Thomas Els

Quantitative Diffusion MR Imaging of Cerebral Tumor and Edema

The detection of brain tumors using standard techniques of qualitative, relaxation-weighted magnetic resonance imaging (MRI) requires the application of contrast agents. We investigated whether or not it is possible to use diffusion-weighted MRI to localize tumors without contrast enhancement. Three different experimental rat brain tumors were studied: F98 glioma, RN6 Schwannoma and E376 neuroblastoma. We found a marked hypointensity in the region of the tumor and edema in heavily diffusion-weighted images, which corresponded well with the histological presentation. Quantitative maps of the apparent diffusion coefficient (ADC) allowed a better localization of the tumor than that obtained by regional presentation of T2 times, particularly under conditions in which peritumoral edema was absent. The ADC differences of the three tumor types were statistically not significant. Based upon regions-of-interest evaluations, tumor could be distinguished from peritumoral edema and normal brain tissue. However, a sharp demarcation between tumor and peritumoral edema was not possible, and this is attributed to a similar enlargement of interstitial space. It was concluded that diffusion-weighted MRI possesses a high potential for the detection of brain tumors but does not allow precise demarcation of the tumor border.

Diffusion-weighted MR imaging of experimental brain tumors in rats

Diffusion-weighted magnetic resonance imaging was used for the description of experimental brain tumors in rat. To validate this approach, diffusion-weighted images (DWI) were compared with nativeT1- andT2-weighted images, and withT1-weighted images following contrast enhancement with the tumor-specific contrast agent manganese (III) tetraphenylporphine sulfonate (MnTPPS). Three tumor types were studied: F98 glioma, RN6 Schwannoma, and E376 neuroblastoma. On heavily diffusion-weighted images, all three tumor types as well as the peritumoral edema were clearly hypointense with respect to the intact brain tissue.T2-weighted images presented mainly peritumoral edema as hyperintense region. A clear demarcation of the tumor was possible only onT1-weighted images after contrast enhancement with MnTPPS. The difference in signal intensity between tumor and homotopic regions in the contralateral hemisphere was comparable in DWIs and in contrast-enhancedT1-weighted images. Spatial comparison of depicted lesion areas in all three imaging modalities indicated that hypointense region on DWI represents both tumor and edema but does not permit their spatial differentiation.

Polyamine metabolism in brain tumours: diagnostic relevance of quantitative biochemistry

OBJECTIVE Activation of polyamine metabolism is closely associated with cellular proliferation. The purpose was to investigate whether the content of the polyamines putrescine, spermidine, and spermine, and the activity of the first metabolic key enzyme of polyamine metabolism, ornithine decarboxylase (ODC), represent biochemical markers of malignancy in brain tumours. METHODS The concentration of putrescine, spermidine, and spermine, and the activity of ODC were biochemically quantified in tissue samples obtained during open microsurgery of 670 patients with brain tumours. Biochemical analysis and histopathological classification were carried out in serial tumour samples. RESULTS The activity of ODC was very low in peritumorous non-neoplastic brain tissue (0.9 (SD 0.6) nmol/g/h). It was significantly higher in gliomas and it significantly increased with a higher grade of malignancy (grade I 2.7 (2.8) nmol/g/h, grade II 3.1 (4.0) nmol/g/h, grade III 5.7 (5.6) nmol/g/h, grade IV 10.6 (11.7) nmol/g/h). High enzyme activity was also found in medulloblastomas (25.5 (15.1) nmol/g/h), malignant lymphomas (52.1 (42.1) nmol/g/h), and metastases from carcinoma (14.9 (22.1) nmol/g/h). Lowest values were measured in epidermoid cysts (0.5 (0.2) nmol/g/h), craniopharyngiomas (1.2 (0.9) nmol/g/h), angioblastomas (1.6 (1.7) nmol/g/h), and neurinomas (2.0 (1.8) nmol/g/h). By contrast with ODC activity, polyamine concentrations did not correlate with the grade of malignancy. Correlation of regional biochemical and histomorphological data in rapidly growing neoplasms showed high enzyme activity in solid tumour parts and low activity in necrotic areas. CONCLUSIONS Novel data relating ODC activation and polyamine concentrations to neuropathology is presented indicating that high ODC activity represents a biochemical marker of malignancy in brain tumours. This information is important for clinical and therapeutic investigations.

Polyamine metabolism in gliomas

SummaryBiosynthesis of the polyamines putrescine, spermidine, and spermine has been found to be activated in tissues with cellular proliferation. In the present study we have investigated polyamine levels and the activity of the first rate-limiting enzyme ornithine decarboxylase (ODC) in tumour samples obtained during operation of 202 patients with gliomas. Biochemical data were closely related to the grading of malignancy and to the morphological characteristics of each sample. Mean ODC activity was significantly higher in all gliomas as compared to peritumoural non-neoplastic brain. Furthermore, it was significantly higher (p ≤ 0.001) in anaplastic gliomas who grade III and IV (9.0 ± 9.6 nmol/g/h) than in gliomas WHO grade I and II (3.3 ± 4.2 nmol/g/h). Highest enzyme activity (58.5 nmol/g/h) was found in solid and vital parts of malignant tumours, whereas predominantly necrotic areas exhibited low ODC activity (< 1 nmol/g/h). Thus, intra- and interindividual variability of ODC activity corresponded well to histomorphological heterogeneity in high-grade gliomas. Putrescine levels also increased with rising grade of malignancy, whereas spermidine and spermine levels did not correlate with the histological grading. In conclusion, high ODC activity represents a biochemical marker of malignancy in gliomas, but low values do not prove benignity. The present study reinforces the need of further and more extensive tumour sampling closely related to follow-up investigations in the heterogeneous group of gliomas.

