Irina Mader

FAIR True-FISP perfusion imaging of the kidneys

Most arterial spin labeling (ASL) techniques apply echoplanar imaging (EPI) because this strategy provides relatively high SNR in short measuring times. Unfortunately, those techniques are very susceptible to static magnetic field inhomogeneities and perfusion signals from organs with fast transverse relaxation might decrease due to the exchange of water molecules in capillaries and organ tissue combined with relatively long echo times of EPI sequences. To overcome these problems a novel imaging technique, FAIR True‐FISP, was developed. It combines a FAIR (flow‐sensitive alternating inversion recovery) perfusion preparation and a true fast imaging with steady precession (True‐FISP) data acquisition strategy. True‐FISP was chosen since this sequence type does not show the mentioned disadvantages of EPI, but provides a similar SNR per measuring time. An important problem of this approach is that True‐FISP sequences usually work in a steady state which is independent of a previous preparation of magnetization. For this reason a sequence structure had to be developed which keeps the advantages of True‐FISP and makes the signal intensity sensitive to the FAIR preparation. Breathhold and nonbreathhold examinations of kidneys are presented and possible strategies to quantitative flow measurements are reported. It is shown that correction of spatially inhomogeneous receiver coil characteristics is easily feasible and leads to clinically valuable perfusion examinations of kidneys without application of potentially nephrotoxic contrast media. Magn Reson Med 51:353–361, 2004.

Comparison of longitudinal metabolite relaxation times in different regions of the human brain at 1.5 and 3 Tesla

In vivo longitudinal relaxation times of N‐acetyl compounds (NA), choline‐containing substances (Cho), creatine (Cr), myo‐inositol (mI), and tissue water were measured at 1.5 and 3 T using a point‐resolved spectroscopy (PRESS) sequence with short echo time (TE). T1 values were determined in six different brain regions: the occipital gray matter (GM), occipital white matter (WM), motor cortex, frontoparietal WM, thalamus, and cerebellum. The T1 relaxation times of water protons were 26–38% longer at 3 T than at 1.5 T. Significantly longer metabolite T1 values at 3 T (11–36%) were found for NA, Cho, and Cr in the motor cortex, frontoparietal WM, and thalamus. The amounts of GM, WM, and cerebrospinal fluid (CSF) within the voxel were determined by segmentation of a 3D image data set. No influence of tissue composition on metabolite T1 values was found, while the longitudinal relaxation times of water protons were strongly correlated with the relative GM content. Magn Reson Med 50:1296–1301, 2003.

Parameterized evaluation of macromolecules and lipids in proton MR spectroscopy of brain diseases

Short echo time (TE) proton MR spectra of the brain include signals of several metabolites as well as macromolecules. In various pathologies, such as brain tumors and multiple sclerosis (MS), the presence of mobile lipids or pathologically altered macromolecules may provide useful additional diagnostic information. A reliable quantitation of these resonances, however, is often not possible due to the lack of adequate prior knowledge. Furthermore, even if advanced fitting procedures are used, a reliable evaluation of metabolites in the presence of pathological lipids or macromolecules often fails if the latter are omitted in the spectral evaluation. In this study, a method is presented for the simultaneous evaluation of all visible components, including metabolites, lipids, and macromolecules, by the use of the fitting procedure LCModel. A standard basis set of brain metabolites was extended by inclusion of parameterized components for macromolecules and lipids that were derived from metabolite‐nulled in vivo spectra of normal brain and high‐grade gliomas, respectively. The improved spectral quantitation is demonstrated in glial brain tumors and MS lesions as well as in normal brain. It is pointed out that both macromolecules and lipids must be included to provide a proper spectral evaluation. Magn Reson Med 49:19–28, 2003.

