Prospective evaluation of in vivo proton MR spectroscopy in differentiation of similar appearing intracranial cystic lesions

Proton MR spectroscopy (PMRS) has been found to be useful in differentiating various cystic intracranial lesions. The purpose of the present study was to prospectively evaluate the spectral pattern of various cystic lesions of brain with similar imaging appearances and to determine the accuracy of this technique in the differential diagnosis of these lesions. Fifty-one patients with intracranial cystic lesions (21 abscesses, 20 gliomas, 3 hydatid cysts, 3 arachnoid cysts, 1 case each of glioependymal cyst, xanthogranuloma, infarction and acoustic neuroma) were evaluated with conventional MR imaging and in vivo PMRS. Ex vivo PMRS of the cystic contents aspirated at surgery in 31 cases was also done to confirm the in-vivo results. Preoperative diagnosis of the lesions was based on the results of in vivo PMRS. In vivo PMRS accurately predicted the pathology in 92% of the cases. We conclude that in-vivo PMRS complements imaging in better characterization of cystic intracranial mass lesions.     

Ex vivo proton MR spectroscopy (1H-MRS) for evaluation of human gastric carcinoma

The present study was performed to determine the characteristics of the biochemical metabolites related to gastric cancer using ex vivo (1)H magnetic resonance spectroscopy (MRS), and to assess the clinical usefulness. A total of 35 gastric specimens resected during surgery for gastric cancer were used to compare MR spectra. A 1.5-T (64-MHz) clinical MR imager equipped with facilities for spectroscopy was used to obtain MR spectra from 33 gastric specimens. High-resolution (1)H nuclear magnetic resonance (NMR) spectra of the remains of two specimens were also examined with a 9.4-T (400-MHz) NMR spectrometer. Localized spectroscopic measurements were performed in two layers of gastric tissue, the proper muscle layer and the composite mucosa/submucosa layer. T(2) FSE and 3D SPGR images were used to determine the voxel size and the location for MRS data collection. MR spectra were obtained using the single-voxel PRESS technique with parameters of TR/TE = 2000/30 ms, NA = 256, and voxel size = 3 x 3 x 3 mm(3) (27 microL). Cancerous and noncancerous gastric tissues in the voxel were determined by histopathological analysis. On 9.4-T ex vivo NMR spectroscopy, the following metabolite peaks were found: lipids at 0.9 ppm (CH(3)) and 1.3 ppm (CH(2)); alanine (beta-CH(3)) at 1.58 ppm; N-Acetyl neuraminic acid (NANA: sialic acid) at 2.03 ppm; and glutathione at 2.25 ppm in normal gastric tissue layers. In the 1.5-T MR system, broad and featureless spectral peaks of the various metabolites in normal human gastric tissue were observed at 0.9 ppm, 1.3 ppm, 2.0 ppm, and 2.2 ppm regardless of gastric tissue layer. In specimens (Borrmann type III) with tubular adenocarcinoma, resonance peaks were observed at 1.26 ppm, 1.36 ppm (doublet of lactate), and 3.22 ppm (choline). Cancer lesions showed decreased levels of lipid peaks, showing the significant lactate doublet peaks, and increased intensity of the choline peak as compared with noncancerous gastric tissue. We found that decreased levels of lipids and increases in lactate and choline peaks in gastric tissue were markers for malignancy in gastric lesions. Information provided by ex vivo (1)H MRS, together with the development of in vivo (1)H MRS with high field strength and high resolution, may be very useful for the diagnosis of gastric cancer in clinical situation.     

N-Acetyl peak in MR spectra of intracranial metastatic mucinous adenocarcinomas

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.     

Proton MR spectroscopy in a child with pyruvate dehydrogenase complex deficiency.

The purpose of this study was the non-invasive quantitative determination by proton MR Spectroscopy (1H MRS) of alterations in cerebral metabolism in a 19-month-old male infant with severe global developmental delay caused by a Pyruvate Dehydrogenase Complex (PDHC) deficiency due to a mutation at the thiamine binding site. Two investigations were performed at different CSF thiamine concentrations to assess the effect of thiamine supplementation. 1H MR spectra were collected at different echo times (20-270 ms) from a voxel located in the striatum; spectroscopic imaging was done on a larger region including occipital white matter. The tissue levels of N-acetylaspartate and choline were in the normal range, while creatine appeared elevated. Abnormally high lactate and alanine signals were observed both in and outside the striatum; the levels of these metabolites were higher during the second measurement at a lower thiamine concentration. Abnormal cerebral levels of alanine have only been described once before in PDHC deficiency. The 1H MRS profile of this patient reflects the diversity of brain metabolite alterations in patients with this genetically heterogeneous disease.     

