T1-Weighted Imaging of the Brain at 3 Tesla Using a 2-Dimensional Spoiled Gradient Echo Technique

The Clinical Utility of Magnetic Resonance Imaging According to Field Strength, Specifically Addressing the Breadth of Current State-of-the-Art Systems, Which Include 0.55 T, 1.5 T, 3 T, and 7 T

ABSTRACT

This review provides a balanced perspective regarding the clinical utility of magnetic resonance systems across the range of field strengths for which current state-of-the-art units exist (0.55 T, 1.5 T, 3 T, and 7 T). Guidance regarding this issue is critical to appropriate purchasing, usage, and further dissemination of this important imaging modality, both in the industrial world and in developing nations. The review serves to provide an important update, although to a large extent this information has never previously been openly presented. In that sense, it serves also as a position paper, with statements and recommendations as appropriate.

Evidence-based guidelines: MAGNIMS consensus guidelines on the use of MRI in multiple sclerosis-clinical implementation in the diagnostic process

The clinical use of MRI in patients with multiple sclerosis (MS) has advanced markedly over the past few years. Technical improvements and continuously emerging data from clinical trials and observational studies have contributed to the enhanced performance of this tool for achieving a prompt diagnosis in patients with MS. The aim of this article is to provide guidelines for the implementation of MRI of the brain and spinal cord in the diagnosis of patients who are suspected of having MS. These guidelines are based on an extensive review of the recent literature, as well as on the personal experience of the members of the MAGNIMS (Magnetic Resonance Imaging in MS) network. We address the indications, timing, coverage, reporting and interpretation of MRI studies in patients with suspected MS. Our recommendations are intended to help radiologists and neurologists standardize and optimize the use of MRI in clinical practice for the diagnosis of MS.

Detection of small brain metastases at 3 T: comparing the diagnostic performances of contrast-enhanced T1-weighted SPACE, MPRAGE, and 2D FLASH imaging

The aim of this study was to compare the diagnostic performance of contrast-enhanced T1-weighted sampling perfection with application-optimized contrasts using different flip angle evolutions (SPACE), magnetization-prepared rapid gradient-echo (MPRAGE), and two-dimensional (2D) fast low angle shot (FLASH) for the detection of small brain metastases. Twelve patients who had brain metastases less than 10 mm in diameter were enrolled. The diagnostic performance was evaluated using alternative free-response receiver operating characteristic analysis. Sensitivity and positive predictive value were also calculated. The mean Az and sensitivities of SPACE for all observers were significantly higher than those of MPRAGE and 2D FLASH.

Comparison of spin-echo T1- and T2-weighted and gradient-echo T1-weighted images at 3T in evaluating very preterm neonates at term-equivalent age

Term-equivalent imaging can assess myelination status in very preterm infants (<30 weeks' gestational age at birth). However, myelination assessment has yet to be compared among GRE-T1WI, SE-T1WI, and SE-T2WI at 3T. We aimed to compare the rates of myelination among those 3 sequences in 11 very preterm neonates who underwent 3T MR imaging at term-equivalent age and subsequently had normal neurologic development. On each sequence, 2 neuroradiologists individually assessed 22 structures. SE-T2WI depicted a higher myelination rate (present in 58.2%-66.4% of all structures) than either GRE-T1WI (51.6%-63.9%) or SE-T1WI (20.5%-38.5%), while GRE-T1WI had the highest interobserver agreement (κ, 0.56; P < .0001). Myelination was present in 90%-100% of patients within the corpus callosum splenium, DSCP, ICP, lateral lemniscus, and spinal tract/nucleus of cranial nerve V on SE-T2WI, and in the DSCP, ICP, lateral lemniscus, medial lemniscus, pyramidal decussation, PLIC, and superior cerebellar peduncle on GRE-T1WI, occurring in similar structures as previously shown at 1.5T and 1T. However, it is not clear whether these findings represent true myelination versus precursors to myelination.

