RESUMEN

Micro-CT is a non-invasive imaging modality usually used to assess morphology in small animals. In our previous work, we have demonstrated that functional micro-CT imaging is also possible. This paper describes a dual micro-CT system with two fixed x-ray/detectors developed to address such challenging tasks as cardiac or perfusion studies in small animals. A two-tube/detector system ensures simultaneous acquisition of two projections, thus reducing scanning time and the number of contrast injections in perfusion studies by a factor of two. The system is integrated with software developed in-house for cardio-respiratory monitoring and gating. The sampling geometry was optimized for 88 microns in such a way that the geometric blur of the focal spot matches the Nyquist sample at the detector. A geometric calibration procedure allows one to combine projection data from the two chains into a single reconstructed volume. Image quality was measured in terms of spatial resolution, uniformity, noise, and linearity. The modulation transfer function (MTF) at 10% is 3.4 lp/mm for single detector reconstructions and 2.3 lp/mm for dual tube/detector reconstructions. We attribute this loss in spatial resolution to the compounding of slight errors in the separate single chain calibrations. The dual micro-CT system is currently used in studies for morphological and functional imaging of both rats and mice.

RESUMEN

This study investigated the testicular changes in the rat induced by the nonspecific phosphodiesterase inhibitor, theophylline using magnetic resonance microscopy (MRM) and ubiquitin immunostaining techniques. In vivo T1- and T2-weighted images were acquired at 2 T under anesthesia. Increased signal observed in the theophylline-treated rats suggests that leakage of MRM contrast was occurring. In vivo MRM results indicate that day 16 testis displayed an increased T1-weighted water signal in the area of the seminiferous tubule that decreased by day 32. These findings were validated by histopathology, suggesting that in vivo MRM has the sensitivity to predict changes in testis and epididymal tissues. The participation of the ubiquitin system was investigated, using probes for various markers of the ubiquitin-proteasome pathway. MRM can be used to detect subtle changes in the vascular perfusion of organ systems, and the up-regulation/mobilization of ubiquitin-proteasome pathway may be one of the mechanisms used in theophylline-treated epididymis to remove damaged cells before storage in the cauda epididymis. The combined use of in vivo MRM and subsequent tissue or seminal analysis for the presence of ubiquitin in longitudinal studies may become an important biomarker for assessing testis toxicities drug studies.

Asunto(s)

RESUMEN

Cardiopulmonary imaging in rodents using micro-computed tomography (CT) is a challenging task due to both cardiac and pulmonary motion and the limited fluence rate available from micro-focus x-ray tubes of most commercial systems. Successful imaging in the mouse requires recognition of both the spatial and temporal scales and their impact on the required fluence rate. Smaller voxels require an increase in the total number of photons (integrated fluence) used in the reconstructed image for constant signal-to-noise ratio. The faster heart rates require shorter exposures to minimize cardiac motion blur imposing even higher demands on the fluence rate. We describe a system with fixed tube/detector and with a rotating specimen. A large focal spot x-ray tube capable of producing high fluence rates with short exposure times was used. The geometry is optimized to match focal spot blur with detector pitch and the resolution limits imposed by the reproducibility of gating. Thus, it is possible to achieve isotropic spatial resolution of 100 microm with a fluence rate at the detector 250 times that of a conventional cone beam micro-CT system with rotating detector and microfocal x-ray tube. Motion is minimized for any single projection with 10 ms exposures that are synchronized to both cardiac and breathing motion. System performance was validated in vivo by studies of the cardiopulmonary structures in C57BL/6 mice, demonstrating the value of motion integration with a bright x-ray source.

