Cerebrovascular Reactivity during Prolonged Breath-Hold in Experienced Freedivers.

BACKGROUND AND PURPOSE: Experienced freedivers can endure prolonged breath-holds despite severe hypoxemia and are therefore ideal subjects to study apnea-induced cerebrovascular reactivity. This multiparametric study investigated CBF, the spatial coefficient of variation as a correlate of arterial transit time and brain metabolism, dynamics during prolonged apnea. MATERIALS AND METHODS: Fifteen male freedivers (age range, 20-64 years; cumulative previous prolonged breath-holds >2 minutes and 30 seconds: 4-79,200) underwent repetitive 3T pseudocontinuous arterial spin-labeling and 31P-/1H-MR spectroscopy before, during, and after a 5-minute breath-hold (split into early and late phases) and gave temporally matching venous blood gas samples. Correlation of temporal and regional cerebrovascular reactivity to blood gases and cumulative previous breath-holds of >2 minutes and 30 seconds in a lifetime was assessed. RESULTS: The spatial coefficient of variation of CBF (by arterial spin-labeling) decreased during the early breath-hold phase (-30.0%, P = .002), whereas CBF remained almost stable during this phase and increased in the late phase (+51.8%, P = .001). CBF differed between the anterior and the posterior circulation during all phases (eg, during late breath-hold: MCA, 57.3 ± 14.2 versus posterior cerebral artery, 42.7 ± 10.8 mL/100 g/min; P = .001). There was an association between breath-hold experience and lower CBF (1000 previous breath-holds reduced WM CBF by 0.6 mL/100 g/min; 95% CI, 0.15-1.1 mL/100 g/min; P = .01). While breath-hold caused peripheral lactate rise (+18.5%) and hypoxemia (oxygen saturation, -24.0%), cerebral lactate and adenosine diphosphate remained within physiologic ranges despite early signs of oxidative stress [-6.4% phosphocreatine / (adenosine triphosphate + adenosine diphosphate); P = .02]. CONCLUSIONS: This study revealed that the cerebral energy metabolism of trained freedivers withstands severe hypoxic hypercarbia in prolonged breath-hold due to a complex cerebrovascular hemodynamic response.

Three-Dimensional Isotropic Fat-Suppressed Proton Density-Weighted MRI at 3 Tesla Using a T/R-Coil Can Replace Multiple Plane Two-Dimensional Sequences in Knee Imaging.

PURPOSE: To evaluate whether a 3 D proton density-weighted fat-suppressed sequence (PDwFS) of the knee is able to replace multiplanar 2D-PDwFS. MATERIALS AND METHODS: 52 patients (26 men, mean age: 41.9 ±â€Š14.5years) underwent magnetic resonance imaging (MRI) of the knee at 3.0 Tesla using a T/R-coil. The imaging protocol included 3 planes of 2D-PDwFS (acquisition time (AT): 6:40 min; voxel sizes: 0.40 - 0.63 × 0.44 - 0.89 × 3mm³) and a 3D-PDwFS (AT: 6:31 min; voxel size: 0.63 × 0.68 × 0.63mm³). Homogeneity of fat suppression (HFS), artifacts, and image sharpness (IS) were evaluated on a 5-point scale (5[excellent] - 1[non-diagnostic]). The sum served as a measure for the overall image quality (OIQ). Contrast ratios (CR) compared to popliteal muscle were calculated for the meniscus (MEN), anterior (ACL) and posterior cruciate ligaments (PCL). In 13 patients who underwent arthroscopic knee surgery, two radiologists evaluated the presence of meniscal, ligamental and cartilage lesions to estimate the sensitivity and specificity of lesion detection. RESULTS: The CR was higher in the ACL, PCL and MEN in 3D- PDwFS compared to 2D-PDwFS (p < 0.01 for ACL and PCL; p = 0.07 for MEN). Compared to 2 D images, the OIQ was rated higher in 3D-PDwFS images (p < 0.01) due to fewer artifacts and HFS despite the lower IS (p < 0.01). The sensitivity and specificity of lesion detection in 3D- and 2D-PDwFS were similar. CONCLUSION: Compared to standard multiplanar 2D-PDwFS knee imaging, isotropic high spatial resolution 3D-PDwFS of the knee at 3.0 T can be acquired with high image quality in a reasonable scan time. Multiplanar reformations in arbitrary planes may serve as an additional benefit of 3D-PDwFS. KEY POINTS: • 3D-PDwFS of the knee is acquired with high image quality• 3D-PDwFS can be achieved in only one measurement with a reasonable scan time• 3D-PDwFS with the advantage of multiplanar reformation may replace 2D-PD-weighted knee MRI Citation Format: • Homsi R, Gieseke J, Luetkens JA et al. Three-Dimensional Isotropic Fat-Suppressed Proton Density-Weighted MRI at 3 Tesla Using a T/R-Coil Can Replace Multiple Plane Two-Dimensional Sequences in Knee Imaging. Fortschr Röntgenstr 2016; 188: 949 - 956.