Proton MR Spectroscopy of Experimental Brain Tumors in vivo

F98 gliomas, E367 neuroblastomas, and RN6 Schwannomas in rat brain were studied non-invasively in vivo by localized proton MR spectroscopy (MRS). The spectra obtained from homotopic brain contralateral to the tumors were qualitatively indistinguishable from those of normal rat brain in vivo and showed resonance lines assigned to N-acetylaspartate, glutamate, total creatine (creatine and phosphocreatine), choline, glucose, and myo-inositol. The tumor spectra displayed marked differences compared to those obtained from contralateral brain. There were increases in choline, myo-inositol and lipids, which are presumably associated with increased membrane turnover. The presence of lactate indicated anaerobic glycolysis. Other differences included the absence of signals from NAA resulting from the destruction or displacement of neuronal tissue by the tumor. There was also a loss of total creatine. Although the spectra of all three tumor types were distinct from contralateral brain, there were no obvious differences between the different tumor types.

Regional distribution of ornithine decarboxylase activity and polyamine levels in experimental cat brain tumors

Biosynthesis of the polyamines putrescine, spermidine, and spermine, and activation of the first key enzyme ornithine decarboxylase (ODC) are closely associated with cellular proliferation. In the present study, the distribution of ODC activity and polyamine levels was investigated for the first time regionally in experimental brain tumors of the cat. Brain tumors were produced by stereotactic xenotransplantation of rat glioma cells. Twenty days after implantation, the brains were frozen in situ, cut into slices, and cryostat sections and tissue samples were taken to determine ODC activity and polyamine levels biochemically. The quantified data were color-coded to present the regional distribution of ODC activity and polyamine levels in the respective section. ODC activity significantly increased in some areas within the tumor, whereas peritumoral tissue showed no difference to the non-tumoral, contralateral hemisphere. This increase turned out in parallel to a high number of mitoses in the same tumor parts (r=0.861). Putrescine levels increased both, in the whole tumor and in the peritumoral edema. Regional differences in putrescine content did not correlate with solid and proliferative parts of the tumor. Spermidine and spermine levels were only slightly increased in some parts of the tumor. Thus, these experiments show the close correlation of a high mitotic rate and activation of ODC within experimental gliomas and underline the relevance of ODC as a biochemical marker of proliferation in brain tumors.

Localization of Experimental Brain Tumors in MRI by Gadolinium Porphyrin

The contrast between edema and F98 glioma in rat brain was distinctly enhanced in T2-weighted MRI (TE 130 ms, TR 3 s) by intraperitoneal injection of the synthetic gadolinium-porphyrin complex, GdTPPS. The T1 relaxation time of the gliomas was selectively shortened by about 50% from 1339 +/- 109 ms to 628 +/- 106 ms, and the T2 relaxation time was shortened by about 35% from 86 +/- 6 ms to 57 +/- 5 ms. The relaxation times of normal tissues under investigation (cortex, corpus callosum, temporal muscle, ventricles) were unaltered. Therefore, GdTPPS-application causes F98 gliomas to appear hyperintense in T1-weighted MRI and hypointense in T2-weighted MRI.

Nmr contrast enhancement of brain tumours: comparison of the blood brain barrier tracer GdDTPA and the tumour-selective contrast agent MnTPPS

Contrast enhancement of two different NMR contrast agents, GdDTPA and MnTPPS, was compared. Sequential recording ofT1-weighted images at 50s intervals allowed the observation of the temporal and spatial evolution of the contrast effect in rats with glioma implanted into the right brain hemisphere. The maximum signal intensity ratio of tumour over contralateral striatum was 1.80±0.10 for GdDTPA and 1.61±0.15 for MnTPPS. The enhancement was maximal 3min after application of GdDTPA and fell rapidly to reach half maximum after 24 min. MnTPPS led to maximum tumour enhancement within 11 min and did not return to control level within the observation period (150 min). In the peritumoural edema, an enhancement effect was absent for MnTPPS, but GdDTPA spread out from the tumour resulting in a delayed but strong enhancement outside the tumour. Thus, GdDTPA, as a blood-brain-barrier tracer, led only to a transient contrast enhancement between tumour and surrounding tissue and no unambiguous demarcation of the tumour against peritumoural edema. Application of MnTPPS resulted in a long-lasting strong tumour enhancement and reliable delineation from peritumoural edema.

Characterisation of Tumorous Tissue in Rat Brain by in Vitro Magnetic Resonance Spectroscopy and Artificial Neural Networks

The NMR data in this study was interpreted statistically without using molecular and spectroscopical prior knowledge. Only the class origin (tumour/healthy tissue) was used as additional information for the training pattern. The samples were consistently classified successfully. This indicates that sample classification can be automated. Sensitivity analysis of the input pattern can be used for interpretation of NMR spectra without adding any medical or biochemical knowledge. The substances NAA, creatine, myo-inositol, choline and alanine were found to be important, the concentration of lactate seems to be an unreliable parameter for this classification problem. These results are exactly in line with clinical findings and medical interpretation of tumor metabolism. This study demonstrated, that NMR spectroscopy in combination with ANN offers a promising potential for the diagnosis of brain tumors.