Functional MRI using multiple receiver coils: BOLD signal changes and signal-to-noise ratio for three-dimensional-PRESTO vs. single shot EPI in comparison to a standard quadrature head coil.

PURPOSE: To compare the performance of single shot echo planar imaging (SSEPI) with three-dimensional-multishot echo-planar imaging (EPI) based on principles-of-echo-shifting-with-a-train-of-observations (PRESTO) in combination with a standard quadrature head coil and, as an alternative, a multiple receiver coil in intraoperative functional magnetic resonance imaging (fMRI). MATERIALS AND METHODS: Six healthy subjects underwent fMRI with visual stimulation using a SSEPI and a PRESTO-sequence with both coil systems. Statistical evaluation was done with a scanner-based post-processing software and SPM 99. The number of activated voxels in the visual cortex, the percent signal change between rest and activation, and finally the signal-to-noise ratio (SNR) during time course were measured and compared for both coil systems and both sequences, used in four different combinations. RESULTS: Blood oxygen level dependent (BOLD) signal changes were the lowest with PRESTO and standard head coil and the highest for SSEPI and phased array coil. For the latter combination, a significantly higher signal change and larger activation size was observed together with a better SNR. SSEPI yielded similar performance using both coils. CONCLUSION: SSEPI was superior due to its better SNR and a higher BOLD signal change in the defined settings, irrespective of the coil used. In a stereotactical setup the phased array coil can be used to generate fMRI data without loss of image quality.

Optimized distortion correction of epi-based statistical parametrical maps for stereotactic neurosurgery.

A new approach is presented for unwarping geometrical distortions in echo planar imaging (EPI)-based statistical parametrical maps (SPM). With the developed method, a substantial reduction of geometrical distortions in the order of 5-15 mm down to a residue of approximately 1-2 mm was possible, thus allowing reliable activation localization and, hence, interpretation after fusion with undistorted conventional anatomic images. The unwarping procedure is an optimized combination of two distortion correction methods, the "inhomogeneity mapping" and the coregistration approach. Local and global distortions, the first one object-dependent, the second one caused by imperfect gradient waveforms, are reduced. With several examples of patients and volunteers, the applicability for stereotactic neurosurgery is demonstrated.

Intraoperative functional MRI as a new approach to monitor deep brain stimulation in Parkinson's disease.

This article deals with technical aspects of intraoperative functional magnetic resonance imaging (fMRI) for monitoring the effect of deep brain stimulation (DBS) in a patient with Parkinson's disease. Under motor activation, therapeutic high-frequency stimulation of the subthalamic nucleus was accompanied by an activation decrease in the contralateral primary sensorimotor cortex and the ipsilateral cerebellum. Furthermore, an activation increase in the contralateral basal ganglia and insula region were detected. These findings demonstrate that fMRI constitutes a promising clinical application for investigating brain activity changes induced by DBS.

Proton spectroscopic metabolite signal relaxation times in preterm infants: a prerequisite for quantitative spectroscopy in infant brain.