Functional hemispherectomy: postoperative motor state and correlation to preoperative DTI.

INTRODUCTION: Functional hemispherectomy (FH) is an infrequent method to reduce seizure frequency in patients with intractable epilepsy. The risk that hemispherotomy injures brain structures involved in residual motor function is challenging to predict. Our purpose was to evaluate MR diffusion tensor imaging (DTI) to preoperatively assess residual ipsilateral motor function prior to FH. METHODS: We applied DTI in 34 patients scheduled for FH to perform fiber tracking in healthy and damaged hemispheres of the corticospinal tracts (CSTs) and of the corpus callosum. We assessed the CSTs and the commissural fibers for streamline count, for fractional anisotropy (FA), and for respective ratios (affected/unaffected side). We correlated these DTI values to post-to-prior changes of muscle strength and evaluated their diagnostic accuracy. RESULTS: FA of the affected CSTs and of commissural fibers was significantly higher in patients with postoperative loss of muscle strength compared to patients without (p = 0.014 and p = 0.008). In contrast, CST FA from healthy hemispheres was not different between both groups. Ratios of streamline counts and FA from CSTs were higher in patients with postoperative reduced muscle strength compared to those without (1.14 ± 0.22 vs. 0.58 ± 0.14, p = 0.040; 0.93 ± 0.05 vs. 0.74 ± 0.03, p = 0.003). CSTs' normalized FA ratio greater than -0.085 predicted loss of muscle strength with 80 % sensitivity and 69.6 % specificity. CONCLUSION: Preoperative tracking of the CST and of commissural fibers contributes to the prediction of postoperative motor outcome after functional hemispherectomy.

Diffusion-weighted magnetic resonance imaging of breast lesions: the influence of different fat-suppression techniques on quantitative measurements and their reproducibility.

OBJECTIVE: The aim of this study was to evaluate the influence of different fat-suppression techniques on quantitative measurements and their reproducibility when applied to diffusion-weighted imaging (DWI) of breast lesions. METHODS: Twenty-five patients with different types of breast lesions were examined on a clinical 1.5-T magnetic resonance imaging (MRI) system. Two diffusion-weighted sequences with different fat-suppression methods were applied: one with spectral presaturation by inversion recovery (SPIR), and one with short-TI inversion recovery (STIR). The acquisition of both sequence variants was repeated with modified shim volume. Lesion-to-background contrast (LBC), apparent diffusion coefficients (ADC) ADC(0,1000) and ADC(50,1000), and their coefficients of variation (CV) were determined. RESULTS: In four patients, the image quality of DWI with SPIR was insufficient. In the other 21 patients, 46 regions of interest (ROI), including 11 malignant and 35 benign lesions, were analysed. The LBC, ADC(0,1000) and ADC(50,1000) values, which did not differ between initial and repeated measurements, were significantly higher for STIR than for SPIR. The mean CV improved from 10.8 % to 4.0 % (P = 0.0047) for LBC, from 6.3 % to 2.9 % (P = 0.0041) for ADC(0,1000), and from 6.3 % to 2.6 % (P = 0.0049) for ADC(50,1000). CONCLUSION: For STIR compared to SPIR fat suppression, improved lesion conspicuity, higher ADC values, and better measurement reproducibility were found in breast DWI. KEY POINTS: • Quality of fat suppression influences quantitative DWI breast lesion measurements. • In breast DWI, STIR fat suppression worked more reliably than SPIR. • Lesion-to-background contrast and its reproducibility were significantly higher with STIR fat suppression. • Lesional ADCs and their reproducibility were significantly higher with STIR fat suppression.

