In vivo bone and cartilage MRI using fully-balanced steady-state free-precession at 7 tesla.

The purpose of this work was to investigated the feasibility of fully-balanced steady-state free-precession (bSSFP) pulse sequence for trabecular bone and knee cartilage imaging in vivo using ultra-high-field (UHF) MRI at 7T in comparison with pulse sequences previously used at 3T. We showed that bSSFP and spin-echo imaging is possible at higher field strengths within 3.2 W/kg specific absorption rate (SAR) constraints. All pulse sequences were numerically optimized based on measured tissue relaxation parameters from six healthy volunteers (T(1) = 820 +/- 128 ms, T(2) = 43.5 +/- 3 ms for bone marrow and T(1) = 1745 +/- 104 ms and T(2) = 30 +/- 4 ms for cartilage). From simulations of the Bloch equation, a signal-to-noise ratio (SNR) increase of more than 1.9 was predicted. Cartilage SNR of bSSFP was 2.4 times higher at 7T (51.3 +/- 4.3) compared with 3T (21.3 +/- 3.3). Bone SNR increased from 11.8 +/- 2.0 to 13.2 +/- 2.5 at the higher field strength. We concluded that there is SNR benefit and great potential for bone and cartilage imaging at higher field strength.     

MRI of the neonatal brain: optimization of spin-echo parameters

OBJECTIVE: Our aim was to measure the relaxation times of the neonatal brain and to use these to derive pulse sequence parameters that enhance the signal-to-noise ratio (SNR) and contrast of MRI scans of the neonatal brain. SUBJECTS AND METHODS: The transverse (T2) and longitudinal (T1) relaxation times were measured for 10 healthy neonates, and the average relaxation times were calculated for both gray and white matter. Simulations using these values were then performed to estimate the optimal pulse sequence parameters. Images were obtained in three neonates using both the optimized and conventional sequence parameters. RESULTS: The measured (mean +/- SD) relaxation times of the neonatal brain at 1.5 T were T1 equals 1712 +/- 235 msec and T2 equals 394 +/- 52 msec in white matter and T1 equals 1144 +/- 245 msec and T2 equals 206 +/- 26 msec in gray matter. The optimized T1-weighted imaging used a turbo spin-echo sequence with an echo-train length of 3 and TR/TE of 850/11 msec and showed increases in both the contrast and the SNR. The optimized T2-weighted sequence used a TE of 270 msec and markedly increased the contrast but at the expense of a reduction in the SNR. CONCLUSION: Parameters of MRI turbo spin-echo sequences for scanning neonates are different from those required for adult studies, and appropriate protocols should be used.     

Measurements of human brain ethanol T(2) by spectroscopic imaging at 4 T.

Previous MRS measurements of ethanol in human brain have yielded a range of transverse relaxation times for ethanol methyl resonance at 1.5 T (200-380 ms). To determine the T(2) of the methyl proton resonance of ethanol in human brain, 8 x 8 spectroscopic images were acquired at 16 different TE values. A frequency-selective refocusing pulse was used to suppress J-modulation of the ethanol triplet, permitting nonintegral multiples of 1/J to be used for TE values. The measured T(2) values for the methyl resonances of ethanol, creatine, and N-acetyl aspartate in mixed tissues were 82 +/- 12, 148 +/- 20, and 227 +/- 25 ms, respectively. Regression analysis of the measured T(2) as a function of gray matter content indicates a shorter T(2) value for ethanol in pure white matter compared to that in pure gray matter. Magn Reson Med 44:35-40, 2000.     

