Quantitative susceptibility mapping (QSM) has enabled magnetic resonance imaging (MRI) of tissue magnetic susceptibility to advance from simple qualitative detection of hypointense blooming artifacts ...to precise quantitative measurement of spatial biodistributions. QSM technology may be regarded to be sufficiently developed and validated to warrant wide dissemination for clinical applications of imaging isotropic susceptibility, which is dominated by metals in tissue, including iron and calcium. These biometals are highly regulated as vital participants in normal cellular biochemistry, and their dysregulations are manifested in a variety of pathologic processes. Therefore, QSM can be used to assess important tissue functions and disease. To facilitate QSM clinical translation, this review aims to organize pertinent information for implementing a robust automated QSM technique in routine MRI practice and to summarize available knowledge on diseases for which QSM can be used to improve patient care. In brief, QSM can be generated with postprocessing whenever gradient echo MRI is performed. QSM can be useful for diseases that involve neurodegeneration, inflammation, hemorrhage, abnormal oxygen consumption, substantial alterations in highly paramagnetic cellular iron, bone mineralization, or pathologic calcification; and for all disorders in which MRI diagnosis or surveillance requires contrast agent injection. Clinicians may consider integrating QSM into their routine imaging practices by including gradient echo sequences in all relevant MRI protocols.
Level of Evidence: 1
Technical Efficacy: Stage 5
J. Magn. Reson. Imaging 2017;46:951–971.
Purpose
To assess the reproducibility of brain quantitative susceptibility mapping (QSM) in healthy subjects and in patients with multiple sclerosis (MS) on 1.5 and 3T scanners from two vendors.
...Materials and Methods
Ten healthy volunteers and 10 patients were scanned twice on a 3T scanner from one vendor. The healthy volunteers were also scanned on a 1.5T scanner from the same vendor and on a 3T scanner from a second vendor. Similar imaging parameters were used for all scans. QSM images were reconstructed using a recently developed nonlinear morphology‐enabled dipole inversion (MEDI) algorithm with L1 regularization. Region‐of‐interest (ROI) measurements were obtained for 20 major brain structures. Reproducibility was evaluated with voxel‐wise and ROI‐based Bland–Altman plots and linear correlation analysis.
Results
ROI‐based QSM measurements showed excellent correlation between all repeated scans (correlation coefficient R ≥ 0.97), with a mean difference of less than 1.24 ppb (healthy subjects) and 4.15 ppb (patients), and 95% limits of agreements of within −25.5 to 25.0 ppb (healthy subjects) and −35.8 to 27.6 ppb (patients). Voxel‐based QSM measurements had a good correlation (0.64 ≤ R ≤ 0.88) and limits of agreements of −60 to 60 ppb or less.
Conclusion
Brain QSM measurements have good interscanner and same‐scanner reproducibility for healthy and MS subjects, respectively, on the systems evaluated in this study. J. MAGN. RESON. IMAGING 2015;42:1592–1600.
•A new framework, LARO, is introduced to accelerate multi-echo gradient echo (mGRE) sequence for quantitative susceptibility mapping.•LARO optimizes a Cartesian multi-echo k-space sampling pattern ...with a deep reconstruction network.•The optimized sampling pattern is implemented in an mGRE sequence for prospective scans.•LARO uses a recurrent temporal feature fusion module to capture signal redundancies along echoes.•LARO is robust with new pathologies and different sequence parameters in the test dataset.
Quantitative susceptibility mapping (QSM) involves acquisition and reconstruction of a series of images at multi-echo time points to estimate tissue field, which prolongs scan time and requires specific reconstruction technique. In this paper, we present our new framework, called Learned Acquisition and Reconstruction Optimization (LARO), which aims to accelerate the multi-echo gradient echo (mGRE) pulse sequence for QSM. Our approach involves optimizing a Cartesian multi-echo k-space sampling pattern with a deep reconstruction network. Next, this optimized sampling pattern was implemented in an mGRE sequence using Cartesian fan-beam k-space segmenting and ordering for prospective scans. Furthermore, we propose to insert a recurrent temporal feature fusion module into the reconstruction network to capture signal redundancies along echo time. Our ablation studies show that both the optimized sampling pattern and proposed reconstruction strategy help improve the quality of the multi-echo image reconstructions. Generalization experiments show that LARO is robust on the test data with new pathologies and different sequence parameters. Our code is available at https://github.com/Jinwei1209/LARO-QSM.git.
