Michael Augustin

A New Rating Scale for Age-Related White Matter Changes Applicable to MRI and CT

Background and Purpose— MRI is more sensitive than CT for detection of age-related white matter changes (ARWMC). Most rating scales estimate the degree and distribution of ARWMC either on CT or on MRI, and they differ in many aspects. This makes it difficult to compare CT and MRI studies. To be able to study the evolution and possible effect of drug treatment on ARWMC in large patient samples, it is necessary to have a rating scale constructed for both MRI and CT. We have developed and evaluated a new scale and studied ARWMC in a large number of patients examined with both MRI and CT. Methods— Seventy-seven patients with ARWMC on either CT or MRI were recruited and a complementary examination (MRI or CT) performed. The patients came from 4 centers in Europe, and the scans were rated by 4 raters on 1 occasion with the new ARWMC rating scale. The interrater reliability was evaluated by using &kgr; statistics. The degree and distribution of ARWMC in CT and MRI scans were compared in different brain areas. Results— Interrater reliability was good for MRI (&kgr;=0.67) and moderate for CT (&kgr;=0.48). MRI was superior in detection of small ARWMC, whereas larger lesions were detected equally well with both CT and MRI. In the parieto-occipital and infratentorial areas, MRI detected significantly more ARWMC than did CT. In the frontal area and basal ganglia, no differences between modalities were found. When a fluid-attenuated inversion recovery sequence was used, MRI detected significantly more lesions than CT in frontal and parieto-occipital areas. No differences were found in basal ganglia and infratentorial areas. Conclusions— We present a new ARWMC scale applicable to both CT and MRI that has almost equal sensitivity, except for certain regions. The interrater reliability was slightly better for MRI, as was the detectability of small lesions.

Diffusion tensor imaging using single-shot SENSE-EPI.

SENSitivity Encoding (SENSE) greatly enhances the quality of diffusion‐weighted echo‐planar imaging (EPI) by reducing blurring and off‐resonance artifacts. Such improvement would also be desirable for diffusion tensor imaging (DTI), but measures derived from the diffusion tensor can be extremely sensitive to any kind of image distortion. Whether DTI is feasible in combination with SENSE has not yet been explored, and is the focus of this study. Using a SENSE‐reduction factor of 2, DTI scans in eight healthy volunteers were carried out with regular‐ and high‐resolution acquisition matrices. To further improve the stability of the SENSE reconstruction, a new coil‐sensitivity estimation technique based on variational calculus and the principles of matrix regularization was applied. With SENSE, maps of the trace of the diffusion tensor and of fractional anisotropy (FA) had improved spatial resolution and less geometric distortion. Overall, the geometric distortions were substantially removed and a significant resolution enhancement was achieved with almost the same scan time as regular EPI. DTI was even possible without the use of quadrature body coil (QBC) reference scans. Geometry‐factor‐related noise enhancement was only discernible in maps generated with higher‐resolution matrices. Error boundaries for residual fluctuations in SENSE reconstructions are discussed. Our results suggest that SENSE can be combined with DTI and may present an important adjunct for future neuroimaging applications of this technique. Magn Reson Med 48:128–136, 2002.

Improved diffusion-weighted single-shot echo-planar imaging (EPI) in stroke using sensitivity encoding (SENSE)

