Fat Signal Research Articles

MR fingerprinting with simultaneous T1, T2, and fat signal fraction estimation with integrated B0 correction reduces bias in water T1 and T2 estimates

PurposeMR fingerprinting (MRF) sequences permit efficient T1 and T2 estimation in cranial and extracranial regions, but these areas may include substantial fat signals that bias T1 and T2 estimates. MRI fat signal fraction estimation is also a topic of active research in itself, but may be complicated by B0 heterogeneity and blurring during spiral k-space acquisitions, which are commonly used for MRF. An MRF method is proposed that separates fat and water signals, estimates water T1 and T2, and accounts for B0 effects with spiral blurring correction, in a single sequence. Theory and methodsA k-space-based fat-water separation method is further extended to unbalanced steady-state free precession MRF with swept echo time. Repeated application of this k-space fat-water separation to demodulated forms of the measured data allows a B0 map and correction to be approximated. The method is compared with MRF without fat separation across a broad range of fat signal fractions (FSFs), water T1s and T2s, and under heterogeneous static fields in simulations, phantoms, and in vivo. ResultsThe proposed method's FSF estimates had a concordance correlation coefficient of 0.990 with conventional measurements, and reduced biases in the T1 and T2 estimates due to fat signal relative to other MRF sequences by several hundred ms. The B0 correction improved the FSF, T1, and T2 estimation compared to those estimates without correction. ConclusionThe proposed method improves MRF water T1 and T2 estimation in the presence of fat and provides accurate FSF estimation with inline B0 correction.

Water/fat separation for distortion-free EPI with point spread function encoding.

Effective removal of chemical-shift artifacts in echo-planar imaging (EPI) is a challenging problem especially with severe field inhomogeneity. This study aims to develop a reliable water/fat separation technique for point spread function (PSF) encoded EPI (PSF-EPI) by using its intrinsic multiple echo-shifted images. EPI with PSF encoding can achieve distortion-free imaging and can be highly accelerated using the tilted-CAIPI technique. In this study, the chemical-shift encoding existing in the intermediate images with different time shifts of PSF-EPI is used for water/fat separation, which is conducted with latest water/fat separation algorithms. The method was tested in T1-weighted, T2-weighted, and diffusion weighted imaging in healthy volunteers. The ability of the proposed method to separate water/fat using intrinsic PSF-EPI signals without extra scans was demonstrated through in vivo T1-weighted, T2-weighted, and diffusion weighted imaging experiments. By exploring different imaging contrasts and regions, the results show that this PSF-EPI based method can separate water/fat and remove fat residues robustly. By using the intrinsic signals of PSF-EPI for water/fat separation, fat signals can be effectively suppressed in EPI even with severe field inhomogeneity. This water/fat separation method for EPI can be extended to multiple image contrasts. The distortion-free PSF-EPI technique, thus, has the potential to provide anatomical and functional images with high-fidelity and practical acquisition efficiency.

Three-dimensional ultrashort echo time imaging with tricomponent analysis for human cortical bone.

To investigate tricomponent analysis of human cortical bone using a multipeak fat signal model with 3D ultrashort TE Cones sequences on a clinical 3T scanner. Tricomponent fitting of bound water, pore water, and fat content using a multipeak fat spectra model was proposed for 3D ultrashort TE imaging of cortical bone. Three-dimensional ultrashort TE Cones acquisitions combined with tricomponent analysis were used to investigate bound and pore water and fractions, as well as fat and fraction in cortical bone. Feasibility studies were performed on 9 human cortical bone specimens with regions of interest selected from the endosteum to the periosteum in 4 circumferential regions. Microcomputed tomography studies were performed to measure bone porosity and bone mineral density for comparison and validation of the bound and pore water analyses. The oscillation of the signal decay was well-fitted with the proposed tricomponent model. The sum of the pore water and fat fractions from tricomponent analysis showed a high correlation with microcomputed tomography porosity (R = 0.74, P < 0.01). Estimated bound-water fraction also demonstrated a high correlation with bone mineral density (R = 0.70, P < 0.01). Tricomponent analysis significantly improves the estimation of bound-water and pore-water fractions in human cortical bone.

Clinical Magnetic Resonance Imaging of the Knee at 7 T: Optimization of Fat Suppression.

