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Aims: The management of congestion is one of the key treatment targets in heart failure. Assessing congestion is, however, difficult. The purpose of this study was to investigate the safety and dynamic response of a novel, passive, inferior vena cava (IVC) sensor in a chronic ovine model. Methods and results: A total of 20 sheep divided into three groups were studied in acute and chronic in vivo settings. Group I and Group II included 14 sheep in total with 12 sheep receiving the sensor and two sheep receiving a control device (IVC filter). Group III included an additional six animals for studying responses to volume challenges via infusion of blood and saline solutions. Deployment was 100% successful with all devices implanted; performing as expected with no device‐related complications and signals were received at all observations. At similar volume states no significant differences in IVC area normalized to absolute area range were measured (55 ± 17% on day 0 and 62 ± 12% on day 120, p = 0.51). Chronically, the sensors were completely integrated with a thin, reendothelialized neointima with no loss of sensitivity to infused volume. Normalized IVC area changed significantly from 25 ± 17% to 43 ± 11% (p = 0.007) with 300 ml infused. In contrast, right atrial pressure required 1200 ml of infused volume prior to a statistically significant change from 3.1 ± 2.6 mmHg to 7.5 ± 2.0 mmHg (p = 0.02). Conclusion: In conclusion, IVC area can be measured remotely in real‐time using a safe, accurate, wireless, and chronic implantable sensor promising to detect congestion with higher sensitivity than filling pressures. [ABSTRACT FROM AUTHOR]

Aims: Remote monitoring of pulmonary artery pressure has reduced heart failure (HF) hospitalizations in chronic HF as elevation of pulmonary artery pressure provides information that can guide treatment. The venous system is characterized by high capacitance, thus substantial increases in intravascular volume can occur before filling pressures increase. The inferior vena cava (IVC) is a highly compliant venous conduit and thus a candidate for early detection of change in intravascular volume. We aimed to compare IVC cross‐sectional area using a novel sensor with cardiac filling pressures during experimental manipulation of volume status, vascular tone, and cardiac function. Methods and results: Experiments were conducted in sheep to manipulate volume status (colloid infusion), vascular tone (nitroglycerin infusion) and cardiac function (rapid cardiac pacing). A wireless implantable IVC sensor was validated ex‐vivo and in‐vivo, and then used to measure the cross‐sectional area of the IVC. Right‐ and left‐sided cardiac filling pressures were obtained via right heart catheterization. The IVC sensor provided highly accurate and precise measurements of cross‐sectional area in ex‐vivo and in‐vivo validation. IVC area changes were more sensitive than the corresponding changes in cardiac filling pressures during colloid infusion (p < 0.001), vasodilatation (p < 0.001) and cardiac dysfunction induced by rapid pacing (p ≤ 0.02). Conclusions: Inferior vena cava area can be remotely and accurately measured in real time with a wireless implantable sensor. Changes in IVC area are more sensitive than corresponding changes in filling pressures following experimental volume loading and fluid redistribution. Additional research is warranted to understand if remote monitoring of the IVC may have advantages over pressure‐based monitors in HF. [ABSTRACT FROM AUTHOR]

Aims Remote monitoring of pulmonary artery pressure has reduced heart failure (HF) hospitalizations in chronic HF as elevation of pulmonary artery pressure provides information that can guide treatment. The venous system is characterized by high capacitance, thus substantial increases in intravascular volume can occur before filling pressures increase. The inferior vena cava (IVC) is a highly compliant venous conduit and thus a candidate for early detection of change in intravascular volume. We aimed to compare IVC cross-sectional area using a novel sensor with cardiac filling pressures during experimental manipulation of volume status, vascular tone, and cardiac function. Methods and results Experiments were conducted in sheep to manipulate volume status (colloid infusion), vascular tone (nitroglycerin infusion) and cardiac function (rapid cardiac pacing). A wireless implantable IVC sensor was validated ex-vivo and in-vivo, and then used to measure the cross-sectional area of the IVC. Right- and left-sided cardiac filling pressures were obtained via right heart catheterization. The IVC sensor provided highly accurate and precise measurements of cross-sectional area in ex-vivo and in-vivo validation. IVC area changes were more sensitive than the corresponding changes in cardiac filling pressures during colloid infusion (p<0.001), vasodilatation (p<0.001) and cardiac dysfunction induced by rapid pacing (p≤0.02). Conclusions Inferior vena cava area can be remotely and accurately measured in real time with a wireless implantable sensor. Changes in IVC area are more sensitive than corresponding changes in filling pressures following experimental volume loading and fluid redistribution. Additional research is warranted to understand if remote monitoring of the IVC may have advantages over pressure-based monitors in HF. [ABSTRACT FROM AUTHOR]

