MR imaging at high magnetic fields

Enhancing MRI brain tumor classification: A comprehensive approach integrating real-life scenario simulation and augmentation techniques

Brain cancer poses a significant global health challenge, with mortality rates showing a concerning surge over recent decades. The incidence of brain cancer-related mortality has risen from 140,000 to 250,000, accompanied by a doubling in new diagnoses from 175,000 to 350,000. In response, magnetic resonance imaging (MRI) has emerged as a pivotal diagnostic tool, facilitating early detection and treatment planning. However, the translation of deep learning approaches to brain cancer diagnosis faces a critical obstacle: the scarcity of public clinical datasets reflecting real-world complexities. This study aims to bridge this gap through a comprehensive exploration and augmentation of training data. Initially, a battery of pre-trained deep models undergoes evaluation on a main brain cancer MRI "BT-MRI" dataset, yielding remarkable performance metrics, including 100% accuracy, precision, recall, and F1-Score, substantiated by the Score-CAM methodology. This initial success underscores the potential of deep learning in brain cancer diagnosis. Subsequently, the model's efficacy undergoes further scrutiny using a supplementary brain cancer MRI "BCD-MRI" dataset, affirming its robustness and applicability across diverse datasets. However, the ultimate litmus test lies in confronting the model with synthetic testing datasets crafted to emulate real-world scenarios. The synthetic testing datasets, a BCD-MRI testing sub-dataset enriched with noise, blur, and simulated patient motion, reveal a sobering reality: the model's performance plummets, exposing inherent limitations in generalization. To address this issue, a diverse set of optimization strategies and augmentation techniques, ranging from diverse optimizers to sophisticated data augmentation methods, are exhaustively explored. Despite these efforts, the problem of generalization persists. The breakthrough emerges with the integration of noise and blur as augmentation techniques during the training process. Leveraging Gaussian noise and Gaussian blur kernels, the model undergoes a transformative evolution, exhibiting newfound robustness and resilience. Retesting the refined model against the challenging synthetic datasets reveals a remarkable transformation, with performance metrics witnessing a notable ascent. This achievement underscores the important role of correct selection of data augmentation in fortifying the generalization of deep learning models for brain cancer diagnosis. This study not only advances the frontiers of diagnostic precision in brain cancer but also underscores the paramount importance of methodological rigor and innovation in confronting the complexities of real-world clinical scenarios.

Effective deep-learning brain MRI super resolution using simulated training data

BACKGROUND

In the field of medical imaging, high-resolution (HR) magnetic resonance imaging (MRI) is essential for accurate disease diagnosis and analysis. However, HR imaging is prone to artifacts and is not universally available. Consequently, low-resolution (LR) MRI images are typically acquired. Deep learning (DL)-based super-resolution (SR) techniques can transform LR images into HR quality. However, these techniques require paired HR-LR data for training the SR networks.

OBJECTIVE

This research aims to investigate the potential of simulated brain MRI data to train DL-based SR networks.

METHODS

We simulated a large set of anatomically diverse, voxel-aligned, and artifact-free brain MRI data at different resolutions. We utilized this simulated data to train four distinct DL-based SR networks and augment their training. The trained networks were then evaluated using real data from various sources.

RESULTS

With our trained networks, we produced 0.7mm SR images from standard 1mm resolution multi-source T1w brain MRI. Our experimental results demonstrate that the trained networks significantly enhance the sharpness of LR input MR images. For single-source images, the performance of networks trained solely on simulated data is slightly inferior to those trained solely on real data, with an average structural similarity index (SSIM) difference of 0.025. However, networks augmented with simulated data outperform those trained on single-source real data when evaluated across datasets from multiple sources.

CONCLUSION

Paired HR-LR simulated brain MRI data is suitable for training and augmenting diverse brain MRI SR networks. Augmenting the training data with simulated data can enhance the generalizability of the SR networks across real datasets from multiple sources.

Efficacy of compressed sensing and deep learning reconstruction for adult female pelvic MRI at 1.5 T

BACKGROUND

We aimed to determine the capabilities of compressed sensing (CS) and deep learning reconstruction (DLR) with those of conventional parallel imaging (PI) for improving image quality while reducing examination time on female pelvic 1.5-T magnetic resonance imaging (MRI).

METHODS

Fifty-two consecutive female patients with various pelvic diseases underwent MRI with T1- and T2-weighted sequences using CS and PI. All CS data was reconstructed with and without DLR. Signal-to-noise ratio (SNR) of muscle and contrast-to-noise ratio (CNR) between fat tissue and iliac muscle on T1-weighted images (T1WI) and between myometrium and straight muscle on T2-weighted images (T2WI) were determined through region-of-interest measurements. Overall image quality (OIQ) and diagnostic confidence level (DCL) were evaluated on 5-point scales. SNRs and CNRs were compared using Tukey's test, and qualitative indexes using the Wilcoxon signed-rank test.

RESULTS

SNRs of T1WI and T2WI obtained using CS with DLR were higher than those using CS without DLR or conventional PI (p < 0.010). CNRs of T1WI and T2WI obtained using CS with DLR were higher than those using CS without DLR or conventional PI (p < 0.003). OIQ of T1WI and T2WI obtained using CS with DLR were higher than that using CS without DLR or conventional PI (p < 0.001). DCL of T2WI obtained using CS with DLR was higher than that using conventional PI or CS without DLR (p < 0.001).

CONCLUSION

CS with DLR provided better image quality and shorter examination time than those obtainable with PI for female pelvic 1.5-T MRI.

RELEVANCE STATEMENT

CS with DLR can be considered effective for attaining better image quality and shorter examination time for female pelvic MRI at 1.5 T compared with those obtainable with PI.

KEY POINTS

Patients underwent MRI with T1- and T2-weighted sequences using CS and PI. All CS data was reconstructed with and without DLR. CS with DLR allowed for examination times significantly shorter than those of PI and provided significantly higher signal- and CNRs, as well as OIQ.

T2-weighted MRI and reduced-FOV diffusion-weighted imaging of the human pancreas at 5 T: A comparison study with 3 T

PURPOSE

The purpose of this study was to explore the feasibility of pancreatic imaging at 5 T and evaluate the practical improvement of T2-weighted MRI and diffusion-weighted imaging (DWI) at 5 T as compared with 3 T.

METHODS

Eighteen healthy subjects were recruited for this pilot study. MRI examinations were performed using 3 and 5 T scanners. MRI sequences included T2-weighted fast spin-echo and DWI with reduced field-of-view. Subjective image analysis using a four-point Likert scale was performed by two experienced radiologists. The SNR, contrast ratio, and apparent diffusion coefficient (ADC) were measured in the pancreatic head, body, and tail. The coefficient of variation (CV) of the ADC was calculated. A series of paired Wilcoxon tests were used to compare the subjective image quality, mean ADC value, and CV of ADC between the 3 and 5 T measurements. p <0.05 was considered statistically significant.

RESULTS

For T2-weighted images, there were no significant differences in image quality ratings between 3 and 5 T. On DWI images (b = 0 and 800 s/mm² ), the image quality ratings were significantly higher at 5 T than at 3 T. The SNRs of both T2-weighted and DWI images were significantly higher at 5 T. There was no significant difference in the mean ADC values and CV of ADC between 3 and 5 T.

CONCLUSION

This initial study proved that 5 T MRI can be used to acquire pancreatic images with higher SNR and sufficient image quality compared to 3 T MRI.

Deep learning reconstruction for the evaluation of neuroforaminal stenosis using 1.5T cervical spine MRI: comparison with 3T MRI without deep learning reconstruction

PURPOSE

To compare image quality and interobserver agreement in evaluations of neuroforaminal stenosis between 1.5T cervical spine magnetic resonance imaging (MRI) with deep learning reconstruction (DLR) and 3T MRI without DLR.