Comparative evaluation of magnetization transfer MR imaging and in-vivo proton MR spectroscopy in brain tuberculomas

We have compared and analyzed the value of in vivo proton MR spectroscopy (PMRS) and T1 weighted magnetization transfer (MT) MR imaging in tissue characterization of brain tuberculomas. We studied 33 cases of proven intracranial tuberculomas with in vivo PMRS and T1 weighted MT MR imaging. MT ratios from the rim and core of the tuberculomas were calculated and compared with metabolites seen on PMRS. Final diagnosis of tuberculoma was based on histopathology (n = 26) and/or associated tuberculous meningitis (n = 7) in all the cases. Out of the 33 patients who underwent both PMRS and T1 weighted MT MR imaging, spectroscopy showed only lipids at 0.9 ppm, 1.3 ppm, 2.0 ppm, and 2.80 ppm in 26 cases while lipids at 0.9 ppm, 1.3 ppm, 2.0 ppm and 2.80 ppm along with choline at 3.22 ppm was seen in remaining 7 patients. MT ratios from the core or solid necrosis varied from 21-29% while from the rim or cellular region varied from 16-24%. MT ratios from all the 33 lesions were consistent with tuberculomas while PMRS showed choline along with lipids in 7 predominantly cellular lesions simulating a neoplasm. We conclude that T1 weighted MT MR imaging appears to be more consistent in the tissue characterization of brain tuberculomas.     

Central neurocytoma: typical magnetic resonance spectroscopy findings and atypical ventricular dissemination

PURPOSE: Central neurocytomas (CNCs) are rare neuronal tumors that have a favorable prognosis and lower rate of recurrence compared with other intraventricular neoplasms. Although it may be difficult to distinguish CNC on conventional neuroimaging, typical MR spectroscopy (MRS) features have been reported. We describe the MRI and MRS features of CNC. MATERIALS AND METHODS: Eight patients with CNC were reviewed. Three patients underwent presurgical in vivo single-voxel MRS at short echo time (TE, 35 ms) and multi-voxel MR spectroscopic imaging at long TE (144 ms). The surgically resected tumor specimen of one of these patients was also studied ex vivo using high-resolution magic angle spinning (HRMAS) nuclear magnetic resonance. RESULTS: All eight tumors were located in the lateral ventricles. In six patients, CNC extended into the third ventricle, and in two patients the tumor showed further contiguous intraventricular dissemination into the fourth ventricle. In all three patients who underwent MRS, a characteristic metabolite peak was detected at 3.55 parts per million (ppm) at both long and short TE. HRMAS confirmed the presence of elevated glycine (Gly) at 3.55 ppm, without increase in the concentration of myo-inositol found at the same chemical shift. Elevated choline (at 3.2 ppm) was also seen in all three patients. CONCLUSION: On MRS, CNCs have a typical appearance with a metabolite peak at 3.55 ppm due to increased Gly, and this feature may be helpful in presurgical diagnosis. Although they are rare benign intraventricular tumors, in atypical cases, CNCs can show extensive intraventricular dissemination into the fourth ventricle.     

Role of diffusion tensor imaging metrics and in vivo proton magnetic resonance spectroscopy in the differential diagnosis of cystic intracranial mass lesions

The purpose of this study was to determine whether proton magnetic resonance spectroscopy (PMRS) and diffusion tensor imaging (DTI) indices, fractional anisotropy (FA) and mean diffusivity (MD) can be used to distinguish brain abscess from cystic brain tumors, which are difficult to distinguish by conventional magnetic resonance imaging (MRI). Fifty-three patients with intracranial cystic mass lesions and 10 normal controls were studied. Conventional MRI, PMRS and DTI of all the patients were performed on a 1.5-T GE scanner. Forty patients were with brain abscess and 13 with cystic tumors. Cytosolic amino acids (AAs) were present in 32 of 40 brain abscess patients. Out of 13 patients with cystic tumors, lactate and choline were seen in 3 and only lactate was present in 10 patients on PMRS. All 40 cases of abscess had high FA, while all 13 cases of tumor cysts had high MD values. We conclude that FA measurements are more sensitive in predicting the abscess, while PMRS and MD are more specific in differentiating abscess from cystic tumors. We suggest that PMRS should be combined with DTI rather than with diffusion-weighted imaging as FA can be used as an additional parameter for separation of abscess from other cystic intracranial mass lesions.     

