Musculoskeletal MRI at 3.0 T and 7.0 T: A comparison of relaxation times and image contrast

Objective

The purpose of this study was to measure and compare the relaxation times of musculoskeletal tissues at 3.0 T and 7.0 T, and to use these measurements to select appropriate parameters for musculoskeletal protocols at 7.0 T.

Materials and methods

We measured the T₁ and T₂ relaxation times of cartilage, muscle, synovial fluid, bone marrow and subcutaneous fat at both 3.0 T and 7.0 T in the knees of five healthy volunteers. The T₁ relaxation times were measured using a spin-echo inversion recovery sequence with six inversion times. The T₂ relaxation times were measured using a spin-echo sequence with seven echo times. The accuracy of both the T₁ and T₂ measurement techniques was verified in phantoms at both magnetic field strengths. We used the measured relaxation times to help design 7.0 T musculoskeletal protocols that preserve the favorable contrast characteristics of our 3.0 T protocols, while achieving significantly higher resolution at higher SNR efficiency.

Results

The T₁ relaxation times in all tissues at 7.0 T were consistently higher than those measured at 3.0 T, while the T₂ relaxation times at 7.0 T were consistently lower than those measured at 3.0 T. The measured relaxation times were used to help develop high resolution 7.0 T protocols that had similar fluid-to-cartilage contrast to that of the standard clinical 3.0 T protocols for the following sequences: proton-density-weighted fast spin-echo (FSE), T₂-weighted FSE, and 3D-FSE-Cube.

Conclusion

The T₁ and T₂ changes were within the expected ranges. Parameters for musculoskeletal protocols at 7.0 T can be optimized based on these values, yielding improved resolution in musculoskeletal imaging with similar contrast to that of standard 3.0 T clinical protocols.     

Intra-individual comparison of image contrast in SPIO-enhanced liver MRI at 1.5T and 3.0T

The purpose of the study was to examine if the higher susceptibility at 3.0 Tesla (T) compared to 1.5 T will affect the contrast in MR imaging of the liver after application of superparamagnetic iron oxide particles (SPIO). The study was approved by our institutional review board and informed consent was obtained. Seventeen healthy volunteers were examined in a prospective, intra-individual comparative study within one day on a 1.5 T and a 3.0 T MRI system. T2 weighted TSE sequences were acquired after bolus injection of a SPIO contrast agent. Image contrast and signal to noise ratio (SNR) were compared between the field strengths. Image contrast was calculated between the liver tissue and the kidneys / spleen / muscles and fluids. The students’T-test was used for statistical analysis. No influence of the higher field strength could be observed on image contrast except for the liver / muscle contrast. This was due to a distinct SNR increase of the muscle tissue at 3.0 T as a result of their relaxation properties. The higher susceptibility at 3.0 T compared to 1.5 T does not translate into a stronger signal attenuation of the SPIO enhanced liver parenchyma.     

Musculoskeletal tumors: T1 and T2 relaxation times

The T1 and T2 relaxation times of primary tumors of the musculoskeletal system were calculated in 54 patients. No correlation was found between the relaxation values and the histopathologic type of the tumors. Lipoma had the same relaxation characteristics as normal fat. Otherwise tumors could be differentiated from normal tissue, but there was no significant difference between malignant and benign tumors, and the mean values for the different histopathologic types differed significantly only in a few instances. Hence T1 and T2 measurements are of limited value for histologic characterization of musculoskeletal tumors.     

T1rho and T2 relaxation times for lumbar disc degeneration: an in vivo comparative study at 3.0-Tesla MRI

Objective

To determine the relative performance of T1rho and T2 relaxation times in disc degeneration assessment.

Methods

Lumbar sagittal MRI was performed at 3?T in 52 subjects. With a spin-lock frequency of 500 Hz, T1rho was measured using a rotary echo spin-lock pulse embedded in a three-dimensional (3D) balanced fast field echo sequence. A multi-echo TSE sequence was used for T2 mapping. Regions of interest (ROIs) were drawn over the T1rho and T2 maps, including nucleus pulposus (NP) and annulus fibrosus (AF). Eight- and five-level disc degeneration semi-quantitative grading was performed.

