Michael Nelles

Dual-Source Parallel Radiofrequency Excitation Body MR Imaging Compared with Standard MR Imaging at 3.0 T: Initial Clinical Experience

PURPOSE To prospectively compare the image quality and homogeneity of magnetic resonance (MR) images obtained by using a dual-source parallel radiofrequency (RF) excitation body MR imaging system with parallel transmission and independent RF shimming with the image quality and homogeneity of single-source MR images obtained by using standard sequences for routine clinical use in patients at 3.0 T. MATERIALS AND METHODS After institutional review board approval and informed patient consent were obtained, a dual-source parallel RF excitation 3.0-T MR system with independent RF shimming and parallel transmission technology was used to examine 28 patients and was compared with a standard 3.0-T MR system with single RF transmission. The RF power was distributed to the independent ports of the system body coil by using two RF transmission sources with full software control, enabling independent control of the phase and amplitude of the RF waveforms. Axial T2-weighted fast spin-echo (SE) and diffusion-weighted (DW) liver images, axial T2-weighted fast SE pelvic images, and sagittal T1- and T2-weighted fast SE spinal images were obtained by using dual- and single-source RF excitation. Two radiologists independently evaluated the images for homogeneity and image quality. Statistical significance was calculated by using the nonparametric Wilcoxon signed rank test. Interobserver agreement was determined by using Cohen kappa and Kendall tau-b tests. RESULTS Image quality comparisons revealed significantly better results with dual-source rather than single-source RF excitation at T2-weighted liver MR imaging (P = .001, kappa = 1.00) and better results at DW liver imaging at a statistical trend level (P = .066, tau-b > 0.7). Owing to reduced local energy deposition, fewer acquisitions and shorter repetition times could be implemented with dual-source RF excitation pelvic and spinal MR imaging, with image acquisition accelerating by 18%, 33%, and 50% compared with the acquisitions with single-source RF excitation. Image quality did not differ significantly between the two MR techniques (P > .05, tau-b > 0.5). CONCLUSION Dual-source parallel RF excitation body MR imaging enables reduced dielectric shading, improved homogeneity of the RF magnetic induction field, and accelerated imaging at 3.0 T.

Dual-source parallel RF transmission for clinical MR imaging of the spine at 3.0 T: intraindividual comparison with conventional single-source transmission.

PURPOSE To prospectively and intraindividually compare single-source radiofrequency (RF) excitation and dual-source parallel RF excitation in 3.0-T magnetic resonance (MR) imaging of the spine. MATERIALS AND METHODS Institutional review board approval and written informed patient consent were obtained. The RF power of a 3.0-T MR imaging system was distributed to two ports of the body coil of the system by using independent RF transmit channels. The maximum B(1) field strength for dual-source parallel RF excitation was maintained, as compared with single-source RF excitation. The repetition time was reduced according to the revised RF setup with dual-source parallel RF excitation while maintaining specific energy absorption limitations. Thirty patients were examined with and without dual-source parallel RF excitation. Diagnostic quality was assessed independently by two radiologists according to a four-point grading system. Image contrast ratios (CRs) were calculated between reference tissues and vertebrae for single-source RF excitation and dual-source parallel RF excitation. RESULTS The mean acceleration achieved with dual-source parallel RF excitation was 36% (range, 18%-50%). The total imaging duration of a three-station total spinal examination was reduced by one-third by using dual-source parallel RF transmission. For all cases investigated, diagnostic image quality without significant differences between the two methods and with a good interobserver agreement was achieved (Kendall tau-b, 0.50-0.84). The observed image contrast changes were predominantly small (<0.10 in 15 of 24 CRs), though they were significantly different (P < .05). CONCLUSION While shortening examination times by approximately one-third, the dual-source parallel RF transmission mode in MR imaging of the spine yielded diagnostic image quality comparable to that with the conventional single-source RF transmission mode.

Focal Liver Lesions at 3.0 T: Lesion Detectability and Image Quality with T2-weighted Imaging by Using Conventional and Dual-Source Parallel Radiofrequency Transmission

