Expression of aquaporin water channels in mouse spinal cord.

Aquaporins (AQPs) are membrane proteins involved in water transport in many fluid-transporting tissues. Aquaporins AQP1, AQP4, and AQP9 have been identified in brain and hypothesized to participate in brain water homeostasis. Here we use reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry to describe the expression and immunolocalization of AQPs in adult mouse spinal cord. AQP4 was expressed in glial cells, predominantly in gray matter, and in astrocytic end-feet surrounding capillaries in spinal cord white matter. AQP9 expression extensively co-localized with glial fibrillary acidic protein-immunoreactive astrocytes, located predominantly in the white matter. AQP5 was detected by RT-PCR but not by immunohistochemical analysis. Interestingly, AQP8 was detected primarily in ependymal cells lining the fluid-filled central canal. The aquaporin expression pattern in spinal cord suggests involvement in water homeostasis and diseases associated with abnormal water fluxes such as spinal cord injury and syringomyelia.

Aquaporin-1 expression in human glial tumors suggests a potential novel therapeutic target for tumor-associated edema.

Aquaporins are membrane proteins involved in water transport in many fluid-transporting tissues. The objective of this study was to investigate the expression of aquaporins in malignant glial tumors associated with cerebral edema. Eighteen human glial tumors were obtained from the UCSF Neurosurgery Tissue Bank. Aquaporin-1 (AQP1) expression was evaluated via Western blot and immunohistochemistry. Intense upregulation of AQP1 expression was found in all glioblastomas. The robust expression of aquaporins in glioblastomas suggests a pathologic role for these membrane water channels, and raises the possibility that selective AQP inhibition might offer a new therapeutic option for tumor-associated cerebral edema.

Aquaporin-1 deletion reduces osmotic water permeability and cerebrospinal fluid production.

Aquaporin-1 (AQP1) is a water channel that is strongly expressed at the ventricular-facing surface of choroid plexus epithelium. Using wildtype and AQP1 null mice, we developed novel methods to compare the water permeability in isolated choroid plexus, and cerebrospinal fluid (CSF) production in living mice. Osmotically-induced water transport was rapid in freshly isolated choroid plexus from wildtype mice as measured by a spatial-filtering optical method, and reduced by 5-fold by AQP1 deletion. CSF production, an isosmolar fluid secretion process, was measured by a dye dilution method involving fluid collections using a second microneedle introduced into the cisterna magna. CSF production in wildtype mice was (in microl/min) 0.37 +/- 0.04 microl/min (control), 0.16 +/- 0.03 microl/min (acetazolamide-treated) and 1.14 +/- 0.15 microl/min (forskolin-treated), and reduced by up to 25% in AQP1 null mice. The impaired CSF production in AQP1 null mice provides direct functional evidence for the involvement of AQP1 in CSF formation.

Relaxation effects of clustered particles.

Relations between spatial distribution of superparamagnetic iron oxide (SPIO) particles and the image contrast caused by SPIO were investigated. Actual clustering pattern of particles was measured in the liver and spleen of animals using intravital laser confocal microscopy. SPIO-doped phantoms with and without Sephadex beads were made to simulate these patterns, and relaxation parameters were measured using a 1.5-T clinical scanner. Finally, these results were compared to clinical image data using SPIO particulate agent. Intravital microscopy indicated that the clustering of latex beads was more predominant in hepatic Kupffer cells than in splenic macrophages (P < 0.001). Phantoms without Sephadex beads showed an approximately linear increase of 1/T1 (R1), 1/T2 (R2) and 1/T2* (R2*) values with increasing SPIO concentration. However, with Sephadex beads, R1 and R2 showed little change with increasing SPIO concentration, while R2* showed the same linear increase with SPIO. Also, the R2* values were higher with Sephadex beads. These results were consistent with the clinical imaging data, where signal reduction was significantly smaller in the spleen (-0.4% +/- 27.4%) than in the liver (50.4% +/- 16.8%, P < 0.00001) on T2*-weighted images, but the reduction in the spleen (47.2% +/- 16.1%) was equivalent to the liver (38.8% +/- 26.0%) on T2-weighted images.

Temperature monitoring with line scan echo planar spectroscopic imaging.