Background: Diffusion magnetic resonance imaging (MRI) is the current-state-of-the-art technique to clinically investigate acute (0-24 h) ischemic stroke tissue. However, reduced apparent diffusion coefficient (ADC) —considered a marker of tissue damage—was observed to reverse spontaneously during the subacute stroke phase (24-72 h) which means that low ADC cannot be used to reflect the damaged tissue after 24 h in experimental and clinical studies. One reason for the change in ADC is that ADC values drop with cytotoxic edema (acute phase) and rise when vasogenic edema begins (subacute phase). Recently, combined 1H- and 23Na-MRI was proposed as a more accurate approach to improve delineation between reversible (penumbra) and irreversible ischemic injury (core). The aim of this study was to investigate the effects of reperfusion on the ADC and the sodium MRI signal after experimental ischemic stroke in rats in well-defined areas of different viability levels of the cerebral lesion, i.e. core and penumbra as defined via perfusion and histology. Transient middle cerebral artery occlusion was induced in male rats by using the intraluminal filament technique. MRI sodium, perfusion and diffusion measurement was recorded before reperfusion, shortly after reperfusion and 24 h after reperfusion. The animals were reperfused after 90 min of ischemia. Results: Sodium signal in core did not change before reperfusion, increased after reperfusion while sodium signal in penumbra was significantly reduced before reperfusion, but showed no changes after reperfusion compared to control. The ADC was significantly decreased in core tissue at all three time points compared to contralateral side. This decrease recovered above commonly applied viability thresholds in the core after 24 h. Conclusions: Reduced sodium-MRI signal in conjunction with reduced ADC can serve as a viability marker for penumbra detection and complement hydrogen diffusion- and perfusion-MRI in order to facilitate time-independent assessment of tissue fate and cellular bioenergetics failure in stroke patients. [ABSTRACT FROM AUTHOR]

Symptoms of attention deficit hyperactivity disorder (ADHD) in children often persist into adulthood and can lead to severe antisocial behavior. However, to-date it remains unclear whether neuro-functional abnormalities cause ADHD, which in turn can then provide a marker of persistent ADHD. Using event-related functional magnetic resonance imaging (fMRI), we measured blood oxygenation level dependent (BOLD) signal changes in subjects during a reversal learning task in which choice of the correct stimulus led to a probabilistically determined 'monetary' reward or punishment. Participants were diagnosed with ADHD during their childhood ( N = 32) and were paired with age, gender, and education matched healthy controls ( N = 32). Reassessment of the ADHD group as adults resulted in a split between either persistent (persisters, N = 17) or remitted ADHDs (remitters, N = 15). All three groups showed significantly decreased activation in the medial prefrontal cortex (PFC) and the left striatum during punished correct responses, however only remitters and controls presented significant psycho-physiological interaction between these fronto-striatal reward and outcome valence networks. Comparing persisters to remitters and controls showed significantly inverted responses to punishment ( P < 0.05, family-wise error corrected) in left PFC region. Interestingly, the decreased activation shown after punishment was located in different areas of the PFC for remitters compared with controls, suggesting that remitters might have learned compensation strategies to overcome their ADHD symptoms. Thus, fMRI helps understanding the neuro-functional basis of ADHD related behavior differences and differentiates between persistent and remittent ADHD. Hum Brain Mapp 36:4648-4663, 2015. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Tissue sodium concentration increases in irreversibly damaged (core) tissue following ischemic stroke and can potentially help to differentiate the core from the adjacent hypoperfused but viable penumbra. To test this, multinuclear hydrogen-1/sodium-23 magnetic resonance imaging (MRI) was used to measure the changing sodium signal and hydrogen-apparent diffusion coefficient (ADC) in the ischemic core and penumbra after rat middle cerebral artery occlusion (MCAO). Penumbra and core were defined from perfusion imaging and histologically defined irreversibly damaged tissue. The sodium signal in the core increased linearly with time, whereas the ADC rapidly decreased by >30% within 20 minutes of stroke onset, with very little change thereafter (0.5-6 hours after MCAO). Previous reports suggest that the time point at which tissue sodium signal starts to rise above normal (onset of elevated tissue sodium, OETS) represents stroke onset time (SOT). However, extrapolating core data back in time resulted in a delay of 72±24 minutes in OETS compared with actual SOT. At the OETS in the core, penumbra sodium signal was significantly decreased (88±6%, P=0.0008), whereas penumbra ADC was not significantly different (92±18%, P=0.2) from contralateral tissue. In conclusion, reduced sodium-MRI signal may serve as a viability marker for penumbra detection and can complement hydrogen ADC and perfusion MRI in the time-independent assessment of tissue fate in acute stroke patients. [ABSTRACT FROM AUTHOR]

