Socioeconomic deprivation and 1 year clinical outcomes after cryablation for atrial fibrillation

Funding Acknowledgements

Type of funding sources: None.

BACKGROUND

Socioeconomic deprivation has previously been demonstrated to result in worse heart failure and myocardial infarction outcomes. Published studies shown lower socioeconomic group to associate with higher prevalence of atrial fibrillation (AF), increased mortality and morbidity. However, the impact of socioeconomic deprivation on clinical outcomes post AF cryoablation has yet to be investigated.

AIM

To assess the impact of socioeconomic deprivation (as categorised by Scottish Index of Multiple Deprivation, SIMD) on the medical management and clinical outcomes of patients with AF treated by cryoablation. 

METHODS

A retrospective study of paroxysmal or persistent AF patients after cryoablation. The parameters included basic demographics, weight, past medical history (inclusive of hypertension, heart failure, diabetes, stroke or transient ischaemic attacks, prior myocardial infarction, obstructive sleep apnoea) and alcohol misuse. Medical treatment post AF ablation (Beta blocker, non-dihydropyridine calcium channel blocker, flecainide, amiodarone, dronaderone, sotolol, anticoagulant use) were also recorded.

Individual’s socioeconomic deprivation index, as described SIMD was also recorded (1 – most deprived and 10 – least deprived), and accordingly placed into quintile (SIMD 1-2,3-4,5-6,7-8, 9-10). Follow-up for 12 months.

Clinical outcome assessed was rate of readmission for symptomatic documented AF, rate of heart failure admission, stroke, bleeding diathesis and all-cause mortality.

RESULTS

312 patients were identified: 65 from the lowest quintile (SIMD 1-2), 57 from SIMD 3-4, 54 from SIMD 5-6, 52 from SIMD 7-8, and 84 from the highest quintile (SIMD 9-10).  No statistical difference exists between age, gender or weight. Lowest socioeconomic quintile has higher incidence of heart failure (p =0.018) but other past medical history was no different. No difference in incidence of alcohol misuse.

Prescription rate/rhythm control agents and anticoagulant use post ablation was not statistically different between all groups.

12 months follow-up demonstrated readmission for symptomatic documented AF was statistically higher among patients of lowest socioeconomic quintile (Keplan Meier plot, p = 0.001). Stepwise multiple regression analysis also confirmed multiple socioeconomic deprivation as an independent predictor for more adverse clinical outcome (p = 0.02).

Risk of readmission for AF in patients from the wealthiest socioeconomic group is almost a quarter as compared to those of most deprived social group (Odd-ratio 0.273 (95% CI 0.122 – 0.607)).

Other clinical outcomes including risk of admissions for heart failure, stroke, bleeding diathesis and all-cause mortality was not statistically different across all groups.

Summary

After cryoablation for AF, patients from the lower socioeconomic group are still more likely to experience readmission for symptomatic AF at 12-month, despite similar post-procedure pharmaceutical agents utilised.

Bumble bees regulate their intake of essential protein and lipid pollen macronutrients

Bee population declines are linked to the reduction of nutritional resources due to land-use intensification, yet we know little about the specific nutritional needs of many bee species. Pollen provides bees with their primary source of protein and lipids, but nutritional quality varies widely among host-plant species. Therefore, bees might have adapted to assess resource quality and adjust their foraging behavior to balance nutrition from multiple food sources. We tested the ability of two bumble bee species, Bombus terrestris and Bombus impatiens, to regulate protein and lipid intake. We restricted B. terrestris adults to single synthetic diets varying in protein:lipid ratios (P:L). The bees over-ate protein on low-fat diets and over-ate lipid on high-fat diets to reach their targets of lipid and protein, respectively. The bees survived best on a 10:1 P:L diet; the risk of dying increased as a function of dietary lipid when bees ate diets with lipid contents greater than 5:1 P:L. Hypothesizing that the P:L intake target of adult worker bumble bees was between 25:1 and 5:1, we presented workers from both species with unbalanced but complementary paired diets to determine whether they self-select their diet to reach a specific intake target. Bees consumed similar amounts of proteins and lipids in each treatment and averaged a 14:1 P:L for B. terrestris and 12:1 P:L for B. impatiens These results demonstrate that adult worker bumble bees likely select foods that provide them with a specific ratio of P:L. These P:L intake targets could affect pollen foraging in the field and help explain patterns of host-plant species choice by bumble bees.

Caffeine in floral nectar enhances a pollinator's memory of reward

Plant defense compounds occur in floral nectar, but their ecological role is not well understood. We provide evidence that plant compounds pharmacologically alter pollinator behavior by enhancing their memory of reward. Honeybees rewarded with caffeine, which occurs naturally in nectar of Coffea and Citrus species, were three times as likely to remember a learned floral scent as were honeybees rewarded with sucrose alone. Caffeine potentiated responses of mushroom body neurons involved in olfactory learning and memory by acting as an adenosine receptor antagonist. Caffeine concentrations in nectar did not exceed the bees' bitter taste threshold, implying that pollinators impose selection for nectar that is pharmacologically active but not repellent. By using a drug to enhance memories of reward, plants secure pollinator fidelity and improve reproductive success.