UNLABELLED: A new magnetic resonance imaging method, line scan echo planar spectroscopic imaging (LSEPSI), is shown capable of providing rapid, internally referenced temperature monitoring from water and fat chemical shifts. METHODS: Orthogonal 90 degrees and 180 degrees slice selective RF pulses inclined by 45 degrees from the image plane solicit a spin echo from a tissue column. The echo is read by asymmetric sampling of 32 gradient echoes spaced 1.4-1.8 ms apart. Sixty-four adjacent columns are sequentially sampled in 4.2-6.4 s with 4,096 voxels sampled with voxel volumes of 0.08-0.13 cm3. Mixed mayonnaise/water phantoms were used to correlate LSEPSI-derived chemical shifts and thermocouple-based temperature measurements from 23 to 60 degrees C with a 1.5 T scanner. Measurement artifacts unrelated to temperature were investigated with the phantom, as was the feasibility of applying the sequence in human breast in vivo. RESULTS: The correlation between LSEPSI and thermocouple-based temperature measurements in the phantom was excellent (r2>0.99). Field drifts affecting the temperature measurements using the water peak alone were corrected by using the water/lipid peak difference. The sequence had an average temperature resolution of 1.4 degrees C in the phantom. The frequency difference measurement reduced the sensitivity to artifacts related to temperature. Both water and lipid peaks were detectable throughout many locations in the breast, suggesting the applicability of LSEPSI in this organ. DISCUSSION: T1-saturation losses occur in conventional and echo-planar based 2D CSI sequences using phase encoding methods with short TR periods. These losses are eliminated when individual columns are sampled in snapshot fashion with LSEPSI since the effective TR becomes the time between scans rather than excitations. T1 saturation can make small spectral peaks difficult to detect at high temperatures and generally lowers the signal-to-noise ratio of the spectra. The rapid acquisition and insensitivity to T1 saturation effects make LSEPSI an attractive technique for monitoring thermal therapies in breast using the internally referenced fat/water frequency separation.

[Fatty liver quantification with line scan echo planar spectroscopic imaging (LSEPSI)].

INTRODUCTION: Although fatty infiltration of liver is a benign process that generally results from chronic alcohol uptake or obesity, such lifestyle factors may lead to chronic disease. Measuring the fat concentration in liver may therefore prove useful in assessing disease status. In this study, we report the usefulness of line scan echo planar spectroscopic imaging (LSEPSI) for this problem. METHODS: Rapid successive column sampling was accomplished using orthogonal slice-selective 90 degrees and 180 degrees pulses and echo planar spectral/spatial encodings. Phantom and clinical studies of 13 patients suspected of having fatty liver were carried out with LSEPSI. Estimated fat fractions obtained with LSEPSI were compared with ultrasound findings. RESULTS: The results showed a good correlation between the actual fat content of phantoms and the estimated fat fraction obtained with LSEPSI (r = 0.95). In the clinical study, the estimated fat fraction tended to rise as the US grade of fatty liver increased. DISCUSSION: LSEPSI is largely free from T1 and T2 relaxation owing to its infinite TR and minimal T2 weighting. Thus, there is no need for relaxation analysis. In addition, the lack of phase encoding reduces motion-related ghosting artifacts. Rapid fat/water spectral quantification of liver with this technique is useful for fatty liver assessment in a clinical setting.

Line scan echo planar spectroscopic imaging.

A line scan echo planar spectroscopic imaging (LSEPSI) sequence is presented which can rapidly produce 2D chemical shift imaging (CSI) data with minimal relaxation weighting and motion-related artifacts. The technique is based on successive "snapshot" 1D CSI acquisitions of individual tissue columns, and avoids T(1) saturation problems associated with the short TR periods needed for very rapid scanning with either conventional or echo planar-based 2D CSI methods. Potential applications include rapid fat/water spectral quantitation in the abdomen and internally referenced temperature monitoring for interventional procedures.

vGRASE: separating phase and T(2) modulations in 2D.

A new fast imaging technique, vGRASE, was designed and implemented on a clinical imager. In the vGRASE scheme, the T(2) modulation ghost, which is the main problem of the GRASE sequence, can be reduced by separating the phase and T(2) modulations in two encoding directions. Although it is not much faster than the original GRASE, vGRASE has much improved image quality, with the same advantages over RARE and EPI as the original GRASE.

MR-based temperature monitoring for hot saline injection therapy.