METHODS

In this prospective study, 21 volunteers (mean age: 42.4 ± 11.9 years; 17 males) underwent cervical spine T2-weighted sagittal 1.5T and 3T MRI on the same day. The 1.5T and 3T MRI data were used to reconstruct images with (1.5T-DLR) and without (3T-nonDLR) DLR, respectively. Regions of interest were marked on the spinal cord to calculate non-uniformity (NU; standard deviation/signal intensity × 100), as an indicator of image noise. Two blinded radiologists evaluated the images in terms of the depiction of structures, artifacts, noise, overall image quality, and neuroforaminal stenosis. The NU value and the subjective image quality scores were compared between 1.5T-DLR and 3T-nonDLR using the Wilcoxon signed-rank test. Interobserver agreement in evaluations of neuroforaminal stenosis for 1.5T-DLR and 3T-nonDLR was evaluated using Cohen's weighted kappa analysis.

RESULTS

The NU value for 1.5T-DLR was 8.4, which was significantly better than that for 3T-nonDLR (10.3; p < 0.001). Subjective image scores were significantly better for 1.5T-DLR than 3T-nonDLR images (p < 0.037). Interobserver agreement (95% confidence intervals) in the evaluations of neuroforaminal stenosis was significantly superior for 1.5T-DLR (0.920 [0.916-0.924]) than 3T-nonDLR (0.894 [0.889-0.898]).

CONCLUSION

By using DLR, image quality and interobserver agreement in evaluations of neuroforaminal stenosis on 1.5T cervical spine MRI could be improved compared to 3T MRI without DLR.

Applicability of deep learning-based reconstruction trained by brain and knee 3T MRI to lumbar 1.5T MRI

Background

Several deep learning-based methods have been proposed for addressing the long scanning time of magnetic resonance imaging. Most are trained using brain 3T magnetic resonance images, but is unclear whether performance is affected when applying these methods to different anatomical sites and at different field strengths.

Purpose

To validate the denoising performance of deep learning-based reconstruction method trained by brain and knee 3T magnetic resonance images when applied to lumbar 1.5T magnetic resonance images.

Material and Methods

Using a 1.5T scanner, we obtained lumber T2-weighted sequences in 10 volunteers using three different scanning times: 228 s (standard), 119 s (double-fast), and 68 s (triple-fast). We compared the images obtained by the standard sequence with those obtained by the deep learning-based reconstruction-applied faster sequences.

Results

Signal-to-noise ratio values were significantly higher for deep learning-based reconstruction-double-fast than for standard and did not differ significantly between deep learning-based reconstruction-triple-fast and standard. Contrast-to-noise ratio values also did not differ significantly between deep learning-based reconstruction-triple-fast and standard. Qualitative scores for perceived signal-to-noise ratio and overall image quality were significantly higher for deep learning-based reconstruction-double fast and deep learning-based reconstruction-triple-fast than for standard. Average scores for sharpness, contrast, and structure visibility were equal to or higher for deep learning-based reconstruction-double-fast and deep learning-based reconstruction-triple-fast than for standard, but the differences were not statistically significant. The average scores for artifact were lower for deep learning-based reconstruction-double-fast and deep learning-based reconstruction-triple-fast than for standard, but the differences were not statistically significant.

Conclusion

The deep learning-based reconstruction method trained by 3T brain and knee images may reduce the scanning time of 1.5T lumbar magnetic resonance images by one-third without sacrificing image quality.

3D Oxygen-Enhanced MRI at 3T MR System: Comparison With Thin-Section CT of Quantitative Capability for Pulmonary Functional Loss Assessment and Clinical Stage Classification of COPD in Smokers

BACKGROUND

Oxygen (O₂ )-enhanced MRI is mainly performed by a 2D sequence using 1.5T MR systems but trying to be obtained by a 3D sequence using a 3T MR system.

PURPOSE

To compare the capability of 3D O₂ -enhanced MRI and that of thin-section computed tomography (CT) for pulmonary functional loss assessment and clinical stage classification of chronic obstructive pulmonary disease (COPD) in smokers.

STUDY TYPE

Prospective study.

POPULATION

Fifty six smokers were included.

FIELD STRENGTH/ SEQUENCE

3T, 3D O₂ -enhanced MRIs were performed with a 3D T₁ -weighted fast field echo pulse sequence using the multiple flip angles.

ASSESSMENTS

Smokers were classified into four stages ("Without COPD," "Mild COPD," "Moderate COPD," "Severe or very severe COPD"). Maps of regional changes in T₁ values were generated from O₂ -enhanced MR data. Regions of interest (ROIs) were then placed over the lung on all slices and averaged to determine mean T₁ value change (ΔT₁ ). Quantitative CT used the percentage of low attenuation areas within the entire lung (LAA%).

STATISTICAL TESTS

ΔT₁ and LAA% were correlated with pulmonary functional parameters, and compared for four stages using Tukey's Honestly Significant Difference test. Discrimination analyses were performed and McNemar's test was used for a comparison of the accuracy of the indexes.

RESULTS

There were significantly higher correlations between ΔT₁ and pulmonary functional parameters (-0.83 ≤ r ≤ -0.71, P < 0.05) than between LAA% and the same pulmonary functional parameters (-0.76 ≤ r ≤ -0.69, P < 0.05). ΔT₁ and LAA% of the "Mild COPD" and "Moderate COPD" groups were significantly different from those of the "Severe or Very Severe COPD" group (P < 0.05). Discriminatory accuracy of ΔT₁ (62.5%) and ΔT1 with LAA% (67.9%) was significantly greater than that of LAA% (48.2%, P < 0.05).

DATA CONCLUSION

Compared with thin-section CT, 3D O₂ -enhanced MRI has a similar capability for pulmonary functional assessment but better potential for clinical stage classification in smokers.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 1.

Basal ganglia volume and shape in anorexia nervosa

Background

Reward-centred models have proposed that anomalies in the basal ganglia circuitry that underlies reward learning and habit formation perpetuate anorexia nervosa (AN). The present study aimed to investigate the volume and shape of key basal ganglia regions, including the bilateral caudate, putamen, nucleus accumbens (NAcc), and globus pallidus in AN.

Methods

The present study combined data from two existing studies resulting in a sample size of 46 women with AN and 56 age-matched healthy comparison (HC) women. Group differences in volume and shape of the regions of interest were examined. Within the AN group, the impact of eating disorder characteristics on volume and shape of the basal ganglia regions were also explored.

Results

The shape analyses revealed inward deformations in the left caudate, right NAcc, and bilateral ventral and internus globus pallidus, and outward deformations in the right middle and posterior globus pallidus in the AN group.

Conclusions

The present findings appear to fit with the theoretical models suggesting that there are alterations in the basal ganglia regions associated with habit formation and reward processing in AN. Further investigation of structural and functional connectivity of these regions in AN as well as their role in recovery would be of interest.

PCOS and Hyperprolactinemia: what do we know in 2019?

Polycystic ovary syndrome (PCOS) and hyperprolactinemia (HPRL) are the two most common etiologies of anovulation in women. Since the 1950s, some authors think that there is a pathophysiological link between PCOS and HPRL. Since then, many authors have speculated about the link between these two endocrine entities, but no hypothesis proposed so far could ever be confirmed. Furthermore, PCOS and HPRL are frequent endocrine diseases and a fortuitous association cannot be excluded. The evolution of knowledge about PCOS and HPRL shows that studies conducted before the 2000s are obsolete given current knowledge. Indeed, most of the studies were conducted before consensual diagnosis criteria of PCOS and included small numbers of patients. In addition, the investigation of HPRL in these studies relied on obsolete methods and did not look for the presence of macroprolactinemia. It is therefore possible that HPRL that has been attributed to PCOS corresponded in fact to macroprolactinemia or to pituitary microadenomas of small sizes that could not be detected with the imaging methods of the time. Recent studies that have conducted a rigorous etiological investigation show that HPRL found in PCOS correspond either to non-permanent increase of prolactin levels, to macroprolactinemia or to other etiologies. None of this recent study found HPRL related to PCOS in these patients. Thus, the link between PCOS and HPRL seems to be more of a myth than a well-established medical reality and we believe that the discovery of an HPRL in a PCOS patient needs a standard etiological investigation of HPRL.

