In vivo fluorine-19 magnetic resonance spectroscopy of cerebral halothane in postoperative patients: Preliminary results

This study reports the use of ¹⁹F MRS to study halothane in the brain of eight patients recovering from halothane anesthesia of short duration. Resonances attributable to halothane were observed up to 90 min after withdrawal of the anesthetic agent. The signal-to-noise ratio for an unlocalized spectrum acquired using a 6 cm surface coil was typically 20 with data collection times of 2 min. In seven patients a single resonance was seen with a mean (±SD) chemical shift of +43.3 (±1.8) ppm, referenced to NaF at 0 ppm. This resonance exhibited a T₁ value of between 0.5 and 1 s, and a T₂* (estimated from the linewidth of the resonance) between 3.5 and 10 ms. In one patient two resonances were observed with chemical shifts of +38 and +41 ppm. Because we cannot exclude the possibility that this was due to field inhomogeneity, the significance of the last finding is uncertain. However, phantom studies show that the chemical shift of halothane in different environments (such as water, olive oil, methanol, and lecithin) can vary to an extent that accounts for the two resonances seen in our patient. These results demonstrate the feasibility of in vivo ¹⁹F MRS studies of fluorinated volatile agents in humans. The potential for clinical ¹⁹F MRS of fluorinated anesthetics is discussed.     

Measurement of spin-lattice relaxation times and kinetic rate constants in rat muscle using progressive partial saturation and steady-state saturation transfer

³¹P spin-lattice relaxation times (T₁) of metabolites in rat calf muscle at 1.9 Tesla and the forward rate through the creatine kinase (CK) reaction have been measured using a new method based on modeling progressive saturation explicitly incorporating the effect of chemical exchange. In a separate series of experiments, we compared our method with inversion recovery both in vitro and in vivo, finding agreement between the techniques. We found that the T₁ values of phosphocreatine (PCr) (6.6 ± 0.3 s), γ-ATP (2.6 ± 0.6 s), α-ATP (2.4 ± 0.4 s) and β-ATP (2.2 ± 0.2 s) are unchanged by stimulation of sufficient intensity to induce a 32% drop in PCr level. The errors in T₁ values which arise when chemical exchange is neglected are calculated. These are found to be on the order of 20% for PCr and 30–50% for γ-ATP under typical conditions. Use of longer repetition times results in larger errors in measured values of T₁. This source of error can be effectively eliminated by use of sufficiently short repetition times. We found that the rate constant of the forward CK reaction was increased 60% by stimulation, from 0.20 ± 0.03 s⁻¹ to 0.32 ± 0.03 s⁻¹, but that the phosphorus flux did not change.     

Studies of Gd-DTPA relaxivity and proton exchange rates in tissue

The image intensity in many contrast agent perfusion studies is designed to be a function of bulk tissue T₁, which is, in turn, a function of the compartmental (vascular, interstitial, and cellular) T₁s, and the rate of proton exchange between the compartments. The goal of this study was to characterize the compartmental tissue Gd-DTPA relaxivities and to determine the proton exchange rate between the compartments. Expressing [Gd-DTPA] as mmol/liter tissue water, the relaxivities at 8.45 T and room temperature were: saline, 3.87 ± 0.06 (mM. s)^?1 (mean ± SE; n = 29); plasma, 3.98 ± 0.05 (mM·s)^?1 (n = 6); and control cartilage (primarily an interstitium), 4.08 f 0.08 (mM·s)^?1 (n = 17), none of which are significantly different. The relexivity of cartilage did not change with compression, trypsinization, or equilibration in plasma, suggesting relaxivity is not influenced by interstitial solid matrix density, charge, or the presence of plasma proteins. T₁ relaxation studies on isolated perfused hearts demonstrated that the cellular-interstitial water exchange rate is between 8 and 27 Hz, while the interstitial-vascular water exchange rate is less than 7 Hz. Thus, for Gd-DTPA concentrations, which would be used clinicallly, the T₁ relaxation rate behavior of intact hearts can be modeled as being in the fast exchange regime for cellular-interstitial exchange but slow exchange for interstitial-vascular exchange. A measured relaxivity of 3.82 ± 0.05 (mM·s)_?1 (n = 8) for whole blood (red blood cells and plasma) and 4.16 ± 0.02 (mM·s)^?1 (n = 3) for frog heart tissue (cells and interstitium) (with T₁ and Gd-DTPA concentration defined from the total tissue water volume) supports the conclusion of fast cellular-extracellular exchange. Knowledge of the Gd-DTPA relaxivity and maintaining Gd-DTPA concentration in the range so as to maintain fast cellular-interstitial exchange allows for calculation of bulk Gd-DTPA concentration from bulk tissue T₁ within a calculable error due to slow vascular exchange.     

