Age, gender, and skeletal variation in bone marrow composition: a preliminary study at 3.0 Tesla

PURPOSE: To evaluate the efficacy of MR Spectroscopy (MRS) at 3.0 Tesla for the assessment of normal bone marrow composition and assess the variation in terms of age, gender, and skeletal site. MATERIALS AND METHODS: A total of 16 normal subjects (aged between eight and 57 years) were investigated on a 3.0 Tesla GE Signa system. To investigate axial and peripheral skeleton differences, non-water-suppressed spectra were acquired from single voxels in the calcaneus and lumbar spine. In addition, spectra were acquired at multiple vertebral bodies to assess variation within the lumbar spine. Data was also correlated with bone mineral density (BMD) measured in six subjects using dual-energy X-ray absorptiometry (DXA). RESULTS: Fat content was an order of magnitude greater in the heel compared to the spine. An age-related increase was demonstrated in the spine with values greater in men compared to female subjects. Significant trends in vertebral bodies within the same subjects were also shown, with fat content increasing L5 > L1. Population coefficient of variation (CV) was greater for fat fraction (FF) compared to BMD. CONCLUSION: Significant normal variations of marrow composition have been demonstrated, which provide important data for the future interpretation of patient investigations.     

Comparison of T1-weighted in- and out-of-phase single shot magnetization-prepared gradient-recalled-echo with three-dimensional gradient-recalled-echo at 3.0 Tesla: preliminary observations in abdominal studies

Purpose:

To describe in‐phase (IP)/out‐of‐phase (OP) imaging with single shot magnetization‐prepared gradient‐recalled‐echo (MP‐GRE) and to compare intra‐individually IP/OP MP‐GRE with IP/OP three‐dimensional gradient‐recalled‐echo (3D‐GRE) at 3.0 Tesla (T).

Materials and Methods:

Thirty‐six subjects (15 males, 21 females; mean age 46.97 ± 14.97) who had abdominal MRI examinations including precontrast T1‐weighted IP/OP MP‐GRE, IP/OP 3D‐GRE were included in the study. Two radiologists independently evaluated the sequences qualitatively for extent of artifacts, lesion detectability, and conspicuity and subjective grading of liver steatosis. Quantitative evaluation was performed by one radiologist and included liver fat index, liver and spleen SNR, and liver‐lesion and liver‐spleen CNR.

Results:

Respiratory ghosting was more pronounced on 3D‐GRE (P < 0.0008). The degrees of parallel imaging residual artifacts, shading and blurring were significantly higher on the 3D‐GRE sequences (P < 0.0008). Spatial misregistration and bounce point artifacts were only observed with MP‐GRE images. Pixel graininess was more apparent on MP‐GRE (P < 0.0008). Lesion detectability, confidence, and conspicuity were considerably higher on MP‐GRE. Visual appreciation of steatosis was superior on 3D‐GRE. Overall image quality was superior on MP‐GRE (P < 0.0008).

Conclusion:

Higher image quality and improved lesion detectability were present with IP/OP MP‐GRE technique. Inversion‐recovery prepared techniques may represent an important evolution for precontrast T1‐weighted image at 3.0T. The good image quality of MP‐GRE sequences acquired in a free breathing manner should recommend its use in patients unable to suspend breathing. J. Magn. Reson. Imaging 2012;35:1187‐1195. © 2011 Wiley Periodicals, Inc.     

Comparison of a single shot T1-weighted in- and out-of-phase magnetization prepared gradient recalled echo with a standard two-dimensional gradient recalled echo: preliminary findings

Purpose:

To compare in‐phase (IP) /out‐of‐phase (OP) single shot magnetization‐prepared gradient‐recalled‐echo (MP‐GRE) with a standard two‐dimensional gradient‐recalled‐echo (2D‐GRE), and to compare image quality of MP‐GRE in cooperative and noncooperative subjects.