Caffeine in floral nectar enhances a pollinator's memory of reward

Plant defense compounds occur in floral nectar, but their ecological role is not well understood. We provide evidence that plant compounds pharmacologically alter pollinator behavior by enhancing their memory of reward. Honeybees rewarded with caffeine, which occurs naturally in nectar of Coffea and Citrus species, were three times as likely to remember a learned floral scent as were honeybees rewarded with sucrose alone. Caffeine potentiated responses of mushroom body neurons involved in olfactory learning and memory by acting as an adenosine receptor antagonist. Caffeine concentrations in nectar did not exceed the bees' bitter taste threshold, implying that pollinators impose selection for nectar that is pharmacologically active but not repellent. By using a drug to enhance memories of reward, plants secure pollinator fidelity and improve reproductive success.

In-vivo MRI and in-vivo electro-anatomical voltage map characteristics of infarct heterogeneity in a swine model

The arrhythmogenic substrate in patients with prior myocardial infarct (MI) is located at the border zone, BZ. In this study we correlated the BZ identified by two methods: electro-anatomical voltage mapping (EAVM) and a novel MRI method, multi-contrast late enhancement (MCLE). A pre-clinical porcine model with chronic MI was used to characterize BZ via MRI and EAVM. Results focus on the comparison between scar percentage and BZ percentage identified by each method. The correlation coefficient for BZ percentage between the two methods was 0.74 with a p-value of less the 0.0001. Bland-Altman plots were also used to compare between the two methods (slope of 0.83 ± 0.045). For a case of subtle infarct, there was only 1.3% infarct identified on EAVM compared to 22.2% on the corresponding slice on MCLE. The percentage of infarct on MCLE in subtle infarct does not relate to percentage of infarct in EAVM. Future registration between T(1) maps and EAVM will permit a quantitative comparison of MRI and EAVM measures.

Inter-model consistency and complementarity: learning from ex-vivo imaging and electrophysiological data towards an integrated understanding of cardiac physiology

Computational models of the heart at various scales and levels of complexity have been independently developed, parameterised and validated using a wide range of experimental data for over four decades. However, despite remarkable progress, the lack of coordinated efforts to compare and combine these computational models has limited their impact on the numerous open questions in cardiac physiology. To address this issue, a comprehensive dataset has previously been made available to the community that contains the cardiac anatomy and fibre orientations from magnetic resonance imaging as well as epicardial transmembrane potentials from optical mapping measured on a perfused ex-vivo porcine heart. This data was used to develop and customize four models of cardiac electrophysiology with different level of details, including a personalized fast conduction Purkinje system, a maximum a posteriori estimation of the 3D distribution of transmembrane potential, the personalization of a simplified reaction-diffusion model, and a detailed biophysical model with generic conduction parameters. This study proposes the integration of these four models into a single modelling and simulation pipeline, after analyzing their common features and discrepancies. The proposed integrated pipeline demonstrates an increase prediction power of depolarization isochrones in different pacing conditions.

Development and validation of a clinical score to identify echocardiographic left ventricular hypertrophy in patients with cardiovascular disease

BACKGROUND

Echocardiographic (echo) left ventricular hypertrophy (LVH) is an independent predictor of mortality. Despite this, screening for LVH in patients with overt cardiovascular diseases is not universally done. To help target echo screening for LVH in patient population, we developed and validated a simple clinical score to help identify those likely to have echo LVH.

METHODS

We performed two studies. The development cohort consisted of 267 patients with angina. The validation cohort consisted of 227 patients with peripheral arterial disease.

RESULTS

The prevalence of echo LVH in both patient cohorts was 50%. Six independent predictors of LVH were identified in the development cohort: age >65 years (1 point), body mass index >30 kg/m2 (1 point), history of hypertension (1 point), previous myocardial infarction (1 point), clinic blood pressure >130/80 mm Hg (1 point) and bundle branch block (BBB) on electrocardiogram (4 points). Our clinical score was strongly associated with the presence of LVH in the validation cohort. It also showed a significant continuous positive relationship (P trend <0.001 in males and P trend = 0.006 in females) with increasing quartiles of LV mass in both cohorts. In those without BBB, a modified clinical score performed equally well.

CONCLUSION

We have developed a simple clinical score which quantifies the chance that any patient with manifest cardiovascular disease has the added risk factor of LVH. This will help target precious echo resources toward individuals who are most likely to have this condition. This could potentially lead to better risk stratification in this patient population.

Cardiac electrophysiology model adjustment using the fusion of MR and optical imaging

Despite important recent efforts in cardiac electrophysiology modelling, there is still a strong need for validating macroscopic models, that are well suited for diagnosis and treatment planning. In this paper we present a method to adjust the parameters of a macroscopic electrophysiology model on depolarisation and repolarisation maps obtained ex-vivo from optical imaging. With this imaging technique, optical fluorescence data are recorded with high spatial and temporal resolution on a large healthy porcine heart. A model of the myocardium is built from the MR images of the same heart, which also integrates the myocardial fibre orientation measured with DTI. We then present the first quantitative adjustment of a personalised volumetric model of the myocardium.