Bilateral lesions of thalamus and basal ganglia: origin and outcome

Twenty-seven MRI examinations from 17 children (7 females, 10 males) with bilateral lesions of the basal ganglia and thalamus, presenting over a period of 8 years, were reevaluated, and correlated with the type of cerebral palsy (CP) as well as motor and cognitive impairment. Children were between 1 year 6 months and 17 years old at last examination (mean 5 years 9 months). Brain damage had occurred as a consequence of birth asphyxia in nine patients and of neonatal shock in four patients. No adverse event could be identified in four children. In these, late prenatal compromise is assumed, as extensive screening (including MR spectroscopy in two patients) did not yield an underlying metabolic disorder. Three different degrees of MRI lesion patterns could be defined: a mild pattern (involvement of nucleus lentiformis and ventro-lateral thalamus only; n=7), an intermediate pattern (involvement of nucleus lentiformis, ventro-lateral thalamus, and pericentral region; n=3), and a severe pattern (involvement of nucleus lentiformis, entire thalamus, pericentral region, and hippocampus; n=7). This grading of MRI findings correlated significantly with the severity of both cognitive and motor impairment and type of CP. Normal cognitive development and mild motor delay was only seen with the mild pattern. All children developed CP: purely dyskinetic CP was only seen with the mild pattern, whereas the dyskinetic-spastic or spastic CP types could be seen in all three lesion patterns, with dyskinetic-spastic CP more related to the moderate, and purely spastic CP more related to the severe pattern.

Parietal somatosensory association cortex mediates affective blindsight

To investigate the neural substrates underlying emotional feelings in the absence of a conscious stimulus percept, we presented a visual stimulus in the blind field of partially cortically blind patients and measured cortical activity (by functional magnetic resonance imaging, fMRI) before and after the stimulus had been paired with an aversive event. After pairing, self-reported negative emotional valence and blood oxygen level–dependent (BOLD) responses in somatosensory association areas were enhanced, whereby somatosensory activity predicted highly corresponding reported feelings and startle reflex amplitudes across subjects. Our data provide direct evidence that cortical activity representing physical emotional states governs emotional feelings.

Reliable detection of macromolecules in single-volume 1H NMR spectra of the human brain.

In short echo time proton MR spectra of the brain, resonances from macromolecules are visible. The macromolecular resonances in the 0.5–2.0 ppm region can be affected by lipid contamination arising from fat‐containing regions outside the selected volume of interest (VOI). This study demonstrates that considerable lipid contamination may remain in stimulated echo acquisition mode (STEAM) spectra even if the spoiling of unwanted coherences is sufficient and the VOI is placed 2 cm or more away from fat‐containing regions. The observed contamination was attributed to residual remote out‐of‐volume excitation, although only very small out‐of‐slice ripples of less than 0.2% of the in‐slice excitation were found in the calculated excitation profile of the RF pulses. Spatial presaturation of fat‐containing regions led to a sufficient suppression of the contamination and enabled the detection of highly reproducible macromolecular resonances. Thus, in single‐volume spectroscopy as well as in spectroscopic imaging (SI or CSI), the combination of volume selection and outer volume presaturation, each in three dimensions, is highly recommended to ensure accurate detection and reliable evaluation of even small pathological alterations in macromolecules, e.g., proteins or lipids, or other resonances in the 0.5–2.0 ppm region. Magn Reson Med 45:948–954, 2001.

Diffusion-weighted MRI in patients with symptomatic internal carotid artery disease

Beside the early detection of ischemia, there is an increasing body of evidence that diffusion-weighted imaging (DWI) can provide important information on stroke etiology. Against the background of an increased use of magnetic resonance angiography in patients being evaluated for carotid endarterectomy (CEA), the question arises if the additional performance of a DWI scan could also yield clinically relevant findings in these patients.In a prospective observational study we analysed the DWI data of 107 patients with high-grade symptomatic carotid artery disease (CAD) being evaluated for CEA.While no patient with a retinal TIA (n = 29) exhibited a DWI lesion, nineteen of the 42 patients with a hemisphere TIA and all patients with a minor stroke (n = 36) showed DWI lesion(s). In patients with TIAs the occurrence of DWI abnormalities was significantly more frequent in patients with long lasting TIAs. The majority of patients had multiple DWI lesions suggestive of acute large-artery thromboembolism as a common morphological phenotype of stroke. The finding of a similar lesion pattern in 4 patients with additional pre-existing atrial fibrillation suggested a symptomatic carotid stenosis. In contrast, unexpected bihemisphere lesions suggested cardioembolism in two patients with a normal circle of Willis and instigated thorough cardiac investigations. In both instances 24-h Holter monitoring revealed intermittent atrial fibrillation, so that a CEA was not performed.In conclusion, we demonstrate a common DWI lesion pattern in patients with symptomatic high-grade CAD eligible for CEA. In patients with known concomitant cardiac disorders the finding of this typical lesion pattern may support the diagnosis of a symptomatic CAD. In contrast, the additional performance of DWI can also reveal an unexpected cardiac source of embolism in some patients, which can substantially influence their further clinical management.