Purpose
To investigate the magnetic susceptibility of intracerebral hemorrhages (ICH) at various stages by applying quantitative susceptibility mapping (QSM).
Materials and Methods
Blood ...susceptibility was measured serially using QSM after venous blood withdrawal from healthy subjects. Forty‐two patients who provided written consent were recruited in this Institutional Review Board‐approved study. Gradient echo magnetic resonance imaging (MRI) data of the 42 patients (17 females; 64 ± 12 years) with ICH were processed with QSM. The susceptibilities of various blood products within hematomas were measured on QSM.
Results
Blood susceptibility continually increased and reached a plateau 96 hours after venous blood withdrawal. Hematomas at all stages were consistently hyperintense on QSM. Susceptibility was 0.57 ± 0.48, 1.30 ± 0.33, 1.14 ± 0.46, 0.40 ± 0.13, and 0.71 ± 0.31 ppm for hyperacute, acute, early subacute, late subacute, and chronic stages of hematomas, respectively. The susceptibility decrease from early subacute (1.14 ppm) to late subacute (0.4 ppm) was significant (P < 0.01).
Conclusion
QSM reveals positive susceptibility in hyperacute hematomas, indicating that even at their hyperacute stage, deoxyhemoglobin may exist throughout the hematoma volume, not just at its rim, as seen on conventional
T2* imaging. QSM also reveals a reduction of susceptibility from early subacute to late subacute ICH, suggesting that methemoglobin concentration decreases at the late subacute stage. J. Magn. Reson. Imaging 2016;44:420–425.
Objectives
Texture analysis performed on MRI images can provide additional quantitative information that is invisible to human assessment. This study aimed to evaluate the feasibility of texture ...analysis on preoperative conventional MRI images in predicting early malignant transformation from low- to high-grade glioma and compare its utility to histogram analysis alone.
Methods
A total of 68 patients with low-grade glioma (LGG) were included in this study, 15 of which showed malignant transformation. Patients were randomly divided into training (60%) and testing (40%) sets. Texture analyses were performed to obtain the most discriminant factor (MDF) values for both training and testing data. Receiver operating characteristic (ROC) curve analyses were performed on MDF values and 9 histogram parameters in the training data to obtain cutoff values for determining the correct rates of discrimination between two groups in the testing data.
Results
The ROC analyses on MDF values resulted in an area under the curve (AUC) of 0.90 (sensitivity 85%, specificity 84%) for T2w FLAIR, 0.92 (86%, 94%) for ADC, 0.96 (97%, 84%) for T1w, and 0.82 (78%, 75%) for T1w + Gd and correctly discriminated between the two groups in 93%, 100%, 93%, and 92% of cases in testing data, respectively. In the astrocytoma subgroup, AUCs were 0.92 (88%, 83%) for T2w FLAIR and 0.90 (92%, 74%) for T1w + Gd and correctly discriminated two groups in 100% and 92% of cases. The MDF outperformed all 9 of the histogram parameters.
Conclusion
Texture analysis on conventional preoperative MRI images can accurately predict early malignant transformation of LGGs, which may guide therapeutic planning.
Key Points
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Texture analysis performed on MRI images can provide additional quantitative information that is invisible to human assessment.
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Texture analysis based on conventional preoperative MR images can accurately predict early malignant transformation from low- to high-grade glioma.
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Texture analysis is a clinically feasible technique that may provide an alternative and effective way of determining the likelihood of early malignant transformation and help guide therapeutic decisions.
Advances in metabolic imaging techniques have allowed for more precise characterization of gliomas, particularly as it relates to tumor recurrence or pseudoprogression. Furthermore, the emerging ...field of radiogenomics where radiographic features are systemically correlated with molecular markers has the potential to achieve the holy grail of neuro-oncologic neuro-radiology, namely molecular diagnosis without requiring tissue specimens. In this section, we will review the utility of metabolic imaging and discuss the current state of the art related to the radiogenomics of glioblastoma.