Characterization of the failing murine heart in a desmin knock-out model using a clinical 3 T MRI scanner.

The purpose of this study was to establish an MRI protocol on a clinical scanner for assessment of left (LV) and right (RV) ventricular myocardial function of the murine heart, and to apply this protocol for the first in vivo assessment of myocardial function in a mouse model of cardiomyopathy (Desmin-/-). MRI was performed on a clinical 3 T whole body MRI system using a dedicated solenoid receive-only coil. Contiguous short axis slices were acquired covering the entire heart using a spoiled cine gradient echo sequence (TR 9-12 ms, TE 3-4 ms, α 25°, 1.0 × 0.23 × 0.23 mm³). Global LV- and RV-myocardial functional parameters such as end-diastolic ventricular volume, ejection fraction (EF), LV mass and cardiac output (CO) of Desmin-/- mice and age-matched controls were determined. Global myocardial functional data of healthy controls (n = 4) were in very good agreement with previously reported data. The transgenic mice (n = 8) revealed a significantly reduced LV- and RV-EF as well as CO. Body weight-normalized LV- and RV-end-diastolic volumes and LV mass were significantly increased. In addition desmin deficient mice exhibited segmental wall thinning and akinesia, suggesting myocardial necrosis. This study demonstrates that clinical 3 T MRI-systems may reliably be used for non-invasive assessment of LV- and RV-myocardial function in normal and in genetically engineered mice with cardiomyopathies. In addition, this proof of principle study presents first in vivo MRI data of the cardiac phenotype of desmin knock-out mice.

Analysing the response in R2* relaxation rate of intracranial tumours to hyperoxic and hypercapnic respiratory challenges: initial results.

OBJECTIVE: To investigate the response in R2* relaxation rate of human intracranial tumours during hyperoxic and hypercapnic respiratory challenges. METHODS: In seven patients with different intracranial tumours, cerebral R2* changes during carbogen and CO(2)/air inhalation were monitored at 3 T using a dynamic multigradient-echo sequence of high temporal and spatial resolution. The R2* time series of each voxel was tested for significant change. Regions of interest were analysed with respect to response amplitude and velocity. RESULTS: The tumours showed heterogeneous R2* responses with large interindividual variability. In the 'contrast-enhancing' area of five patients and in the 'non-tumoral' tissue most voxels showed a decrease in R2* for carbogen. For the 'contrast-enhancing' area of two patients hardly any responses were found. In areas of 'necrosis' and perifocal 'oedema' typically voxels with R2* increase and no response were found for both gases. For tissue responding to CO(2)/air, the R2* changes were of the same order of magnitude as those for carbogen. The response kinetic was generally attenuated in tumoral tissue. CONCLUSION: The spatially resolved determination of R2* changes reveals the individual heterogeneous response characteristic of intracranial human tumours during hyperoxic and hypercapnic respiratory challenges.

A multicenter (1)H-MRS study of the medial temporal lobe in AD and MCI.

