Effects of osmotic manipulation of intracellular hydration of HeLa S-3 cells on their proton NMR relaxation times

Pellets of HeLa from suspension cultured cells in isotonic medium (300 mosmolar) were introduced into a Bruker CXP100 NMR spectrophotometer at 80 mHz within 5 min of the start of centrifugation. T1 and T2 times were measured within a total elapsed time of 20-25 min at 80 mHz and 37 degrees C, and averaged 1430 msec and 120 msec, respectively. Extrapolation to zero extracellular space gave a corrected T1 of 1370 msec. For cells collected after 10 min in hypotonic medium (down to 30 mosmolar) increased proton density correlated well with increased cell water content, but relaxation times did not rise in proportion to that predicted for the entry of "bulk" water (T1 of 4700 msec), except when swelling approached lysis point. Cells partially dehydrated by 10 min in hypertonic medium of up to 1500 mosmolar have also been analyzed, but once again the shortening of T1 was not proportional to the loss of "free" (bulk phase) water. At the upper limit of hypertonic treatment, lacunae or vacuoles of a watery nature separated within the cytomatrix, preventing maximum dehydration. The relationship of cell water to T1 is complex over the whole range of tonicity that HeLa S-3 cells tolerate. The data indicate, however, that hypotonically induced water probably has an average T1 time considerably lower than bulk phase water. In contrast, raising the total extracellular volume with medium had precisely the predicted effect on T1 time, further strengthening the case that water taken up by cell acquires a shorter T1 time. Cells adapting to hypotonic conditions oscillated in size and water content over 2-3 hr before returning to near their initial volume. Under these circumstances, T1 oscillated in the same way but with a reduced amplitude, consistent with the above findings.     

1H-NMR relaxation times and water compartmentalization in experimental tumor models

The present studies were conducted with RIF-1, M5076 and Panc02 subcutaneous tumor models to assess the relationship between tissue-free water compartmentalization and observed tissue T1 and T2 changes at 10 MHz. Observed T1 was shown to correlate directly with total extracellular water and interstitial water volumes. T1 and T2 were also inversely related to intracellular water volumes. T1 and T2 decreases after dexamethasone treatment were, however, most closely correlated with changes in tumor extracellular water and not changes in cell or total water volumes. Studies to assess Gd-DTPA-dimeg dose dependent T1 and T2 modification in model serum protein solutions indicated that although the Gd concentration that reduced T2 by 50% was about 2.5 fold greater than that required to reduce T1 equally, the of the concentration dependent T1 and T2 modifications were similar. In studies with tumor models, the injected dose of Gd-DTPA-dimeg that reduced T1 by 50% was inversely correlated with tumor extracellular water volumes. The slopes for dose dependent T1 modification in all tumors were similar and similar to that observed for model protein solutions. Gd-DTPA-dimeg had a different effect on observed T2 values for the 3 tumor models. Exponential slopes were about twice that observed for T2 modification of serum protein solutions, and Gd-DTPA-dimeg doses that reduced observed tumor T2 ranged from 9 to 50 times that necessary to similarly reduce T1. The results from these studies indicate that the observed T1, for these tumors, was dominated by relaxation of water protons in interstitial water but that the observed T2 was most strongly influenced by proton relaxation in water compartments that were unavailable to the Gd labeled probe.     

Regional variation in rat brain proton relaxation times and water content

Relaxation times (T1 and T2) and water content are measured in frontal cortex, amygdaloid cortex, hippocampus, mid-brain and cerebellum of rat brain. Differences are found in relaxation times, between areas containing a mixture of grey and white matter, and grey matter only. Differences were also found between certain grey matter areas. Relaxation times correlated with water content.     

The effect of dexamethasone on tissue water distribution and proton relaxation in Panc02 tumors

The present experiments were conducted to determine the effects of dexamethasone mediated changes in tumor water distribution on proton relaxation times (T1, T2) in a murine pancreatic adenocarcinoma (Panc02). Spin lattice (T1) and spin-spin (T2) relaxation times were determined by ex vivo methods (10MHz) and by in vivo imaging techniques (6.25 MHz) at various intervals after single or multiple dexamethasone treatments. In complementary studies, dexamethasone mediated changes in tumor capillary permeability, tumor water distribution, relative tumor blood flow and tumor cell proliferation were also determined.