Magnetic resonance imaging of the fetal brain at 3 Tesla: Preliminary experience from a single series

To report our preliminary experience with cerebral fetal magnetic resonance imaging (MRI) with a 3 Tesla (3T) scanner. We assessed feasibility, time of acquisition, and possibility to establish a diagnosis.Fifty-nine pregnant women had fetal MRI performed during the third trimester of pregnancy due to clinical or sonography concern of a central nervous system anomaly. No fetal or maternal sedation was used. The MRI protocol consisted of T2 turbo-spin-echo images in 3 planes of space. No T1-weighted images were performed. All images were analyzed by 2 pediatric neuroradiologists, who evaluated spatial resolution, artifacts, time of acquisition, and possibility to establish a diagnosis suspected by sonography.Examinations were performed safely for all patients. The images required longer time of acquisition (approximately 75 seconds for each plane in the space). The specific absorption rate was not exceeded in any fetus. Cerebral fetal MRI was normal in 22 cases. The spectrum of diagnostics included isolated ventriculomegaly, posterior fossa malformation, corpus callosum malformation, gyration anomalies, craniosynostosis, tuberous sclerosis, microcephaly, external hydrocephaly, midline arachnoid cyst, cerebral lesions, and persistent hyperplastic primitive vitreous.In our series, 3 T MRI of fetal brain was feasible and able to establish a diagnosis but required longer time of acquisition.

Comparison of a fast 5-min knee MRI protocol with a standard knee MRI protocol: a multi-institutional multi-reader study

PURPOSE

To compare diagnostic performance of a 5-min knee MRI protocol to that of a standard knee MRI.

MATERIALS AND METHODS

One hundred 3 T (100 patients, mean 38.8 years) and 50 1.5 T (46 patients, mean 46.4 years) MRIs, consisting of 5 fast, 2D multi-planar fast-spin-echo (FSE) sequences and five standard multiplanar FSE sequences, from two academic centers (1/2015-1/2016), were retrospectively reviewed by four musculoskeletal radiologists. Agreement between fast and standard (interprotocol agreement) and between standard (intraprotocol agreement) readings for meniscal, ligamentous, chondral, and bone pathology was compared for interchangeability. Frequency of major findings, sensitivity, and specificity was also tested for each protocol.

RESULTS

Interprotocol agreement using fast MRI was similar to intraprotocol agreement with standard MRI (83.0-99.5%), with no excess disagreement (≤ 1.2; 95% CI, -4.2 to 3.8%), across all structures. Frequency of major findings (1.1-22.4% across structures) on fast and standard MRI was not significantly different (p ≥ 0.215), except more ACL tears on fast MRI (p = 0.021) and more cartilage defects on standard MRI (p < 0.001). Sensitivities (59-100%) and specificities (73-99%) of fast and standard MRI were not significantly different for meniscal and ligament tears (95% CI for difference, -0.08-0.08). For cartilage defects, fast MRI was slightly less sensitive (95% CI for difference, -0.125 to -0.01) but slightly more specific (95% CI for difference, 0.01-0.5) than standard MRI.

CONCLUSION

A fast 5-min MRI protocol is interchangeable with and has similar accuracy to a standard knee MRI for evaluating internal derangement of the knee.

Fast T1 mapping of the brain at high field using Look-Locker and fast imaging

This study aims to develop and evaluate a new method for fast high resolution T1 mapping of the brain based on the Look-Locker technique. Single-shot turboflash sequence with high temporal acceleration is used to sample the recovery of inverted magnetization. Multi-slice interleaved acquisition within one inversion slab is used to reduce the number of inversion pulses and hence SAR. Accuracy of the proposed method was studied using simulation and validated in phantoms. It was then evaluated in healthy volunteers and stroke patients. In-vivo results were compared to values obtained by inversion recovery fast spin echo (IR-FSE) and literatures. With the new method, T₁ values in phantom experiments agreed with reference values with median error <3%. For in-vivo experiments, a T1 map was acquired in 3.35s and the T1 maps of the whole brain were acquired in 2min with two-slice interleaving, with a spatial resolution of 1.1×1.1×4mm³. The T₁ values obtained were comparable to those measured with IR-FSE and those reported in literatures. These results demonstrated the feasibility of the proposed method for fast T1 mapping of the brain in both healthy volunteers and stroke patients at 3T.

Diagnostic Accuracy of MRI for Assessment of T Category and Circumferential Resection Margin Involvement in Patients With Rectal Cancer: A Meta-Analysis

BACKGROUND

The prognosis of rectal cancer is directly related to the stage of the tumor at diagnosis. Accurate preoperative staging is essential for selecting patients to receive optimal treatment.

OBJECTIVE

The purpose of this study was to evaluate the diagnostic performance of MRI in tumor staging and circumferential resection margin involvement in rectal cancer.

DATA SOURCES

A systematic literature search was performed in MEDLINE, EMBASE, PubMed, Cochrane Database of Systematic Reviews, and Web of Science database.

STUDY SELECTION

Original articles from 2000 to 2016 on the diagnostic performance of MRI in the staging of rectal cancer and/or assessment of mesorectal fascia status were eligible.

MAIN OUTCOME MEASURES

Pooled diagnostic statistics including sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio were calculated for invasion of muscularis propria, perirectal tissue, and adjacent organs and for circumferential resection margin involvement through bivariate random-effects modeling. Summary receiver operating characteristic curves were fitted, and areas under summary receiver operating characteristic curves were counted to evaluate the diagnostic performance of MRI for each outcome.

RESULTS

Thirty-five studies were eligible for this meta-analysis. Preoperative MRI revealed the highest sensitivity of 0.97 (95% CI, 0.96-0.98) and specificity of 0.97 (95% CI, 0.96-0.98) for muscularis propria invasion and adjacent organ invasion. Areas under summary receiver operating characteristic curves indicated good diagnostic accuracy for each outcome, with the highest of 0.9515 for the assessment of adjacent organ invasion. Significant heterogeneity existed among studies. There was no notable publication bias for each outcome.

LIMITATIONS

This meta-analysis revealed relatively high diagnostic accuracy for preoperative MRI, although significant heterogeneity existed. Therefore, exploration should be focused on standardized interpretation criteria and optimal MRI protocols for future studies.

CONCLUSIONS

MRI showed relatively high diagnostic accuracy for preoperative T staging and circumferential resection margin assessment and should be reliable for clinical decision making.

Mouse brain magnetic resonance microscopy: Applications in Alzheimer disease

Over the past two decades, various Alzheimer's disease (AD) trangenetic mice models harboring genes with mutation known to cause familial AD have been created. Today, high-resolution magnetic resonance microscopy (MRM) technology is being widely used in the study of AD mouse models. It has greatly facilitated and advanced our knowledge of AD. In this review, most of the attention is paid to fundamental of MRM, the construction of standard mouse MRM brain template and atlas, the detection of amyloid plaques, following up on brain atrophy and the future applications of MRM in transgenic AD mice. It is believed that future testing of potential drugs in mouse models with MRM will greatly improve the predictability of drug effect in preclinical trials.