Materials and Methods:

Ninety‐six consecutive subjects (52 males, 44 females; mean age, 53.2 ± 16.7 years), both cooperative (n = 73) and noncooperative (n = 23) subjects who had MRI examinations including precontrast T1‐weighted IP/OP MP‐GRE with or without IP/OP 2D‐GRE were included in the study. The sequences were independently qualitatively evaluated by two radiologists. Quantitative analysis of liver fat index, signal‐to‐noise ratio (SNR) and liver‐lesion contrast‐to‐noise ratio (CNR) was also performed. Data were subjected to statistical analysis.

Results:

The visual detection of the presence or absence of liver steatosis showed no differences between 2D‐GRE and MP‐GRE imaging (k = 1). Minor differences were observed on image quality between MP‐GRE and 2D‐GRE in cooperative subjects, and between MP‐GRE sequences performed in cooperative and noncooperative subjects. Liver fat index results were strongly positively correlated (r = .98; 95% confidence interval [CI] 0.97 to 0.98; P < .0001). Intercept (.14; 95% CI .13 to .15; P < .0001) and slope (.83; 95% CI .79 to .86; P < .0001) were statistically significant.

Conclusion:

IP/OP MP‐GRE and 2D‐GRE comparably demonstrate the presence or absence of hepatic steatosis. Image quality of MP‐GRE was also comparable to 2D‐GRE, and was not substantially adversely affected if subjects were unable to cooperate with breathholding instructions. J. Magn. Reson. Imaging 2011;33:1482–1490. © 2011 Wiley‐Liss, Inc.     

T1 independent,T2* corrected MRI with accurate spectral modeling for quantification of fat: Validation in a fat‐water‐SPIO phantom

Purpose:

To validate a T₁‐independent, T₂*‐corrected fat quantification technique that uses accurate spectral modeling of fat using a homogeneous fat‐water‐SPIO phantom over physiologically expected ranges of fat percentage and T₂* decay in the presence of iron overload.

Materials and Methods:

A homogeneous gel phantom consisting of vials with known fat‐fractions and iron concentrations is described. Fat‐fraction imaging was performed using a multiecho chemical shift‐based fat‐water separation method (IDEAL), and various reconstructions were performed to determine the impact of T₂* correction and accurate spectral modeling. Conventional two‐point Dixon (in‐phase/out‐of‐phase) imaging and MR spectroscopy were performed for comparison with known fat‐fractions.

Results:

The best agreement with known fat‐fractions over the full range of iron concentrations was found when T₂* correction and accurate spectral modeling were used. Conventional two‐point Dixon imaging grossly underestimated fat‐fraction for all T₂* values, but particularly at higher iron concentrations.

Conclusion:

This work demonstrates the necessity of T₂* correction and accurate spectral modeling of fat to accurately quantify fat using MRI. J. Magn. Reson. Imaging 2009;30:1215–1222. © 2009 Wiley‐Liss, Inc.     

Independent estimation of T*2 for water and fat for improved accuracy of fat quantification

Noninvasive biomarkers of intracellular accumulation of fat within the liver (hepatic steatosis) are urgently needed for detection and quantitative grading of nonalcoholic fatty liver disease, the most common cause of chronic liver disease in the United States. Accurate quantification of fat with MRI is challenging due the presence of several confounding factors, including T*₂ decay. The specific purpose of this work is to quantify the impact of T*₂ decay and develop a multiexponential T*₂ correction method for improved accuracy of fat quantification, relaxing assumptions made by previous T*₂ correction methods. A modified Gauss‐Newton algorithm is used to estimate the T*₂ for water and fat independently. Improved quantification of fat is demonstrated, with independent estimation of T*₂ for water and fat using phantom experiments. The tradeoffs in algorithm stability and accuracy between multiexponential and single exponential techniques are discussed. Magn Reson Med 63:849–857, 2010. © 2010 Wiley‐Liss, Inc.     

Quantification of hepatic steatosis with MRI: The effects of accurate fat spectral modeling

Purpose

To develop a chemical‐shift–based imaging method for fat quantification that accounts for the complex spectrum of fat, and to compare this method with MR spectroscopy (MRS). Quantitative noninvasive biomarkers of hepatic steatosis are urgently needed for the diagnosis and management of nonalcoholic fatty liver disease (NAFLD).