Inversion-recovery-prepared SSFP for cardiac-phase-resolved delayed-enhancement MRI

Delayed-enhancement magnetic resonance imaging (DE-MRI) can be used to visualize myocardial infarction (MI). DE-MRI is conventionally acquired with an inversion-recovery gradient-echo (IR-GRE) pulse sequence that yields a single bright-blood image. IR-GRE imaging requires an accurate estimate of the inversion time (TI) to null the signal from the myocardium, and a separate cine acquisition is required to visualize myocardial wall motion. Simulations were performed to examine the effects of a steady-state free precession (SSFP) readout after an inversion pulse in the setting of DE-MRI. Using these simulations, a segmented IR-SSFP sequence was optimized for infarct visualization. This sequence yields both viability and wall motion images over the cardiac cycle in a single breath-hold. Viability images at multiple effective TIs are produced, providing a range of image contrasts. In a study of 11 patients, IR-SSFP yielded infarct sizes and left ventricular ejection fractions (LVEFs) similar to those obtained by IR-GRE and standard SSFP, respectively. IR-SSFP images yielded improved visualization of the infarct-blood border because of the simultaneous nulling of healthy myocardium and blood. T(1) (*) recovery curves were extracted from IR-SSFP images and showed excellent qualitative agreement with theoretical simulations.

T2 fluctuations in ischemic and post-ischemic viable porcine myocardium in vivo

T2 relaxation can augment delayed-enhancement viability imaging because it is sensitive to tissue edema and microcirculatory oxygen state. We demonstrate the T2 'signatures' of sub-lethal ischemia and stunning in porcine myocardium perfused by the distal left anterior descending artery, by imaging during percutaneous balloon occlusion for 25 minutes and subsequent reperfusion (n = 9). Muscle displayed ischemic dysfunction and partial post-ischemic functional recovery (p < or = 0.0004), concommitant with an elevated post-ischemic T2 (deltaT2 = 27 +/- 18%, p = 0.005). TTC staining verified muscle viability. The T2 fluctuations may reflect hyperemia and tissue cellular edema in accord with the known pathophysiology of ischemic and post-ischemic yet viable muscle.

MRI relaxation fluctuations in acute reperfused hemorrhagic infarction

MRI evaluations of intramyocardial hemorrhage in acute infarction have relied on T(2) and T(2)(*) shortening only. We propose a more comprehensive evaluation of hemorrhagic infarction based on the concept that fluctuations in T(2) and T(1) relaxation in acute reperfused infarction will reflect transient edema and hemoglobin oxidative denaturation to uncompartmentalized methemoglobin. Anteroapical infarction was created via percutaneous balloon in young swine (22-25 kg, N = 12). T(2), T(1), diastolic wall thickness (DWT), and the Gd-DTPA partition coefficient (lambda) were measured on days 0, 2, and 7. DWT was elevated at 1 hr postreperfusion (128% +/- 53%, P = 0.0001), and alleviated on days 2 and 7 (48% +/- 10%, P = 0.008; 53% +/- 24%, P = 0.003). T(2) and T(1) elevations were coincident with early edema (DeltaT(2) = 55% +/- 24%, P < 0.0001; DeltaT(1) = 27% +/- 18%, P < 0.04). T(2) and T(1) were nearly normal on day 2 (DeltaT(2) = 8% +/- 8%, P = 0.27; DeltaT(1) = 0% +/- 1%, P = 0.65). On day 7, T(2) increased while T(1) decreased (DeltaT(2) = 27% +/- 16%, P = 0.005; DeltaT(1) = -14% +/- 10%, P = 0.02). Lambda was elevated by >150% at all time points (P < or = 0.002). Histology verified hemorrhagic injury. T(1) and T(2) fluctuations are consistent with transient edema, as well as hemoglobin oxidative denaturation to decompartmentalized methemoglobin. This methodological development may broaden our understanding of hemorrhagic microvascular injury and improve its detection in clinical populations.

Natriuretic peptides as a prognostic marker and therapeutic target in heart failure

Natriuretic peptides may have an increasing role in assisting clinicians to target treatment in patients with chronic heart failure.

Application of MCBEND to PBMR shielding analysis

Shielding analysis of an early design of Pebble Bed Modular Reactor (PBMR) has been carried out by using the Monte Carlo code MCBEND. The issues of concern were damage to the core barrel and the reactor pressure vessel (RPV), activation of the core barrel, RPV, top plate and bottom plate, and also burn-up of boron in the control layer underneath the core. The analysis below the core was complicated due to the presence of the de-fuelling chute, which meant that multiplication had to be taken into account. The analysis of boron burn-up was particularly challenging and was tackled using a combination of MCBEND and the criticality code MONK in the depletion mode. The application of MCBEND to the shielding analysis of the PBMR is described, with particular attention being paid to the regions below the core.

