Echo Proton Research Articles

Comparison of MRI graded cartilage and MRI based volume measurement in knee osteoarthritis.

The aim of this study was to investigate the relationship between the femoral, tibial and patellar cartilage volume and MRI grading of the articular cartilage in patients with knee OA. Articular cartilage volumes of 65 postmenopausal women were determined by processing images acquired in the sagittal plane using a fast spin echo proton density-weighted sequence. The articular cartilages were divided into 5 compartments including lateral and medial tibial, lateral and medial femoral and patellar compartments. The articular cartilages were graded using a modified Outerbridge classification. Grade 0 indicated intact cartilage, grade 1 chondral softening with normal contour, grade 2 superficial fraying, grade 3 surface irregularity and thinning and grade 4 full thickness cartilage loss. The grades of articular cartilage were compared with cartilage volume measurements. In medial femoral cartilage, grade 1 had more volume compared to grade 0 cartilage (p: 0.017). In medial tibial cartilage, grade 1 had more volume compared to grade 0 and grade 2 cartilage (p: 0.045 and p: 0.027, respectively). In patellar cartilage, grade 1 cartilage had significantly more volume than grade 0 cartilage (p: 0.007). In lateral tibial and femoral cartilages, no significant difference was observed between grade 0 and grade 1 cartilage. Cartilage volume correlates well with MR grading of articular cartilage. The higher the grade of the cartilage the less the volume, with the exception of grade 1 lesions. Grade 1, reflects oedema in the cartilage and has a conflicting effect on volume measurement. The combination of MRI based volume measurement and grading of articular cartilage may provide an accurate method for the non-invasive evaluation and follow-up of articular cartilage.

Comparison of MRI graded cartilage and MRI based volume measurement in knee osteoarthritis.

The aim of this study was to investigate the relationship between the femoral, tibial and patellar cartilage volume and MRI grading of the articular cartilage in patients with knee OA. Articular cartilage volumes of 65 postmenopausal women were determined by processing images acquired in the sagittal plane using a fast spin echo proton density-weighted sequence. The articular cartilages were divided into 5 compartments including lateral and medial tibial, lateral and medial femoral and patellar compartments. The articular cartilages were graded using a modified Outerbridge classification. Grade 0 indicated intact cartilage, grade 1 chondral softening with normal contour, grade 2 superficial fraying, grade 3 surface irregularity and thinning and grade 4 full thickness cartilage loss. The grades of articular cartilage were compared with cartilage volume measurements. In medial femoral cartilage, grade 1 had more volume compared to grade 0 cartilage (p: 0.017). In medial tibial cartilage, grade 1 had more volume compared to grade 0 and grade 2 cartilage (p: 0.045 and p: 0.027, respectively). In patellar cartilage, grade 1 cartilage had significantly more volume than grade 0 cartilage (p: 0.007). In lateral tibial and femoral cartilages, no significant difference was observed between grade 0 and grade 1 cartilage. Cartilage volume correlates well with MR grading of articular cartilage. The higher the grade of the cartilage the less the volume, with the exception of grade 1 lesions. Grade 1, reflects oedema in the cartilage and has a conflicting effect on volume measurement. The combination of MRI based volume measurement and grading of articular cartilage may provide an accurate method for the non-invasive evaluation and follow-up of articular cartilage.

Magnetic resonance imaging of the palmar aspect of the equine podotrochlear apparatus: normal appearance.

