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The purpose of the present study is to determine whether muscle functional MRI (mfMRI) can be used to obtain three-dimensional (3-D) images useful for evaluating muscle activity, and if so, to measure the distribution of muscle activity within a medial gastrocnemius (MG) muscle. Seven men performed 5 sets of 10 repetitions of a calf-raise exercise with additional 15% of body-weight load. Magnetic resonance images were obtained before and immediately after the exercise. To threshold images, only those pixels showing transverse relaxation time (T2) greater than the mean+1 S.D. of the entire regions of interest (ROIs) in the preexercise image and T2 lower than the mean+1 S.D. of the entire ROIs in the postexercise image were identified. The survived pixels showing T2 are defined as active muscle. Those thresholded images were 3-D reconstructed, and this was used to determine area of active muscle along transverse, longitudinal and vertical axes. At the exercise level used in the present study, the percentage volume of activated muscle in the MG was 62.8+/-4.5%. There was a significant correlation between percentage volume of activated muscle and integrated electromyography (r=.78, P.05). Percentage areas of activated muscle were significantly larger in the medial than in the lateral region, in the anterior than in the posterior region and in the distal than in the proximal region (P.05). These results suggest that mfMRI can be used to evaluate the muscle activity and to determine intramuscular variations of activity within skeletal muscle.

Transverse relaxation time (T(2*))-weighted (1)H-MRI of mouse lungs has been performed using partial liquid ventilation (PLV) with a perfluorocarbon (PFC)-in-water emulsion as a contrast modality for lung MRI. Significant sensitivity enhancement in MRI of mouse lungs has been demonstrated with the protocol. The results show that the T(2*) value in lung is approximately proportional to the infusion dose up to a dose of 5 ml/kg body weight (BW) (4.5 g PFC/kg BW) and becomes essentially constant beyond this dosage. T(2*) maps of lungs have been calculated and T(2*) in lungs is in the range of 10-35 ms with this technique, which is an order of magnitude greater than the T(2*) value of mouse lungs without using a PFC-in-water emulsion. T(2*)-weighted (1)H-MR images of mouse lungs have been obtained with good quality under our experimental conditions. We have applied this technique to detect tumors in mouse lungs. Our technique can detect small lung tumors of B16 melanoma, about 1 mm in diameter, in mice. With its significant MR sensitivity enhancement and technical simplicity, T(2*)-weighted (1)H-MRI using PLV with PFC-in-water emulsion offers a promising approach to investigate lung cancers using rodent models.

Quantitative mapping of the effective transverse relaxation time, T2* and proton density was performed in a motor activation functional MRI (fMRI) study using multi-echo, echo planar imaging (EPI) and NumART2* (Numerical Algorithm for Real time T2*). Comparisons between NumART2* and conventional single echo EPI with an echo time of 64 ms were performed for five healthy participants examined twice. Simulations were also performed to address specific issues associated with the two techniques, such as echo time-dependent signal variation. While the single echo contrast varied with the baseline T2* value, relative changes in T2* remained unaffected. Statistical analysis of the T2* maps yielded fMRI activation patterns with an improved statistical detection relative to conventional EPI but with less activated voxels, suggesting that NumART2* has superior spatial specificity. Two effects, inflow and dephasing, that may explain this finding were investigated. Particularly, a statistically significant increase in proton density was found in a brain area that was detected as activated by conventional EPI but not by NumART2* while no such changes were observed in brain areas that showed stimulus correlated signal changes on T2* maps.

An accurate measurement of the transverse relaxation time T2, and the histogram of T2 in the brain parenchyma can be accomplished in vivo using a multi-echo magnetic resonance imaging sequence. An estimate of the error in the T2 measurement is derived using copper sulfate doped water phantoms. Correction factors are calculated and applied to the signal intensity of each voxel prior to the in vivo T 2 evaluation. These corrected T2 are in good agreement with the theoretical values calculated from copper sulfate concentrations. This technique is then applied to calculate T2 histograms of the brain. The population studied was composed of normal volunteers and multiple sclerosis patients. The corrected T 2 histogram method discriminates the normal control population from the MS population, and also discriminates between relapsing-remitting patients and primary progressive or secondary progressive patients. Moreover using this approach we are able to detect in MS patients a global shift of the T2 of the white mater toward higher values. The results of this study showed that the method is easy to implement and may be used to characterize MS pathology. © 2002 Elsevier Science Inc. All rights reserved.