In Vitro Generation and Stability of the Lactokinin β-Lactoglobulin Fragment (142–148)

The objectives of this study were to investigate the generation of beta-lactoglobulin fragment (142-148) (beta-LG f(142-148) during the hydrolysis of whey proteins, and the in vitro stability of this fragment upon incubation with gastrointestinal and serum proteinases and peptidases. An enzyme immunoassay (EIA) protocol was developed for the quantification of beta-LG f(142-148) in whey protein hydrolysates and in human blood serum. The minimum detection limit was 3 ng/mL. The level of the peptide in whey protein hydrolysates was influenced by the degree of hydrolysis (DH). As expected, highest levels of this peptide were found in hydrolysates generated with trypsin. Sequential incubation of hydrolysates at different DH values with pepsin and Corolase PP, to simulate gastrointestinal digestion, generally resulted in the degradation of beta-LG f(142-148) as determined by EIA. Reversed-phase HPLC and angiotensin-I-converting enzyme (ACE) activity assays demonstrated that synthetic beta-LG f(142-148) was rapidly degraded upon incubation with human serum. Furthermore, beta-LG f(142-148) could not be detected by EIA in the sera of 2 human volunteers following its oral ingestion or in sera from these volunteers subsequently spiked with beta-LG f(142-148). These in vitro results indicate that beta-LG f(142-148) is probably not sufficiently stable to gastrointestinal and serum proteinases and peptidases to act as an hypotensive agent in humans following oral ingestion. The in vitro methodology described herein has general application in evaluating the hypotensive potential of food protein-derived ACE inhibitory peptides.

In vitro generation and stability of the lactokinin beta-lactoglobulin fragment (142-148)

The objectives of this study were to investigate the generation of beta-lactoglobulin fragment (142-148) (beta-LG f(142-148) during the hydrolysis of whey proteins, and the in vitro stability of this fragment upon incubation with gastrointestinal and serum proteinases and peptidases. An enzyme immunoassay (EIA) protocol was developed for the quantification of beta-LG f(142-148) in whey protein hydrolysates and in human blood serum. The minimum detection limit was 3 ng/mL. The level of the peptide in whey protein hydrolysates was influenced by the degree of hydrolysis (DH). As expected, highest levels of this peptide were found in hydrolysates generated with trypsin. Sequential incubation of hydrolysates at different DH values with pepsin and Corolase PP, to simulate gastrointestinal digestion, generally resulted in the degradation of beta-LG f(142-148) as determined by EIA. Reversed-phase HPLC and angiotensin-I-converting enzyme (ACE) activity assays demonstrated that synthetic beta-LG f(142-148) was rapidly degraded upon incubation with human serum. Furthermore, beta-LG f(142-148) could not be detected by EIA in the sera of 2 human volunteers following its oral ingestion or in sera from these volunteers subsequently spiked with beta-LG f(142-148). These in vitro results indicate that beta-LG f(142-148) is probably not sufficiently stable to gastrointestinal and serum proteinases and peptidases to act as an hypotensive agent in humans following oral ingestion. The in vitro methodology described herein has general application in evaluating the hypotensive potential of food protein-derived ACE inhibitory peptides.

A comparison of nutritional regulation in solitarious- and gregarious-phase nymphs of the desert locust Schistocerca gregaria

Nutritional regulatory responses were compared for the cryptic ‘solitarious’ and the conspicuously coloured, aggregating ‘gregarious’ phases of the desert locust Schistocerca gregaria. The desert locust has the genetic potential to exist in either phase, changing between them within a lifetime and epigenetically across generations. Our aim was to compare final-instar nymphs of the two phases with respect to key nutritional variables, including (i) points of regulated intake (the ‘intake target’) for protein and carbohydrate, (ii) the nature of trade-offs between over-eating nutrients in excess and under-eating those in deficit when fed nutritionally unbalanced foods, (iii) diet-related patterns of nutrient utilisation, and (iv) the performance consequences of eating nutritionally unbalanced diets. When provided with pairs of nutritionally unbalanced but complementary foods, both phases regulated their intake of protein and carbohydrate to a similar point. However, when confined to foods that were of unbalanced protein to carbohydrate ratio, gregarious nymphs ate more than solitarious insects. Both phases regulated protein growth, but gregarious insects did so to a lower adult body protein content and converted ingested protein to growth less efficiently. When fed a food high in carbohydrate and low in protein, gregarious nymphs deposited more body lipid and survived less well than did solitarious insects. Solitarious nymphs developed more quickly than gregarious nymphs except on the two most extremely unbalanced diets, on which development time was similar. The results are discussed with respect to the different nutritional ecologies of the two phases and used to develop the hypothesis that animals have evolved to trade-off the cost of eating excess of a nutritionally unbalanced diet against the probability of encountering foods of complementary composition in the future.

Intracranial arteriovenous malformations: real-time auto-triggered elliptic centric-ordered 3D gadolinium-enhanced MR angiography--initial assessment

Auto-triggered elliptic centric-ordered three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography was compared with 3D multiple overlapping thin-slab acquisition time-of-flight (TOF) MR angiography in the evaluation of intracranial arteriovenous malformations (AVMs) in 10 patients. Intraarterial digital subtraction angiography (DSA) was the reference standard. Gadolinium-enhanced MR angiograms were found to be equivalent to DSA images in AVM component depiction in 70%--90% of cases and were consistently superior to TOF MR angiograms.