Feasibility of using hyperpolarized [1-13C]lactate as a substrate for in vivo metabolic 13C MRSI studies

The development of dynamic nuclear polarization in solution has enabled in vivo 13C MR studies at high signal-to-noise ratio following injection of prepolarized 13C substrates. While prior studies have demonstrated the ability to observe metabolism following injection of hyperpolarized 13C pyruvate, the goal of this study was to develop and test a new hyperpolarized agent for investigating in vivo metabolism, [1-13C]lactate. A preparation for prepolarized 13C lactate and the requisite dissolution media were developed to investigate the feasibility for in vivo 13C MRS/MRSI studies following injection of this hyperpolarized agent. This study demonstrated, for the first time, not only the ability to detect hyperpolarized [1-13C]lactate in vivo but also the metabolic products 13C pyruvate, 13C alanine and 13C bicarbonate following injection in normal rats. The use of 13C lactate as a substrate provided the opportunity to study the conversion of lactate to pyruvate in vivo and to detect the secondary conversions to alanine and bicarbonate through pyruvate. This study also demonstrated the potential value of this hyperpolarized agent to investigate in vivo lactate uptake and metabolism in preclinical animal models.     

Detection of rectal cancer and response to concurrent chemoradiotherapy by proton magnetic resonance spectroscopy

Introduction

To diagnose rectal cancer and monitor treatment response after preoperative concurrent chemoradiotherapy (CCRT) in rectal cancer patients using proton-1 magnetic resonance spectroscopy (¹H-MRS).

Materials and Methods

We enrolled 134 rectal cancer patients before treatment, of whom 34 underwent preoperative CCRT and follow-up MR spectroscopy before surgery. ¹H-MRS was performed using a six-channel phased-array coil at 3.0 T. We evaluated the presence of a choline peak at 3.2 ppm, and lipid peaks at 0.9 and 1.3 ppm, and glutamine and glutamate peaks at 2.1-2.3 and 2.7 ppm seen at two TEs (40 and 135 ms). We divided MR spectra patterns into two groups (A and B).

Results

A choline peak at 3.2 ppm seen in both TEs was characteristic for rectal cancer before treatment. Of 103 patients, 55 (53%) showed an elevated choline peak before treatment (type A). Type A spectra were seen in 68% of patients (23/34) before preoperative CCRT. After CCRT, the choline peak disappeared, resulting in only the lipid peak at 1.3 ppm (type B) in 97% of patients (33/34).

Discussion

We optimized a localized in vivo¹H-MRS method for detection of rectal adenocarcinoma and monitoring treatment response after preoperative CCRT. The method appears to be a promising and feasible noninvasive modality.     

Ethanol-induced fatty liver in the rat examined by in vivo 1H chemical shift selective magnetic resonance imaging and localized spectroscopic methods.

In vivo 1H magnetic resonance imaging (MRI), chemical shift selective imaging (CSI), and localized (VOSY) 1H magnetic resonance spectroscopy (MRS) were used to study fatty infiltration in the livers of rats chronically fed an ethanol-containing all-liquid DeCarli-Lieber diet. Conventional total proton MRI showed a somewhat hyperintense liver for ethanol-fed rats, compared with pair-fed controls. CSI showed a dramatic increase in the fat signal intensity for ethanol-treated rats that was fairly homogeneous throughout the liver. However, CSI also showed a substantial decrease in the water signal intensity for the ethanol-treated rats compared to pair-fed control rats. 1H VOSY MR spectra also showed a 5.5-fold increase in the methylene resonance (1.3 ppm) of fat and a 50-70% decrease in the water resonance (4.8 ppm). Relative in vivo proton T1 and T2 relaxation times for the water resonance separate from the fat resonance, determined from modified VOSY experiments, were found to tend to increase and decrease, respectively, for ethanol-treated rat livers compared with controls. The decrease in hepatic water signal intensity could be accounted for by the decrease in T2 and decrease in water density due to the presence of accumulated hepatic fat (approximately 25 mg/g wet weight of liver). When ethanol was withdrawn from the chronically treated rats, fatty infiltration was observed by both CSI and VOSY spectra to revert toward control values with a half-life of 2-4 days. By day 16, however, the signal intensity for hepatic fat was still significantly higher than control levels. In vitro 1H MRS studies of chloroform-methanol extracts confirmed the 5.5-fold increase in total hepatic fat induced by the chronic ethanol treatment, and showed further that triacylglycerols were increased 7.7-fold, cholesterol was increased fourfold, and phospholipids were increased 3.3-fold, compared with liver extracts from pair-fed control rats.     