The aim of this study was to evaluate the efficiency and performance of different fat suppression techniques for clinical 7 T knee magnetic resonance imaging including the slice-selective gradient reversal (SSGR) technique. This article is an ethical board-approved prospective study with written informed consent from 8 volunteers (mean, 31 ± 4 years). It included fat phantom and knee magnetic resonance imaging at 3 T (Magnetom Skyra; Siemens Healthcare) and at 7 T (Achieva, Philips Healthcare). At 3 T, an axial proton density-weighted turbo spin echo sequence with spectral adiabatic inversion recovery (SPAIR) was acquired. At 7 T, a series of 5 proton density-weighted turbo spin echo sequences was acquired: (a) without fat suppression, (b) with spectral presaturation with inversion recovery (SPIR), (c) with SPAIR, (d) with SSGR, and (e) with the combination of SSGR + SPIR. Additional noise scans allowed pixelwise calculation of signal-to-noise ratio and contrast-to-noise ratio maps. Quantitative data at 7 T were compared with each other but not to 3 T. Two independent radiologists evaluated overall image quality, homogeneity and grade of fat suppression, and the delineation between 2 adjacent structures. Results were compared using Wilcoxon signed rank and paired sample t tests. Relative signal-to-noise ratios of fat demonstrated that the SPIR technique reduced the fat signal to 45% ± 5.4%; SPAIR, 18% ± 1.2%; SSGR, 14% ± 1.1%; and SSGR + SPIR, 11% ± 0.3%. Contrast-to-noise ratio showed superior contrast between muscle-fat (P < 0.001) and fluid-fat (P ≤ 0.001) for SSGR and SSGR + SPIR. The radiologists rated the overall image quality higher at 7 T than 3 T. The homogeneity and grade of fat suppression as well as the delineation between 2 different (adjacent) structures were rated best for SSGR + SPIR. At 7 T, fat saturation for clinical knee imaging using SSGR and the combination of SSGR + SPIR was superior compared with standard methods based on spectrally selective radiofrequency pulses.

Robust water-fat separation for multi-echo gradient-recalled echo sequence using convolutional neural network.

To accurately separate water and fat signals for bipolar multi-echo gradient-recalled echo sequence using a convolutional neural network (CNN). A CNN architecture was designed and trained using the relationship between multi-echo images from the bipolar multi-echo gradient-recalled echo sequence and artifact-free water-fat-separated images. The artifact-free water-fat-separated images for training the CNN were obtained from multiple signals with different TEs by using iterative decomposition of water and fat with echo asymmetry and the least-squares estimation method, in which multiple signals at different TEs were acquired using a single-echo gradient-recalled echo sequence. We also proposed a data augmentation method using a synthetic field inhomogeneity to generate multi-echo signals, including various bipolar multi-echo gradient-recalled echo artifacts so that the CNN could prevent overfitting and increase the separation accuracy. We trained the CNN using in vivo knee images and tested it using in vivo knee, head, and ankle images. In vivo imaging results showed that the proposed CNN could separate water-fat images accurately. Although the proposed CNN was trained using only in vivo knee images, the proposed CNN could also separate water-fat images of different imaging regions. The proposed data augmentation method could prevent overfitting even with a limited number of training data sets and make the method robust to magnetic field inhomogeneities. The proposed CNN could obtain water-fat-separated images from the multi-echo images acquired from the bipolar multi-echo gradient-recalled echo sequence, which included artifacts from the bipolar gradients.

Fat suppression for ultrashort echo time imaging using a single-point Dixon method.

In ultrashort echo time (UTE) imaging, fat suppression can improve short T2 * contrast but can also reduce short T2 * signals. The conventional two-point Dixon (2p-Dixon) method does not perform well due to short T2 * decay. In this study, we propose a new method to suppress fat for high contrast UTE imaging of short T2 tissues, utilizing a single-point Dixon (1p-Dixon) method. The proposed method utilizes dual-echo UTE imaging, where UTE is followed by the second TE, chosen flexibly. Fat is estimated by applying a 1p-Dixon method to the non-UTE image after correction of phase errors, which is used to suppress fat in the UTE image. In vivo ankle and knee imaging were performed at 3T to evaluate the proposed method. It was observed that fat and water signals in tendons were misestimated by the 2p-Dixon method due to signal decay, while the 1p-Dixon method showed reliable fat and water separation not affected by the short T2 * signal decay. Compared with the conventional chemical shift based fat saturation technique, the 1p-Dixon based approach showed much stronger signal intensities in the Achilles, quadriceps, and patellar tendons, with significantly improved contrast to noise ratios (CNRs) of 11.8±2.2, 16.0±1.6, and 26.8±1.3 with the 1p-Dixon method and 0.6±0.2, 4.6±1.0, and 17.5±1.4 with regular fat saturation, respectively. The proposed 1p-Dixon based fat suppression allows more flexible selection of imaging parameters and more accurate fat and water separation over the conventional 2p-Dixon in UTE imaging. Moreover, the proposed method provides much improved CNR for short T2 tissues over the conventional fat saturation method.

