Conventional GRE Research Articles

Application of the magnetic resonance 3D multiecho Dixon sequence for quantifying hepatic iron overload and steatosis in patients with thalassemia

ObjectiveTo investigate the feasibility and diagnostic efficacy of a 3D multiecho Dixon (qDixon) research application for simultaneously quantifying the liver iron concentration (LIC) and steatosis in thalassemia patients. Materials and methodsThis prospective study enrolled participants with thalassemia who underwent 3 T MRI of the liver for the evaluation of hepatic iron overload. The imaging protocol including qDixon and conventional T2* mapping based on 2D multiecho gradient echo (ME GRE) sequences respectively. Regions of interest (ROIs) were drawn in the liver on the qDixon maps to obtain R2* and proton density fat fraction (PDFF). The reference R2* value was measured and calculated on conventional T2* mapping using the CMRtools software. Correlation analysis, Linear regression analysis, and Bland–Altman analysis were performed. Results84 patients were finally included in this study. The median R2*-ME-GRE was 366.97 (1/s), range [206.68 (1/s), 522.20 (1/s)]. 8 patients had normal hepatic iron deposition, 16 had Insignificant, 42 had mild, 18 had moderate. The median of R2*-qDixon was 376.88 (1/s) [219.33 (1/s), 491.75 (1/s)]. A strong correlation was found between the liver R2*-qDixon and the R2*-ME-GRE (r = 0.959, P < 0.001). The median value of PDFF was 1.76% (1.10%, 2.95%). 8 patients had mild fatty liver, and 1 had severe fatty liver. ConclusionMR qDixon research sequence can rapidly and accurately quantify liver iron overload, that highly consistent with the measured via conventional GRE sequence, and it can also simultaneously detect hepatic steatosis, this has great potential for clinical evaluation of thalassemia patients.

Super-resolution QSM in little or no additional time for imaging (NATIve) using 2D EPI imaging in 3 orthogonal planes

Quantitative Susceptibility Mapping has the potential to provide additional insights into neurological diseases but is typically based on a quite long (5–10 min) 3D gradient-echo scan which is highly sensitive to motion. We propose an ultra-fast acquisition based on three orthogonal (sagittal, coronal and axial) 2D simultaneous multi-slice EPI scans with 1 mm in-plane resolution and 3 mm thick slices. Images in each orientation are corrected for susceptibility-related distortions and co-registered with an iterative non-linear Minimum Deformation Averaging (Volgenmodel) approach to generate a high SNR, super-resolution data set with an isotropic resolution of close to 1 mm. The net acquisition time is 3 times the volume acquisition time of EPI or about 12 s, but the three volumes could also replace “dummy scans” in fMRI, making it feasible to acquire QSM in little or No Additional Time for Imaging (NATIve). NATIve QSM values agreed well with reference 3D GRE QSM in the basal ganglia in healthy subjects. In patients with multiple sclerosis, there was also a good agreement between the susceptibility values within lesions and control ROIs and all lesions which could be seen on 3D GRE QSMs could also be visualized on NATIve QSMs. The approach is faster than conventional 3D GRE by a factor of 25–50 and faster than 3D EPI by a factor of 3–5. As a 2D technique, NATIve QSM was shown to be much more robust to motion than the 3D GRE and 3D EPI, opening up the possibility of studying neurological diseases involving iron accumulation and demyelination in patients who find it difficult to lie still for long enough to acquire QSM data with conventional methods.

Thermo-mechanical characterization of sea water immersed GO based GRE hybrid composite

The present work is aimed to investigate the durability of graphene oxide (GO) dispersed GFRP hybrid polymer composite subject to exposure in natural sea water for 4 weeks. Conventional GFRP and GO (0.5 wt%) based GFRP were fabricated by taking 12 layers of woven E-glass fibre as reinforcement and epoxy thermosetting polymer as matrix. GO was synthesized in laboratory by modified Hummer’s method. Synthesis of GO was confirmed through XRD and Raman spectroscopy. Short beam shear (SBS) specimens of all types (both conventional and hybrid) of as-cured composites in desired dimension were immersed in natural sea water for various lengths of duration (maximum up to 4 weeks). All the sea water treated composite samples were characterized through 3-point bend test to reveal inter laminar shear strength (ILSS). About 35 % decrease in ILSS was reported for conventional GRE composite after 4 week of sea water immersion. Decrease in ILSS for GO reinforced GFRP composite was found to be 24.8 %, which is lesser than that compared to conventional GFRP composite. Low temperature Differential scanning calorimetry (DSC) test was conducted to access the glass transition temperature (Tg) of sea water immersed composite samples. After 4 weeks of sea water immersion, conventional GRE and GO-GRE composite exhibited 16% and 15.2% of decrease in Tg. Mechanism of bonding across fibre–matrix interface embedded with GO filler was investigated through the fractographic images, as obtained by scanning electron microscope (SEM).