CT evaluation of trabecular and cortical bone mineral density of the lumbar spine in patients on hemodialysis

It is difficult to evaluate the severity of bone involvement in patients on maintenance hemodialysis (HD) by the measurement of vertebral bone mineral density (BMD), since many endocrine factors influence bone metabolism, making the value of BMD variable from high to low. It is also difficult to interpret the BMD measured in one ROI (region of interest) since bone density distribution is sometimes very heterogenous. On the other hand QCT method is useful to evaluate the value of trabecular and cortical bone mineral density separately. Vertebral BMD was measured in 138 patients on maintenance HD, by using DEQCT (dual energy QCT). 161 patients without bone metabolic disorders were studied for control group. In patients on HD, various BMD values ranging from high to low were observed, and there was no correlation between BMD value and duration of HD. The number of patients with low mineral content was greater than that with high mineral content in both cortical and trabecular bone. The trabecular BMD decreased with age, and the speed of BMD decline was the same in both sexes. The rapid decrease of trabecular BMD after menopause seen in control female group was not observed in female patients on hemodialysis. The deviation of BMD from the age-matched average BMD value was smaller in older male patients than that in young male and female patients. In order to evaluate the difference of change between the trabecular and cortical bone at the same vertebra, cases in which discrepancy of Z-score was more than 0.2 were divided into three groups; group A: increased trabecular BMD (Z-score greater than 1), group B: decreased trabecular BMD (-1 greater than Z-score), group C: normal trabecular BMD (-1 less than Z-score less than 1), and in each group T/C ratio (Z-score of trabecular BMD/Z-score of cortical BMD ratio) was evaluated. In group A, almost all cases showed trabecular BMD to be higher than cortical, and in group B, 60% cases showed trabecular BMD to be lower than cortical, suggesting that the change of BMD in trabecular bone is greater than that in cortical bone.     

Peripheral quantitative Computed Tomography (PQCT) in the evaluation of bone geometry, biomechanics and mineral density in postmenopausal women

AIM: Non-invasive assessment of bone geometry, biomechanics, and mineral content in postmenopausal women by peripheral quantitative Computed Tomography (pQCT). MATERIAL AND METHODS: Total, trabecular and cortical mineral density (totBMD, cortBMD, trabBMD), and the geometrical (total area, trabecular area, cortical area) and biomechanical properties of bone (strength-strain index, cortical thickness) were assessed in 93 consecutive post-menopausal women (mean age: 63+/-7 yrs; age at menopause: 49+/-6 yrs; years since menopause: 14+/-9 yrs) by pQCT at the ultradistal radius of non-dominant forearm. RESULTS: Compared with 50 healthy women at peak of bone mass, volumetric total, trabecular and cortical bone densities were significantly reduced in postmenopausal subjects (TotBMD: 318+/-106 mg/cm3 vs ctr 442+/-100, -28%, p<0.001; TrabBMD: 117+/-59 mg/cm3 vs ctr: 203+/-47, -42%, p<0.001; CorBMD: 764+/-159 mg/cm3 vs 921+/-111, -17%, p<0.001). The bone loss was greater in trabecular bone. Cortical area (0.7+/-0,1 cm2 vs ctr: 0.8+/-0.1, -12.5%, p<0.001), cortical thickness (0.151+/-0.02 cm vs ctr: 0.169+/-0.03, -11%, p<0.001), and strength-strain index (686+/-207 mm3 vs ctr: 883+/-165, -22%, p<0.001) were significantly lower in post-menopausal women in comparison with the controls. Years since menopause and age showed a significant negative correlation with bone mineral densities and biomechanical parameters. CONCLUSIONS: In post-menopausal women pQCT showed: 1) osteopoenia in all bone compartments, greater at the trabecular level, related to age and years since menopause; 2) reduced cortical density and cortical thickness, consistent with a reduced ability of bone to absorb loading forces; 3) reduced strength-strain index, indicative of inability to adapt to mechanical use and augmented risk for fracture. We conclude that pQCT is a valuable tool for measuring the true volumetric mineral density and the geometrical and biomechanical indexes of bone, which could be proposed in current clinical practice for the assessment of osteoporosis.     

