Spin-echo Mode Research Articles

Role of magnetic resonance spectroscopy & diffusion weighted imaging in differentiation of supratentorial brain tumors

PurposeTo evaluate the role of magnetic resonance spectroscopy & diffusion weighted imaging (DWI) in differentiating between primary and secondary brain tumors. Patients & methodsThis prospective study was performed for 40 patients. Diffusion weighted image (DWI) and apparent diffusion co-efficient (ADC) maps were acquired by using b-values of 0 and 1000mm2/s. Standard mean ADC values were calculated automatically and expressed in 10−3mm2/s in both intra-lesional and peri-lesional regions. Multi voxel MR spectroscopy was performed using a spin-echo mode sequence.The metabolites were identified including the following: N-acetylaspartate (NAA) at 2.0ppm, creatine (Cr) at 3.0ppm, choline (Cho) at 3.2ppm, lipid at the range of 0.7–1.3ppm, lactate at 1.33ppm and myoinositol at 3.56ppm. The ratios that were calculated include the following: Cho/NAA and Cho/Cr in both intralesional and perilesional regions. ResultsIntralesional ADC values showed no difference between the metastases (0.6: 1×10−3mm2/s with mean 0.86) and high grade primary tumors (0.6: 1.1×10−3mm2/s with mean 0.73). Perilesional ADC value Findings in the study revealed that primary tumors have low ADC values (0.9: 1.1×10−3mm2/s with mean 0.95) in their peri-lesional voxels denoting peri-lesional infiltration, while higher ADC values in metastasis (1.3–1.6×10−3mm2/s mean 1.41) due to the absence of peri-lesional infiltration increase in CHO/Cr ratios (>1) in primary high grade tumors (indicating perilesional infiltration) while there was no increase in CHO/Cr ratio in cases of metastases. Low grade primary tumors showed low lactate and lipid, with increasing malignancy, and tumors showed increasing levels of lactate and lipid peaks (indicating necrosis) with remarkable difference in lipid peaks between low and high grade tumors. There was no significant difference between primary & metastatic brain tumors as regards lactate peak. ConclusionIntra-lesional ADC values are not useful in the differentiation between primary and metastatic tumors. Perilesional ADC values can differentiate between primary & metastatic brain tumors. Intralesional MRS values (CHO/Cr ratio) were able to grade the tumor and differentiate between high and low grade tumors, while Perilesional MRS values (CHO/Cr ratio) could be able to differentiate primary tumors from metastasis.

Wavelength-independent constant period spin-echo modulated small angle neutron scattering

Spin-Echo Modulated Small Angle Neutron Scattering (SEMSANS) in Time-of-Flight (ToF) mode has been shown to be a promising technique for measuring (very) small angle neutron scattering (SANS) signals and performing quantitative Dark-Field Imaging (DFI), i.e., SANS with 2D spatial resolution. However, the wavelength dependence of the modulation period in the ToF spin-echo mode has so far limited the useful modulation periods to those resolvable with the limited spatial resolution of the detectors available. Here we present our results of an approach to keep the period of the induced modulation constant for the wavelengths utilised in ToF. This is achieved by ramping the magnetic fields in the coils responsible for creating the spatially modulated beam in synchronisation with the neutron pulse, thus keeping the modulation period constant for all wavelengths. Such a setup enables the decoupling of the spatial detector resolution from the resolution of the modulation period by the use of slits or gratings in analogy to the approach in grating-based neutron DFI.

1H and 2H NMR: Diagonal suppressed total correlation spectroscopy in spin echo mode

We report a novel diagonal suppressed two-dimensional total correlation experiment in solution state and demonstrate its performance in 1H and 2H NMR. In DIagonal Suppressed spin echo TOtal Correlation SpectroscopY (DISTOCSY), diagonal peaks which occur around F1=0 in spin echo mode are removed by conversion to unobservable multiple quantum or longitudinal terms in each scan of a two scan procedure, on application of an appropriately phased 90° pulse at the time of the echo maximum. The limitation of this approach to short FID acquisition times is discussed, and an alternative two-scan version of DISTOCSY for high resolution situations is presented.

EXPERIMENTAL EVALUATION OF MN(II)-TRANS-1,2-DIAMINOCYCLEHEXANE-N,N,N',N'TETRAACETATE AS PARAMAGNETIC CONTRAST AGENT FOR ENHANCEMENT OF CEREBRAL MENINGEOMAS IN DOGS

