Atrophic enlargement of CSF volume after subarachnoid hemorrhage: correlation with neuropsychological outcome

BACKGROUND AND PURPOSE

Ventricular dilation and sulcal enlargement are common sequelae after aSAH. Our aim was to quantify the late ventricular dilation and volumes of the CSF spaces after aSAH and to determine if they correlate with neurologic and cognitive impairments frequently detected in these patients.

MATERIALS AND METHODS

3D T1-weighted images needed for volumetry were available in 76 patients 1 year after aSAH, along with 75 neuropsychological assessments. Volumes of CSF segments and ICV were quantified by SPM in 76 patients and 30 control subjects to determine CSF/ICV ratios. The mCMI was calculated to roughly evaluate the ventricular dilation. The contributing factors for enlarged ventricles and CSF volumes were reviewed from radiologic, clinical, and neuropsychological perspectives.

RESULTS

The mCMI was higher in patients with aSAH (0.23 +/- 0.06) compared with control subjects (0.20 +/- 0.04; P = .020). In line with these planimetric measurements, the SPM-based CSF/ICV ratios were higher in patients with aSAH (35.58 +/- 7.0) than in control subjects (30.36 +/- 6.25; P = .001). Preoperative hydrocephalus, higher HH and Fisher grades, and focal parenchymal lesions on brain MR imaging, but not the treatment technique, were associated with ventricular enlargement. The clinical outcome and presence of neuropsychological deficits correlated significantly with CSF enlargement.

CONCLUSIONS

Ventricular and sulcal enlargement, together with reduced GM volumes, after aSAH may indicate general atrophy rather than hydrocephalus. Enlarged CSF spaces correlate with cognitive deficits after aSAH. A simple measure, mCMI proved to be a feasible tool to assess the diffuse atrophic brain damage after aSAH.

Study of manganese bacteriopheophorbide as a potential contrast agent for magnetic resonance tomography

The use of manganese bacteriopheophorbide characterized by a high relaxation capacity and selectively accumulating in the tumor as a contrast agent for magnetic resonance tomography significantly improves tumor contrasting against the background of normal tissues. The pharmacokinetics and selectivity of accumulation were studied by diffuse reflection spectroscopy.

Subarachnoid hemorrhage is followed by temporomesial volume loss: MRI volumetric study

OBJECTIVE

To assess whether subarachnoid hemorrhage (SAH) and its treatment is followed by volume loss in temporomesial structures.

METHODS

One hundred fifty-five consecutive patients with aneurysmal SAH were randomly assigned to surgical or endovascular treatment. Volumetric MRI was performed in 77 SAH patients with good or moderate clinical outcome 1 year after hemorrhage. A comprehensive neuropsychological test battery was used to evaluate the cognitive performance of the subjects. Thirty healthy individuals were imaged as MRI controls.

RESULTS

The normalized hippocampal (HC) volumes were 24.7/23.7 (right/left), and the amygdaloid (AM) volumes were 21.0/20.5 in the matched control population. In SAH patients, the corresponding volumes were smaller, HC 23.2/21.3 (p = 0.072/0.002) and AM 18.4/18.7 (p = 0.012/0.045). In addition, the AM ipsilateral to the ruptured aneurysm was smaller in patients who had undergone surgical treatment (15.7) vs endovascular treatment (20.3; p < 0.001). Treatment modality did not significantly affect the measured HC volumes. The hippocampal but not amygdaloid volumes correlated with the scores of several neuropsychological tests.

CONCLUSION

Subarachnoid hemorrhage and its treatment may be followed by atrophy in temporomesial structures. A clear correlation was demonstrated between neuropsychological performance and reduced temporomesial volumes.

Observation of electro-osmotic flow echoes in porous media by nuclear magnetic resonance

A method for assessing the time reversibility of molecular displacements in fluids is presented. The method utilizes pulsed field gradient NMR experiments, in which the flow driving force is inverted during the magnetization lifetime in each measurement cycle. The method is suitable for opaque three-dimensional systems and short displacements, and provides inherent separation between thermal diffusion and displacements driven by externally controlled forces. This approach was applied to study the time reversibility of an electric-field-driven flow of water in natural sand samples, over time scales of up to 0.4 s and displacement scales of the order of one particle diameter. It is demonstrated that the intensity loss of the NMR signal, caused by flow-induced phase dispersion, is fully refocused upon inversion of the polarity of the applied electric field, resulting in flow echoes.

Significant differences in the retention of the borocaptate monomer (BSH) and dimer (BSSB) in malignant cells

The (10)B enriched form of Na(2)B(12)H(11)SH (BSH) is used in a binary cancer radiation treatment, known as boron neutron capture therapy (BNCT). The BSH anion can also form a dimer, [B(24)H(22)S(2)](4-) (BSSB), previously used in animal model studies. It is demonstrated here that the retention of BSSB in mouse M2R melanoma and rat C6 glioma cells is significantly longer than that of the monomer BSH. The washout of the BNCT agents from cultured cells was followed using (11)B nuclear magnetic resonance spectroscopy. One hour after switching to boron-free culture medium, the relative amount of BSSB retained in M2R cells was at least about six times higher than that of BSH. The initial washout rate (over the first approximately 4 h) of BSSB was 4x10(-3) min(-1) (t(1/2), approximately 3 h) for M2R cells, and of the same order of magnitude for glioma cells.