Results

For NP, T1rho and T2 decreased quadratically with disc degeneration grades and had no significant trend difference (P?=?0.40). For AF, T1rho decreased linearly as the disc degenerated and had a slope of ?3.02 and ?4.56 for eight- and five-level gradings respectively; while the slopes for T2 values were ?1.43 and ?1.84 respectively, being significantly flatter than those of T1rho (P?<?0.001). There was no significant difference in T1rho and T2 values for both NP and AF among discs of grade 5/8 to 8/8 degeneration.

Conclusion

T1rho is better suited for evaluating AF in degenerated disc than T2. In NP, T1rho and T2 decrease in a similar pattern following disc degeneration.

Key Points

? MRI provides unique information about the lumbar disc nucleus pulposus ? Both T1rho and T2 relaxation times decrease similarly following disc degeneration ? AF T1rho relaxation times decrease progressively faster than T2 relaxation times ? T2 and T1rho relaxation times do not reduce further by disc-space narrowing     

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.     

NMR relaxation times in the human brain at 3.0 tesla

Relaxation time measurements at 3.0 T are reported for both gray and white matter in normal human brain. Measurements were made using a 3.0 T Bruker Biospec magnetic resonance imaging (MRI) scanner in normal adults with no clinical evidence of neurological disease. Nineteen subjects, 8 female and 11 male, were studied for T1 and T2 measurements, and 7 males were studied for T2. Measurements were made using a saturation recovery method for T1, a multiple spin-echo experiment for T2, and a fast low-angle shot (FLASH) sequence with 14 different echo times for T2. Results of the measurements are summarized as follows. Average T1 values measured for gray matter and white matter were 1331 and 832 msec, respectively. Average T2 values measured for gray matter and white matter were 80 and 110 msec, respectively. The average T2 values for occipital and frontal gray matter were 41.6 and 51.8 msec, respectively. Average T2 values for occipital and frontal white matter were 48.4 and 44.7 msec, respectively. ANOVA tests of the measurements revealed that for both gray and white matter there were no significant differences in T1 from one location in the brain to another. T2 in occipital gray matter was significantly higher (0.0001 < P < .0375) than the rest of the gray matter, while T2 in frontal white matter was significantly lower (P < 0.0001). Statistical analysis of cerebral hemispheric differences in relaxation time measurements showed no significant differences in T1 values from the left hemisphere compared with the right, except in insular gray matter, where this difference was significant at P = 0.0320. No significant difference in T2 values existed between the left and right cerebral hemispheres. Significant differences were apparent between male and female relaxation time measurements in brain.     

Abdominal MRI at 3.0 T: the basics revisited

OBJECTIVE: The purpose of our article is to describe the underlying physics concepts of abdominal MRI at 3.0 T and their impact on signal-to-noise ratio, susceptibility artifacts, chemical shift artifacts, and dielectric effects. CONCLUSION: Abdominal MR sequence protocols optimized for 1.5-T scanners should not be transferred to 3.0 T without substantial modification. In addition, specific patient groups--for example, large patients with ascites--are not well suited to undergo an abdominal MRI study at 3.0 T.     

3．OT MRI定量动态对比增强对乳腺疾病的应用价值研究

目的 研究3.0T MRI动态对比增强定量参数对乳腺疾病的诊断价值.方法 采用3.0T MRI扫描仪和16通道乳腺相控阵线圈对45例怀疑乳腺肿瘤患者进行动态对比增强MRI检查,共发现病灶52个,其中5例为2个病灶（1例为双侧,4例为单侧）,1例为3个病灶（双侧）,所有2个以上病灶都取最大的病灶纳入研究.分别测量定量血流动力学参数,包括容量转移常数（volume transfer constant,Kttrans）和血管外细胞外间隙容积比（extravascular extracellular space distribute volume per unit tissue volume,Ve）.采用单因素方差分析比较乳腺癌、纤维瘤和其他良性病变的组间差异,受试者特性曲线（receiver operating characteristic curve,ROC）分析良、恶性病变的组间差异.结果 乳腺癌（n=23）的Ktrans和Ve均值分别为（10.18±2.65） min-1和7.64±1.20;良性病变（n=22）的Ktrans和Ve均值分别为（5.68±1.15）nind和8.44±2.01;良性病变中纤维瘤（n=12）的上述均值分别为（7.31±1.42） min1和11.25±2.75,其他良性病变（n=10）的上述均值分别为（3.73±0.83） min1和5.07±1.13.乳腺癌与良性病变间Ktrans的差异有统计学意义（F值为4.271,P值＜0.05）,Ve的差异无统计学意义（F值为1.553,P值＞0.05）;乳腺癌、乳腺纤维瘤与其他良性病变3组间Ktrans和Ve的差异均有统计学意义（F值分别为4.316和3.944,P值均＜0.05）.以最大约登指数为最佳诊断切点值,Ktrans和Ve判断乳腺良恶性病变的敏感度分别为87.5％和8l.3％;特异度分别为55.6％和38.9％.综合2个定量参数作为联合指标诊断良、恶性病变的敏感度、特异度和准确度分别为91..％（21/23）,77.3％ （17/22）和84.4％（38/45）.结论 3.0T MRI动态对比增强定量血流动力学参数Ktrans对乳腺良恶性病变的鉴别诊断具有很高的诊断价值,Ve对鉴别乳腺癌与纤维瘤具有一定的诊断价值.     