Proton spin lattice (T1) and spin-spin (T2 relaxation times for Panc02 tumors shortened within two hours of a single dexamethasone treatment. The time course and magnitude of this response was dexamethasone dose dependent. The time dependent changes in T1 and T2 after dexamethasone were similar at 10 MHz (ex vivo) and 6.25 MHz (in vivo imaging). Although dexamethasone produced little or no change in total tumor water content and tumor cell proliferation, transient changes in the physiologic distribution of tumor water were clearly demonstrated.

The data supports the idea that dexamethasone induced changes in the distribution of tumor water were mediated by changes in capillary permeability and tumor blood flow. These physiologic responses produced serial changes in tumor extracellular extravascular water content that were consistent with the observed changes in tumor T1 and T2. The results from these experiments might imply that therapy associated changes in tumor proton relaxation times may not only reflect changes in tissue water content, but may also reflect physiologic responses which alter the distribution of tissue water and solute.     

Fat/water quantitation and differential relaxation time measurement using chemical shift imaging technique

The use of chemical shift imaging for fat and water quantitation and differential measurement of relaxation times for the fat and water component is demonstrated using a hybrid technique. The efficacy of the imaging technique for fat and water quantitation has been tested by comparing the results of imaging to the results of volumetric measurements in phantoms with oil and water homogeneously mixed, fat extraction in ground meat of different grades, and biopsy in preliminary clinical studies. Good correlation is found between the fat and water content measured by imaging and that measured by other means except for the inability to differentiate unsaturated fat protons from water protons. Longitudinal (T1) and transverse (T2) relaxation times for water and fat are also shown to be measurable independently when fat and water signal are suppressed accordingly. The independently measured relaxation times correspond closely to those of the pure samples except that unsaturated protons give decreased water relaxation estimates.     

Proton MR properties of lyophilized urine samples from normal and stone former individuals

Proton MR measurements were performed in lyophilized urine samples collected from 5 normals (N) and 5 idiopathic hypercalciuric recurrent stone formers (SF). T1 and T2 relaxation times were measured with a Bruker PC Multispec at 20 MHz and 37 degrees C in the lyophilized samples and in samples gradually rehydrated. Significantly (p less than 0.01) prolonged T1 and T2 relaxation times were measured after addition of water to the lyophilized samples. The relaxation time prolongation patterns were significantly different (p less than 0.01) for the two groups; the rehydration curves of the lyophilized urine samples from the SF group had relatively shorter lag than that of N group. In calculations of water compartmentalization for similar water content, significant (p less than 0.01) differences in the fraction of bound water (FB) were found between the two groups. These results may reflect differences in the macromolecular properties, contents, in the amount of water binding sites and/or in the water multilayer thickness between the two groups. These differences, expressed as changes of the relaxation times values may provide new diagnostic possibilities of different renal pathologies.     

Proton MR study of different types of experimental acute renal failure in rats

Kidney cortical and medullary spin-lattice (T1) and spin-spin (T2) relaxation times were measured in several types of experimental acute renal failure in rats with a Bruker PC "Multispec." Gentamicin ARF was obtained after one i.p. injection of 100mg Gentamicin/kg BW/day for 8 days. Glycerol ARF: 24 hours after one i.m. injection of 10 ml 50% Glycerol/kg BW. Obstruction ARF: 3 days after complete ureteral ligation. Renal tissue total water content, hydration fraction, fraction bound, blood urea and creatinine were measured at the end of the experiments. Shortened T1 and prolonged T2 were found in both cortex and medulla in the Glycerol ARF group. Gentamicin renal toxicity and the non-functioning kidney with ureteral obstruction are characterized by significant prolongation of T1 and T2 in cortex, while the medullary T1 and T2 were prolonged only in obstruction ARF. The highest T1 and T2 were found in the obstructed non-functioning kidney. The total water content decreased in the Glycerol ARF, increased in the obstruction and remain unchanged in Gentamicin ARF. The hydration fraction and the fraction bound changed significantly in the opposite direction with the total water content. Different profiles of renal cortical and medullary magnetic resonance properties found in several models of experimental ARF in rats indicate that MR properties may provide etiopathogenetic diagnostic possibilities.     