Bone marrow in children with acute lymphocytic leukemia: MR relaxation times

Magnetic resonance imaging of the lumbar spine was performed in 17 children with acute lymphocytic leukemia (ALL): eight with newly diagnosed ALL, four with ALL in relapse, and five with ALL in remission. Eleven age-matched children were also imaged as controls. The T1 and T2 relaxation times of the bone marrow in the lumbar spine were calculated for all the children. The T1 relaxation times of the bone marrow were as follows (mean +/- standard deviation): newly diagnosed ALL, 968 msec +/- 68; ALL in relapse, 765 msec +/- 19; ALL in remission, 404 msec +/- 135; and age-matched controls, 441 msec +/- 82. T1 relaxation time was statistically significant in differentiating children with newly diagnosed ALL from normal children and from children with ALL in remission. In addition, T1 may be useful in differentiating children with ALL in relapse from children with ALL in remission and from healthy children. T2 was not significantly different among the four groups.     

Comparison of permeability in high-grade and low-grade brain tumors using dynamic susceptibility contrast MR imaging

OBJECTIVE: The purpose of this study was to compare permeability measurements in high-grade and low-grade glial neoplasms using a T2(*)-weighted method. Our hypothesis was that permeability measurements using a T2(*)-weighted technique would show permeability in high-grade neoplasms to be higher than that in low-grade neoplasms. MATERIALS AND METHODS: Twelve patients with biopsy-proven high-grade neoplasms and 10 patients with biopsy-proven low-grade neoplasms underwent dynamic susceptibility contrast MR perfusion imaging (TR/TE, 1500/80) after bolus infusion of 0.2 mmol/kg of MR contrast material. Color-coded permeability-weighted maps were created using a model that weights relative contributions to signal intensity from intravascular T2(*) effects and extravascular T1 effects from blood-brain barrier permeability. Two measures of permeability were performed: mean value of highest permeability found on three images through the tumor (mean regional value) and highest value found at any region of interest in the tumor (single area of maximum permeability). Depending on the normality of the data sets, we used the Wilcoxon's rank sum test or the two-tailed Student's t test for statistical analysis. RESULTS: For low-grade tumors, the range was 0.006-0.041, and the median of the mean regional value for each image was 0.017. For high-grade tumors, the range was 0.005-0.092, and the median of the mean regional value was 0.035 (p = 0.025). For low-grade tumors, the range was 0.008-0.045, and the mean of the single area of maximum values was 0.02. For high-grade tumors, the range was 0.007-0.136, and the mean of the single area of maximum values was 0.054 (p = 0.018). CONCLUSION: Permeability values for high-grade tumors obtained using a T2(*)-weighted method were significantly greater than those for low-grade tumors and are consistent with previous studies reporting results using T1-weighted methods.     

T 1 rho-relaxation mapping of human femoral-tibial cartilage in vivo

PURPOSE: To demonstrate the in vivo feasibility of measuring spin-lattice relaxation time in the rotating frame (T(1rho)); and T(1rho)-dispersion in human femoral cartilage. Furthermore, we aimed to compute the baseline T(1rho)-relaxation times and spin-lock contrast (SLC) maps on healthy volunteers, and compare relaxation times and signal-to-noise ratio (SNR) with corresponding T(2)-weighted images. MATERIALS AND METHODS: All MR imaging experiments were performed on a 1.5 T GE Signa scanner (GEMS, Milwaukee, WI) using a custom built 15-cm transmit-receive quadrature birdcage radio-frequency (RF) coil. The T(1rho)-prepared magnetization was imaged with a single-slice two-dimensional fast spin-echo (FSE) pulse sequence preencoded with a three-pulse cluster consisting of two hard 90 degrees pulses and a low power spin-lock pulse. T(1rho)-dispersion imaging was performed by varying the spin-lock frequency from 100 to 500 Hz in five steps in addition to varying the length of the spin-lock pulse. RESULTS: The average T(1rho)-relaxation times in the weight-bearing (WB) and nonweight-bearing (NWB) regions of the femoral condyle were 42.2 +/- 3.6 msec and 55.7 +/- 2.3 msec (mean +/- SD, N = 5, P < 0.0001), respectively. In the same regions, the corresponding T(2)-relaxation times were 31.8 +/- 1.5 msec and 37.6 +/- 3.6 msec (mean +/- SD, N = 5, P < 0.0099). T(1rho)-weighted images have approximately 20%-30% higher SNR than the corresponding T(2)-weighted images for similar echo time. The average SLC in the WB region of femoral cartilage was 30 +/-4.0%. Furthermore, SLC maps provide better contrast between fluid and articular surface of femoral-tibial joint than T(1rho)-maps. The T(1rho)-relaxation times varied from 32 msec to 42 msec ( approximately 31%) in the WB and 37 msec to 56 msec ( approximately 51%) in NWB regions of femoral condyle, respectively, in the frequency range 0-500 Hz (T(1rho)-dispersion). CONCLUSION: The feasibility of performing in vivo T(1rho) relaxation mapping in femoral cartilage at 1.5T clinical scanner without exceeding Food and Drug Administration (FDA) limits on specific absorption rate (SAR) of RF energy was demonstrated.     

