3.0 T magnetic resonance in neuroradiology

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.

Prevalence of the interthalamic adhesion in the human brain: a review of literature

The interthalamic adhesion (IA) is a midline structure connecting the two thalami. Though it has been studied for centuries its exact function remains elusive. Early studies had noted its peculiar absence even among some healthy individuals. Population studies have investigated the differences in prevalence of IA in pathologic conditions and healthy controls. However, there is a general lack of consensus on IA prevalence in the healthy population. Understanding the true prevalence is critical in providing context for future studies, as well as uncovering further clues regarding IA's function. We systematically reviewed the existing literature to evaluate the prevalence of IA. The average prevalence among reviewed studies was higher than previously reported, at 87.3%. Studies utilizing magnetic resonance imaging rather than cadaveric specimens reported higher rates of IA prevalence. A higher prevalence among females was noted throughout the literature that persisted regardless of acquisition modality utilized.

Effect Evaluation of Combined Application of Magnetic Resonance Diffusion Tensor Imaging and Brain Function Imaging in Radiation Therapy of Brain Tumours Involving Motor Pathways

This study is an attempt to find a way for functional imaging information to be applied clinically in radiation therapy. The basal nucleus is a collective term for a group of neural nucleus in the central nervous system that connects the pontine, brainstem, and cerebral cortex, including the caudate nucleus, the bean-shaped nucleus, the screen-shaped nucleus, and the amygdala. It is difficult to find the exact position of these neural nuclei on the computed tomography (CT) image or the T1 or T2 sequence of magnetic resonance. However, the development of neurosurgery has partially confirmed that these functional nuclei are involved in advanced cognitive functions such as memory, emotion, and learning. Neurosurgery has tried to avoid damaging these nucleus groups during surgery to improve the quality of life of patients, and there is currently no clear strategy for this in radiotherapy. Because CT and magnetic resonance spin echo (SE) sequences are difficult to find the anatomical location of the nucleus, it is difficult to have any strategy to protect these functions in radiotherapy planning. This article uses diffusion tensor imaging (DTI) images and fiber bundle tracking to obtain a more accurate anatomical position of the nerve nucleus on the image, and provides some available strategies for radiotherapy to protect patients’ brain function. The conclusion of this paper is that the combined application of DTI and functional magnetic resonance imaging (fMRI) can better observe the relationship among tumours, functional areas and white matter fibers, and guide the designation of radiotherapy plans.

Factors associated with the size of the adhesio interthalamica based on 3.0-T magnetic resonance images

BACKGROUND

Adhesio interthalamica (AI) is a small structure connecting bilateral thalami.

PURPOSE

To evaluate the effects of patient age, sex, and lateral diameter of the third ventricle on the long diameter of the AI using multivariate analyses based on magnetic resonance (MR) images obtained with 3.0-T scanners.

MATERIAL AND METHODS

This clinical retrospective study included images of 153 patients who underwent MR examination using 3.0-T scanners. The long diameter of the AI and lateral diameter of the third ventricle were measured on images in the mid-sagittal plane and axial plane at the anterior commissure, respectively. Univariate and multivariate analyses were performed.

RESULTS

AI was observed in 138 patients (70 men, 68 women; mean age = 63.7 ± 13.7 years; mean AI size =5.34 ± 1.63 mm). By univariate analyses, patient age (r = -0.262, P = 0.002), sex ( P = 0.010), and lateral diameter of the third ventricle (r = -0.642, P < 0.001) were significantly associated with the long diameter of the AI. With multiple linear regression analyses with a stepwise selection of parameters, only the lateral diameter of the third ventricle (estimate = -0.432, P < 0.001) was significantly associated with the long diameter of the AI. The lateral diameter of the third ventricle was longer in patients without AI (15 patients) than in those with AI ( P = 0.006).

CONCLUSION

The lateral diameter of the third ventricle was a major factor negatively associated with the long diameter of the AI.