OBJECTIVE: The need for biological markers of Alzheimer disease (AD) is constantly increasing. Proton magnetic resonance spectroscopy ((1)H-MRS) studies have provided consistent evidence for a reduction of the neuronal marker N-acetylaspartate (NAA) in patients with AD. Within the German Competence Network on Dementia, we conducted a (1)H-MRS study in patients with mild dementia and mild cognitive impairment (MCI) at four sites to investigate the multicenter feasibility of (1)H-MRS. METHODS: In total, 130 patients with dementia (98 AD, 32 non-AD), 136 subjects with MCI (70 of AD type, 66 of non-AD type), and 45 unimpaired control subjects were included. Single-volume (1)H-MRS of the left medial temporal lobe was performed at long and short echo times. Metabolites were quantified and metabolic ratios were determined. RESULTS: We found a significant reduction of NAA concentration in patients with AD as compared to healthy volunteers and compared to patients with MCI of AD type. NAA/Cr (creatine/phosphocreatine) was also lower in patients with AD compared to control subjects. NAA, choline compounds, and Cr were lower in patients with AD compared to patients with non-AD dementia. CONCLUSIONS: We demonstrated the multicenter feasibility of proton magnetic resonance spectroscopy ((1)H-MRS) of the medial temporal lobe in mild dementia and mild cognitive impairment, which is a prerequisite for the application of (1)H-MRS in large-scale clinical trials. Since the concentration measures of the metabolites are adjusted for brain tissue volume, these findings are indicators of biochemical pathology beyond brain atrophy.

Combined 3T diffusion tensor tractography and 1H-MR spectroscopy in motor neuron disease.

BACKGROUND AND PURPOSE: Diagnostic confidence in motor neuron disease may be improved by the use of advanced MR imaging techniques. Our aim was to assess the accuracy (sensitivity/specificity) and agreement of combined (1)H-MR spectroscopy (proton MR spectroscopy) and diffusion tensor imaging (DTI) at 3T in patients with suspected motor neuron disease regarding detection of upper motor neuron (UMN) dysfunction. MATERIALS AND METHODS: Eighteen patients with suspected motor neuron disease were studied with MR spectroscopy/DTI and clinically rated according to the El-Escorial and ALSFRS-R scales. For MR spectroscopy, absolute N-acetylaspartate (NAA), choline (Cho), and phosphocreatine (PCr) concentrations and relative NAA/Cho and NAA/PCr ratios of corresponding volumes of interest within the primary motor cortex were calculated. For DTI, fractional anisotropy (FA) and mean diffusivity (MD) were measured bilaterally at the level of the precentral gyrus, corona radiata, internal capsule, cerebral peduncles, pons, and pyramid. FA and MD statistics were averaged on the corticospinal tracts (CSTs) as a whole to account for a region-independent analysis. RESULTS: MR spectroscopy indicated NAA reduction beyond the double SD of controls in 6 of 8 patients with clinical evidence for UMN involvement. Congruently, the mean FA of these patients was significantly lower in the upper 3 regions of measurements (P < .01). Overall, MR spectroscopy and DTI were concordant in all except 3 cases: 1 was correctly excluded from motor neuron disease by DTI (genetically proved Kennedy syndrome), whereas MR spectroscopy indicated CST involvement. MR spectroscopy and DTI each were false-positive for CST affection in 1 patient with lower motor neuron involvement only. CONCLUSION: Combined MR spectroscopy/DTI at 3T effectively adds to the detection of motor neuron disease with a high degree of accordance.

MR imaging of the prostate at 3.0T with external phased array coil - preliminary results.

INTRODUCTION: Among all imaging modalities, MRI of the prostate has the highest sensitivity to predict extracapsular tumor spread, seems to have added value for the preoperative treatment planning. It is an adjunct tool in patients with high suspicion of prostate cancer and so far negative TRUS-guided biopsies. Due to the higher intrinsic signal, it is expected that 3.0T enables to image the prostate without endorectal coil. Aim of this study was to evaluate the diagnostic accuracy of phased array coil 3.0T MRI in patients with suspicion of prostate cancer. MATERIAL AND METHODS: A high spatial resolution T2-w 3.0T pulse sequence (0.47 x 0.47 x 3mm voxel size) was performed in 26 patients prior to US-guided biopsy. Qualitative analysis comprised visual signal to noise, tissue contrasts and motion artifacts. MR diagnoses were correlated with histology. Diagnostic indices for the detection of prostate cancer in the peripheral zone were calculated. RESULTS: Histopathologic examination revealed pro?state cancer in 12 and benign prostate disorders in 14 patients. Motion artifacts due to peristalsis were rated moderate. Mean visual signal to noise was high. Contrast between peripheral and central zone of the prostate was excellent. MRI had 4 false negative and 2 false positive diagnoses (sensitivity 66.7 %, specificity 86.7 % diagnostic accuracy 76.9%). CONCLUSION: At 3.0T, diagnostic indices for cancer detection seem to be comparable to data reported about endorectal 1.5T MRI. Thus 3.0 T offers new options for MR imaging of the prostate in selected patients who cannot or are not willing to be examined with the endorectal coil.

