlation between cyclodextrin treatment and ultracentrifugation. Unlike the use of organic solvents or ultracentrifugation, the proposed system provides a simple, mild, non-hazardous, and effective means for removing interfering lipid particles from biological specimens.     

Antiviral Action and Cellular Toxicity of Four Thymidine Analogues: 5-Ethyl-, 5-Vinyl-, 5-Propyl-, and 5-Allyl-2′-Deoxyuridine

5-Ethyl-, 5-vinyl-, 5-propyl-, and 5-allyl-2'-deoxyuridine (dUrd) had antiviral activity against herpes simplex type 1 and type 2 grown in HeLa TK(-) cells, in the order 5-vinyl-dUrd, 5-ethyl-dUrd, 5-propyl-dUrd, 5-allyl-dUrd, but they were inactive against a TK(-) mutant of herpes simplex type 1. The antiviral activity of these compounds could be partially reversed by thymidine. Except for 5-vinyl-dUrd, they were not toxic to WI-38 and HeLa TK(-) cells at a concentration of 25 muM. All four analogues inhibited the growth of herpes simplex type 1-transformed HeLa TK(-) cells at a concentration of 1 muM.     

SLATE: virtualizing multiscale CT training

Training on micro- and nano- computed tomography (CT) scanners has been traditionally conducted via extensive practice on the instrument. This entails presence of an instructor to guide through the training procedure, until reasonable experience is attained. Modern tomographic instruments being expensive to maintain, the operational costs escalates with increasing number of training conducted. In a pioneering approach, the technical know-how to operate such equipment has been partly imparted via virtual reality environment running on the Second Life grid. The experimentation has indicated a reduction of the total training time. The authors hope that in the long run, such techniques will aid in significant reduction of instruction time and costs associated with training.     

Impact of changes in viral marker screening assays

BACKGROUND: Monitoring the performance of routinely used infectious disease serologic tests is necessary to evaluate their effectiveness in identifying true-positive units and erroneously disqualifying safe blood donors. METHODS: With two large screening test data sets collected between 1991 and 1998 and between 1997 and 2000, the impact of changes in screening assays for HIV, HCV, and HBsAg was analyzed with regard to the prevalence of confirmed-positive, indeterminate, and confirmed-negative results and the deferral of donors with an indeterminate or negative results (donor loss). RESULTS: The prevalence of indeterminate results and donors loss increased significantly in the 6 months after introduction of an HIV-1/2 EIA. A second-generation HCV EIA increased the detection of confirmed-positive donations in repeat donors (p < 0.001) and increased the prevalence of indeterminate donations. Implementation of a third-generation HCV EIA resulted in a significant decrease in indeterminate results in first-time donors. Nonspecific test results increased when HBsAg test kits from a different manufacturer were introduced or different lots of HIV antibody screening test kits from the same manufacturer were used. CONCLUSION: Introduction of newly licensed versions of assays, switching kit manufacturers, and lot-to-lot variations have an impact on rates of deferrals of safe donors as well as sensitivity of routine screening. Before considering changes in screening tests, blood centers should be aware of, and evaluate, the potential impact on donor loss.     

Demonstration of viral thymidine kinase inhibitor and its effect on deoxynucleotide metabolism in cells infected with herpes simplex virus.

The thymidine analog 5'-ethynylthymidine was a potent inhibitor of herpes simplex virus type 1 (strain KOS)-induced thymidine kinase with a Ki value of 0.09 microM. 5'-Ethynylthymidine was less inhibitory against herpes simplex virus type 2 (strain 333)-induced thymidine kinase with a Ki of 0.38 microM and showed no inhibition against human cytosolic thymidine kinase under the conditions tested. The compound was effective against the altered thymidine kinase induced by acyclovir- and bromovinyldeoxyuridine-resistant virus variants. At 100 microM 5'-ethynylthymidine, the cellular pool size of dTTP in herpes simplex virus type 1-infected cells was 5% that of infected cells receiving no drug treatment, while there was no significant effect on the pool sizes of dATP, dGTP, and dCTP. There was a positive correlation between dTTP pools and the intracellular thymidine kinase activity of herpes simplex virus type 1-infected cells. When tested alone, 5'-ethynylthymidine exhibited no antiviral activity, but it antagonized the antiviral efficacy of five compounds which require viral thymidine kinase for their action.