Role of Diffusion-weighted Imaging, Perfusion Magnetic Resonance Imaging, and Magnetic Resonance Spectroscopy in Evaluating Histopathologically Confirmed Brain Tumors in 3-Tesla Magnetic Resonance Imaging

Objective: Our aim was to evaluate the diagnostic capabilities of physiological magnetic resonance imaging (MRI) in differentiatingtype and grades of tumor and correlation with prospective histopathology results.Materials and Methods: We evaluated 70 patients in 3-tesla MRI preoperatively using conventional and physiological MRsequences (diffusion, perfusion, and spectroscopy) of common brain tumors who were prospectively confirmed by histopathology.Post-imaging analysis was done by available software and ratio was calculated. Data were expressed as mean ± standarddeviation and median (range) and Kolmogorov–Smirnov analysis was used to check distribution. Multiple statistical tests wereapplied and receiver operating characteristic (ROC) curve was plotted wherever feasible.Results: We obtained a significant difference in spectroscopic parameters, relative cerebral blood volume, and apparent diffusioncoefficient values between different tumor groups and also between different tumor grades. ROC curve plotted among groupsshowed sensitivity and specificity of diagnostic capability. Time-intensity curve showed a significant difference between differenttumor groups and correlation with grades of tumor.Conclusion: We propose an algorithm for differentiating different types and grades of common brain tumor using physiologicalMRI in addition to conventional MR sequences.

Comparison of the Diagnostic Accuracies of 1.5T and 3T Stress Myocardial Perfusion Cardiovascular Magnetic Resonance for Detecting Significant Coronary Artery Disease

OBJECTIVE: To compare the diagnostic performance of cardiovascular magnetic resonance (CMR) myocardial perfusion at 1.5- and 3-tesla (T) for detecting significant coronary artery disease (CAD), with invasive coronary angiography (ICA) as the reference method. MATERIALS AND METHODS: We prospectively enrolled 281 patients (age 62.4 ± 8.3 years, 193 men) with suspected or known CAD who had undergone 1.5T or 3T CMR and ICA. Two independent radiologists interpreted perfusion defects. With ICA as the reference standard, the diagnostic performance of 1.5T and 3T CMR for identifying significant CAD (≥ 50% diameter reduction of the left main and ≥ 70% diameter reduction of other epicardial arteries) was determined. RESULTS: No differences were observed in baseline characteristics or prevalence of CAD and old myocardial infarction (MI) using 1.5T (n = 135) or 3T (n = 146) systems. Sensitivity, specificity, positive and negative predictive values, and area under the receiver operating characteristic curve (AUC) for detecting significant CAD were similar between the 1.5T (84%, 64%, 74%, 76%, and 0.75 per patient and 68%, 83%, 66%, 84%, and 0.76 per vessel) and 3T (80%, 71%, 71%, 80%, and 0.76 per patient and 75%, 86%, 64%, 91%, and 0.81 per vessel) systems. In patients with multi-vessel CAD without old MI, the sensitivity, specificity, and AUC with 3T were greater than those with 1.5T on a per-vessel basis (71% vs. 36%, 92% vs. 69%, and 0.82 vs. 0.53, respectively). CONCLUSION: 3T CMR has similar diagnostic performance to 1.5T CMR in detecting significant CAD, except for higher diagnostic performance in patients with multi-vessel CAD without old MI.

Efficacy of Maximum Intensity Projection of Contrast-Enhanced 3D Turbo-Spin Echo Imaging with Improved Motion-Sensitized Driven-Equilibrium Preparation in the Detection of Brain Metastases