Asunto(s)

RESUMEN

Magnetic resonance imaging (MRI)-based volume measurements of brain structures are useful indicators of pending cognitive decline in humans suffering from neurodegenerative diseases. Transgenic mouse models that mimic the clinical conditions of these disorders have been developed. Noninvasive methods that can follow progression and regression of relevant pathology in these mice are therefore in great demand. In this study we tested whether high-resolution MRI (micro-MRI) in a mouse model of neurodegeneration (cerebral ischemia) could reliably track development of brain atrophy. We first established that diffusion imaging at a spatial resolution of 1.6 x 10(-3) mm(3) allowed superior visualization of forebrain, ventricles, and dorsal hippocampus in the mouse brain compared to either T2*- or T1-weighted MR imaging. Using this predetermined protocol we subsequently scanned C56BL/6J (C57) and ApoE-deficient (ApoE(-/-)) mice before and after ischemia. Four groups were studied: C57/sham (n = 9), ApoE(-/-)/sham (n = 9), C57/ischemia (n = 9), and ApoE(-/-)/ischemia (n = 11). All mice received a baseline 3D diffusion scan. One week later C57/ischemia and ApoE(-/-)/ischemia mice were exposed to 10 min of ischemia and scanned again on the 3rd and 30th postischemic day. The C57/sham and ApoE(-/-)/sham mice served as controls and were scanned at corresponding time points. Diffusion images of ApoE(-/-)/ischemia mice on the 3rd postischemic day revealed multiple localized high signal intensity areas. An increase in ventricle and a decrease in dorsal hippocampal volumes (which included the associated cortex laterally) at 30 days confirmed brain atrophy in C57 mice after ischemia. Excessive mortality of ApoE(-/-)/ischemia mice restricted statistical analysis, but ventricle enlargement postischemia was demonstrated. Our results show that volume changes in the brain of a 30-g mouse can be tracked by micro-MRI in a model of neurodegeneration. Clearly the ability to follow progression of pathology in mice will greatly aid our understanding of neurodegenerative diseases and facilitate the many possibilities to intervene pharmacologically.

Asunto(s)

RESUMEN

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were Toshio Narahashi and Bo Söderpalm. The presentations were (1) Nicotinic mechanisms and ethanol reinforcement: Behavioral and neurochemical studies, by Bo Söderpalm, M. Ericson, P. Olausson, and J. A. Engel; (2) Chronic nicotine and ethanol: Differential regulation in gene expression of nicotinic acetylcholine receptor subunits, by X. Zhang and A. Nordberg; (3) Nicotine-ethanol interactions at neuronal nicotinic acetylcholine receptors, by Toshio Narahashi, William Marszalec, and Gary L. Aistrup; (4) Relapse prevention in alcoholics by cigarette smoking? Treatment outcome in an observational study with acamprosate, by L.G. Schmidt, U. Kalouti, M. Smolka, and M. Soyka; and (5) Effect of nicotine on voluntary ethanol intake and development of alcohol dependence in male rats, by L. Hedlund and G. Wahlström.

Asunto(s)

RESUMEN

Using in vivo magnetic resonance microscopy, registered (1)H and hyperpolarized (3)He images of the rat lung were obtained with a resolution of 0.098 x 0.098 x 0.469 mm (4.5 x 10(-3) mm(3)). The requisite stability and SNR was achieved through an integration of scan-synchronous ventilation, dual-frequency RF coils, anisotropic projection encoding, and variable RF excitation. The total acquisition time was 21 min for the (3)He images and 64 min for the (1)H image. Airways down to the 6th and 7th orders are clearly visible. Magn Reson Med 45:365-370, 2001.

Asunto(s)

RESUMEN

Hyperpolarized (3)He spin-lattice relaxation was investigated in the guinea pig lung using spectroscopy and imaging techniques with a repetitive RF pulse series. T(1) was dominated by interactions with oxygen and was used to measure the alveolar O(2) partial pressure. In animals ventilated with a mixture of 79% (3)He and 21% O(2), T(1) dropped from 19.6 sec in vivo to 14.6 sec after cardiac arrest, reflecting the termination of the intrapulmonary gas exchange. The initial difference in oxygen concentration between inspired and alveolar air, and the temporal decay during apnea were related to functional parameters. Estimates of oxygen uptake were 29 +/- 11 mL min(-1) kg(-1) under normoxic conditions, and 9.0 +/- 2.0 mL min(-1) kg(-1) under hypoxic conditions. Cardiac output was estimated to be 400 +/- 160 mL min(-1) kg(-1). The functional residual capacity derived from spirometric magnetic resonance experiments varied with body mass between 5.4 +/- 0.3 mL and 10.7 +/- 1.1 mL. Magn Reson Med 45:421-430, 2001.