Aim of research. We have evaluated the abilities of new original paramagnetic contrast agent Mn-DCTA (0,5 mol solution of Manganese(II) complex with trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetate, registered trade mark Cyclomang) for contrast-enhanced imaging of brain meningeomas in dogs.Material and methods. Twelve animals were included, all with brain tumors reveald during out-patient veterinary examinations. In ten of twelve the diagnosis was verified later by pathomorphologic study. The cerebral MRI has been carred out as set of axial, sagittal and coronal slices as thin as three to five mm, covering all the volume of brain.The scanning parameters in T1-weighted spin-ech mode were as follows: TR = 400–500 ms, TE = 15–20 ms, the dose of injected paramagnetic was standardised as 1 mmol per 10 kg of body weight. For quantitative analysis the index of enhancement was calculated.Results. In all cases the sure enhancement with clear visualization of cerebral tumor was obtained due to highly intensive uptake of Mn-DCTA to the tumor tissue. When evaluated quantitatively the uptake of Mn-DCTA to the tumor gave the index of enhancement in T1-weighted spin-echo mode as high as IE = 1,72 ± 0,18 for the central parts of tumor and IE = 2,08 ± 0,23 for the peripheral ones, where as in control animals it was far below these values. Intravenous injection of Mn-DCTA to dogs with cerebral tumors did not induce any detectable pathologic or even physiologic effects.Conclusion. Henceforth we conclude the Mn-DCTA provides highly available methodologically simple imaging of cerebral meningeomas and can be thought out as promising paramagnetic agent for clinical magnetic resonance imaging in humans.

Neutron multiwave spin echo

The neutron multiwave interference mode is investigated using the spin echo technique. In this mode a neutron wave repeatedly splits in the magnetic field of resonance coils, which results in the appearance of additional maxima of a constructive interference being absent in the well-known classical and resonance neutron spin echo modes. Simple analytical expressions well describing the experimental data are presented. It is demonstrated that the multiwave part of a spin echo signal appears when the spin flip probability in radiofrequency coils of a resonance spin echo device is ρ < 1. The possibility to use the neutron multiwave spin echo mode for investigation of high-order correlation functions, spatial and time correlations of three and more particles, is discussed.

Application of the magnetic resonance sounding method to the investigation of aquifers in the presence of magnetic materials

It has been previously reported that the magnetic resonance sounding (MRS) method does not produce reliable data in areas where magnetic rocks perturb the geomagnetic field. The applicability of the MRS can be extended by using the spin echo (SE) measuring technique instead of the commonly used measuring scheme based on recordings of the free induction decay (FID) signal. Modifications to the MRS method are presented for measuring and interpreting SE signals. Field results obtained in Cyprus (1999), Canada (2008), and India (2008) reveal that in test sites MRS measurements in the SE mode make it possible to apply the MRS method where the subsurface is composed of sand and gravel that contain magnetite or basalt and in aquifers composed of nonmagnetic sand overlying a magnetic basement. Con-sidering the widespread occurrence of magnetic rocks, this development increases the area where MRS can be applied. However, experience shows that it is more time consuming to measure the SE and more complicated to interpret the field data than it is to work with FID measurements. Numerical results show that the MRS method in the SE mode is less efficient than the FID technique because of the smaller amplitude and wider band of the SE signal. Due to instrumental limitations and unknown distribution of the magnetic fields within the investigated volume, accuracy of the presented MRS-SE approach is site dependent. In a general case, MRS-SE in its current implementation is not able to provide robust estimates of the initial amplitude, which renders MRS estimate of the water content qualitative. For accurate estimate of the water content, more sophisticated approaches need to be developed.

Fusion of MRIs and CT Scans for Surgical Treatment of Cholesteatoma of the Middle Ear in Children

To evaluate the efficiency of diffusion-weighted magnetic resonance imaging (MRI) and high-resolution computed tomographic (CT) scan coregistration in predicting and adequately locating primary or recurrent cholesteatoma in children. Prospective study. Tertiary care university hospital. Ten patients aged 2 to 17 years (mean age, 8.5 years) with cholesteatoma of the middle ear, some of which were previously treated, were included for follow-up with systematic CT scanning and MRI between 2007 and 2008. Computed tomographic scanning was performed on a Siemens Somaton 128 (0.5/0.2-mm slices reformatted in 0.5/0.3-mm images). Fine cuts were obtained parallel and perpendicular to the lateral semicircular canal in each ear (100×100-mm field of view). Magnetic resonance imaging was undertaken on a Siemens Avanto 1.5T unit, with a protocol adapted for young children. Diffusion-weighted imaging was acquired using a single-shot turbo spin-echo mode. To allow for diagnosis and localization of the cholesteatoma, CT and diffusion-weighted MRIs were fused for each case. In 10 children, fusion technique allowed for correct diagnosis and precise localization (hypotympanum, epitympanum, mastoid recess, and attical space) as confirmed by subsequent standard surgery (positive predictive value, 100%). In 3 cases, the surgical approach was adequately determined from the fusion results. Lesion sizes on the CT-MRI fusion corresponded with perioperative findings. Recent developments in imaging techniques have made diffusion-weighted MRI more effective for detecting recurrent cholesteatoma. The major drawback of this technique, however, has been its poor anatomical and spatial discrimination. Fusion imaging using high-resolution CT and diffusion-weighted MRI appears to be a promising technique for both the diagnosis and precise localization of cholesteatomas. It provides useful information for surgical planning and, furthermore, is easy to use in pediatric cases.