Myocardial and liver iron status using a fast T*2 quantitative MRI (T*2qMRI) technique.

This work demonstrates the use of a fast and precise methodology for evaluating myocardial and liver iron status in multitransfused thalassemic patients by means of a fast T(2) (*) quantitative MRI (T(2) (*)qMRI) technique. Myocardial and liver T(2) (*) values were calculated in 48 thalassemic patients and 21 normal subjects on a 1.5T MRI system using a breath-hold 2D single-slice multiecho gradient-echo (MEGRE) sequence (16 echoes, TR/TE1/TE16/FA = 160/2.7/37.65 ms/25 degrees ). No ECG gating was used. Myocardial T(2) (*), liver T(2) (*), and myocardial to muscle (CR/MS) and liver to muscle (LV/MS) T(2) (*) ratios were correlated with serum ferritin concentration (SFC) levels for all patients. Significant differences in myocardial and liver mean T(2) (*), CR/MS, and LV/MS T(2) (*) values between patients and normal subjects were found (P < 0.0005). Differences in paraspinous muscle mean T(2) (*) values between patients and normal subjects were not significant. Myocardial T(2) (*) and CR/MS T(2) (*) values were not correlated with SFC levels. Liver T(2) (*) and LV/MS T(2) (*) values were significantly correlated with SFC (r = 0.540, P < 0.0005). Myocardial T(2) (*) and CR/MS T(2) (*) values were not correlated with either liver T(2) (*) or LV/MS T(2) (*) values, respectively. We conclude that myocardial and liver iron deposition can be evaluated using the fast non-ECG-gated T(2) (*)qMRI technique.     

Increased anterior temporal lobe T2 times in cases of hippocampal sclerosis: a multi-echo T2 relaxometry study at 3 T

BACKGROUND AND PURPOSE: Increased T2 relaxation times in the ipsilateral hippocampus are present in patients with hippocampal sclerosis. Visual assessment of T2-weighted images of these patients suggests increased signal intensity in the anterior temporal lobe as well. Our aim was to assess hippocampal and anterior temporal T2 relaxation times in patients with partial epilepsy by using a new T2-relaxometry sequence implemented by using a 3-T General Electric imaging unit. METHODS: Coronal view T2 maps were generated by using an eight-echo Carr-Purcell-Meiboom-Gill sequence (TE, 28-231) with an acquisition time of 7 min on a 3-T General Electric Signa Horizon LX imaging unit. T2 relaxation times were measured in the hippocampus and anterior temporal lobe of 30 healthy control volunteers and 20 patients with partial epilepsy. RESULTS: For the 30 control volunteers, the mean hippocampal T2 relaxation time was 98 +/- 2.8 ms. In all measured areas, the asymmetry index was small (<0.01). For the 15 patients with independent evidence of hippocampal sclerosis established by visual, volumetric, and, when available, pathologic criteria, mean hippocampal T2 relaxation times were 118 +/- 7 ms (P <.0001) on the ipsilateral side and 101 +/- 4 ms (P =.005) on the contralateral side. The T2 values were also increased in the anterior temporal lobe (ipsilateral: 82 +/- 6 ms, P <.0001; contralateral: 79 +/- 6 ms, P =.01) as compared with the values for the control volunteers (75 +/- 3 ms). The five patients with focal cortical dysplasia had hippocampal T2 relaxation times that were not different from control values. CONCLUSION: T2 relaxometry at 3 T is feasible and useful and confirmed marked ipsilateral hippocampal signal intensity increase in patients with hippocampal sclerosis. Importantly, definite signal intensity change was also present in the anterior temporal lobe. T2 relaxometry is a sensitive means of identifying abnormalities in the hippocampus and other brain structures.     