Are ejection fractions from gated SPECT perfusion studies clinically useful? A comparison with radionuclide ventriculography

Gated SPECT (GSPECT) was evaluated for the measurement of left ventricular ejection fraction (LVEF) by comparing with equilibrium gated radionuclide ventriculography (RNVG). A total of 99 subjects underwent GSPECT and RNVG imaging. All studies were acquired in list mode with GSPECT studies processed to give 16- and 8-frames per R-R interval, and RNVG studies 24 frames per R-R interval. The Cedars-Sinai QGS software was used to calculate ejection fraction from GSPECT studies. RNVG studies were processed using a manually drawn single region of interest technique. Comparison of LVEF from GSPECT with RNVG yielded correlation coefficients of 0.82 and 0.81 for 16- and 8-frame GSPECT studies respectively. The mean 95% prediction interval was 33 +/- 11 percentage points for both 16- and 8-frame studies, indicating a great disparity between predicted ejection fraction values from GSPECT and actual RNVG values. Subgroup analysis of 29 patients with pathological Q-wave evidence of myocardial infarction demonstrated a poorer correlation coefficient of r = 0.69. Subgroup analysis of 32 patients with end-diastolic volumes < 100 ml demonstrated a poorer correlation coefficient of r = 0.32. Ejection fractions calculated from 16- and 8-frame studies showed a correlation of 0.99 with a mean 95% prediction interval of 8.7 +/- 0.04 percentage points. The 8-frame studies underestimated LVEF by 3.6 +/- 2.3% compared to the 16-frame studies. In conclusion, left ventricular ejection fractions calculated using the QGS algorithm from GSPECT studies are inadequate for use in clinical practice.

Monitoring blood oxygen state in muscle microcirculation with transverse relaxation

Oxygen uptake from the microcirculation is a direct measure of tissue function. Magnetic resonance is capable of detecting differences between oxygenated and deoxygenated blood due to the paramagnetic properties of deoxyhemoglobin. At the level of the microcirculation, however, imaging methods cannot directly visualize the vessels. Instead, bulk MR parameters are investigated for their ability to monitor blood oxygen saturation (%O(2)) changes in the microcirculation of tissue, specifically skeletal muscle. Experiments in an in vitro model verified the feasibility of detecting changes in exponential decay signals, and also verified the prediction of only two distinct decay components. Experiments in a rabbit model demonstrate that T(2)' and monoexponential T(2) decay are not sensitive to blood oxygen changes, but that the long-T(2) component in a biexponential fit is correlated to the blood oxygen state. Assuming a two-pool model for water protons in muscle, and with knowledge of the T(2)-%O(2) relation, estimates of the microcirculation blood oxygen state can be made with some reasonable assumptions. Magn Reson Med 45:662-672, 2001.

Partial discrete Fourier transform (PDFT) multiband encoding

For conventional multiband encoding techniques such as Hadamard encoding, scan time scales linearly with the number of slices encoded simultaneously. In this work, a new multiband encoding technique called partial discrete Fourier transform (PDFT) encoding is introduced, which overcomes this restriction. This technique incorporates the principle of partial Fourier imaging, allowing the tradeoff of SNR and imaging time without changing the number of slices. The theory behind PDFT encoding and its inherent sensitivity to phase errors are outlined. The theory was validated through simulations, showing that phase errors result in degraded slice localization. The feasibility of PDFT encoding of 12 slices was tested with experimental excitation profile measurements and heart images of a human subject using commercial MRI equipment. Imaging time was reduced to 66% with SNR reduced to 82%. Magn Reson Med 45:118-127, 2001.

Quantitative gated SPECT myocardial perfusion imaging with 201Tl: an assessment of the limitations

Gated SPECT (GSPECT) perfusion imaging has been increasing in popularity both with 99Tc(m) agents and 201Tl. However, both higher activities than administered in the UK and multi-headed cameras are often used. The aim of this study was to assess GSPECT imaging using lower activities of 201Tl with a single-headed camera. Seventy patients underwent stress and redistribution GSPECT imaging after a mean injected activity of 62 +/- 7 MBq 201Tl. These patients also underwent radionuclide ventriculography (RNVG) imaging. The Cedars Sinai Quantitative Gated SPECT (QGS) package was used to calculate left ventricular ejection fraction (LVEF) from the GSPECT studies. Comparison of ejection fractions calculated using GSPECT with those calculated using RNVG yielded a correlation coefficient of 0.70 for the stress studies and 0.71 for the redistribution studies. The width of the mean 95% prediction interval ranged from 22 to 74 percentage points for the stress studies and 22 to 86 percentage points for the redistribution studies. Ejection fractions calculated from stress and redistribution GSPECT studies showed a correlation of 0.80 with a mean 95% prediction interval of 42.6 +/- 0.4 percentage points. In conclusion, left ventricular ejection fractions calculated using the QGS algorithm from 201Tl GSPECT studies are inadequate for use in clinical practice.

Prostate cancer: MR imaging and thermometry during microwave thermal ablation-initial experience

Percutaneous interstitial microwave thermoablation of locally recurrent prostate carcinoma was continually guided with magnetic resonance (MR) imaging. Phase images and data were obtained with a rapid gradient-echo technique and were used to derive tissue temperature change on the basis of proton-resonance shift. Thermally devitalized regions correlated well with the phase image findings. MR imaging-derived temperatures were linearly related to the fluoroptic tissue temperatures. MR imaging can be used to guide thermoablation.