PURPOSE: To determine relaxation times of metabolite signals in proton magnetic resonance (MR) spectra of immature brain, which allow a correction of relaxation that is necessary for a quantitative evaluation of spectra acquired with long TE. Proton MR spectra acquired with long TE allow a better definition of metabolites as N-acetyl aspartate (NAA) and lactate especially in children. MATERIALS AND METHODS: Relaxation times were determined in the basal ganglia of 84 prematurely born infants at a postconceptional age of 37.8 +/- 2.2 (mean +/- SD) weeks. Metabolite resonances were investigated using the double-spin-echo volume selection method (PRESS) at 1.5 T. T1 was determined from intensity ratios of signals obtained with TRs of 1884 and 6000 msec, measured at 3 TEs (25 msec, 136 msec, 272 msec). T2 was determined from signal intensity ratios obtained with TEs of 136 msec and 272 msec, measured at 2 TR. Taking only long TEs reduced baseline distortions by macromolecules and lipids. For myo-inositol (MI), an apparent T2 for short TE was determined from the ratio of signals obtained with TE = 25 msec and 136 msec. Intensities were determined by fitting a Lorentzian to the resonance, and by integration. RESULTS: Relaxation times were as follows: trimethylamine-containing compounds (Cho): T1 = 1217 msec/T2 = 273 msec; total creatine (Cr) at 3.9 ppm: 1010 msec/111 msec; Cr at 3.0 ppm: 1388 msec/224 msec; NAA: 1171 msec/499 msec; Lac: 1820 msec/1022 msec; MI: 1336 msec/173 msec; apparent T2 at short TE: 68 msec. CONCLUSION: T1 and T2 in the basal ganglia of premature infants do not differ much from previously published data from basal ganglia of older children and adults. T2 of Cho was lower than previous values. T2 of Cr at 3.9 ppm and Lac have been measured under different conditions before, and present values differ from these data.

Femoral pseudoaneurysms: management with percutaneous thrombin injections--success rates and effects on systemic coagulation.

PURPOSE: To determine the success rate of percutaneous ultrasonographically (US) guided thrombin injection in the treatment of femoral pseudoaneurysms and to evaluate the effects of thrombin injection on systemic coagulation parameters. MATERIALS AND METHODS: Fifty femoral pseudoaneurysms (37 simple pseudoaneurysms with one lobe and 13 complex pseudoaneurysms with two or three lobes) were treated with US-guided percutaneous thrombin injections. Pseudoaneurysm size, neck length and width, thrombin dose, outcome of therapy, and complications were documented prospectively. Duplex sonographic follow-up examinations were performed at 12-24 hours and 5-7 and 21-25 days. In 25 patients, activated thromboplastin time, Quick test (prothrombin time), thrombin time, fibrinogen, D-dimer, antithrombin III, thrombin-antithrombin III complex, and prothrombin fragments 1 and 2 were determined before and at 2, 5, and 10 minutes after thrombin injection. Differences in results before and those after thrombin injection were evaluated by means of the one-sample t test. RESULTS: Mean volume of pseudoaneurysms was 5.84 cm(3) +/- 4.89 (SD). Fifty-eight thrombin injections were performed. Mean thrombin dose was 357 IU +/- 291 in simple and 638 IU +/- 549 in complex pseudoaneurysms. Primary success rate was 36 of 37 (97%) for simple and eight of 13 (61%) for complex pseudoaneurysms. Reperfusion occurred in four complex pseudoaneurysms (none in simple ones). Secondary success rate was 100%. No thromboembolic, infectious, or allergic complications occurred. During follow-up, reperfusion was detected in one patient with a complex pseudoaneurysm. Levels of thrombin-antithrombin III complex increased significantly (P <.05) after thrombin injection, whereas changes in all other laboratory tests were not significant. CONCLUSION: US-guided percutaneous injection of thrombin is successful and safe in the management of femoral pseudoaneurysms. The increase of thrombin-antithrombin III complex indicates the possibility of thrombin passage into the arterial circulation.

An isolated fourth ventricle in neurosarcoidosis: MRI findings.

We report on an isolated enlargement of the fourth ventricle in a patient with neurosarcoidosis which developed 3 years after the insertion of a ventriculo-atrial shunt. Repeated MRI images were obtained in a patient with known neurosarcoidosis between 1995 and 2000. Imaging findings were correlated to the medical course of the patient, who developed a hydrocephalus and a trapped fourth ventricle consecutively. The isolation was presumably due to granulomatous inflammation of the ependyma surrounding the fourth ventricular outlets. The isolated fourth ventricle was responsible for a deterioration of neurological status. Neurosarcoidosis is a severe complication in sarcoidosis patients. An isolated enlargement of the fourth ventricle is a rare complication in clinically deteriorated patients with neurosarcoidosis and ventricular drainage, which may require neurosurgical treatment.