The purpose of this study was to describe the normal magnetic resonance (MR) imaging characteristics of the palmar structures of the equine podotrochlear apparatus by means of retrospective evaluation of MR imaging studies of 16 cadaver limbs. The articular aspect of the distal sesamoid bone was not evaluated in this study. Equine digits were imaged with a human knee radiofrequency coil in a 1.5 T magnetic field, using spin echo (SE) T1-weighted, turbo spin echo proton density (TSE PD)-weighted with and without fat saturation (FS), and FS TSE T2-weighted sequences. The limbs were dissected after imaging to validate the absence of gross abnormalities of the flexor aspect of the distal sesamoid bone, of the deep digital flexor tendon, and the distal impar sesamoidean ligament. Seven deep digital flexor tendons were subjected to histologic examination to exclude any microscopic tendon pathology. The anatomic structures of the podotrochlear apparatus were easily identified on MR images. Compact bone of the flexor cortex of the distal sesamoid bone had low intensity signal on all sequences. In 11 digits an increased signal was seen within the thickness of the sagittal eminence of the flexor cortex in SE T1-weighted images and in TSE PD-weighted images without FS. Trabecular bone had a granular appearance and high signal in SE T1-weighted sequences and TSE images without FS. The deep digital flexor tendon had low signal on FS T2-weighted images, while on short echo time sequences (T1- and PD-weighted sequences), the tendon signal varied depending on the relative orientation between its fibers and the static magnetic field. Seven tendons had stippled appearance due to small intratendonous foci of slightly increased signal on transverse T1-weighted images. MR imaging provides a thorough evaluation of the anatomical structure of the podotrochlear apparatus: A good knowledge of the MR imaging appearance and anatomy and an awareness of potential pitfalls will improve diagnostic specificity for the detection of pathologic changes.

Brain tumor classification based on long echo proton MRS signals

There has been a growing research interest in brain tumor classification based on proton magnetic resonance spectroscopy ( 1 H MRS) signals. Four research centers within the EU funded INTERPRET project have acquired a significant number of long echo 1 H MRS signals for brain tumor classification. In this paper, we present an objective comparison of several classification techniques applied to the discrimination of four types of brain tumors: meningiomas, glioblastomas, astrocytomas grade II and metastases. Linear and non-linear classifiers are compared: linear discriminant analysis (LDA), support vector machines (SVM) and least squares SVM (LS-SVM) with a linear kernel as linear techniques and LS-SVM with a radial basis function (RBF) kernel as a non-linear technique. Kernel-based methods can perform well in processing high dimensional data. This motivates the inclusion of SVM and LS-SVM in this study. The analysis includes optimal input variable selection, (hyper-) parameter estimation, followed by performance evaluation. The classification performance is evaluated over 200 stratified random samplings of the dataset into training and test sets. Receiver operating characteristic (ROC) curve analysis measures the performance of binary classification, while for multiclass classification, we consider the accuracy as performance measure. Based on the complete magnitude spectra, automated binary classifiers are able to reach an area under the ROC curve (AUC) of more than 0.9 except for the hard case glioblastomas versus metastases. Although, based on the available long echo 1 H MRS data, we did not find any statistically significant difference between the performances of LDA and the kernel-based methods, the latter have the strength that no dimensionality reduction is required to obtain such a high performance.

15N T2' relaxation times of bacteriorhodopsin transmembrane amide nitrogens.

15N T(2)' relaxation times of bacteriorhodopsin (BR) amide nitrogens were determined in the temperature range from 40 to -60 degrees C using a Hahn echo pulse sequence and proton decoupling during the echo and detection times. Using oriented membrane samples, with their bilayer normal parallel to the external magnetic field, the (15)N amide nitrogens belonging to the transmembrane helices could be selected for the analysis. The experiments were performed on purple membrane fragments (in which BR is organized in a 2D crystalline network) and on BR reconstituted into dimyristoylphosphatidylcholine at a 1:150 molar ratio (in which BR is in a freely diffusing monomeric state at 40 degrees C and in an aggregated state at 4 degrees C and below). The results are discussed in terms of helix dynamics, mosaic spread and resolution of the (15)N spectra for the various samples and experimental conditions.