In vivo imaging of the neutron capture therapy agent BSH in mice using (10)B MRI

Boron neutron capture therapy (BNCT) is an experimental cancer treatment modality requiring the targeting of (10)B-enriched compounds to the tumor, which is then irradiated by low-energy neutrons. One of the boron-containing compounds used for this purpose is the mercaptoborane Na(2)B(12)H(11)SH (BSH). The first in vivo MR images of (10)B-enriched BSH are presented here. BSH, injected into the tail vein of mice with implanted M2R melanoma xenografts, was imaged using 3D gradient echo (10)B MRI. (10)B NMR spectroscopy, localized mainly to the tumor by virtue of the use of a small surface coil, was applied to measure the T(1) (2.9 +/- 0.3 ms) and T(2) (1.75 +/- 0.25 ms) values of the (10)B signal. The MRI experiments detected levels of about 20 ppm (microg boron / g tissue) at 6 x 6 x 6 mm spatial resolution in a total scan time of 16 min. Magn Reson Med 46:13-17, 2001.

Magnetization transfer and double-quantum filtered imaging as probes for motional restricted water in tulip bulbs

Parameter sensitive MRI experiments were performed on tulip bulbs before and after storage at two different temperatures, 4 degrees C (chilled), and 20 degrees C (non-chilled). Quantitative measurements of the amount of magnetization transfer (MT) in the storage scales of the bulbs, were compared to the average values of the relaxation rates R(1) and R(2), and the apparent normalized spin density (NSD). At the end of the storage period, bulbs were also scanned using 1H double quantum (DQ) filtered imaging. Both MT and DQ filtered imaging revealed significant differences between chilled and non-chilled bulbs, which were consistent with the differences observed in the average values of NSD, R(1,) and R(2.) The results indicated a smaller fraction of solid protons (e.g., starch, sugars, and possibly bound water), or less contact between these solid protons and (free) water in the storage scales of the chilled bulbs, after 8 weeks of storage at low temperature.

Antivascular treatment of solid melanoma tumors with bacteriochlorophyll-serine-based photodynamic therapy

We describe here a strategy for photodynamic eradication of solid melanoma tumors that is based on photo-induced vascular destruction. The suggested protocol relies on synchronizing illumination with maximal circulating drug concentration in the tumor vasculature attained within the first minute after administrating the sensitizer. This differs from conventional photodynamic therapy (PDT) of tumors where illumination coincides with a maximal concentration differential of sensitizer in favor of the tumor, relative to the normal surrounding tissue. This time window is often achieved after a delay (3-48 h) following sensitizer administration. We used a novel photosensitizer, bacteriochlorophyll-serine (Bchl-Ser), which is water soluble, highly toxic upon illumination in the near-infrared (lambda max 765-780 nm) and clears from the circulation in less than 24 h. Nude CD1 mice bearing malignant M2R melanotic melanoma xenografts (76-212 mm3) received a single complete treatment session. Massive vascular damage was already apparent 1 h after treatment. Changes in vascular permeability were observed in vivo using contrast-enhanced magnetic resonance imaging (MRI), with the contrast reagent Gd-DTPA, by shortening spin-spin relaxation time because of hemorrhage formation and by determination of vascular macromolecular leakage. Twenty-four hours after treatment a complete arrest of vascular perfusion was observed by Gd-DTPA-enhanced MRI. Histopathology performed at the same time confirmed primary vascular damage with occlusive thrombi, hemorrhage and tumor necrosis. The success rate of cure of over 80% with Bchl-Ser indicates the benefits of the short and effective treatment protocol. Combining the sensitizer administration and illumination steps into one treatment session (30 min) suggests a clear advantage for future PDT of solid tumors.

Optimal detection of the neutron capture therapy agent borocaptate sodium (BSH): a comparison between 1H and 10B NMR

Boron Neutron Capture Therapy (BNCT), an experimental binary cancer treatment modality, requires selective targeting of 10B containing compounds to tumors. One of the compounds under evaluation in an EORTC phase I trial, and used in Japan for patient treatments for many years, is borocaptate sodium (BSH, also known as sulfhydril boron hydride). To optimize the clinical applications, a noninvasive method is needed to monitor the distribution of the boron compound, and NMR may offer such a possibility. A comparison between the relative sensitivities for detecting BSH by 10B or 1H NMR was conducted at two magnetic field strengths: 2 and 4.7 T. At each field strength, similar-sized radio frequency (rf) coils were used for both nuclei. Theoretical predictions for the intrinsic signal to noise (S/N) advantage of 1H over 10B detection vary between a factor of 5.4 and a factor of 28.9, depending on whether the effective resistance is dominated by coil losses or sample losses. Our tests, conducted on relatively small aqueous samples, which loaded the coils less than expected for animal or human subjects, resulted nevertheless in advantage factors close to the lower limit of this range. The measured S/N detection advantage factors for 1H were about 5.2 at 4.7 T, using a dedicated 1H coil, and 7.7 at 2 T, where the measurements were conducted with a double-tuned coil. However, when predicting the expected performance for in vivo MRS or MRI, one should bear in mind that proton detection has to be conducted by spectral-editing pulse sequences with an inherent S/N loss by at least a factor of 2, and that the T1 relaxation time for 10B in BSH is about 30 times shorter than the 1HT1 value. In view of these considerations, direct 10B detection could well be the preferred strategy for MRI/MRS of BSH in vivo.