[Improvement of Brain Contrast Using Spin Echo T1-weighted Image at 3 T MRI]

Brain T₁-weighted images using spin echo (SE) sequence has poor contrast at 3.0 Tesla magnetic resonance imaging (3.0 T MRI) systems from the influence of crosstalk and magnetized transfer (MT) effect, and prolongation of the T₁ value. Therefore, improving of scan parameters has been reported such as excitation flip angle (FA) and interleave data acquisition. The purpose of this study was to show the effects of alterations of presaturation pulse amplitude and chemical shift selective (CHESS) pulse amplitude. Gray-to-white matter contrast increased with decreasing amplitude of presaturation pulse in whole brain imaging. Presaturation and CHESS pulse consist of radio frequency pulse. Therefore, both pulses have a similar effect on MT pulse. Manual alteration of presaturation pulse amplitude for each scan lacks versatility on clinical use. However, decreasing amplitude of presaturation pulse is equal to decreasing thickness of presaturation pulse. About CHESS pulse, it requires no manual alteration for each scan. For example, switching fat suppression mode from strong to weak increase T₁ contrast. Our study demonstrated that using not only low excitation FA and interleave date acquisition but also low amplitude of presaturation and CHESS pulse increase the contrast in T₁ SE brain scans at 3.0 T MRI.

Low-cost Volumetric Ultrasound by Augmentation of 2D Systems: Design and Prototype

Conventional two-dimensional (2D) ultrasound imaging is a powerful diagnostic tool in the hands of an experienced user, yet 2D ultrasound remains clinically underutilized and inherently incomplete, with output being very operator dependent. Volumetric ultrasound systems can more fully capture a three-dimensional (3D) region of interest, but current 3D systems require specialized transducers, are prohibitively expensive for many clinical departments, and do not register image orientation with respect to the patient; these systems are designed to provide improved workflow rather than operator independence. This work investigates whether it is possible to add volumetric 3D imaging capability to existing 2D ultrasound systems at minimal cost, providing a practical means of reducing operator dependence in ultrasound. In this paper, we present a low-cost method to make 2D ultrasound systems capable of quality volumetric image acquisition: we present the general system design and image acquisition method, including the use of a probe-mounted orientation sensor, a simple probe fixture prototype, and an offline volume reconstruction technique. We demonstrate initial results of the method, implemented using a Verasonics Vantage research scanner.

Optimization of scan parameters for T₁-FLAIR imaging at 1.5 and 3T using computer simulation

PURPOSE

We attempted to optimize scan parameters for T₁-weighted fluid-attenuated inversion recovery (T₁-FLAIR) sequence at 3 and 1.5 tesla (T) using computer simulation.

METHODS

We measured the T₁ and T₂ relaxation time values (T₁v and T₂v) of gray (GM) and white matter (WM) at 3 and 1.5T, generated computer-simulated T₁-FLAIR (CS-T₁-FLAIR) images using those values, and compared the simulated and actual T₁-FLAIR images to verify the contrast reliability of our computer simulation. We mathematically and visually evaluated CS-T₁-FLAIR images at various repetition times (TR) and echo times (TE).

RESULTS

At 3T, the measured relaxation values for GM were T₁v, 1524 ms, and T₂v, 85 ms, and for WM, T₁v, 750 ms, and T₂v, 65 ms. At 1.5T, the measured relaxation values for GM were T₁v, 1251 ms, and T₂v, 99 ms, and for WM, T₁v, 623 ms, and T₂v, 75 ms. Contrast of CS-T₁-FLAIR and actual T₁-FLAIR images was identical. An optimal TR of 3140 ms was determined for T₁-FLAIR at 3T and 2440 ms at 1.5T based on mathematical evaluation. The optimal TR ranges were 2400 to 3900 ms at 3T and 1800 to 3200 ms at 1.5T based on visual assessment of CS-T₁-FLAIR. A shorter TE provided better T₁ contrast.

CONCLUSION

We optimized T₁-FLAIR by focusing on its most important scan parameters using computer simulations and determined that a longer TR was suitable at 3T than at 1.5T. Our computer simulation was useful for determining the optimal scan parameters.

