Showing papers in "Journal of Magnetic Resonance Imaging in 2010"

Adaptive non‐local means denoising of MR images with spatially varying noise levels

Abstract: PURPOSE: To adapt the so-called nonlocal means filter to deal with magnetic resonance (MR) images with spatially varying noise levels (for both Gaussian and Rician distributed noise). MATERIALS AND METHODS: Most filtering techniques assume an equal noise distribution across the image. When this assumption is not met, the resulting filtering becomes suboptimal. This is the case of MR images with spatially varying noise levels, such as those obtained by parallel imaging (sensitivity-encoded), intensity inhomogeneity-corrected images, or surface coil-based acquisitions. We propose a new method where information regarding the local image noise level is used to adjust the amount of denoising strength of the filter. Such information is automatically obtained from the images using a new local noise estimation method. RESULTS: The proposed method was validated and compared with the standard nonlocal means filter on simulated and real MRI data showing an improved performance in all cases. CONCLUSION: The new noise-adaptive method was demonstrated to outperform the standard filter when spatially varying noise is present in the images.

Real-time Diffusion-Perfusion Mismatch Analysis in Acute Stroke

Abstract: Diffusion-perfusion mismatch can be used to identify acute stroke patients that could benefit from reperfusion therapies. Early assessment of the mismatch facilitates necessary diagnosis and treatment decisions in acute stroke. We developed the RApid processing of PerfusIon and Diffusion (RAPID) for unsupervised, fully automated processing of perfusion and diffusion data for the purpose of expedited routine clinical assessment. The RAPID system computes quantitative perfusion maps (cerebral blood volume, CBV; cerebral blood flow, CBF; mean transit time, MTT; and the time until the residue function reaches its peak, T(max)) using deconvolution of tissue and arterial signals. Diffusion-weighted imaging/perfusion-weighted imaging (DWI/PWI) mismatch is automatically determined using infarct core segmentation of ADC maps and perfusion deficits segmented from T(max) maps. The performance of RAPID was evaluated on 63 acute stroke cases, in which diffusion and perfusion lesion volumes were outlined by both a human reader and the RAPID system. The correlation of outlined lesion volumes obtained from both methods was r(2) = 0.99 for DWI and r(2) = 0.96 for PWI. For mismatch identification, RAPID showed 100% sensitivity and 91% specificity. The mismatch information is made available on the hospital's PACS within 5-7 min. Results indicate that the automated system is sufficiently accurate and fast enough to be used for routine care as well as in clinical trials.

Diagnosis of cirrhosis with intravoxel incoherent motion diffusion MRI and dynamic contrast-enhanced MRI alone and in combination: preliminary experience.

Abstract: PURPOSE: To report our preliminary experience with the use of intravoxel incoherent motion (IVIM) diffusion-weighted magnetic resonance imaging (DW-MRI) and dynamic contrast-enhanced (DCE)-MRI alone and in combination for the diagnosis of liver cirrhosis. MATERIALS AND METHODS: Thirty subjects (16 with noncirrhotic liver, 14 with cirrhosis) were prospectively assessed with IVIM DW-MRI (n = 27) and DCE-MRI (n = 20). IVIM parameters included perfusion fraction (PF), pseudodiffusion coefficient (D*), true diffusion coefficient (D), and apparent diffusion coefficient (ADC). Model-free DCE-MR parameters included time to peak (TTP), upslope, and initial area under the curve at 60 seconds (IAUC60). A dual input single compartmental perfusion model yielded arterial flow (Fa), portal venous flow (Fp), arterial fraction (ART), mean transit time (MTT), and distribution volume (DV). The diagnostic performances for diagnosis of cirrhosis were evaluated for each modality alone and in combination using logistic regression and receiver operating characteristic analyses. IVIM and DCE-MR parameters were compared using a generalized estimating equations model. RESULTS: PF, D*, D, and ADC values were significantly lower in cirrhosis (P = 0.0056-0.0377), whereas TTP, DV, and MTT were significantly increased in cirrhosis (P = 0.0006-0.0154). There was no correlation between IVIM- and DCE-MRI parameters. The highest Az (areas under the curves) values were observed for ADC (0.808) and TTP-DV (0.952 for each). The combination of ADC with DV and TTP provided 84.6% sensitivity and 100% specificity for diagnosis of cirrhosis. CONCLUSION: The combination of DW-MRI and DCE-MRI provides an accurate diagnosis of cirrhosis.