Water-fat separation and parameter mapping in cardiac MRI via deep learning with a convolutional neural network.

Water-fat separation is a postprocessing technique most commonly applied to multiple-gradient-echo magnetic resonance (MR) images to identify fat, provide images with fat suppression, and to measure fat tissue concentration. Recently, Numerous advancements have been reported. In contrast to early methods, the process of water-fat separation has become complicated due to multiparametric analytic models, optimization methods, and the absence of a unified framework for diverse source data. To determine the feasibility and performance of MRI water-fat separation and parametric mapping via deep learning (DL) with a range of inputs. Retrospective data usage. Ninety cardiac MR examinations from normal control, acute, subacute, and chronic myocardial infarction subjects were obtained, providing 1200 multiple gradient-echo acquisitions. 1.5 T/2D multiple gradient-echo pulse sequence ASSESSMENT: Ground-truth training and validation water-fat separation were obtained using a graph cut method with R2 *, off-resonance correction, and a multipeak fat spectrum. U-Net DL training with single and multiecho, complex, and magnitude inputs were compared using quantitative and three-observer subjective analysis. DL methods' image structural similarity, and quantitative proton density fat fraction (PDFF), R2 *, and off-resonance quantitative values were statistically compared with the GraphCut reference standard using Student's t-test and Pearson's correlation. Myocardial fat deposition in chronic myocardial infarction and intramyocardial hemorrhage in acute myocardial infarction were well visualized in the DL results. Predicted values for R2 *, off-resonance, water, and fat signal intensities were well correlated with a conventional model-based water fat separation (R2 ≥ 0.97, P < 0.001) with appropriate inputs. DL parameter maps had a 14% higher signal-to-noise ratio (P < 0.001) when compared with a conventional method. DL water-fat separation is feasible with a wide range of inputs, while R2 * and off-resonance mapping requires multiple echoes and complex images. With appropriate inputs, DL provides quantitative and subjective results comparable to conventional model-based methods. 1 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;50:655-665.

Focal hypersteatosis: a pseudolesion in patients with liver steatosis.

We aimed to describe ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI) findings of focal hypersteatosis (FHS). We retrospectively reviewed our database for patients with hypersteatosis. Over a 5-year period (February 2005 to September 2010) a total of 17 321 patients underwent abdominal CT scan and 28 patients were determined to have FHS. All patients had US, CT, and MRI studies. Size, area, and density measurements were performed on CT images. Fat signal percentage (FSP) was measured on T1-weighted in- and out-of-phase gradient-echo images. FHS was defined based on MRI findings, as an area of greater signal drop on out-of phase images compared with the rest of the fatty liver. The period prevelance of focal hypersteatosis was measured as 0.16% over the 5-year period. Cancer was the most common diagnosis (22 of 28 patients, 78.5%), with the breast (32.1%) and colorectal (25%) cancers predominating. FHS was seen in segment 4 (n=26, 92.8%), segment 8 (n=1, 3.6%), and segment 3 (n=1, 3.6%). Shape was nodular in 21 patients (75%), while triangular or amorphous in the remaining 7 patients (25%). FHS was hyperechoic and isoechoic in 5 (17.9%) and 23 (82.1%) patients, respectively. FHS was hypodense on CT of all patients relative to fatty liver. On MRI, the FHS was hyperintense on T1-weighted in-phase images in 17 patients (60.7%). Median liver parenchymal FSP was 21.5% (range, 10%-41.4%) and median FSP of hypersteatotic area was 32.5% (range, 19%-45%). Focal hypersteatosis is a pseudolesion that can be observed in patients with liver steatosis. It appears hypodense on CT and mostly isoechoic on US relative to fatty liver. It may mimic metastasis in cancer patients with steatosis, due to nodular shape and atypical location. MRI should be used for correct diagnosis in patients with equivocal findings on CT to avoid biopsy.