Deep versus periventricular white matter lesions and cognitive function in a community sample of middle-aged participants

The association of cerebral white matter lesions (WMLs) with cognitive status is not well understood in middle-aged individuals. Our aim was to determine the specific contribution of periventricular hyperintensities (PVHs) and deep white matter hyperintensities (DWMHs) to cognitive function in a community sample of asymptomatic participants aged 50 to 65 years. One hundred stroke- and dementia-free adults completed a comprehensive neuropsychological battery and brain MRI protocol. Participants were classified according to PVH and DWMH scores (Fazekas scale). We dichotomized our sample into low grade WMLs (participants without or with mild lesions) and high grade WMLs (participants with moderate or severe lesions). Analyses were performed separately in PVH and DWMH groups. High grade DWMHs were associated with significantly lower scores in executive functioning (-0.45 standard deviations [SD]), attention (-0.42 SD), verbal fluency (-0.68 SD), visual memory (-0.52 SD), visuospatial skills (-0.79 SD), and psychomotor speed (-0.46 SD). Further analyses revealed that high grade DWMHs were also associated with a three- to fourfold increased risk of impaired scores (i.e.,<1.5 SD) in executive functioning, verbal fluency, visuospatial skills, and psychomotor speed. Our findings suggest that only DWMHs, not PVHs, are related to diminished cognitive function in middle-aged individuals. (JINS, 2012, 18, 1-12).

Simultaneous electroencephalography-functional MRI at 3 T: an analysis of safety risks imposed by performing anatomical reference scans with the EEG equipment in place

PURPOSE

To describe heating effects to be expected in simultaneous electroencephalography (EEG) and magnetic resonance imaging (MRI) when deviating from the EEG manufacturer's instructions; to test which anatomical MRI sequences have a sufficiently low specific absorption rate (SAR) to be performed with the EEG equipment in place; and to suggest precautions to reduce the risk of heating.

MATERIALS AND METHODS

Heating was determined in vivo below eight EEG electrodes, using both head and body coil transmission and sequences covering the whole range of SAR values.

RESULTS

Head transmit coil: temperature increases were below 2.2°C for low SAR sequences, but reached 4.6°C (one subject, clavicle) for high SAR sequences; the equilibrium temperature T(eq) remained below 39°C. Body transmit coil: temperature increases were higher and more frequent over subjects and electrodes, with values below 2.6°C for low SAR sequences, reaching 6.9°C for high SAR sequences (T8 electrode) with T(eq) exceeding a critical level of 40°C.

CONCLUSION

Anatomical imaging should be based on T1-weighted sequences (FLASH, MPRAGE, MDEFT) with an SAR below values for functional MRI sequences based on gradient echo planar imaging. Anatomical sequences with a high SAR can pose a significant risk, which is reduced by using head coil transmission.

[Evaluation of crosstalk effect on spin-echo images at 1.5 and 3 T]

The purpose of this study is to evaluate the crosstalk effect on spin-echo (SE) images at 1.5 and 3 T MRI. We examined the influence of crosstalk by comparing the full width at half-maximum (FWHM) and slice profile of images of a wedge-shaped phantom for various slice gaps. We also assessed crosstalk effect in the brain by comparing image contrast among healthy volunteers (n=8). Among the subjects, the shapes of the slice profiles at 1.5 T were similar to those at 3 T for long repetition times (TRs); however, at shorter TRs, differences in slice profiles were observed among the subjects and were more apparent at 3 than at 1.5 T. The relative contrast between white matter and gray matter on T(1)-weighted images was lower at 3 than at 1.5 T. The crosstalk effect was strongest when the TR of the excitation pulse was short. The influence of the adjacent excitation pulse is important in the process of T(1) relaxation because T(1) values are greater at 3 T. In conclusion, the influence of crosstalk on SE T(1)-weighted images is greater at 3 than at 1.5 T.