Predicting and monitoring cancer treatment response with diffusion‐weighted MRI

Abstract: An imaging biomarker that would provide for an early quantitative metric of clinical treatment response in cancer patients would provide for a paradigm shift in cancer care. Currently, nonimage based clinical outcome metrics include morphology, clinical, and laboratory parameters, however, these are obtained relatively late following treatment. Diffusion-weighted MRI (DW-MRI) holds promise for use as a cancer treatment response biomarker as it is sensitive to macromolecular and microstructural changes which can occur at the cellular level earlier than anatomical changes during therapy. Studies have shown that successful treatment of many tumor types can be detected using DW-MRI as an early increase in the apparent diffusion coefficient (ADC) values. Additionally, low pretreatment ADC values of various tumors are often predictive of better outcome. These capabilities, once validated, could provide for an important opportunity to individualize therapy thereby minimizing unnecessary systemic toxicity associated with ineffective therapies with the additional advantage of improving overall patient health care and associated costs. In this report, we provide a brief technical overview of DW-MRI acquisition protocols, quantitative image analysis approaches and review studies which have implemented DW-MRI for the purpose of early prediction of cancer treatment response.

Fat and water magnetic resonance imaging.

Abstract: A wide variety of fat suppression and water-fat separation methods are used to suppress fat signal and improve visualization of abnormalities. This article reviews the most commonly used techniques for fat suppression and fat-water imaging including 1) chemically selective fat suppression pulses "FAT-SAT"; 2) spatial-spectral pulses (water excitation); 3) short inversion time (TI) inversion recovery (STIR) imaging; 4) chemical shift based water-fat separation methods; and finally 5) fat suppression and balanced steady-state free precession (SSFP) sequences. The basic physical background of these techniques including their specific advantages and disadvantages is given and related to clinical applications. This enables the reader to understand the reasons why some fat suppression methods work better than others in specific clinical settings.

Susceptibility mapping as a means to visualize veins and quantify oxygen saturation

Abstract: Purpose: To create an orientation-independent, 3D reconstruction of the veins in the brain using susceptibility mapping. Materials and Methods: High-resolution, high-pass filtered phase images usually used for susceptibility weighted imaging (SWI) were used as a source for local magnetic field behavior. These images were subsequently postprocessed using an inverse procedure to generate susceptibility maps of the veins. Regularization and interpolation of the data in k-space of the phase images were used to reduce reconstruction artifacts. To understand the effects of artifacts, and to fine-tune the methodology, simulations of blood vessels were performed with and without noise. Results: With sufficient resolution, major veins in the brain could be visualized with this approach. The usual geometry-dependent phase dipole effects are removed by this processing, leaving basically images of the veins. Different sized vessels show a different level of contrast depending on their partial volume effects. Vessels that are 8 mm or 16 mm in size show quantitative values expected for normal oxygen saturation levels. Smaller vessels show smaller values due to errors in the methodology and due to partial volume effects. Larger vessels show a bias toward a reduced susceptibility approaching 90% of the expected value. Limitations of the method and artifacts related to different sources of errors are demonstrated. Conclusion: Susceptibility maps can successfully create venograms of the brain with varying levels of contrast-to-noise depending on the size of the vessel. Partial volume effects render this approach more useful as an imaging tool or a visualization tool, although certain larger vessels have measured susceptibilities close to expected values associated with normal blood oxygen saturation levels. J. Magn. Reson. Imaging 2010;32:663–676. © 2010 Wiley-Liss, Inc.

Reducing the impact of white matter lesions on automated measures of brain gray and white matter volumes.

Abstract: Purpose: To develop an automated lesion-filling technique (LEAP; LEsion Automated Preprocessing) that would reduce lesion-associated brain tissue segmentation bias (which is known to affect automated brain gray [GM] and white matter [WM] tissue segmentations in people who have multiple sclerosis), and a WM lesion simulation tool with which to Lest it.Materials and Methods: Simulated lesions with differing volumes and signal intensities were added to volumetric brain images from three healthy subjects and then automatically filled with values approximating normal WM. We tested the effects of simulated lesions and lesion-filling correction with LEAP on SPM-derived tissue volume estimates.Results: GM and WM tissue volume estimates were affected by the presence of WM lesions. With simulated lesion volumes of 15 mL at 70% of normal WM intensity, the effect was to increase GM fractional (relative to intracranial) volumes by approximate to 2.3%, and reduce WM fractions by approximate to 3.6%. Lesion filling reduced these errors toConclusion: The effect of WM lesions on automated GM and WM volume measures may be considerable and thereby obscure real disease-mediated volume changes. Lesion filling with values approximating normal WM enables more accurate GM and WM volume measures and should be applicable to structural scans independently of the software used for the segmentation.

Validation of functional diffusion maps (fDMs) as a biomarker for human glioma cellularity.