Asunto(s)

RESUMEN

Emphysema is a pulmonary disease characterized by alveolar wall destruction, resulting in enlargement of gas exchange spaces without fibrosis. This condition is a part of chronic obstructive pulmonary disease (COPD), which causes 3.5% of deaths worldwide [Anonymous (1990) World Health Stat. Q. Special, 1-51] and contributes greatly to the global burden of disease [Murray, C. J. & Lopez, A. D. (1996) Science 274, 740-743]. Alveolar regeneration has been shown in animal models and could have potential for clinical treatment of early-stage emphysema. However, current techniques for detection of emphysema are not sensitive at the initial stages. Early-stage human panacinar emphysema is modeled in elastase-treated animals. Here, we provide an in vivo imaging method for differentiating normal and emphysematous rat lungs by measuring the apparent diffusion coefficient (ADC) of hyperpolarized (3)He by using magnetic resonance imaging. These data show that the ADC is significantly larger in elastase-treated rats, indicating alveolar expansion. Whereas these rats were clinically asymptomatic, conventional histology confirmed presence of injury. Our results indicate that measurement of the hyperpolarized (3)He ADC can be a valuable research tool and has potential application in the clinical setting.

Asunto(s)

RESUMEN

In a model of psychological dependence, a very stable ethanol intake was induced by a chronic (1-year) intermittent (once a week) exposure to intoxicating amounts of ethanol (24 h choice between ethanol and water, followed by 2.0 g/kg i.p.). After this year, the rats had continuous access to ethanol and water. Stability was shown by the ability of the rats to take the same dose of ethanol (in g/kg) when the concentration was changed from 10 to 20%. To study possible priming or inhibiting effects on ethanol intake, ethanol was injected i.p., first as 20%, 40% or 60% of the intake in the 24 h prior to the injection, then as fixed doses of 0.5, 1, and 2 g/kg, and the ethanol intake during the following 24-h period was recorded. The results showed that, following a low dose of ethanol, voluntary ethanol intake was increased in rats with a low, and decreased in rats with a high, ethanol intake, while high doses of ethanol seemed to decrease voluntary ethanol intake in all rats. The results are discussed in relation to theories about loss of control of drinking and relapse in humans.

Asunto(s)

RESUMEN

We describe an MR-compatible ventilator that is computer controlled to generate a variety of breathing patterns, to minimize image degrading effects of breathing motion, and to support delivery of gas anesthesia and experimental inhalational gases. A key feature of this ventilator is the breathing valve that attaches directly to the endotracheal tube to reduce dead volume and allows independent control of inspiratory and expiratory phases of ventilation. This ventilator has been used in a wide variety of MR and x-ray microscopy studies of small animals, especially for MR imaging the lungs with hyperpolarized gases ((3)He & (129)Xe).

Asunto(s)

RESUMEN

Hyperpolarized helium (HP (3)He) is useful for direct MR imaging of the gas spaces of small animal lungs. Previously, breaths of 100% HP (3)He were alternated with breaths of air to maximize helium signal in the lungs and to minimize the depolarizing effects of O(2). However, for high-resolution imaging requiring many HP (3)He breaths (hundreds) and for pulmonary disease studies, a method was needed to simultaneously deliver O(2) and HP (3)He with each breath without significant loss of polarization. We modified our existing computer-controlled ventilator by adding a plastic valve, additional relays and a controller. O(2) and HP (3)He are mixed at the beginning of each breath within the body of a breathing valve, which is attached directly to the endotracheal tube. With this mixing method, we found that T(1) relaxation of HP (3)He in the guinea pig lung was about 20 s compared to 30 s with alternate air/HP (3)He breathing. Because imaging times during each breath are short (about 500 ms), the HP (3)He signal loss from O(2) contact is calculated to be less than 5%. We concluded that the advantages of mixing HP (3)He with O(2), such as shorter imaging times (reduced T(1) losses in reservoir) and improved physiologic stability, outweigh the small signal loss from the depolarizing effects of oxygen on HP (3)He.