We applied magnetic resonance (MR) phase mapping methods to monitor the thermal frequency shift of water in order to study temperature changes from percutaneous hot saline injection therapy (PSIT) using in vitro swine livers and in vivo rabbit livers. The thermal coefficients calculated from the shifts of the water frequency with thermocouple based temperature measurements were -0.0085 +/- 0.0019 ppm/ degrees C for the in vitro studies and -0.0089 ppm/ degrees C for the in vivo studies. The error range was estimated to be +/- 3 degrees C and +/- 4.5 degrees C, respectively. Color-coded temperature maps were compared with macroscopic lesion sizes of the specimen. Regions defined using a 20 degrees C elevation in the initial images following hot saline injection (around 55 degrees C in absolute temperature) closely correlated with visible coagulation in size. We conclude that MR temperature monitoring of PSIT is quite feasible and may be helpful in expanding the clinical use of this thermal therapeutic tool for liver tumors.

Human brain glucose metabolism mapping using multislice 2D (1)H-(13)C correlation HSQC spectroscopy.

A method for multivolume 2D (1)H-(13)C correlation spectroscopy, multislice heteronuclear single quantum coherence (HSQC), is proposed. This permits human brain metabolism from glucose to amino acids to be followed using a 2-T whole-body scanner. The modifications from the conventional HSQC are that the 180 degrees ((13)C) and 180 degrees ((1)H) pulses are separated in time in the preparation period and that the 180 degrees ((13)C) pulse is applied at 1/(4J(CH)) before the 90 degrees ((1)H) polarization transfer (PT) pulse. The preparation (echo) time can be set longer than 1/(2J(CH)) so that, even in a whole-body system, slice-selective pulses and gradients can be applied. Another modification is that the 90 degrees ((1)H) reverse PT pulses after the creation of 2I(z)S(z) are used as multislice pulses. The time-course of glutamate C4 could be followed with 15-min temporal resolution from the HSQC spectra obtained from the brains of volunteers after the oral administration of glucose C1, and the maximum S/N was 3.

3D localized 1H-13C heteronuclear single-quantum coherence correlation spectroscopy in vivo.

A method for spatially three-dimensional (3D) localized two-dimensional (2D) 1H-13C correlation spectroscopy, localized HSQC, is proposed. This method has the following special feature in the preparation period. The 180 degrees (13C) and 180 degrees (1H) pulses are separated in time, and the 180 degrees (13C) pulse is applied at 1/4 1JCH) before the 90 degrees (1H) polarization transfer pulse. The preparation (echo) period 2tau can then be set substantially longer than 1/(2 1JCH), so that even in a whole-body system, slice-selective 90 degrees (1H) pulses and gradient pulses can be applied in that period. The localization capabilities of this method were confirmed in a phantom experiment. The 3D localized 2D 1H-13C correlation spectra from a monkey brain in vivo were obtained after [1-13C]glucose injection, and amino acid metabolism was detected; that is, [4-13C]glutamate appeared immediately after the injection, followed by the appearance of [2-13C]glutamate, [3-13C]glutamate, and [4-13C]glutamine.

Temperature mapping using the water proton chemical shift: self-referenced method with echo-planar spectroscopic imaging.

An echo-planar spectroscopic imaging method of temperature mapping is proposed. This method is sufficiently faster than the so-called 3D magnetic resonance spectroscopic imaging (3D-MRSI) method and does not require image subtractions, unlike the conventional phase mapping method when an internal reference signal is detectable. The water proton chemical shift measured by using the tissue lipid as an internal reference clearly visualized the temperature change in a porcine liver sample in vitro. It was also demonstrated that the internally referenced echo-planar spectroscopic imaging method could markedly reduce a temperature error caused by a simple, translational motion between scans compared with the phase-mapping method.

A preliminary comparative study of the guided tissue regeneration and free gingival graft procedures for adjacent facial root coverage.

OBJECTIVE: The purpose of this study was to compare the clinical efficacy of guided tissue regeneration with expanded polytetrafluoroethylene membranes to that of free gingival graft for treatment of adjacent facial gingival recession. METHOD AND MATERIALS: Eight adjacent gingival recession sites with Miller class I or II defects containing at least a maxillary or mandibular canine were selected in 6 patients. Four recession sites in 3 patients were treated with guided tissue regeneration, and the other 4 sites in the remaining 3 patients were treated with free gingival graft. Probing depth, gingival recession, attachment level, width of keratinized gingiva, and root coverage were recorded before surgery (baseline) and 6 months and 1 year postoperatively. RESULTS: Statistically significant improvements were found for gingival recession, attachment level, and root coverage from baseline to 6 months and 1 year postoperatively in both groups. Both procedures produced the same average reduction in gingival recession, gain in attachment level, and amount of root coverage after 1 year. Probing depths did not differ between groups throughout the study. The width of keratinized gingiva was significantly greater in the grafted group than in the guided tissue regeneration group. CONCLUSION: Both procedures produced the same average amount of root coverage, reduction in gingival recession, and gain in clinical attachment. The guided tissue regeneration procedure provided a better esthetic appearance without any difference in gingival color or architecture in cases of adjacent facial gingival recession.