Diffusion‐weighted single‐shot EPI (sshEPI) is one of the most important tools for the diagnostic assessment of stroke patients, but it suffers from well known artifacts. Therefore, sshEPI was combined with SENSitivity Encoding (SENSE) to further increase EPIs potential for stroke imaging. Eight healthy volunteers and a consecutive series of patients (N = 8) with suspected stroke were examined with diffusion‐weighted SENSE‐sshEPI using different reduction factors (1.0 ≤ R ≤ 3.0). Additionally, a high‐resolution diffusion‐weighted SENSE‐sshEPI scan was included. All examinations were diagnostic and of better quality than conventional sshEPI. No ghostings or aliasing artifacts were discernible, and EPI‐related image distortions were markedly diminished. Chemical shift artifacts and eddy current‐induced image warping were still present, although to a markedly smaller extent. Measured direction‐dependent diffusion‐coefficients and isotropic diffusion values were comparable to previous findings but showed less fluctuation. We have demonstrated the technical feasibility and clinical applicability of diffusion‐weighted SENSE‐sshEPI in patients with subacute stroke. Because of the faster k‐space traversal, this novel technique is able to reduce typical EPI artifacts and increase spatial resolution while simultaneously remaining insensitive to bulk motion. Magn Reson Med 46:548–554, 2001.

Magnetic resonance diffusion tensor imaging for characterizing diffuse and focal white matter abnormalities in multiple sclerosis

High‐resolution diffusion tensor imaging (DTI) was performed in 14 patients with clinically definite multiple sclerosis (MS) and the trace of the diffusion tensor (〈D〉) and the fractional anisotropy (FA) were determined in normal appearing white matter (NAWM) and in different types of focal MS lesions. A small but significant increase of the 〈D〉 in NAWM compared to control white matter ((840 ± 85) × 10–6 mm2/sec vs. (812 ± 59) × 10–6 mm2/sec; P < 0.01) was found. In addition, there was a significant decrease in the FA of normal‐appearing regions containing well‐defined white matter tracts, such as the genu of the internal capsule. In non‐acute lesions, the 〈D〉 of T1‐hypointense areas was significantly higher than that of T1‐isointense lesions ((1198 ± 248) × 10–6 mm2/sec vs. (1006 ± 142) × 10–6 mm2/sec; P < 0.001), and there was a corresponding inverse relation of FA. Diffusion characteristics of active lesions with different enhancement patterns were also significantly different. DTI with a phase navigated interleaved echo planar imaging technique may be used to detect abnormalities of isotropic and anisotropic diffusion in the NAWM and selected fiber tracts of patients with MS throughout the entire brain, and it demonstrates substantial differences between various types of focal lesions. Magn Reson Med 44:583–591, 2000.

Diffusion‐weighted imaging of the spinal cord: Interleaved echo‐planar imaging is superior to fast spin‐echo

To compare and evaluate two novel diffusion‐weighted sequences, based either on fast spin‐echo (FSE) or interleaved echo‐planar imaging (EPI) methods, as potential tools for investing spinal cord abnormalities.

Long-Term Follow-Up after Treatment of Intracranial Aneurysms with the Pipeline Embolization Device: Results from a Single Center

BACKGROUND AND PURPOSE: Stent-like, self-expandable devices, the so-called flow diverters, are increasingly used for the treatment of wide-neck cerebral aneurysms. The immediate and short-term results are promising, but no long-term results are available. The purpose of our research was to report the long-term angiographic and cross-sectional imaging results after placement of a PED in 12 patients with wide-neck intracranial aneurysms. MATERIALS AND METHODS: Twelve wide-neck or otherwise untreatable cerebral aneurysms in 12 patients were treated with the PED. Angiography was performed at 6 and 24 months after treatment. Additional MR and CT angiograms were acquired. RESULTS: In all patients, angiographic or cross-sectional imaging follow-up of at least 27 months demonstrated complete occlusion of the aneurysms treated with the PED. There were no cases of aneurysm recurrence. Angiography at around 6 months showed complete occlusion in all cases, except 1 that showed complete occlusion at the 29-month follow-up. In 1 patient, a clinically asymptomatic 75% in-stent stenosis was seen on the angiography at 6 months but was resolved completely by balloon dilation. Device placement was successful in all patients. Distal embolization had occurred in 1 patient, but the clot was resolved completely without clinical sequelae. Almost immediate angiographic occlusion was achieved in 2 aneurysms and flow reduction in 10 aneurysms. CONCLUSIONS: Treatment of wide-neck intracranial aneurysms by PED placement led to successful and durable occlusion in all cases, without severe complications. Endovascular treatment for in-stent stenosis should be considered cautiously, because the underlying stenosis may be transient and disappear within 12 months after treatment.