A substorm-associated drift echo of energetic protons observed by Geotail: Radial density gradient structure

[1] We found a drifting population with a fairly long (∼several tens of minutes) dispersion at a geocentric distance >9 RE, indicating that energetic particles can lie on a closed drift path around the Earth much farther than the geosynchronous distance. In this event, Geotail was situated in the plasma sheet in the post-midnight sector at a distance of ∼10 RE and observed a drift echo of energetic protons with energies of several tens to hundreds of keV. This drifting population showed an azimuthal sector anisotropy in particle distribution as it passed by the spacecraft. The drift echo showed a lack of duskward-directed particle fluxes in its leading portion, became isotropic in the middle of the event, and finally showed enhanced duskward-directed fluxes in its trailing portion. Since the magnetic field was dominated by the Bz component during this event, this sequence of anisotropy can be considered in terms of a density gradient structure of the drifting population with a scale of the order of proton gyroradius (∼0.5 RE) in the equatorial plane. Because the duskward-directed flux at the spacecraft can be attributed to protons with their guiding centers sunward of the observation point, it is suggested that the drifting proton echo has a spatial structure such that protons are localized tailward of the spacecraft at the leading portion, while a sunward density gradient exists around the trailing portion. Thus the present study shows that a drift echo is not an uniform population but has a complicated structure with a sharp density gradient in the radial direction, which may reflect some characteristics of its source site as well as its drift path.

Mapping cerebral glutamate 13C turnover and oxygen consumption by in vivo NMR.

Regional rates of 13C incorporation from glucose to glutamate were detected in anesthetized rat brain in vivo at 7T with high temporal and spatial resolution using NMR method ICED PEPSI (in vivo carbon edited detection with proton echo planar spectroscopic imaging). Time courses of regional glutamate 13C turnover were fitted by a metabolic model to obtain regional tri-carboxylic acid (TCA) cycle flux and cerebral metabolic rate of oxygen consumption (CMRO2) in each voxel (8 microL) of rat cortex. CMRO2 maps obtained for rats under either alpha-chloralose or morphine anesthesia revealed average cortical values of 1.5 +/- 0.2 (n = 3) and 3.2 +/- 0.3 (n = 4) mumol/g/min, respectively. These values of CMRO2 are in good agreement with previous cortical measurements with coarser spatial resolution. The heterogeneity within each map, which depicted predominantly gray and white matter differences, was significantly greater under morphine (higher cortical activity) than under-alpha-chloralose (lower cortical activity) anesthesia. The regional variations in the basal awake state, which are expected to be even greater, should be considered to avoid partial-volume artifacts in functional activation studies of awake subjects.

Comparison of surface coil and knee coil for evaluation of the patellar cartilage by MR imaging

Purpose: The aim of this work was to compare the knee coil and the surface coil for the visualisation of the patellar cartilage. Materials and methods: In 28 patients (17 women, 11 men) with an average age of 40 years (range 14–76) with knee pain MR was performed. Transverse images were obtained using a fast spin echo proton density weighted sequence on a Philips Gyroscan Intera 1.5 T clinical system. Transverse images were obtained at the level of the patellar cartilage using both the surface and the knee coil. All images were evaluated by consensus of two radiologists. They evaluated a number of quality criteria on a 4-point scale. Criteria for artefacts were also graded on a 4-point scale. Results: For the visualisation of fluid there was no significant difference between the knee coil and the surface coil ( P=0.021). For all other criteria regarding image quality and presence of imaging artefacts there was a significant difference between both coils ( P<0.001) with the surface coil obtaining the better result. Conclusion: The use of the surface coil in the visualisation of the patellar cartilage can be recommended at knee MR.