Imaging of articular cartilage

We tried to review the role of magnetic resonance imaging (MRI) in understanding microscopic and morphologic structure of the articular cartilage. The optimal protocols and available spin-echo sequences in present day practice are reviewed in context of common pathologies of articular cartilage. The future trends of articular cartilage imaging have been discussed with their appropriateness. In diarthrodial joints of the body, articular cartilage is functionally very important. It is frequently exposed to trauma, degeneration, and repetitive wear and tear. MRI has played a vital role in evaluation of articular cartilage. With the availability of advanced repair surgeries for cartilage lesions, there has been an increased demand for improved cartilage imaging techniques. Recent advances in imaging strategies for native and postoperative articular cartilage open up an entirely new approach in management of cartilage-related pathologies.

Journal Club: Comparison of assessment of preoperative pulmonary vasculature in patients with non-small cell lung cancer by non-contrast- and 4D contrast-enhanced 3-T MR angiography and contrast-enhanced 64-MDCT

OBJECTIVE

The purpose of this article is to prospectively and directly compare the capabilities of non-contrast-enhanced MR angiography (MRA), 4D contrast-enhanced MRA, and contrast-enhanced MDCT for assessing pulmonary vasculature in patients with non-small cell lung cancer (NSCLC) before surgical treatment.

SUBJECTS AND METHODS

A total of 77 consecutive patients (41 men and 36 women; mean age, 71 years) with pathologically proven and clinically assessed stage I NSCLC underwent thin-section contrast-enhanced MDCT, non-contrast-enhanced and contrast-enhanced MRA, and surgical treatment. The capability for anomaly assessment of the three methods was independently evaluated by two reviewers using a 5-point visual scoring system, and final assessment for each patient was made by consensus of the two readers. Interobserver agreement for pulmonary arterial and venous assessment was evaluated with the kappa statistic. Then, sensitivity, specificity, and accuracy for the detection of anomalies were directly compared among the three methods by use of the McNemar test.

RESULTS

Interobserver agreement for pulmonary artery and vein assessment was substantial or almost perfect (κ=0.72-0.86). For pulmonary arterial and venous variation assessment, there were no significant differences in sensitivity, specificity, and accuracy among non-contrast-enhanced MRA (pulmonary arteries: sensitivity, 77.1%; specificity, 97.4%; accuracy, 87.7%; pulmonary veins: sensitivity, 50%; specificity, 98.5%; accuracy, 93.2%), 4D contrast-enhanced MRA (pulmonary arteries: sensitivity, 77.1%; specificity, 97.4%; accuracy, 87.7%; pulmonary veins: sensitivity, 62.5%; specificity, 100.0%; accuracy, 95.9%), and thin-section contrast-enhanced MDCT (pulmonary arteries: sensitivity, 91.4%; specificity, 89.5%; accuracy, 90.4%; pulmonary veins: sensitivity, 50%; specificity, 100.0%; accuracy, 95.9%) (p>0.05).

CONCLUSION

Pulmonary vascular assessment of patients with NSCLC before surgical resection by non-contrast-enhanced MRA can be considered equivalent to that by 4D contrast-enhanced MRA and contrast-enhanced MDCT.

In vivo chemical exchange saturation transfer imaging allows early detection of a therapeutic response in glioblastoma

Glioblastoma multiforme (GBM), which account for more than 50% of all gliomas, is among the deadliest of all human cancers. Given the dismal prognosis of GBM, it would be advantageous to identify early biomarkers of a response to therapy to avoid continuing ineffective treatments and to initiate other therapeutic strategies. The present in vivo longitudinal study in an orthotopic mouse model demonstrates quantitative assessment of early treatment response during short-term chemotherapy with temozolomide (TMZ) by amide proton transfer (APT) imaging. In a GBM line, only one course of TMZ (3 d exposure and 4 d rest) at a dose of 80 mg/kg resulted in substantial reduction in APT signal compared with untreated control animals, in which the APT signal continued to increase. Although there were no detectable differences in tumor volume, cell density, or apoptosis rate between groups, levels of Ki67 (index of cell proliferation) were substantially reduced in treated tumors. In another TMZ-resistant GBM line, the APT signal and levels of Ki67 increased despite the same course of TMZ treatment. As metabolite changes are known to occur early in the time course of chemotherapy and precede morphologic changes, these results suggest that the APT signal in glioma may be a useful functional biomarker of treatment response or degree of tumor progression. Thus, APT imaging may serve as a sensitive biomarker of early treatment response and could potentially replace invasive biopsies to provide a definitive diagnosis. This would have a major impact on the clinical management of patients with glioma.

High resolution MRI anatomy of the cat brain at 3 Tesla

BACKGROUND

Feline models of neurologic diseases, such as lysosomal storage diseases, leukodystrophies, Parkinson's disease, stroke and NeuroAIDS, accurately recreate many aspects of human disease allowing for comparative study of neuropathology and the testing of novel therapeutics. Here we describe in vivo visualization of fine structures within the feline brain that were previously only visible post mortem.

NEW METHOD

3Tesla MR images were acquired using T1-weighted (T1w) 3D magnetization-prepared rapid gradient echo (MPRAGE) sequence (0.4mm isotropic resolution) and T2-weighted (T2w) turbo spin echo (TSE) images (0.3mm×0.3mm×1mm resolution). Anatomic structures were identified based on feline and canine histology.

RESULTS

T2w high resolution MR images with detailed structural identification are provided in transverse, sagittal and dorsal planes. T1w MR images are provided electronically in three dimensions for unrestricted spatial evaluation.

COMPARISON WITH EXISTING METHODS

Many areas of the feline brain previously unresolvable on MRI are clearly visible in three orientations, including the dentate, interpositus and fastigial cerebellar nuclei, cranial nerves, lateral geniculate nucleus, optic radiation, cochlea, caudal colliculus, temporal lobe, precuneus, spinocerebellar tract, vestibular nuclei, reticular formation, pyramids and rostral and middle cerebral arteries. Additionally, the feline brain is represented in three dimensions for the first time.

CONCLUSIONS

These data establish normal appearance of detailed anatomical structures of the feline brain, which provide reference when evaluating neurologic disease or testing efficacy of novel therapeutics in animal models.

Imaging of VSOP labeled stem cells in agarose phantoms with susceptibility weighted and T2* weighted MR Imaging at 3T: determination of the detection limit

OBJECTIVES

This study aimed to evaluate the detectability of stem cells labeled with very small iron oxide particles (VSOP) at 3T with susceptibility weighted (SWI) and T2* weighted imaging as a methodological basis for subsequent examinations in a large animal stroke model (sheep).

MATERIALS AND METHODS

We examined ovine mesenchymal stem cells labeled with VSOP in agarose layer phantoms. The experiments were performed in 2 different groups, with quantities of 0-100,000 labeled cells per layer. 15 different SWI- and T2*-weighted sequences and 3 RF coils were used. All measurements were carried out on a clinical 3T MRI. Images of Group A were analyzed by four radiologists blinded for the number of cells, and rated for detectability according to a four-step scale. Images of Group B were subject to a ROI-based analysis of signal intensities. Signal deviations of more than the 0.95 confidence interval in cell containing layers as compared to the mean of the signal intensity of non cell bearing layers were considered significant.

RESULTS

GROUP A

500 or more labeled cells were judged as confidently visible when examined with a SWI-sequence with 0.15 mm slice thickness. Group B: 500 or more labeled cells showed a significant signal reduction in SWI sequences with a slice thickness of 0.25 mm. Slice thickness and cell number per layer had a significant influence on the amount of detected signal reduction.

CONCLUSION

500 VSOP labeled stem cells could be detected with SWI imaging at 3 Tesla using an experimental design suitable for large animal models.