Developmental changes and water status in tulip bulbs during storage: visualization by NMR imaging

Magnetic Resonance Imaging (MRI) and light and scanning electron microscopy (SEM) were used to follow time-dependent morphological changes and changes in water status of tulip bulbs (Tulipa gesneriana L., cv. 'Apeldoorn') during bulb storage for 12 weeks at 20 degrees C (non-chilled) or 4 degrees C (chilled) and after planting. MR images reflecting the water content, the relaxation times T1 and T2 (or their reciprocal values, the relaxation rates R1 and R2), and the apparent self-diffusion coefficient of water molecules (ADC), were obtained for intact bulbs. After planting, scape elongation and flowering occurred only in chilled bulbs, while elongation in non-chilled bulbs was retarded. Microscopic observations showed different structural components and high heterogeneity of the bulb tissues. MRI revealed the elongation of the flower bud during storage, which was significantly faster in the chilled bulbs. In addition, MRI demonstrated a redistribution of water between different bulb organs, as well as significant differences in the pattern of this redistribution between the chilled and non-chilled bulbs. Generally, R2 relaxation rates became faster in all bulb organs during storage. At the same time, ADC values remained constant in the chilled bulbs, while exhibiting a significant increase in the non-chilled bulbs.

Uptake and washout of borocaptate sodium and borono-phenylalanine in cultured melanoma cells: a multi-nuclear NMR study

The cellular uptake and washout of the two principal boron neutron capture therapy (BNCT) agents, borocaptate sodium (BSH) and borono-phenylalanine (BPA), were monitored on-line, noninvasively, using nuclear magnetic resonance (NMR) spectroscopy. The uptake and washout of inorganic borate (B(i)) was also followed for comparison. M2R mouse melanoma cells grown on polystyrene microspheres were perfused inside the NMR sample tube. (11)B NMR was used to detect the presence of B(i), BSH and BPA, and (19)F NMR was applied to detect fluorinated BPA ((19)F-BPA). The results revealed chemical modifications of BSH due to spontaneous formation of the borocaptate dimer, BSSB, in the culture medium. BPA readily formed a complex with glucose contained in the culture medium but was also converted in the cells to a yet unidentified compound in a reaction that probably involves the hydrolysis of BPA and the release of B(i). The cellular accumulation ratio for BPA was significantly higher than 1 and was also significantly higher than that for BSH. On the other hand, the cellular retention time observed for BSH was much longer than for BPA, indicating a strong trapping of BSH in cells.

Line narrowing of I = 12 spins coupled to quadrupolar nuclei in liquids: effects of weak decoupling fields

In this paper an exact description of the observed transverse magnetization of spin 12 nuclei, coupled to quadrupolar spins which are subjected to RF irradiation, is presented. It is shown that for on-resonance CW decoupling at weak to intermediate irradiation levels, the transverse decay of the spin 12 magnetization is modulated with a period of 1/nu(2), where nu(2) is the amplitude of the decoupling irradiation. When the spin 12 signal is created as a spin echo, and the quadrupolar resonance continuously irradiated during the echo evolution, the echo amplitudes experience much stronger modulation with period 2/nu(2). In previous treatments of such spin systems, the regime of weak decoupling power was usually neglected, and approximate analytical expressions seeking to define the "adequate" or "minimal" decoupling power, necessary to achieve the collapse of the spin 12 multiplet into a single narrow line, were derived. It is demonstrated here, both by experiments and by simulations using a full Redfield formalism, that simple analytical predictions for the T(2) decay of the spin 12 magnetization are still possible, even when the scalar relaxation is not in the "fast exchange" limit and the transverse decay is considerably modulated due to insufficient decoupling power. In this case, the expected single exponential decay rate is obtained for the nonmodulated component of the signal. The theoretical solution for spin I = 12 coupled to S = 3 is derived, and results for the proton decay in (10)B-enriched sodium borocaptate in aqueous solution are presented. The effects of irradiation by several composite pulse decoupling sequences are also considered. Copyright 1999 Academic Press.