We present relaxivities measurements for both the longitudinal and transverse relaxations of two types of liposomes loaded with ultra small superparamagnetic iron oxide nanoparticles. The magnetoliposome systems presented are soybean phosphatidylcholine liposomes, with and without cholesterol, in the phospholipid bilayer with different molar ratios lipid:cholesterol. In fact, cholesterol is needed to obtain stable liposomes for intravenous administration. The longitudinal and transverse relaxivities were measured with a NMR spectrometer in a 7 T magnetic field. For the studied concentrations, the liposomes show a negligible effect on the longitudinal relaxation time T1 of the medium, but they are very efficient on decreasing the transverse relaxation time T2, the behaviour one expects for a negative CA. We observed a lower transverse relaxivity for the magnetoliposome nanosystem with cholesterol, which strongly decreases with the cholesterol content in the liposome bilayer.

The purpose of this study was to investigate the usefulness and feasibility of magnetic resonance imaging (MRI) with ultrasmall superparamagnetic iron oxide (USPIO) (USPIO-enhanced MRI) for imaging inflammatory tissues. First, we investigated the relationship between the apparent transverse relaxation rate (R2*) and the concentration of USPIO by phantom studies and measured the apparent transverse relaxivity (r2*) of USPIO. Second, we performed animal experiments using a total of 30 mice. The mice were divided into five groups [A (n=6), B (n=6), C (n=6), sham control (n=6), and control (n=6)]. The mice in Groups A, B, C and control were subcutaneously injected with 0.1 ml of turpentine oil on Day 0, while those in the sham control group were subcutaneously injected with 0.1 ml of saline. The mice in Groups A, B, C and sham control were intraperitoneally injected with 200 μmol Fe per kilogram body weight of USPIO (28 nm in diameter) immediately after the first MRI study on Days 3, 5, 7 and 7, respectively, and those in the control group were not injected with USPIO. The second and third MRI studies were performed at 24 and 48 h after USPIO administration, respectively. The maps of R2* were generated from the apparent transverse relaxation time (T2*)-weighted images with six different echo times. The phantom studies showed that there was a linear relationship between R2* and the concentration of USPIO (r=0.99) and the r2* value of USPIO was 105.7 mM−1 s−1. There was a significant increase of R2* in inflammatory tissues in Group C at 24 h after USPIO administration compared with the precontrast R2* value. Our results suggest that USPIO-enhanced MRI combined with R2* measurement is useful for detecting inflammatory tissues.

Localized tissue transverse relaxation time ( T 2 ) is obtained by fitting a decaying exponential to the signals from several spin-echo experiments at different echo times (TE). Unfortunately, time constraints in magnetic resonance spectroscopy (MRS) often mandate in vivo acquisition schemes at short repetition times (TR), that is, comparable with the longitudinal relaxation constant ( T 1 ). This leads to different T 1 -weighting of the signals at each TE. Unaccounted for, this varying weighting causes systematic underestimation of the T 2 's, sometimes by as mush as 30%. In this article, we (i) analyze the phenomenon for common MRS spin-echo T 2 acquisition schemes; (ii) propose a general post hoc T 1 -bias correction for any (TR, TE) combination; (iii) show that approximate knowledge of T 1 is sufficient, since a 20% uncertainty in T 1 leads to under 3% bias in T 2 ; and consequently, (iv) efficient, precision-optimized short TR spin-echo T 2 measurement protocols can be designed and used without risk of accuracy loss. Tables of correction for single-refocusing (conventional) spin-echo and double refocusing, such as, PRESS acquisitions, are provided.