Magnetic resonance imaging and safety aspects

Magnetic resonance imaging (MRI) is a technique that uses a magnetic field and radio waves to create detailed images of the organs and tissues within your body. MRI is safe, but if something goes wrong, it can go very wrong. Most reported cases of MRI-related injuries and the few fatalities that have occurred have apparently been the result of failure to follow safety guidelines or of use of inappropriate or outdated information related to the safety aspects of biomedical implants and devices. To prevent accidents in the MRI environment, therefore, it is necessary to revise information on biologic effects and safety according to changes that have occurred in MRI technology and with regard to current guidelines for biomedical implants and devices. This review provides an overview of and update on MRI biologic effects, discusses new or controversial MRI safety topics and issues, and presents evidence-based guidelines to ensure safety for patients and staff.

Dorsal visual pathway changes in patients with comitant extropia

Background

Strabismus is a disorder in which the eyes are misaligned. Persistent strabismus can lead to stereopsis impairment. The effect of strabismus on human brain is not unclear. The present study is to investigate whether the brain white structures of comitant exotropia patients are impaired using combined T1-weighted imaging and diffusion tensor imaging (DTI).

Principal Findings

Thirteen patients with comitant strabismus and twelve controls underwent magnetic resonance imaging (MRI) with acquisition of T1-weighted and diffusion tensor images. T1-weighted images were used to analyze the change in volume of white matter using optimized voxel-based morphology (VBM) and diffusion tensor images were used to detect the change in white matter fibers using voxel-based analysis of DTI in comitant extropia patients. VBM analysis showed that in adult strabismus, white matter volumes were smaller in the right middle occipital gyrus, right occipital lobe/cuneus, right supramarginal gyrus, right cingulate gyrus, right frontal lobe/sub-gyral, right inferior temporal gyrus, left parahippocampa gyrus, left cingulate gyrus, left occipital lobe/cuneus, left middle frontal gyrus, left inferior parietal lobule, and left postcentral gyrus, while no brain region with greater white matter volume was found. Voxel-based analysis of DTI showed lower fractional anisotropy (FA) values in the right middle occipital gyrus and right supramarginal gyrus in strabismus patients, while brain region with increased FA value was found in the right inferior frontal gyrus.

Conclusion

By combining VBM and voxel-based analysis of DTI results, the study suggests that the dorsal visual pathway was abnormal or impaired in patients with comitant exotropia.

Role of contrast-enhanced magnetic resonance angiography in spinal dural arteriovenous fistula

Spinal dural arteriovenous fistulae (SDAVF) are the most common vascular malformations of the spine. Although digital subtraction angiography (DSA) remains the standard of reference to diagnose and classify vascular spinal lesions, we investigated the clinical value of contrast-enhanced MR angiography (CE-MRA), equipped with TRICKS sequences, in localizing SDAVF before selective catheter angiography and possible subsequent treatment. We studied 16 consecutive patients suspected of harbouring vascular spinal cord malformations and we tried to determine the level and the side of the arterial feeder to the arteriovenous abnormality. In 12 cases the results were compared with DSA and/or possible post-operative findings. In nine cases CE-MRA correctly depicted the origin of the fistula: in particular one patient was treated surgically only on the basis of MRA results. Thanks to its elevated spatial and temporal resolution, spinal contrast-enhanced MRA using TRICKS sequences proved reliable in detecting and localizing the SDAVF arterial feeders and can be used as a guide to subsequent selective DSA examination.

Construction and assessment of a 3-T MRI brain template

New MR imaging protocols enable visualization of brain structures. However, for dedicated clinical applications such as targeting deep brain stimulation (DBS), a more accurate localization requires the use of atlases. We developed a three-dimensional digitized mono-subject anatomical template of the human brain based on 3-T magnetic resonance images (MRI). By averaging 15 registered T1 image acquisitions, we have shown that the final image corresponds to an optimal image, limited by the performance of the 3-T MR machine. We compared different preprocessing workflows for template construction. With the optimal strategy, along with validated existing processing methods, one T1 template and one T1-T2 mixing template were created in order to improve visualization of spatially complex deep structures. Reduction of voxel size to 0.25 mm(3) was also advantageous to observe fine structures and white matter/gray matter intensity crossings. Results demonstrated that such a template also improved inter-patient registration for population comparison in DBS. These MR templates are made freely available to our community (http://www.vmip.org/mritemplate) to serve as a reference for neuroimage processing methods.