Altered brain glucose metabolism in transgenic-PFKL mice with elevated L-phosphofructokinase: in vivo NMR studies

The gene for the liver-type subunit of phosphofructokinase (PFKL) resides on chromosome 21 and is overexpressed in Down syndrome (DS) patients. Transgenic PFKL (Tg-PFKL) mice with elevated levels of PFKL were used to determine whether, as in DS, overexpression of PFKL was also associated with altered sugar metabolism. We found that Tg-PFKL mice had an abnormal glucose metabolism with reduced clearance rate from blood and enhanced metabolic rate in brain. Transgenic-PFKL mice exhibited elevated activity of phosphofructokinase in both blood and brain, as compared to control non-transgenic (ntg) mice. Following glucose infusion, the rate of glucose clearance from the blood of Tg-PFKL mice was significantly slower than that of control ntg mice, although the basal blood glucose levels were similar. However, unlike the slower rate of glucose metabolism in blood, the initial rate of glucose utilization in the brain of the transgenic mice, was 58% faster than in control ntg mice. This was determined by infusion of [1-13C]-glucose followed by in vivo nuclear magnetic resonance (NMR) measurements of brain glucose metabolism. The faster utilization of glucose in Tg-PFKL brain is similar to the increased rate of cerebral glucose metabolism found in the brain of young adult DS patients, which may play a role in the etiology of their cognitive disabilities.

Choline metabolism in breast cancer; 2H-, 13C- and 31P-NMR studies of cells and tumors

Choline metabolism in breast cancer cells and tumors has been investigated by multinuclear NMR in order to provide the biochemical basis for the presence of high phosphocholine in breast carcinoma relative to benign breast tumors and normal breast tissue. Choline was found to be transported into MCF7 human breast cancer cells and rapidly phosphorylated to phosphocholine which was then accumulated in the cells to high concentrations. The increased level of phosphocholine did not affect the rate of synthesis of phosphatidylcholine, indicating tight regulation of this pathway. The incorporation of [1,2-13C]choline (100 microM) into phosphocholine and phosphatidylcholine after 24 h was 69.5 and 36% of the total respective pools. Incorporation of 2H9-choline to tumors implanted in nude mice was achieved by infusing the deuterated choline to the blood circulation. The metabolism of deuterated choline was then monitored by 2H localized MRS. The blood level of choline before the infusion was 58.6 +/- 10.3 microM (measured by 1H-NMR of plasma samples) and increased approximately 5-fold during the infusion (measured by 2H-NMR). This increase in the blood level resulted in a gradual increase of a signal at 3.2 ppm due to deuterated choline metabolites. It appears that the increased availability of choline in the blood circulation leads to accumulation of phosphocholine in the tumors by the same mechanism as in the cells.

Boron-11 NMR of borocaptate: relaxation and in vivo detection in melanoma-bearing mice

Longitudinal and transverse relaxation rates for the 11B resonances in sodium borocaptate (BSH) at varying concentrations were measured in undiluted horse serum in a 4.7 Tesla field. The results could be fit by a model that assumes fast exchange of the BSH molecule between a free and a bound state, using values of 0.77+/-0.7 MHz for the 11B quadrupole coupling constant and (6.3+/-0.9) x 10(-9) s for the rotational correlation time in the bound state. These results were used as a basis for assessing the requirements and limitations of quantitative determination of BSH concentrations in vivo, using 11B NMR. Surface coil 11B NMR spectroscopy was performed on a total of 14 mice injected with BSH. Some of the animals (n=9) had implanted M2R melanoma tumors grown to various sizes in the rear thigh, in which case the surface coil was placed against the tumor, whereas for the other animals (without tumor), the coil was placed against the rear thigh muscle. NMR spectra were acquired under fully relaxed conditions. The spectra were quantitated by peak integration; apparent absolute BSH concentrations were derived by comparison with spectra from a phantom with known BSH concentration, using extrapolation of the time-domain data to zero preacquisition delay. The results indicate significantly higher 11B BSH signal intensities in tumors, compared with muscle tissue, whereas the uptake and clearance kinetics were similar.

Quadrupolar relaxation of spin 3 in the intermediate omega0tauc regime

The equations for the quadrupolar relaxation of spin 3 were derived for the Redfield limit where the molecular reorientation rate is much faster than the size of the quadrupolar interaction. In the extreme narrowing regime (omega0tauc << 1), the results converge to the analytical expressions for the relaxation rates available in the literature. For slower motions, both longitudinal (spin-lattice) and transverse (spin-spin) relaxations are described by a superposition of three exponentials, where both the rates themselves and their relative weights are functions of omega0tauc. Numerical calculations of the relevant relaxation parameters in the intermediate omega0tauc regime are presented. Spin-lattice relaxation is described to very good approximation by a single exponential for all values of omega0tauc, with the weight of the dominant decay mode exceeding 0. 97 for the entire range. The predictions of these simulations were found to be in good agreement with experimentally measured relaxation rates of the 10B resonances in the sodium salt of Na2B12H12S, mercaptoundecahydro-closo-dodecaborane (sodium borocaptate or BSH) dissolved in glycerol, determined at omega0 = 53. 73 MHz, between temperatures of 268 and 323 K. The fit to the experimental results yielded a value of 1.25 MHz for the average 10B quadrupolar coupling constant in this molecule. Copyright 1997 Academic Press. Copyright 1997Academic Press

The role of boron MRI in boron neutron capture therapy

Boron magnetic resonance imaging (MRI) and spectroscopy (MRS) are being developed for use in boron neutron capture therapy (BNCT). With continued development, boron MRI may be used to locate BNCT agents in vivo, evaluate the pharmacokinetics of BNCT agents, and aid in treatment planning.