Axonal damage but no increased glial cell activity in the normal-appearing white matter of patients with clinically isolated syndromes suggestive of multiple sclerosis using high-field magnetic resonance spectroscopy.

BACKGROUND AND PURPOSE: Proton MR spectroscopy ((1)H-MR spectroscopy) is a well-established method for the in vivo investigation of the normal-appearing white matter (NAWM) in patients with multiple sclerosis (MS). Metabolic changes in NAWM are of special interest in patients with clinically isolated syndromes (CIS) suggestive of MS regarding further prognostic classifications. The purpose of this study was to investigate metabolic alterations in NAWM in patients with CIS with use of high-field (1)H-MR spectroscopy and to compare the results to those in patients with an early course of MS. MATERIALS AND METHODS: With use of a 3T whole-body MR imaging system, single-voxel (1)H-MR spectroscopy (PRESS; TR: 2000 ms; TE: 38 ms and 140 ms) of the parietal NAWM was performed in 20 control subjects, 36 patients with CIS, and 12 patients with MS. Metabolite ratios and concentrations of N-acetylaspartate (tNAA), myo-inositol (mIns), choline, and total creatine (tCr) were determined. RESULTS: Compared with the control group, mean NAWM mIns concentrations were significantly elevated in the MS group (4.56 mmol/L versus 3.75 mmol/L, P = .02) but not in the CIS group (4.04 mmol/L, P = .44). The higher concentration of mIns in the MS group was also reflected in the increased Ins/tCr ratio (P = .02). The mean NAWM tNAA was significantly decreased in both patient groups compared with the control group (CIS, 13.42 mmol/L, P = .02; MS, 12.77 mmol/L versus 14.51 mmol/L, P = .008). CONCLUSIONS: A significant increase of the activity of the glial cells can only be observed in patients with an established diagnosis of MS but not in patients with CIS. Axonal damage occurs already during the first demyelinating episode in patients with CIS as well as in patients with definite MS.

[Molecular imaging of apoptosis in cardiovascular diseases]. / Molekulare Bildgebung der Apoptose bei kardiovaskulären Erkrankungen.

Molecular imaging of functional parameters such as apoptosis (programmed cell death) in vivo opens new possibilities in clinical diagnostic and scientific research. Especially in the case of cardiovascular diseases that are mainly responsible for both morbidity and mortality in Western industrial nations, innovative non-invasive examination strategies are necessary for early diagnosis of these diseases. Since apoptosis unlike necrosis is present even after minor alterations of the microenvironment of cells and has been shown to be involved in a large number of cardiovascular diseases, there are currently several experimental studies underway with the goal of imaging apoptosis in vivo. The review discusses the basics of apoptosis in myocardial infarction, myocarditis, atherosclerosis, restenosis after angioplasty and stent implantation, currently used imaging techniques, achieved results, and future possibilities for molecular imaging of apoptosis.

Double inversion recovery brain imaging at 3T: diagnostic value in the detection of multiple sclerosis lesions.