Differentiating Components of Cerebral Arteriovenous Malformations Using T1-Weighted Gradient Recall Echo MR Imaging

Cerebral arteriovenous malformation (AVM) typically shows signal void on conventional MR images, making differentiation of each component difficult. We analyzed the MR signal intensity of AVM components on T1-weighted gradient recalled echo pulse sequence images. We retrospectively studied 29 patients with AVM between 2006 and 2008. Patients were excluded if they had 1) intracranial hemorrhage, 2) previous intervention for AVM. All patients underwent MR study on a 3T system (Magentom TIM Trio, Siemens). Pulse sequences included T1-weighted gradient recalled echo (T1GRE), T2-weighted (T2), time-of-flight (TOF), and contrast-enhanced T1-weighted (cT1) images. Digital subtracted angiography (DSA) was performed in all patients as a diagnostic standard. Signal intensity of each AVM component was recorded and compared between pulse sequences. Nine patients were studied (five men; mean age 39.1 years) and nine AVM were identified (mean size, 3.9 cm). Three different signal intensities (hypo-, iso-, and hyper-intensity) were observed in all nine patients on T1GRE. Only one signal intensity was seen on T2 (flow void) and cT1 images (hyperintensity) in nine patients. Two different signal intensities were observed in all seven patients with TOF images. The T1GRE image showed the largest number of different signal intensities of AVM when compared with other pulse sequences, thus providing clearer structural delineation. Routine use of the T1GRE pulse sequence can help pre-therapeutic planning or follow-up of AVM.

Three-dimensional gradient echo versus spin echo sequence in contrast-enhanced imaging of the pituitary gland at 3T

INTRODUCTION

To clarify whether a three-dimensional-gradient echo (3D-GRE) or spin echo (SE) sequence is more useful for evaluating sellar lesions on contrast-enhanced T1-weighted MR imaging at 3.0Tesla (T).

METHODS

We retrospectively assessed contrast-enhanced T1-weighted images using 3D-GRE and SE sequences at 3.0T obtained from 33 consecutive patients with clinically suspected sellar lesions. Two experienced neuroradiologists evaluated the images qualitatively in terms of the following criteria: boundary edge of the cavernous sinus and pituitary gland, border of sellar lesions, delineation of the optic nerve and cranial nerves within the cavernous sinus, susceptibility and flow artifacts, and overall image quality.

RESULTS

At 3.0T, 3D-GRE provided significantly better images than the SE sequence in terms of the border of sellar lesions, delineation of cranial nerves, and overall image quality; there was no significant difference regarding the boundary edge of the cavernous sinus and pituitary gland. In addition, the 3D-GRE sequence showed fewer pulsation artifacts but more susceptibility artifacts.

CONCLUSION

Our results indicate that 3D-GRE is the more suitable sequence for evaluating sellar lesions on contrast-enhanced T1-weighted imaging at 3.0T.

Usefulness of contrast-enhanced T1-weighted sampling perfection with application-optimized contrasts by using different flip angle evolutions in detection of small brain metastasis at 3T MR imaging: comparison with magnetization-prepared rapid acquisition of gradient echo imaging

BACKGROUND AND PURPOSE

Early accurate diagnosis of brain metastases is crucial for a patient's prognosis. This study aimed to compare the conspicuity and detectability of small brain metastases between contrast-enhanced 3D fast spin-echo (sampling perfection with application-optimized contrasts by using different flip angle evolutions [SPACE]) and 3D gradient-echo (GE) T1-weighted (magnetization-prepared rapid acquisition of GE [MPRAGE]) images at 3T.

MATERIALS AND METHODS

Sixty-nine consecutive patients with suspected brain metastases were evaluated prospectively by using SPACE and MPRAGE on a 3T MR imaging system. After careful evaluation by 2 experienced neuroradiologists, 92 lesions from 16 patients were selected as brain metastases. We compared the shorter diameter, contrast rate (CR), and contrast-to-noise ratio (CNR) of each lesion. Diagnostic ability was compared by using receiver operating characteristic (ROC) analysis. Ten radiologists (5 neuroradiologists and 5 residents) participated in the reading.