Wertigkeit von SE-, IE- und GE-Sequenzen bei Tumoren im Kopf-Hals-Bereich

In a review of 82 patients having different benign and malignant head and neck tumours we studied the value of spin echo (SE), inversion echo (IE) and gradient echo (GE) sequences. The strong T1 weighted IE mode is highly sensitive to demonstrate pathological tissue. Tumour diagnosis was in 20% and lymph node diagnosis in 29% better than T2 weighted SE sequences. According to this experience we choose the IE mode as the first one for all patients examined for tumour staging. All other sequences and orientations are planned on this tomograms knowing the location of the tumour and lymph nodes. T1 weighted SE mode is indispensable and should be recorded in transversal orientation, covering the whole head and neck region. This mode has the best imaging of anatomical structures as the known fatty limitations. The best differentiation of the tumour is usually obtained after contrast enhancement by i.v. Gd-DTPA. The highest contrast enhancement is seen on T1 weighted GE tomograms, which we prefer. T2 weighted SE sequences are less sensitive than IE sequences and T1 weighted tomograms after Gd-DTPA to show the tumour. The T2 weighted SE mode cannot be replaced by the T2 weighted GE mode having a better signal to noise ratio. To minimise the scan-time of T2 weighted SE mode, only one measurement is performed; the quality of the tomograms is satisfactory.

Spin-echo small-angle neutron scattering in neutron reflectometry

A new method to perform neutron reflectometry measurements is discussed. The method is based on Larmor precession of polarized neutrons in the spin-echo mode. Two different modes of application are discussed, giving successively information about the structure perpendicular to and parallel to the sample plane. After describing the method, simulated results of the perpendicular mode are compared with those obtained by conventional neutron reflectometry methods. In this comparison, first the results obtained by the SESANS method are translated to those obtained by conventional methods. After that, more specific applications of the new method are considered. In the comparison, attention is focused on measuring statistics and resolution as readily comparable quantities.

Novel instrumentation concepts using polarised neutrons

A new Larmor precession device, consisting of two separate precession modules, is introduced. It operates as a high-resolution neutron diffractometer, without the need of a highly collimated beam, necessary in conventional high-resolution neutron diffraction. A spin-echo mode of the same instrument, operates in different modes as an effective small-angle scattering device or accurately determines the line profile, the lattice plane orientation or the angular spread. A dramatic intensity gain in all applications discussed can be obtained, due to the possibility to use a relaxed wavelength and angular resolution.

Characteristics of intracranial meningioma imaged by magnetic resonance tomography

Twenty-three patients with intra cranial meningiomas were examined by means of magnetic resonance tomography (MRT). In 13 patients the paramagnetic contrast medium gadolinium DTPA was used. Meningiomas show only slight changes in signal intensity compared with brain in the spin-echo mode, the greatest contrast being found on photon density images (TR 1600 ms, TE 35 ms). In T1 images, more than 50% patients showed a low signal margin between tumour and brain, Hyperostosis of the calvarium is easily recognised, but MRT is unreliable for showing tumour calcification. After intravenous injection of gadolinium DTPA, there was marked homogeneous uptake in the meningiomas. These signs are useful for the diagnosis of a meningioma by MRT.

Magnetic resonance tomography in syringomyelia

Thirteen patients with a clinical diagnosis of syringomyelia were examined by nuclear tomography (0.35 T magnet) in the spin-echo mode. In all thirteen patients, the T1 images (SE 400/35) showed a longitudinal cavity with a signal intensity of CSF. The shape and extent of the syrinx could be adequately demonstrated in 12 of the 13 examinations. Downward displacement of the cerebellar tonsils was seen in eight cases. The examination took between half and one hour. Advantages of magnetic resonance tomography (nuclear tomography) include the absence of artifacts, images in the line of the lesion and its non-invasiveness.

Magnetic resonance imaging of abdominal and pelvic lymphadenopathy.

The authors report their experience with magnetic resonance imaging (MR) in 20 patients with CT-proved lymphadenopathy of the abdomen and pelvis. Signal intensity from abnormal nodes was intermediate between fat and muscle (T1 longer than fat and muscle; T2 equal to or slightly shorter than fat but longer than muscle) and was shown best in the spin-echo mode with a TR of 900 msec. and a TE of 30 msec. Abnormal nodes were identified by their increased size and other morphological changes rather than by tissue characteristics established by signal intensity information. Lymphadenopathy due to lymphoma could not be differentiated from that due to metastases. MR detected all lymphadenopathy originally documented by CT and in addition easily distinguished blood vessels from lymph nodes; on the other hand, CT offered better spatial resolution and could be completed in less time.

Experience with NMR tomography of the skeletal system

The value of nuclear magnetic resonance (NMR) tomography in the skeleton is analysed in 27 patients who had been examined by a prototype NMR scanner (resistive magnet, 0.2 Tesla). Anatomical structures and detail can be seen using the spin-echo mode and brief sequences. There is marked contrast difference between normal and abnormal tissues. Pathological changes lead to marked alterations in relaxation times. Inflammatory conditions, tumours and aseptic bone necrosis are demonstrated with a high degree of sensitivity. Tomography in the three geometric planes, with any desired additional plane, shows the extent and localisation of bone abnormalities.