T2* measurement during first-pass contrast-enhanced cardiac perfusion imaging.

First-pass contrast-enhanced (CE) myocardial perfusion imaging will experience T(2) (*) effects at peak concentrations of contrast agent. A reduction in the signal intensity of left ventricular (LV) blood due to T(2) (*) losses may effect estimates of the arterial input function (AIF) used for quantitative perfusion measurement. Imaging artifacts may also result from T(2) (*) losses as well as off-resonance due to the bolus susceptibility. We hypothesized that T(2) (*) losses would not be significant for measurement of the AIF in full-dose studies using a short echo time (TE = 0.6 ms). The purpose of this study was to directly measure T(2) (*) in the LV cavity during first-pass perfusion. For single-dose Gd-DTPA (0.1 mmol/kg at 5 ml/s), the LV blood pool T(2) (*) had a mean value of 9 ms (N = 10) at peak enhancement. Distortion of the AIF due to T(2) (*) signal intensity loss will be less than 10% using TE = 0.6 ms.     

Magnetic resonance osteodensitometry in human heel bones: correlation with quantitative computed tomography using different measuring parameters

RATIONALE AND OBJECTIVES: Density of trabecular bone structures in human heel bones was assessed by 3D magnetic resonance (MR) gradient echo imaging (GEI) with multiple echoes. Different spatial resolutions were applied to investigate the influence of the pixel size on signal characteristics in GEI and to find suitable measuring parameters for a maximum correlation between GEI and bone mineral density obtained by quantitative computed tomography (QCT). METHODS: Thirty-five patients aged 31 to 65 years with suspected osteoporosis underwent MR and QCT examinations of the heel bones. The MR protocol included 3D GEI with three echo times (TE1 = 9.3, TE2 = 27.9, and TE3 = 46.5 ms) and isotropic pixel sizes of (0.6 mm)3, (1.2 mm)3, and (2.4 mm)3. Several subregions in the heel bones were analyzed. For determination of signal reduction with increasing TE, signal intensity ratios were calculated pixelwise from images with TE2/TE1 and TE3/TE1. RESULTS: All examinations showed that the T2*-related signal decrease was more pronounced for lower spatial resolution. In the dorsal part of the heel bones, the correlation between signal ratios in GEI and QCT-based bone mineral density values was between r = -0.86 for a spatial resolution of (0.6 mm)3 and r = -0.73 for (2.4 mm)3. Areas with low trabecular density in the ventral part of the heel bones showed clearly lower correlation coefficients (-0.65 < r < -0.67). CONCLUSIONS: Spatial resolution in 3D GEI clearly influences the T2*-related signal characteristics. Despite measuring different physical properties of spongy bone by GEI and QCT, a relatively high correlation between GEI with small pixel sizes and QCT was obtained in the dorsal part of the heel bones, but not in the ventral part with partly thickened trabeculae and irregular distribution. However, standardized measuring protocols with preferably small pixel sizes (as low as [0.6 mm]3) should be applied, and correlation curves must be determined, dependent on the actual bone marrow site, before clinical routine MR osteodensitometry becomes possible.     