Cerebral mucormycosis: proton MR spectroscopy and MR imaging

Proton magnetic resonance spectroscopy (MRS) was integrated with magnetic resonance imaging (MRI) in the evaluation of a case of cerebral mucormycosis. MRS showed markedly elevated lactate, depleted N-acetyl aspartate and metabolite resonances attributable to succinate and acetate. The spectroscopy profile is essentially similar to that of bacterial abscess but without the commonly seen resonances of the amino acids valine, leucine and isoleucine. Our extensive literature review did not yield any reports of MRS findings on cerebral mucormycosis. MRS prospectively limited the differential diagnoses given the otherwise nonspecific and complex MR imaging findings in our immunosuppressed patient.     

Quantification of cerebral metabolites in glioma patients with proton MR spectroscopy using T2 relaxation time correction

This study was aimed to investigate the significance of absolute concentration of metabolites in glioma patients using proton MR spectroscopy (MRS) with T2 relaxation time correction using three different echo times. The absolute concentrations of metabolites in 7 normal subjects and in 23 gliomas (10 low-grade, 13 high-grade) were obtained by proton MRS using a tissue water signal as an internal standard. The signal intensities of metabolites and tissue water were corrected by T2 relaxation time. In low-grade glioma, the T2 relaxation time of NAA was shorter, and T2 relaxation time of water was prolonged as compared to normal subjects (p < 0.001). In high-grade glioma, the T2 relaxation time of NAA (p < 0.001) and T2 relaxation time of Cr (p < 0.01) were shorter, and T2 relaxation time of water (p < 0.001) was prolonged as compared to normal subjects. Moreover, high-grade gliomas revealed a shorter T2 relaxation time of Cr than low-grade gliomas (p < 0.05). In glioma, NAA and Cr concentration were decreased, and Cho were increased as compared to normal subjects. Moreover, high-grade glioma revealed a significant lower Cr (p < 0.001) and Cho (p < 0.01) concentration compared to low-grade gliomas. Low Cr concentration is the most reliable indicator of malignancy in glioma. Cho concentration did not correlate with malignancy in gliomas.     

Time-course magnetic resonance imaging of rat pancreatic cyst after experimental pancreatitis

Fast magnetic resonance (MR) imaging of the rat pancreas was carried out using a snapshot method to observe three-dimensional (3D) and temporal development of the pancreatic cyst after experimental pancreatitis. Acute pancreatitis was induced by a retrograde infusion of the trypsin-taurocholate solution into the pancreatic duct in 23 rats, of which seven survived for one month. Under 2% enflurane anesthesia, (1)H images of the rat abdomen were taken by a 4.7 T magnetic resonance spectrometer under spontaneous breathing. 3D images of the pancreas and cyst were reconstructed from the axial, sagittal and coronal images taken before, 24 h, 7 days, 14 days, 21 days and 28 days after the induction of pancreatitis. The 3D images reconstructed from different slice orientations at each time point showed good agreement with each other. The calculated volumes of the cyst on 7th, 14th, 21st, and 28th day were 0.3 +/- 0.1, 0.8 +/- 0.3, 2.1 +/- 0.6, 6.5 +/- 1.3 mL, respectively. The cystic fluid volume on 28th day was 6.4 +/- 1.4 mL, which confirmed reliability of volume measurement by MR imaging. Fast MR imaging (snapshot) together with 3D reconstruction allows us to understand the detailed chronological and spatial development of pancreatic cyst after acute pancreatitis in rats.     

Three-dimensional susceptibility-weighted imaging at 3 T using various image analysis methods in the estimation of grading intracranial gliomas

Object

Although three-dimensional (3D), high-spatial resolution susceptibility-weighted imaging (SWI) appears to be valuable in the evaluation of central nervous system gliomas, several evaluation methods are proposed in the literature. The purpose of this study was to evaluate the use of 3D SWI for grading intracranial gliomas with various analysis methods.

Materials and Methods

Twenty-three patients suspected of having gliomas participated in this study. SWI was performed in addition to conventional MR sequences. In 15 cases, post-gadolinium enhanced SWI was also obtained. Imaging evaluation criteria were conventional grade, hypointensity ratio in the tumor-dominant structure of hypointensity on SWI (hemorrhage or vascular structure) and presence of abnormal enhancement surrounding the tumor.

