Search

Background: It is common to treat patients with metastatic disease from gastrointestinal neuroendocrine (NE) tumors with surgical reduction to prolong survival. This can be combined with hepatic arterial embolization (HAE) and medical treatment to reduce hormonal symptoms. Today there are no rapid and reliable methods to evaluate the efficacy of HAE in the treatment of neuroendocrine liver metastasis., Purpose: To investigate metabolic changes in hepatic metastases of NE tumors following HAE, and to establish if there are any early spectral patterns that might indicate therapeutic efficacy based on in vivo (31)P MRS data., Material and Methods: Volume selective (31)P MRS was used to study 11 patients with disseminated NE tumors with regional lymph nodes and bilobar liver metastases. Measurements were performed before and 1 and 3 days after HAE., Results: Non-responders had significantly higher PME/Pi and αNTP/ΣNTP ratios than the responders before HAE (P < 0.05). Three days after HAE, non-responders still had significantly higher αNTP/ΣNTP than the responders did (P < 0.05). We also observed trends for increased PME ratios 3 days after HAE, decreased ATP-levels, and liberated Pi in responders., Conclusion: This (31)P-MRS study showed significant differences in PME/Pi and αNTP/ΣP ratios between responders and non-responders on the day before HAE, which is an interesting finding that may reflect intrinsic properties of the tumor tissue. We also observed trends for cell membrane renewal and increased energy consumption in responders after HAE. These results demonstrate potentials for (31)P-MRS to predict individual responsiveness prior to HAE.

Absence of N-acetylaspartate (NAA) is one important diagnostic criterion of MR spectroscopy (MRS) that may suggest that an intracranial mass lesion is a metastasis. We report two cases of histopathology-confirmed intracranial metastatic mucinous adenocarcinoma, which predominantly showed a large metabolite peak at 2.0 ppm, mimicking an NAA peak of normal brain tissue. This finding could be of help in the interpretation of MRS in cases of intracranial enhancing mass lesions, metastases or gliomas., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Background: The concentration of N-acetylaspartate (NAA) in hippocampus, as measured with magnetic resonance spectroscopy (MRS), and the ratio of NAA/(choline (Cho) + creatine (Cr)) are valuable tools in the lateralization of temporal lobe epilepsy (TLE). MRS of hippocampus is also increasingly used to study certain psychiatric and degenerative diseases. However, the reliability of such measurements of hippocampus has been questioned., Purpose: To re-evaluate MRS imaging data from prior control subjects with regard to variation of metabolite concentrations in hippocampus from anterior to posterior and the partial volume (R)contribution to the measurements from adjacent tissue., Material and Methods: Twelve healthy subjects, mean age 33 years, were studied with MRS imaging. The measurement volume was angled along the temporal horns and metabolite concentration images were reconstructed at the MR system. Regions of interest (ROIs) in the anterior, medial, and posterior parts of both hippocampi were evaluated. Signal normalization to the total MRS signal from all ROIs permitted pooling of individual data with different and unknown signal scaling. One subject was re-examined with a high resolution three-dimensional (3D) volume of the brain for evaluation of partial volumes in the MRS examination., Results: Overall, there were significantly lower concentrations of NAA in the anterior parts, and of (Cho+Cr) in the posterior parts, while the NAA/(Cho+Cr) ratio in the posterior parts of the mesial temporal lobes was significantly higher. Hippocampus accounted for one-half, one-third, and one-quarter of the anterior, middle, and posterior ROIs, respectively. The NAA/(Cho+Cr) ratio thus showed a reverse relationship to the relative volume of hippocampal tissue within the ROI., Conclusion: Metabolite concentrations in the mesial temporal lobe obtained with MRS imaging represent the mean value of hippocampus and a considerable amount of adjacent tissue. To assess the hippocampus alone, an actual voxel well below 1 cm(3) and a sub-centimeter slice thickness are required.

1H magnetic resonance spectroscopy (1H MRS) studies exploring brain metabolites, especially glutamine + glutamate (Glx), in obsessive compulsive disorder (OCD) are of vital interest for trying to understand more about the pathophysiology of OCD. Therefore, we conducted the present 1H MRS study with the aims of (1) comparing MRS metabolites in a group of adult patients with OCD and a group of healthy controls, and (2) examining the relationship between MRS metabolite concentrations and symptom severity in the patient group. Three brain regions were studied, the right caudate nucleus, the anterior gyrus cinguli and the occipital cortex bilaterally. Since multivariate analysis is a highly useful tool for extraction of 1H MRS data, we applied principal component analysis (PCA) and partial least square projection to latent structures (PLS) to the MRS data. PLS disclosed a strong relationship between several of the metabolites and OCD symptom severity, as measured with Yale-Brown obsessive-compulsive scale (YBOCS): the YBOCS score was found to be positively correlated to caudate creatine, Glx, glutamate, and choline compounds as well as occipital cortex myoinositol, and negatively correlated to occipital cortex Glx. The negative correlation between occipital cortex Glx and YBOCS was the most impressive. PCA did not reveal any tendency for a separation between the patients with OCD and controls with respect to MRS metabolites. The results are discussed in relation to corticostriatothalamocortical feedback and previous observations of poor visuospatial ability in OCD.