Abstract: Purpose—To present comprehensive examinations of the assumptions made in functional diffusion map (fDM) analyses and provide a biological basis for fDM classification. Materials and Methods—Sixty-nine patients with gliomas were enrolled in this study. To determine the sensitivity of ADC to cellularity, cell density from stereotactic biopsy specimens was correlated with pre-operative ADC maps. For definition of ADC thresholds used for fDMs, the 95% confidence intervals (C.I.) for changes in voxel-wise ADC measurements in normal appearing tissue was analyzed. The sensitivity and specificity to progressing disease was examined using both radiographic and neurological criteria. Results—Results support the hypothesis that ADC is inversely proportional to cell density with a sensitivity of 1.01 × 10 -7 [mm 2 /s]/[nuclei/mm 2 ]. The 95% C.I. for white matter = 0.25×10 -3 mm 2 /s, gray matter = 0.31×10 -3 mm 2 /s, a mixture of white and gray matter = 0.40×10 -3 mm 2 /s, and a mixture of white matter, gray matter, and cerebrospinal fluid = 0.75×10 -3 mm 2 /s. Application of these measurements as ADC thresholds produce varying levels of sensitivity and specificity to disease progression, which were all significantly better than chance. Conclusion—This study suggests fDMs are valid biomarkers for brain tumor cellularity.

Performance of imaging modalities in diagnosis of liver metastases from colorectal cancer: a systematic review and meta-analysis.

Abstract: Surgery of liver metastases can be effective, and the appropriate selection of surgical candidates relies first on imaging. Different techniques are available, but information on their relative performance is unclear. The aim of this overview is to assess the imaging modality performance in the diagnosis of colorectal cancer (CRC) liver metastases. MEDLINE and EMBASE were searched for articles published from January 2000 to August 2008. Eligible trials had to be conducted on patients with diagnosis/suspicion of CRC liver metastases, comparing more than two modalities among MRI, computed tomography (CT), positron emission tomography using fluoro-18-deoxyglucose (FDG-PET), ultrasonography (US). Pooled estimates of sensitivity, specificity were calculated and pair-wise comparisons were performed. Of 6030 screened articles, 25 were eligible. Sensitivity and specificity on a per-patient basis for US, CT, MRI, and FDG-PET were 63.0% and 97.6%, 74.8% and 95.6%, 81.1% and 97.2, and 93.8% and 98.7%, respectively. On a per-lesion basis, sensitivity was 86.3%, 82.6%, 86.3%, and 86.0%, respectively. Specificity was reported in few studies. MRI showed a better sensitivity than CT in per-patient (odds ratio [OR]: 0.69; 95% confidence interval [CI]: 0.47-0.99; P = 0.05) and in per-lesion analysis (OR: 0.66; 95% CI: 0.55-0.80; P < 0.0001). In per-lesion analysis, the difference was higher when liver-specific contrast agents were administered. Available evidence supports the MRI use for the detection of CRC liver metastases.

Prostate cancer detection with 3 T MRI: comparison of diffusion-weighted imaging and dynamic contrast-enhanced MRI in combination with T2-weighted imaging.

Abstract: Purpose: To evaluate the diagnostic ability of diffusion-weighted imaging (DWI) and dynamic contrast-enhanced imaging (DCEI) in combination with T2-weighted imaging (T2WI) for the detection of prostate cancer using 3 T magnetic resonance imaging (MRI) with a phased-array body coil. Materials and Methods: Fifty-three patients with elevated serum levels of prostate-specific antigen (PSA) were evaluated by T2WI, DWI, and DCEI prior to needle biopsy. The obtained data from T2WI alone (protocol A), a combination of T2WI and DWI (protocol B), a combination T2WI and DCEI (protocol C), and a combination of T2WI plus DWI and DCEI (protocol D) were subjected to receiver operating characteristic (ROC) curve analysis. Results: The sensitivity, specificity, accuracy, and area under the ROC curve (Az) for region-based analysis were: 61%, 91%, 84%, and 0.8415, respectively, in protocol A; 76%, 94%, 90%, and 0.8931, respectively, in protocol B; 77%, 93%, 89%, and 0.8655, respectively, in protocol C; and 81%, 96%, 92%, and 0.8968, respectively in protocol D. ROC analysis revealed significant differences between protocols A and B (P = 0.0008) and between protocols A and D (P = 0.0004). Conclusion: In patients with elevated PSA levels the combination of T2WI, DWI, DCEI using 3 T MRI may be a reasonable approach for the detection of prostate cancer. J. Magn. Reson. Imaging 2010;31:625–631. © 2010 Wiley-Liss, Inc.

Imaging of lung function using hyperpolarized helium-3 magnetic resonance imaging: Review of current and emerging translational methods and applications

Abstract: During the past several years there has been extensive development and application of hyperpolarized helium-3 (HP (3)He) magnetic resonance imaging (MRI) in clinical respiratory indications such as asthma, chronic obstructive pulmonary disease, cystic fibrosis, radiation-induced lung injury, and transplantation. This review focuses on the state-of-the-art of HP (3)He MRI and its application to clinical pulmonary research. This is not an overview of the physics of the method, as this topic has been covered previously. We focus here on the potential of this imaging method and its challenges in demonstrating new types of information that has the potential to influence clinical research and decision making in pulmonary medicine. Particular attention is given to functional imaging approaches related to ventilation and diffusion-weighted imaging with applications in chronic obstructive pulmonary disease, cystic fibrosis, asthma, and radiation-induced lung injury. The strengths and challenges of the application of (3)He MRI in these indications are discussed along with a comparison to established and emerging imaging techniques.