Coronary venous oximetry using MRI

Based on the Fick law, coronary venous blood oxygen measurements have value for assessing functional parameters such as the coronary flow reserve. At present, the application of this measure is restricted by its invasive nature. This report describes the design and testing of a noninvasive coronary venous blood oxygen measurement using MRI, with a preliminary focus on the coronary sinus. After design optimization including a four-coil phased array and an optimal set of data acquisition parameters, quality tests indicate measurement precision on the order of the gold standard optical measurement (3%O(2)). Comparative studies using catheter sampling suggest reasonable accuracy (3 subjects), with variability dominated by sampling location uncertainty ( approximately 7%O(2)). Intravenous dipyridamole (5 subjects) induces significant changes in sinus blood oxygenation (22 +/- 9% O(2)), corresponding to flow reserves of 1.8 +/- 0.4, suggesting the potential for clinical utility. Underestimation of flow reserve is dominated by right atrial mixing and the systemic effects of dipyridamole. Magn Reson Med 42:837-848, 1999.

Four new tetranortriterpenoids from cedrela odorata associated with leaf rejection by exopthalmus jekelianus

Four new tetranortriterpenoids, 3-deoxo-3beta,8beta-epoxy-6, 14alpha-dihydroxy-8,14-dihydromexicanolide (cedrodorin, 1); 3-deoxo-3beta,8beta-epoxy-6-acetoxy-14alpha-hydroxy-8, 14-dihydromexicanolide (6-acetoxycedrodorin, 2); 3-deoxo-3beta, 8beta-epoxy-6-deoxy-9alpha,14alpha-dihydroxy-8, 14-dihydromexicanolide (6-deoxy-9alpha-hydroxycedrodorin, 3); and 3-deoxo-3beta,8beta-epoxy-6,9alpha,14alpha-trihydroxy-8, 14-dihydromexicanolide (9alpha-hydroxycedrodorin, 4), have been isolated from the leaves of Cedrela odorata by HPLC. Their molecular structures were determined by 1D and 2D NMR. Three of the compounds are associated with leaf rejection by the polyphagous, folivorous weevil, Exopthalmus jekelianus. The importance of these compounds as insect deterrents in C. odorata, and their potential value in the selection of insect-resistant clones for timber plantations is discussed.

Effects of a thirteen-week inhalation exposure to ethyl tertiary butyl ether on fischer-344 rats and CD-1 mice

The 1990 Clean Air Act Amendments require that oxygenates be added to automotive fuels to reduce emissions of carbon monoxide and hydrocarbons. One potential oxygenate is the aliphatic ether ethyl tertiary butyl ether (ETBE). Our objective was to provide data on the potential toxic effects of ETBE. Male and female Fisher 344 rats and CD-1 mice were exposed to 0 (control), 500, 1750, or 5000 ppm of ETBE for 6 h/day and 5 days/wk over a 13-week period. ETBE exposure had no effect on mortality and body weight with the exception of an increase in body weights of the female rats in the 5000-ppm group. No major changes in clinical pathology parameters were noted for either rats or mice exposed to ETBE for 6 (rats only) or 13 weeks. Liver weights increased with increasing ETBE-exposure concentration for both sexes of rats and mice. Increases in kidney, adrenal, and heart (females only) weights were noted in rats. Degenerative changes in testicular seminiferous tubules were observed in male rats exposed to 1750 and 5000 ppm but were not seen in mice. This testicular lesion has not been reported previously for aliphatic ethers. Increases in the incidence of regenerative foci, rates of renal cell proliferation, and alpha2u-globulin containing protein droplets were noted in the kidneys of all treated male rats. These lesions are associated with the male rat-specific syndrome of alpha2u-globulin nephropathy. Increases in the incidence of centrilobular hepatocyte hypertrophy and rates of hepatocyte cell proliferation were seen in the livers of male and female mice in the 5000-ppm group, consistent with a mitogenic response to ETBE. These two target organs for ETBE toxicity, mouse liver and male rat kidney, have also been reported for methyl tertiary butyl ether and unleaded gasoline.

In vivo flow-independent T2 measurements of superior mesenteric vein blood in diagnosis of chronic mesenteric ischemia: a preliminary evaluation

RATIONALE AND OBJECTIVES

The authors attempted to determine whether the T2 relaxation time of superior mesenteric vein (SMV) blood would decrease in patients with chronic mesenteric ischemia after a meal.

MATERIALS AND METHODS

Thirty-two patients without chronic mesenteric ischemia and eight patients with symptomatic chronic mesenteric ischemia underwent magnetic resonance (MR) imaging. All examinations were performed with a 1.5-T unit, a modified Carr-Purcell-Meiboom-Gill sequence, final section-selective pulse of 180 degrees, and spiral readout gradients. Measurements of SMV blood T2 were obtained after at least 6 hours of fasting and 15 and 35 minutes after ingestion of 240 mL of a liquid nutritional supplement. Maximal change of the SMV blood T2 was expressed as a percentage of the fasting T2 in all patients.

RESULTS

In control patients, SMV blood T2 increased postprandially by 9.4% +/- 1.3 (95% confidence level; range, 6.8%-11.9%) (data range, -7.3% to 25.6%) compared with fasting T2. In symptomatic patients, SMV blood T2 decreased postprandially by 15.8% +/- 2.2 (95% confidence level; range, -20.1% to -10.7%) (data range, -7.9% to -25.3%). The difference between the two groups was statistically significant (P < .0001 by Student unpaired t test).