Materials and Methods

Hepatic steatosis was measured with “fat‐fraction” images in 31 patients using a multiecho chemical‐shift–based water‐fat separation method at 1.5T. Fat‐fraction images were reconstructed using a conventional signal model that considers fat as a single peak at –210 Hz relative to water (“single peak” reconstruction). Fat‐fraction images were also reconstructed from the same source images using two methods that account for the complex spectrum of fat; precalibrated and self‐calibrated “multipeak” reconstruction. Single‐voxel MRS that was coregistered with imaging was performed for comparison.

Results

Imaging and MRS demonstrated excellent correlation with single peak reconstruction (r² = 0.91), precalibrated multipeak reconstruction (r² = 0.94), and self‐calibrated multipeak reconstruction (r² = 0.91). However, precalibrated multipeak reconstruction demonstrated the best agreement with MRS, with a slope statistically equivalent to 1 (0.96 ± 0.04; P = 0.4), compared to self‐calibrated multipeak reconstruction (0.83 ± 0.05, P = 0.001) and single‐peak reconstruction (0.67 ± 0.04, P < 0.001).

Conclusion

Accurate spectral modeling is necessary for accurate quantification of hepatic steatosis with MRI. J. Magn. Reson. Imaging 2009;29:1332–1339. © 2009 Wiley‐Liss, Inc.     

Cartilage imaging at 3.0T with gradient refocused acquisition in the steady-state (GRASS) and IDEAL fat-water separation

PURPOSE: To demonstrate the feasibility of evaluating the articular cartilage of the knee joint at 3.0T using gradient refocused acquisition in the steady-state (GRASS) and iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) fat-water separation. MATERIALS AND METHODS: Bloch equation simulations and a clinical pilot study (n = 10 knees) were performed to determine the influence of flip angle of the IDEAL-GRASS sequence on the signal-to-noise ratio (SNR) of cartilage and synovial fluid and the contrast-to-noise ratio (CNR) between cartilage and synovial fluid at 3.0T. The optimized IDEAL-GRASS sequence was then performed on 30 symptomatic patients as part of the routine 3.0T knee MRI examination at our institution. RESULTS: The optimal flip angle was 50 degrees for IDEAL-GRASS cartilage imaging, which maximized contrast between cartilage and synovial fluid. The IDEAL-GRASS sequence consistently produced high-quality fat- and water-separated images of the knee with bright synovial fluid and 0.39 x 0.67 x 1.0 mm resolution in 5 minutes. IDEAL-GRASS images had high cartilage SNR and high contrast between cartilage and adjacent joint structures. The IDEAL-GRASS sequence provided excellent visualization of cartilage lesions in all patients. CONCLUSION: The IDEAL-GRASS sequence shows promise for use as a morphologic cartilage imaging sequence at 3.0T.     

Non-invasive quantification of hepatic fat fraction by fast 1.0, 1.5 and 3.0 T MR imaging

INTRODUCTION: Even mild hepatic steatosis in a split liver donor may cause general liver failure and death in the donor. So far, CT density measurements or percutaneous biopsy is used to determine the presence of hepatic steatosis. Magnetic resonance imaging (MRI) may be an elegant method of non-invasive and non-radiation quantification of hepatic fat content. METHODS: Fast gradient echo (GRE) technique was used to discriminate between fat and water spins. Echo time (TE) was adjusted for field strength dependent in-phase and out-of-phase states at 1.0, 1.5 and 3.0 T. Continuous MR signal transition from 100% water to 100% fat was investigated using a wedge water-oil phantom, which was positioned in such a way, that no spatial resolution occurred, thereby combining water and fat in one slice. RESULTS: Using the phantom, a significant difference for a 5% difference in fat content was demonstrated in the range from 20 to 80% fat content (p<0.05) for all tested field strengths. In 25 patients MRI data were correlated with the percentage of fat determined by histologic evaluation of a CT-guided liver biopsy. Using the linear correlation calculated from the MRI phantom data at 1.0 T, we determined the liver fat from each patient's MRI measurements. Comparison of these data with the histologic quantified fat fraction of liver tissue showed a strong correlation (r(2)=0.93 for TE 6 ms and r(2)=0.91 for TE 10 ms). CONCLUSION: The described method can be used to determine the presence of hepatic steatosis of >10% with p<0.05.     