Spin-echo T1-weighted imaging of the brain with interleaved acquisition and presaturation pulse at 3 T: a feasibility study before clinical use

RATIONALE AND OBJECTIVES

Although spin-echo (SE) sequence has some advantages over gradient-echo sequence in brain imaging, gradient-echo sequence is commonly used for T1-weighted imaging (T1WI) at 3 T because contrast on SE T1WI is widely believed to be poor at 3 T. Recently, gray-white matter contrast on single-slice and multi-slice SE imaging with interslice gap was reported as better at 3 T than at 1.5 T. This study examined the feasibility of interleaved SE T1WI of the brain at 3 T. This study also examined whether presaturation pulse (PP) sufficiently suppresses intra-arterial signals because these signals tend to be hyperintense due to longer T1 at 3 T.

MATERIALS AND METHODS

Subjects consisted of 18 healthy volunteers. Two sets of T1WI were performed using SE sequence. One set consisted of imaging without PP, and the other consisted of imaging with PP. Each set contained three types of gapless imaging as follows; sequential, 100% interleaved, and 200% interleaved imaging. In each subject, contrast-to-noise ratio between gray-matter and white-matter (CNR(GM-WM)) and intra-arterial signals were evaluated.

RESULTS

CNR(GM-WM) was significantly higher on interleaved images than on sequential images, regardless of PP (P < .0001). PP sufficiently suppressed intra-arterial signals (P < .0001).

CONCLUSION

CNR(GM-WM) on SE T1WI at 3 T can be improved by interleaved acquisition, and PP sufficiently suppressed intra-arterial signals. Interleaved SE T1WI with PP appears clinically feasible at 3 T.

Phenylketonuria: white-matter changes assessed by 3.0-T magnetic resonance (MR) imaging, MR spectroscopy and MR diffusion

PURPOSE

This study evaluated the sensitivity of a 3.0-Tesla (T) magnetic resonance imaging (MRI) in measuring cerebral phenylalanine using proton magnetic resonance spectroscopy and in assessing MR-documented white-matter changes by means of diffusion studies (diffusion-weighted imaging, apparent diffusion coefficient map; diffusion tensor imaging) in patients with phenylketonuria.

MATERIALS AND METHODS

Thirty-two patients with the classical clinical and biochemical deficits of phenylketonuria underwent biochemical (blood phenylalanine), genotypic (phenylalanine hydroxylase gene) and radiological investigation by means of MRI, proton magnetic resonance spectroscopy and diffusion magnetic resonance imaging with a 3.0-T scanner.

RESULTS

Periventricular and subcortical white-matter changes were detected on all MR scans. In 29/32 patients, proton magnetic resonance spectroscopy easily documented abnormal signal elevation at 7.36 ppm, corresponding to phenylalanine, despite its low concentration. Phenylalanine signal amplitude relative to the creatine/phosphocreatine signal increased linearly with blood phenylalanine values (r 0.7067; p<0.001). Diffusion MRI demonstrated hyperintensity in the areas exhibiting MRI changes as well as decreased apparent diffusion coefficient values, but fractional anisotropy indices were normal.

CONCLUSIONS

The high signal, together with better spectral, spatial, contrast and temporal resolution, makes the 3.0-T MR the most suitable technique in the study of the phenylketonuria. In particular, the multimodal approach with MRI, proton magnetic resonance spectroscopy and diffusion magnetic resonance imaging can provide more information than previous studies performed with low-field systems.

