Alterations of lactate (+lipid) concentration in brain tumors with in vivo hydrogen magnetic resonance spectroscopy during radiotherapy

Detecting response of rat C6 glioma tumors to radiotherapy using hyperpolarized [1- 13C]pyruvate and 13C magnetic resonance spectroscopic imaging

We show here that hyperpolarized [1-(13) C]pyruvate can be used to detect treatment response in a glioma tumor model; a tumor type where detection of response with (18) fluoro-2-deoxyglucose, using positron emission tomography, is limited by the high background signals from normal brain tissue. (13) C chemical shift images acquired following intravenous injection of hyperpolarized [1-(13) C]pyruvate into rats with implanted C6 gliomas showed significant labeling of lactate within the tumors but comparatively low levels in surrounding brain.Labeled pyruvate was observed at high levels in blood vessels above the brain and from other major vessels elsewhere but was detected at only low levels in tumor and brain.The ratio of hyperpolarized (13) C label in tumor lactate compared to the maximum pyruvate signal in the blood vessels was decreased from 0.38 ± 0.16 to 0.23 ± 0.13, (a reduction of 34%) by 72 h following whole brain irradiation with 15 Gy.

MR spectroscopic evaluation of brain tissue damage after treatment for pediatric brain tumors

PURPOSE

The aim of this study was to evaluate the metabolic profile of uninvolved brain tissue after treatment for pediatric brain tumors.

MATERIAL

A group of 24 patients aged 4-18 years was analyzed after combined treatment for brain tumors. In this group, there were nine medulloblastomas, seven low-grade gliomas, three high-grade gliomas, two ependymomas and three children with conservatively treated diffuse brainstem gliomas.

METHODS

Short echo-time (TE = 30 ms) point-resolved spectra were acquired using a 2 T clinical scanner (Elscint Prestige). The ratios of signal intensities for N-acetylaspartate (NAA), choline (Cho), myo-inositol (mI), lactate (Lac), and lipids (Lip) were calculated using the creatine (Cr) signal as an internal reference. The spectra were acquired both from the tumor bed and from contralateral uninvolved brain tissue; only control spectra were analyzed. The first examination was made between the third and sixth month after therapy (24 spectra), the second examination occurred 8-12 months after treatment (15 spectra available), and the third was performed approximately 18 months after completion of therapy (eight spectra available). The results were compared using the t-test for dependent samples.

RESULTS

At all time points, the metabolite ratios showed alterations indicating brain tissue damage. The most important were the decrease of NAA/Cr and increase of Lac/Cr and Lip/Cr ratios. The mean NAA/Cr values were 0.91, 0.91, and 0.86, respectively, for the three examinations, while the Lac/Cr and Lip/Cr values were 1.66, 2.11, 1.19 and 12.24, 12.05, 5.69, respectively. Interestingly, in children with supratentorial tumors, a significant increase in NAA/Cr value was observed (from 0.82 to 1.11 in the first and second examinations, respectively; p = 0.0487), which may be indicative of neuronal function recovery.

CONCLUSIONS

MRS examinations of uninvolved brain tissue indicate long-lasting metabolic disturbances. However, the NAA/Cr ratio increase may be a sign of at least partial recovery of metabolic function of the brain.

Magnetic resonance spectroscopic evaluation of brain tissue metabolism after irradiation for pediatric brain tumors in long-term survivors: a report of two cases

OBJECTIVE

The aim of our study was to evaluate the metabolic profile of brain tissue of two long-term survivors of childhood brain tumors.

MATERIALS

Two males who were 25 and 33 years old at the time of examination and had been irradiated for brain tumors at the age of 17 and 13 years respectively. The first subject had been operated on radically for medulloblastoma and received craniospinal axis irradiation composed of a whole brain radiotherapy with boost to the posterior fossa (total dose (TD) = 59.4 Gy in 33 fractions) and spinal canal irradiation (TD = 30 Gy in 20 fractions) according to the protocol at the time of treatment. The second subject had previously received whole brain irradiation (TD = 45 Gy in 19 fractions) because of inoperable central region tumor of unknown histology.

METHODS

Short echo-time (TE = 30 ms) point-resolved spectra were obtained using a 2 T magnet. Ratios of N-acetylaspartate (NAA), choline (Cho), myo-inositol (mI), lactate (Lac) and lipids (Lip) signal intensities were calculated using the creatine (Cr) signal as an internal reference. The spectra were acquired both from the tumor bed area and uninvolved brain tissue in the first subject, and from uninvolved brain areas of frontal and occipital lobes in the second subject.

RESULTS

In both cases, MRS examination revealed ratios of NAA/Cr, Cho/Cr and mI/Cr within normal range in most spectra. Nevertheless, a slight elevation of Lac/Cr (2.47 and 1.05) and a more pronounced elevation of Lip/Cr proportions (45.77 and 3.97 respectively, in uninvolved sites) were detected in both patients.