Effect of tissue fat and water content on nuclear magnetic resonance relaxation times of cardiac and skeletal muscle

Understanding tissue determinants that affect the nuclear magnetic resonance (NMR) properties of myocardium would improve noninvasive characterization of myocardial tissue. To determine if NMR relaxation times would reflect changes in tissue fat content, two experimental models were investigated. First, an idealized model using mixtures of beef skeletal muscle and beef fat was studied to investigate the effects of a wide range of tissue fat content. Second, myocardium with varying fat content from hogs raised to have varying degrees of ponderosity was analyzed. Tissue fat and water contents and spin-lattice (T1) and spin-spin (T2) relaxation times at 20 MHz were measured. The skeletal muscle/fat mixtures ranged in fat content from 35% to 95% with water content variations from 50% to 75%. Water content decreased as fat content increased. A significant inverse linear relationship was found between T1 and sample fat content (r = -0.997). Spin-spin relaxation times showed a significant positive curvilinear relationship with fat content (r2 = 0.96). In the animal experiments, 18 hogs were studied with samples obtained from both right and left ventricular (LV) free walls, with care taken to avoid epicardial fat. Myocardial fat content ranged from 3% to 25%. A significant correlation was found between LV fat content and corrected LV mass (r = 0.62), which suggested that the increase in LV mass could be explained, at least in part, by changes in myocardial fat content. Similar to the muscle/fat mixture model, a significant positive curvilinear relationship was found between myocardial T2 and tissue fat content (r2 = 0.67) for all the myocardial samples.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of hyperosmotic mannitol on magnetic resonance relaxation parameters in reperfused canine myocardial infarction

To determine how administration of a hyperosmotic agent alters regional nuclear magnetic resonance (NMR) relaxation parameters and imaging characteristics in ischemic-reperfused myocardium, 7 dogs were infused with mannitol for 15 minutes before and after the release of a 3 hour left anterior descending coronary artery (LAD) occlusion. Nine control animals received normal saline during the 3 hour occlusion and 1 hour reperfusion periods. Normal posterior left ventricular (LV) wall and the ischemic anterior LV wall (risk area) myocardium was sampled for calculation of segmental microsphere myocardial blood flow, % tissue water content, NMR relaxation times (T1, T2) and myocyte ultrastructure using electron microscopy. Mean infarct T1 values were 14% greater than normal segments in saline-treated controls, but only 5% greater after mannitol. The difference in tissue water content between infarcted and normal segments was 4% in saline-treated (83 vs. 79%) compared to 2% in mannitol-treated dogs (79 vs. 77%). T1, T2 and % water content of control infarct segments were greater than treated infarcts (p less than 0.01). T1 and T2 rose as occlusion flow fell below 0.5 ml/min/g in control hearts but did not rise until flows were reduced to 0.1 ml/min/g in mannitol-treated hearts. Areas of increased signal in T1 and T2 NMR images correlated well with histochemical infarct volume (r = 0.98, SEE = 1.1 cc) in mannitol-treated dogs, but infarct borders were qualitatively less well-defined than in controls. We concluded that mannitol (1) diminishes tissue edema and reduces NMR relaxation parameters (T1, T2) in infarcted myocardium; and (2) attenuates the rise in T1 and T2 and ultrastructural myocyte injury in ischemic-reperfused myocardium.     

Recurrent hepatocellular carcinoma versus radiation-induced hepatic injury: differential diagnosis with MR imaging

The objective of this study was to assess the value of MR imaging in the differentiation between a recurrent hepatocellular carcinoma (HCC) and a radiation-induced hepatic injury. Nine male patients with suspected recurrence after radiotherapy for HCC underwent T(2)-, T(1)-weighted imaging and Gd-DTPA enhanced dynamic studies. T(2) relaxation times, signal intensity ratios in T(1)-weighted images (WI) and the relative enhancement of the dynamic study were calculated. Recurrent tumors and the irradiated area showed similar image characteristics: hypointense in T(1)-WI and hyperintense in T(2)-WI. T(2) values and signal intensity ratios in the T(1)-WI were not significantly different. In the gadolinium-enhanced dynamic study, a recurrent HCC showed early enhancement, followed by a rapid washout. However, the irradiated liver parenchyma showed hyperintensity from an early phase, and contrast enhancement tended to be more prominent and prolonged at the end of the dynamic studies. The characteristic findings of the dynamic MR study enable us to distinguish between a recurrent HCC and a radiation-induced hepatic injury.     