Differentiation of Pulmonary Lymphoma Manifestations and Nonlymphoma Infiltrates in Possible Invasive Fungal Disease Using Fast T1-weighted Magnetic Resonance Imaging at 3 T Comparison of Texture Analysis, Mapping, and Signal Intensity Quotients.

This study aimed to evaluate the diagnostic performance of texture analysis (TA), T1 mapping, and signal intensity quotients derived from fast T1-weighted gradient echo (T1w GRE) sequences for differentiating pulmonary lymphoma manifestations and nonlymphoma infiltrates in possible invasive fungal disease in immunocompromised hematological patients. Twenty patients with hematologic malignancies and concomitant immunosuppression (including 10 patients with pulmonary lymphoma manifestations and 10 patients with nonlymphoma infiltrates) prospectively underwent 3 T magnetic resonance imaging using a conventional T1w GRE sequence and a T1w GRE mapping sequence with variable flip angle. A region of interest was placed around the most representative lesion in each patient. TA was performed using PyRadiomics. T1 relaxation times were extracted from precompiled maps and calculated manually. Signal intensity quotients (lesion/muscle) were calculated from conventional T1w GRE sequences. Of all TA features, variance, mean absolute deviation, robust mean absolute deviation, interquartile range, and minimum were significantly different between the 2 entities (P<0.05), with excellent diagnostic performance in receiver operating characteristic analysis (area under the curve [AUC] >80%). Neither T1 relaxation times from precompiled maps (AUC=63%; P=0.353) nor manual calculation (AUC=63%; P=0.353) nor signal intensity quotients (AUC=70%; P=0.143) yielded significant differences. TA from fast T1w GRE images can differentiate pulmonary lymphoma manifestations and nonlymphoma infiltrates in possible invasive fungal disease with excellent diagnostic performance using the TA features variance, mean absolute deviation, robust mean absolute deviation, interquartile range, and minimum. Combining a fast T1w GRE sequence with TA seems to be a promising tool to differentiate these 2 entities noninvasively.

Comparative study between black blood T2∗ and conventional bright GRE sequences in assessment of myocardial iron concentration

PurposeTo compare the efficacy and reproducibility of black blood T2∗ to the conventional bright blood sequence in the assessment of myocardial iron concentration. Materials and methodsWe performed both conventional bright blood and black blood MRI T2∗ sequences in 50 thalassemia major patients, the results were statistically analyzed to assess the correlation of techniques, study reproducibility and interobserver agreement. ResultsCardiac T2∗ values ranged from 2.39 to 47.9ms using bright blood sequence and 2.07 to 46.81 using the black blood sequence. There was positive significant correlation of both sequences in all patients. However the black blood technique was superior to bright blood technique as regards the study reproducibility (R2∗1.9± versus 2.4±14.7 p<0.001) in addition to the better inter-observer agreement of black blood technique compared to the bright blood technique (3.2±1.2 versus 8.3±2.4 p<0.001). ConclusionsBlack blood T2∗ technique provides clearly defined septal borders, avoids bright blood signal contamination of the myocardium, has superior study reproducibility and inter-observer agreement which favors this technique in the assessment of iron myocardial concentration.

The do’s and dont’s of liver CT and MR imaging

Contrast enhanced multi-detector CT (MD CT) is now the most commonly used imaging modality for detection of liver metastases and work-up of equivocal lesions found at ultrasound. MR imaging is an established technique for non-invasive characterisation of liver masses and for preoperative potentially resectable liver tumours. Diagnostic value of each modality strongly depends on the scan technique. With MDCT, the role of thin slice imaging has been well established, with slice thicknesses of 5–7.5 mm being inferior to thinner slices in terms of lesion detection [1]. The amount of contrast material as well as the flow rate influence enhancement of hypervascular lesions in the arterial phase and the magnitude of liver parenchyma enhancement in the venous phase, respectively [2,3]. The number of CT scans varies with the local indication, with single-phasic venous scans to 4-phasic scans, as recommended by European and US guidelines for HCC detection and characterisation. For MR imaging, a multi-point DIXON technique has replaced conventional T1-weighted GRE pulse sequences; with this technique in one breathhold in-phase, opposed-phase, fat-suppressed, and water-suppressed images can be obtained, without any spatial misregistration. Diffusion-weighted pulse sequences significantly improve detection of metastases [4,5]. As a black-blood technique with T2-weighted image impression, it demonstrates small lesions without any blurring by an adjacent high signal intensity of vessels of bile ducts [6]. Administration of contrast agents is mandatory for liver MRI, with the choice of either non-specific gadolinium chelates or liver specific contrast agents. Indications for liver-specific contrast agents include preoperative evaluation of liver metastases and characterisation of hepatocellular lesions (FNH, adenoma), whereas non-specific gadolinium chelates are used for characterisation of haemangiomas, after liver resection or tumour ablation. The choice of the imaging techniques and the scan or contrast agent protocol should be tailored according to the clinical question.

