Combination of single-voxel proton MR spectroscopy and apparent diffusion coefficient calculation in the evaluation of common brain tumors

Abstract

Background and purpose: MR spectroscopy and apparent diffusion coefficient (ADC) calculation have been used frequently for tumor grading and differentiation during the last decade. We evaluated whether the combination of these two techniques can improve the diagnostic effectiveness of MR imaging in patients with brain tumors.

Methods: Forty-nine patients with histologically proved brain tumors (eight high- and 12 low-grade astrocytomas, eight metastases, eight nonastrocytic gliomas, seven meningiomas, three dysembryoplastic neuroepithelial tumors (DNETs), and three tuberculomas) were prospectively evaluated with contrast material-enhanced MR imaging, single-voxel proton MR spectroscopy (TE = 135 ms), and diffusion-weighted imaging (b = 0, 500, and 1000 s/mm(2)) before surgery.

Results: MR spectroscopy could differentiate benign from malignant tumors but was not useful in grading malignant tumors. In the differentiation of malignant from benign tumors, N-acetylaspartate (NAA)/choline (Cho), NAA/Cho + creatine (Cr), lactate/Cr, and alanin/Cr ratios (P <.001) were statistically more significant than NAA/Cr and lactate/lipid ratios (P <.05). Increase in lipid/Cr and alanin/Cr ratios could distinguish metastasis and meningiomas from other tumors, respectively (P <.001). DNETs could be diagnosed by their normal spectra and high ADC values (116.25 +/- 6.93 x 10(-3) mm(2)/s). Increase in lactate/Cr ratio correlated with degree of malignancy (r = -0.71). ADCs were effective for grading malignant tumors (P <.001) but not for distinguishing different tumor types with the same grade. High-grade malignant tumors (87.16 +/- 10.41 x 10(-3) mm(2)/s) had significantly lower ADC values than did low-grade malignant (115.33 +/- 11.67 x 10(-3) mm(2)/s) and benign (107.69 +/- 8.05 x 10(-3) mm(2)/s) tumors. Peritumoral ADCs were significantly higher in low-grade than in high-grade astrocytomas (P <.05).

Conclusion: Combination of calculated ADC values from tumoral core and specific relative metabolite ratios acquired by MR spectroscopy added more information to MR imaging in the differentiation and grading of brain tumors and were more useful together than each alone.

Fig 1.

71-year-old woman with brain metastasis from ovarian cancer. A, FLAIR image shows a high-signal-intensity necrotic tumor with prominent peritumoral edema. Irregular ringlike enhancement was seen on the T1-weighted image (not shown). B, ADC map shows the tumor (1) and adjacent edema (2) have higher signal intensity than does the cerebellar parenchyma. Calculated ADC value (83 × 10⁻³ mm²/s), which is significantly lower than that of low-grade astrocytomas and nonastrocytic gliomas, helps to differentiate metastasis from low-grade malignant tumors, but not from high-grade ones. C, MR spectrum shows low NAA level (NAA/Cho = 0.92) with prominent lactate and lipid peaks (lipid/Cr = 0.58). High lipid/Cr ratio helps to differentiate metastasis from other primary malignant tumors.

Fig 2.

51-year-old man with high-grade astrocytoma in the left periventricular white matter. A, T1-weighted image shows heterogeneous contrast enhancement of the tumor with extensive peritumoral edema. B, ADC map shows that the tumor (1) and adjacent tumor (2) nearly isointense with cerebral white matter (2). This tumor’s calculated ADC value is 87 × 10⁻³ mm²/s, which helps to differentiate it from low-grade malignant tumors, but not from metastasis. C, Proton MR spectrum shows prominent decrease in NAA and increase in Cho (NAA/Cho = 0.19) and lactate (lactate/Cr = 0.28). Absence of prominent lipid peak with low lipid/Cr ratio helps to differentiate this tumor from metastasis.

Fig 3.

25-year-old woman with low-grade astrocytoma in right thalamus and subsequent invasion of the left thalamus via the massa intermedia. A, FLAIR image shows hyperintense tumor without significant edema. Faint enhancement was seen on the T1-weighted image (not shown). B, ADC map shows that the tumor (1) has slightly higher signal intensity than that of normal thalamus. Calculated ADC value of 110 × 10⁻³ mm²/s indicates low-grade malignant tumor, but this was not useful to differentiate it from other low-grade malignant tumors. C, MR spectrum shows decreased NAA/Cho ratio (0.66) with prominent lactate peak. This is a common finding for primary malignant brain tumors, but does not allow us to make a subtype classification.

Fig 4.

22-year-old man with oligodendroglioma involving the left temporal lob and basal ganglia region. A, FLAIR image shows hyperitense mass without significant edema. No contrast enhancement was present on the T1-weighted image (not shown). B, ADC map shows that the tumor (1) has a heterogeneous pattern and higher signal intensity than that of the contralateral basal ganglia region. Its calculated ADC value is 118 × 10⁻³ mm²/s and strongly suggests low-grade malignant or benign tumor. C, MR spectrum shows mild decrease in both NAA and Cho (NAA/Cho = 0.72) with small lactate peak. This spectrum helps to differentiate this tumor from benign tumors but is not useful to distinguish the histologic subtypes.

Fig 5.

52-year-old woman with meningioma located in the left prepontine cistern. A, T1-weighted image shows a well-demarcated, strongly enhanced extraaxial mass. B, ADC map shows that the tumor (1) has slightly higher signal intensity than that of adjacent brain parenchyma. ADC value of 109 × 10⁻³ mm²/s does not help to distinguish this tumor from other benign lesions. C, MR spectrum shows decreased NAA/Cho ratio (0.76) with prominent lipid and alanin peaks at 1.5 ppm (alanin/Cr = 0.68). Prominent alanin peak with low NAA and high Cho levels helps to distinguish meningioma from other tumor groups.