Measurement of in vivo multi-component T2 relaxation times for brain tissue using multi-slice T2 prep at 1.5 and 3 T

The objective of this study was to implement a clinically relevant multi-slice multi-echo imaging sequence in order to quantify multi-component T2 relaxation times for normal volunteers at both 1.5 and 3 T. Multi-echo data were fitted using a nonnegative least square algorithm. Twelve echo data with nonlinear echo sampling were acquired using a receive-only eight-channel phased array coil and volume head coil for phantoms and normal volunteers, and compared to 32-echo data with linear echo sampling. It was observed that the performance of the 180 degrees refocusing trains was more spatially uniform for the receive-only eight-channel phased array coil than for the head coil, particularly at 3 T. The phantom study showed that the estimated T2 relaxation times were accurate and reproducible for both single- and multi-slice acquisition from a commercial phantom with known T2 relaxation times. Short T2 components (T2 <50 ms) were mainly observed within the white matter for normal volunteers, and the fraction of short T2 water components (i.e., myelin water) was 7-12% of total water. It was observed that the calculated myelin water fraction map from the nonlinearly sampled 12-echo data was comparable with that from the linearly sampled 32-echo data. Quantification of T2 relaxation times from multi-slice images was accomplished with a clinically acceptable scan times (16 min) for normal volunteers by using a nonselective T2 prep imaging sequence. The use of the eight-channel head coil involved more accurate quantification of T2 relaxation times particularly when the number of echoes was limited.     

In vitro 4 MHz NMR proton relaxation times and in vitro mechanical behavior at low extension of human common carotid arterial wall

We investigated the influence of the biomechanical behavior of human common carotid arterial wall on the NMR proton relaxation times using a Bruker Minispec at 4 MHz. The study was limited to low extension in simple longitudinal elongation of the carotid wall (the maximum loading stretch ratio being 40%). Twenty-five carotid samples divided into 2 longitudinal strips were tested. The first strip was used to determine the nondimensional elastic parameter alpha according to the mechanical model of Fung. The second strip was used to measure the proton relaxation times. T1 value was 316.8 ms +/- 27.6 and T2 value was 59.9 ms +/- 6.8. A significant linear correlation was found between T1 and Ln alpha (p = 0.02). T1 and T2 were not correlated to the age but linearly correlated to the tissue water content (p less than 0.0001), however the age and alpha were not correlated to the tissue water content. These results may reflect the differences in the amount of water binding sites of the elastin which is involved in the elasticity of the carotid wall at low extension.     

Manganese-enhanced magnetic resonance microscopy of mineralization

Paramagnetic manganese (II) can be employed as a calcium surrogate to sensitize magnetic resonance microscopy (MRM) to the processing of calcium during bone formation. At high doses, osteoblasts can take up sufficient quantities of manganese, resulting in marked changes in water proton T(1), T(2) and magnetization transfer ratio values compared to those for untreated cells. Accordingly, inductively coupled plasma mass spectrometry (ICP-MS) results confirm that the manganese content of treated cell pellets was 10-fold higher than that for untreated cell pellets. To establish that manganese is processed like calcium and deposited as bone, calvaria from the skull of embryonic chicks were grown in culture medium supplemented with 1 mM MnCl(2) and 3 mM CaCl(2). A banding pattern of high and low T(2) values, consistent with mineral deposits with high and low levels of manganese, was observed radiating from the calvarial ridge. The results of ICP-MS studies confirm that manganese-treated calvaria take up increasing amounts of manganese with time in culture. Finally, elemental mapping studies with electron probe microanalysis confirmed local variations in the manganese content of bone newly deposited on the calvarial surface. This is the first reported use of manganese-enhanced MRM to study the process whereby calcium is taken up by osteoblasts cells and deposited as bone.     