Asunto(s)

RESUMEN

Hyperpolarized (HP) 3He can be encapsulated within biologically compatible microspheres while retaining sufficient polarization to be used as a signal source for MRI. Two microsphere sizes were used, with mean diameters of 5.3 +/- 1.3 microm and 10.9 +/- 3.0 microm. These suspensions ranged in concentration from 0.9-7.0% gas by volume. Spectroscopic measurements in phantoms at 2 T yielded 3He relaxation times that varied with gas concentration. At the highest 3He concentration, the spinlattice relaxation time, T1, was 63.8 +/- 9.4 sec, while the transverse magnetization decayed with a time constant of T2* = 11.0 +/- 0.4 msec. In vivo MR images of the pelvic veins in a rat were acquired during intravenous injection of 3He microspheres (SNR approximately equal 15). Advantages such as intravascular confinement, lack of background signal, and limited recirculation indicate quantitative perfusion measurements may be improved using this novel signal source.

Asunto(s)

RESUMEN

OBJECT: It is taken for granted that patients with hypertension are at greater risk for intracerebral hemorrhage during neurosurgical procedures than patients with normal blood pressure. The anesthesiologist, therefore, maintains mean arterial blood pressure (MABP) near the lower end of the autoregulation curve, which in patients with preexisting hypertension can be as high as 110 to 130 mm Hg. Whether patients with long-standing hypertension experience more hemorrhage than normotensive patients after brain surgery if their blood pressure is maintained at the presurgical hypertensive level is currently unknown. The authors tested this hypothesis experimentally in a rodent model. METHODS: Hemorrhage and edema in the brain after needle biopsy was measured in vivo by using three-dimensional magnetic resonance (MR) microscopy in the following groups: WKY rats, acutely hypertensive WKY rats, spontaneously hypertensive rats (SHR strain), and SHR rats treated with either sodium nitroprusside or nicardipine. Group differences were compared using Tukey's studentized range test followed by individual pairwise comparisons of groups and adjusted for multiple comparisons. There were no differences in PaCO2, pH, and body temperature among the groups. The findings in this study indicated that only acutely hypertensive WKY rats had larger volumes of hemorrhage. Chronically hypertensive SHR rats with MABPs of 130 mm Hg did not have larger hemorrhages than normotensive rats. There were no differences in edema volumes among groups. CONCLUSIONS: The brains of SHR rats with elevated systemic MABPs are probably protected against excessive hemorrhage during surgery because of greater resistance in the larger cerebral arteries and, thus, reduced cerebral intravascular pressures.

Asunto(s)

RESUMEN

In imaging of hyperpolarized noble gases, a knowledge of the diffusion coefficient (D) is important both as a contrast mechanism and in the design of pulse sequences. We have made diffusion coefficient maps of both hyperpolarized (3)He and (129)Xe in guinea pig lungs. Along the length of the trachea, (3)He D values were on average 2.4 cm(2)/sec, closely reproducing calculated values for free gas (2.05 cm(2)/sec). The (3)He D values measured perpendicular to the length of the trachea were approximately a factor of two less, indicating restriction to diffusion. Further evidence of restricted diffusion was seen in the distal pulmonary airspaces as the average (3)He D was 0.16 cm(2)/sec. An additional cause for the smaller (3)He D in the lung was due to the presence of air, which is composed of heavier and larger gases. The (129)Xe results show similar trends, with the trachea D averaging 0.068 cm(2)/sec and the lung D averaging 0.021 cm(2)/sec. Magn Reson Med 42:721-728, 1999.