OBJECTIVE: To evaluate the diagnostic benefits of 5-mm maximum intensity projection of improved motion-sensitized driven-equilibrium prepared contrast-enhanced 3D T1-weighted turbo-spin echo imaging (MIP iMSDE-TSE) in the detection of brain metastases. The imaging technique was compared with 1-mm images of iMSDE-TSE (non-MIP iMSDE-TSE), 1-mm contrast-enhanced 3D T1-weighted gradient-echo imaging (non-MIP 3D-GRE), and 5-mm MIP 3D-GRE. MATERIALS AND METHODS: From October 2014 to July 2015, 30 patients with 460 enhancing brain metastases (size > 3 mm, n = 150; size ≤ 3 mm, n = 310) were scanned with non-MIP iMSDE-TSE and non-MIP 3D-GRE. We then performed 5-mm MIP reconstruction of these images. Two independent neuroradiologists reviewed these four sequences. Their diagnostic performance was compared using the following parameters: sensitivity, reading time, and figure of merit (FOM) derived by jackknife alternative free-response receiver operating characteristic analysis. Interobserver agreement was also tested. RESULTS: The mean FOM (all lesions, 0.984; lesions ≤ 3 mm, 0.980) and sensitivity ([reader 1: all lesions, 97.3%; lesions ≤ 3 mm, 96.2%], [reader 2: all lesions, 97.0%; lesions ≤ 3 mm, 95.8%]) of MIP iMSDE-TSE was comparable to the mean FOM (0.985, 0.977) and sensitivity ([reader 1: 96.7, 99.0%], [reader 2: 97, 95.3%]) of non-MIP iMSDE-TSE, but they were superior to those of non-MIP and MIP 3D-GREs (all, p 0.75) for all lesions in both sequences. CONCLUSION: MIP iMSDE-TSE showed high detectability of brain metastases. Its detectability was comparable to that of non-MIP iMSDE-TSE, but it was superior to the detectability of non-MIP/MIP 3D-GREs. With a shorter reading time, the false-positive results of MIP iMSDE-TSE were greater. We suggest that MIP iMSDE-TSE can provide high diagnostic performance and low false-positive rates when combined with 1-mm sequences.

RM de corpo inteiro: avaliação de protocolo em equipamento 3T com 48 canais em menos de 40 minutos. Resultados preliminares / Whole-body MRI: comprehensive evaluation on a 48-channel 3T MRI system in less than 40 minutes. Preliminary results

OBJECTIVE: To evaluate a comprehensive MRI protocol that investigates for cancer, vascular disease, and degenerative/inflammatory disease from the head to the pelvis in less than 40 minutes on a new generation 48-channel 3T system. MATERIALS AND METHODS: All MR studies were performed on a 48-channel 3T MR scanner. A 20-channel head/neck coil, two 18-channel body arrays, and a 32-channel spine array were employed. A total of 4 healthy individuals were studied. The designed protocol included a combination of single-shot T2-weighted sequences, T1-weighted 3D gradient-echo pre- and post-gadolinium. All images were retrospectively evaluated by two radiologists independently for overall image quality. RESULTS: The image quality for cancer was rated as excellent in the liver, pancreas, kidneys, lungs, pelvic organs, and brain, and rated as fair in the colon and breast. For vascular diseases ratings were excellent in the aorta, major branch vessel origins, inferior vena cava, portal and hepatic veins, rated as good in pulmonary arteries, and as poor in the coronary arteries. For degenerative/inflammatory diseases ratings were excellent in the brain, liver and pancreas. The inter-observer agreement was excellent. CONCLUSION: A comprehensive and time efficient screening for important categories of disease processes may be achieved with high quality imaging in a new generation 48-channel 3T system.

OBJETIVO: Avaliar protocolo de RM para investigação de neoplasia, doenças vascular e degenerativa/inflamatória da cabeça à pelve em menos de 40 minutos em equipamento 3T com 48 canais. MATERIAIS E MÉTODOS: Todos os exames foram realizados em equipamento 3T com 48 canais. Foram utilizadas bobinas de cabeça/pescoço (20 canais), duas de corpo interligadas (18 canais) e uma de coluna (32 canais). Quatro voluntários saudáveis foram estudados. Foi utilizado protocolo com sequências single shot pesadas em T2 e gradiente-eco 3D pesadas em T1 pré e pós-gadolínio. Todas as imagens foram avaliadas quanto à qualidade, retrospectivamente, por dois radiologistas de forma independente. RESULTADOS: A qualidade da imagem foi classificada como excelente para o fígado, pâncreas, rins, pulmões, órgãos pélvicos e encéfalo, e como adequada para cólon e mamas. Para as doenças vasculares as imagens foram classificadas como excelentes para aorta e seus ramos principais, veia cava inferior, veias porta e hepáticas, como boas para artérias pulmonares, e como inadequadas para coronárias. As classificações para doenças degenerativas/inflamatórias foram excelente no encéfalo, fígado e pâncreas. A concordância interobservador foi excelente. CONCLUSÃO: Um rastreamento abrangente de importantes categorias de doenças pode ser realizado utilizando imagens de alta qualidade obtidas em uma nova geração de equipamento 3T com 48 canais.