MR imaging of prostate cancer at 3T with an external phased-array coil: evaluation of T2-weighted images

1.5T Magnetic resonance (MR) imaging has become an accepted method for assessing prostate cancer. However, the role of 1.5T MRI in local staging of prostate cancer is limited. It is hoped that 3.0T MRI will be more useful in local staging of prostate cancer. The purpose of this study was to evaluate the tissue contrast, artifact presence, and image quality of T2-weighted images (T2WI) of prostate cancer using 3T MRI with a phased-array coil at different slice thicknesses and fields of view (FOV). We examined 15 patients with prostate cancer. We obtained MR images at slice thicknesses of 2 mm and 5 mm in both small and large FOV. The image obtained at a slice thickness of 2 mm with a small FOV had inferior tissue contrast compared to the other images (P<0.05), but there was no statistically significant difference in contrast between images obtained at a slice thickness of 2 mm with a large FOV and those obtained at a slice thickness of 5 mm. Artifacts were rated equally among the parameter combinations. The overall image quality obtained at a slice thickness of 2 mm with a large FOV was significantly superior to the other three imaging parameters (p<0.05). The image obtained at a slice thickness of 2 mm with a large FOV was superior to the other three images in evaluating T2WI of prostate cancer with 3T MRI.

Hypoxia-induced acute mountain sickness is associated with intracellular cerebral edema: a 3 T magnetic resonance imaging study

Acute mountain sickness is common among not acclimatized persons ascending to high altitude; the underlying mechanism is unknown, but may be related to cerebral edema. Nine healthy male students were studied before and after 6-h exposure to isobaric hypoxia. Subjects inhaled room air enriched with N(2) to obtain arterial O(2) saturation values of 75 to 80%. Acute mountain sickness was assessed with the environmental symptom questionnaire, and cerebral edema with 3 T magnetic resonance imaging in 18 regions of interest in the cerebral white matter. The main outcome measures were development of intra- and extracellular cerebral white matter edema assessed by visual inspection and quantitative analysis of apparent diffusion coefficients derived from diffusion-weighted imaging, and B0 signal intensities derived from T2-weighted imaging. Seven of nine subjects developed acute mountain sickness. Mean apparent diffusion coefficient increased 2.12% (baseline, 0.80+/-0.09; 6 h hypoxia, 0.81+/-0.09; P=0.034), and mean B0 signal intensity increased 4.56% (baseline, 432.1+/-98.2; 6 h hypoxia, 450.7+/-102.5; P<0.001). Visual inspection of magnetic resonance images failed to reveal cerebral edema. Cerebral acute mountain sickness scores showed a negative correlation with relative changes of apparent diffusion coefficients (r=-0.83, P=0.006); there was no correlation with relative changes of B0 signal intensities. In conclusion, isobaric hypoxia is associated with mild extracellular (vasogenic) cerebral edema irrespective of the presence of acute mountain sickness in most subjects, and severe acute mountain sickness with additional mild intracellular (cytotoxic) cerebral edema.

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.

Gray matter-white matter contrast on spin-echo T1-weighted images at 3 T and 1.5 T: a quantitative comparison study

Discrepancies exist in the literature regarding contrast between gray and white matter on spin-echo (SE) T1-weighted MR imaging at 3 T. The present study quantitatively assessed differences in gray matter-white matter contrast on both single- and multi-slice SE T1-weighted imaging between 3 and 1.5 T. SE T1-weighted sequences with the same parameters at both 3 and 1.5 T were used. Contrast-to-noise ratio (CNR) between gray and white matter (CNR(GM-WM)) was evaluated for both frontal lobes. To assess the effects of interslice gap, multi-slice images were obtained with both 0 and 25% interslice gap. Single-slice CNR(GM-WM) was higher at 3 T (17.66 +/- 2.68) than at 1.5 T (13.09 +/- 2.35; P < 0.001). No significant difference in CNR(GM-WM) of multi-slice images with 0% gap was noted between 3 and 1.5 T (3T, 8.61 +/- 2.55; 1.5T, 7.43 +/- 1.20; P > 0.05). Multi-slice CNR(GM-WM) with 25% gap was higher at 3T (12.47 +/- 3.31) than at 1.5 T (9.73 +/- 1.37; P < 0.001). CNR(GM-WM) reduction rate of multi-slice images with 0% gap compared with single-slice images was higher at 3T (0.47 +/- 0.13) than at 1.5 T (0.38 +/- 0.09; P = 0.02). CNR(GM-WM) on single-slice SE T1-weighted imaging and CNR(GM-WM) on multi-slice images with 25% interslice gap were better at 3 T than at 1.5 T. The influence of multi-slice imaging on CNR(GM-WM) was significantly larger at 3T than at 1.5 T.

