New partially parallel acquisition technique in cerebral imaging: preliminary findings

Cortical and striatal contributions to automaticity in information-integration categorization

In information-integration categorization, accuracy is maximized only if information from two or more stimulus components is integrated at some pre-decisional stage. In many cases the optimal strategy is difficult or impossible to describe verbally. Evidence suggests that success in information-integration tasks depends on procedural learning that is mediated largely within the striatum. Although many studies have examined initial information-integration learning, little is known about how automaticity develops in information-integration tasks. To address this issue, each of ten human participants received feedback training on the same information-integration categories for more than 11,000 trials spread over 20 different training sessions. Sessions 2, 4, 10, and 20 were performed inside an MRI scanner. The following results stood out. 1) Automaticity developed between sessions 10 and 20. 2) Pre-automatic performance depended on the putamen, but not on the body and tail of the caudate nucleus. 3) Automatic performance depended only on cortical regions, particularly the supplementary and pre-supplementary motor areas. 4) Feedback processing was mainly associated with deactivations in motor and premotor regions of cortex, and in the ventral lateral prefrontal cortex. 5) The overall effects of practice were consistent with the existing literature on the development of automaticity.

Venous obstruction and jugular valve insufficiency in idiopathic intracranial hypertension

The pathophysiology of elevated intracranial pressure in idiopathic intracranial hypertension (IIH) is unclear. Cerebral venous outflow obstruction and elevated intracranial venous pressure may play an etiological role. We examined jugular valve insufficiency as a potential factor contributing to intracranial hypertension. Jugular venous valve function was assessed bilaterally by duplex sonography in 20 consecutive patients with diagnosis of IIH and in 20 healthy controls matched for age, gender and body mass index. Diagnosis of valvular insufficiency was based on reflux duration during a controlled Valsalva maneuver. Intracranial venous outflow was evaluated in 11 patients (MR venography in 10, digital subtraction angiography (DSA) in two cases). As a principle result, valvular insufficiency was significantly more frequent in patients with IIH (70 vs. 30%; p < 0.05). This finding was associated with irregular leaflet structures on B-mode imaging (p < 0.01). Bilateral insufficiency was more frequent in the patient group which, however, was not significant (p = 0.08). In addition, sinovenous outflow obstruction was found in five of six patients that had undergone contrast-enhanced MR venography and DSA. The detection rate was inferior in phase-contrast MR imaging (one of five patients). In conclusion, this study gives evidence that valvular insufficiency may play a causal role in IIH. Obesity is a major risk factor for the disease and weight reduction leads to improvement of symptoms. Possibly, increased intra-abdominal pressure is transmitted into the intracranial venous system, causing intracranial hypertension. Jugular valve insufficiency may facilitate pressure transmission. As transverse sinus stenosis was a concomitant finding, these factors may be complementary.

MRI of degenerative lumbar spine disease: comparison of non-accelerated and parallel imaging

INTRODUCTION

Parallel imaging techniques such as GRAPPA have been introduced to optimize image quality and acquisition time. For spinal imaging in a clinical setting no data exist on the equivalency of conventional and parallel imaging techniques. The purpose of this study was to determine whether T1- and T2-weighted GRAPPA sequences are equivalent to conventional sequences for the evaluation of degenerative lumbar spine disease in terms of image quality and artefacts.

METHODS

In patients with clinically suspected degenerative lumbar spine disease two neuroradiologists independently compared sagittal GRAPPA (acceleration factor 2, time reduction approximately 50%) and non-GRAPPA images (25 patients) and transverse GRAPPA (acceleration factor 2, time reduction approximately 50%) and non-GRAPPA images (23 lumbar segments in six patients). Comparative analyses included the minimal diameter of the spinal canal, disc abnormalities, foraminal stenosis, facet joint degeneration, lateral recess, nerve root compression and osteochondrotic vertebral and endplate changes. Image inhomogeneity was evaluated by comparing the nonuniformity in the two techniques. Image quality was assessed by grading the delineation of pathoanatomical structures. Motion and aliasing artefacts were classified from grade 1 (severe) to grade 5 (absent).

RESULTS

There was no significant difference between GRAPPA and non-accelerated MRI in the evaluation of degenerative lumbar spine disease (P>0.05), and there was no difference in the delineation of pathoanatomical structures. For inhomogeneity there was a trend in favour of the conventional sequences. No significant artefacts were observed with either technique.

CONCLUSION

The GRAPPA technique can be used effectively to reduce scanning time in patients with degenerative lumbar spine disease while preserving image quality.

Comparison of parallel acquisition techniques generalized autocalibrating partially parallel acquisitions (GRAPPA) and modified sensitivity encoding (mSENSE) in functional MRI (fMRI) at 3T

PURPOSE

To evaluate the parallel acquisition techniques, generalized autocalibrating partially parallel acquisitions (GRAPPA) and modified sensitivity encoding (mSENSE), and determine imaging parameters maximizing sensitivity toward functional activation at 3T.

MATERIALS AND METHODS

A total of eight imaging protocols with different parallel imaging techniques (GRAPPA and mSENSE) and reduction factors (R = 1, 2, 3) were compared at different matrix sizes (64 and 128) with respect to temporal noise characteristics, artifact behavior, and sensitivity toward functional activation.

RESULTS

Echo planar imaging (EPI) with GRAPPA and a reduction factor of 2 revealed similar image quality and sensitivity than full k-space EPI. A higher incidence of artifacts and a marked sensitivity loss occurred at R = 3. Even though the same eight-channel head coil was used for signal detection in all experiments, GRAPPA generally showed more benign patterns of spatially-varying noise amplification, and mSENSE was also more susceptible to residual unfolding artifacts than GRAPPA.

CONCLUSION

At 3T and a reduction factor of 2, parallel imaging can be used with only little penalty with regard to sensitivity. With our implementation and coil setup the performance of GRAPPA was clearly superior to mSENSE. Thus, it seems advisable to pay special attention to the employed parallel imaging method and its implementation.

Comparison of volume, four- and eight-channel head coils using standard and parallel imaging

Array coils can potentially offer increased signal-to-noise ratio (SNR) over standard coils adjacent to the array elements, while preserving the SNR at the center of the volume. The SNR advantage should theoretically increase with the number of array elements. Parallel acquisition techniques (PAT), on the other hand, can benefit acquisition times or spatial resolution at a cost to SNR as well as image quality. This study examines the question of whether SNR and image quality are still acceptable with two different array coils (four and eight channels) in conjunction with PAT when compared to standard imaging with a volume coil. All imaging was on a 1.5 T MR scanner. T2-weighted, FLAIR, diffusion-weighted, and time of flight (TOF) angiography images were performed with and without PAT in a phantom and in ten healthy volunteers. The phantom measurements demonstrated superior SNR for the eight-channel coil versus the four-channel and standard head coils. Using the eight-channel head coil for in vivo imaging, image quality with PAT (acceleration factor=2) was scored similar to images without PAT using the volume coil. The four-channel head coil suffered from inhomogeneity, lower SNR and poorer image quality when using PAT compared to standard imaging with the volume head coil. Both the in vivo and the phantom results indicate that the eight-channel head coil should be used for the highest quality brain images; this coil can be combined with PAT sequences for shorter acquisition time without a significant decrease in image quality relative to a volume coil without PAT.