Quantitative diffusion imaging in implanted human breast tumors

Quantitative diffusion measurements were performed in tumors arising from inoculation of nude mice with two human breast cancer cell lines (MCF7 and T47D) to evaluate the specificity of this technique for characterizing solid tumors. ADC maps were compared to histology and correlated well with gross tumor morphology. Measured ADCs were highly specific for viable and necrotic tumor in the five T47D tumors included in this study (P < 0.02), while only two of the five MCF7 tumors studied developed distinguishable areas of necrosis. No statistically significant difference was observed in ADCs from viable tumor between the different cell lines (P > 0.05).

The ontogeny of a neurotoxic lesion in rat brain revealed by combined MRI and histology

We have used magnetic resonance imaging (MRI) of the living rat brain to longitudinally analyze the ontogenesis of an ibotenic acid lesion targeted at the piriform cortex. The MRI data were systematically compared with data obtained from a battery of histopathological techniques, including Nissl stain, hematoxylin stain, and a stain for cytochrome oxidase activity. Two days after the lesioning, widespread and heterogeneous damage was detected in, around and distant from the toxin-targeted area. Some damage apparently diminished within approximately 10 days, whereas other damage remained throughout the length of this study (60 days). We found that the small-animal MRI technology used by us is useful in determining the initial, transient impact of surgery and neurotoxic lesioning, and in delineating the gross effects of the lesion over time. This is particularly useful for early elimination of animals from the protocol of physiological and behavioral experiments in which the lesion exceeds the target area. Our data also indicate that, in order to avoid confounding effects of transient post-lesioning phenomena, behavioral and physiological tests should be carried out in neurotoxically lesioned animals > 2 weeks after infliction of the lesion.

In vivo detection of a boron-neutron-capture agent in melanoma by proton observed 1H-10B double resonance

The Cesium salt of BSSB (Cs4B24H22S2), a common boron-neutron-capture-therapy (BNCT) agent, was injected into M2R mouse melanoma xenografts, and detected in vivo by 1H-observed, 10B-edited NMR spectroscopy. The technique of spin-echo difference spectroscopy, in which a proton spin-echo is detected following the alternating presence and absence of a 10B 180 degrees pulse was used. This method provides much higher sensitivity than direct 10B NMR detection, and should thus be suitable for in vivo detection in patients about to undergo BNCT treatment, where the infused agents are 95% isotopically enriched in 10B.

Snapshot MRI with T2*-weighted magnetization preparation

A method for encoding T2*-dependent contrasts into the preparation period of magnetization-prepared ultrafast MRI sequences is demonstrated and validated. The preparation block consists of a 90 degrees---tau---90 degrees p sequence, where p is shifted by 90 degrees for successive images. By adding two such successive images in quadrature, a combined image is obtained, in which the pixel intensities depend on the incoherent intravoxel dephasing that occurred during tau in a way that is similar to the dependence of TE in a gradient-echo sequence. The method could therefore be useful for applications that require very short repetition times for good temporal resolution, together with detection of T2*-weighted contrasts, such as functional MRI in the brain.

Correlation of MR imaging and histologic findings in mouse melanoma

M2R melanoma tumors in male C57 black mice were used to correlate magnetic resonance (MR) images with the corresponding histologic slices and to determine if analysis of the achievable correlation can provide a basis for predicting gross histologic features with MR imaging alone. The MR imaging sections obtained at 4.7 T were each 680 microns thick, with an in-plane resolution of 195 microns. The distribution of melanin within the histologic slices correlated well with the high-signal-intensity regions on the T1-weighted images (T1WIs), while these regions had low signal intensity on the T2-weighted images (T2WIs), providing evidence that melanin or melanin-associated paramagnetic species are responsible for the observed proton relaxation rate enhancement. Viable melanoma cells typically showed intermediate signal intensity on T2WIs, T1WIs, and proton-density images. Necrosis typically had high signal intensity on T2WIs, T1WIs, and proton-density images. Quantitation of the MR imaging results, followed by statistical analysis, demonstrated statistically significant differences between melanin-rich, viable-melanoma, and necrotic regions on MR images.