RESULTS

The mean diameter was significantly larger by using SPACE than MPRAGE (mean, 4.5 +/- 3.7 versus 4.3 +/- 3.7 mm, P = .0014). The CR and CNR of SPACE (mean, 57.3 +/- 47.4%, 3.0 +/- 1.9, respectively) were significantly higher than those of MPRAGE (mean, 37.9 +/- 41.2%, 2.6 +/- 2.2; P < .0001, P = .04). The mean area under the ROC curve was significantly larger with SPACE than with MPRAGE (neuroradiologists, 0.99 versus 0.88, P = .013; residents, 0.99 versus 0.78, P = .0001).

CONCLUSIONS

Lesion detectability was significantly higher on SPACE than on MPRAGE, irrespective of the experience of the reader in neuroradiology. SPACE should be a promising diagnostic technique for assessing brain metastases.

[Suppression of CSF artifact in fast FLAIR sequence at 3.0 Tesla]

The purpose of this study was to suppress CSF flow artifacts in the fast FLAIR sequence at 3.0T MRI. We investigated the influence of thickness of the inversion pulse in the sequence on the high-intensity CSF flow artifacts based on the flow phantom and in-vivo studies at 1.5T and 3.0T. Results demonstrated that CSF flow artifacts at 3.0T were clearly stronger than at as 1.5T. Moreover, 3.0T was influenced by the crosstalk between each inversion pulse compared with 1.5T. The optimal setting of inversion pulse for two interleaving acquisitions for fast FLAIR imaging at 3.0T was approximately 1.5 fold on the basis of sum of slice thickness and slice gap. The appropriate setting of thickness of inversion pulse in fast FLAIR imaging reduces the incidence of CSF flow artifacts at 3.0T.

Contrast-enhanced MR imaging of metastatic brain tumor at 3 tesla: utility of T(1)-weighted SPACE compared with 2D spin echo and 3D gradient echo sequence

We evaluated the newly developed whole-brain, isotropic, 3-dimensional turbo spin-echo imaging with variable flip angle echo train (SPACE) for contrast-enhanced T(1)-weighted imaging in detecting brain metastases at 3 tesla (T). Twenty-two patients with suspected brain metastases underwent postcontrast study with SPACE, magnetization-prepared rapid gradient-echo (MP-RAGE), and 2-dimensional T(1)-weighted spin echo (2D-SE) imaging at 3T. We quantitatively compared SPACE, MP-RAGE, and 2D-SE images by using signal-to-noise ratios (SNRs) for gray matter (GM) and white matter (WM) and contrast-to-noise ratios (CNRs) for GM-to-WM, lesion-to-GM, and lesion-to-WM. Two blinded radiologists evaluated the detection of brain metastases by segment-by-segment analysis and continuously-distributed test. The CNR between GM and WM was significantly higher on MP-RAGE images than on SPACE images (P<0.01). The CNRs for lesion-to-GM and lesion-to-WM were significantly higher on SPACE images than on MP-RAGE images (P<0.01). There was no significant difference in each sequence in detection of brain metastases by segment-by-segment analysis and the continuously-distributed test. However, in some cases, the lesions were easier to detect in SPACE images than in other sequences, and also the vascular signals, which sometimes mimic lesions in MP-RAGE and 2D-SE images, were suppressed in SPACE images. In detection of brain metastases at 3T magnetic resonance (MR) imaging, SPACE imaging may provide an effective, alternative approach to MP-RAGE imaging for 3D T(1)-weighted imaging.

Advances in magnetic resonance (2007)

Advances in clinical magnetic resonance (MR) are discussed in this review in the context of publications from Investigative Radiology during 2006 and 2007. The articles relevant to this topic, published during this 2 year time period, are considered as organized by anatomic region. An additional final focus of discussion is in regards to those studies involving MR contrast media.