Changes in concentration of high energy phosphates and pH were studied during rest, exercise and subsequent recovery in the anterior tibial muscle of 10 patients with late effects of poliomyelitis and 10 age- and sex-matched healthy volunteers using 31P MRS. The exercise was dynamic and isometric, and the force levels were individually adapted to each subject and stepwise increased. In general, there were no differences in metabolite changes between the groups, except for lower Pi and Pi/PCr for the volunteers during the recovery phase, also reflected by shorter recovery half-time for Pi. The interindividual variation was much higher for the patient group. Some of the patients showed deviating results probably because of differences in muscle fibre type.

It is well known that the quality of a quantitative 31P MRS measurement relies largely on the performance of the volume selection method, and that image selected in vivo spectroscopy (ISIS) suffers from contaminating signal caused mostly by T1 smearing. However, these signal errors and their magnitude are seldom addressed in clinical studies. The aim of this study was therefore to investigate the magnitude of signal errors in 31P MRS when using ISIS. The results from the measurements with a homogeneous head phantom are as follows: at low TR/T1 ratios the contamination increases rapidly, especially for small (<27 cm3) VOI sizes; at TR/T1=1, the signal from a 27 cm3 VOI was 20% too high, and from an 8 cm3 VOI 150% too high. The signal obtained from different VOI positions varied between 80 and 127%. The signal varied linearly with the 31P concentration in the object. However, a too high signal was obtained when the concentration was lower in the region of interest (inner container) than in the rest of the phantom. The agreement between the simulations and measurements shows that the results of this study are generally applicable to the measurement geometry and the ISIS experiment order rather than being specific for the MR system studied. The errors obtained both experimentally and in computer simulations are too large to be ignored in clinical studies using the ISIS pulse sequence.

2D MRSI suffers from the effect of the spatial response function due to the truncation of the sampling of k-space. Filtering of the k-space data-set is often used to suppress the side lobes caused by the effects of the SRF, where the sampled data-set is multiplied with a weighting function before inverse FT. Commonly used filters in MRSI are the cosine, Hanning and Hamming filters. The data-set is often interpolated into a larger image matrix size for analysis, where "Fourier interpolation" (FoI) and "cubic spline interpolation" (CSpI) are two common methods. In this work, the effects of k-space filtering in practical usage was examined, and the image representations of the object for the two interpolation methods were compared. This study showed that application of filtering improves the image representation of the structures in the object and should be used in MRSI. FoI correctly visualizes the information inherent in the data-set, while the features of the object were dependent on the position of the object relative the original matrix in the CSpI interpolated images. FoI should therefore be used for quantitative evaluation of MRSI images.

We carried out spectroscopic imaging (MRSI) on nine consecutive patients with temporal lobe epilepsy being assessed for epilepsy surgery, and nine neurologically healthy, age-matched volunteers. A volume of interest (VOI) was angled along the temporal horns on axial and sagittal images, and symmetrically over the temporal lobes on coronal images. Images showing the concentrations of N-acetylaspartate (NAA) and of choline-containing compounds plus creatine and phosphocreatine (Cho + Cr) were used for lateralisation. We compared assessment by visual inspection and by signal analysis from regions of interest (ROI) in different positions, where side-to-side differences in NAA/(Cho + Cr) ratio were used for lateralisation. The NAA/ (Cho + Cr) ratio from the different ROI was also compared with that in the brain stem to assess if the latter could be used as an internal reference, e. g., for identification of bilateral changes. The metabolite concentration images were found useful for lateralisation of temporal lobe abnormalities related to epilepsy. Visual analysis can, with high accuracy, be used routinely. ROI analysis is useful for quantifying changes, giving more quantitative information about spatial distribution and the degree of signal loss. There was a large variation in NAA/ (Cho + Cr) values in both patients and volunteers. The brain stem may be used as a reference for identification of bilateral changes.

Image selected in vivo spectroscopy (ISIS) is a volume selection method often used for in vivo (31)P MRS, since it is suitable for measurements of substances with short T(2). However, ISIS can suffer from significant signal contributions caused by T(1) smearing from regions outside the VOI. A computer model was developed to simulate this contamination. The simulation results for the ISIS experiment order implemented in our MR system (ISIS-0) were in agreement with results obtained from phantom measurements. A new extended ISIS experiment order (E-ISIS) was developed, consisting of four "optimal" ISIS experiment orders (ISIS-1 to ISIS-4) performed consecutively with dummy ISIS experiments in between. The simulation results show that contamination due to T(1) smearing is, effectively, eliminated with E-ISIS and is significantly lower than for ISIS-0 and ISIS-1. E-ISIS offers increased accuracy for quantitative and qualitative determination of substances studied using in vivo MRS. Hence, E-ISIS can be valuable for both clinical and research applications.