CONCLUSION

Measurement of SMV blood T2 is a promising test for chronic mesenteric ischemia diagnosis. Therefore, conversion of T2 measurements to estimate oxygen saturation may not be necessary for all cases of this clinical indication.

Tracking oxygen effects on MR signal in blood and skeletal muscle during hyperoxia exposure

Blood and muscle T1 and T2 relaxivity was examined under normoxic (air; 20.8% O2) and hyperoxic (100% O2) conditions to determine whether the oxygenation state of blood in the large vessels and in the microcirculation can be monitored in vivo. The femoral artery/vein and the soleus and gastrocnemius muscles were examined in healthy human male volunteers. Arterial blood T1 decreased with hyperoxia, while venous blood T2 increased, due to increased dissolved O2 and decreased deoxyhemoglobin, respectively. A biexponential T2 model of muscle is proposed, where the short T2 component reflects primarily the intracellular and interstitial compartments (in fast exchange), and the long T2 reflects blood. In this model, the long T2 component increased with hyperoxia exposure. This was more evident in slow twitch (soleus) than in fast twitch (gastrocnemius) muscle. It is concluded that changes in the long T2 component reflect change in the microcirculation oxygenation state.

Differentiation of hepatic malignancies from hemangiomas and cysts by T2 relaxation times: early experience with multiply refocused four-echo imaging at 1.5 T

The purpose of this study was to examine hepatic lesions with a sequence designed to yield improved T2 measurements and evaluate the clinical utility of these measurements in distinguishing malignant from benign disease. Using a modified Carr-Purcell sequence incorporating features designed to compensate for imperfections in the imaging system, including a train of refocusing pulses emitted in an MLEV pattern oriented in composite fashion along all three coordinate axes, and a single spatially selective pulse placed immediately before a spiral readout, 14 benign lesions and 13 malignant lesions were evaluated prospectively with a conventional 1.5 T imager. The maximum, minimum, and mean T2 values of malignant lesions, hemangiomas, and cysts exceeded corresponding published values from spin-echo and echoplanar studies. The mean T2 value of the malignant lesions differed significantly (P < 0.0001) from those of hemangiomas and cysts. All malignant lesions and all benign lesions were distinguishable by their T2 values, which had ranges of no greater than 118.6 msec and no less than 134.3 msec, respectively. This early experience suggests that improved T2 measurements can facilitate the differentiation of hepatic malignancies from hemangiomas and cysts.

Design of practical T2-selective RF excitation (TELEX) pulses

Traditional T2-based imaging techniques are geared toward imaging long-T2 species. Traditional techniques are, therefore, not optimal in clinical situations where the information of interest lies in the short-T2 species. T2-selective RF excitation (TELEX) is a technique for obtaining a T2-based contrast that highlights short-T2 values while suppressing long-T2 values-opposite to traditional T2 contrast. Previously, TELEX has been demonstrated qualitatively to highlight only very short-T2 values (T2 approximately 0.001 s). When applied to longer T2 values (T2 > or = 0.01 s), TELEX becomes sensitive to deltaB0 non-uniformities. This restricts its application to problems in which the T2 of interest is very short. In this study, TELEX is characterized quantitatively. Furthermore, a bandwidth broadening scheme is developed that reduces the deltaB0 sensitivity of TELEX. This permits the technique to be applied to longer T2 values. The capabilities and limitations of a practical implementation of TELEX are discussed.

Partial volume effects on vascular T2 measurements

Quantitative, vascular T2 measurements are of interest for applications such as MR oximetry. In the situation of a vessel with long T2 relaxation times embedded in tissue with relatively short T2 values, contamination of the blood signal from the surrounding tissue can bias T2 measurements. Limited data sampling and vessels running obliquely through the imaging slice can cause significant signal contamination. Using a model of these effects to predict the behavior of T2 measurements under a range of conditions, a set of parameters that provides the best combination of measurement accuracy with a signal-to-noise ratio as high as possible is proposed.

Dynamic scan-plane tracking using MR position monitoring

An MR-based method for tracking subject motion is presented. The technique identifies subject motion from the three-dimensional positions of three small samples attached to the subject in a fixed, triangular configuration. The updated positions of these samples relative to their initial positions determine a rigid body transformation. Applied to the MRI scan prescription via adaptive feedback controls, this transformation yields an updated MRI scan plane that tracks the prescribed imaging section as the subject moves. The scan-plane tracking procedure is demonstrated experimentally for two-dimensional imaging of a standard imaging phantom and the head of a human subject. Sets of images were acquired sequentially, with motion (translations and/or rotations) introduced between image frames. The scan-plane tracking system provides well registered image slices of the same section, adaptively compensating for the subject motion.