In Vivo 3D MRI Measurement of Tumour Volume in an Orthotopic Mouse Model of Prostate Cancer.

Prostate cancer (CaP) is the most commonly diagnosed cancer in males in western countries. Orthotopic implantation is considered as an ideal xenograft model for CaP study, and noninvasive measurement of tumor volume changes is important for monitoring responses to anticancer therapies. In this study, the T2-weighted fast spin echo sequence magnetic resonance imaging (MRI) was performed on a CaP orthotopic non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mouse model weekly for 6 weeks post PC-3 CaP cell inoculation, and the fat signal was suppressed using a chemical shift-selective pulse. Subsequently, the MRI data were imported into the image processing software Avizo Standard and stacked into three-dimensional (3D) volumes. Our results demonstrate that MRI, combined with 3D reconstruction, is a feasible and sensitive method to assess tumor growth in a PC-3 orthotopic CaP mouse model and this established monitoring approach is promising for longitudinal observation of CaP xenograft development after anticancer therapy in vivo. Further investigation is needed to validate this protocol in a larger cohort of mice to generate enough statistical power.

Simultaneous fat-free isotropic 3D anatomical imaging and T2 mapping of knee cartilage with lipid-insensitive binomial off-resonant RF excitation (LIBRE) pulses.

Improved knee cartilage morphological delineation and T2 mapping precision necessitates isotropic 3D high-resolution and efficient fat suppression. To develop and assess an isotropic 3D lipid-insensitive T2 mapping technique of the knee for improved cartilage delineation and precise measurement of T2 relaxation times. Prospective. Phantoms (n = 6) used in this study were designed to mimic the T1 and T2 relaxation times of cartilage and fat. The study cohort comprised healthy volunteers (n = 7) for morphometry and T2 relaxation time measurements. A high-resolution isotropic 3D T2 mapping technique that uses sequential T2 -prepared segmented gradient-recalled echo (Iso3DGRE) images and lipid-insensitive binomial off-resonant radiofrequency (RF) excitation (LIBRE) at 3T. Numerical simulations and phantom experiments were performed to optimize the LIBRE pulse. Phantom studies were carried out to test the accuracy of the technique against reference standard spin-echo (SE) T2 mapping. Subsequently, T2 maps with and without LIBRE pulses were acquired in knees of healthy volunteers and the T2 relaxation time values in different cartilage compartments were compared. A two-tailed paired Student's t-test was used to compare the average T2 values and the relative standard deviations (inverse measurement of the precision) obtained with and without LIBRE pulses. A LIBRE pulse of 1 msec suppressed fat with an RF excitation frequency offset of 1560 Hz and optimal RF excitation angle of 35°. These results were corroborated by phantom and knee experiments. Robust and homogeneous fat suppression was obtained (a fat signal-to-noise ratio (SNR) decrease of 86.4 ± 2.4%). In phantoms, T2 values were found in good agreement when comparing LIBRE-Iso3DGRE with SE (slope 0.93 ± 0.04, intercept 0.11 ± 1.6 msec, R2 >0.99). In vivo, LIBRE excitation resulted in more precise T2 estimation (23.7 ± 7.4%) than normal excitation (30.5 ± 9.9%, P < 0.0001). Homogeneous LIBRE fat signal suppression was achieved with a total RF pulse duration of 1 msec, allowing for the removal of chemical shift artifacts and resulting in improved cartilage delineation and precise T2 values. 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:1275-1284.

Imaging of a high concentration of iron labeled cells with positive contrast in a rat knee.