The purpose was to analyse magnetic susceptibility effects on accuracy of point-wise measurements of signal profiles in the assessment of MRS volume selection performance. An existing phantom design consisting of a sphere with a movable signal source was used for the investigation. The influence from the phantom on magnetic field homogeneity was measured with phase sensitive 1H imaging and 31P spectroscopy on a 1.5 T whole body MR system. The susceptibility effects for such a phantom design can be separated in 1/ A variation in the background magnetic field, which is caused by the stationary structures and has a significant influence on spatial accuracy. 2/ A magnetic field distortion, which is caused by the movable signal source and has very little influence on accuracy. The spatial inaccuracy due to susceptibility effects in this phantom, was 0.03 mm for positions of the signal source covering a 40-mm VOI. Susceptibility effects from the movable signal source were substantial but had very little influence on spatial accuracy. Still, improvements of this phantom design are possible. Point-wise measurements using a phantom with a movable signal source is inherently insensitive to susceptibility effects from the signal source and permits accurate signal profile measurements of high spatial (sub-mm) resolution.

The volume-selection performance was studied for single- and double-volume-of-interest (VOI) acquisition with the volume-selection method image-selected in vivo spectroscopy for 31P magnetic resonance spectroscopy. High-resolution signal profiles were measured using a phantom simulating a brain. Inside the phantom there was a small, remotely controlled, movable signal source filled with ortho-phosphoric acid. Signal profiles of the VOI were measured in three perpendicular directions for 1VOI (single VOI) and 2VOI (double VOI) acquisition. The measured signal profiles for both acquisitions were very similar, but they showed a discrepancy with regard to the intended VOI (iVOI). The transition regions were on average 3.8 mm and the average full width at half maximum of the signal profile was 30 mm for an iVOI size of 30*30*30 (mm3). No displacement was observed in the signal profiles. To avoid overlapping signal profiles, the minimum separation between two iVOIs was found to be 10 mm in our magnetic resonance (MR) system. A substantial negative signal contribution from regions outside the iVOI was measured in the y-direction for 1VOI acquisition and one of the two VOIs in 2VOI acquisition. The other VOI in 2VOI acquisition exhibited only minor contamination. The measurements presented underline the importance of detailed knowledge on the volume selection performance in in vivo magnetic resonance spectroscopy.

Purpose: The purpose of this study was to examine the potential of 31P-MRS (MR spectroscopy) in the pre- and postoperative evaluation of patients referred for endarterectomy., Material and Methods: Nine patients with unilateral, hemodynamically significant stenosis in the region of the common carotid bifurcation were examined pre- and post-operatively with CT, SPECT (regional cerebral blood flow), transcranial Doppler, and duplex sonography, and they also underwent neuropsychologic investigation. Phosphorus-31 MRS of each hemisphere was performed before and 27-148 days after surgery. The relative concentrations of phosphomono- and -diesters, inorganic phosphate, phosphocreatine, and ATP were estimated., Results: No definite changes in concentrations could be detected for any of the metabolites., Conclusion: The lack of changes was probably due to well-functioning collaterals and to the partial volume effect, whereby changes in a focal region are hidden when larger volumes are studied.

High-resolution signal profiles obtained with a test phantom were used in this study to evaluate the volume-selection performance of an implementation of ISIS (Image Selected In vivo Spectroscopy). The phantom simulated the brain with regard to volume and loading of coil. A remotely controlled, movable signal source inside the phantom was filled with orthophosphoric acid. Signal profiles of the volume of interest (VOI) were measured in three perpendicular directions. Special interest was focused on the transition zones, the position of the profiles, and the effects of off-resonance and T1 smearing. The transition zones were on average 5.6 mm wide and the full width at half maximum (FWHM) was 35 mm for a VOI of 40 x 40 x 40 mm3. The positions of the centre of the signal profiles were x = 3.2, y = -0.7 and z = 3.3 mm off-centre. The deviation of the volume position could be explained by off-resonance effects during imaging and spectroscopy. These data illustrate the importance of detailed knowledge of the volume-selection performance when attempting precision measurements using image-guided in vivo MRS.

In vivo MR spectroscopy (MRS) requires some kind of volume selection method to be able to measure the signal from a selected part of the body. To be able to interpret the spectra correctly, the quality of the volume selection must be investigated for each new MRS application using phantom measurements. A new phantom, especially suitable for precision measurements of the volume selection performance, is presented. It contains a small, remotely controlled signal source placed inside a larger vessel. This principle can be applied to various body regions, coil types and nuclei. The measurement conditions are close to the clinical situation. The phantom does not have to be repositioned during a signal profile measurement and the signal contribution from each point along the profile is determined regarding sign and amplitude.