Easy fabrication of a tunable high-pass birdcage resonator

Imaging Capabilities of the ¹H-X-Nucleus Metamaterial-Inspired Multinuclear RF-Coil

In this paper, we present the initial experimental investigation of a two-coil receive/transmit design for small animals imaging at 7T MRI. The system uses a butterfly-type coil tuned to 300 MHz for scanning the ¹H nuclei and a non-resonant loop antenna with a metamaterial-inspired resonator with the ability to tune over a wide frequency range for X-nuclei. ¹H, ³¹P, ²³Na and ¹³C, which are of particular interest in biomedical MRI, were selected as test nuclei in this work. Coil simulations show the two parts of the radiofrequency (RF) assembly to be decoupled and operating independently due to the orthogonality of the excited RF transverse magnetic fields. Simulations and phantom experimental imaging show sufficiently homogeneous transverse transmit RF fields and tuning capabilities for the pilot multiheteronuclear experiments.

Geometric decoupling of a mouse array coil using a dual plane pair design with crisscrossed return paths and custom mounting fixture

An element design for receive array coils that decouples from the transmit coil without external active detuning is presented for magnetic resonance imaging (MRI) of mice. The array element uses a crisscrossed geometry on the return paths to reduce the current induced by the transmit coil. Without the need for an external active detune network, the proposed method simplifies the construction of MRI coil systems and also mitigates problems in space-limited MRI applications. In addition, an adaptable scissor-jack-like fixture is presented that allows the receive array to move parallel to the transmit coil to maintain the decoupling condition while maintaining close contact with varying sizes of mice.

Deferoxamine improves early postresuscitation reperfusion after prolonged cardiac arrest in rats

The no-reflow phenomenon and delayed hypoperfusion after transient cardiac arrest (CA) impede postischemic recovery. Activation of lipid peroxidation (LPO) after ischemia and reperfusion is considered one of the mechanisms responsible for such abnormalities. The present study investigates the influence of iron-dependent LPO inhibitor deferoxamine (DFO) on the cerebral perfusion after prolonged CA and resuscitation. Fourteen male Sprague-Dawley rats were subjected to 17 minutes of CA, induced by esmolol (an ultrashort-acting beta-blocker) and apnea, followed by resuscitation by retrograde intraaortic infusion of oxygenated donor blood mixed with a resuscitation cocktail inside a vertical-bore 9.4-T magnetic resonance imaging (MRI) magnet. Animals were randomized double-blindly into two groups to receive DFO or saline, respectively. Cerebral perfusion was measured by MRI continuously using the arterial spin-labeling method before, during, and after CA. All animals were successfully resuscitated in 1.36 +/- 0.04 minutes with well-controlled arrest time (17.99 +/- 0.03 minutes) in both groups. Deferoxamine significantly increased cerebral perfusion in hippocampus, thalamus, hypothalamus, and amygdala, but not in cortex, during the first 20 minutes of reperfusion. In the DFO-treated group, the neurologic deficit score was significantly better (400 +/- 30 vs. 250 +/- 47, out of 500 as the best, P < 0.05) and weight loss was significantly less (33 +/- 6 vs. 71 +/- 19 g, P < 0.05) 5 d after arrest. The finding supports the notion that early reperfusion immediately after resuscitation is important for long-term outcome and that LPO may be involved in microvascular disorders during the reperfusion, particularly in the brain after prolonged cardiac arrest and resuscitation.

Dependence of early cerebral reperfusion and long-term outcome on resuscitation efficiency after cardiac arrest in rats

BACKGROUND AND PURPOSE

While it is well known that longer duration of cardiac arrest (CA) is often associated with poorer long-term outcome, the influence of resuscitation efficacy on postischemia recovery is less clear. The objective of the present study is to investigate whether an inadequate and prolonged resuscitation after a shorter CA can lead to worse long-term outcomes than an effective resuscitation after a longer CA, provided that the total time from the onset of CA to the return of spontaneous circulation is comparable.

METHODS

Thirty-eight rats were randomized into 2 groups with nominal 9 minutes (group 1) and 15 minutes (group 2) of normothermic asphyxial CA. Each group was further divided into 2 subgroups on the basis of the duration of resuscitation efforts (labeled as S and L for short and long, respectively). Thus, the asphyxia and nominal resuscitation times were 8 and 1 minute, respectively, for group 1S, 5 and 4 minutes for group 1L, 14 and 1 minute for group 2S, and 11 and 4 minutes for group 2L. Cerebral perfusion was measured continuously at the dorsal hippocampus level before, during, and after the CA, with the use of the arterial spin labeling MRI technique. The survival time, histological damage, and neurological deficit were evaluated 5 days after resuscitation.

RESULTS

Groups 1S and 1L had nearly the same duration of CA (9.02 +/- 0.17 minutes, n=6 versus 8.58 +/- 0.80 minutes, n=6). The same is true for groups 2S and 2L (15.51 +/- 0.59 minutes, n=11 versus 15.65 +/- 1.25 minutes, n=15). Despite longer asphyxia, shorter and more effective resuscitation was associated with significantly improved long-term outcomes and higher cerebral perfusion at the early stage of reperfusion.