Common data elements in radiologic imaging of traumatic brain injury

Abstract: Traumatic brain injury (TBI) has a poorly understood pathology. Patients suffer from a variety of physical and cognitive effects that worsen as the type of trauma worsens. Some noninvasive insights into the pathophysiology of TBI are possible using magnetic resonance imaging (MRI), computed tomography (CT), and many other forms of imaging as well. A recent workshop was convened to evaluate the common data elements (CDEs) that cut across the imaging field and given the charge to review the contributions of the various imaging modalities to TBI and to prepare an overview of the various clinical manifestations of TBI and their interpretation. Technical details regarding state-of-the-art protocols for both MRI and CT are also presented with the hope of guiding current and future research efforts as to what is possible in the field. Stress was also placed on the potential to create a database of CDEs as a means to best record information from a given patient from the reading of the images.

Magnetic resonance imaging near metal implants.

Abstract: The desire to apply magnetic resonance imaging (MRI) techniques in the vicinity of embedded metallic hardware is increasing. The soft-tissue contrast available with MR techniques is advantageous in diagnosing complications near an increasing variety of MR-safe metallic hardware. Near such hardware, the spatial encoding mechanisms utilized in conventional MRI methods are often severely compromised. Mitigating these encoding difficulties has been the focus of numerous research investigations over the past two decades. Such approaches include view-angle tilting, short echo-time projection reconstruction acquisitions, single-point imaging, prepolarized MRI, and postprocessing image correction. Various technical advances have also enabled the recent development of two alternative approaches that have shown promising clinical potential. Here, the physical principals and proposed solutions to the problem of MRI near embedded metal are discussed. J. Magn. Reson. Imaging 2010;32:773–787. © 2010 Wiley-Liss, Inc.

Differential diagnosis of mammographically and clinically occult breast lesions on diffusion-weighted MRI

Abstract: Purpose: To investigate the diagnostic performance of diffusion-weighted imaging (DWI) for mammographically and clinically occult breast lesions. Materials and Methods: The study included 91 women with 118 breast lesions (91 benign, 12 ductal carcinoma in situ [DCIS], 15 invasive carcinoma) initially detected on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and assigned BI-RADS category 3, 4, or 5. DWI was acquired with b = 0 and 600 s/mm2. Lesion visibility was assessed on DWI. Apparent diffusion coefficient (ADC) values were compared between malignancies, benign lesions, and normal (no abnormal enhancement on DCE-MRI) breast tissue, and the diagnostic performance of DWI was assessed based on ADC thresholding. Results: Twenty-four of 27 (89%) malignant and 74/91 (81%) benign lesions were hyperintense on the b = 600 s/mm2 diffusion-weighted images. Both DCIS (1.33 ± 0.19 × 10−3 mm2/s) and invasive carcinomas (1.30 ± 0.27 × 10−3mm2/s) were lower in ADC than benign lesions (1.71 ± 0.43 × 10−3mm2/s; P < 0.001), and each lesion type was lower in ADC than normal tissue (1.90 ± 0.38 × 10−3mm2/s, P ≤ 0.001). Receiver operating curve (ROC) analysis showed an area under the curve (AUC) of 0.77, and sensitivity = 96%, specificity = 55%, positive predictive value (PPV) = 39%, and negative predictive value (NPV) = 98% for an ADC threshold of 1.60 × 10−3mm2/s. Conclusion: Many mammographically and clinically occult breast carcinomas were visibly hyperintense on diffusion-weighted images, and ADC enabled differentiation from benign lesions. Further studies evaluating DWI while blinded to DCE-MRI are necessary to assess the potential of DWI as a noncontrast breast screening technique. J. Magn. Reson. Imaging 2010;1:562–570. © 2010 Wiley-Liss, Inc.

Enhanced image quality in black-blood MRI using the improved motion-sensitized driven-equilibrium (iMSDE) sequence.

Abstract: Purpose To propose an improved motion-sensitized driven-equilibrium (iMSDE) pulse sequence to enhance the tissue signal-to-noise ratio (SNR) while maintaining the same flow suppression capability in black-blood carotid artery MRI.