Biexponential T2 Relaxation Time Analysis of the Brain

To measure T2 relaxation times of normal white and gray matter using a novel CPMG sequence and investigate if any correlation exists between magnetization transfer ratio (MTR) and T2 relaxation-related parameters. Seventeen normal volunteers participated on this study. A single-slice 32-echo sequence was used to calculate the T2 relaxation time of frontal and occipital white matter and cortical gray matter. T2 relaxation analysis included monoexponential and biexponential fitting whereas an F test was used to determine if biexponential fitting was statistically more accurate than monoexponential fitting. Short and long T2 constants were calculated as well as the signal fractions of each pool. MTR calculations were based on a three-dimensional gradient echo (3D FFE) proton density weighted sequence with and without an on-resonance composite prepulse. MTR and T2 relaxation times were calculated and linear regression analysis was applied. Biexponential fitting was more accurate comparing with monoexponential fitting in all WM and GM regions (F > 2.47, P < 0.01). Mean values of short T2 constant for frontal white matter (fWM), occipital white matter (oWM) and gray matter (GM) were 8.10, 9.36, and 22.23 milliseconds, respectively, whereas the mean values of long T2 constant were 85.1, 93.02, and 118.72 milliseconds, respectively. Mean restricted water percentages (RWP)-corresponding to the signal fraction of the protons with short T2-for the fWM, oWM, and GM were 22.01%, 23.36%, and 18.7%. Mean free water percentages (FWP)-corresponding to the signal fraction of the protons with long T2-for the fWM, oWM and GM were 77.99%, 76.64%, and 81.3%. Mean MTR values for fWM, oWM and GM were 68.4%, 68.2%, and 61.3%, respectively. No significant correlation was found in fWM and oWM between MTR and RWP, short and long T2 components while a moderate correlation existed in GM between MTR and RWP (r = 0.57; P = 0.02), MTR and short T2 component (r = -0.69; P = 0.004) and MTR and long T2 component (r = -0.62; P = 0.012). Two proton pools with different T2 decay characteristics can be separated in normal gray and white matter when using a multiecho sequence with short echo spacing. MTR and T2 relaxation times were significantly correlated in gray matter and the combination of both types of measurements may be helpful in studying myelin related disorders.

MR imaging of alar ligament in whiplash-associated disorders: an observer study.

Rotational CT studies have been previously used in whiplash-associated disorders (WAD) to document rotatory instability of the upper cervical spine thought to be due to alar ligamentous injury. More recently MR imaging has been employed to image such injury more directly. Our study aimed to assess the reliability and reproducibility of such MRI findings. In 12 WAD patients and six asymptomatic controls the alar ligaments were imaged in the coronal plane with an 0.5-T MRI system using a quadrature neck coil and applying a fast spin echo proton density/T2-weighted sequence (TR/TE/ETL 2,500/18 ms/16, FOV 140 mm, matrix 200 x 256, 16 x 3 mm slices, scan time 25 min). Images were graded for symmetry of imaging plane using a 3-point scale and also for presence of ligamentous injury with a 4-point scale, by two independent observers on two separate occasions. The alar ligaments could be identified in all cases. Asymmetry of the imaging plane was found to some degree in over half of the cases. Such images were much more likely to be graded as indicating injury. Of a total of 72 assessments, clearly and probably normal grades were given in 75%, and clearly or probably abnormal grades in 25%. Kappa values for intra- and inter-observer agreement were moderate to very poor, however, and the grading system could not reliably distinguish between patients and controls. It was concluded that with MRI techniques presently employed, alar ligamentous damage as a causative factor in WAD has not been proven.

Grey matter abnormalities in multiple sclerosis: proton magnetic resonance spectroscopic imaging.

Pathologically defined abnormalities in the cortical gray matter (GM) are well described in multiple sclerosis (MS) but are infrequently seen by conventional magnetic resonance imaging (MRI). We systematically evaluated 52 relapsing-remitting MS patients and 20 normal volunteers with high resolution MRI and short echo proton magnetic resonance spectroscopic imaging (MRSI). Individual tissue contributions to the spectroscopic voxels were estimated based on MRI that incorporated both CSF suppression and magnetization transfer, or double inversion images in which both CSF and GM were suppressed. Strong resonances in the 0.8 to 1.5 p.p.m. spectral region were observed in 13 MS patients. Image segmentation based on the MRI characteristics of tissues contributing to the spectroscopic voxels showed that these additional peaks originated mainly from GM. The presence of these additional peaks suggests that the normal appearance GM on MRI, is biochemically abnormal in a substantial proportion of relapsing-remitting MS patients.

The nature and fate of punctate (type IV) cavernous malformations.