Asunto(s)

RESUMEN

The transverse relaxation time, T *(2), of hyperpolarized (HP) gas in the lung in vivo is an important parameter for pulse sequence optimization and image contrast. We obtained T *(2) maps of HP (3)He and (129)Xe in guinea pig lungs (n = 17) and in human lungs. Eight different sets of (3)He guinea pig studies were acquired, with variation of slice selection, tidal volume, and oxygen level. For example, for a (3)He tidal volume of 3 cm(3) and no slice selection, the average T *(2) in the trachea was 14.7 ms and 8.0 ms in the intrapulmonary airspaces. The equivalent (129)Xe experiment yielded an average T *(2) of 40.8 ms in the trachea and 18.5 ms in the intrapulmonary airspaces. The average (3)He T *(2) in the human intrapulmonary airspaces was 9.4 ms. The relaxation behavior was predicted by treating the lung as a porous medium, resulting in good agreement between estimated and measured T *(2) values in the intrapulmonary airspaces. Magn Reson Med 42:729-737, 1999.

Asunto(s)

RESUMEN

BACKGROUND AND OBJECTIVES: Pathophysiologic mechanisms underlying persistent neurologic deficits after continuous spinal anesthesia using hyperbaric 5% lidocaine are still not well understood. It has been suggested that high-dose intrathecal lidocaine induces irreversible conduction block and even ischemia in white matter tracts by breakdown of the blood-nerve barrier. In this study, we use diffusion-weighted magnetic resonance microscopy to characterize the effect of intrathecal hyperbaric 5% lidocaine in rat spinal cord. The parameter measured with DWM, is an "apparent diffusion coefficient," (ADC), which can be used to exclude the presence of ischemia. METHODS: Female Fischer CDF rats were used. Group 1 (n = 5) was exposed to ischemia, group 2 (n = 7) was exposed to intrathecal 5% hyperbaric lidocaine, and group 3 (n = 5) was exposed to intrathecal 7.5% glucose. Diffusion-weighted MR images in group 1 were acquired before and after ischemia induced by cardiac arrest and in groups 2 and 3 rats prior to and during perfusion of the spinal catheter with either 5% hyperbaric lidocaine or 7.5% glucose. RESULTS: Ischemia decreased the ADC by 40% in gray matter and by 30% in white matter of spinal cord. Continuous intrathecal anesthesia with hyperbaric 5% lidocaine did not affect the spinal cord ADC. Further, 7.5% intrathecal glucose had no effect on ADCs in gray or white matter of spinal cord. CONCLUSIONS: Ischemia reduced the ADC in both spinal cord white and gray matter. Hyperbaric 5% lidocaine did not affect the spinal cord ADC during the first 1.5 hours. We suggest that 5% hyperbaric lidocaine does not induce irreversible neurologic deficits by causing spinal cord ischemia.

Asunto(s)