The sweep imaging with Fourier transformation (SWIFT) imaging technique has been shown to provide positive contrast from diluted cell suspensions labeled with super-paramagnetic iron oxide (SPIO) in a tissue, as an alternative to T2*-weighted imaging. Here we demonstrate a variation of the SWIFT technique that yields a hyperintense signal from a concentrated cell suspension. The proposed technique provides minimal background signal from host tissue and facilitates visualization of injected cells. The proton resonance frequency and linewidth were determined for SPIO solutions of different concentrations. The original SWIFT sequence was modified and a dual saturation Gaussian shape RF pulse with ~200 Hz bandwidth was incorporated into the acquisition protocol to suppress host tissue and fat signals. This modification of the original acquisition protocol permits the detection of a hyperintense signal from grafted cells with minimal background signal from the host tissue. SPIO particles not only induce broadening of NMR line-width but also an initiate proton resonance frequency shift. This shift is linearly proportional to the concentration of the iron oxide particles and induced by the bulk magnetic susceptibility of SPIOs. The shift of the resonance frequency of iron labeled cells allowed us effectively suppress the host tissues with saturation RF pulse to improve MRI detection of grafted cells. Iron oxide particles increase the resonance frequency of water proton signal. This shift permitted us to add the tissue/fat saturation RF pulse into the original SWIFT acquisition protocol and detect distinct hyperintense signals from grafted cells with minimal background signal from the host tissue.

Measuring fetal adipose tissue using 3D water-fat magnetic resonance imaging: a feasibility study

Purpose: Analysis of fetal adipose tissue volumes may provide useful insight towards assessment of overall fetal health, especially in cases with abnormal fetal growth. Here, we assess whether fetal adipose tissue volume can be reliably measured using 3D water-fat MRI, using a quantitative assessment of the lipid content of tissues.Materials and methods: Seventeen women with singleton pregnancies underwent a fetal MRI and water-only and fat-only images were acquired (modified 2-point Dixon technique). Water and fat images were used to generate a fat signal fraction (fat/(water + fat)) from which subcutaneous adipose tissue was segmented along the fetal trunk. Inter-rater (three readers) and intrarater reliability was assessed using intraclass-correlation coefficients (ICC) for 10 image sets. Relationships between adipose tissue measurements and gestational age and estimated fetal weight percentiles were examined.Results: The ICC of the inter-rater reliability was 0.936 (p < .001), and the ICC of the intrarater reliability was 0.992 (p < .001). Strong positive correlations were found between adipose tissue measurements (lipid volume, lipid volume/total fetal volume, mean fat signal fraction) and gestational age.Conclusions: 3D water-fat MRI can reliably measure volume and quantify lipid content of fetal subcutaneous adipose tissues.

Non-alcoholic fatty liver disease-associated hepatocellular carcinoma: effect of hepatic steatosis on major hepatocellular carcinoma features at MRI.

To evaluate the effect of hepatic steatosis on LI-RADS® major features at MRI in patients with non-alcoholic fatty liver disease (NAFLD)-associated hepatocellular carcinoma (HCC). HCC and liver parenchyma features at MRI from 48 consecutive patients with NAFLD and histology proven HCC (mean ± SD; 4.5 ± 3.4 cm) were independently reviewed by three radiologists. Inter-rater agreement was determined by prevalence/bias-adjusted kappa. Hepatic fat signal fraction (FS%) was independently calculated. HCC features were compared by FS% at MRI using logistic regression analysis and histologic steatosis grade using Cochran-Armitage test for trend, stratified by cirrhotic liver morphology or histologic fibrosis stage. Receiver operating characteristic curves were generated to determine the sensitivity and specificity for major HCC features by FS%. Major HCC features included arterial phase hyperenhancement (APHE) in 45 (93%), portal venous phase washout (PVWO) in 30 (63%), delayed phase washout (DPWO) in 38 (79%) and enhancing "capsule" in 34 (71%). Cirrhotic morphology was present in 22 (46%). Inter-rater agreement was 0.75 for APHE, 0.42-0.58 for PVWO, 0.58-0.71 for DPWO and 0.38-0.67 for enhancing "capsule". There was an 18%, 14% and 22% increase in the odds of absent PVWO, DPWO and capsule appearance for every 1% increase in hepatic FS% in patients with non-cirrhotic liver morphology (p = 0.011, 0.040 and 0.029, respectively). Hepatic FS% ≥ 14.8% had a sensitivity and specificity of 64 and 100% for absent PVWO and 71 and 90% for absent DPWO in patients with non-cirrhotic liver morphology. Absent washout and capsule appearance are associated with increasing hepatic steatosis in patients with non-cirrhotic, NAFLD-associated HCC. In patients with non-cirrhotic, non-alcoholic fatty liver disease (NAFLD)-associated hepatocellular carcinoma (HCC), absent HCC washout and capsule appearance are associated with increasing hepatic steatosis, thereby potentially impacting the noninvasive imaging diagnosis of HCC in these patients. Lack of washout or capsule appearance in steatotic livers at MRI may require alternative criteria for the diagnosis of HCC in patients with non-cirrhotic NAFLD.