MR lymphangiography using dendrimer-based contrast agents: A comparison at 1.5T and 3.0T

Most macromolecular contrast agents (CAs) show lower r1 and higher r2 relaxivities at 3.0T than at 1.5T. MR lymphangiography in mice using a macromolecular G6 dendrimer-based CA was serially performed and compared at both 1.5T and 3.0T. The r1 and r2 relaxivities of the G6 CA were 25 and 78/s/mM at 1.5T and 17 and 82/s/mM at 3.0T, respectively. The lymph node (LN)-to-fat ratios (LN signal intensity (SI)/fat SI) of T1-weighted 3D-fast spoiled gradient-echo (3D-FSPGR) were 3.2+/-0.4 (mean+/-standard deviation (SD)) at 1.5T and 2.7+/-0.3 at 3.0T (P=0.021), and the LN-to-fat ratios of T2/T1-weighted 3D-fast imaging employing steady-state acquisition with phase cycling (3D-FIESTA-C) were 1.8+/-0.2 at 1.5T and 1.2+/-0.4 at 3.0T (P=0.003). Although 3D-FSPGR successfully delineated the LNs at both 1.5T and 3.0T, 3D-FIESTA-C at 3.0T failed to visualize the LNs.

Safety concerns related to magnetic field exposure

The recent development of superconducting magnets has resulted in a huge increase in human exposure to very large static magnetic fields of up to several teslas (T). Considering the rapid advances in applications and the great increases in the strength of magnetic fields used, especially in magnetic resonance imaging, safety concerns about magnetic field exposure have become a key issue. This paper points out some of these safety concerns and gives an overview of the findings about this theme, focusing mainly on mechanisms of magnetic field interaction with living organisms and the consequent effects.

High spatial resolution contrast-enhanced MR angiography of the supraaortic arteries using the quadrature body coil at 3.0T: A feasibility study

To examine whether the the increased signal-to-noise (S/N) available at 3.0T would permit the use of the quadrature body coil for high spatial resolution contrast-enhanced (CE) MR angiography (MRA), and whether the large FOV that was used in our routine 1.5T protocol would also be feasible at 3.0T. In a prospective study, 43 patients and five volunteers were examined on a clinical whole-body 3.0T MR unit (Intera, Philips Medical Systems, Best, The Netherlands) after institutional review board approval and informed consent. Three-dimensional CE MRA (T1 gradient echo-sequence with TR/TE = 5.7/1.93 msec.; acquisition time, 1:54 min.) using randomly segmented central k-space ordering (CENTRA) was acquired with the quadrature body coil, using over a FOV of 350 mm. A high-image matrix of 432x432 yielded a non-zero filled voxel size of 0.81 mm x 0.81 mm x 1.0 mm (0.66 mm(3)). For quantitative analysis, contrast ratios (CR) between vessels (S) and signal in surrounding tissue (ST) were calculated [(S-ST)/(S+ST)]. For qualitative analysis, image quality and presence of artifacts were rated by two radiologists in consensus on a five-point scale (1=excellent to 5=nondiagnostic). Digital subtraction angiography (DSA) served as the standard of reference in patients with vascular disease. In the five volunteers, 1.5T CE MRA using a phased array neurovascular coil was available for intraindividual comparison. 3.0T CE MRA was successfully performed in 48/48 subjects (100%). Mean CR+/- SD were 0.76 (139.30/182.42) and 0.87 (235.18/270.14) at 3.0T and 1.5T respectively . Mean image quality was 3.82+/-0.86. Intraindividual comparison between 1.5T and 3.0T CE MRA in the volunteers revealed no significant difference in image quality (4.2+/-0.74 vs 4.6+/-0.80; p>0.05). Vascular disease was correctly identified in 13/13 patients with DSA correlation. CE MRA of the supraaortic arteries is feasible at 3.0T using a large FOV of 350 mm. The signal gain at 3.0T enables high spatial resolution contrast-enhanced MR angiography by using the built-in quadrature body coil only.