The systemic effect of cancers on human sera proton NMR relaxation times

In animal models of cancer, an elevation of T1 and T2 in uninvolved tissues and in the blood of tumor bearing animals has been termed "the systemic effect." This study reports T1 values in sera of human patients from Genoa, Italy, with several types of cancer and non-cancerous diseases. T1 values were significantly elevated over normal controls (1628 +/- 113 ms) in colorectal cancers (1725 +/- 149 ms) and stomach cancers (1817 +/- 219 ms). However a systemic effect was not demonstrated in acute myeloid leukemia, chronic lymphatic leukemia, chronic myeloid leukemia, or plasma cell myeloma, or in pancreatic and lung cancers. Noncancerous states of cirrhosis, chronic hepatitis, and monoclonal gammapathies did not show a T1 elevation. In general, T1 values of sera correlated with protein content of the sera; however, a disproportionate contribution of gamma-globulin protein on water proton relaxation times was observed in several cases.     

Significance of proton relaxation time measurement in brain edema, cerebral infarction and brain tumors

We examined the proton relaxation times in vitro in various neurological diseases using experimental and clinical materials, and consequently obtained significant results for making a fundamental analysis of magnetic resonance imaging (MRI) as followings. 1) In the brain edema and cerebral infarction, T1 prolonged and T2 separated into two components, one fast and one slow. Prolongation of T1 referred to the volume of increased water in tissue. The slow component of T2 reflects both the volume and the content of increased edema fluid in tissue. 2) In the edematous brain tissue with the damaged Blood-Brain-Barrier (BBB), the slow component of T2 became shorter after the injection of Mn-EDTA. Paramagnetic ion could be used as an indicator to demonstrate the destruction of BBB in the brain. 3) After the i.v. injection of glycerol, the slow component of T2 became shorter in the edematous brain with the concomitant decrease of water content. The effects of therapeutic drug could be evaluated by the measurement of proton relaxation times. 4) Almost all tumor tissue showed a longer T1 and T2 values than the normal rat brain, and many of them showed two components in T2. It was difficult to determine the histology of tumor tissue by the relaxation time alone because of an overlap of T1 and T2 values occurred among various types of brain tumors. 5) In vivo T1 values of various brain tumor were calculated from the data of MRIs by zero-crossing method, and they were compared with the in vitro T1 values which were measured immediately after the surgical operation. Though the absolute value did not coincide with each other due to differences in magnetic field strength, the tendency of the changes was the same among all kinds of tumors. It is concluded that the fundamental analysis of proton relaxation times is essentially important not only for the study of pathophysiology in many diseases but also for the interpretation of clinical MRI.     

Evaluation of water content by spatially resolved transverse relaxation times of human articular cartilage

Non-invasive assessment of cartilage properties, specifically water content, could prove helpful in the diagnosis of early degenerative joint diseases. Transverse relaxation times T(2) of human articular cartilage (34 cartilage slices of three donors) were measured on a pixel-by-pixel basis in a clinical whole body MR system in vitro. In vivo feasibility to measure quantitative T(2) maps was shown for human patellar cartilage. The relaxation times of cartilage with collagen in the radial zone oriented perpendicular to the magnetic field increased from approximately 10 ms near the bone to approximately 60 ms near the articular surface. Cartilage water content of the tibial plateau and femoral condyles could be determined from the correlation with T(2) (R(2) = 0.71) with an error of approximately 2 wt.%. In vivo, directional variation would need to be considered. If confirmed in vivo, T(2) measurements could potentially serve as a non-invasive tool for the evaluation of the status and distribution of water content in articular cartilage.     

Constrained modeling for spectroscopic measurement of bi-exponential spin-lattice relaxation of water in vivo