Efficacy of 3D VIBE Dixon fat quantification for differentiating clear-cell from non-clear-cell renal cell carcinoma

To assess the efficacy of three-dimensional (3D) volumetric interpolated breath-hold examination (VIBE) magnetic resonance imaging (MRI) with Dixon quantification for differentiating clear-cell from non-clear-cell types of renal cell carcinoma (RCC). The 3D VIBE Dixon renal MRI examinations of 44 patients with 45 histologically confirmed RCCs was analysed. The fat fractions and signal intensity indexes (SIindex) of the solid portions of clear-cell and non-clear-cell RCCs were measured and compared using Student's t-test and receiver operating characteristic (ROC) curves. The agreement of measurements among observers was evaluated by the intraclass correlation coefficient (ICC), and Bland-Altman plots. The mean values of fat fraction (13.16±7.16%) and SIindex (22.64±15.7%) in clear-cell RCCs were significantly higher than that in non-clear-cell RCCs (7.7±2% and 7.9±4.8%; p<0.001, respectively). With the area under the ROC curve (AUC) of the fat fraction at 0.811, 75% (95% CI: 55.1-89.43%) sensitivity and 76.5% (95% CI: 50.1-93.2%) specificity for diagnosing clear-cell RCC were obtained at a cut-off fat fraction value of 8.9%. With a cut-off value of 8.89%, the diagnostic sensitivity and specificity were 85.7% (95% CI: 67.3-96%) and 70.6% (95% CI: 44-89.7%), respectively. The AUC of the SIindex was 0.870 (0.766-0.973). ICC and Bland-Altman plots show excellent agreement of the tumour fat fraction and SIindex measurement between the two observers. Intracellular lipid content analysis using the 3D Dixon technique can help to differentiate clear-cell from non-clear-cell RCCs.

Fat Shadows from DEXA for Documentation of Fat Distribution in Patients with Lipodystrophy

Lipodystrophy (LD) syndromes are a heterogeneous group of disorders causing atypical diabetes, associated with selective absence of fat with diagnosis mostly depending on the clinical acumen of the physician. With niche therapies either approved or under investigation, development of objective diagnostic tools for these syndromes are urgently needed. Here we describe a new method using the built-in features of the enCore software v14.10 to render out non-fat tissues from Dual Energy X-ray Absorptiometry (DEXA) scans to derive a “fat-shadow” (Figure). We evaluated fat-shadows from 58 LD (50F:8M) patients and 91 non-LD patients (51F:40M). Among the LD, 3 had Generalized LD, 2 had Acquired Partial LD, and 53 had Familial Partial LD. Controls consisted of a mixed population of lean (12F:14M) or obese patients (39F:26M) with or without metabolic disease. There was substantial overlap in % body fat between the LD and non-LD groups (interquartile range: total, 22.2-39.8% vs. 33.6-45.9%; trunk, 27.0-46.8% vs. 39.1-50.2%; legs, 16.6-30.6% vs. 27.7-42.6%). However, fat-shadows obtained from patients with LD stood out due to the paucity of fat signal either in a generalized or regional manner compared to controls. Overall, fat-shadows provided sufficient qualitative information to infer clinical phenotype. We propose that these fat-shadows could be used for accurate documentation of fat distribution in LD. Disclosure R. Meral: None. B.J. Ryan: None. J.F. Horowitz: None. E.A. Oral: Advisory Panel; Self; Aegerion Pharmaceuticals. Research Support; Self; Aegerion Pharmaceuticals, Akcea Therapeutics. Advisory Panel; Self; Akcea Therapeutics. Research Support; Self; Ionis Pharmaceuticals, Inc., AstraZeneca. Other Relationship; Self; Aegerion Pharmaceuticals.