Spin-Echo planar spectroscopic imaging for fast lipid characterization in bone marrow.

Lipid characterization of bone marrow in vivo with proton magnetic resonance spectroscopy was performed using Spin-Echo Planar Spectroscopic Imaging sequences. The methods are shown capable of rapidly generating two-dimensional chemical shift imaging data sets suitable for measuring lipid indices that reflect unsaturation levels among triglycerides, as demonstrated in oil phantoms and bone marrow from a healthy volunteer. The volume coverage, spatial resolution, acquisition speed, and spectral characteristics of Spin-Echo Planar Spectroscopic Imaging should make it attractive for clinical studies of diseases affecting normal lipid chemical composition.

Selection of high-definition 2D virtual profiles with multiple RF pulse excitations along interleaved echo-planar k-space trajectories.

A method for spatially selective excitation of 2D RF profiles is reported. The method makes use of multiple shots to traverse interleaved echo-planar trajectories in 2D k space during each RF pulse excitation. Results from each of the interleaved excitations are summed, with the net effect being the excitation of a virtual profile. The method allows for the excitation of high-definition 2D profiles with standard gradient hardware. Signal to noise is enhanced by a factor equal to the square root of the number of interleaved excitations, compared with a single-shot excitation. Potential applications for volume-localized spectroscopy, functional MRI, and high-resolution reduced-field-of-view imaging are discussed.

Optimization of chemical shift selective suppression of fat.

Strategies to optimize flip angles for chemical shift selective fat suppression are discussed. Mathematical models for fat suppression in spoiled gradient recalled acquisition, spin echo, and RARE, which incorporate steady state conditions and multiple spectral components of fat, are developed. The optimal suppression flip angle is found to be larger than that determined with a single fat component model by more than 10 degrees due to contributions from unflipped components such as olefinic and glycerol protons that lie outside the suppression band.

In vivo 3D localized 13C spectroscopy using modified INEPT and DEPT.

The 3D localized 13C spectroscopy methods LINEPT and LODEPT, which are modifications of INEPT and DEPT, are proposed. As long as a 13C inversion pulse (180-degree pulse) is applied at 1/(4J) before the proton echo time in LINEPT and a 13C excitation pulse (90-degree pulse) is applied at 1/(2J) before the proton echo time in LODEPT, the proton echo time can be set to any value longer than 1/(2J) in LINEPT and longer than 1/J in LODEPT. As a result, the proton and the 13C pulses can be applied separately and these proton pulses can be made slice-selective pulses. These localization features of LINEPT and LODEPT were evaluated using a phantom consisting of a cylinder filled with ethanol placed inside another cylinder filled with oil, and localized ethanol spectra could be obtained. In vivo 3D localized 13C spectra from the brain of a monkey could be obtained using decoupled LINEPT, and glutamate C-4 appeared directly after the administration of glucose C-1, followed by the appearance of glutamate C-2, C-3 and glutamine C-2, C-3, C-4.

Rapid tip tracking with MRI by a limited projection reconstruction technique.

To rapidly track invasive devices within MRI systems, a novel approach using a limited projection reconstruction technique is presented. Our method exploits the difference between images reconstructed from a limited number of projections and serves to depict the tip of a needle during its advancement. This method was implemented on a standard MRI system with a radial fast-spin-echo sequence and examined in phantom studies. We demonstrated that the proposed method could track the tip every 300 msec and the tip depicted by the present technique was consistently displaced along the needle by a small distance (5 mm).

Temperature mapping using the water proton chemical shift: a chemical shift selective phase mapping method.

A proton-chemical-shift-based temperature imaging method, called chemical shift selective phase mapping, is proposed. The technique uses frequency-selective suppression to provide frequency selectivity to the phase mapping method. Separate imaging of the phase distributions of the water and nonwater signals reduced the error due to the presence of a nonwater signal in measuring the water proton chemical shift change in two-component samples. Imaging of the phase difference between water and oil yielded an internally referenced water proton chemical shift measurement to visualize the temperature change distribution, which was unaffected by motion-induced susceptibility changes.