Four types of cavernous malformations (Types I-IV) have been described on the basis of their magnetic resonance imaging (MRI) appearance. The nature of the Type IV cavernous malformation is unclear. It has been suggested that these small lesions, which are well observed only on gradient echo MRI scans, are capillary telangiectasias. We sought to understand the relationship of Type IV cavernous malformations to the other cavernous malformation subtypes. We examined serial MRI scans obtained between 1987 and 2000 from 68 patients with more than 228 cavernous malformations. Sixteen patients harbored Type IV cavernous malformations (total, >114 Type IV lesions). Spin echo T1-weighted, T2-weighted, proton density, and (when available) gradient echo MRI scans were reviewed. Cavernous malformations that met the Zabramski criteria for Type IV (poorly observed on T1- and T2-weighted images) were reviewed in serial scans from individual patients to characterize their radiographic behavior over time. Type IV cavernous malformations were best observed on gradient echo images and have an MRI appearance distinct from capillary telangiectasias. Proton density images demonstrate more Type IV lesions than T1- and T2-weighted images, but far fewer Type IV lesions than gradient echo images. When observed on T1- and T2-weighted images, Type IV cavernous malformations are generally punctate and hypointense. These lesions rarely enhance with gadolinium. Four of the Type IV cavernous malformations observed serially evolved into Type I and Type II cavernous malformations, for an approximate rate of progression of 0.05 per patient year. Although most Type IV cavernous malformations remain stable over time, a small subset of these lesions progress into Types I and II cavernous malformations.

Long-term cerebral metabolite changes on proton magnetic resonance spectroscopy in patients cured of acute lymphoblastic leukemia with previous intrathecal methotrexate and cranial irradiation prophylaxis

Purpose: To evaluate the long-term brain metabolite changes on 1H-MRS in acute lymphoblastic leukemia (ALL) patients who had intrathecal methotrexate (ITMTX) and cranial irradiation (CRT) for central nervous system (CNS) prophylaxis against CNS relapse. Methods and Materials: Thirty-seven ALL patients (12 females, 25 males) with history of ITMTX and CRT for CNS prophylaxis were studied. Age ranges at the time of diagnosis and at magnetic resonance examination were 0.8–13 years and 12–27 years, respectively. The interval since diagnosis was 5.6–19 years. T2-weighted and gradient-recalled echo (GRE) magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy ( 1H-MRS) were performed to assess brain injury. Results: On MRI, 3 leukoencephalopathy (LEP) and 1 infarct were detected. Twenty-two patients had evidence of hemosiderin. On 1H-MRS no statistically significant difference in choline (Cho)/creatine (Cr) and N-acetylaspartate (NAA)/Cr was associated with LEP. A lower Cho/Cr ( p = 0.006) and NAA/Cr ( p = 0.078) was observed in brains with hemosiderin. Linear-regression analysis showed no statistically significant relationship between NAA/Cr or Cho/Cr with age at diagnosis, but there was a statistically significant decreasing trend of NAA/Cr and Cho/Cr with the interval since diagnosis. Conclusion: Long-term brain injury in ALL survivors after CNS prophylaxis with ITMTX and CRT was reflected by decreasing NAA/Cr and Cho/Cr with the interval since diagnosis. The lower Cho/Cr associated with hemosiderin but not LEP suggested a different pathophysiology for these brain lesions.

Mismatch between lactate and the apparent diffusion coefficient of water in progressive focal ischemia.

In this study, we examined mismatch in the area indicated by the normal apparent diffusion coefficient (ADC) of water and increased lactate in the early stage of focal cerebral ischemia. Five rats were subjected to permanent middle cerebral artery (MCA) occlusion. Diffusion-weighted echo planar imaging (DWEPI) and proton echo planar spectroscopic imaging (EPSI) were performed from 20 to 170 min after MCA occlusion, and lactate and N-acetyl asparate images were obtained by EPSI. Postmortem histological analysis was also performed. The areas of increased lactate and normal ADC were observed in the surrounding border zone of ischemia at approximately 20 min after MCA occlusion. This initial lactate in the border zone was significantly higher than that in the normal area, but lower than that in the ischemic core, which showed a reduction of ADC. However, this area was progressively involved in the ischemic core at 170 min without any treatment. The lactate-ADC mismatch in the initial period of ischemia may offer unique diagnostic information for ischemic tissue at high risk, followed by progressive involvement in the ischemic core without treatment. Considering that the accumulation of initial lactate in this area was not excessive, our findings may suggest that the lactate-ADC mismatch in the early period of ischemia indicates potentially salvageable tissue at high risk, requiring aggressive treatment.