Tamoxifen induced changes in MCF7 human breast cancer: in vitro and in vivo studies using nuclear magnetic resonance spectroscopy and imaging

The effects of 17 beta-estradiol versus tamoxifen on the growth and metabolism of MCF7 human breast cancer cells, in culture and in tumors implanted in nude mice, were studied by 31P and 13C nuclear magnetic resonance spectroscopy and by proton magnetic resonance imaging. In culture, the content of the phosphate metabolites including nucleoside triphosphates (NTP), phosphomonoesters, phosphodiesters and inorganic phosphate (Pi) were not affected by tamoxifen treatment. However, in the presence of estrogen the rate of glucose consumption and lactate production via glycolysis (270 and 280 fmol/cell.h, respectively) were twice that of tamoxifen treated cells. Estrogen rescue of tamoxifen treated cells indicated that glycolysis induction occurs at the early stages of the hormonal response. The in vivo studies included recording of proton images that provided an accurate measure of tumor size and distribution of tumor cells, necrotic regions and stromal tissue. Tamoxifen caused enhanced necrosis extending from the center of the tumor during the first two days of treatment (12 h to 6 days). This was followed by growth of reparative tissue along with tumor regression. Tamoxifen also modified the content of the phosphate metabolites, increasing markedly (P less than 0.0002) the ratio of NTP to Pi from 0.41 before treatment to 1.75 9-19 days after treatment. This change was attributed to the enhanced growth of repair tissue. The results provide new information regarding the response of human breast cancer to hormonal treatment and suggest a mechanism for the induction of tumor regression by tamoxifen.

Thin-section MR imaging of rat brain at 4.7 T

The brains of anesthetized 7-month-old male hooded rats were imaged in coronal, sagittal, and horizontal planes at 4.7 T. Images were obtained with a section thickness of 0.6 mm and in-plane pixel size of 0.18-0.20 mm, resulting in finer combined spatial and contrast resolution than in most previously published reports. This allowed detailed anatomic assignment of many brain structures on the basis of comparison with a histologic brain atlas. T1, apparent T2, and water proton density values of gray matter, white matter, and cerebrospinal fluid (CSF) were derived from saturation-recovery and multi-echo measurements. These values were used to calculate expected contrast-to-noise ratios as a function of TR and TE in spin-echo imaging sequences. The optimal simultaneous contrast between gray and white matter and between CSF and gray matter was obtained on images with moderate T2 weighing, with a TR of 3.6 seconds and a TE of 45 msec. The use of thin sections was found to be essential for resolving many fine structures, and the improved sensitivity provided by the high magnetic field strength was crucial for imaging such thin sections at adequate signal-to-noise ratios.

Quantitation of ventricular size in normal and spontaneously hypertensive rats by magnetic resonance imaging

Magnetic resonance imaging (MRI) performed at high field (4.7 Tesla), and high spatial resolution (0.6 mm slice thickness, 0.18 mm inplane) enabled noninvasive quantitative measurement of the ventricular vol. in live rats. Comparing the results for 15 male Wistar-Kyoto (WKY) rats, aged 2.5-10 months, with those from 17 spontaneously hypertensive rats (SHR), clearly confirmed the previously reported elevated ventricular vols. in the SHR strain. A significant difference in ventricular vol. between the two strains was detected above the age of 3 months. For mature animals above the age of 6 months the mean vol. in the SHR strain was elevated by about a factor of two compared to the WKY control animals.

In vivo studies by magnetic resonance imaging and spectroscopy of the response to tamoxifen of MCF7 human breast cancer implanted in nude mice

Magnetic resonance 1H-imaging and 31P-localized spectroscopy were utilized to monitor, noninvasively, MCF7 human breast cancer tumors implanted in immunodeficient mice. The tumors were followed during estrogen dependent growth and tamoxifen induced remission. Early after tamoxifen administration enhanced necrosis developed, extending to most of the tumor volume. This was followed by growth of repair tissue along with tumor regression. The short-term tamoxifen treatment also modified the content of the phosphate metabolites, increasing the nucleoside triphosphate to inorganic phosphate ratio from 0.41 +/- 0.15 (n = 14) before treatment to 1.10 +/- 0.70 (n = 8, P less than 0.025) and to 1.75 +/- 0.66 (n = 9, P less than 0.0002) 4-7 days and 9-19 days, respectively, after treatment. This change was attributed to the growth of reparative tissue. The results provide new information regarding the response and the mechanism of action of tamoxifen.

In vivo boron-11 MRI and MRS using (B24H22S2)4- in the rat

In vivo boron-11 magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) were performed on a rat that had been infused with a potential boron neutron capture therapy agent, Na4B24H22S2, using methods for detecting nuclei with a short T2 relaxation time. MRI and MRS were also performed on a euthanized rat that had been similarly infused in vivo. Boron-11 spectral intensities decreased in the living rat over a 25-h period. The results demonstrate the capability of MRI and MRS to noninvasively monitor the distribution and excretion of boron agents in vivo.