Radiofrequency ablation of bone with cooled probes and impedance control energy delivery in a pig model: MR imaging features

PURPOSE: To determine the coronal marrow ablation length and detect cortical thinning after radiofrequency ablation (RFA) of bone in a pig model. MATERIALS AND METHODS: Twelve pigs underwent RFA with a 1- or 2-cm single internally cooled electrode placed at the mid-diaphyseal point of their long bones at 1, 7, or 28 days before euthanasia. Twelve minutes of impedance control radiofrequency energy was delivered at maximum output from a 200-W generator. Pigs were imaged with axial and coronal turbo spin-echo (SE) T1- and T2-weighted frequency-selective fat suppression sequences by using spectral presaturation with inversion recovery (SPIR). A radiologist blinded to the timing of the treatment and the results of other imaging sequences measured the coronal ablation zone length and cortical thickness. The pigs were euthanized, and the ablated bone underwent histologic examination. RESULTS: At SPIR imaging, the zone of marrow ablation was defined as an area of low signal intensity surrounded by a high-signal-intensity band. At T1-weighted imaging, the zone of marrow ablation was defined as a heterogeneously isointense area surrounded by a low-signal-intensity band. The mean (+/-standard deviation) coronal marrow ablation zone measurement with SPIR imaging at 28 days was 47 mm +/- 9 (range, 34-73 mm) for the 1-cm electrode and 51 mm +/- 7 (range, 33-67 mm) for the 2-cm electrode. Two humeral fractures occurred at 21 and 28 days after therapy. Thinning of the cortex adjacent to the electrode insertion site was identified in the humeral group only. CONCLUSION: The change in the marrow signal intensity with impedance-controlled RFA is larger than that reported for temperature-controlled protocols. RFA leads to bone weakening.     

Proton spectroscopic metabolite signal relaxation times in preterm infants: a prerequisite for quantitative spectroscopy in infant brain

PURPOSE: To determine relaxation times of metabolite signals in proton magnetic resonance (MR) spectra of immature brain, which allow a correction of relaxation that is necessary for a quantitative evaluation of spectra acquired with long TE. Proton MR spectra acquired with long TE allow a better definition of metabolites as N-acetyl aspartate (NAA) and lactate especially in children. MATERIALS AND METHODS: Relaxation times were determined in the basal ganglia of 84 prematurely born infants at a postconceptional age of 37.8 +/- 2.2 (mean +/- SD) weeks. Metabolite resonances were investigated using the double-spin-echo volume selection method (PRESS) at 1.5 T. T1 was determined from intensity ratios of signals obtained with TRs of 1884 and 6000 msec, measured at 3 TEs (25 msec, 136 msec, 272 msec). T2 was determined from signal intensity ratios obtained with TEs of 136 msec and 272 msec, measured at 2 TR. Taking only long TEs reduced baseline distortions by macromolecules and lipids. For myo-inositol (MI), an apparent T2 for short TE was determined from the ratio of signals obtained with TE = 25 msec and 136 msec. Intensities were determined by fitting a Lorentzian to the resonance, and by integration. RESULTS: Relaxation times were as follows: trimethylamine-containing compounds (Cho): T1 = 1217 msec/T2 = 273 msec; total creatine (Cr) at 3.9 ppm: 1010 msec/111 msec; Cr at 3.0 ppm: 1388 msec/224 msec; NAA: 1171 msec/499 msec; Lac: 1820 msec/1022 msec; MI: 1336 msec/173 msec; apparent T2 at short TE: 68 msec. CONCLUSION: T1 and T2 in the basal ganglia of premature infants do not differ much from previously published data from basal ganglia of older children and adults. T2 of Cho was lower than previous values. T2 of Cr at 3.9 ppm and Lac have been measured under different conditions before, and present values differ from these data.     

Differentiation between hemangiomas and metastases of the liver with ultrafast MR imaging: preliminary results with T2 calculations

We studied the efficacy of T2 measurements at high field strength in distinguishing between liver hemangiomas and hepatic metastases when an ultrafast (single-excitation) MR imaging technique is used. Fourteen patients with known liver tumors were imaged in a 2.0-T prototype ultrafast MR scanner with a spin-echo (infinite TR and TE of 30-340 msec) pulse sequence. Each image was obtained with a total data acquisition time of 20 msec. T2 calculations for hepatic metastases (n = 6) showed a mean of 79.3 +/- 13.5 msec, whereas hemangiomas (n = 8) showed a T2 of 139.8 +/- 18.8 msec (p less than .0001). T2 values of lesions had a smaller relative standard deviation than previously reported, and the range of T2 values of hemangiomas (119-181 msec) and metastases (68-103 msec) did not overlap. Our preliminary results suggest that T2 calculations with ultrafast MR imaging may be useful for differentiating hemangiomas from metastases. We hypothesize that T2 values obtained from ultrafast MR images are more reliable than those obtained from conventional MR images, primarily because of the elimination of T1 information and effects of motion on image signal intensity.     