Brain Tumor Enhancement in MR Imaging at 3 Tesla

PURPOSE

The purpose of this study was to compare brain and tumor signal characteristics of T1-weighted turbo spin-echo (TSE) and gradient recalled echo (GRE) sequence techniques at 3 T compared to TSE at 1.5 T, focusing on the detection of contrast enhancement, in a standardized animal model of a brain glioma.

MATERIALS AND METHODS

Twelve rats with implanted brain gliomas were evaluated at 1.5 and 3 T using matched hardware configurations. At 1.5 T, scanning was performed using a TSE sequence optimized for field strength (480/15 milliseconds; 125 Hz/Px) with postcontrast scans acquired at multiple time points after gadoteridol injection (0.1 mmol/kg). At 3 T, scanning was performed using the 1.5 T equivalent TSE as well as with TSE and GRE techniques optimized for 3 T. Signal-to-noise ratio (SNR) of brain and tumor and tumor contrast-to-noise ratio (CNR) were evaluated for all techniques at both field strengths.

RESULTS

Postcontrast tumor SNR (63.7 +/- 10.8 vs. 29.5 +/- 4.3; P < 0.0001) and brain SNR (35.8 +/- 1.5 vs. 19.1 +/- 0.7; P < 0.0001) showed significant increase at 3 T using matched TSE. Comparing TSE optimized to each field strength (for optimized gray-white contrast), tumor and brain SNR still showed a significant increase at 3 T of 73% and 56%, respectively (both P < 0.0001). Comparing TSE at 1.5 T and GRE at 3 T, tumor SNR increased by 105%, whereas brain SNR increased by 141% (both P < 0.0001). Tumor CNR with matched TSE increased by 168% (P < 0.0001), with optimized TSE by 111% (P < 0.0001), and with GRE at 3 T versus TSE at 1.5 T by 36% (P < 0.001). With additional adjustments for echo time the gain in tumor CNR for 2D GRE may again reach 60%.

CONCLUSIONS

With TSE at 3 T, the SNR gain comes close to the theoretically expected doubling with an even higher tumor CNR increase. In a clinical like setting at 3 T, where a T1w GRE sequence is used, tumor CNR gain is limited. Contrast dose should therefore not be decreased at 3 T.

High-Resolution Whole-Body Magnetic Resonance Imaging Applications at 1.5 and 3 Tesla

OBJECTIVES

To analyze the impact of altered magnetic field properties on image quality and on potential artifacts when an established whole-body magnetic resonance imaging (WB-MRI) protocol at 1.5 Tesla (T) is migrated to 3 T.

MATERIALS AND METHODS

Fifteen volunteers underwent noncontrast magnetic resonance imaging (MRI) on 32-channel whole body-scanners at 1.5 and 3 T with the use of parallel acquisition techniques (PAT). Coronal T1-weighted TSE- and short tau inversion recovery (STIR)-sequences at 4 body levels including sagittal imaging of the whole spine were performed. Additional axial HASTE-imaging of lung and abdomen, T1-/T2-weighted-TSE- and EPI-sequences of the brain and T2-weighted respiratory-triggered imaging of the liver was acquired. Both data sets were compared by 2 independent readers in respect to artifacts and image quality using a 5-point scale. Regions of pronounced artifacts were defined.

RESULTS

Overall image impression was both qualitatively rated as "good" at 1.5 and 3 T for T1-w-TSE- and STIR-imaging of the whole body and spine. At 1.5 T, significantly better quantitative values for overall image quality were found for WB-STIR, T2-w-TSE imaging of the liver and brain (Wilcoxon Mann-Whitney U Test; P < 0.05), overall rated as good at 3 T. Significantly higher dielectric effects at 3 T were affecting T1-w- and STIR-WB-MRI, and HASTE of the abdomen and better image homogeneity at 1.5 T was observed for T1-weighted-/STIR-WB-MRI and T1-w-TSE-imaging of the spine. Pulsation artifacts were significantly increased at 3 T for T1-w WB-MRI. Significantly higher susceptibility artifacts were found for GRE-sequences of the brain at 3 T. Motion artifacts, Gibbs-Ringing, and image distortion was not significantly different and showed slightly higher quantitative values at 3 T (except for HASTE imaging of the abdomen). Overall scan time was 45 minutes and 44 seconds at 1.5 T and 40 minutes and 28 seconds at 3 T at identical image resolution.