Measurement of liver fat content using selective saturation at 3.0 T

PURPOSE: To validate an MRI technique for measuring liver fat content by calibrating MRI readings with liver phantoms and comparing MRI measurements in human subjects with estimates of liver fat content on liver biopsy specimens. MATERIALS AND METHODS: The MRI protocol consisted of fat and water imaging by selective saturation using a 3.0-T scanner. A water phantom and liver phantoms were scanned before each of 10 human subjects who underwent a liver biopsy to assess for nonalcoholic fatty liver disease (NAFLD). Liver fat content in human subjects was derived from a calibration curve generated by scanning the phantoms. Liver fat was also estimated by optical image analysis and pathologists' assessment of histologic sections. RESULTS: MRI measurements of the liver phantoms were highly reproducible. Measurements of liver fat content in human subjects made by MRI in two areas of the liver were strongly correlated (r=0.98, P<0.001). MRI measurements were highly associated with estimates of liver fat content made by optical image analysis (r=0.96, P<0.001) and with estimates made by the pathologists (r=0.93, P<0.001). CONCLUSION: We validated a technique for quantifying liver fat content based on selective fat and water imaging. The technique is accurate and reproducible and provides a noninvasive method to obtain serial measurements of liver fat content in human subjects.     

3.0T磁共振脑转移瘤IVIM与MR灌注加权成像的相关性研究

目的初步探讨利用体素内不一致运动磁共振成像(introvoxelincoherent motion MR imaging,IVIM-MRI)评价脑转移瘤的灌注,并与灌注加权成像(perfusion weighted Imaging,PWI)的指标进行相关性评价。方法收集在本院2012年6月~2012年12月间26例经手术证实的不同类型癌症发生脑转移的患者行MRI增强检查。扫描序列包括IVIM及PWI。选取颅内转移病灶共60个,应用工作站后处理软件分别测定瘤体及对侧Slow ADC(SADC)、Fast ADC(FADC)、Fraction of FastADC(FFADC)和血流量(cerebral blood flow,CBF)、血容量(cerebral blood volume,CBV),并计算出各个参数的相对值(r),即:r值=(实质病灶值/对侧正常值)×100%。将瘤体与正常侧的IVIM指标进行统计学比较,并将IVIM与PWI的各参数进行Pearson相关性分析。对IVIM和PWI的参数进行转移瘤诊断的ROC分析。结果转移瘤的SADC为(0.437±0.023)×10-3 mm2/s),其对侧脑组织的SADC为(0.223±0.010)×10-3 mm2/s),两者间差异有统计学意义(t=4.83,P0.01);转移瘤的FADC为(3.65±0.11)×10-3 mm2/s),其对侧脑组织的FADC为(2.27±0.12)×10-3 mm2/s),两者间差异有统计学意义(t=8.36,P0.05);转移瘤的FFADC为441.67×10-3±21.19×10-3,其对侧脑组织的FFADC为276.5×10-3±8.07×10-3,两者间差异有统计学意义(t=7.28,P0.01)。转移瘤的rFADC为5.57±31.66,rCBV为2.79±1.27,Person相关性分析显示rFADC与rBV呈弱相关(r=0.274,P0.05),而rFFADC、rSADC与rCBF、rCBV无明显相关性。FADC、FFADC、SADC、CBF、CBV的ROC曲线分析显示,AUCFADC=0.924(P=0.025);AUCFFADC=0.860(P=0.034);AUCSADC=0.896(P=0.030);AUCCBF=0.849(P=0.035);AUCCBV=0.865(P=0.034)。FADC的ROC曲线的AUC最大,诊断准确性更高。结论 IVIM的参数测量能反映转移瘤的灌注特性,但是由于与PWI的技术原理不同,灌注的测量指标之间只具有弱相关性。     

Cartilage morphology at 3.0T: Assessment of three‐dimensional magnetic resonance imaging techniques

Purpose:

To compare six new three‐dimensional (3D) magnetic resonance (MR) methods for evaluating knee cartilage at 3.0T.

