Application of 31P MR spectroscopy to the brain tumors

Abstract

Objective: To evaluate the clinical feasibility and obtain useful parameters of (31)P magnetic resonance spectroscopy (MRS) study for making the differential diagnosis of brain tumors.

Materials and methods: Twenty-eight patients with brain tumorous lesions (22 cases of brain tumor and 6 cases of abscess) and 11 normal volunteers were included. The patients were classified into the astrocytoma group, lymphoma group, metastasis group and the abscess group. We obtained the intracellular pH and the metabolite ratios of phosphomonoesters/phosophodiesters (PME/PDE), PME/inorganic phosphate (Pi), PDE/Pi, PME/adenosine triphosphate (ATP), PDE/ATP, PME/phosphocreatine (PCr), PDE/PCr, PCr/ATP, PCr/Pi, and ATP/Pi, and evaluated the statistical significances.

Results: The brain tumors had a tendency of alkalization (pH = 7.28 ± 0.27, p = 0.090), especially the pH of the lymphoma was significantly increased (pH = 7.45 ± 0.32, p = 0.013). The brain tumor group showed increased PME/PDE ratio compared with that in the normal control group (p = 0.012). The ratios of PME/PDE, PDE/Pi, PME/PCr and PDE/PCr showed statistically significant differences between each brain lesion groups (p < 0.05). The astrocytoma showed an increased PME/PDE and PME/PCr ratio. The ratios of PDE/Pi, PME/PCr, and PDE/PCr in lymphoma group were lower than those in the control group and astrocytoma group. The metastasis group showed an increased PME/PDE ratio, compared with that in the normal control group.

Conclusion: We have obtained the clinically applicable (31)P MRS, and the pH, PME/PDE, PDE/Pi, PME/PCr, and PDE/PCr ratios are helpful for differentiating among the different types of brain tumors.

Keywords: Brain; MRS; Magnetic resonance imaging; Tumor.

Fig. 1

Flow chart of patient selection. On basis of histopathologic results, patients were classified into 22 cases of brain tumor and 6 cases of abscess. Brain tumors were subdivided into 13 cases of astrocytoma group, 4 cases of lymphoma group, and 5 cases of metastasis group. MRS = magnetic resonance spectroscopy

Fig. 2

Measuring pH in lesion. Intracelluar pH of brain lesions is calculated by using measured δ Pi (arrow), which is chemical shift, from PCr to Pi. PME = phosphomonoester, PDE = phosphodiester, PCr = phosphocreatine, ATP = adenosine triphosphate, Pi = inorganic phosphate

Fig. 3

44-year-old man with high grade astrocytoma of brain. A. Localizer image for ³¹P MRS shows huge mass in right frontal lobe without cyst or hemorrhage. B. ³¹P MRS shows high level of PME (303), low level of Pi (90) and relatively low level of PDE (433). Calculated PME/PDE ratio (0.70) is higher than its mean value in control group (0.47). PME = phosphomonoester, PDE = phosphodiester, PCr = phosphocreatine, MRS = magnetic resonance spectroscopy, Pi = inorganic phosphate

Fig. 4

53-year-old man with large B cell lymphoma. A. Localizer image for ³¹P MRS shows large mass with marked surrounding edema in left basal ganglia area. B. ³¹P MRS shows high level of PME (305), high level of PCr (1222) and low level of PDE (373). Calculated ratio shows high PME/PDE ratio (0.81). Calculated PDE/Pi ratio (2.76) is lower than its mean value of control group (3.44) and astrocytoma group (3.27). Calculated PDE/PCr ratio (0.31) is also lower than that of astrocytoma group (0.77). PME = phosphomonoester, PDE = phosphodiester, PCr = phosphocreatine, MRS = magnetic resonance spectroscopy, Pi = inorganic phosphate

Fig. 5

73-year-old man with brain abscess. A. FID signal for ³¹P MRS was obtained at left basal ganglia mass lesion. B. Fluid-attenuated inversion recovery image shows heterogeneous signal intensity mass with central low signal intensity in left basal ganglia. C. ³¹P MRS shows low level of PME (284), low level of PCr (584) and relatively high level of PDE (486). Calculated ratio of PME/PDE (0.58) is lower than its mean value of metastasis group (0.68). FID = free induction decay, PME = phosphomonoester, PDE = phosphodiester, PCr = phosphocreatine, MRS = magnetic resonance spectroscopy, Pi = inorganic phosphate