Imaging of activated microglia with PET and [11C]PK 11195 in corticobasal degeneration.

Positron emission tomography (PET) using [11C]PK 11195, a ligand for peripheral benzodiazepine receptor binding sites, offers the opportunity to image activated microglia in vivo. This tool may therefore be used to display the occurrence of microglial activation in the course of neurodegeneration. A patient with the clinical diagnosis of corticobasal degeneration (CBD) and left‐sided symptoms was studied using fluorodeoxyglucose (FDG) and [11C]PK 11195 PET. We found a marked right hemispheric hypometabolism and asymmetric microglial activation in corresponding areas of the basal ganglia and right temporal and parietal cortex. [11C]PK 11195 PET suggests involvement of microglial activation in the pathogenesis of CBD.

MRI for the management of neonatal cerebral infarctions: importance of timing

PurposeFocal ischemic stroke in neonates is a rare occurrence. Diagnosis with most imaging modalities is difficult, but necessary for initiating an anticoagulatory treatment. The purpose of this study was to evaluate the sensitivity of MRI sequences within the first 14xa0days of birth.Patients and methodsFour patients with neonatal stroke presenting as seizures were examined using a standard MRI protocol including diffusion-weighted images (DWI) and magnetic resonance angiography (MRA) within 72xa0h of birth. The time between the onset of symptoms and MRI ranged from 6xa0h to 48xa0h. Follow-up examinations were performed on daysxa05 (n=1), 7 (n=2), and 14 (n=1) for the control of a treatment with low-molecular heparin.ResultsEight infarctions were detected in the four patients, 5 in the middle cerebral artery (MCA), three in the posterior cerebral artery (PCA) territory. All lesions were visible using DWI, four on T2-weighted images. Whereas in two patients small lesions contralateral to a large stroke were missed on T2-weighted images, the diagnosis would have been missed altogether without DWI in one patient. On follow-up, the visibility of the infarctions had declined using DWI after 5xa0 days and the lesions were invisible after 1xa0week. Fourteen days after the stroke, an increased diffusion was detected in the infarcted brain tissue. By this time, all lesions were visible on T2-weighted images.ConclusionIn neonates, infarcted brain tissue can be detected using DWI with high sensitivity during the first 2xa0days after stroke and before other sequences are diagnostic. However, the diffusion restriction does not persist beyond 1xa0week. After 5xa0days, diagnosis has to rest mainly on T2-weighted images.

MRI and proton MR spectroscopy in acute disseminated encephalomyelitis

IntroductionAcute disseminated encephalomyelitis (ADEM) is one of a group of demyelinating disorders of the central nervous system (CNS). It is said to be attributed to an overshooting immunologic response following an infection or vaccination. The clinical course and type of manifestation is heterogeneous. The early application of corticosteroids has been shown to be beneficial to outcome; thus, an early diagnosis is highly desirable.MethodsThe potential diagnostic value of advanced MR techniques such as proton MR spectroscopy and diffusion-weighted imaging (DWI) was investigated in two paediatric patients with ADEM, one of whom had a remitting and relapsing clinical course and presented with additional cranial nerve involvement. Proton MR spectroscopy revealed typical signs of acute demyelination, such as increased macromolecules, not found in other forms of non-necrotising pathology.ConclusionThe addition of proton MR spectroscopy and DWI adds to the diagnostic power of MRI in the setting of post-infectious demyelinating disorders of the CNS or ADEM and may obviate the need for biopsy.