Materials and Methods:

We compared: fast‐spin‐echo cube (FSE‐Cube), vastly undersampled isotropic projection reconstruction balanced steady‐state free precession (VIPR‐bSSFP), iterative decomposition of water and fat with echo asymmetry and least‐squares estimation combined with spoiled gradient echo (IDEAL‐SPGR) and gradient echo (IDEAL‐GRASS), multiecho in steady‐state acquisition (MENSA), and coherent oscillatory state acquisition for manipulation of image contrast (COSMIC). Five‐minute sequences were performed twice on 10 healthy volunteers and once on five osteoarthritis (OA) patients. Signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) were measured from the volunteers. Images of the five volunteers and the five OA patients were ranked on tissue contrast, articular surface clarity, reformat quality, and lesion conspicuity. FSE‐Cube and VIPR‐bSSFP were compared to IDEAL‐SPGR for cartilage volume measurements.

Results:

FSE‐Cube had top rankings for lesion conspicuity, overall SNR, and CNR (P < 0.02). VIPR‐bSSFP had top rankings in tissue contrast and articular surface clarity. VIPR and FSE‐Cube tied for best in reformatting ability. FSE‐Cube and VIPR‐bSSFP compared favorably to IDEAL‐SPGR in accuracy and precision of cartilage volume measurements.

Conclusion:

FSE‐Cube and VIPR‐bSSFP produce high image quality with accurate volume measurement of knee cartilage. J. Magn. Reson. Imaging 2010;32:173–183. © 2010 Wiley‐Liss, Inc.     

Reproducibility of MRI‐determined proton density fat fraction across two different MR scanner platforms

Purpose:

To evaluate magnetic resonance imaging (MRI)‐determined proton density fat fraction (PDFF) reproducibility across two MR scanner platforms and, using MR spectroscopy (MRS)‐determined PDFF as reference standard, to confirm MRI‐determined PDFF estimation accuracy.

Materials and Methods:

This prospective, cross‐sectional, crossover, observational pilot study was approved by an Institutional Review Board. Twenty‐one subjects gave written informed consent and underwent liver MRI and MRS at both 1.5T (Siemens Symphony scanner) and 3T (GE Signa Excite HD scanner). MRI‐determined PDFF was estimated using an axial 2D spoiled gradient‐recalled echo sequence with low flip‐angle to minimize T1 bias and six echo‐times to permit correction of T2* and fat‐water signal interference effects. MRS‐determined PDFF was estimated using a stimulated‐echo acquisition mode sequence with long repetition time to minimize T1 bias and five echo times to permit T2 correction. Interscanner reproducibility of MRI determined PDFF was assessed by correlation analysis; accuracy was assessed separately at each field strength by linear regression analysis using MRS‐determined PDFF as reference standard.

Results:

1.5T and 3T MRI‐determined PDFF estimates were highly correlated (r = 0.992). MRI‐determined PDFF estimates were accurate at both 1.5T (regression slope/intercept = 0.958/‐0.48) and 3T (slope/intercept = 1.020/0.925) against the MRS‐determined PDFF reference.