T2-hypointense rim of breast mass lesions on magnetic resonance images: Radiologic-pathologic correlation

We investigated the radiologic-pathologic correlation of a strong hypointense rim on T2-weighted images (T2-hypo-rim) surrounding breast mass lesions and evaluated its clinical significance. We retrospectively reviewed 3503 consecutive breast magnetic resonance imaging (MRI) examinations. The T2-hypo-rim was defined as a border of strong hypointensity compared with the fat signal on fat-suppressed T2-weighted images. Detected lesions with T2-hypo-rim were classified as a solid or cystic mass with MRI and correlated with histopathologic findings. Sixty-two masses (2%; 34 solid, 28 cystic) with T2-hypo-rim were detected [44 breast cancers, 18 benign lesions, including 15 (24%) papillary tumors]. Patients with cancer were significantly older than those with benign lesions (P=.002). Breast cancers were significantly larger than benign masses (P=.023). In 49 of 62 lesions (24 solid and 16 cystic cancers; three solid and six cystic benign masses), the rims were accurately correlated with the histopathologic findings. All malignant and benign cystic masses exhibited hemosiderin deposits in the cyst walls. However, 22 of 24 solid cancers and no solid benign masses exhibited hemosiderin at the tumor periphery (92% and 0%, respectively, P<.001). In addition, a thick fibrous capsule was present in nine (38%) of 24 solid cancers and none of the solid benign lesions. Strong T2-hypo-rims mostly correlated with hemosiderin deposits and/or sometimes fibrous capsules. Although the rims could not distinguish malignant from benign cystic lesions, they indicated malignancy in solid mass lesions on MRI. Additionally, the rims often indicated papillary tumors.

Methodological considerations in region of interest definitions for paraspinal muscles in axial MRIs of the lumbar spine

BackgroundMagnetic Resonance Imaging (MRI) is commonly used to assess the health of the lumbar spine and supporting structures. Studies have suggested that fatty infiltration of the posterior lumbar muscles is important in predicting responses to treatment for low back pain. However, methodological differences exist in defining the region of interest (ROI) of a muscle, which limits the ability to compare data between studies. The purpose of this study was to determine reliability and systematic differences within and between two commonly utilized methodologies for ROI definitions of lumbar paraspinal muscle.MethodsT2-weighted MRIs of the mid-L4 vertebrae from 37 patients with low back pain who were scheduled for lumbar spine surgery were included from a hospital database. Fatty infiltration for these patients ranged from low to high, based on Kjaer criteria. Two methods were used to define ROI: 1) segmentation of the multifidus and erector spinae based on fascial planes including epimuscular fat, and 2) segmentation of the multifidus and erector spinae based on visible muscle boundaries, which did not include epimuscular fat. Total cross sectional area (tCSA), fat signal fraction (FSF), muscle cross sectional area, and fat cross sectional area were measured. Degree of agreement between raters for each parameter was assessed using intra-class correlation coefficients (ICC) and area fraction of overlapping voxels.ResultsExcellent inter-rater agreement (ICC > 0.75) was observed for all measures for both methods. There was no significant difference between area fraction overlap of ROIs between methods. Method 1 demonstrated a greater tCSA for both the erector spinae (14–15%, p < 0.001) and multifidus (4%, p < 0.016) but a greater FSF only for the erector spinae (11–13%, p < 0.001).ConclusionThe two methods of defining lumbar spine muscle ROIs demonstrated excellent inter-rater reliability, although significant differences exist as method 1 showed larger CSA and FSF values compared to method 2. The results of this study confirm the validity of using either method to measure lumbar paraspinal musculature, and that method should be selected based on the primary outcome variables of interest.

MRI Detection of Intratumoral Fat in Colorectal Liver Metastases After Preoperative Chemotherapy.