Magnetic resonance imaging in real time: Advances using radial FLASH

Abstract: Purpose: To develop technical advances for real-timemagnetic resonance imaging (MRI) that allow for improvedimage quality and high frame rates.Materials and Methods: The approach is based on acombination of fast low-angle shot (FLASH) MRI sequen-ces with radial data sampling and view sharing of succes-sive acquisitions. Gridding reconstructions provideimages free from streaking or motion artifacts and with aflexible trade-off between spatial and temporal resolution.Immediate image reconstruction and online display isaccomplished with the use of an unmodified 3 T MRI sys-tem. For receive coils with a large number of elementsthis process is supported by a user-selectable channelcompression that is based on a principal component anal-ysis and performed during initial preparation scans.Results: In preliminary applications to healthy volun-teers, real-time radial FLASH MRI visualized continuousmovements of the temporomandibular joint during volun-tary opening and closing of the mouth at high spatial re-solution (0.75 mm in-plane) and monitored cardiac func-tions at high temporal resolution (20 images per second)during free breathing and without synchronization to theelectrocardiogram.Conclusion: Real-time radial FLASH MRI emerges as asimple and versatile tool for a large range of clinicalapplications.Key Words: real-time MRI; cardiovascular MRI; temporo-mandibular joint; radial MRIJ. Magn. Reson. Imaging 2010; 31:101–109.

Utility of diffusion-weighted MRI in distinguishing benign and malignant hepatic lesions

Abstract: Purpose: To evaluate apparent diffusion coefficient (ADC) values for characterization of a variety of focal liver lesions and specifically for differentiation of solid benign lesions (focal nodular hyperplasia [FNH] and adenomas) from solid malignant neoplasms (metastases and hepatocellular carcinoma [HCC]) in a large case series. Materials and Methods: A total of 542 lesions in 382 patients were evaluated. ADC values were measured in 166 hemangiomas, 112 hepatomas, 107 metastases, 95 cysts, 10 abscesses, 43 FNH, and nine adenomas. ADCs of 1.5 and 1.6 (×10−3 mm2/second) were selected as threshold values to separate benign and malignant lesions. Sensitivity, specificity, positive, and negative predictive values (PPV, NPV) were calculated. Comparisons were carried out with studentized range test. Results: There was high interobserver agreement in ADC measurements for all lesion types. The mean ADCs for cysts was 3.40 (×10 −3 mm2/second), hemangiomas 2.26, FNH 1.79, adenomas 1.49, abscesses 1.97, HCC 1.53, and metastases 1.50. The mean ADC for benign lesions was 2.50 and for malignant lesions was 1.52. Cysts were easily distinguished from other lesions. There was, however, overlap between solid benign and malignant lesions. Conclusion: Benign lesions have higher mean ADC values than malignant lesions. However, ADC values of solid benign lesions (FNH and adenomas) are similar to malignant lesions (metastases, HCC) limiting the value of diffusion weighted imaging (DWI) for differentiating solid liver masses. J. Magn. Reson. Imaging 2010;32:138–147. © 2010 Wiley-Liss, Inc.

International reproducibility of single breathhold T2* MR for cardiac and liver iron assessment among five thalassemia centers.

Abstract: Purpose: To examine the reproducibility of the single breathhold T2* technique from different scanners, after installation of standard methodology in five international centers. Materials and Methods: Up to 10 patients from each center were scanned twice locally for local interstudy reproducibility of heart and liver T2*, and then flown to a central MR facility to be rescanned on a reference scanner for intercenter reproducibility. Interobserver reproducibility for all scans was also assessed. Results: Of the 49 patients scanned, the intercenter reproducibility for T2* was 5.9% for the heart and 5.8% for the liver. Local interstudy reproducibility for T2* was 7.4% for the heart and 4.6% for the liver. Interobserver reproducibility for T2* was 5.4% for the heart and 4.4% for the liver. Conclusion: These data indicate that T2* MR may be developed into a widespread test for tissue siderosis providing that well-defined and approved imaging and analysis techniques are used. J. Magn. Reson. Imaging 2010;32:315–319. © 2010 Wiley-Liss, Inc.

Computed tomography and magnetic resonance imaging of mediastinal tumors

Abstract: We describe the clinical, pathological, and imaging findings of mediastinal tumors with focus on thymic hyperplasia, thymic epithelial tumors, and germ cell tumors, malignant lymphoma, and various cystic masses. Chemical shift magnetic resonance imaging (MRI) is useful in characterization of the normal thymus and differentiation of hyperplastic thymus and thymic tumors. In contrast to noninvasive thymomas, invasive thymomas and thymic carcinomas show a more aggressive growth pattern. Local invasion and pleural spread are characteristic of invasive thymoma and mediastinal lymphadenopathy and distant metastasis suggest thymic carcinomas. Mature teratoma typically shows various computed tomography (CT) attenuation, and MR signal intensity depending on its contents and fat tissue and bone within the lesions are its characteristic findings. Seminomas typically have homogenous internal CT attenuation and MR signal intensity with minimal contrast enhancement. Nonseminomatous malignant germ cell tumors characteristically show prominent internal degenerative changes and invasion to the adjacent structures. In mediastinal lymphomas, a residual mass is common after treatment and MRI provides important information in distinguishing viable tumors from residual benign masses. Some mediastinal cysts may reveal high attenuation similar to solid lesions on CT depending on their contents and MRI can be useful in the differentiation of cystic masses from solid lesions.