Magnetic resonance properties of ex vivo breast tissue at 1.5 T

The magnetic resonance absorption spectrum, T₁ and T₂ relaxation time distributions, and magnetization transfer properties of ex vivo breast tissue have been characterized at 1.5 T and 37°C. The fraction of fibroglandular tissue within individual tissue samples (n = 31) was inferred from the tissue volumetric water content obtained by integration of resolvable broad-line fat and water resonances. The spectroscopically estimated water content was strongly correlated with that extracted enzymatically (Pearson correlation coefficient 0.98, P « 0.01), which enabled the assignment of principal relaxation components for fibroglandular tissue (T₂ = 0.04 ± 0.01, T₁ = 1.33 ± 0.24 s), and for adipose tissue (T₂ = 0.13 ± 0.01, T₁ = 0.23 ± 0.01 s, and T₂ = 0.38 ± 0.03, T₁ = 0.62 ± 0.16 s). The relaxation components for fibroglandular tissue exhibited strong magnetization transfer, whereas those for adipose tissue showed little magnetization transfer effect. These results ultimately have applicability to the optimization of clinical magnetic resonance imaging and research investigations of the breast.     

Assessment of 31P relaxation times in the human calf muscle: A comparison between 3 T and 7 T in vivo

Phosphorus (³¹P) T₁ and T₂ relaxation times in the resting human calf muscle were assessed by interleaved, surface coil localized inversion recovery and frequency‐selective spin‐echo at 3 and 7 T. The obtained T₁ (mean ± SD) decreased significantly (P < 0.05) from 3 to 7 T for phosphomonoesters (PME) (8.1 ± 1.7 s to 3.1 ± 0.9 s), phosphodiesters (PDE) (8.6 ± 1.2 s to 6.0 ± 1.1 s), phosphocreatine (PCr) (6.7 ± 0.4 s to 4.0 ± 0.2 s), γ‐NTP (nucleotide triphosphate) (5.5 ± 0.4 s to 3.3 ± 0.2 s), α‐NTP (3.4 ± 0.3 s to 1.8 ± 0.1 s), and β‐NTP (3.9 ± 0.4 s to 1.8 ± 0.1 s), but not for inorganic phosphate (Pi) (6.9 ± 0.6 s to 6.3 ± 1.0 s). The decrease in T₂ was significant for Pi (153 ± 9 ms to 109 ± 17 ms), PDE (414 ± 128 ms to 314 ± 35 ms), PCr (354 ± 16 ms to 217 ± 14 ms), and γ‐NTP (61.9 ± 8.6 ms to 29.0 ± 3.3 ms). This decrease in T₁ with increasing field strength of up to 62% can be explained by the increasing influence of chemical shift anisotropy on relaxation mechanisms and may allow shorter measurements at higher field strengths or up to 62% additional signal‐to‐noise ratio (SNR) per unit time. The fully relaxed SNR increased by +96%, while the linewidth increased from 6.5 ± 1.2 Hz to 11.2 ± 1.9 Hz or +72%. At 7 T ³¹P‐MRS in the human calf muscle offers more than twice as much SNR per unit time in reduced measurement time compared to 3 T. This will facilitate in vivo ³¹P‐MRS of the human muscle at 7 T. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Scalar coupling and zero-quantum coherence relaxation in STEAM: Implications for spectral editing of lactate

Accurate values were obtained for the lactate zero-quantum coherence frequency, ω_ZQ = ω_i-ω_s = CH₃–CH chemical shift difference, and scalar coupling constant, J, by using the methyl signal's amplitude modulation during the TM period of a STEAM sequence, 90°–TE/2–90°–TM–90°–TE/2- Acquire. Although most previous work has used J= 7.35 Hz, or 1/J= 136 ms, the actual value is J= 6.93 ± 0.05 Hz or 1/J = 144.3 ± 1 ms. In addition, the CH₃–CH chemical shift difference = 2.7956 ± 0.0005 ppm, and the relaxation time for zero-quantum coherence, T_ZQ, was much shorter than either T₂ or T₁ for the methyl resonance. A small component of the signal with TE= 144 ms, which was not modulated at the zero-quantum coherence frequency or by scalar coupling, was assigned to longitudinal two-spin order magnetization (I_zS_z) created by imperfect radio frequency pulse profiles. This information will allow improved editing of the lactate signal and more accurate quantitation of lactate concentrations.     