Feasibility of an intracranial EEG-fMRI protocol at 3T: risk assessment and image quality

Integrating intracranial EEG (iEEG) with functional MRI (iEEG-fMRI) may help elucidate mechanisms underlying the generation of seizures. However, the introduction of iEEG electrodes in the MR environment has inherent risk and data quality implications that require consideration prior to clinical use. Previous studies of subdural and depth electrodes have confirmed low risk under specific circumstances at 1.5T and 3T. However, no studies have assessed risk and image quality related to the feasibility of a full iEEG-fMRI protocol. To this end, commercially available platinum subdural grid/strip electrodes (4×5 grid or 1×8 strip) and 4 or 6-contact depth electrodes were secured to the surface of a custom-made phantom mimicking the conductivity of the human brain. Electrode displacement, temperature increase of electrodes and surrounding phantom material, and voltage fluctuations in electrode contacts were measured in a GE Discovery MR750 3T MR scanner during a variety of imaging sequences, typical of an iEEG-fMRI protocol. An electrode grid was also used to quantify the spatial extent of susceptibility artifact. The spatial extent of susceptibility artifact in the presence of an electrode was also assessed for typical imaging parameters that maximize BOLD sensitivity at 3T (TR=1500 ms; TE=30 ms; slice thickness=4mm; matrix=64×64; field-of-view=24 cm). Under standard conditions, all electrodes exhibited no measurable displacement and no clinically significant temperature increase (<1°C) during scans employed in a typical iEEG-fMRI experiment, including 60 min of continuous fMRI. However, high SAR sequences, such as fast spin-echo (FSE), produced significant heating in almost all scenarios (>2.0°C) that in some cases exceeded 10°C. Induced voltages in the frequency range that could elicit neuronal stimulation (<10 kHz) were well below the threshold of 100 mV. fMRI signal intensity was significantly reduced within 20mm of the electrodes for the imaging parameters used in this study. Thus, for the conditions tested, a full iEEG-fMRI protocol poses a low risk at 3T; however, fMRI sensitivity may be reduced immediately adjacent to the electrodes. In addition, high SAR sequences must be avoided.

Intracranial EEG-fMRI analysis of focal epileptiform discharges in humans

PURPOSE

Combining intracranial electroencephalography (iEEG) with functional magnetic resonance imaging (fMRI) is of interest in epilepsy studies as it would allow the detection of much smaller interictal epileptiform discharges than can be recorded using scalp EEG-fMRI. This may help elucidate the spatiotemporal mechanisms underlying the generation of interictal discharges. To our knowledge, iEEG-fMRI has never been performed at 3 Tesla (3T) in humans. We report our findings relating to spike-associated blood oxygen level-dependent (BOLD) signal changes in two subjects.

METHODS

iEEG-fMRI at 3T was performed in two subjects. Twelve channels of iEEG were recorded from subdural strips implanted on the left posterior temporal and middle frontal lobes in a 20-year-old female with bilateral periventricular gray matter heterotopia. Twenty channels of iEEG were recorded bilaterally from two subdural strips laid anterior-posterior along mesial temporal surfaces in a 29-year-old woman with bilateral temporal seizures and mild left amygdalar enlargement on MRI. Functional MRI (fMRI) statistical maps were generated and thresholded at p = 0.01.

KEY FINDINGS

No adverse events were noted. A total of 105 interictal discharges were recorded in the posterior middle temporal gyrus of Subject 1. In Subject 2, 478 discharges were recorded from both mesial temporal surfaces (n = 194 left, 284 right). The right and left discharges were modeled separately, as they were independent. Subject 1 showed spike-associated BOLD signal increases in the left superior temporal region, left middle frontal gyrus, and right parietal lobe. BOLD decreases were seen in the right frontal and parietal lobes. In Subject 2, BOLD signal increases were seen in both mesial temporal lobes, which when left and right spikes were modeled independently, were greater on the side of the discharge. In addition, striking BOLD signal decreases were observed in the thalamus and posterior cingulate gyrus.

SIGNIFICANCE

iEEG-fMRI can be performed at 3T with low risk. Notably, runs of only 5 or 10 min of EEG-fMRI were performed as part of our implementation protocol, yet a significant number of epileptiform discharges were recorded, allowing meaningful analyses. With these studies, we have shown that deactivation can be seen in individual subjects with focal epileptiform discharges. These preliminary observations suggest a novel mechanism through which focal interictal discharges may have widespread cortical and subcortical influences.

T2*-weighted image/T2-weighted image fusion in postimplant dosimetry of prostate brachytherapy

Computed tomography (CT)/magnetic resonance imaging (MRI) fusion is considered to be the best method for postimplant dosimetry of permanent prostate brachytherapy; however, it is inconvenient and costly. In T2*-weighted image (T2*-WI), seeds can be easily detected without the use of an intravenous contrast material. We present a novel method for postimplant dosimetry using T2*-WI/T2-weighted image (T2-WI) fusion. We compared the outcomes of T2*-WI/T2-WI fusion-based and CT/T2-WI fusion-based postimplant dosimetry. Between April 2008 and July 2009, 50 consecutive prostate cancer patients underwent brachytherapy. All the patients were treated with 144 Gy of brachytherapy alone. Dose-volume histogram (DVH) parameters (prostate D90, prostate V100, prostate V150, urethral D10, and rectal D2cc) were prospectively compared between T2*-WI/T2-WI fusion-based and CT/T2-WI fusion-based dosimetry. All the DVH parameters estimated by T2*-WI/T2-WI fusion-based dosimetry strongly correlated to those estimated by CT/T2-WI fusion-based dosimetry (0.77 ≤ R ≤ 0.91). No significant difference was observed in these parameters between the two methods, except for prostate V150 (p = 0.04). These results show that T2*-WI/T2-WI fusion-based dosimetry is comparable or superior to MRI-based dosimetry as previously reported, because no intravenous contrast material is required. For some patients, rather large differences were observed in the value between the 2 methods. We thought these large differences were a result of seed miscounts in T2*-WI and shifts in fusion. Improving the image quality of T2*-WI and the image acquisition speed of T2*-WI and T2-WI may decrease seed miscounts and fusion shifts. Therefore, in the future, T2*-WI/T2-WI fusion may be more useful for postimplant dosimetry of prostate brachytherapy.

Imaging at higher magnetic fields: 3 T versus 1.5 T

Clinical hepatobiliary magnetic resonance (MR) imaging continues to evolve at a fast rate. However, three basic requirements must still be satisfied if novel high-field MR imaging techniques are to be included in the hepatobiliary imaging routine: improvement of parenchymal contrast, suppression of respiratory motion artifact, and anatomic coverage of the entire hepatobiliary system. This article outlines the various arenas involved in MR imaging of the hepatobiliary system at 3 Tesla (T) compared with 1.5 T by (1) highlighting magnetic field-dependent MR contrast phenomena that contribute to the overall appearance of high-field hepatobiliary imaging; (2) summarizing the biodistributions of different gadolinium chelates used as MR contrast agents and their effectiveness regarding the static magnetic field; (3) showing the implementation of advanced imaging techniques such as three-dimensional acquisition schemes and parallel acceleration techniques used in T1-, T2-, and diffusion-weighted hepatobiliary imaging; and (4) addressing artifact mechanisms exacerbated by, or originating from, increase of the static magnetic field.

A combined solenoid-surface RF coil for high-resolution whole-brain rat imaging on a 3.0 Tesla clinical MR scanner

Rat brain models effectively simulate a multitude of human neurological disorders. Improvements in coil design have facilitated the wider utilization of rat brain models by enabling the utilization of clinical MR scanners for image acquisition. In this study, a novel coil design, subsequently referred to as the rat brain coil, is described that exploits and combines the strengths of both solenoids and surface coils into a simple, multichannel, receive-only coil dedicated to whole-brain rat imaging on a 3.0 T clinical MR scanner. Compared with a multiturn solenoid mouse body coil, a 3-cm surface coil, a modified Helmholtz coil, and a phased-array surface coil, the rat brain coil improved signal-to-noise ratio by approximately 72, 61, 78, and 242%, respectively. Effects of the rat brain coil on amplitudes of static field and radiofrequency field uniformity were similar to each of the other coils. In vivo, whole-brain images of an adult male rat were acquired with a T(2)-weighted spin-echo sequence using an isotropic acquisition resolution of 0.25 x 0.25 x 0.25 mm(3) in 60.6 min. Multiplanar images of the in vivo rat brain with identification of anatomic structures are presented. Improvement in signal-to-noise ratio afforded by the rat brain coil may broaden experiments that utilize clinical MR scanners for in vivo image acquisition.