Blood flow in the carotid arteries: quantification by using phase-sensitive MR imaging

The feasibility of MR phase-sensitive imaging for the quantification of blood flow in the carotid arteries was studied in two normal volunteers and six patients with carotid artery and/or cerebrovascular disease. The technique consists of sensitizing the phase of the MR signal to blood flow velocity gated to different times in the cardiac cycle. Flow velocities and volumes were measured by using transverse planes in the common, internal, and external carotid arteries, and flow curves were generated. Measurements made by using flow phantoms correlated well with calculated results. The MR measurements yielded values between 250 and 580 ml/min for the total flow through each of the common carotid arteries in the two normal volunteers. Markedly reduced flow (about 50% below normal) was detected in a patient whose arteriogram showed severe occlusion of the internal carotid artery. In a second patient, who had a large frontal intracranial arteriovenous malformation noted by arteriography, the MR-quantified flow was abnormally high (about 1 liter/min). In the remaining four patients, the findings on phase-sensitive quantification were consistent with those expected from clinical and other laboratory studies (including arteriography and sonography). These preliminary findings suggest that MR phase mapping may be a feasible tool for the noninvasive quantification of carotid blood flow.

Boron-11 MRI and MRS of intact animals infused with a boron neutron capture agent

Boron neutron capture therapy (BNCT) depends on the delivery of boron-containing drugs to a targeted lesion. Currently, the verification and quantification of in vivo boron content is a difficult problem. Boron-11 spectroscopy was utilized to confirm the presence of a dimeric sulfhydryl dodecaborane BNCT agent contained in an intact animal. Spectroscopy experiments revealed that the decay time of transverse magnetization of the boron-11 spins was less than 1 ms which precluded the use of a 2DFT imaging protocol. A back-projection protocol was developed and utilized to generate the first boron-11 image of a BNCT agent in the liver of an intact Fisher 344 rat.

An analysis of fast imaging sequences with steady-state transverse magnetization refocusing

Recently, several groups have proposed and demonstrated the use of rapid imaging methods, using short pulse repetition times and gradient-reversal echoes. Here, we analyze the behavior of the magnetization and the resulting image contrasts in such sequences for the case where the pulse repetition time TR is of the order of, or shorter than, the transverse relaxation time T2, and the transverse magnetization is not destroyed between phase-encoding cycles. Exact analytical expressions describing the signal evolution between the pulses are derived, taking into account the effects of resonance offsets and flip angles, and examining the influence of constant-phase or alternate-phase RF pulse trains. It is shown that for typical imaging sequences two distinct echo signals will develop between pulses, which may have a detrimental effect on image quality if they partially overlap within the sampling window. It is shown that artifact-free images can be obtained only if the two echo signals overlap precisely, which seems technically close to impossible to achieve, or if they are sufficiently separated in time to allow sampling of only one of the signals.

T2-weighted contrasts in rapid low flip-angle imaging

Expressions for the contrast-to-noise (C/N) behavior in images obtained from rapid low flip-angle excitation pulses are derived, taking into account both T1- and T2-dependent contrasts. It is shown, and demonstrated experimentally, that images with T2-weighted contrasts can be efficiently acquired with such sequences, by a suitable choice of TR, TE, and tip angle.

The effects of simultaneous pulsing in different gradient coils on the nuclear magnetic resonance imaging of oblique slices

The definition and mapping of oblique planes by magnetic resonance imaging (MRI) requires the simultaneous application of two or three orthogonal gradients to define the desired intermediate direction of the frequency encoding or "readout" gradient. Each of the three main gradient coils produces different patterns of eddy currents. Consequently, the application of dephasing and rephasing lobes of these gradients will produce echoes at slightly different times for each gradient. If two or three gradients are applied simultaneously to create an arbitrary view direction, the resulting echo will therefore be shifted in time and considerably reduced in intensity. In this article, we present an analysis of the behavior of the magnetization in a typical two-dimensional Fourier transform pulse sequence for the imaging of oblique slices. The theoretical displacements in time and reduction in intensity of the echo amplitudes are calculated and compared to the experimental behavior. We show that, in spite of this phenomenon, the final image suffers only marginally in signal-to-noise ratio, provided the slice width is small compared to the field of view. This is due to the fact that there always exists a cycle in the sequence in which the phase-encoding gradient almost completely compensates for the above described effect.

One- and two-dimensional 90.5-MHz 13C-NMR spectroscopy of the N-linked triantennary oligosaccharide units of calf fetuin

Complete assignments of all anomeric resonances in the proton and carbon spectra of the N-linked oligosaccharide units of fetuin were made using one- and two-dimensional NMR spectroscopy. We are able to confirm the presence of microheterogeneity in the N-acetylneuraminic acid linkages to the galactose residues and the presence of a unique triantennary structure which carries a side chain: NeuAc alpha(1-3)Gal beta(1-3)GlcNac beta(1-4)-. Anomeric carbon chemical shifts changes resulting from long-range conformational effects were observed.

Measurement of the helix opening rate in Z-DNA by 1H nuclear magnetic resonance relaxation spectroscopy

The exchange rate of the hydrogen-bonded guanine imino protons N(1) in the high-salt form of Poly(dG-dC) was measured by following the non-selective inversion-recovery of their 1H NMR signal at 360 MHz, in the temperature range between 77 degrees C and 90 degrees C. In a 4.5M NaCl solution, Poly(dG-dC) is believed to adapt the left-handed Z-conformation, and the results reported here represent the first quantitative measurements of this rate process for Z-DNA by Nuclear Magnetic Resonance, complementing previous measurements made by tritium exchange at 0 degrees C (Ramstein, J. and Leng, M. (1980) Nature 288, 413-414). The results confirm that this process is much slower in the Z-form, compared to the B-structure, and that this difference in rates results mainly from a large decrease in the entropy of activation for Z-DNA.