CONCLUSIONS

Metabolic parameters correlated with neuronal function (NAA/Cr) and cell membrane metabolites turnover (Cho/Cr) seem to recover to normal values in long-term survivors of brain tumors. Lac/Cr and Lip/Cr proportions could be considered parameters indicating permanent radiation-induced brain damage; however, this proposal requires further investigation.

Dynamics of metabolic changes in intracranial metastases and distant normal-appearing brain tissue after stereotactic radiosurgery: a serial proton magnetic resonance spectroscopy study

The present study evaluated the dynamics of metabolic changes in intracranial metastases and distant normal-appearing brain after stereotactic radiosurgery (SRS). Forty neoplasms were evaluated with single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) both before and after treatment. From one to six examinations (median, 3) were done in each individual case during follow-up. At the time of each investigation additional (1)H-MRS was obtained from the normal-appearing brain distant from the radiosurgical target. Investigated metabolites included N-acetylaspartate (NAA), choline-containing compounds (Cho), creatine (Cr), and mobile lipids (Lip). Within the first month after SRS responded tumors showed a statistically significant increase in NAA/Cho ratio, and decrease of Cho content and Lip-to-normal brain Cr (nCr) ratio. By contrast, statistically significant metabolic alterations were not detected in stabilized tumors. Statistically significant volumetric and metabolic changes were not marked between three and 12 months after treatment in non-progressing lesions. Alternatively, decrease of NAA/Cho ratio, NAA content and Cr content, and increase in Lip/nCr ratio and Cho content were evident in progressive neoplasms, and subtle metabolic alterations could be revealed even before the increase in the lesion volume. Metabolic characteristics of normal-appearing brain distant from the radiosurgical target did not show statistically significant changes within the first year after treatment. In conclusion, additional use of serial (1)H-MRS during follow-up after SRS for intracranial metastases permits detailed evaluation of the metabolic tumor response and may be potentially helpful for early prediction of recurrence.

Proton magnetic resonance spectroscopy in immunocompetent patients with primary central nervous system lymphoma

BACKGROUND

Magnetic resonance spectroscopy imaging (MRSI) non-invasively evaluates the metabolic profile of normal and abnormal brain tissue. Primary central nervous system lymphoma (PCNSL) is a highly aggressive tumor responsive to high-dose methotrexate based regimens. Patients often have complete responses but relapses are common. We characterized the MR spectra of PCNSL patients, correlated MRSI with MRI and evaluated whether early recurrence could be detected by MRSI.

METHODS

Patients with PCNSL had multi-voxel MRSI before, during, and after treatment. The region of interest was defined using axial FLAIR images. Metabolites assessed were N-acetyl-aspartate (NAA), choline (Cho), creatine (Cr), lipid, and lactate. Ratios of Cho/Cr, NAA/Cho, and NAA/Cr were calculated and correlated with MRI. Overall survival (OS), progression free survival (PFS), and relative risks of each of the ratios were determined.

RESULTS

MRSI was performed on 11 men and seven women; median age of 59. Sixty-seven MRSI studies were performed, 17 baseline and 48 follow-up studies. Median ratios in 16 pretreated patients were Cho/Cr-1.90, NAA/Cho-0.39, and NAA/Cr-1.27. Two patients had lipid at baseline, five had lactate and two had both. MRSI correlated with tumor response or progression on MRI; in three patients MRSI suggested disease progression prior to changes on MRI. Univariate analysis of metabolite ratios, lipid, and lactate revealed that none significantly affected PFS or OS. Kaplan-Meier analysis of the presence or absence of lipid, lactate or both revealed a trend for increased PFS.

CONCLUSION

MRSI and MRI correlate with tumor response or progression and may allow early detection of disease recurrence. The presence or absence of lipid and/or lactate may have prognostic significance. Further research using MRSI needs to be done to validate our findings and determine the role of MRSI in PCNSL.

Noninvasive histologic grading of solid astrocytomas using proton magnetic resonance spectroscopy

BACKGROUND

Proton magnetic resonance spectroscopy (1H MRS) constitutes a promising modality to assess intracranial pathology. We present our experience using this method in grading solid brain astrocytomas.

MATERIAL AND METHODS

Using a 1.5-Tesla MRI unit, 71 patients with the radiographic diagnosis of astrocytoma were examined. Water-suppressed single-voxel 1H MRS was employed in all of our patients. The concentrations of choline (Cho), N-acetyl-aspartate (NAA), phosphocreatine-creatine (Pcr-Cr), myo-inositol (MI), lactate (Lac), lipids (Lip) as well as the metabolite ratios of Cho/Pcr-Cr, NAA/PCr-Cr and NAA/Cho were calculated. An appropriate surgical biopsy was performed. Standard pathology examination was employed in a double-blinded fashion.