A new ytterbium chelate as contrast agent in chemical shift imaging and temperature sensitive probe for MR spectroscopy

A paramagnetic Yb(lll) complex that is the prototype of a novel class of probes for MRI and MRS has been developed. The complex displays highly shifted ¹H resonances that are characterized by short relaxation times and, as such, may prove to be a valuable alternative in applications that currently require fluorine-containing probes. Selective excitation of the para-magnetically shifted resonances allows the spatial distribution of the complex to be mapped. This communication reports the images that were obtained by selectively exciting the most intense methyl group (?14.2 ppm at 27°C) for complex concentrations ranging from 0.003?0.1 M. Spectroscopically, the complex may be used as a temperature probe since the proton chemical shifts exhibit a strong temperature dependence. In human serum the chemical shift difference of a selected pair of proton resonances was observed to follow a gradient of ?0.42 ± 0.01 ppm/°C. Furthermore, since the chemical shift of the methyl resonance displays a temperature coefficient of ?0.04 ± 0.01 ppm/°C, it should be possible to use the image phase for thermal mapping.     

Changes of relaxation times (T1, T2) and apparent diffusion coefficient after permanent middle cerebral artery occlusion in the rat: temporal evolution,regional extent,and comparison with histology

The quantitative NMR parameters T₁, T₂, p, and apparent diffusion coefficient (ADC) were determined during the 7 h after middle cerebral artery occlusion in rats. In the normal caudate-putamen (CP), 869 ± 145 ms and 72 ± 2ms for T₁ and for T₂, respectively, were found; the corresponding values for cortex were 928 ± 117 ms and 73 ± 2 ms. The ADC showed significant dependence on gradient direction: diffusion along x resulted in 534 ± 53 μm²/s (CP) and 554 ± 62 μm²/s (cortex), and along y in 697 ± 58 μm²/s (CP) and 675 ± 53 μm²/s (cortex). In the ischemic territory, a continuous increase over time of both relaxation times was observed in the CP, leading to an increase of 29 ± 20% (T₁) and 51 ± 41% (T₂ above control level. ADC dropped to 63 ± 15% of control in the CP and to 74 ± 4% of control in the temporal cortex. No significant change was noted in proton density during the observation period. Strongest ADC reduction was in the center of the ischemic territory (≤ 60% of control) surrounded by a region of lesser reduction (≤ 80% of control). During the early part of the study, the area of reduced ADC was larger than that of elevated relaxation times. Toward the end of the experiment, the area of increased relaxation times approached that of decreased ADC at ≤ 80% of control. Good agreement of histological presentation of infarct with the total area of decreased ADC (≤ 80%) was demonstrated.     

Quantitative nmr microscopy of multicellular tumor spheroids and confrontation cultures

In cancer research, tumor spheroids are a well established system to study tumor metabolism resembling the situation in vivo more closely cell monolayers. Spherical aggregates of malignant melanoma cells (MV3) and their invasion into rat brain aggregates have been investigated by quantitative NMR microscopy. Relaxation times (T₁, T₂) and diffusion parameter images were acquired with an in-plane resolution of 14 × 14 μm². The authors were able to demonstrate that the morphology of the spheroids can be visualized on these NMR maps. The contrast was mainly manifested in relaxation maps, where average relaxation times T₁ = 1.94 ± 0.17 s and T₂ = 42.8 ± 6.3 ms were obtained for proliferating cells, and T₁ = 2.49 ± 0.31 s and T₂ = 104.3 ± 29.4 ms for the necrobiotic center. The mean diffusion coefficients were 0.59 ± 0.12 μm²/ms and 0.85 ± 0.14 μm²/ms, respectively. The authors could follow the dynamic process of tumor cell invasion in the investigated co-culture system. Knowledge about tumor cell migration and tumor cell invasion is essential for the understanding of cancer and its therapy. Quantitative NMR microscopy can study this dynamic process noninvasively and therefore may help to assess the influence of therapy on the micromilieu of these spheroids.     