Contrast behavior and image quality of magnetic resonance cholangiopancreatography imaging using variable echo times at 3.0 T

Twenty-five volunteers were examined at three different echo times (TE) using magnetic resonance cholangiopancreatography (MRCP) images obtained with half-Fourier-acquired single-shot turbo spin echo (HASTE) thick-slab and multislice HASTE to identify the optimal TE at 3.0 T. No significant difference in the overall image quality was found comparing three different TEs within commonly used ranges. We observed an almost identical duct visibility with different TEs, while we found a trend toward superior visibility of the cystic duct at shorter TE.     

1H metabolite relaxation times at 3.0 tesla: Measurements of T1 and T2 values in normal brain and determination of regional differences in transverse relaxation

PURPOSE: To measure 1H relaxation times of cerebral metabolites at 3 T and to investigate regional variations within the brain. MATERIALS AND METHODS: Investigations were performed on a 3.0-T clinical whole-body magnetic resonance (MR) system. T2 relaxation times of N-acetyl aspartate (NAA), total creatine (tCr), and choline compounds (Cho) were measured in six brain regions of 42 healthy subjects. T1 relaxation times of these metabolites and of myo-inositol (Ins) were determined in occipital white matter (WM), the frontal lobe, and the motor cortex of 10 subjects. RESULTS: T2 values of all metabolites were markedly reduced with respect to 1.5 T in all investigated regions. T2 of NAA was significantly (P < 0.001) shorter in the motor cortex (247 +/- 13 msec) than in occipital WM (301 +/- 18 msec). T2 of the tCr methyl resonance showed a corresponding yet less pronounced decrease (162 +/- 16 msec vs. 178 +/- 9 msec, P = 0.021). Even lower T2 values for all metabolites were measured in the basal ganglia. Metabolite T1 relaxation times at 3.0 T were not significantly different from the values at 1.5 T. CONCLUSION: Transverse relaxation times of the investigated cerebral metabolites exhibit an inverse proportionality to magnetic field strength, and especially T2 of NAA shows distinct regional variations at 3 T. These can be attributed to differences in relative WM/gray matter (GM) contents and to local paramagnetism.     

MRI of prostate cancer at 1.5 and 3.0 T: comparison of image quality in tumor detection and staging

OBJECTIVE: This prospective study was performed to compare the image quality, tumor delineation, and depiction of staging criteria on MRI of prostate cancer at 1.5 and 3.0 T. SUBJECTS AND METHODS: Twenty-four patients with prostate cancer underwent MRI at 1.5 T using the combined endorectal-body phased-array coil and at 3.0 T using the torso phased-array coil, among them 22 before undergoing radical prostatectomy. The prostate was imaged with T2-weighted sequences in axial and coronal orientations at both field strengths and, in addition, with an axial T1-weighted sequence at 1.5 T. Preoperative analysis of all MR images taken together was compared with the histologic findings to determine the accuracy of MRI for the local staging of prostate cancer. In a retroanalysis, the image quality, tumor delineation, and conspicuity of staging criteria were determined separately for both field strengths and compared. Statistical analysis was performed using Wilcoxon's and the McNemar tests. RESULTS: In the preoperative analysis, MRI (at both 1.5 and 3.0 T) had an accuracy of 73% for the local staging of prostate cancer. The retroanalysis yielded significantly better results for 1.5-T MRI with the endorectal-body phased-array coil in terms of image quality (p < 0.001) and tumor delineation (p = 0.012) than for 3.0-T MRI with the torso phased-array coil. Analysis of the individual staging criteria for extracapsular disease did not reveal a superiority of either of the two field strengths in the depiction of any of the criteria. CONCLUSION: Intraindividual comparison shows that image quality and delineation of prostate cancer at 1.5 T with the use of an endorectal coil in a pelvic phased-array is superior to the higher field strength of 3.0 T with a torso phased-array coil alone. As long as no endorectal coil is available for 3-T imaging, imaging at 1.5 T using the combined endorectal-body phased-array coil will continue to be the gold standard for prostate imaging.     