Results

Mean grading scores of conventional grade showed no statistically significant difference among WHO grades. Mean grading scores of hypointensity ratios in the tumor were higher for WHO Grades 3 and 4 than for lower grade tumors (P=.05, Mann–Whitney U test). Hemorrhagic foci were more frequently seen in the higher grade tumor. Post-contrast susceptibility-weighted images of five of 11 WHO Grade 3 and 4 cases showed bright enhancement surrounding the tumor, suggesting a breakdown of the blood–brain barrier.

Conclusions

SWI at 3 T may be a useful method to analyze the structural characteristics of gliomas and to evaluate pathology in vivo. Assessment of hypointensity ratios in the glioma was the most preferable method in grading glioma. However, more studies, specifically concerning a suitable method for image analysis, are needed to establish SWI at 3 T as a useful tool in clinical routine.     

3D spin-lock imaging of human gliomas

We investigated whether the simultaneous use of paramagnetic contrast medium and 3D on-resonance spin lock (SL) imaging could improve the contrast of enhancing brain tumors at 0.1 T. A phantom containing serial concentrations of gadopentetate dimeglumine (Gd-DTPA) in cross-linked bovine serum albumin (BSA) was imaged. Eleven patients with histologically verified glioma were also studied. T₁-weighted 3D gradient echo images with and without SL pulse were acquired before and after a Gd-DTPA injection. SL effect, contrast, and contrast-to-noise ratio (CNR) were calculated for each patient. In the glioma patients, the SL effect was significantly smaller in the tumor than in the white and gray matter both before (p = 0.001, p = 0.025, respectively), and after contrast medium injection (p < 0.001, p < 0.001, respectively). On post-contrast images, SL imaging significantly improved tumor contrast (p = 0.001) whereas tumor CNR decreased slightly (p = 0.024). The combined use of SL imaging and paramagnetic Gd-DTPA contrast agent offers a modality for improving tumor contrast in magnetic resonance imaging (MRI) of enhancing brain tumors. 3D gradient echo SL imaging has also shown potential to increase tissue characterization properties of MR imaging of human gliomas.     

Reproducibility of GABA measurements using 2D J-resolved magnetic resonance spectroscopy

We determined the reproducibility of GABA (gamma-aminobutyric acid) measurements using 2D J-resolved magnetic resonance spectroscopy (MRS) on a clinical 1.5-T MR imaging scanner. Two-dimensional J-resolved spectra were acquired in vitro across five GABA concentrations using a volume head coil and a 5-in. surface coil. Additional spectra using a sixth GABA phantom with a very low concentration and from a healthy volunteer were recorded in the 5-in. surface coil only. In each case, the 3.01-ppm GABA resonance was quantified; for comparison, the peak integrals of choline (3.2 ppm) and creatine (3.03 ppm) were recorded. At a physiological concentration (1.2 mM), in vitro GABA measurement was significantly more reproducible in the surface coil than in the volume coil (P=.005), with coefficients of variation (CVs) being less than 16% with the surface coil and up to 68% with the volume head coil. At the smallest concentration of in vivo GABA reported using other spectroscopy techniques (0.8 mM) and detected only using the surface coil, the CV for GABA was 23% and was less than 10% for choline and creatine, which compare favorably with results from published studies. In vivo, the CV for GABA measurement was 26%, suggesting that 2D J-resolved MRS would be suitable for detecting physiological changes in GABA, similar to those reported using other methods.     

Absolute metabolite quantification by in vivo NMR spectroscopy: I. introduction,objectives and activities of a concerted action in biomedical research

By utilizing achievements and results of two previous concerted research projects on magnetic resonance imaging and spectroscopy (MRS), the EU BIOMED 1 Concerted Action on “Cancer and brain disease characterization and therapy assessment by quantitative MRS” was specifically aimed at: 1) developing at a multicentre level harmonized methodologies and protocols for quantitative and reproducible MRS measurements, as a basis for validating these procedures in well controlled clinical and experimental conditions; and 2) providing multicentre critical reviews on the present understanding of the significance of MRS parameters as possible new markers of diagnosis, prognosis and response to therapy. The programme comprised the following main areas of collaborative research and multicentre evaluation: a) development of methods and protocols for quality assessment, calibration and absolute metabolite quantification in in vivo localized, volume-selective MRS; b) design and validation of a new method for assessing localization performance in spectroscopic imaging (MRSI); c) interlaboratory comparison of different methods of signal processing and data analysis, for improving signal quantification in vivo and in vitro MRS spectra; d) quality assessment of high resolution MRS analyses of biological fluids; e) protocol for assembling a pilot data base of MR spectra of tumour extracts for pattern recognition analysis; f) multicentre review on evaluation of the significance of MRS parameters in monitoring lipid metabolism and function in cancer; and g) multicentre review on evaluation of drug pharmacokinetics and metabolism using MRS. The main results and conclusions of four multi-centre trials on items (a), (b) and (c), which involved 24 teams, are reported in the accompanying papers of this series.     