Detection of liver fibrosis with magnetic cross-relaxation

The utility of MRI using magnetization transfer (MT) enhanced pulse sequences to diagnose hepatic cirrhosis in a rat model was investigated. Hepatic T₁ was measured with and without MT off-resonance RF pulses in 17 treated and six control rats. The livers were evaluated histologically, and the hydroxyproline content quantitatively measured. We did not find a statistically significant linear correlation between the MR relaxation times and the degree of tissue injury. However, the MR measurements performed with MT were superior to those without differentiating the treated and control groups. Specifically, the T₁ times were 695 ±76 ms for the treated group, versus 748 ± 61 ms in the controls; P= 0.095. The T_1sat times were also lower in the treated group, with statistical significance: 367 ± 51 ms versus 421 ± 38 ms, P = 0.016. Finally, the change in the relaxation rates (the inverse of the relaxation times) with and without saturation were 1.31 ± 0.22 s^?1 (treated group) versus 1.05 ± 0.12 s^?1 (controls), which differed significantly, P= 0.001.     

Functional hepatocyte cation compartmentation demonstrated with 133Cs NMR.

This study utilized the large intrinsic chemical shift range of (133)Cs, a potassium congener, in an NMR study of intracellular cation distribution. It demonstrates two distinct intracellular environments in isolated perfused hepatocytes from cesium-fed rats, evident as compartments with different (133)Cs chemical shifts and containing different proportions of total detected cesium. The chemical shifts of the two intracellular compartments were 2.44 +/- 0.07 and 1.21 +/- 0.18 ppm, relative to the cesium signal from the perfusate. The observation of two distinct intracellular cesium signals suggests slow exchange on an NMR chemical shift time-scale (k exchange > 0.02 s). The area of the high-frequency component represented 62 +/- 10% (N = 12) of the total intracellular cesium signal. Manipulation of the intracellular environment using anoxia with aglycemia or digitonin produced changes in the distribution between the two intracellular compartments, showing their dynamic nature. Changes measured in association with metabolic manipulation suggest cytoplasm and mitochondria as the origin of the high and low-frequency intracellular peaks, respectively.     

Perfusion imaging with a freely diffusible hyperpolarized contrast agent

Contrast agents that can diffuse freely into or within tissue have numerous attractive features for perfusion imaging. Here we present preliminary data illustrating the suitability of hyperpolarized ¹³C labeled 2‐methylpropan‐2‐ol (also known as dimethylethanol, tertiary butyl alcohol and tert‐butanol) as a freely diffusible contrast agent for magnetic resonance perfusion imaging. Dynamic ¹³C images acquired in rat brain with a balanced steady‐state free precession sequence following administration of hyperpolarized 2‐methylpropan‐2‐ol show that this agent can be imaged with 2–4s temporal resolution, 2 mm slice thickness, and 700 μm in‐plane resolution while retaining adequate signal‐to‐noise ratio. ¹³C relaxation measurements on 2‐methylpropan‐2‐ol in blood at 9.4T yield T₁ = 46 ± 4s and T₂ = 0.55 ± 0.03s. In the rat brain at 4.7T, analysis of the temporal dynamics of the balanced steady‐state free precession image intensity in tissue and venous blood indicate that 2‐methylpropan‐2‐ol has a T₂ of roughly 2–4s and a T₁ of 43 ± 24s. In addition, the images indicate that 2‐methylpropan‐2‐ol is freely diffusible in brain and hence has a long residence time in tissue; this in turn makes it possible to image the agent continuously for tens of seconds. These characteristics show that 2‐methylpropan‐2‐ol is a promising agent for robust and quantitative perfusion imaging in the brain and body. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Chemical shift sodium imaging in a mouse model of thromboembolic stroke at 9.4 T

Purpose:

To estimate changes in the ²³Na density and in the ²³Na relaxation time T₂* in the anatomically small murine brain after stroke.

Materials and Methods:

Three‐dimensional acquisition weighted chemical shift imaging at a resolution of 0.6 × 0.6 × 1.2 mm³ was used for sodium imaging and relaxation parameter mapping. In vivo measurements of the mouse brain (n = 4) were performed 24 hours after stroke, induced by microinjection of purified murine thrombin into the right middle cerebral artery. The measurement time was 14 minutes in one mouse and 65 minutes in the other three. An exponential fit estimation of the free induction decay was calculated for each voxel enabling the reconstruction of locally resolved relaxation parameter maps.