CONCLUSION

Three Tesla WB-MRI is feasible with good image quality comparable to 1.5 T. 3.0 T WB-MRI shows significantly more artifacts with a mild to moderate impact on image assessment. Therefore 1.5 T WB-MRI is the preferred image modality. Overall scan time at 3 T is reduced with the use of parallel imaging at a constant image resolution.

Advances in Magnetic Resonance (2006)

Advances in the field of magnetic resonance (MR) as it pertains to clinical diagnostic radiology are examined in this review on the basis of publications in Investigative Radiology over the past 2 years (2005-2006). The articles published during that timeframe are discussed, organizationally wise, by anatomic region with an additional focus on studies involving MR contrast media.

Brain magnetic resonance imaging at 3 Tesla using BLADE compared with standard rectilinear data sampling

OBJECTIVES

We sought to evaluate Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction (PROPELLER; BLADE) data acquisition in comparison with standard k-space sampling techniques for axial and sagittal brain imaging at 3 T regarding imaging artifacts.

MATERIAL AND METHODS

Forty patients who gave consent were included in a prospective comparison of standard and PROPELLER (BLADE) k-space sampling techniques. All examinations were performed at 3 T with comparison of standard T2-weighted fluid-attenuated inversion recovery (FLAIR) to PROPELLER T2-weighted FLAIR in the axial image orientation and standard T1-weighted gradient echo to PROPELLER T1-weighted FLAIR in the sagittal image orientation. Imaging protocols were matched for spatial resolution, with data evaluation performed by 2 experienced neuroradiologists. Image data were compared regarding various image artifacts and overall image quality. Reader agreement was assessed by Cohen's kappa statistics.

RESULTS

PROPELLER T2-weighted axial data acquisition showed significantly less pulsation and Gibb's artifacts than the standard T2-weighted scan. Even without motion correction, the frequency of ghosting (motion) artifacts was substantially lower in the PROPELLER T2-weighted data and readers concordantly (kappa = 1) rated PROPELLER as better than or equal to the standard T2-weighted scan in the majority of cases (95%; P < 0.0001). In the comparison of sagittal T1-weighted data sets, readers showed only fair agreement (kappa = 0.24) and noted consistent wrap artifacts in PROPELLER T1-weighted FLAIR.

CONCLUSION

PROPELLER (BLADE) brain magnetic resonance imaging is also applicable at 3 T. In addition to minimizing motion artifacts, the PROPELLER acquisition scheme reduces other magnetic resonance artifacts that would otherwise degrade scan quality.

Magnetic resonance imaging at 3.0 tesla detects more lesions in acute optic neuritis than at 1.5 tesla

OBJECTIVE

We sought to assess whether magnetic resonance imaging (MRI) at 3.0 T detects more brain lesions in acute optic neuritis (ON) than MRI at 1.5 T.

MATERIALS AND METHODS

Twenty-eight patients with acute ON were scanned at both field-strengths using fast-fluid-attenuated inversion recovery (FLAIR), proton density and T2-weighted turbo spin echo, and T1-weighted spin echo after contrast. In addition, magnetization-prepared rapid acquisition gradient echo (MPRAGE) was obtained after contrast at 3.0 T. Lesion number and volumes were assessed by an observer blind to patient identity and field strength.

RESULTS

Scans at 3.0 T showed a significantly increase in number of lesions detected on FLAIR images (P = 0.002) relative to scanning at 1.5 T. MPRAGE proved to be suitable for detecting enhancing lesions in ON.

CONCLUSION

The MRI protocol at 3.0 T was more sensitive to hyperintense brain lesions in ON than the standard MRI protocol at 1.5 T.