BACKGROUND AND PURPOSE: To prospectively determine the sensitivity in the detection of multiple sclerosis (MS) lesions by using double inversion recovery (DIR), fluid-attenuated inversion recovery (FLAIR), and T2-weighted turbo spin-echo (T2 TSE) MR imaging at 3T. METHODS: Seventeen patients presenting with a clinically isolated syndrome (CIS) suggestive of MS, 9 patients with definite MS, and 6 healthy control subjects were included. Imaging was performed on a 3T MR system using DIR, FLAIR, and T2 TSE sequences. Lesions were counted and classified according to 5 anatomic regions: infratentorial, periventricular, deep white matter, juxtacortical, and mixed white matter-gray matter. The sensitivity at DIR was compared with the corresponding sensitivity at FLAIR and T2 TSE sequence. The contrast between lesions and normal-appearing gray matter, normal-appearing white matter, and CSF was determined for all sequences. RESULTS: Because of higher lesion-white matter contrast, the DIR showed a higher number of lesions compared with the FLAIR (7% gain, P = 0.04) and the T2 TSE (15% gain, P = 0.01). The higher sensitivity was also significant for the infratentorial region compared with the FLAIR (56% gain, P = 0.02) and the T2 TSE (44% gain, P = 0.02). Compared with the FLAIR, no significant changes of the lesion load measurements were observed in the supratentorial brain: slightly higher numbers of periventricular and mixed gray matter-white matter lesions on the DIR were counterbalanced by a slightly reduced sensitivity regarding juxtacortical lesions. CONCLUSION: DIR brain imaging at 3T provides the highest sensitivity in the detection of MS lesions especially in the infratentorial region.

[MR techniques for noninvasive diagnosis of prostate cancer]. / MR-Techniken zur nicht-invasiven Diagnostik des Prostatakarzinoms.

The diagnosis of prostate cancer is suggested on the basis of an elevated PSA level, abnormal digital exam, and abnormal transrectal ultrasound. US-guided biopsy is used to confirm the diagnosis, but up to 30% of prostate cancer may be missed with this approach. Meanwhile MR imaging and proton MR spectroscopy have emerged as the most sensitive additional tools for the noninvasive evaluation of prostate cancer. This article reviews the clinical indications for MRI of the prostate and summarizes new techniques such as high field strength (3 tesla) and dynamic contrast-enhanced MRI.

[Molecular imaging of apoptosis and necrosis -- basic principles of cell biology and use in oncology]. / Molekulare Bildgebung von Apoptose und Nekrose -- Zellbiologische Grundlagen und Einsatz in der Onkologie.

Soon molecular imaging techniques will play a prominent role in basic scientific research and clinical approaches. In particular, important aspects of medicine such as apoptosis and gene- and stem-cell therapy will play a pivotal role in radiology too. This review presents the basic principles of apoptosis, recent results and future perspectives of apoptosis imaging. Apoptosis or programmed cell death is a precisely regulated, complex cascade of molecular events to eliminate individual cells. Disturbances may lead to diseases like malignancies and neurodegenerative diseases that are of clinical relevance. Several therapeutic strategies in oncology are based on apoptosis induction; conversely, resistance to therapy is indicative of decreased apoptosis induction. Whereas up to now the clinician had to depend exclusively on biopsy specimens to detect apoptosis, the feasibility of non-invasive imaging of this cell-biological phenomenon in vivo opens up new horizons in future. This review focuses on different modifications of this imaging technique, with and without the use of molecular probes (e. g. annexin V, synaptotagmin I), in vitro and in vivo using the various detector systems (like MRI, flow cytometry) currently available. Future perspectives are also addressed.

Etiopathogenetic mechanisms in long-term course of schizophrenia.

Schizophrenia is a severe mental disorder with a relapsing long-term course in 80 % of the sufferers. The underlying neurobiological principles of the long-term course are widely unknown. Therefore an attempt is made to evaluate data from structural imaging and neuropsychology to shed some light on these mechanisms. Interestingly there was a significant correlation between length of illness and volume reduction in the prefrontal grey matter in schizophrenia. There was a lack of such a correlation for the whole brain volume, white matter volume or the grey matter volume outside the prefrontal lobe. Furthermore none of the neuropsychological measures correlated with length of illness. Both findings are supported by data from prospective studies up to five years demonstrating a significant loss of frontal grey matter volume, but no change of cognitive dysfunction in the course of time. The attempt is made to connect prefrontal grey matter loss with post-mortem findings of reduced neuropil but preserved cytoarchitecture leading to recently described candidate genes and their function.