Results:

The infarcted areas showed an increase in sodium density between 160% and 250%, while the T₂* relaxation time increased by 5%–72% compared to unaffected contralateral brain tissue.

Conclusion:

²³Na chemical shift imaging at a resolution of 0.6 × 0.6 × 1.2 mm³ enabled sodium imaging of the anatomical small mouse brain and the acquired data allowed calculating relaxation parameter maps and hence a more exact evaluation of sodium signal changes after stroke. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

In vivo differentiation of two vessel wall layers in lower extremity peripheral vein bypass grafts: Application of high‐resolution inner‐volume black blood 3D FSE

Lower extremity peripheral vein bypass grafts (LE‐PVBG) imaged with high‐resolution black blood three‐dimensional (3D) inner‐volume (IV) fast spin echo (FSE) MRI at 1.5 Tesla possess a two‐layer appearance in T1W images while only the inner layer appears visible in the corresponding T2W images. This study quantifies this difference in six patients imaged 6 months after implantation, and attributes the difference to the T₂ relaxation rates of vessel wall tissues measured ex vivo in two specimens with histologic correlation. The visual observation of two LE‐PVBG vessel wall components imaged in vivo is confirmed to be significant (P < 0.0001), with a mean vessel wall area difference of 6.8 ± 2.7 mm² between contrasts, and a ratio of T1W to T2W vessel wall area of 1.67 ± 0.28. The difference is attributed to a significantly (P < 0.0001) shorter T₂ relaxation in the adventitia (T₂ = 52.6 ± 3.5 ms) compared with the neointima/media (T₂ = 174.7 ± 12.1 ms). Notably, adventitial tissue exhibits biexponential T₂ signal decay (P < 0.0001 vs monoexponential). Our results suggest that high‐resolution black blood 3D IV‐FSE can be useful for studying the biology of bypass graft wall maturation and pathophysiology in vivo, by enabling independent visualization of the relative remodeling of the neointima/media and adventitia. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

A precise and fast temperature mapping using water proton chemical shift

A new temperature measurement procedure using phase mapping was developed that makes use of the temperature dependence of the water proton chemical shift. Highly accurate and fast measurements were obtained during phantom and in vivo experiments. In the pure water phantom experiments, an accuracy of more than ± 0.5°C was obtained within a few seconds/slice using a field echo pulse sequence (TR/TE = 115/13 ms, matrix = 128 × 128, number of slices = 5). The temperature dependence of the water proton chemical shift was found to be almost the same for different materials with a chemical composition similar to living tissues (water, glucide, protein). Using this method, the temperature change inside a cat's brain was obtained with an accuracy of more than ± 1°C and an in-plane resolution of 0.6 x 0.6 mm. The temperature measurement error was affected by several factors in the living system (B₀ shifts caused by position shifts of the sample, blood flow, etc.), the position shift effect being the most serious.     

Migration and biodegradation of free silicone from silicone gel-filled implants after long-term implantation

In vivo¹H NMR chemical shift imaging (CSI), ¹H NMR localized spectroscopy (STEAM) and multinuclear NMR spectroscopy ²⁹sl, ¹³C, ¹H) were used to characterize the aging process of silicone gel-filled implants in a rat model after long-term implantation. Although no significant changes could be observed in the implants or surrounding tissue by in vivo ¹H chemical shift imaging, in vivo ¹H localized spectroscopy of the livers from the longer term population revealed the presence of silicone. Ex vivo ²⁹Sl spectroscopy of the liver, spleen, and the capsule formed around the 9 and 12 month implants clearly demonstrated and confirmed for the first time that a significant amount of free silicone migrates from silicone gel-filled implants. Also, these results show that silicones are not metabolically inert, and their biodegradation in tissue and within the implant can be monitored after 9 and 12 months by changes in the ²⁹Sl chemical shifts seen in corresponding ex vivo spectra. The NMR findings are supported by those obtained by atomic absorption spectroscopy. Silicone aging changes not only the chemical composition of the gel, but also its proton T₂ relaxation times, which increase with long implantation times. The three dimensional structure of the gel disintegrates (i.e., polymer chain rupture), increasing the molecular mobility of the polymer and, consequently, its protons T₂ values. The relaxation data we obtained reflect this in vivo degradation, especially in the case of implant rupture. Additionally, small concentrations of fat in the silicone gel were found within the implants. The presence of these lipophilic substances also might increase the T₂ values (plasticizer effect). These findings may assist in evaluating the implant integrity and disease symptoms related to their presence in humans.     