Conclusion:

MRI‐determined PDFF estimation is reproducible and, using MRS‐determined PDFF as reference standard, accurate across two MR scanner platforms at 1.5T and 3T. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

MRA of intracranial aneurysms embolized with platinum coils: a vascular phantom study at 1.5T and 3T

PURPOSE: To analyze the influence of matrix and echo time (TE) of three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) on the depiction of residual flow in aneurysms embolized with platinum coils at 1.5T and 3T. MATERIALS AND METHODS: A simulated intracranial aneurysm of the vascular phantom was loosely packed to maintain the patency of some residual aneurysmal lumen with platinum coils and connected to an electromagnetic flow pump with pulsatile flow. MRAs were obtained altering the matrix and TE of 3D TOF sequences at 1.5T and 3T. RESULTS: The increased spatial resolution and the shorter TE offered better image quality at 3T. For the depiction of an aneurysm remnant, the high-spatial-resolution 3T MRA (matrix size of 384 x 224 and 512 x 256) with a short TE of < or =3.3 msec were superior to the 1.5T MRA obtained with any sequences. CONCLUSION: 3T MRA is superior to 1.5T MRA for the assessment of aneurysms embolized with platinum coils; the combination of the 512 x 256 matrix and short TE (3.3 msec or less) seems feasible at 3T.     

Liver-vessel cancellation artifact on in-phase and out-of-phase MRI imaging: a sign of ultra-high liver fat content

Purpose:

To describe a new MRI sign, the liver‐vessel cancellation artifact, on In‐Phase and Out‐of‐Phase gradient‐echo sequences related to ultra‐high liver fat content (>90%) by qualitative histology.

Materials and Methods:

Institutional review board approval was obtained for this retrospective HIPAA‐compliant study with waived informed consent. Patients with liver steatosis were searched in MRI (n = 195) and pathology (n = 116) databases between January 1, 2008, and June 20, 2010. Two readers blindly reviewed all MR images for the presence of the liver‐vessel cancellation sign. Cross‐reference of patients with biopsy‐proven steatosis and MRI within one month was performed (n = 54; 25 males, 29 females; mean age 41.0 ± 18.9), with a population of 6 patients with ultra‐high liver fat content (1 male, 5 females; mean age 15.5 ± 11.2). Performance diagnostic tests, including sensitivity and specificity, were performed.

Results:

Liver‐vessel cancellation sign was present in all patients with ultra‐high liver fat content but in none of the remaining patients. Calculated sensitivity and specificity for the detection of ultra‐high liver fat content with this sign were 100% (95% confidence interval [CI]: 69.1–100%) and 100% (95% CI: 98.4–100%), respectively.

Conclusion:

The presence of liver‐vessel cancellation artifact around intra‐hepatic vessels is a feature of ultra‐high liver fat content. J. Magn. Reson. Imaging 2012;35:1112‐1118. © 2011 Wiley Periodicals, Inc.     

Comparative MR study of hepatic fat quantification using single-voxel proton spectroscopy, two-point dixon and three-point IDEAL.

Hepatic fat fraction (HFF) was measured in 28 lean/obese humans by single-voxel proton spectroscopy (MRS), a two-point Dixon (2PD), and a three-point iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) method (3PI). For the lean, obese, and total subject groups, the range of HFF measured by MRS was 0.3-3.5% (1.1 +/- 1.4%), 0.3-41.5% (11.7 +/- 12.1), and 0.3-41.5% (10.1 +/- 11.6%), respectively. For the same groups, the HFF measured by 2PD was -6.3-2.2% (-2.0 +/- 3.7%), -2.4-42.9% (12.9 +/- 13.8%), and -6.3-42.9% (10.5 +/- 13.7%), respectively, and for 3PI they were 7.9-12.8% (10.1 +/- 2.0%), 11.1-49.3% (22.0 +/- 12.2%), and 7.9-49.3% (20.0 +/- 11.8%), respectively. The HFF measured by MRS was highly correlated with those measured by 2PD (r = 0.954, P < 0.001) and 3PI (r = 0.973, P < 0.001). With the MRS data as a reference, the percentages of correct differentiation between normal and fatty liver with the MRI methods ranged from 68-93% for 2PD and 64-89% for 3PI. Our study demonstrates that the apparent HFF measured by the MRI methods can significantly vary depending on the choice of water-fat separation methods and sequences. Such variability may limit the clinical application of the MRI methods, particularly when a diagnosis of early fatty liver needs to be performed. Therefore, protocol-specific establishment of cutoffs for liver fat content may be necessary.