Measurement of the relaxation rate of the magnetization in Mn12O12-acetate using proton NMR echo

We present a novel method to measure the relaxation rate W of the magnetization of Mn 12O (12)-acetate (Mn12) magnetic molecular cluster in its S = 10 ground state at low T. It is based on the observation of an exponential growth in time of the proton NMR signal during the thermal equilibration of the magnetization of the molecules. We can explain the novel effect with a simple model which relates the intensity of the proton echo signal to the microscopic reversal of the magnetization of each individual Mn12 molecule during the equilibration process. The method should find wide application in the study of magnetic molecular clusters in off-equilibrium conditions.

A short echo proton magnetic resonance spectroscopy study of the left mesial-temporal lobe in first-onset schizophrenic patients

Background: Past 1H magnetic resonance spectroscopy (MRS) studies of the temporal lobe in schizophrenic patients have shown decreased levels of N-acetylaspartate (NAA) suggesting reduced neuronal density in this region. However, the measured volumes have been large and included contributions from mostly white matter. Methods: Short echo 1H MRS was used to measure levels of NAA and other metabolites (i.e., glutamate and glutamine) from a 6 cm 3 volume in the left mesial-temporal lobe of 11 first-episode schizophrenic patients and 11 healthy control subjects of comparable age, gender, handedness, education, and parental education levels. Spectra were quantified without operator interaction using automated software developed in our laboratory. Metabolite levels were normalized to the internal water concentration of each volume studied. Images were also obtained to determine temporal lobe gray and white matter volumes. Results: No significant differences were found between levels of NAA or other metabolites, or gray and white matter volumes, in first-episode schizophrenic patients and comparison subjects. Conclusions: Since the volume studied was small compared to previous studies and contained mostly gray matter, this result suggests consequential NAA decreases may be restricted to regions of white matter.

Appearance of anterior cruciate ligament autografts in their tibial bone tunnels on oblique axial MRI

The objective of this study was to observe the changing appearance of human anterior cruciate ligament (ACL) grafts in their tibial bone tunnels by MRI using oblique axial images. One-hundred and eight knees in 75 patients were studied by MRI at 1–33 months after arthroscopic ACL reconstructions using double-looped, autogenous semitendinosus and/or gracilis tendons. Knees with poor stability were excluded from this study. The examinations were performed at 0.2T with spin echo proton density and T 2-weighted oblique axial images. Appearances of grafts were mainly described on spin echo proton density images based upon time after surgery. The grafts appeared as homogeneous, low signal intensity areas in the bone tunnels at 1 month after the surgery. Ring-shaped low signal intensity areas were observed along the wall of the bone tunnels in the 2- to 3-month group. In many grafts from this group, each tendinous bundle appeared as a low signal area separated by a high signal intensity area. In all cases in the 4- to 6-month group, the thickness of the ring-shaped low signal intensity area had increased, whereas the thickness of the high signal intensity area had decreased. In almost all of the cases, the interior of the bone tunnel gradually became a homologous low signal intensity region by 7 to 12 months after the surgery. According to these results, it is suggested that the maturation of the tendon-bone interface was completed from 6 to 12 months after the ACL reconstruction.