[High field MR imaging: magnetic field interactions of aneurysm clips, coronary artery stents and iliac artery stents with a 3.0 Tesla MR system]. / Hochfeld-Magnetresonanztomographie: Magnetische Anziehungs- und Rotationskräfte auf metallische Implantate bei 3.0 T.

PURPOSE: To evaluate magnetic field interactions of commonly used biomedical implants at 3.0 Tesla. MATERIALS AND METHODS: Fourteen aneurysm clips designed for permanent placement in intracranial aneurysms, 19 coronary artery stents and 20 iliac artery stents were evaluated in an actively shielded compact 3.0 T MR system (Intera, Philips Medical Systems, Best, The Netherlands, length of magnet 1.57 m). The magnetic deflection forces (translational movement) were evaluated as follows: The implants were suspended by a fine string and placed in the magnet bore at the location of the maximum magnetic field gradient. The translational forces F (z) were calculated from the measured angle of deflection from the vertical axis. The magnetic field-induced torque (rotational forces) was evaluated as follows: Each implant was placed in the center of the magnetic bore parallel to the static magnetic field B0 (position 0 degrees ). Any possible displacement of the implant was noted on a millimeter scale and any torque qualitatively evaluated using a 5 point grading scale (0: no torque; + 4: very strong torque). The implant was turned in steps of 45 degrees, and the procedure was repeated to encompass a full 360 degrees rotation. RESULTS: In 52 of the 53 devices tested, the deflection force (deflection angle: range 0-21 degrees, translational force: range 0-3.8 mN) was less than the gravitational force (i.e., the implant's weight). These devices (n = 52/53) did not show any alignment to or rotation in the magnetic field at any of the various 45 degrees -increment positions corresponding to a qualitative torque evaluation of grade 0/4. One device (n = 1/53), an iliac artery stent made of stainless steel (Zenith, Cook, Mönchengladbach, BRD), was found to have deflection forces (deflection angle 88 degrees translational force 299 mN) greatly exceeding the gravitational force as well as a pronounced torque (grade 4/4). CONCLUSION: Out of 53 biomedical implants evaluated for magnetic field interactions at 3.0 T, one iliac artery stent made of stainless steel was found to be potentially unsafe based on ASTM criteria. MR imaging at 3.0 Tesla may be performed safely in patients with any of the other 52 different implants evaluated in this study with respect to magnetic field translational attraction and torque.

Perfusion and molecular diffusion-weighted MR imaging of the brain: in vivo assessment of tissue alteration in cerebral ischemia.

The combined use of perfusion imaging (PI) and diffusion-weighted imaging (DWI) is opening a new window into the processes that occur during the first hours of ischemia. DWI detects changes in molecular diffusion associated with cytotoxic edema. PI characterizes the degree of regional hypoperfusion. Regions showing mismatches between DWI and PI, i.e. hypoperfused areas with normal diffusion behavior are considered potentially salvageable. We present results of 11 patients with an occlusion of the middle cerebral artery stem and spontaneous stroke evolution. Whereas the infarct was clearly visible on initial DWI and PI, surrounding tissue at risk of infarction was marked in all patients by an increased blood volume and transit time, but only in a subgroup (n = 3) where alteration were more pronounced this tissue at risk was progressively infarcted. These human DWI and PI data show alterations in the area of tissue at risk which correlates with infarct progression.

In-vivo proton MR-spectroscopy of the human brain: assessment of N-acetylaspartate (NAA) reduction as a marker for neurodegeneration.

Proton magnetic resonance spectroscopy ((1)H-MRS) is a non-invasive method to investigate changes in brain metabolite composition in different cerebral diseases. We performed proton spectroscopy in patients with dementia of the Alzheimer's type (AD) and in patients with motor neuron disease (MND) with the aim to detect the specific metabolic pattern for these neurodegenerative disorders. In the MND group we found a significant reduction of NAA/tCr metabolite ratios in the motor cortex, which correlates with the disease severity and the clinical lateralization of neurological symptoms and further decreases in the time course of the disease. In AD patients a reduction of NAA/tCr was observed in the medial temporal lobe. Since NAA is exclusively expressed in neurons as shown by immunohistochemical studies, reduced NAA levels suggest neuronal loss or dysfunction in the observed regions. The observed regional metabolic alterations reflect the neuronal basis of the characteristic neurological symptoms in AD (dementia) and MND (muscular palsy) and mirrors the disease progress over time.