Comparison of multi-echo and single-echo gradient-recalled echo sequences for SPIO-enhanced liver MRI at 3 T

AIM

To assess the utility of a T2*-weighted, multi-echo data imaging combination sequenced on superparamagnetic iron oxide (SPIO)-enhanced liver magnetic resonance imaging (MRI) using a 3 T system.

MATERIALS AND METHODS

Fifty patients underwent SPIO-enhanced MRI at 3 T using T2*-weighted, single-echo, gradient-recalled echo (GRE) sequences [fast imaging with steady precession; repetition time (TR)/echo time (TE), 126 ms/9 ms; flip angle, 30°] and multi-echo GRE (multi-echo data image combination) sequences (TR/TE, 186 ms/9 ms; flip angle, 30°). Three radiologists independently reviewed the images in a random order. The sensitivity and accuracy for the detection of focal hepatic lesions (a total of 76 lesions in 33 patients; 48 solid lesions, 28 non-solid lesions) were compared by analysing the area under the receiver operating characteristic curves. Image artefacts (flow artefacts, susceptibility artefacts, dielectric artefacts, and motion artefacts), lesion conspicuity, and overall image quality were evaluated according to a four-point scale: 1, poor; 2, fair; 3, good; 4, excellent. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the lesions were compared.

RESULTS

Image artefacts were more frequent with single-echo GRE (p<0.05). The mean scale of image quality assessment for flow, susceptibility, dielectric, and motion artefacts were 2.76, 3.13, 3.42, and 2.89 with single-echo, respectively, compared with 3.47, 3.43, 3.47, and 3.39, respectively, with multi-echo GRE. There was no significant difference in lesion conspicuity between single-echo (3.15) and multi-echo (3.30) GRE sequences. The overall image quality was significantly (p<0.05) better with multi-echo (3.37) than with single-echo GRE (2.89). The mean SNR and CNR of the lesions were significantly (p<0.05) higher on multi-echo (79±23 and 128±59, respectively) images than on single-echo (38±11 and 102±44, respectively) images. Lesion detection accuracy and sensitivity were not significantly different between the two sequences. Mean accuracies and sensitivities were 0.864 and 0.785 for single-echo and 0.847 and 0.785 for multi-echo GRE, respectively.

CONCLUSION

At 3 T, the T2*-weighted, multi-echo data image combination sequence performs comparably to the T2*-weighted, single-echo GRE sequence for SPIO-enhanced MRI with good overall image quality and a decrease in undesired artefacts.

Prospective study on the mismatch concept in acute stroke patients within the first 24 h after symptom onset - 1000Plus study

Background

The mismatch between diffusion weighted imaging (DWI) lesion and perfusion imaging (PI) deficit volumes has been used as a surrogate of ischemic penumbra. This pathophysiology-orientated patient selection criterion for acute stroke treatment may have the potential to replace a fixed time window. Two recent trials - DEFUSE and EPITHET - investigated the mismatch concept in a multicenter prospective approach. Both studies randomized highly selected patients (n = 74/n = 100) and therefore confirmation in a large consecutive cohort is desirable. We here present a single-center approach with a 3T MR tomograph next door to the stroke unit, serving as a bridge from the ER to the stroke unit to screen all TIA and stroke patients. Our primary hypothesis is that the prognostic value of the mismatch concept is depending on the vessel status. Primary endpoint of the study is infarct growth determined by imaging, secondary endpoints are neurological deficit on day 5-7 and functional outcome after 3 months.

Methods and design

1000Plus is a prospective, single centre observational study with 1200 patients to be recruited. All patients admitted to the ER with the clinical diagnosis of an acute cerebrovascular event within 24 hours after symptom onset are screened. Examinations are performed on day 1, 2 and 5-7 with neurological examination including National Institute of Health Stroke Scale (NIHSS) scoring and stroke MRI including T2*, DWI, TOF-MRA, FLAIR and PI. PI is conducted as dynamic susceptibility-enhanced contrast imaging with a fixed dosage of 5 ml 1 M Gadobutrol. For post-processing of PI, mean transit time (MTT) parametric images are determined by deconvolution of the arterial input function (AIF) which is automatically identified. Lesion volumes and mismatch are measured and calculated by using the perfusion mismatch analyzer (PMA) software from ASIST-Japan. Primary endpoint is the change of infarct size between baseline examination and day 5-7 follow up.

Discussions

The aim of this study is to describe the incidence of mismatch and the predictive value of PI for final lesion size and functional outcome depending on delay of imaging and vascular recanalization. It is crucial to standardize PI for future randomized clinical trials as for individual therapeutic decisions and we expect to contribute to this challenging task.

Trial Registration

clinicaltrials.gov NCT00715533

Measurement of T1, T2, and magnetization transfer properties during embryonic development at 7 Tesla using the chicken model

PURPOSE

To evaluate whether techniques of high field magnetic resonance imaging may be used to characterize embryonic tissue during proliferation and differentiation.

MATERIALS AND METHODS

Thirteen chicken embryos with incubation times between 5 days and 16 days have been measured in a small animal magnetic resonance imager (ClinScan, Bruker) at 7 Tesla using the built-in resonator. T1, T2-, and magnetization transfer imaging was performed using fast spin-echo with inversion recovery, half acquisition single shot turbo spin-echo, and spoiled gradient-echo sequences with and without off-resonance pulse, respectively. T1, T2, and magnetization transfer ratio (MTR) maps were calculated on a pixel-by-pixel basis.

RESULTS

T1-, T2-, and MTR maps showed good image quality allowing for delineation of embryonic organs. During embryonic development, a decrease of T1 and T2 relaxation times was found, whereas, embryonic tissue typically showed an increase of magnetization transfer, for example, liver properties at day 5: T1 = 2431 +/- 163 ms, T2 = 122 +/- 12 ms, MTR = 9.2 +/- 4.2%; liver properties at day 16: T1 = 1763 +/- 89 ms, T2 = 71 +/- 4 ms, MTR = 16.9 +/- 2.2%.

CONCLUSION

Embryonic tissues show changing relaxation and magnetization transfer properties during development, therefore, high field MRI seems suitable for characterization of tissue replacement derived from embryonic stem cells.

3-T MRI with phased-array coil in local staging of prostatic cancer

RATIONALE AND OBJECTIVES

To evaluate the diagnostic accuracy of a 3-T magnetic resonance imaging (MRI) system with a phased-array coil (3T MRI) in the local staging of prostatic cancer.

MATERIALS AND METHODS

Between July 2004 and September 2007, 59 patients (mean age 66 years) with a histologic diagnosis of prostatic cancer underwent 3-T MRI with a phased-array coil. A total of 42/59 patients underwent a radical prostatectomy within 3 weeks of the MRI examination. Two radiologists with differing experience in the interpretation of prostatic imaging used a 1-5 scale score to assess extracapsular spread, seminal vesicle and neurovascular bundle infiltration, and prostatic apex involvement. The anatomopathologic examination conducted on histologic macrosections was the reference test used to evaluate the results of 3-T MRI. Interobserver reliability was assessed using the k value.

RESULTS

The sensitivity, specificity, and accuracy values obtained by the expert radiologist were 68%, 92%, and 83%, respectively, compared to 50%, 85%, and 71% for the identification of extracapsular spread and 81%, 62%, and 84% compared to 63%, 50%, and 55% for apex involvement. Interobserver reliability was good (k=0.71). Seminal vesicle infiltration was correctly identified in four of five cases and neurovascular bundle infiltration was identified in four of four cases.