PURPOSE To prospectively compare T2-weighted single-shot turbo spin-echo (TSE) sequences performed with parallel and conventional radiofrequency (RF) transmission at 3.0 T for liver lesion detection, image quality, lesion conspicuity, and lesion contrast. MATERIALS AND METHODS After written informed consent and institutional review board approval, 52 consecutive patients (32 men, 20 women; mean age, 56.6 years ± 13.7 [standard deviation]) underwent routine magnetic resonance (MR) imaging with a clinical 3.0-T unit. Two independent readers reviewed images acquired with conventional and dual-source parallel RF transmission for detection of focal liver lesions, with separate reading of a third radiologist, including all available imaging findings, clinical history, and histopathologic findings, as reference. Image quality and lesion conspicuity were rated on five- and three-point evaluation scales, respectively. Contrast ratios between focal liver lesions and adjacent liver parenchyma were calculated. Significance was determined by using nonparametric Wilcoxon signed-rank and marginal homogeneity tests. RESULTS With the reference standard, 106 index lesions were identified in 22 patients. Detection rate significantly improved from 87% (92 of 106) to 97% (103 of 106) (reader 1) and from 85% (90 of 106) to 96% (102 of 106) (reader 2) with parallel RF transmission (reader 1, P = .0078; reader 2, P = .002). Quality of parallel RF transmission images was assigned scores significantly higher, compared with quality of conventional RF transmission images (mean for reader 1, 2.88 ± 0.73 vs 4.04 ± 0.44; mean for reader 2, 2.81 ± 0.72 vs 4.04 ± 0.39; P < .0001 for both). Lesion conspicuity scores were significantly higher on parallel RF transmission images, compared with conventional RF transmission images (mean for reader 1, 2.02 ± 0.64 vs 2.92 ± 0.27; mean for reader 2, 2.06 ± 0.67 vs 2.90 ± 0.30; P < .0001 for both). Contrast ratios were significantly higher with parallel RF transmission (P < .05). CONCLUSION Compared with conventional RF transmission, parallel RF transmission significantly improved liver lesion detection rate, image quality, lesion conspicuity, and lesion contrast. SUPPLEMENTAL MATERIAL http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101429/-/DC1.

Mechanical Thrombectomy Compared to Local-Intraarterial Thrombolysis in Carotid T and Middle Cerebral Artery Occlusions

PurposeThe aim of the study was to examine the effects of mechanical thrombectomy using the Solitaire stent in patients with thromboembolic occlusions of the intracranial carotid artery bifurcation (carotid T) or middle cerebral artery (MCA) and to compare the results with a historical cohort treated with local intraarterial thrombolysis using urokinase.MethodsThe time intervals from stroke onset to treatment, recanalization rates, occlusion sites, recanalization times and functional outcomes on the modified Rankin scale at 3 months in 25 patients treated with the Solitaire stent between 2010 and 2011 were evaluated. The data were compared with those of a historical cohort of 62 patients treated with local intraarterial thrombolysis between 1992 and 2001.ResultsA total of 15 out of 25 (60%) patients treated with mechanical thrombectomy and 25 out of 62 (40%) treated with local intraarterial thrombolysis achieved a modified Rankin score of  £ 2 (p = 0.07). Occlusion sites, intervals from stroke onset to treatment and rates of parenchymal hematomas, 3 out of 25 (12%) versus 8 out of 62 (13%), were similar in both cohorts while the recanalization rate was significantly higher, 22 out of 25 (88%) versus 33 of 62 (53%), in the mechanical thrombectomy group (p £ 0.01).ConclusionThe data show that mechanical thrombectomy is superior to local intraarterial thrombolysis with respect to the recanalization rate in patients with thrombeoembolic carotid T or MCA occlusions.

Neuropsychological outcome after selective amygdalohippocampectomy: subtemporal versus transsylvian approach

Objective In the context of discussions on the optimal cognitive outcome of temporal lobe epilepsy surgery, and stimulated by recent reports on the beneficial effects of a selective subtemporal approach to memory function, this study evaluated the cognitive consequences of subtemporal versus transsylvian selective amygdalohippocampectomy (SAH) in patients with mesial temporal lobe epilepsy, taking verbal/figural memory and language functions into account. Methods We contrasted cognitive outcomes of 26 subtemporal SAH patients with those observed in a transsylvian SAH control group. The surgical groups were pairwise matched with regard to clinical and demographic characteristics. Preoperative and 1 year postoperative memory and language evaluations served as within group factors, and surgical approach (transsylvian vs subtemporal) and side of surgery (right vs left) as between group factors. Results Both surgical approaches caused decline in verbal memory to a similar degree. Differential effects were seen with regard to decline in verbal recognition memory (more affected by left transsylvian SAH) as well as in figural memory and verbal fluency (more affected by subtemporal SAH). Interpretation Different from previous optimistic reports, this study demonstrates that subtemporal surgery, such as transsylvian surgery, poses similar risks for verbal memory. Differences between the approaches appear to reflect the effect of different collateral temporal lobe lesions due to the approach. Different cognitive outcomes across studies on the subtemporal approach are discussed as being in part due to study design and the chosen dependent functional measures.

Cerebral arteriovenous malformations at 3.0 T: intraindividual comparative study of 4D-MRA in combination with selective arterial spin labeling and digital subtraction angiography.