RESULTS

An increased concentration of Cho and decreased concentrations of Pcr-Cr and NAA were detected. The concentrations of Lac, Lip and MI varied inconsistently, even among tumors of the same histologic grade. The Cho/Pcr-Cr ratio was calculated. This ratio was found to be 2.15 +/- 0.26 in 27 patients with astrocytomas grade I and II, 2.78 +/- 0.09 in 18 patients with grade III, and 5.40 +/- 0.16 in 26 patients with grade IV.

DISCUSSION

The increased concentration of Cho is due to the increased cellularity and a relatively increased number of membranous structures in highly malignant tumors. In abnormal anaerobic metabolic tumor states there is relatively less phosphorylization of creatine. By using the Cho/Pcr-Cr ratio the concomitant effects of structural and metabolic alteration can thereby be emphasized for diagnostic advantage.

CONCLUSION

The Cho/Pcr-Cr is a very important and statistically significant marker (p = 0.043) determining the degree of intracranial astrocytoma malignancy.

1H-MR spectroscopy of normal brain tissue before and after postoperative radiotherapy because of primary brain tumors

PURPOSE

Brain metabolism after surgery and postoperative radiotherapy (pRT) because of primary brain tumors was assessed by proton magnetic resonance spectroscopy ((1)H-MRS) in vivo. The study was designed to reveal the impact of pRT on normal brain tissue metabolism, which may potentially help in delineating the target volumes for reirradiated patients.

METHODS AND MATERIALS

Spectra of 43 patients ages 16-63 years treated with pRT for primary glial tumors in the Center of Oncology Maria Curie Memorial Institute Branch in Gliwice were analyzed. The control group consisted of spectra acquired for 30 healthy volunteers. All patients were treated with 3D conformal techniques using 6-20 MV photons to total doses of 60 Gy. Spectra were acquired from the control region before pRT and from three uninvolved regions 9-12 months after the end of pRT. Voxels were located in the region of low (<6 Gy), medium (29-39 Gy), and high radiation dose ( approximately 60 Gy). Relative intensities of the signals relating to N-acetyl-aspartate (NAA), choline-based compounds, creatine and phosphocreatine (Cr), mio-Inositol, lactate, and lipids were obtained.

RESULTS

The spectra of "normal brain" taken 9 months after pRT are significantly different from those obtained for control volunteers and from the spectra acquired before radiotherapy. The lactate and lipids signals are very strong; however, they are not correlated with absorbed dose. NAA/Cr ratios are significantly lower than before radiotherapy even for the low-dose regions. Differences increase with radiation dose: the NAA/Cr ratio is significantly lower for the regions of brain receiving a high dose of radiation than for the low-dose areas.

CONCLUSION

Combined treatment of primary brain tumors (surgery + postoperative radiotherapy) causes alteration of brain metabolism, even in regions of the brain far from the postoperative tumor bed and receiving relatively low total doses of radiation. Single voxel MRS spectroscopy in vivo cannot help in delineating target volumes for secondary irradiation.

Clinical applications of proton MR spectroscopy in oncology

Proton magnetic resonance spectroscopy (H1-MRS) has been increasingly receiving more attention from radiologists, neurosurgeons, radiation and medical oncologists in the "in situ" clinical evaluation of human tumors. The utilization of H1-MRS, especially in human brain tumors, coupled to both routine magnetic resonance imaging (MRI) and functional MRI techniques provides greater information concerning tumor grading and extension and characterization of the normal surrounding tissue than what is possible with any other imaging technique alone. In this paper, we will review the current status of proton MR spectroscopy with emphasis on its clinical utility to diagnose tumors, its utility in planning surgical and radiation therapy interventions, and in its use in monitoring tumor treatment.

In vivo proton magnetic resonance spectroscopy of brain tumors

The ability of magnetic resonance spectroscopy (MRS) to differentiate neoplastic brain cells and their metabolic and structural characteristics is evaluated. We examined 120 patients with brain tumors using a 1.5-tesla MRI unit and MRS. The peak areas of N-acetyl-aspartate (NAA), phosphocreatine-creatine (Pcr-Cr), choline-containing compounds (Cho), lactate, lipids, myoinositol, amino acids and the ratios of NAA/Pcr-Cr, NAA/Cho and Cho/Pcr-Cr were calculated by a standard integral algorithm. In normal brain tissue, the following metabolites were identified: NAA at 2.0 ppm, Pcr-Cr at 3.0 ppm and Cho at 3.2 ppm. The different concentrations of the metabolites examined and their role in the biochemical profile of different types of tumors are discussed. The confidence interval of the MRS versus pathology was between 0.9 and 0.954, while it was between 0.52 and 0.631 for MRI versus pathology. The Cho/Pcr-Cr ratio is a very important malignancy marker for histologic tumor grading of astrocytomas. The greater this ratio, the higher the grade of the astrocytoma. NAA/Pcr-Cr together with Cho/Pcr-Cr help specify the presence or absence of a neoplasm. Proton MRS is a useful and promising diagnostic modality not only in diagnosing but also in grading solid brain tumors.