The purposes of this study were to visualize the human median nerve on diffusion tensor imaging and to determine the normal fractional anisotropy (FA) value and apparent diffusion coefficient (ADC) ...of the normal median nerve.
The wrists of 20 healthy volunteers and of two patients with carpel tunnel syndrome were examined with a 3-T MRI system with a standard eight-channel sensitivity-encoding head coil. Diffusion tensor imaging was performed with a spin-echo echo-planar sequence. A T1-weighted sequence was performed for anatomic reference. After tractography, the FA value and ADC of the whole nerve were calculated automatically. Manual focal measurements also were obtained at the levels of the flexor retinaculum, wrist, and forearm.
We visualized the median nerve with MR diffusion tensor tractography and followed the nerve for approximately 77.5 mm. We found the normative diffusion values of the median nerve were an FA of 0.709 +/- 0.046 (SD) and an ADC of 1.016 +/- 0.129 x 10(-3) mm2/s. There was a statistically significant difference between the FA values obtained at the level of the flexor retinaculum and the values obtained from the other parts of the median nerve (p < 0.0001). We found a decrease in FA value (p < 0.01) and an increase in ADC (p < 0.05) with advancing age.
The normative diffusion values of the human median nerve can be used as a reference in evaluation, diagnosis, and follow-up of entrapment, trauma, and regeneration of the median nerve.
Patients with glioblastoma multiforme (GBM) face a dismal prognosis, with an average survival of 6-7 months after recurrence. There remains no consensus for managing these patients due to the ...heterogeneity of these tumors. Imaging may affect treatment decisions by helping to stratify patient prognosis. The purpose of this analysis was to evaluate the added utility of 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) over magnetic resonance (MR) imaging metrics in predicting survival.
Forty-four consecutive patients who underwent FDG-PET for first recurrence of GBM were included in this analysis. Tumor sizes, using cross products, and volumes on FDG-PET and MRI, maximum standardized uptake value (SUV), minimum apparent diffusion coefficient (ADC) value, presence of satellite lesions, presence of multifocal lesions, and presence of bilateral tumor were considered as prognostic variables. Survival was assessed using Cox hazard and logistic regression models based on the time interval between the PET scan and the patient's date of death.
Tumor volumes on FDG-PET (P = .046), tumor cross products on FDG-PET (P = .017), and tumor cross products on MRI (P = .031) were significant prognostic variables, adjusting for the extent of the initial resection. Enhancing tumor volume, tumor cross product on a T2-weighted MRI sequence, maximum SUV on FDG-PET, minimum ADC value, presence of satellites, multifocality, and bilaterality were not prognostic (P > .5). Prognostic accuracy of predicting short survival increased from 58% with tumor cross product on MRI alone to 74% after including tumor cross product from PET.
Tumor size on FDG-PET adds prognostic information to enhancing tumor size on MRI at first suspected recurrence of GBM.
Adaptive Total Field Inversion is described for quantitative susceptibility mapping (QSM) reconstruction from total field data through a spatially adaptive suppression of shadow artifacts through ...spatially adaptive regularization. The regularization for shadow suppression consists of penalizing low-frequency components of susceptibility in regions of small susceptibility contrasts as estimated by R2∗ derived signal intensity. Compared with a conventional local field method and two previously proposed regularized total field inversion methods, improvements were demonstrated in phantoms and subjects without and with hemorrhages. This algorithm, named TFIR, demonstrates the lowest error in numerical and gadolinium phantom datasets. In COSMOS data, TFIR performs well in matching ground truth in high-susceptibility regions. For patient data, TFIR comes close to meeting the quality of the reference local field method and outperforms other total field techniques in both clinical scores and shadow reduction.
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•TFIR's adaptive regularization obtains magnetic susceptibility from magnetic field•TFIR has low artifact incidence on both quantitative and clinical scores•The error for TFIR is low on various numerical and ground truth tests•Clinical applications for TFIR include hemorrhages and whole head mapping
Nuclear Magnetic Resonance; Magnetism; Physics Magnetic Resonance Imaging; Algorithms
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