NMR measurement of 39K detectability and relaxation constants in rat tissue

Differences in the NMR detectability of ³⁹K in various excised rat tissues (liver, brain, kidney, muscle, and testes) have been observed. The lowest NMR detectability occurs for liver (61 ± 3% of potassium as measured by flame photometry) and highest for erythrocytes (100 ± 7%). These differences in detectability correlate with differences in the measured ³⁹K NMR relaxation constants in the same tissues. ³⁹K detectabilities were also found to correlate inversely with the mitochondrial content of the tissues. Mitochondria prepared from liver showed greatly reduced ³⁹K NMR detectability when compared with the tissue from which it was derived, 31.6 ± 9% of potassium measured by flame photometry compared to 61 ± 3%. The detectability of potassium in mitochondria was too low to enable the measurement of relaxation constants. This study indicates that differences in tissue structure, particularly mitochondrial content are important in determining ³⁹K detectability and measured relaxation rates.     

Nonexponential T2* decay in white matter

Visualizing myelin in human brain may help the study of diseases such as multiple sclerosis. Previous studies based on T₁ and T₂ relaxation contrast have suggested the presence of a distinct water pool that may report directly on local myelin content. Recent work indicates that T₂* contrast may offer particular advantages over T₁ and T₂ contrast, especially at high field. However, the complex mechanism underlying T₂* relaxation may render interpretation difficult. To address this issue, T₂* relaxation behavior in human brain was studied at 3 and 7 T. Multiple gradient echoes covering most of the decay curve were analyzed for deviations from mono‐exponential behavior. The data confirm the previous finding of a distinct rapidly relaxing signal component (T₂* ～ 6 ms), tentatively attributed to myelin water. However, in extension to previous findings, this rapidly relaxing component displayed a substantial resonance frequency shift, reaching 36 Hz in the corpus callosum at 7 T. The component's fractional amplitude and frequency shift appeared to depend on both field strength and fiber orientation, consistent with a mechanism originating from magnetic susceptibility effects. The findings suggest that T₂* contrast at high field may be uniquely sensitive to tissue myelin content and that proper interpretation will require modeling of susceptibility‐induced resonance frequency shifts. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Changes in T2*-Weighted Images During Hyperoxia Differentiate Tumors from Normal Tissue

Experiments were performed to determine whether changes in T₂*-weighted MR images during and after hyperoxia differentiate tumors from normal tissue. Mammary adenocarcinomas implanted in the right hind limbs of rats were studied. Gradient echo images were obtained at 2 Tesla with an evolution time of 20 ms and a recycle time of 1 s. Breathing gas was either air or 100% O₂. Significant increases in image intensity were observed in tumor centers and rims during hyperoxia while much smaller changes were detected in the surrounding muscle. The relaxation rate (1/T₂*) in tumors decreased during hyperoxia by an average of 2.5 ± 1.0 s^?1, while in muscle the average change was an increase of 0.6 ± 2.1 s^?1. The largest decreases in relaxation rate were detected in non-necrotic tumor regions with relatively low density of blood vessels. Immediately following hyperoxia significant decreases in intensity were detected in tumors while much smaller decreases were detected in the surrounding muscle.     

NOE Enhancements and T1 Relaxation Times of Phosphorylated Metabolites in Human Calf Muscle at 1.5 Tesla

Nuclear Overhauser effect (NOE) enhancements and relaxation times of ³¹P metabolites in human calf were measured in 12 volunteers (4 men and 8 women) at 1.5 T using a dual tuned four-ring birdcage. The NOE enhancements of inorganic phosphate (P₁), phosphocreatine (PCr), γ-, α-, and β-nucleoside triphosphate (NTP) from 19 measurements were 0.51 ± 0.10, 0.64 ± 0.03, 0.53 ± 0.03, 0.56 ± 0.08, and 0.47 ± 0.05, respectively. The relaxation times were independent of proton irradiation and from 23 measurements were 3.49 ± 0.35, 4.97 ± 0.58, 4.07 ± 0.36, 2.90 ± 0.25, and 3.61 ± 0.25 s for P₁, PCr, γ-, α-, and β-NTP, respectively. No significant differences between gender and age were observed for either NOE enhancements or relaxation times. Also, among nine volunteers, we observed no significant differences in T₁ between the coupled and decoupled cases.