The (1)H NMR water signal from spectroscopic voxels localized in gray matter contains contributions from tissue and cerebral spinal fluid (CSF). A typically weak CSF signal at short echo times makes separating the tissue and CSF spin-lattice relaxation times (T(1)) difficult, often yielding poor precision in a bi-exponential relaxation model. Simulations show that reducing the variables in the T(1) model by using known signal intensity values significantly improves the precision of the T(1) measurement. The method was validated on studies on eight healthy subjects (four males and four females, mean age 21 +/- 2 years) through a total of twenty-four spectroscopic relaxation studies. Each study included both T(1) and spin-spin relaxation (T(2)) experiments. All volumes were localized along the Sylvian fissure using a stimulated echo localization technique with a mixing time of 10 ms. The T(2) experiment consisted of 16 stimulated echo acquisitions ranging from a minimum echo time (TE) of 20 ms to a maximum of 1000 ms, with a repetition time of 12 s. All T(1) experiments consisted of 16 stimulated echo acquisition, using a homospoil saturation recovery technique with a minimum recovery time of 50 ms and a maximum 12 s. The results of the T(2) measurements provided the signal intensity values used in the bi-exponential T(1) model. The mean T(1) values when the signal intensities were constrained by the T(2) results were 1055.4 ms +/- 7.4% for tissue and 5393.5 ms +/- 59% for CSF. When the signal intensities remained free variables in the model, the mean T(1) values were 1085 ms +/- 19.4% and 5038.8 ms +/- 113.0% for tissue and CSF, respectively. The resulting improvement in precision allows the water tissue T(1) value to be included in the spectroscopic characterization of brain tissue.     

Prolonged bone marrow T1-relaxation in patients with polycythemia vera

In vitro as well as in vivo studies have shown prolonged T1 relaxation times in patients with acute leukemia. The mechanism behind this finding is not known. In order to evaluate if this was specific for leukemia we examined eight patients with polycythemia vera, representing a condition with a rather benign bone marrow neoplasia. In this group of patients we found prolonged T1 relaxation times but normal T2 relaxation times. This may indicate that the prolonged T1 relaxation time seen in leukemic bone marrow is not due to the malignant cell per se.     

Measurement of proliferation activity in human melanoma xenografts by magnetic resonance imaging

Tumor proliferation may be predictive for malignant progression and response to fractionated therapy of cancer. The purpose of the present work was to investigate whether the proliferation activity of solid tumors can be assessed in vivo from the proton relaxation times, T1 and T2. Tumors of four amelanotic human melanoma xenograft lines were studied. Three parameters were used to represent tumor proliferation activity; the volume doubling time, Tvol, the potential doubling time, Tpot, and the fraction of cells in S-phase. Tvol was determined from volumetric growth data. Tpot and S-phase fraction were determined by flow cytometric analysis of tumor cells after bromodeoxyuridine (BrdU) incorporation in vivo. T1 and T2 were measured by 1H-MRI in vivo, using spin-echo pulse sequences. The proliferation parameters and relaxation times differed considerably among the tumor lines. Significant correlations were found between the proliferation parameters and the relaxation times, regardless of whether Tvol, Tpot, or S-phase fraction was considered. Tumors with short Tvol and Tpot and high S-phase fraction had long T1 and T2 compared to tumors with long Tvol and Tpot and low S-phase fraction. The elongated T1 and T2 of fast growing tumors were probably due to increased interstitial and/or intravascular water content. The present results suggest that in vivo spin-echo 1H-MRI can be used to discriminate between tumors of high and low proliferation activity.     

Characterization of water mobility and distribution in low- and intermediate-moisture food systems

The mechanism of water uptake in low moisture cereals and cookies has been studied by NMR relaxometry and solid imaging technology implemented on a low-resolution benchtop NMR spectrometer. A comparison between classical MRI and SPRITE imaging are also presented to highlight the benefits of each technology. The spin lattice (T(1)) and spin spin (T(2)) relaxation times, the 1D and 2D SPRITE imaging, were determined on Smacks, corn flakes, chocolate chips cookies, soft caramel candies with a chocolate crème filler, and corn starch/water systems. The Smacks and corn flakes were studied based on the soaking time in milk, and the results showed that T(1) and T(2) decreased in the first 20 sec of soaking and then increased with the soaking time. For Smacks stored at different relative humidity, T(1) decreased during the first day of storage and then was relatively constant over storage time indicating that the system reached an equilibrium. 1D SPRITE profiles indicated an increase in signal intensity over storage time for cookies in 58% RH. However, the moisture uptake was insignificant indicating that the water mobility (and not the amount of water) changed due to various chemical interactions in the system (hydrogen bonding, starch retrogradation, glassy/rubbery equilibrium). The T(1) and T(2) of corn starch/water systems decreased as the concentration in starch increased and temperature increased from 30 degrees C to 60 degrees C. However, for temperatures higher than 60 degrees C, the relaxation times increased showing more mobility and flexibility of the polymer chains during gelatinization.