Technical report: Magnetic resonance direct thrombus imaging at 3 T field strength in patients with lower limb deep vein thrombosis: a feasibility study

AIM

To investigate the feasibility of imaging lower limb deep vein thrombosis using magnetic resonance imaging (MRI) at 3.0 T magnetic field strength with an optimized a T1 magnetization prepared rapid gradient echo technique (MP-RAGE) in patients with normal volunteers as controls.

MATERIALS AND METHODS

Patients with deep vein thrombosis (n = 4), thrombophlebitis (n = 2) and healthy volunteers (n = 9) were studied. MRI of the distal thigh and upper calf was performed at 3.0 T with MP-RAGE using two pre-pulses to suppress blood and fat (flip angle 15 degrees, echo time 5 ms, and repetition time 10 ms). A qualitative analysis was performed for detection of thrombi and image quality. Contrast-to-noise ratios were determined in thrombosed and patent veins.

RESULTS

Thrombi were clearly visible as high-signal intensity structures with good suppression of the anatomical background. A blinded reader accurately diagnosed 15 out of 16 cases. The contrast-to-noise ratio measurements showed a positive contrast of thrombus over background muscle 16.9 (SD 4.3, 95% CI: 12.5-21.3) and a negative contrast of the lumen to muscle in patent veins of normal volunteers -7.8 (SD 4.3, 95% CI: -11.1 to -4.5), with p = 0.0015.

CONCLUSION

Thrombi generate high signal intensity at 3.0 T allowing for their direct visualization if flowing blood, stationary blood and fat are sufficiently suppressed. This preliminary data supports the development of these techniques for other vascular applications.

MRI of the pelvis at 3 T: very high spatial resolution with sensitivity encoding and flip-angle sweep technique in clinically acceptable scan time

OBJECTIVE

The higher signal at 3.0-T allows spatial resolution to be increased without loss in image quality. We evaluated a T2-weighted turbo spin-echo sequence with high spatial resolution (3T-HR) to determine whether this provides clinically useful pelvic MRI.

MATERIALS AND METHODS

We designed a sequence with high spatial resolution (3T-HR) (0.45x0.46x4 mm) that was combined with parallel imaging and the variable refocusing angle technique (8.06 min). We examined 23 patients with gynecological disorders using 3T-HR and a standard sequence (3T-SP; 4.03 min; equivalent to 1.5 T). Two radiologists analyzed tissue contrast, signal to noise, detail delineation and artifact level.

RESULTS

Tissue contrasts and signal to noise were rated equal. Motion artifacts occurred more often with 3T-SP despite the longer scanning time of 3T-HR. The higher spatial resolution provided additional information in four patients. In two patients small myomas were detected, in one patient a lymph node metastasis was apparent, and in one patient 3T-HR excluded tumor invasion.

CONCLUSIONS

High spatial resolution pelvic studies with high image quality can be obtained at 3 T in acceptable scan time. The higher spatial resolution that is feasible at 3 T also provides more clinically relevant information.

High-throughput magnetic resonance imaging in mice for phenotyping and therapeutic evaluation

High-throughput mouse magnetic resonance imaging (MRI) is seeing rapidly increasing demand in development of therapeutics. Recent advances including higher-field systems, new gradient and radio frequency coils and new pulse sequences, coupled with efficient animal preparation and data handling, allow high-throughput MRI under certain protocols. However, with current shifts from anatomic to functional and molecular imaging, innovative technology is required to meet new throughput demands. The first multiple mouse imaging strategies have provided a glimpse of the future state-of-the-art. However, the successful translation of standard clinical MRI technology to preclinical MRI is required to facilitate next-generation high-throughput MRI.

Advances in Head and Neck Imaging

This article discusses new techniques in head and neck imaging.