3.0T磁共振弥散加权成像在直肠病变的应用

目的 探讨3T磁共振弥散加权成像(diffusion-weighted imaging,DWI)在直肠病变诊断中的价值.方法 使用3T双梯度短磁体全身磁共振系统,8通道相控阵表面线圈,对55例直肠癌及直肠周围病变患者进行DWI.选用5个不同的b值(200、400、600、800、1000 s/mm2),采用Single shot DWI EPI序列,扫描层数6～11层,层厚7 mm,层间距1 mm,扫描时间17～35 s.测量不同直肠病变在不同b值下DWI图像上的信号强度值和表观弥散系数(apparent diffusion coefficient,ADC),并进行比较.所有数据利用SPSS11.5软件包进行处理.结果 随b值的升高,各类直肠病变在DWI图像上的平均信号强度呈 下降趋势,b值为400 s/mm2时病变显示最明显.随b值的升高,各类直肠病变的ADC值逐渐减小,并渐趋稳定.不同直肠病变的ADC值的差别随b值的增加逐渐明显,至b值为800 s/mm2和1000 s/mm2时出现显著性差异(P<0.05),存在于间质瘤与其他病种.不同T分期的直肠癌ADC值差别明显,随肿瘤浸润深度的增加,ADC值明显降低(P<0.05).结论 DWI及ADC值可以作为直肠癌诊断和鉴别诊断、评价预后的指标.     

MR lymphangiography using dendrimer-based contrast agents: a comparison at 1.5T and 3.0T.

Most macromolecular contrast agents (CAs) show lower r1 and higher r2 relaxivities at 3.0T than at 1.5T. MR lymphangiography in mice using a macromolecular G6 dendrimer-based CA was serially performed and compared at both 1.5T and 3.0T. The r1 and r2 relaxivities of the G6 CA were 25 and 78/s/mM at 1.5T and 17 and 82/s/mM at 3.0T, respectively. The lymph node (LN)-to-fat ratios (LN signal intensity (SI)/fat SI) of T1-weighted 3D-fast spoiled gradient-echo (3D-FSPGR) were 3.2+/-0.4 (mean+/-standard deviation (SD)) at 1.5T and 2.7+/-0.3 at 3.0T (P=0.021), and the LN-to-fat ratios of T2/T1-weighted 3D-fast imaging employing steady-state acquisition with phase cycling (3D-FIESTA-C) were 1.8+/-0.2 at 1.5T and 1.2+/-0.4 at 3.0T (P=0.003). Although 3D-FSPGR successfully delineated the LNs at both 1.5T and 3.0T, 3D-FIESTA-C at 3.0T failed to visualize the LNs.     

Postmortem MRI of human brain hemispheres: T2 relaxation times during formaldehyde fixation

Unlike in vivo imaging, postmortem MRI allows for invasive examination of the tissue specimen immediately after the MR scan. However, natural tissue decomposition and chemical fixation cause the postmortem tissue's MRI properties to be different from those found in vivo. Moreover, these properties change as postmortem fixation time elapses. The goal of this study was to characterize the T₂ relaxation changes that occur over time in cadaveric human brain hemispheres during fixation. Five hemispheres immersed in formaldehyde solution were scanned on a weekly basis for 3 months postmortem, and once again at 6 months postmortem. The T₂ relaxation times were measured throughout the hemispheres. Over time, T₂ values near the edges of the hemispheres decreased rapidly after death, while T₂ values of deep tissue decreased more slowly. This difference is likely due to the relatively large distance from the hemisphere surface, and other barriers limiting diffusion of formaldehyde molecules to deep tissues. In addition, T₂ values in deep tissue did not continuously decay to a plateau, but instead reached a minimum and then increased to a plateau. This final increase may be due to the effects of prolonged tissue decomposition, a hypothesis that is supported by numerical simulations of the fixation process. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.