[1H-MR Spectroscopy of brain tumors in the course of radiation therapy: Use of fast spectroscopic imaging and single-voxel spectroscopy for diagnosing recurrence]. / 1H-MR-Spektroskopie von Hirntumoren im Verlauf der Strahlentherapie: Anwendung von schneller spektroskopischer Bildgebung und Einzelvolumen-MRS in der Rezidivdiagnostik.

PURPOSE: To improve differential diagnosis of residual or recurrent tumor vs. tissue necrosis in the course of radiation therapy of neurosurgically-treated brain tumors by application of fast (1)H-MR spectroscopic imaging in combination with single-voxel spectroscopy (SVS). METHODS: 54 patients after with malignant brain tumor (44 cases of glioblastoma, 10 other high-grade gliomas) were examined post-surgically in a total of 140 proton MRS examinations in the course of radiotherapy and in follow-up controls. Fast SI acquisition was performed as single-slice or double-slice TSI sequence with 32 x 32 phase encodings within 11 or 15 minutes, respectively. SVS with TR/TE 2000/272 ms yielded relative metabolite ratios, and in 15 patients the time courses of the absolute concentrations of brain metabolites were also determined. RESULTS: In the group of 44 patients that could be tracked by MRS until therapy completion, TSI localized in 23 patients a persistent or newly arisen distinct choline accumulation indicating residual or recurrent tumor after radiation therapy. In all these cases MRS diagnosis was confirmed histologically or by short-term follow-up. However, in 6 of 15 patients showing a normal choline pattern in the TSI acquisition, tumor recurrence appeared within three months. SVS provided early recognition of recurrent tumor when detecting characteristic alterations of metabolite concentrations oin therapy follow-up. CONCLUSION: TSI and SVS represent complementary MRS techniques and are able to diagnose tumor recurrence early and unambiguously in cases where focal choline accumulation is detected.

Time-efficient T2 relaxometry of the entire hippocampus is feasible in temporal lobe epilepsy.

OBJECTIVE: To test the clinical usefulness and reliability of a new dual-echo turbo-spin-echo (TSE) sequence for rapid and regional hippocampal T2 relaxometry. METHODS: Hippocampal T2 relaxation time (HRT) was determined by a TSE sequence on three to four consecutive coronal images in 16 control subjects and 12 patients with mesial temporal lobe epilepsy. HRT was related to neuropathology findings in hippocampal specimens including neuronal cell density (ND), results of visual analysis of MR images, clinical outcome after epilepsy surgery, and hippocampal volumetry. RESULTS: Rapid HRT differentiated patients from control subjects; all cases of hippocampal sclerosis (HS; n = 10) were correctly diagnosed. HRT showed a strong correlation with ND in CA1 (p < 0.02) and CA3 (p < 0.05). Diagnoses based on rapid relaxometry concurred fully with results of visual inspection. Mean HRT was prolonged ipsilaterally in all patients with excellent postoperative seizure outcome and bilaterally prolonged or normal in patients with poorer outcome. Rapid HRT was concordant with hippocampal volumetry in 10 of 12 patients. Regional HRT of control subjects revealed significantly higher values in the anterior than posterior hippocampus. In patients with unilateral HS, this gradient was absent. The gradient was also absent contralaterally to HS, although surgical outcome was excellent. CONCLUSIONS: Hippocampal dual-echo TSE-relaxometry can be regarded a reliable technique to detect and quantify HS. With a scan time of 3.31 minutes and immediate off-line analysis lasting a few minutes only, TSE-T2 relaxometry is easy to integrate in the routine diagnostic assessment of hippocampal morphology in large numbers of patients.