Imaging cerebral microbleeds using susceptibility weighted imaging: One step toward detecting vascular dementia

Abstract: Purpose: To monitor changes in the number of cerebral microbleeds (CMBs) in a longitudinal study of healthy controls (HC) and mild-cognitively impaired (MCI) patients using susceptibility weighted imaging (SWI). Materials and Methods: SWI was used to image 28 HC and 75 MCI patients annually at 1.5 Tesla over a 4-year period. Magnitude and phase data were used to visualize CMBs for the first and last scans of 103 subjects. Results: Preliminary analysis revealed that none of the 28 HC had more than three CMBs. In the 75 MCI patients, five subjects had more than three CMBs in both first and last scans, while one subject had more than three bleeds only in the last scan. In five of these six MCI patients, the number of CMBs increased over time and all six went on to develop progressive cognitive impairment (PCI). Of the 130 total CMBs seen in the last scans of the six MCI cases, most were less than 4 mm in diameter. Conclusion: SWI can reveal small CMBs on the order of 1 mm in diameter and this technique can be used to follow their development longitudinally. Monitoring CMBs may be a means by which to evaluate patients for the presence of microvascular disease that leads to PCI. J. Magn. Reson. Imaging 2010;31:142–148. © 2009 Wiley-Liss, Inc.

Diffusion tensor MRI: preliminary anisotropy measures and mapping of breast tumors.

Abstract: Purpose: To investigate whether diffusion tensor imaging (DTI) measures of anisotropy in breast tumors are different from normal breast tissue and can improve the discrimination between benign and malignant lesions. Materials and Methods: The study included 81 women with 105 breast lesions (76 malignant, 29 benign). DTI was performed during breast MRI examinations, and fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were measured for breast lesions and normal tissue in each subject. FA and ADC were compared between cancers, benign lesions, and normal tissue by univariate and multivariate analyses. Results: The FA of carcinomas (mean ± SD: 0.24 ± 0.07) was significantly lower than normal breast tissue in the same subjects (0.29 ± 0.07; P < 0.0001). Multiple logistic regression showed that FA and ADC were each independent discriminators of malignancy (P < 0.0001), and that FA improved discrimination between cancer and normal tissue over ADC alone. However, there was no difference in FA between malignant and benign lesions (P = 0.98). Conclusion: Diffusion anisotropy is significantly lower in breast cancers than normal tissue, which may reflect alterations in tissue organization. Our preliminary results suggest that FA adds incremental value over ADC alone for discriminating malignant from normal tissue but does not help with distinguishing benign from malignant lesions. J. Magn. Reson. Imaging 2010; 31: 339–347. © 2010 Wiley-Liss, Inc.

Clinical evaluation of aortic coarctation with 4D flow MR imaging

Abstract: Results: Direct comparison of blood flow calculated with 4D and 2D PC data at standard levels for analysis in coarct patients showed good correlation and agreement between the two techniques; a comparison of representative data sets is included as Figure C. Strong correlation of blood flow data is demonstrated at the Prox DsAo (r = 0.99, limits of agreement -4.09 to 10.47 ml/beat) and at the diaphragm (r = 0.99, LOA = 0.28 to 5.2 ml/beat). The change in flow from the Prox DsAo to the diaphragm, which is key for evaluation of collateral flow, also shows good correlation; for the numerical change, r = 0.98 and LOA = -4.69 to 5.58 ml/beat, and for the percentage change, r = 0.99 and LOA = -7% to 9%. These results are comparable to previously reported data comparing 2D and 4D flow data without parallel imaging in healthy subjects [5]. With 4D visualization techniques, secondary blood flow features were evaluated in patients and compared to healthy subjects, both those included in our study and those from the literature [2,4]. There appears to be a tendency toward exaggerated, left-handed helical flow in the DsAo in patients status post coarct repair. This is best demonstrated in a patient with an angulated aortic arch and aneurysmal prox DsAo status post patch repair of coarct (Figures A and B). Discussion: 4D volumetric acquisition of PC MR data throughout the cardiac cycle is an effective way of evaluating blood flow in the thoracic aorta. Our study offers clinical validation of flow data generated by 4D Flow, and employs parallel imaging to reduce scan time in order to make the technique clinically feasible. Direct comparison of 2D and 4D PC blood flow data at the levels used for routine clinical evaluation of collateral flow in coarct patients demonstrates good correlation and agreement between the two techniques. One clear advantage of 4D Flow is that it affords the ability to arbitrarily place cut-planes throughout datasets without being hindered by the prospective acquisition of traditional 2D PC MR. The principal advantage of 4D Flow, however, is its ability to dynamically visualize blood flow in 3D throughout the cardiac cycle. With 3D visualization software, we have employed tools such as vector fields, streamlines and particle traces to characterize complex, secondary blood flow features unique to coarct patients. We have observed a tendency toward exaggerated helical flow in the descending aorta in these patients. While work needs to be done to evaluate whether abnormal secondary flow features visualized by 4D Flow in patients with aortic pathology are of clinical significance, we postulate that detailed characterization of abnormal flow patterns may be useful for better understanding and possibly predicting post-intervention complications in patients status post repair of aortic coarctation. This is one of the first clinical applications of 4D Flow in patients with aortic coarctation.