CONCLUSIONS

Despite presenting diagnostic accuracy values lower than those reported in literature using 1.5-T endorectal coil MRI, the use of 3-T MRI with a phased-array coil could constitute a valid alternative to MRI techniques using endorectal coils in selected patients. Direct comparative studies between the two methods on large caseloads are required to confirm this hypothesis.

Diagnostic accuracy of 3.0-Tesla rectal magnetic resonance imaging in preoperative local staging of primary rectal cancer

OBJECTIVES

To evaluate the diagnostic accuracy of 3.0-T rectal magnetic resonance imaging (MRI) in the preoperative local staging of primary rectal cancer.

MATERIALS AND METHODS

Forty-two patients with surgically and pathologically proven primary rectal cancer who underwent preoperative gadobenate dimeglumine-enhanced 3.0-T rectal MRI, were enrolled in this retrospective study. Two radiologists, who were blinded to the pathology results, independently reviewed the MR images and recorded their confidence level for determination of perirectal extension, and regional lymph node (LN) involvement using a 5-point scale. The diagnostic accuracy of each reviewer for local staging was calculated by receiver operating characteristic (ROC) curve analysis. Interobserver agreement was also calculated using linear weighted kappa statistics.

RESULTS

The diagnostic accuracy (area under the ROC curve, Az) for determining perirectal extension was for reviewer 1, 0.860 (95% confidence interval, 0.72-0.95) and for reviewer 2, 0.853 (0.71-0.94), respectively. The Az for determination of regional LN involvement was for reviewer 1, 0.902 (0.77-0.97) and for reviewer 2, 0.843 (0.70-0.94), respectively. Interobserver agreement included, respectively, good, and moderate agreement for perirectal extension, and regional LN involvement (kappa = 0.662, and 0.522, respectively).

CONCLUSIONS

3.0-T rectal MRI can provide accurate information of perirectal extension and regional LN involvement in the preoperative local staging of primary rectal cancer.

3-Tesla MRI for the evaluation of myocardial viability: a comparative study with 1.5-Tesla MRI

PURPOSE

We compared 3-Tesla (3-T) and 1.5-Tesla (1.5-T) cardiac magnetic resonance imaging (MRI) for the assessment of myocardial viability in nearly identical experimental conditions.

MATERIALS AND METHODS

Thirty-five patients (mean age 63+/-11; 94.2% men) submitted to primary coronary angioplasty underwent both 3-T and 1.5-T cardiac MRI, which was considered the gold standard. Comparison was performed on the basis of the same viability imaging protocol, which included resting cine-MR [balanced fast-field echo (B-FFE) sequence] followed by contrast-enhanced MR to evaluate perfusion and delayed enhancement (DE). We then performed functional index measurements and visual estimation of kinesis, perfusion and DE referring to a 5-point scale. Image quality was assessed on the basis of signal to noise ratio (SNR) and contrast to noise ratio (CNR).

RESULTS

We found nonsignificant differences between the two scanners (P=NS) in measuring the functional and viability parameters. Myocardial SNR was significantly higher with 3-T MRI compared with 1.5-T MRI (61.3% gain). Even though a loss of CNR was recorded in B-FFE and in first-pass perfusion sequences (12.4% and 23.7%, respectively), on DE images, we quantified the increase of SNR and CNR of infarction of 387.8% and 330%, respectively.

CONCLUSIONS

We found that 3-T MRI showed high concordance with 1.5-T MRI in the evaluation of functional and viability parameters and provided better evidence of damaged myocardium.

Adaptations in trabecular bone microarchitecture in Olympic athletes determined by 7T MRI

PURPOSE

To produce in vivo high-resolution images of the knee and to determine the feasibility of using 7T MR to detect changes in trabecular bone microarchitecture in elite athletes (Olympic fencers) who undergo high impact activity.

MATERIALS AND METHODS

The dominant knees of four males from the U.S. Olympic Fencing Team and three matched healthy male controls were scanned in a 7T whole-body scanner using a quadrature knee coil with three-dimensional (3D) fast low angle shot (FLASH): 50 axial images at the distal femur (0.156 mm x 0.156 mm) and 80 axial images at the knee joint (0.195 mm x 0.195 mm). Bone volume fraction (BVF) and marrow volume fraction (MVF) images were computed and fuzzy distance transform (FDT) and digital topological analysis (DTA) were applied to determine: trabecular number (Tb.N), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp); BVF (BV/TV); trabecular and marrow space surface-to-curve ratio (SC, marker of plate to rod ratio); and trabecular and marrow space erosion index (EI, inverse marker for network connectivity). Quadriceps muscle volume (MV) was calculated as well. We calculated group means and performed two-tailed t-tests to determine statistical significance.

RESULTS

Compared to controls, fencers had: decreased Tb.Sp (P = 0.0082 at femur, P = 0.051 at joint); increased Tb.N (P < 0.05 at both femur and joint) and BV/TV (P < 0.001 at both femur and joint); increased trabecular SC and decreased marrow space SC (P < 0.01 at both femur and joint); decreased trabecular EI and increased marrow space EI (P < 0.01 at both femur and joint); and increased MV (P = 0.038). There was no difference in Tb.Th at the distal femur (P = 0.92) or joint (P = 0.71) between groups.

CONCLUSION

To our knowledge, this is the first study to perform 7T MRI of the knee in vivo. Elite athletes who undergo high impact activity have increased MV and improved trabecular bone structure compared to controls.

Optimal 3-T MRI for depiction of the finger A2 pulley: comparison between T1-weighted, fat-saturated T2-weighted and gadolinium-enhanced fat-saturated T1-weighted sequences

OBJECTIVE

To compare three spin-echo sequences, transverse T1-weighted (T1WI), transverse fat-saturated (FS) T2-weighted (T2WI), and transverse gadolinium-enhanced (Gd) FS T1WI, for the visualisation of normal and abnormal finger A2 pulley with magnetic resonance (MR) imaging at 3 tesla (T).

MATERIALS AND METHODS

Sixty-three fingers from 21 patients were consecutively investigated. Two musculoskeletal radiologists retrospectively compared all sequences to assess the visibility of normal and abnormal A2 pulleys and the presence of motion or ghost artefacts.

RESULTS

Normal and abnormal A2 pulleys were visible in 94% (59/63) and 95% (60/63) on T1WI sequences, in 63% (40/63) and 60% (38/63) on FS T2WI sequences, and in 87% (55/63) and 73% (46/63) on Gd FS T1WI sequences when read by the first and second observer, respectively. Motion and ghost artefacts were higher on FS T2WI sequences. Seven among eight abnormal A2 pulleys were detected, and were best depicted with Gd FS T1WI sequences in 71% (5/7) and 86% (6/7) by the first and the second observer, respectively.

CONCLUSION

In 3-T MRI, the comparison between transverse T1WI, FS T2WI, and Gd FS T1WI sequences shows that transverse T1WI allows excellent depiction of the A2 pulley, that FS T2WI suffers from a higher rate of motion and ghost artefacts, and transverse Gd FS T1WI is the best sequence for the depiction of abnormal A2 pulley.

Progress in application of high-field-strength MR to diagnosis and treatment of hepatocellular carcinoma

Magnetic resonance imaging (MRI), a modern imaging modality, cannot only diagnose diseases, but also participate in their treatment. With the increase in static magnetic field strength, the features of high-field-strength MRI become increasingly predominant, thus MRI has been widely used in the diagnosis and treatment of diseases. MRI at high field strength can provide information on abnormal function and metabolism, monitor therapeutic procedures and reactions, and present excellent morphologic images for hepatocellular carcinoma.