CONCLUSIONS

Effective resuscitation increased early reperfusion and improved survival after CA. The clinical implication is that inadequate and prolonged resuscitation may have detrimental effects on the recovery of CA patients.

Late reversal of cerebral perfusion and water diffusion after transient focal ischemia in rats

Region-specific cerebral blood flow (CBF) and the apparent diffusion coefficient (ADC) of tissue water in the rat brain were quantified by high-field magnetic resonance imaging at 9.4 T in the rat suture occlusion model. Cerebral blood flow and ADC were compared during the short- (4.5 hours) and long-term (up to 6 days) reperfusion after 80 minutes of transient middle cerebral artery occlusion, and correlated with the histology analysis. On occlusion, average CBF fell from approximately 100 to less than 50 mL x 100 g(-1) x min(-1) in the cortex, and to less than 20 mL x 100 g(-1) x min(-1) in the caudate putamen (CP). Corresponding ADC values decreased from (6.98 +/- 0.82) x 10(-4) to (5.49 +/- 0.54) x 10(-4) mm2/s in the cortex, and from (7.16 +/- 0.58) x 10(-4) to (4.86 +/- 0.62) x 10(-4) mm2/s in the CP. On average, CBF recovered to approximately 50% of baseline in the first 24 hours of reperfusion. After 2 to 4 days, a strong hyperperfusion in the ipsilateral cortex and CP, up to approximately 300 mL x 100 g(-1) x min(-1), was observed. The ADC ratio in the ipsilateral and contralateral CP was also inverted in the late reperfusion period. Histology revealed more severe tissue damage at the late stage of reperfusion than at 4.5 hours. Significant reversal of CBF and ADC during the late reperfusion period may reflect the impairment of autoregulation in the ischemic regions. Vascular factors may play an important role in the infarct development after 80-minute focal ischemia.

ADC characterization of region-specific response to cerebral perfusion deficit in rats by MRI at 9.4 T

Region-specific cerebral blood flow (CBF) and apparent diffusion coefficient (ADC) of water in the rat brain were quantified in vivo by high-field MRI (9.4 T) for 6-7 h after middle cerebral artery occlusion (MCAO). Upon occlusion, average CBF fell from about 1.5-2 ml/g/min to below 0.5 ml/g/min in cortical areas and the amygdala, and below 0.2 ml/g/min in the caudate putamen. CBF in some of the homologous contralateral areas also decreased by 20-30%. Average ADC decreased from about 8 center dot 10(-4) to 5 center dot 10(-4) mm(2)/s in the caudate putamen and parietal cortex. Corresponding changes in ADC were lower in the frontal cortex and negligible in the piriform cortex, suggesting that the perfusion threshold for ADC decrease may be different for different brain regions in the same animal. The area of decreased ADC correlated well with the infarction area revealed by 2,3,5-triphenyltetrazolium chloride (TTC) staining of brain slices in vitro. A better understanding of the mechanisms linking ADC and CBF changes to ischemic cell disorders may prove useful in characterizing the degree of tissue damage, and in developing and evaluating treatment strategies.

Regional dependence of cerebral reperfusion after circulatory arrest in rats

The severity of neurologic dysfunction after circulatory arrest depends on cerebral reperfusion during and after resuscitation. The objective of current study was to investigate the temporal and spatial patterns of the cerebral perfusion immediately after resuscitation. Precise control of circulatory arrest was achieved in rats by combination of asphyxia and transient blockage of cardiac-specific beta-adrenergic receptors with esmolol, an ultra-short-acting beta-blocker. Animals were randomized into 3 groups with resuscitation starting 0.5 (sham group, no asphyxia, n = 5), 4 (Group 2, n = 5), or 12 minutes (Group 3, n = 8) later by retrograde intraarterial infusion of donor blood along with a resuscitation mixture. Cerebral perfusion was measured by magnetic resonance imaging (MRI) using arterial spin labeling. The average perfusion before arrest was 163 +/- 27 mL 100 g(-1) min(-1) under isoflurane anesthesia. Resuscitation led to transient perfusion increase, which started from thalamus and hypothalamus and later shifted to the cortex. Severe hypoperfusion to as low as 6% to 20% of the normal level developed in the first 10 to 20 minutes of reperfusion and lasted for at least 2 hours. On the fifth day after circulatory arrest, all animals showed a normal level of perfusion (159 +/- 57 mL 100 g(-1) min(-1) ) and minimal neurologic deficit. Nevertheless, histologic examination revealed extensive changes in the CA1 region of the hippocampus consistent with global ischemia and reperfusion damage. The combination of an improved circulatory arrest model and noninvasive MRI cerebral perfusion measurements provides a powerful tool for investigations of circulatory arrest and resuscitation, allowing for evaluation of therapies aimed at modulating cerebral reperfusion.