Symptomatic stenosis of the vertebrobasilar arteries: results of extra- and intracranial stent-PTA

Background and purpose:  About half of all transient ischaemic attacks (TIAs) or strokes in the posterior circulation are caused by the arterial stenosis. The purposes of this study were to determine the safety of stent‐assisted percutaneous transluminal angioplasty (stent‐PTA) and its efficacy for the prevention of recurrent stroke in patients with symptomatic artery stenosis in the extra‐ and intracranial posterior circulation.

Acute Subdural Hematoma without Subarachnoid Hemorrhage or Intraparenchymal Hematoma Caused by Rupture of a Posterior Communicating Artery Aneurysm: Case Report and Review of the Literature

BACKGROUND Acute subdural hematoma without subarachnoid hemorrhage or intraparenchymal hematoma is rare. CASE REPORT We report on a 47-year-old women without previous trauma who presented with an acute subdural hematoma without subarachnoid hemorrhage. The hematoma was evacuated immediately. Further evaluation with a cerebral four-vessel angiography revealed a left-sided posterior communicating artery aneurysm that was occluded by endovascular embolization. The patient recovered without neurological deficit. CONCLUSIONS Ruptured intracranial aneurysm should be considered as a cause of nontraumatic subdural hematoma. Immediate subdural hematoma removal after aneurysm coiling can be performed in such patients, even those in poor neurological condition.

Fast patient workup in acute stroke using parallel imaging.

Treatment of ischemic stroke is a very frustrating topic for neurologists. Presently, the most promising therapy seems to be thrombolysis of the clot. However, this intervention is associated with complication risks, most significantly the risk of post-treatment hemorrhage. This risk of bleeding increases not only with the size of the ischemic brain tissue but also with the time-to-treatment interval. Studies suggest a time window of 3 hours for most effective treatment. Hence, there is demand for a rapid imaging workup, which thus far has been accomplished with computed tomography. Because of the risks associated with thrombolytic therapy, more detailed information is desirable. The distinction between patients with viable ischemically challenged neural tissue and those with complete infarcts is of great importance, and computed tomography is insufficient for this task. This is also true for outlining the etiology of stroke, which may impact treatment. For these tasks, magnetic resonance imaging has been proposed. However, comprehensive imaging protocols take time, which is limited in stroke treatment. Therefore, new imaging techniques are required that provide both in-depth information and short scanning times. Parallel imaging is uniquely suited for this purpose.

Parallel imaging strategies for high-speed magnetic resonance diffusion imaging

By using multiple receiver coils in conjunction with parallel MR signal reception, the speed of image acquisition can be dramatically increased. In this work the feasibility of such parallel imaging (PI) methods for fast brain imaging was studied along with their potential application for diffusion- weighted imaging (DWI). All measurements were performed by using a four-element prototype-surface coil. Parallel image reconstruction in the image domain was performed off-line on a dedicated MR image processing workstation. For appropriate image quality, coil sensitivity maps must be of sufficient quality or must be properly filtered. Thus, a novel filtering method was employed. By means of diffusion-weighted single- shot PI, the advantage of motion insensitivity of single shot echo-planar imaging (EPI) and the increased k-space velocity of multi-shot EPI can be combined; hence, they need not be phase navigated. Therefore, the images are free from ghostings, and artifacts arising from resonance offsets (e.g., B0, susceptibility artifacts, and chemical shift) are less prominent than in conventional single-shot EPI. Furthermore, image blurring was markedly reduced. Preliminary results in neuroimaging promise that PI can become a helpful tool for rapid imaging in the CNS, although further improvement of coil sensitivity is required for sufficient SNR in parallel DWI.