Introduction to high field strength magnetic resonance imaging

Recently 3 tesla (T) magnetic resonance imaging (MRI) has been increasingly used in the clinical field. 3T MRI has many advantages, such as a better signal-to-noise ratio, increased chemical shift, and increased susceptibility, whereas it has several disadvantages such as increased relaxation time, radiofrequency field inhomogeneity, and increased specific absorption rate. The awareness of these advantages and disadvantages of 3T MRI will lead to better outcomes in clinical and research applications.

High field strength magnetic resonance imaging of cardiovascular diseases

Given the continuous advances in the hardware and software of magnetic resonance imaging (MRI), cardiac MRI has come to be a routine imaging modality in clinical settings for evaluating both cardiac function and anatomy in various cardiovascular diseases. Recently, 3 tesla (T) MRI has become available and has demonstrated advantages over 1.5T in a broad range of clinical applications although some technical challenges still remain. This review will focus on the potential advantages and limitations of 3T cardiac MRI and its current clinical applications.

High field strength magnetic resonance imaging of abdominal diseases

Due to the development of dedicated receiver coils for 3 tesla (T) magnetic resonance (MR) imaging and increased gradient performance, 3T MR imaging of the abdomen is rapidly becoming a part of routine clinical practice. The most important advantage of 3T MR imaging is a higher signal-to-noise ratio and contrast-to-noise ratio compared with 1.5T systems, which can be used to improve spatial resolution and shorten image acquisition time. In the abdomen, the improved image quality of non-enhanced and enhanced solid organ imaging, MR angiography, MR cholangiopancreatography, and MR spectroscopy can be obtained at 3T due to the increased signal-to-noise ratio and contrast-to-noise ratio. However, 3T abdominal MR imaging also presents several technical challenges, such as increased energy deposition within the patient's body, standing wave artifacts, and increased susceptibility artifacts. Therefore, abdominal MR imaging at 3T requires adjustments in the sequence parameters of pulse sequences designed for 1.5T to optimize image quality. At present, 3T abdominal MR imaging is feasible with high image quality in an acceptable scan time, but 3T imaging is not significantly superior to 1.5T imaging in terms of cost-effectiveness. Future improvements in coil technology and new sequences suitable for 3T may enable wider clinical use of 3T for abdominal MR imaging.

High field strength magnetic resonance imaging of musculoskeletal diseases

Musculskeletal magnetic resonance imaging (MRI) applications are making the transition rapidly from 1.5 tesla (T) to 3T. The higher signal-to-noise ratio (SNR) that is available with a 3T MRI system allows for greater spatial resolution and provides the potential to improve the diagnostic capability of musculoskeletal MRI. With the use of 3T systems, one can enhance the SNR, spatial resolution, and contrast-to-noise ratio of intrinsic joint structures such as osseous, tendinous, cartilaginous, and ligamentous structures, which makes them more discernable and amenable to proper radiologic assessment. The SNR gain and coil technology advances allow for a smaller voxel-size and parallel imaging, reducing the acquisition time without significant signal loss. Three-dimensional (3D) fast spin echo sequences with isotropic resolution reduce partial volume artifacts through the acquisition of thin continuous sections and enable free 3D-multiplanar-reformatting without loss of image quality. This technique may be a promising method to replace currently used 2D sequences in clinical practice. In addition to current clinical applications, 3T MRI will contribute to the development of new molecular and functional MRI techniques.