A double-tuned 23Na/¹H resonator system was developed to record multinuclear MR image data during and after transient cerebral ischemia. ¹H-diffusion-, ¹H perfusion, ¹H T2-, ¹H arterial blood flow- and 23Na spin density-weighted images were then acquired at three time points in a rodent stroke model: (I) during 90 min artery occlusion, (II) directly after arterial reperfusion and (III) one day after arterial reperfusion. Normal 23Na was detected in hypoperfused stroke tissue which exhibited a low ¹H apparent diffusion coefficient (ADC) and no changes in ¹H T2 relaxation time during transient ischemia, while 23Na increased and ADC values recovered to normal values directly after arterial reperfusion. For the first time, a similar imaging protocol was set-up on a clinical 3T MRI site in conjunction with a commercial double-tuned ¹H/23Na birdcage resonator avoiding a time-consuming exchange of resonators or MRI systems. Multinuclear 23Na/¹H MRI data sets were obtained from one stroke patient during both the acute and non-acute stroke phases with an aquisition time of 22 min. The lesion exhibiting low ADC was found to be larger compared to the lesion with high 23Na at 9 h after symptom onset. It is hoped that the presented pilot data demonstrate that fast multinuclear 23Na/¹HMRI preclinical and clinical protocols can enable a better understanding of how temporal and regional MRI parameter changes link to pathophysiological variations in ischemic stroke tissue. [ABSTRACT FROM AUTHOR]

Abstract: The design and construction of a two-port surface transceiver resonator for both 1H-and 23Na-MRI in the rodent brain at 7T is described. Double-tuned resonators are required for accurately co-registering multi-nuclei data sets, especially when the time courses of 1H and 23Na signals are of interest as, for instance, when investigating the pathological progression of ischaemic stroke tissue in vivo. In the current study, a single-element two-port surface resonator was developed wherein both frequency components were measured with the same detector element but with each frequency signal routed along different output channels. This was achieved by using the null spot technique, allowing for optimal variable tuning and matching of each channel in situ within the MRI scanner. The 23Na signal to noise ratio, measured in the ventricles of the rat brain, was increased by a factor of four compared to recent state-of-the-art rat brain studies reported in the literature. The resonator’s performance was demonstrated in an in vivo rodent stroke model, where regional variations in 1H apparent diffusion coefficient maps and the 23Na signal were recorded in an interleaved fashion as a function of time in the acute phase of the stroke without having to exchange, re-adjust, or re-connect resonators between scans. Using the practical construction steps described in this paper, this coil design can be easily adapted for MRI of other X-nuclei, such as 17O, 13C, 39K, and 43Ca at various field strengths. [Copyright &y& Elsevier]

Introduction: The purpose of this study was to demonstrate the feasibility and efficiency of cardiac MR at 3 Tesla using local four-channel RF coil transmission and benchmark it against large volume body RF coil excitation. Methods: Electromagnetic field simulations are conducted to detail RF power deposition, transmission field uniformity and efficiency for local and body RF coil transmission. For both excitation regimes transmission field maps are acquired in a human torso phantom. For each transmission regime flip angle distributions and blood-myocardium contrast are examined in a volunteer study of 12 subjects. The feasibility of the local transceiver RF coil array for cardiac chamber quantification at 3 Tesla is demonstrated. Results: Our simulations and experiments demonstrate that cardiac MR at 3 Tesla using four-channel surface RF coil transmission is competitive versus current clinical CMR practice of large volume body RF coil transmission. The efficiency advantage of the 4TX/4RX setup facilitates shorter repetition times governed by local SAR limits versus body RF coil transmission at whole-body SAR limit. No statistically significant difference was found for cardiac chamber quantification derived with body RF coil versus four-channel surface RF coil transmission. Our simulation also show that the body RF coil exceeds local SAR limits by a factor of ~2 when driven at maximum applicable input power to reach the whole-body SAR limit. Conclusion: Pursuing local surface RF coil arrays for transmission in cardiac MR is a conceptually appealing alternative to body RF coil transmission, especially for patients with implants. [ABSTRACT FROM AUTHOR]