In VivoLactate Editing with Simultaneous Detection of Choline, Creatine, NAA, and Lipid Singlets at 1.5 T Using PRESS Excitation with Applications to the Study of Brain and Head and Neck Tumors

Two T2-independentJ-difference lactate editing schemes for the PRESS magnetic resonance spectroscopy localization sequence are introduced. The techniques, which allow for simultaneous acquisition of the lactate doublet (1.3 ppm) and edited singlets upfield of and including choline (3.2 ppm), exploit the dependence of the in-phase intensity of the methyl doublet upon the time interval separating two inversion (BASING) pulses applied to its coupling partner after initial excitation. Editing method 1, which allows for echo times TE =n/J(n= 1, 2, 3, …), alters the BASING carrier frequency for each of two cycles so that, for one cycle, the quartet is inverted, whereas, for the other cycle, the quartet is unaffected. Method 2, which also provides water suppression, allows for editing for TE > 1/Jby alternating, between cycles, the time interval separating the inversion pulses. Experimental results were obtained at 1.5 T using a Shinnar Le–Roux-designed maximum phase inversion pulse with a filter transition bandwidth of 55 Hz. Spectra were acquired from phantoms andin vivofrom the human brain and neck. In a neck muscle study, the lipid suppression factor, achieved partly through the use of a novel phase regularization algorithm, was measured to be over 10³. Spectra acquired from a primary brain and a metastatic neck tumor demonstrated the presence of lactate and choline signals consistent with abnormal spectral patterns. The advantages and limitations of the methods are analyzed theoretically and experimentally, and significance of the results is discussed.     

MRI and MRS on preserved samples as a tool in fish ecology

Magnetic Resonance Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS) gain increasing attention and importance as a tool in marine ecology. So far, studies were largely limited to morphological studies, e.g. for the creation of digital libraries. Here, the utility of MRI and MRS for ecologists is tested and exemplified using formalin preserved samples of the Antarctic silverfish, Pleuragramma antarctica. As this species lacks a swim bladder, buoyancy is attained by the deposition of large amounts of lipids that are mainly stored in subcutaneous and intermuscular lipid sacs. In this study MRI and MRS are not only used to study internal morphology, but additionally to investigate functional morphology and to measure parameters of high ecological interest. The data are compared with literature data obtained by means of traditional ecological methods.The results from this study show that MR scans are not only an alternative to histological sections (as shown before), but even allow the visualization of particular features in delicate soft tissues, such as Pleuragramma's lipid sacs. 3D rendering techniques proved to be a useful tool to study organ volumes and lipid content, which usually requires laborious chemical lipid extraction and analysis. Moreover, the application of MRS even allows for an analysis of lipids and fatty acids within lipid sacs, which wouldn't be possible using destructive methods. MRI and MRS, in particular when used in combination, have the capacity to provide useful data on parameters of high ecological relevance and thus have proven to be a highly valuable addition, if not alternative, to the classical methods.     

In vivo lactate editing in single voxel proton spectroscopy and proton spectroscopic imaging by homonuclear polarisation transfer

Volume-selective lactate editing has been performed successfully in vitro and in vivo in the brain on a clinical scanner using a PRESS-based single voxel ¹H spectroscopy and a ¹H spectroscopic imaging sequence. The PRESS sequence was made sensitive to homonuclear polarisation by replacing the standard 180° refocusing pulses with 90° pulses. Two acquisitions were made at a total echo time around 2/J (J is the coupling constant for CH and CH₃ spins in lactate ≈7 Hz) whose individual echo times differed by 5.5 ms. Subtraction of one signal from the other yielded the lactate resonance alone. The technique is an effective method of separating the overlapping signals of lactate and lipids. Furthermore this editing method can be performed without state of the art MRI scanner hardware.