T2* and proton density measurement of normal human lung parenchyma using submillisecond echo time gradient echo magnetic resonance imaging.

OBJECTIVE: To obtain T2* and proton density measurements of normal human lung parenchyma in vivo using submillisecond echo time (TE) gradient echo (GRE) magnetic resonance (MR) imaging. MATERIALS AND METHODS: Six normal volunteers were scanned using a 1.5-T system equipped with a prototype enhanced gradient (GE Signa, Waukausha, WI). Images were obtained during breath-holding with acquisition times of 7-16 s. Multiple TEs ranging from 0.7 to 2.5 ms were tested. Linear regression was performed on the logarithmic plots of signal intensity versus TE, yielding measurements of T2* and proton density relative to chest wall muscle. Measurements in supine and prone position were compared, and effects of the level of lung inflation on lung signal were also evaluated. RESULTS: The signal from the lung parenchyma diminished exponentially with prolongation of TE. The measured T2* in six normal volunteers ranged from 0.89 to 2.18 ms (1.43 +/- 0.41 ms, mean +/- S.D.). The measured relative proton density values ranged between 0.21 and 0.45 (0.29 +/- 0.08, mean +/- S.D.). Calculated T2* values of 1.46 +/- 0.50, 1.01 +/- 0.29 and 1.52 +/- 0.18 ms, and calculated relative proton densities of 0.20 +/- 0.03, 0.32 +/- 0.13 and 0.35 +/- 0.10 were obtained from the anterior, middle and posterior portions of the supine right lung, respectively. The anterior-posterior proton density gradient was reversed in the prone position. There was a pronounced increase in signal from lung parenchyma at maximum expiration compared with maximum inspiration. The ultrashort TE GRE technique yielded images demonstrating signal from lung parenchyma with minimal motion-induced noise. CONCLUSION: Quantitative in vivo measurements of lung T2* and relative proton density in conjunction with high-signal parenchymal images can be obtained using a set of very rapid breath-hold images with a recently developed ultrashort TE GRE sequence.     

Measurement of glycine in human brain by triple refocusing 1H-MRS in vivo at 3.0T.

A new (1)H-MRS filtering strategy for selective measurement of glycine (Gly) in human brain in vivo at 3.0T is proposed. Investigation of multiple refocusing following a 90 degrees excitation pulse indicated that triple refocusing is most effective for suppression of the strongly coupled resonances of myo-inositol (mI) at the Gly 3.55-ppm resonance. The echo times of the triple refocusing were optimized, with numerical analysis of the filtering performance, as {TE(1), TE(2), TE(3)} = {67, 62, 69} ms. Compared with the 90 degrees -acquired mI signal the mI suppression ratios of the filter were 170 and 1000, in terms of peak amplitude and area, respectively, between 3.51 and 3.59 ppm. From LCModel analyses, using density-matrix calculated spectra as basis functions, the concentration of Gly in parieto-occipital cortex of healthy adults was estimated to be 0.5 +/- 0.1 mM (mean +/- SD, n = 6), with reference to creatine at 8 mM.     