Respiratory self-gating for free-breathing magnetization transfer MRI of the abdomen.

Magnetization transfer (MT) MRI can be effective for the diagnosis of a broad range of fibrotic diseases, including liver fibrosis. However, respiratory motion, a major source of artifacts in thoracic and abdominal MR imaging, can obscure important anatomic structures, making diagnosis difficult. In this study, we explored the potential to combine free-breathing (FB) respiratory self-gating (RSG) methods with MT saturation for FB MT ratio (MTR) measurements of abdominal organs. A respiratory self-gated multiple-gradient recalled echo sequence with MT presaturation (RSG-MT GRE) was developed and applied in a series of seven normal volunteers. We compared the MTR values of liver, pancreas, kidney, spleen, and posterior paraspinal muscle measured using our RSG-MT GRE sequence and a conventional MT GRE sequence. RSG consistently reduced motion artifacts within MT-weighted images acquired during FB, improved the accuracy of FB MTR measurements, and produced comparable MTRs to breath-holding MTR measurements. RSG approaches may offer to improve the utility of MT-weighted imaging methods for the assessment of fibrotic diseases and tumor desmoplasia in abdominal organs.

MRI diffusion-weighted imaging in intracranial hemorrhage (ICH)

PurposeTo assess the role of MRI DWI in detection and characterization of ICH. Patients and methods61 patients with intracranial hemorrhage who underwent MRI (including DWI, ADC, and GRE) and CT were retrospectively included in this study. MRI DWIs were analyzed for age, type, (primary parenchymal hemorrhage or hemorrhagic lesion) and location of the hemorrhage. The results were compared with conventional MRI sequences, GRE, and CT to assess the diagnostic accuracy of DWI in assessment of patients with intracranial hematoma. ResultsWe had 61 patients with intracranial hemorrhage, six cases were missed by DWI. MRI DWI was accurate for the detection of hyperacute, medium, large sized acute, early and late sub acute, subdural, hemorrhagic components of arterial and venous infarction, intraventricular hemorrhage. DWI showed low sensitivity in detection of subarachnoid and small intraparenchymal hemorrhage The ADC measurements in hyperacute, acute, early and late subacute hematoma were statistically equivalent and were significantly less than the late subacute hematoma as well as the contralateral white matter. ConclusionMRI DWI was accurate in detection, characterization and staging hyperacute, acute, subacute hemorrhage as well as hemorrhagic components of arterial and venous infarctions and of low diagnostic accuracy in subarachnoid and small parenchymal hemorrhage.

The value of T2*-weighted gradient echo imaging for detection of familial cerebral cavernous malformation: A study of two families

The aim of this study was to investigate the value of T2*-weighted gradient echo imaging (GRE T2*-WI) for the detection of familial cerebral cavernous malformation (FCCM). Twenty-six members of 2 families with FCCM were examined using computed tomography (CT), conventional magnetic resonance imaging (MRI) and GRE T2*-WI sequences. We identified 12 cases of FCCM using GRE T2*-WI sequences. These 12 patients had multiple lesions (mean 23). The lesions were most commonly located in the ganglia. Other areas included the cortex-subcortex, thalamus, cerebellum and brainstem. These lesions appeared as a reticulated core of mixed signal intensity with a surrounding rim of decreased signal intensity representing hemosiderin from previous hemorrhages. The mean numbers of lesions and cases of FCCM identified by various conventional MRI sequences were 5–17 and 3–9, respectively. Conventional MRI examination involved T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), T2-fluid-attenuated inversion recovery (T2Flair), diffusion-weighted imaging (DWI) and spin-echo imaging (SE) sequences, in that order. The numbers of lesions identified by MRI were fewer than those identified by GRE T2*-WI. CT only identified 3 cases with large lesions combined with hemorrhage and calcification. These findings suggest that GRE T2*-WI is the first choice when diagnosing FCCM compared with CT and conventional MRI.