The objective of this study was to investigate the incidence and clinical significance of intratumoral fat deposition in colorectal liver metastases (CLMs) after preoperative chemotherapy using dual-echo gradient-recalled echo MRI. Our institutional review board approved this retrospective radiographic study and waived the requirement for informed patient consent. Fifty-nine patients (33 men, 26 women; median age, 62 years old) who underwent preoperative MRI and curative hepatic resection for colorectal liver metastases after chemotherapy were selected. Twenty patients also underwent MRI before chemotherapy. On dual-echo gradient-recalled echo MR images, intratumoral fat deposition and fat signal fraction at the densest areas of fat deposition in colorectal liver metastases were evaluated. Predictors of overall survival and intratumoral fat deposition after chemotherapy were identified by multivariate analyses. Before and after chemotherapy, 0 (0%) and 32 (54%) of the patients exhibited intratumoral fat deposition, respectively. Independent predictors of poor overall survival were presence of five or more CLMs (p < 0.001), fat signal fraction of 12% or more (p = 0.01), age of 65 years or older (p = 0.02), and tumor response classified as progressive or stable disease by the Response Evaluation Criteria in Solid Tumors 1.1 (p = 0.049). Predictors of tumor fat signal fraction being 12% or greater after chemotherapy were largest tumor size of 5 cm or more (p = 0.005), tumor calcification (p = 0.008), and history of cetuximab or panitumumab administration (p = 0.04). CLMs after preoperative chemotherapy frequently exhibit intratumoral fat deposition.

Molecular In Vivo Imaging of Bone Marrow Adipose Tissue

The in vivo study of molecular processes in human bone marrow is important for both diagnostics and understanding of disease pathophysiology. Traditionally, the hematopoietic component of the bone marrow has been a research focus, but recently, the role of bone marrow adipose tissue has been gaining interest in many applications. The purpose of the present review is to give an overview of existing imaging modalities allowing in vivo molecular imaging of bone marrow adipose tissue in humans with an emphasis on technical aspects: the characteristics of the extracted parameters and their application in bone marrow adipose tissue. Magnetic resonance (MR) imaging (MRI) and spectroscopy (MRS) are the most frequently used imaging methods for the examination of bone marrow adipose tissue as they provide rich soft tissue contrast and come without ionizing radiation. Existing MR methods allow the extraction of many different measures including proton density fat fraction, fatty acid characteristics, and diffusion and perfusion properties. However, many available techniques have to be carefully adjusted to be used in the investigation of the fat signal component, especially in the presence of trabecular bone. Dual-energy computed tomography (DECT) is an emerging technique—not yet widely available—which appears to be a promising alternative to MR for rapid fat fraction assessment. Positron emission tomography (PET) allows additional functional metabolic imaging and therefore provides valuable additional information (e.g., glucose uptake) to MR-based parameters at the cost of ionizing radiation. Bone marrow imaging still appears to be a niche with remaining technical challenges using existing imaging modalities. A good working knowledge of the underlying physical and technical principles is required as most techniques are yet not available out of the box and may need to be adjusted to fit the requirements for bone marrow adipose tissue imaging. In summary, MR, DECT, and PET enable the measurement of several inherently different parameters in in vivo molecular imaging of bone marrow adipose tissue. The growing interest for molecular imaging markers of bone marrow, thanks to its high metabolic and clinical significance, may eventually lead to new developments, as well as improvements of emerging techniques as soon as they become more broadly available.

Is a single-level measurement of paraspinal muscle fat infiltration and cross-sectional area representative of the entire lumbar spine?

Lumbar paraspinal muscle morphology has recently been evaluated in several studies with conflicting results. Several studies have performed single-slice evaluations of paraspinal muscle morphology, whereas other studies have done a multi-level assessment; this methodological difference might explain the observed different results. Our study evaluated if a single-slice axial measurement is representative of the entire lumbar musculature. We included 80 adult patients who were consecutively evaluated with magnetic resonance imaging (MRI) for spinal symptoms. Using T2-weighted axial images, we measured the fat signal fractions (FSF) and cross-sectional area (CSA) of the erector spinae and multifidus at the five levels of the lumbar spine (from L1-L2 to L5-S1). We used the ANOVA test for repeated measurements (with Bonferroni correction) to compare the FSF and CSA among the levels. Erector spinae showed an increasing FSF from L1-L2 to L5-S1; all erector spinae FSF comparisons among the different levels were significantly different. Multifidus FSF also increased caudally below L2-L3, although significant differences were observed only with two or more levels of distance. The CSA of the erector spinae showed a caudal decrease (L4-L5 and L5-S1 being significantly smaller than all the levels above). The CSA of the multifidus showed that all levels exhibited a significantly different area compared to their adjacent level (except L5-S1 compared to L4-L5). No single-level FSF or CSA is representative of the whole lumbar spine. A standardized multi-level evaluation of the paraspinal musculature should be used in future research.