MR imaging relaxation times of abdominal and pelvic tissues measured in vivo at 3.0 T: preliminary results

PURPOSE: To measure T1 and T2 relaxation times of normal human abdominal and pelvic tissues and lumbar vertebral bone marrow at 3.0 T. MATERIALS AND METHODS: Relaxation time was measured in six healthy volunteers with an inversion-recovery method and different inversion times and a multiple spin-echo (SE) technique with different echo times to measure T1 and T2, respectively. Six images were acquired during one breath hold with a half-Fourier acquisition single-shot fast SE sequence. Signal intensities in regions of interest were fit to theoretical curves. Measurements were performed at 1.5 and 3.0 T. Relaxation times at 1.5 T were compared with those reported in the literature by using a one-sample t test. Differences in mean relaxation time between 1.5 and 3.0 T were analyzed with a two-sample paired t test. RESULTS: Relaxation times (mean +/- SD) at 3.0 T are reported for kidney cortex (T1, 1,142 msec +/- 154; T2, 76 msec +/- 7), kidney medulla (T1, 1,545 msec +/- 142; T2, 81 msec +/- 8), liver (T1, 809 msec +/- 71; T2, 34 msec +/- 4), spleen (T1, 1,328 msec +/- 31; T2, 61 msec +/- 9), pancreas (T1, 725 msec +/- 71; T2, 43 msec +/- 7), paravertebral muscle (T1, 898 msec +/- 33; T2, 29 msec +/- 4), bone marrow in L4 vertebra (T1, 586 msec +/- 73; T2, 49 msec +/- 4), subcutaneous fat (T1, 382 msec +/- 13; T2, 68 msec +/- 4), prostate (T1, 1,597 msec +/- 42; T2, 74 msec +/- 9), myometrium (T1, 1,514 msec +/- 156; T2, 79 msec +/- 10), endometrium (T1, 1,453 msec +/- 123; T2, 59 msec +/- 1), and cervix (T1, 1,616 msec +/- 61; T2, 83 msec +/- 7). On average, T1 relaxation times were 21% longer (P <.05) for kidney cortex, liver, and spleen and T2 relaxation times were 8% shorter (P <.05) for liver, spleen, and fat at 3.0 T; however, the fractional change in T1 and T2 relaxation times varied greatly with the organ. At 1.5 T, no significant differences (P >.05) in T1 relaxation time between the results of this study and the results of other studies for liver, kidney, spleen, and muscle tissue were found. CONCLUSION: T1 relaxation times are generally higher and T2 relaxation times are generally lower at 3.0 T than at 1.5 T, but the magnitude of change varies greatly in different tissues.     

Magnetic resonance relaxation times of normal tissue in the course of chemotherapy: a study in patients with bone sarcoma

To study the effect of chemotherapy on normal fat, skeletal muscle, and bone marrow, T1 and T2 relaxation times were measured in 15 patients with bone sarcoma before and after each cycle of preoperative chemotherapy. A section plane containing the tumor and if possible the nonaffected extremity was imaged with combined multiecho spin echo and inversion recovery pulse sequences. T1 and T2 relaxation times were calculated in the normal-appearing tissues. Although some variation was found in the values in the individual patient and between patients, no systematic changes of relaxation times of fat, muscle, or bone marrow occurred in the course of treatment. We conclude that the chemotherapy used in bone sarcoma has no effect on relaxation times of normal fat, muscle, and bone marrow, and that therefore these tissues may serve as a reference for the signal intensity of tumor.     

Contrast enhancement of short T2 tissues using ultrashort TE (UTE) pulse sequences

AIM: To review the effects of contrast administration on tissues with short T2s using a pulse ultrashort echo time (UTE) sequence. MATERIALS AND METHODS: Pulse sequences were implemented with echo times of 0.08 ms and three later gradient echoes. A fat-suppression option was used and later echo images were subtracted from the first echo image. Contrast enhancement with gadodiamide (0.3 mmol/kg) was used for serial studies in a volunteer. The images of 10 patients were reviewed for evidence of contrast enhancement in short T2 tissues. RESULTS: Contrast enhancement was seen in normal meninges, falx, tendons, ligaments, menisci, periosteum and cortical bone. In addition more extensive enhancement than with conventional pulse sequences was seen in meningeal disease, intervertebral disc disease, periligamentous scar tissue and periosteum after fracture. Subtraction of an image taken with a longer TE from the first image was of value in differentiating enhancement in short T2 tissues from that in long T2 tissues or blood. CONCLUSION: Contrast enhancement can be identified in tissues with short T2s using UTE pulse sequences in health and disease.