RESUMEN

Buspirone, a 5-HT1A agonist, has been shown to decrease the intake of ethanol when given as a single dose to rats with a psychological dependence induced according to our rat model of alcoholism. The present experiment evaluates the effects different treatments with buspirone have on voluntary ethanol intake in these psychologically dependent rats. As a first treatment, buspirone was given once daily for 23 days at the dose of 20 mg/kg/day. Ethanol was withheld except for the first and the last day of the treatment. On the first day, the buspirone injection decreased ethanol intake from the pretreatment value (1.94+/-0.18 g/kg/day), down to 1.36+/-0.18 g/kg (p < 0.01, n = 12). The rats were again given a choice between water and 10% ethanol after the last injection of buspirone. During the following 24 hr period, the ethanol intake was increased to 3.56+/-0.24 g/kg/day (p < 0.001 vs. the pretreatment intake, n = 12). A loss of correlation with the pretreatment intake of ethanol indicated an altered regulation of ethanol intake for approximately 3 more weeks. Fifteen weeks after the start of the first treatment, buspirone (20 mg/kg) was re-tested as a single dose, with no effect on ethanol intake. Twenty-two weeks after the start of the first treatment, a 1-week treatment with 20 mg/kg/day of buspirone was started. During this treatment, the rats had a continuous choice between 10% ethanol and water. There was, as in the first re-test, no effect on ethanol intake on the first day of the treatment. However, on the last 2 days of the treatment, the ethanol intake was increased to 2.86+/-0.28 g/kg and to 2.89+/-0.26 g/kg respectively (p < 0.05, n = 10 on both days, compared with the pretreatment intake of 1.78+/-0.36 g/kg). Thus, an acute dose of buspirone can decrease voluntary ethanol intake in psychologically dependent rats, but long-lasting changes in the effect of buspirone seem to develop during a 3-week treatment period.

Asunto(s)

RESUMEN

A new strategy designed to provide functional magnetic resonance images of the lung in small animals at microscopic resolution using hyperpolarized 3He is described. The pulse sequence is based on a combination of radial acquisition (RA) and CINE techniques, referred to as RA-CINE, and is designed for use with hyperpolarized 3He to explore lung ventilation with high temporal and spatial resolution in small animal models. Ventilation of the live guinea pig is demonstrated with effective temporal resolution of 50 msec and in-plane spatial resolution of <100 microm using hyperpolarized 3He. The RA-CINE sequence allows one to follow gas inflow and outflow in the airways as well as in the distal part of the lungs. Regional analysis of signal intensity variations can be performed and can help assess functional lung parameters such as residual gas volume and lung compliance to gas inflow.

Asunto(s)

RESUMEN

Three-dimensional magnetic resonance images of the guinea pig lung were acquired in vivo using hyperpolarized (HP) noble gases and radial projection encoding (PE). Results obtained with 3He (voxel size 17 microl) demonstrated high image quality showing airway structure down to the 5th or 6th generations. Signal-to-noise ratios (SNRs) of 129Xe images (voxel size 40 microl) were lower by about 1 order of magnitude as a consequence of the smaller gyromagnetic ratio, a more rapid relaxation in the gas reservoir, and lower polarization and isotope abundance. Comparison between experimentally obtained SNRs and results from calculations based on a model that accounts for the three-dimensional PE acquisition scheme and the non-equilibrium situation in HP gas imaging yielded excellent agreement for small flip angles. A theoretical examination of the potential resolution in HP gas MR microscopy of the lungs suggests that in vivo visualization of alveolar clusters distal to respiratory bronchioles may be possible.

Asunto(s)

RESUMEN

Hyperpolarized (HP) 129Xe can be dissolved in biologically compatible lipid emulsions while maintaining sufficient polarization for in vivo vascular imaging. For xenon in Intralipid 30%, in vitro spectroscopy at 2 T yielded a chemical shift of 197 +/- 1 ppm with reference to xenon gas, a spin-lattice relaxation time T1 = 25.3 +/- 2.1 sec, and a T2* time constant of 37 +/- 5 msec. Angiograms of the abdominal and pelvic veins in the rat obtained with 129Xe MRI after intravenous injection of HP 129Xe/Intralipid 30% into the tail demonstrated signal-to-noise ratios between 8 and 29. An analysis of the inflow effect on time-of-flight images of two segments of the inferior vena cava yielded additional information. The mean blood flow velocity was 34.7 +/- 1.0 mm/sec between the junction of the caudal veins and the kidneys and 13.3 +/- 0.8 mm/sec at the position of the diaphragm. The mean volume flow rates in these segments were 7.2 +/- 3.4 ml/min and 11.0 +/- 2.8 ml/min, respectively. Intravenous delivery of HP 129Xe dissolved in a carrier may lead to novel biomedical applications of laser-polarized gases.

Asunto(s)