Identification of brown adipose tissue in mice with fat-water IDEAL-MRI.

Abstract: Results: A broad fat fraction range for BAT was observed (40‐80%), in comparison to a tighter and higher WAT range of 90‐93%, in both excised tissue samples and in situ. Using the fat fraction metric, the interscapular BAT depot in each carcass could be clearly identified, as well as peri-renal and inguinal depots that exhibited a mixed BAT and WAT phenotype appearance. Conclusion: Due to BAT’s multi-locular fat distribution and extensive mitochondrial, cytoplasm, and vascular supply, its fat content is significantly less than that of WAT. We have demonstrated that the fat fraction metric from IDEAL-MRI is a sensitive and quantitative approach to noninvasively characterize BAT.

Repeatability of magnetic resonance elastography for quantification of hepatic stiffness.

Abstract: Purpose: To determine the sources of variability of MRE hepatic stiffness measurements using healthy volunteers and patients and to calculate the minimum change required for statistical significance. Hepatic stiffness measured with magnetic resonance elastography (MRE) has demonstrated tremendous potential as a noninvasive surrogate of hepatic fibrosis, although the underlying repeatability of MRE for longitudinal tracking of liver disease has not been documented. Materials and Methods: MRE stiffness measurements from 20 healthy volunteers and 10 patients were obtained twice on the same day, and repeated 2–4 weeks later for volunteers in this institutional review board-approved study. A linear mixed effects model was used to estimate the component sources of variability in the data. Results: The standard deviation of MRE measurements of the same individual on different days is 11.9% (percent of the measured stiffness) using the same reader and 12.0% using different readers. The standard deviation of the difference between two measurements (i.e., longitudinal change in an individual) is 17.4%; the corresponding 95% confidence interval for zero change is (−27.0%, 37.0%). Conclusion: MRE is a repeatable method for quantifying liver stiffness. Using the described MRE technique, changes greater than 37.0% of the smaller measured stiffness value represent meaningful changes in longitudinal liver stiffness measurements. J. Magn. Reson. Imaging 2010;31:725–731. © 2010 Wiley-Liss, Inc.

Imaging biomarkers in multiple sclerosis

Abstract: Recent years have witnessed impressive advances in the use of magnetic resonance imaging (MRI) for the assessment of patients with multiple sclerosis (MS). Complementary to the clinical evaluation, conventional MRI provides crucial pieces of information for the diagnosis of MS. However, the correlation between the burden of lesions observed on conventional MRI scans and the clinical manifestations of the disease remains weak. The discrepancy between clinical and conventional MRI findings in MS is explained, at least partially, by the limited ability of conventional MRI to characterize and quantify the heterogeneous features of MS pathology. Other quantitative MR-based techniques, however, have the potential to overcome such a limitation of conventional MRI. Indeed, magnetization transfer MRI, diffusion tensor MRI, proton MR spectroscopy, and functional MRI are contributing to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. Such techniques are likely to benefit from the use of high-field MR systems and thus allow in the near future providing additional insight into all these aspects of the disease. This review summarizes how MRI is dramatically changing our understanding of the factors associated with the accumulation of irreversible disability in MS and highlights the reasons why they should be used more extensively in studies of disease evolution and clinical trials.

Correlation of putative iron content as represented by changes in R2* and phase with age in deep gray matter of healthy adults

Abstract: Purpose: To establish a correlation between putative iron content using susceptibility weighted imaging (SWI) phase and T2* weighted magnitude values in the basal ganglia and the thalamus as a function of age in healthy human brains. Materials and Methods: One hundred healthy adults (range, 20–69 years; mean, 43 years) were evaluated for this study using a gradient echo sequence. The original magnitude and high pass filtered phase data were analyzed as proxy variables for iron content in the substantia nigra, red nucleus, globus pallidus, putamen, caudate nucleus, thalamus, and pulvinar thalamus. Each structure was broken into two parts, a high iron content region and a low iron content region. Results: Both magnitude and phase data showed an increase in putative iron content with age. However, the high iron content region revealed two new pieces of information: both the average iron content per pixel and the area of high iron increased with age. Furthermore, significant increase in iron uptake as a function of age was found past the age of 40. Conclusion: A two region of interest analysis of iron is a much more sensitive means to evaluate iron content change over time. Contrary to the current belief that iron content increases level off with age, the putative iron deposition in the high iron content region is seen to increase with age. J. Magn. Reson. Imaging 2010;32:561–576. © 2010 Wiley-Liss, Inc.