Objective:Prospective intraindividual comparison of 4-dimensional contrast-enhanced MR angiography (4D-MRA) in combination with selective arterial spin labeling (ASL) at 3.0 Tesla and digital subtraction angiography (DSA) for anatomic and functional characterization of cerebral arteriovenous malformations (AVMs). Materials and Methods:In a prospective intraindividual comparative study, 16 patients diagnosed with symptomatic cerebral AVMs underwent 4D-MRA at an isotropic spatial resolution of 1.1 × 1.1 × 1.1 mm3 and a temporal resolution of 572 milliseconds, regional brain perfusion imaging using selective ASL and DSA. Selective ASL was performed for selective labeling of both carotid arteries and the vertebrobasilar complex. In a stepwise approach, all images were evaluated by 2 radiologists according to technical success rate, Spetzler-Martin classification, identification of arterial feeders, and existence of anatomic variants or functional cross-filling. Results:4D-MRA allowed for the same Spetzler-Martin classification as DSA in all patients. Of 28, 26 (93%) feeding arteries were correctly identified by both readers using 4D-MRA alone. Selective ASL provided additional functional or anatomic information in 4 of 16 cases (25%), enabling the detection of a cross-filling feeding artery that was not identified by 4D-MRA without selective ASL, thus improving the sensitivity of MRI in identification of arterial feeders from 26/28 (93%) to 27/28 (96%). The additional functional information regarding anatomic variants and cross-filling provided by selective ASL was confirmed by DSA in all cases. Conclusion:4D-MRA in combination with selective arterial spin labeling is a promising tool for the noninvasive assessment of cerebral AVMs providing functional information that so far has been gained only with DSA.

Intravascular CNS lymphoma: Successful therapy using high-dose methotrexate-based polychemotherapy.

Intravascular diffuse large B-cell lymphoma limited to the CNS (cIVL) is a very rare malignant disorder characterized by a selective accumulation of neoplastic lymphocytes (usually B cells) within the lumen of CNS blood vessels but not in the brain parenchyma. In the past, treatment of cIVL with anthracycline-based regimens was unsatisfactory with very short survival times. In the case of cIVL presented here, high-dose methotrexate-based polychemotherapy according to the Bonn protocol plus rituximab therapy was successful and led to a complete clinical and MRI remission which is ongoing 29 months after diagnosis.

Pre- and postoperative MR brain imaging with automatic planning and scanning software in tumor patients: an intraindividual comparative study at 3 Tesla.

To evaluate the feasibility of automatic planning and scanning of brain MR imaging (MRI) protocols on a clinical 3 Tesla system in tumor patients before and after neurosurgical intervention.

Clinical CMR at 3.0 Tesla using parallel RF transmission with patient-adaptive B1 shimming: initial experience

Introduction The clinical implementation of high-field CMR systems has introduced new challenges for cardiac imaging due to B0 and B1 field inhomogeneities. TSE Black-Blood sequences (BB) are compromised by dielectric artifacts, whereas SSFP cine-sequences are known to suffer from dark-band artifacts. The flip-angle non-uniformity across the field of view affects image homogeneity of both sequences. The use of a multi-source RF transmission system may help reduce dielectric effects, improve flip-angle uniformity and avoid local SAR peaks, thus allowing a shorter minimum TR/TE in SSFP-sequences.

Extraretinal Induced Visual Sensations during IMRT of the Brain

BACKGROUND We observed visual sensations (VSs) in patients undergoing intensity modulated radiotherapy (IMRT) of the brain without the beam passing through ocular structures. We analyzed this phenomenon especially with regards to reproducibility, and origin. METHODS AND FINDINGS Analyzed were ten consecutive patients (aged 41-71 years) with glioblastoma multiforme who received pulsed IMRT (total dose 60Gy) with helical tomotherapy (TT). A megavolt-CT (MVCT) was performed daily before treatment. VSs were reported and recorded using a triggered event recorder. The frequency of VSs was calculated and VSs were correlated with beam direction and couch position. Subjective patient perception was plotted on an 8x8 visual field (VF) matrix. Distance to the orbital roof (OR) from the first beam causing a VS was calculated from the Dicom radiation therapy data and MVCT data. During 175 treatment sessions (average 17.5 per patient) 5959 VSs were recorded and analyzed. VSs occurred only during the treatment session not during the MVCTs. Plotting events over time revealed patient-specific patterns. The average cranio-caudad extension of VS-inducing area was 63.4mm (range 43.24-92.1mm). The maximum distance between the first VS and the OR was 56.1mm so that direct interaction with the retina is unlikely. Data on subjective visual perception showed that VSs occurred mainly in the upper right and left quadrants of the VF. Within the visual pathways the highest probability for origin of VSs was seen in the optic chiasm and the optic tract (22%). CONCLUSIONS There is clear evidence that interaction of photon irradiation with neuronal structures distant from the eye can lead to VSs.