A review of MR physics: 3T versus 1.5T

This article illustrates changes in the underlying physics concepts related to increasing the main magnetic field from 1.5T to 3T. The effects of these changes on tissue constants and practical hardware limitations is discussed as they affect scan time, quality, and contrast. Changes in susceptibility artifacts, chemical shift artifacts, and dielectric effects as a result of the increased field strength are also illustrated. Based on these fundamental considerations, an overall understanding of the benefits and constraints of signal-to-noise ratio and contrast-to-noise ratio changes between 1.5T and 3T MR systems is developed.

MR microscopy of the lung in small rodents

Understanding how the mammalian respiratory system works and how it changes in disease states and under the influence of drugs is frequently pursued in model systems such as small rodents. These have many advantages, including being easily obtained in large numbers as purebred strains. Studies in small rodents are valuable for proof of concept studies and for increasing our knowledge about disease mechanisms. Since the recent developments in the generation of genetically designed animal models of disease, one needs the ability to assess morphology and function in in vivo systems. In this article, we first review previous reports regarding thoracic imaging. We then discuss approaches to take in making use of small rodents to increase MR microscopic sensitivity for these studies and to establish MR methods for clinically relevant lung imaging.

Body and Cardiovascular MR Imaging at 3.0 T

Potential advantages of magnetic resonance (MR) imaging at 3 T include higher signal-to-noise ratios, better image contrast, particularly in gadolinium-enhanced applications, and better spectral separation for spectroscopic applications. In terms of clinical imaging, these advantages can mean higher-spatial-resolution images, faster imaging, and improved MR spectroscopy. However, achieving superior imaging and spectroscopic quality at 3 T can be challenging. This review discusses many of the problems encountered in body and cardiovascular MR imaging at 3 T, such as increased susceptibility, B1 field inhomogeneity, and increased specific absorption rate. The article also considers solutions that are being pursued, such as parallel imaging, variable-rate selective excitation, and variable flip angle sequences. A review of the most commonly used pulse sequences provides practical tips on how these can be optimized for 3-T imaging. In the coming few years, substantial improvements in 3-T technology for clinical imaging and spectroscopy will undoubtedly be seen. An understanding of the basic principles on which these developments are based will help radiologists translate the advances into better imaging studies and, ultimately, better patient care.

Virchow-Robin spaces at MR imaging

Virchow-Robin (VR) spaces surround the walls of vessels as they course from the subarachnoid space through the brain parenchyma. Small VR spaces appear in all age groups. With advancing age, VR spaces are found with increasing frequency and larger apparent sizes. At visual analysis, the signal intensity of VR spaces is identical to that of cerebrospinal fluid with all magnetic resonance imaging sequences. Dilated VR spaces typically occur in three characteristic locations: Type I VR spaces appear along the lenticulostriate arteries entering the basal ganglia through the anterior perforated substance. Type II VR spaces are found along the paths of the perforating medullary arteries as they enter the cortical gray matter over the high convexities and extend into the white matter. Type III VR spaces appear in the midbrain. Occasionally, VR spaces have an atypical appearance. They may become very large, predominantly involve one hemisphere, assume bizarre configurations, and even cause mass effect. Knowledge of the signal intensity characteristics and locations of VR spaces helps differentiate them from various pathologic conditions, including lacunar infarctions, cystic periventricular leukomalacia, multiple sclerosis, cryptococcosis, mucopolysaccharidoses, cystic neoplasms, neurocysticercosis, arachnoid cysts, and neuroepithelial cysts.

Clinical evaluation of a speed optimized T2 weighted fast spin echo sequence at 3.0 T using variable flip angle refocusing, half-Fourier acquisition and parallel imaging

This paper aims to demonstrate the capabilities of a speed optimized T(2) weighted single-shot turbo spin echo sequence, using parallel imaging, variable flip angle refocusing and half-Fourier acquisition (FAS-TSE), in comparison with a standard TSE (sTSE) sequence in patients with suspected multiple sclerosis (MS). 33 patients presenting with a clinically isolated syndrome (CIS) suggestive of MS were prospectively examined on a 3.0 T MR system using FAS-TSE and a sTSE sequence. The FAS-TSE (scan time 11 s) and the sTSE (scan time 122 s) were compared regarding lesion detectability, lesion contrast, grey/white matter contrast, overall image quality and artefacts. Scanning parameters affecting image contrast and spatial resolution were kept identical. 208 lesions were detected using the sTSE sequence compared with 183 lesions (88%) using the FAS-TSE. The FAS-TSE was rated inferior regarding lesion contrast. The mean value/range/standard deviation of the lesion/white matter contrast were 0.26/0.06-0.49/0.089, respectively, with the sTSE vs 0.21/0.04-0.40/0.081 with the FAS-TSE. The FAS-TSE was rated inferior regarding overall image quality, but superior regarding motion artefacts. The grey/white matter contrast was qualitatively judged as comparable for both sequences. FAS-TSE provides sufficient T2-SE contrast and diagnostic image quality for whole brain studies in 11 s. It is suited to reduce motion artefacts in restless patients and for fast acquisition of additional scanning planes.

High-resolution magnetic resonance imaging (MRI) at 3.0 Tesla in the short-term follow-up of patients with proven cervical artery dissection

PURPOSE

For the imaging evaluation of patients with suspected cervical artery dissection (CAD) in the last decade, magnetic resonance imaging (MRI) has become the first line imaging modality. However, CAD is a highly dynamic process with rapid changes over time. Aim of this study was to assess the short-term morphologic changes in patients with proven CAD by MRI within 2 weeks after the initial diagnosis using a multicontrast high-resolution noninvasive vessel wall imaging approach at 3.0 T.

MATERIALS AND METHODS

Eighty-two patients with clinically suspected CAD were examined using a 3.0 T system (Gyroscan Intera, Philips). Imaging protocol consisted of 3-dimensional inflow MRA (repetition time [TR]/echo time [TE]/flip angle [FA] = 25 milliseconds/3.1 milliseconds/16 degrees, reconstructed voxel size 0.3 x 0.3 x 0.8 mm), black blood T1w 3-dimensional spoiled gradient echo (TR/TE/FA = 31 milliseconds/7.7 milliseconds/15 degrees, 0.3 x 0.3 x 1.0 mm), and fat suppressed T2w turbo spin echo (TSE) (TR/TE/echo train length = 3 heart beats/44 milliseconds/7, 0.3 x 0.3 x 2 mm). Three observers in consensus performed image analysis. Images were assessed with regard to presence and size of intramural hematoma, degree of stenosis, presence of intraluminal thrombus, development of pseudoaneurysm, and incidence of additional dissections. In 29 patients (35%) a dissection had initially been proven by direct visualization of an intramural hematoma. Twenty-one patients (72%; 7 male, 14 female; mean age 41.5 years) were available for follow-up studies leading to a total of 24 diseased cervical arteries being reevaluated 2 weeks later for prospective follow-up.

RESULTS

Mean interval between initial study and follow-up was 14.2 days (range 7-30 days). Eighteen patients had presented with an acute CAD in 1 artery, 3 patients with an acute CAD in 2 arteries. At follow-up, degree of stenosis had increased in 2 arteries, remained unchanged in 13, and decreased in 5 arteries. Four initially occluded arteries were recanalized at follow-up. In 3 arteries a pseudoaneurysm had been visible in the initial study and remained unchanged at follow-up; in 1 artery a new pseudoaneurysm was observed. In 3 arteries, new dissections were identified during follow-up.

CONCLUSION

High-resolution MRI of acute CAD at 3.0 T permits a refined cross-sectional and longitudinal analysis of the morphologic features of CAD. The increased signal-to-noise ratio at 3.0 T allows for a high spatial resolution permitting detailed analysis of the diseased vessel segment. An unequivocal distinction between intramural hematoma and thrombus was possible. Information could be gained with regard to recanalization, degree of stenosis, formation of pseudoaneurysm, and appearance of new dissections making short-term follow-up in pts with acute CAD recommendable. Further studies are needed to assess the relationship between short-term results and definite outcome.