Inflow effects on functional MRI

Blood inflow from the upstream has contribution or contamination to the blood oxygen level-dependent (BOLD) functional signal both in its magnitude and time courses. During neuronal activations, regional blood flow velocity increases which results in increased fMRI signals near the macrovasculatures. The inflow effects are dependent on RF pulse history, slice geometry, flow velocity, blood relaxation times and imaging parameters. In general, the effect is stronger with more T(1) weighting in the signal, e.g. by using a short repetition time and a large flip angle. This article reviews the basic principle of the inflow effects, its appearances in conventional GRE, fast spin-echo (FSE) and echo-planar imaging (EPI) acquisitions, methods for separating the inflow from the BOLD effect as well as the interplay between imaging parameters and other physiological factors with the inflow effects in fMRI. Based on theoretical derivation and human experiments, the inflow effects have been shown to contribute significantly in conventional GRE but negligible in FSE acquisitions. For gradient-echo EPI experiments, the blood inflow could modulate both amplitude and the temporal information of the fMRI signal, depending on the imaging parameters and settings.

Application and technical analysis of enhanced T*2 star weighted angiography sequence in the detection of hemorrhagic shearing lesions associated with diffuse axonal injury

Objective To compare the efficiency of enhanced T2* weighted angiography (ESWAN) sequence with that of a conventional T2*-weighted gradient-recalled-echo (GRE T2*WI) sequence for the detection of hemorrhagic shearing lesions in patients with diffuse axonal injury (DAI). And combined with MRI parameters, to further discuss the principles and virtues of ESWAN sequence. Methods Seventeen patients with DAI were enrolled in this study. The raw data acquired from ESWAN scan were postprocessed by using the mean square root of multi-echoes. Then, the postprocessed images were compared with the conventional GRE T2* weighted images. The global and regional (superficial, deep and posterior fossa) lesion numbers determined by both sequences were compared by using Wilcoxon signed ranks test (two-tailed). Differences were considered to be significant at P≤0.05. Results Hemorrhagic lesions were more obvious on ESWAN images than those on conventional GRE T2* weighted images. The median and range value of the detected lesion numbers on ESWAN images were 27 and (1-239) in whole brain, 13 and (1-89) in cerebral superficial region, 5 and (0-111) in cerebral deep region and 1 and (0-39) in posterior fossa region, respectively; whereas, on GRE T2* weighted images, they were 7 and (1-34) in whole brain, 5 and (1-27) in cerebral superficial region, 2 and (0-25) in cerebral deep region and 0 and (0-4) in posterior fossa region, respectively. There were significant statistical differences between the two sequences in revealing the lesions in all the four regions (Z=-3.519,-3.182,-3.185,-2.677,P＜0.05). Conclusion In ESWAN sequence, multi-echo acquisition ensured sufficient magnetic susceptibility for detecting small hemorrhagic lesions. So, ESWAN is more sensitive to small hemorrhage, which revealed more hemorrhagic lesions than conventional GRE T2*WI and presented more valuable information for the diagnosis of DAI. Key words: Diffuse axonal injury; Cerebral hemorrhage; Magnetic resonance imaging

Combining complex signal change in functional MRI

With the development of functional magnetic resonance imaging (fMRI) techniques, data analysis methods based on complex MR data have been proposed. However, the methods have not been popular for fMRI community, in part because the phase activation in conventional GRE fMRI has been suggested to originate from the large veins (1). Recently, novel fMRI methods such as transition-band SSFP fMRI and an alternating balanced SSFP method for neuronal current measurement (2) have been proposed. In these methods, the functional contrasts exist in the complex domain, providing significant and localized complex signal change. Hence, the usefulness of the complex-data analysis methods has become increasingly important for these applications by allowing them to reliably obtain complex activation. As mentioned in his letter, Dr. Rowe has proposed a complex-data analysis method based on the generalized likelihood ratio test (3). Despite the usefulness of the method, the computational complexity of the method, which requires multiple iterations to estimate the parameters, hampers the routine use of the method. This is particularly true for high-resolution studies that we targeted in our study. To overcome this inefficiency, we have proposed a new method based on T 2 statistics combined with generalized linear model (4). Dr. Rowe’s letter expressed concerns about the relationship of our model to his model and some mathematical errors. Here we present our responses to his points:

Preoperative fast MRI of brain tumors using three-dimensional segmented echo planar imaging compared to three-dimensional gradient echo technique

The purpose of this study was to compare the diagnostic efficacy of a newly developed T 1-weighted three-dimensional segmented echo planar imaging (3D EPI) sequence versus a conventional T 1-weighted three dimensional spoiled gradient echo (3D GRE) sequence in the evaluation of brain tumors. Forty-four patients with cerebral tumors and infections were examined on a 1.0 T MR unit with 23 mT/m gradient strength. The total scan time for the T 1 3D EPI sequence was 2 min 12 s, and for a conventional 3D GRE sequence it was 4 min 59 s. Both sequences were performed after administration of a contrast agent. The images were analyzed by three radiologists. Image assessment criteria included lesion conspicuity, contrast between different types of normal tissue, and image artifacts. In addition, signal-to-noise and contrast-to-noise-ratio (C/N) were calculated. The gray-white differentiation and C/N ratio of 3D EPI were found to be inferior to conventional 3D GRE images, but the difference was not statistically significant. In the qualitative comparison, lesion detection and conspicuity of 3D EPI images and conventional 3D GRE images were similar, but a tow-fold reduction of the scanning time was obtained. With the 3D EPI technique, a 50% scan time reduction could be achieved with acceptable image quality compared to conventional 3D GRE. Thus, the 3D EPI technique could replace conventional 3D GRE in the preoperative imaging of brain.

Analysis of the DNA-binding Site for XenopusGlucocorticoid Receptor Accessory Factor: CRITICAL NUCLEOTIDES FOR BINDING SPECIFICITY IN VITROAND FOR AMPLIFICATION OF STEROID-INDUCED FIBRINOGEN GENE TRANSCRIPTION

In addition to the glucocorticoid receptor, DNA-binding proteins called accessory factors play a role in hormone activation of many glucocorticoid-responsive genes. Hormonal regulation of the gamma-fibrinogen subunit gene from the frog Xenopus laevis requires a novel DNA sequence that binds a liver nuclear protein called Xenopus glucocorticoid receptor accessory factor (XGRAF). Here we demonstrate that the recognition site for XGRAF encompasses GAGTTAA at positions -175 to -169 relative to the start site of transcription. This sequence is not closely related to the binding sites for known transcription factors. The two guanosines make close contact with XGRAF, as shown by the methylation interference assay. Single-point mutagenesis of every nucleotide in the 9-base pair region from positions -177 to -169 showed an excellent correlation between ability to bind XGRAF in vitro and ability to amplify hormone-induced transcription from DNA transfected into Xenopus primary hepatocytes. Conversely, XGRAF had little or no effect on basal transcription of the gamma-fibrinogen gene. Maximal hormonal induction also requires three half-glucocorticoid response elements (half-GREs) homologous to the downstream half of the consensus GRE. Interestingly, the XGRAF-binding site is immediately adjacent to the most important half-GRE. This close proximity suggests a new mechanism for activation of a gene lacking a conventional full GRE.

Clot-Blood Contrast in Fast Gradient-Echo Magnetic Resonance Imaging

Contrast between clot and blood in magnetic resonance imaging (MRI) at 1.5T using fast gradient-echo pulse sequences (fast GRE), with 8 ms < TR < 20 mseconds was studied both in vitro and in clinical human deep venous thrombosis (DVT) to assess whether good contrast could be obtained at such short repetition times and at clinically relevant flow rates. In vitro studies used an apparatus that contained flowing MnCl2[aq] (water adjusted with manganese chloride to have T1, T2 similar to blood) and an immobilized clot (T1, T2 similar to those in DVT) for flow velocities between 0 and 16.5 cm/sec. Seven patients with DVT were imaged with the fast GRE sequences to observe the clot-blood contrast in vivo. Peak contrast-to-noise ratio (CNR) was achieved using flip angles between 20 degrees and 40 degrees (increasing with flow velocity) with or without radiofrequency "spoiling," consistent with a natural spoiling effect of flow. The CNR between MnCI2[aq] and clot decreased less than 10% as TR was reduced 56% from 18 mseconds to 8 mseconds (30 degrees flip angle). In four patients with nonocclusive DVT, fast GRE imaging provided good contrast while in occlusive cases (three patients) the contrast was not as good as conventional GRE sequences with longer TR values (TR = 33 mseconds). A fast GRE sequence with TR = 8 mseconds, TE = 3 mseconds, and a flip angle = 40 degrees is a promising approach to speeding up the detection of nonocclusive clinical DVT.