Both cryoporometry and relaxometry are tools to determine the pore size distribution (PSD) of a porous material with NMR. The melting point depression is described by the Gibbs-Thomson equation, yielding the PSD from cryoporometry. The enhanced relaxivity is caused by the surface of the porous material, yielding the PSD from relaxometry. The description in the classical paper of Brownstein and Tarr is only valid for one pore (size). The extended theory of McCall et al. is needed to describe a heterogeneous coupled porous system. As testing material a series of silica-gels called Nucleosil is chosen with typical pore sizes of 5, 10, 12 and 30 nm. Transverse relaxation time distributions are measured using a CPMG-sequence for every temperature of the cryoporometry measurement. These show a mono exponential behaviour, indicating a strongly coupled porous structure. Using the cryoporometry data, an attempt is made to reproduce the averaged relaxivity. Agreement is found for pores with typical pore sizes between 10 nm and 1 microm. The model is not valid for pores smaller than 10 nm.

The aim of this study was to compare proton T2 and apparent diffusion coefficient (ADC) variations induced by exercise in skeletal muscle, to provide some more information on the source of their variations. T2 and ADC were measured in the forearm flexor digitorum muscles in 12 healthy volunteers at rest and after an exercise, using a sequence allowing simultaneous measurements of both parameters. At rest, T2 was 30.6 ± 1.8 ms (mean ± 1 SD) and ADC was 1.82 ± 0.11 × 10−9 m2/s. With exercise, T2 varied by +28 ± 12% (p < .001 vs. rest) and ADC varied by +12 ± 3% (p < .001). The recovery of T2 after exercise was faster than that of ADC, with half-times of 7 ± 2 min and of 15 ± 8 min (p < .01), respectively. It is concluded that both T2 and ADC increase with exercise. However, the mechanisms of variation of T2 and ADC with exercise are probably different, T2 mostly reflecting changes in water content and ADC reflecting temperature variations.

Dual spin-echo magnetic resonance imaging may be used for calculation of transverse myocardial relaxation time from the signal intensity of the echoes considered. In this study, the ability of myocardial transverse relaxation time (T2) to quantitate myocardial edema of the right ventricle (RV) and left ventricle (LV) was tested. Dual spin-echo magnetic resonance images of the entire hearts were obtained and T2 of the RV and LV myocardium calculated from the signal intensities within multiple regions of interest distributed over the myocardium. Six hearts were intermittently perfused through an aortic cannula with three perfusates of decreasing osmolality. Biopsies were obtained for water content (WC) analysis both before and after imaging the hearts at baseline and post-perfusion. A seventh (control) heart was not perfused; instead dual spin-echo imaging was performed at the same time intervals as in the perfused hearts. Prior to any intervention, there was no significant difference between baseline RV (79.49 +/- 2.10%) and LV (77.99 +/- 2.44%, p = .2) myocardial water content; RV myocardial T2 (59.9 +/- 5.8 msec) was slightly but not significantly longer than that of the LV (54.6 +/- 5.7 msec, p = .1). After induction of edema, strong correlation was found between right ventricular myocardial water content measurements and right ventricular T2 (RV WC = 68.5 + 0.19 x RV T2; N = 27, R = 0.92, p < .0001, SEE = 1.56%). Similarly, strong correlation was found between left ventricular myocardial water content and T2 (LV WC = 62.1 + 0.29 x LV T2; N = 27, R = 0.92, p < .0001, SEE = 1.80%).(ABSTRACT TRUNCATED AT 250 WORDS)

Spin-echo sequences with echo times as short as 3.5 msec were implemented on a standard 1.5 T NMR whole-body imager for 1 H imaging of polymers in the solid-state. No modification of the NMR hardware designed for clinical usage was made. Beside images of different polymers a “self-portrait” of the polymeric materials of the receiver coil is given as a neat application. Based on imaging experiments the longitudinal and transverse relaxation time of polymers were investigated. The results indicate that using a standard whole-body imager, it is possible to provide additional information to other examination techniques in polymer and materials science.

Contrast medium compositions for delineation of bowel during magnetic resonance imaging (MRI) of the abdomen are provided for oral or rectal administration. The compositions consist of aqueous suspensions of clay in finely-divided particles which expose a large surface area to the suspending water and impose a condition of dynamic anisotropy upon the adjacent water, resulting in reduction predominantly in the transverse relaxation time of the water and subsequent loss of signal from the bowel lumen.