Echo projection imaging-a method to obtain NMR images undistorted by magnetic field inhomogeneities

It is proposed to use a modified form of Mansfield's echo planar imaging to obtain NMR images which are entirely undistorted by background inhomogeneities of the magnetic field. In the proposed method, a train of 180 degrees pulses is applied in the presence of a periodically switched or sinusoidally modulated linear field gradient. The time-domain signal is sampled at half the distance between the 180 degrees pulses. At these points the magnetization will be modulated by the gradient, but will be independent of any mechanisms of inhomogeneous broadening, such as static field inhomogeneities, local susceptibility effects, or chemical shifts. A Fourier transform of the function comprising these points will therefore yield a faithful projection of the spin density, although the magnitude of the superimposed gradient need not be large compared to the inhomogeneous broadenings. This paper demonstrates the application of the proposed pulse sequence to a small-scale one-dimensional phantom. The major problem in upscaling this technique to human-scale dimensions lies in the limited available and allowed RF power, which in turn limits the maximal tolerable field inhomogeneities as well as the maximal practical field strength. An analysis of the tolerance of the proposed technique to these factors is presented, based on numerical simulation of its performance, using the Bloch equations. It is concluded that its use may be feasible on low-field systems, providing the advantages of increased signal-to-noise, lower required gradient strength, and drastically reduced sensitivity to the homogeneity and stability of the magnetic field, at the expense of larger RF power.

Deuterium NMR in the solid-state and in solution of the molecular motion of the bases in poly(I) and poly(I) . poly(C)

To provide information regarding the conformational flexibility of nucleic acids, in particular the rate and amplitude of base motions, we have observed the deuterium NMR from single-stranded and double-stranded polynucleotides. Poly(I) was deuterated at the 8-position of the base, and the deuterium NMR was examined in solution (at 23.0 and 55.4 MHz) and for hydrated and dry fibers (at 23.0 MHz). In the solid state, the deuterium signal of dry poly(I) exhibits a powder pattern with the maximal expected quadrupolar splitting, while the relatively short spin-lattice relaxation time indicates the presence of a rapid internal reorientation of the C-D bond with an amplitude of that motion of at least +/- 2.4 degrees. Hydrating the poly(I) fibers to the extent of eight molecules of water per nucleotide results in the disappearance of the deuterium signal, apparently due to a decreased spin-spin relaxation time shorter than the instrumental dead-time (even using the quadrupolar echo technique); this could occur if conformational fluctuations are occurring at a rate comparable to the deuterium quadrupole interaction strength, i.e., 175 kHz. In solution, a theoretical fit to the measured Lorentzian linewidths and spin-lattice relaxation times necessitates the inclusion of at least two motional correlation times, with a subnanosecond internal motion. Double-stranded poly(I) . poly(C) yielded a solid state spectrum similar to poly(I), albeit with a longer T1, which reduced the lower limit for the amplitude of an internal motion to +/- 1.9 degrees. The 2H signal from the poly(I) . poly(C), hydrated to a degree of approx. eight molecules of water per base pair, retained its solid-state lineshape (with a reduced T1 value, indicating increased internal mobility of the bases with a lower limit on amplitude of +/- 4.7 degrees). In solution, however, the 2H-NMR signal from poly(I) . poly(C) became virtually undetectable, even in solid-echo experiments, when the echo was observed after 52 microseconds. This indicates that the spin-spin relaxation time of the deuterium nucleus must be close to its theoretical minimum of about 9 microseconds, and the correlation time for an isotropic reorientation of the C-D vector can be estimated to be between 0.2 and 200 microseconds.

Structural and dynamic differences between supercoiled and linear DNA from proton NMR

Proton NMR experiments on an intact plasmid supercoiled DNA molecule are reported. Spectra of the hydrogen-bonded exchangeable imino protons and nonexchangeable aromatic protons of pIns36 (7,200 base pairs; Mr 5 x 10(6)) were examined at 240 and 360 MHz. In contrast to linear DNA of comparable size in which the signals from these protons are broadened almost beyond detection, the supercoiled DNA exhibits a remarkably well-resolved spectrum in the range 12-15 ppm, with linewidths characteristic of linear DNA molecules with molecular weight nearly two orders of magnitude smaller. These results imply an extraordinary degree of mobility in accord with our earlier discovery of unusually long 31P spin-spin relaxation times in the supercoiled molecule. Alterations in the chemical shift of the imino proton resonance positions in supercoiled DNA compared to linear DNA imply that the structure is modified in the A . T base pairs with at least two distinct structures apparent from the spectrum. However, little or no alteration is evident in the resonances due to the G . C base pairs.