High field strength magnetic resonance imaging of brain lesion

The primary merit of a 3 tesla (T) magnetic resonance (MR) scanner is the increase in the signal-to-noise ratio (SNR). It can offer high spatial and temporal image resolution and its diagnostic potential for brain lesions can be improved at the magnetic strength of 3T. In addition to the increased SNR, strong prolongation of T1 relaxation time at high field MR leads to overall improvements in enhancing lesions versus non-enhancing tissue on contrast-enhanced T1-weighted images and blood versus tissue contrast on time-of-flight MR angiography. Increased chemical shift and susceptibility can improve the spectral resolution in MR spectroscopy and the sensitivities in the micro-hemorrhage detection of gradient echo image, the perfusion change of perfusion MRI, and the blood oxygen level-dependent effect of functional magnetic resonance imaging (MRI). The short acquisition time of diffusion MRI at 3T can decrease motion artifacts in irritable stroke patients and it can be easier to estimate anisotrophy and to increase the efficiency of tractography in diffusion tensor imaging with high numbers of gradient directions. On the other hand, the regulation of the specific absorption rate due to increased radio-frequency energy deposition and the controls for signal loss and increased artifacts at 3T are the main clinical problems. If the drawbacks can be addressed by parallel imaging or pulse sequence changes, 3T MRI can be a useful diagnostic tool and increase the diagnostic accuracy in various brain lesions, such as stroke, trauma, epilepsy, multiple sclerosis, dementia, and brain tumors.

High field strength magnetic resonance imaging in children

Thanks to the benefits of 3 tesla (T) magnetic resonance imaging (MRI), its clinical use is increasing in pediatric patients. However, technical considerations and clinical applications of 3T MRI have not been comprehensively reviewed. Potential advantages of 3T imaging over 1.5T imaging include a higher signal-to-noise ratio, higher contrast-to-noise ratio, higher spatial resolution, and shorter scan time. These merits are easily achieved in neuroimaging, musculoskeletal imaging, and pelvic imaging, while body imaging is substantially limited by dielectric shading and an increased specific absorption rate (SAR) owing to B1 inhomogeneity and increased susceptibility artifacts. T1 and T2 relaxation times as well as chemical shifts are influenced by the higher magnetic field strength. SAR issues and dielectric shading of 3T body MRI are less problematic in pediatric patients having a smaller body size. Improved image quality can be achieved by using parallel imaging, the shortest echo time or echo train length, the highest receiver bandwidth, and improved local shimming. Potential reduction of scan time at 3T should be emphasized for pediatric patients. Three-dimensional MRI with post-processing can improve the image quality in a short acquisition time and, therefore, has become a clinical reality at 3T. A dual-source parallel radiofrequency excitation system can reduce dielectric shading, SAR, and scan time by increasing B1 homogeneity, which eventually improves the image quality of 3T body MRI. The usefulness of 3T MRI in pediatric patients can be maximized by further technical developments and optimization.

T1-weighted MR Imaging of the Neonatal Brain at 3.0 Tesla: Comparison of Spin Echo, Fast Inversion Recovery, and Magnetization-prepared Three Dimensional Gradient Echo Techniques

PURPOSE: The purpose of this study was to evaluate the usefulness of fast inversion recovery (FIR) and magnetization-prepared three dimensional gradient echo sequence (3D GRE) T1-weighted sequences for neonatal brain imaging compared with spin echo (SE) sequence in a 3T MR unit. MATERIALS AND METHODS: T1-weighted axial SE, FIR and 3D GRE sequences were evaluated from 3T brain MR imaging in 20 neonates. The signal-to-noise ratio (SNR) of different tissues was measured and contrast-to-noise ratios (CNR) were determined and compared in each of the sequences. Visual analysis was carried out by grading gray-white matter differentiation, myelination, and artifacts. The Wilcoxon signed ranked test was used for evaluation of the statistical significance of CNR differences between the sequences. RESULTS: Among the three sequences, the 3D GRE had the best SNRs. CNRs obtained with FIR and 3D GRE were statistically superior to those obtained with SE; these CNRs were better on the 3D GRE compared to the FIR. Gray to white matter differentiation and myelination were better delineated on the FIR and 3D GRE than the SE. However, motion artifacts were more commonly observed on the 3D GRE and flow-related artifacts of vessels were frequently seen on the FIR. CONCLUSION: FIR and 3D GRE are valuable alternative T1-weighted sequences to conventional SE imaging of the neonatal brain at 3T providing superior image quality.