Susceptibility weighted imaging with multiple echoes.

Abstract: Purpose: To extend susceptibility weighted imaging (SWI) to multiple echoes with an adapted homodyne filtering of phase images for the computation of venograms with improved signal to noise ratio (SNR) and contrast to noise ratio (CNR) and to produce high resolution maps of R2 * relaxation. Materials and Methods: Three-dimensional multi echo gradient echo data were acquired with five equidistant echoes ranging from 13 to 41 ms. The phase images of each echo were filtered with filter parameters adjusted to the echo time, converted into a phase mask, and combined with the corresponding magnitude images to obtain susceptibility weighted images. The individual images were then averaged. Conventional single echo data were acquired for comparison. Maps of R2 relaxation rates were computed from the magnitude data. Field maps derived from the phase data were used to correct R2 for the influences from background inhomogeneities of the static magnetic field. Results: Compared with the single echo images, the combined images had an increase in SNR by 46% and an improvement in CNR by 34 to 80%, improved visibility of small venous vessels and reduced blurring along the readout direction. The R2 values of different tissue types are in good agreement with values from the literature. Conclusion: Acquisition of SWI with multiple echoes leads to an increase in SNR and CNR and it allows the computation of high resolution maps of R2 relaxation.

Machine learning study of several classifiers trained with texture analysis features to differentiate benign from malignant soft-tissue tumors in T1-MRI images

Abstract: Purpose: To study, from a machine learning perspective, the performance of several machine learning classifiers that use texture analysis features extracted from soft-tissue tumors in nonenhanced T1-MRI images to discriminate between malignant and benign tumors. Materials and Methods: Texture analysis features were extracted from the tumor regions from T1-MRI images of clinically proven cases of 49 malignant and 86 benign soft-tissue tumors. Three conventional machine learning classifiers were trained and tested. The best classifier was compared to the radiologists by means of the McNemar's statistical test. Results: The SVM classifier performs better than the neural network and the C4.5 decision tree based on the analysis of their receiver operating curves (ROC) and cost curves. The classification accuracy of the SVM, which was 93% (91% specificity; 94% sensitivity), was better than the radiologist classification accuracy of 90% (92% specificity; 81% sensitivity). Conclusion: Machine learning classifiers trained with texture analysis features are potentially valuable for detecting malignant tumors in T1-MRI images. Analysis of the learning curves of the classifiers showed that a training data size smaller than 100 T1-MRI images is sufficient to train a machine learning classifier that performs as well as expert radiologists. J. Magn. Reson. Imaging 2010;31:680–689. © 2010 Wiley-Liss, Inc.

Carotid arterial wall MRI at 3T using 3D variable‐flip‐angle turbo spin‐echo (TSE) with flow‐sensitive dephasing (FSD)

Abstract: Purpose To evaluate the effectiveness of flow-sensitive dephasing (FSD) magnetization preparation in improving blood signal suppression of three-dimensional (3D) turbo spin-echo (TSE) sequence (SPACE) for isotropic high-spatial-resolution carotid arterial wall imaging at 3T.

Diurnal stability of gamma-aminobutyric acid concentration in visual and sensorimotor cortex

Abstract: Purpose:To establish the diurnal stability of edited magnetic resonance spectroscopy measurements of gamma-aminobutyric acid (GABA) in visual and sensorimotor regions of the brain. Materials and Methods:GABA measurements were made in two regions of the brain (an occipital, “visual” region and a “sensorimotor” region centered on the precentral gyrus) using the MEGA-PRESS editing method, scanning eight healthy adults at five timepoints during a single day. GABA concentration was quantified from the ratio of the GABA integral to the unsuppressed water signal. Results:No significant effect of time on GABA concentration was seen (P = 0.35). GABA was shown to be significantly more concentrated in visual regions than in sensorimotor regions (1.10 i.u. and 1.03 i.u., respectively; P = 0.050). Coefficients of variability (CVs) across all subjects of 9.1% and 12% (visual and sensorimotor) were significantly higher than mean within-subjects CVs of 6.5% and 8.8. Conclusion:This study demonstrates the excellent reproducibility of MEGA-PRESS detection of GABA, demonstrating that the method is sufficiently sensitive to detect inter-subject variability, and suggests that (within the sensitivity limits of current measurements) time of day can be ignored in the design of MRS studies of visual and sensorimotor regions.