Sex Differences in Brain Gray and White Matter in Healthy Young Adults: Correlations with Cognitive Performance

Sex-related differences in behavior are extensive, but their neuroanatomic substrate is unclear. Indirect perfusion data have suggested a higher percentage of gray matter (GM) in left hemisphere cortex and in women, but differences in volumes of the major cranial compartments have not been examined for the entire brain in association with cognitive performance. We used volumetric segmentation of dual echo (proton density and T2-weighted) magnetic resonance imaging (MRI) scans in healthy volunteers (40 men, 40 women) age 18-45. Supertentorial volume was segmented into GM, white matter (WM), and CSF. We confirmed that women have a higher percentage of GM, whereas men have a higher percentage of WM and of CSF. These differences sustained a correction for total intracranial volume. In men the slope of the relation between cranial volume and GM paralleled that for WM, whereas in women the increase in WM as a function of cranial volume was at a lower rate. In men the percentage of GM was higher in the left hemisphere, the percentage of WM was symmetric, and the percentage of CSF was higher in the right. Women showed no asymmetries. Both GM and WM volumes correlated moderately with global, verbal, and spatial performance across groups. However, the regression of cognitive performance and WM volume was significantly steeper in women. Because GM consists of the somatodendritic tissue of neurons whereas WM comprises myelinated connecting axons, the higher percentage of GM makes more tissue available for computation relative to transfer across distant regions. This could compensate for smaller intracranial space in women. Sex difference in the percentage and asymmetry of the principal cranial tissue volumes may contribute to differences in cognitive functioning.

In Vivo3D Localized13C Spectroscopy Using Modified INEPT and DEPT

The 3D localized13C spectroscopy methods LINEPT and LODEPT, which are modifications of INEPT and DEPT, are proposed. As long as a13C inversion pulse (180-degree pulse) is applied at 1/(4J) before the proton echo time in LINEPT and a13C excitation pulse (90-degree pulse) is applied at 1/(2J) before the proton echo time in LODEPT, the proton echo time can be set to any value longer than 1/(2J) in LINEPT and longer than 1/Jin LODEPT. As a result, the proton and the13C pulses can be applied separately and these proton pulses can be made slice-selective pulses. These localization features of LINEPT and LODEPT were evaluated using a phantom consisting of a cylinder filled with ethanol placed inside another cylinder filled with oil, and localized ethanol spectra could be obtained.In vivo3D localized13C spectra from the brain of a monkey could be obtained using decoupled LINEPT, and glutamate C-4 appeared directly after the administration of glucose C-1, followed by the appearance of glutamate C-2, C-3 and glutamine C-2, C-3, C-4.

Topside sounder proton‐cyclotron echo generation from a plasma memory process and electron Bernstein‐wave propagation

Evidence is presented for the radiation of an electron Bernstein wave from a radio frequency pulse simulated by proton‐cyclotron motion. The protons are energized by an ionospheric topside sounder transmitter pulse and take part in a plasma memory process that simulates the original transmitter pulse. These echoes appear on topside ionograms as thin traces. At frequencies below the electron cyclotron frequency fH, the proton echo delay is a multiple of the proton‐cyclotron period tp. At frequencies above fH, there can be an additional delay to tp depending on two factors: 1) the antenna orientation and 2) the closeness of the proton echo frequency f to fH. A model is presented here in which protons passing within a few tens of centimeters of the antenna are energized and modulated by the RF pulse by an amount depending on the RF phase. At multiples of tp later, these protons return to almost the same field line they were on at the time of the RF pulse, although they may have moved some tens of meters parallel or antiparallel to the field line. At multiples of tp, ntp, the protons are thus located in a plane defined by the linear dipole antenna (73 m long tip to tip) at the time of the pulse and the direction of the Earth's magnetic field B. At ntp the protons produce a field which simulates the original field of the RF pulse, and, if wave propagation in the plasma is possible, a pulse is produced which propagates to the new position of the antenna which has moved in the plasma at the satellite velocity Vs. For f &gt; fH, the perpendicularly propagating electron Bernstein waves are responsible for the propagation. No such Bernstein waves exist for f &lt; fH, and proton echoes can be observed at these frequencies if Vs is approximately in the plane of the energized protons at ntp so that wave propagation is not necessary to produce a signal that appears as an echo. For the second factor above, as the wave frequency approaches the electron cyclotron frequency, the group velocity of the Bernstein waves approaches zero, and consequently the propagation time to the antenna increases. This change in group velocity explains the observed increase in tp, which can be as much as several percent.