Three-dimensional MP-RAGE--an alternative to conventional three-dimensional FLASH sequences for the diagnosis of viscerocranial tumours?

Stationary EEG pattern relates to large-scale resting state networks - An EEG-fMRI study connecting brain networks across time-scales

Relating brain dynamics acting on time scales that differ by at least an order of magnitude is a fundamental issue in brain research. The same is true for the observation of stable dynamical structures in otherwise highly non-stationary signals. The present study addresses both problems by the analysis of simultaneous resting state EEG-fMRI recordings of 53 patients with epilepsy. Confirming previous findings, we observe a generic and temporally stable average correlation pattern in EEG recordings. We design a predictor for the General Linear Model describing fluctuations around the stationary EEG correlation pattern and detect resting state networks in fMRI data. The acquired statistical maps are contrasted to several surrogate tests and compared with maps derived by spatial Independent Component Analysis of the fMRI data. By means of the proposed EEG-predictor we observe core nodes of known fMRI resting state networks with high specificity in the default mode, the executive control and the salience network. Our results suggest that both, the stationary EEG pattern as well as resting state fMRI networks are different expressions of the same brain activity. This activity is interpreted as the dynamics on (or close to) a stable attractor in phase space that is necessary to maintain the brain in an efficient operational mode. We discuss that this interpretation is congruent with the theoretical framework of complex systems as well as with the brain's energy balance.

3D fast low-angle shot (FLASH) technique for 3T contrast-enhanced brain MRI in the inpatient and emergency setting: comparison with 3D magnetization-prepared rapid gradient echo (MPRAGE) technique

PURPOSE

To retrospectively evaluate the diagnostic performance of a 1-min contrast-enhanced 3D-FLASH pulse sequence for detecting intracranial enhancing lesions compared to standard contrast-enhanced 3D-MPRAGE pulse sequence.

METHODS

Contrast-enhanced 3D-FLASH (acquisition time 49 s) and contrast-enhanced 3D-MPRAGE (4 min 35 s) pulse sequences were performed consecutively in 110 inpatient/emergency department 3T MRI brain examinations and analyzed by two independent neuroradiologist readers. For each sequence, the readers recorded (1) number of enhancing intracranial lesions; (2) intracranial susceptibility artifact (presence or absence; mm depth of intracranial signal loss); and (3) motion artifact (none, mild, moderate, severe). Inter and intra-reader agreement and reader accuracy relative to a reference standard were determined, and sequence comparison with respect to susceptibility and motion artifacts was performed.

RESULTS

There was substantial intra-reader, inter-sequence agreement [reader 1, κ = 0.70 (95% CI: [0.60, 0.81]); reader 2, κ = 0.70 (95% CI: [0.59, 0.82])] and substantial intra-sequence, inter-reader agreement [3D-MPRAGE assessment, κ = 0.76 (95% CI: [0.66, 0.86]); 3D-FLASH assessment, κ = 0.86 (95% CI: [0.77, 0.94]) for detection of intracranial enhancing lesions. For both readers, the diagnostic accuracy of 3D-FLASH and 3D-MPRAGE was similar (3D-MPRAGE: 86.4 and 88.1%; 3D-FLASH: 88.2 and 84.5%), with no inter-sequence diagnostic accuracy discordancy between the sequences for either reader. 3D-FLASH was associated with less susceptibility artifact (p < 0.001 both readers) and less motion artifact (p < 0.001 both readers).

CONCLUSION

On 3T brain MRI in the inpatient and emergency department setting, 1-min 3D-FLASH pulse sequence achieved comparable diagnostic performance to 4.5 min 3D-MPRAGE pulse sequence for detecting enhancing intracranial lesions, with reduced susceptibility and motion artifacts.

3D magnetization prepared elliptical centric fast gradient echo imaging

3D magnetization-prepared fast gradient echo MR sequences, such as MP-RAGE and IR-SPGR, provide good spatial resolution and gray-white contrast. The efficiency and image quality of these techniques can be further improved with an interleaved, recessed elliptical centric view order. It is shown that this novel acquisition strategy, along with skipping the acquisition of views in k-space corners can provide images with higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), while reducing artifact level and scan time compared to standard MP-RAGE.