Dermal absorption and pharmacokinetics of isopropanol in the male and female F-344 rat

Isopropanol (IPA), as a 70% aqueous solution, was applied under occluded conditions to the shaved backs of male and female Fischer F-344 rats for a period of 4 hr. Maximum analyzed blood concentrations of IPA were attained at 4 hr and decreased steadily following removal of the test material. Blood concentrations were below the limit of quantification at 8 hr. Acetone (ACE) blood levels rose steadily during the 4-hr exposures and continued to rise following removal of the test material, reaching peak analyzed levels at 4.5 hr (male) and 5 hr (females). ACE blood concentrations were below the limit of quantification at 24 hr. Basic pharmacokinetic parameters were similar for male and female rats with mean, first-order elimination half-lives for IPA and ACE of 0.8 to 0.9 hr and 2.1 to 2.2 hr, respectively. Following iv administration of [14C]IPA, 50-55% of the dose was eliminated as 14CO2 with lesser amounts recovered as expired volatiles or in urine. Total recoveries following iv administration were 83% for both males and females. Following a 4-hr dermal exposure to [14C]IPA (70% aqueous solution), 84-86% of the dose was recovered from the application site. Dermal absorption rates were calculated by two independent methods. The values obtained were 0.78 +/- 0.03 and 0.85 +/- 0.04 mg/cm2/hr for males and 0.77 +/- 0.13 and 0.78 +/- 0.16 mg/cm2/hr for females. Calculated permeability coefficients of 1.37 to 1.50 x 10(-3) cm/hr for males and 1.35 to 1.37 x 10(-3) cm/hr for females indicate that in the rat, IPA is rapidly absorbed dermally when applied under occluded conditions.

Water dynamics in human blood via combined measurements of T2 relaxation and diffusion in the presence of gadolinium

An analytical model of tissue relaxation and restricted diffusion in human blood is presented. The blood tissue model is composed of three different compartments: red blood cells, plasma, and macromolecular protons. The relaxation rate constants and free diffusion coefficients of intracellular and extracellular water may differ. Analytical formulas for signal loss due to relaxation and diffusion in the Carr-Purcell Meiboom-Gill and pulsed-field-gradient multispin echo experiments for this tissue model are derived. The model is fitted to the experimental data for human blood with various concentrations of Gadolinium contrast agent. The obtained model parameters are realistic. The validity and sensitivity of the model are also discussed.

Mesenteric ischemia due to hemorrhagic shock: MR imaging diagnosis and monitoring in a canine model

PURPOSE

To test whether changes in the percentage of oxygenated hemoglobin (%HbO2) and blood flow in the superior mesenteric vein (SMV), as measured with magnetic resonance (MR) imaging in vivo, can be used to diagnose and monitor mesenteric ischemia due to hemorrhagic shock in a canine model.

MATERIALS AND METHODS

Eight mongrel dogs (weight range, 20-30 kg) underwent fasting for 24 hours before the experiments. MR imaging measurements of SMV %HbO2 and volume flow rate were obtained at the resting state and after 5%, 10%, and 15% of the blood volume of the dogs had been removed sequentially, which led to a total blood volume depletion of 30%. In four dogs, resuscitation was performed with normal saline solution in a volume equal to the total volume of blood removed.

RESULTS

SMV %HbO2 and SMV flow measurements at the different stages of blood removal were all significantly different (P < .05) from baseline measurements and from each other. After volume replacement with normal saline solution, SMV %HbO2 and flow were not significantly different (P > .05) from the baseline values.

CONCLUSION

SMV %HbO2 and volume flow rate, as measured with MR imaging in vivo, can be used to diagnose and monitor mesenteric ischemia due to hemorrhagic shock in a canine model.

Test bolus examination in the carotid artery at dynamic gadolinium-enhanced MR angiography

At magnetic resonance angiography in nine patients, a test bolus of gadopentetate dimeglumine was injected to determine transit time from venous injection to arrival in the carotid arteries. Mean times to onset of enhancement were calculated (arterial, 15.7 seconds [range, 10-22 seconds]; venous, 23.4 seconds [range, 16-30 seconds]; optimal imaging time, 7.78 seconds [range, 6-10 seconds]). Transit time was calculated correctly with a test bolus examination.

T2 accuracy on a whole-body imager

MR oximetry requires a T2 measurement that is accurate within 5% in vivo. Simple methods are susceptible to signal loss and tend to underestimate T2. Current methods utilize RF pulses or RF cycling patterns that prevent signal loss at each data acquisition. However, using these methods with imperfect pulses, T2 tends to be overestimated due to temporary storage of the magnetization along the longitudinal axis where it decays more slowly with a time constant T1 > T2. To reduce the T1 dependence while preventing signal loss, we utilize simple 90x180y90x composite pulses and good RF cycling patterns. These trains are critical for T2 accuracy over typical ranges of RF and static field inhomogeneities and refocusing intervals. T1 signal decay during each 90x180y90x pulse must be accounted for to yield accuracy within 5% when the pulse-width is 10% or more of the refocusing interval. A simple correction scheme compensates for this T1-related error effectively.

Three-dimensional flow-independent peripheral angiography

A magnetization-prepared sequence, T2-Prep-IR, exploits T1, T2, and chemical shift differences to suppress background tissues relative to arterial blood. The resulting flow-independent angiograms depict vessels with any orientation and flow velocity. No extrinsic contrast agent is required. Muscle is the dominant source of background signal in normal volunteers. However, long-T2 deep venous blood and nonvascular fluids such as edema also contribute background signal in some patients. Three sets of imaging parameters are described to address patient-specific contrast requirements. A rapid, spiral-based, three-dimensional readout is utilized to generate high-resolution angiograms of the lower extremities. Comparisons with x-ray angiography and two-dimensional time-of-flight angiography indicate that this flow-independent technique has unique capabilities to accurately depict stenoses and to visualize slow flow and in-plane vessels.