Comparative study of 3D-SPGR vs 2D-SE T1WI after enhancement in the brain

The utility of three-dimensional spoiled gradient recalled acquisition in steady state (3D-SPGR) imaging in the cerebral diseases was evaluated and 3D-SPGR after enhancement in depicting contrast enhancement of all lesions and 2D-SE T1WI comparatively analyzed. 117 patients were subjected to MRI by a GE 1.5T MR system. After performance of axial T1WI and T2WI in all patients, MRA (3D-MOTSA) images were acquired in 6 cases (8 lesions) of aneurysms. After enhancement, 3D-SPGR images were obtained in all the remaining patients. Quality parameters (SNR, C and CNR) were calculated on enhanced 2D-SE T1WI and 3D-SPGR images. And a four-point scale was used to measure the signal intensity of the main lesions on both sequences, then statistical analysis of the average score was performed with "t" test. Except for aneurysms, 2D-SE T1WI detected 134 lesions and 3D-SPGR disclosed 147 lesions. It was found that there was no statistically significant difference between the two average scores as determined by the "t" test (t = 1,894, P > 0.05). The enhancement degree of the main lesion was equivalent on 3D-SPGR and 2D-SE T1WI. Quality parameters (SNR, C and CNR) on 2D-SE T1WI were much larger than that of 3D-SPGR, increasing by an average of 57%, 20% and 97% respectively. 3D-SPGR imaging with MPR could clearly depict vascularity related to neoplasms in 20 cases and demonstrate shifted, deformed and blocked vessels involved by tumors. Six cases of large aneurysms (8 lesions) were visualized more clearly on 3D-SPGR than MRA (3D-MOTSA): 3D-SPGR could display aneurysm necks and differentiate thrombosed portion from the patent lumen, and disclose relationship of aneurysm to surrounding structures. It was concluded that enhanced 3D-SPGR played an important role in the depiction of the cerebral lesions and was superior to 2D-SE T1WI in many aspects.

Comparison of 2-D turbo spin echo and 3-D gradient echo sequences for the detection of the trigeminal nerve and branches anatomy

The aim of this study was to assess the detectability of the trigeminal nerve and its branches using T1 weighted (w.) 3-D magnetization prepared rapid gradient echo (MP-RAGE), T2* w. 3D CISS and T2 w. 2-D turbo spin echo MR sequences. Thirty healthy volunteers were examined for this purpose using a 1.5 Tesla MR unit. The detectability of the trigeminal nerve and Gasser's Ganglion, i.e. structures that are surrounded by liquor was best using 3-D CISS. In the case of the ophthalmic, maxillary and mandibular nerves, the T1 w. 3-D MPRAGE was significantly better than T2* w. CISS and T2 w. 2-D turbo spin echo. The latter yielded the poorest results. We conclude that both high resolution T2* w. and T1 w. 3-D sequences are necessary in order to detect the liquor-surrounded trigeminal nerve and its soft tissue-surrounded branches. We would therefore recommend the inclusion of constructive interference in steady state (CISS) and MP-RAGE in a MR imaging protocol of the trigeminal nerve and its branches.

Comparison of 2D and 3D MRI of the optic and oculomotor nerve anatomy

A total of 30 healthy volunteers underwent magnetic resonance imaging (MRI) with T1 weighted (w.) 3D magnetization prepared rapid gradient echo (MP-RAGE), T2 w. 2D turbo spin echo (TSE) and T2* w. 3D constructive interference in steady state (CISS) sequences to evaluate the detectability of the optic, oculomotor, trochlear and abducens nerves. CISS yielded the best results for the trochlear and abducens nerve, MP-RAGE for the optic chiasm and tract. The optic and oculomotor nerves were very well detectable using both CISS and MP-RAGE without any statistically significant difference between the two.

MRI of inner ear anatomy using 3D MP-RAGE and 3D CISS sequences

The aim of this study was to compare contrast enhanced 3D MP-RAGE (magnetization prepared rapid gradient echo), unenhanced 3D MP-RAGE and 3D CISS (constructive interference in steady state) in the evaluation of anatomical detail of the inner ear and facial nerve. 60 persons with no abnormalities and no or non-specific symptoms were examined with MRI. All examinations were performed using a 1.5 T MR unit. The detectability of anatomical details was evaluated by agreement of three radiologists. Statistical evaluation of the results was achieved by the two-tailed Wilcoxon's test. In 86-95% of the cases, 3D CISS resulted in excellent visibility of the basal and second turn and apex of the cochlea, the vestibule and semicircular canals, as well as the nerves within the internal auditory canal. There was a significantly better visualization with CISS than with MP-RAGE. Detectability of the extrameatal facial nerve was best using contrast enhanced 3D MP-RAGE in 91-96% of the cases (labyrinthine segment 96.7%; geniculate ganglion 95%; tympanic segment 91.7%; vertical segment 95%). The detection of the meatal seventh nerve was best using CISS, whilst unenhanced MP-RAGE gave significantly better results than contrast enhanced MP-RAGE. These results suggest that unenhanced and contrast enhanced 3D MP-RAGE and 3D CISS sequences are complementary and not alternative MRI techniques. Both T1 and T2 weighted 3D MR imaging of the temporal bone is of advantage when compared with 2D MR sequences due to improved contrast, geometrical resolution and the possibility of adequate reconstruction of anatomical structures.