Diffusion‐weighted magnetic resonance imaging and magnetic resonance spectroscopy in the evaluation of focal cerebral tubercular lesions

Abstract

Purpose: To review magnetic resonance (MR) diffusion‐weighted imaging (DWI) and spectroscopy findings in patients with focal cerebral tuberculosis and to assess whether these techniques can adequately characterize focal cerebral tubercular lesions. Material and Methods: Sixteen patients with single or multiple lesions were evaluated on a 1.5T MR system. DWI was performed with three ‘b’ values of 50, 500, and 1000 s/mm2 and the apparent diffusion coefficient maps were calculated. MR spectroscopy was performed using the point‐resolved single‐voxel technique with 2 echo time values of 135 ms and 270 ms. The signal intensities of the tubercular lesions on diffusion images and the apparent diffusion coefficients (ADCs) of their centers, along with MR spectroscopy findings, were analyzed in relation to their T2‐weighted MR appearances. Results: DWI identified 17 of the 20 lesions evaluated. Increased signal intensity was seen in 9 of the 17 lesions. The ADCs of the lesions ranged from 0.406 to 2.64×10−3 mm2/s (mean±SD: 1.038±0.609 mm2/s). Most of the lesions with hyperintense centers on T2‐weighted images were of increased intensity on diffusion images, while those with hypointense centers on T2‐weighted images were of decreased signal intensity on diffusion images. However, no statistical difference in the ADCs was found between lesions with increased and those with decreased signal intensity centers on T2‐weighted images. MR spectroscopy revealed a lipid peak at 0.9–1.3 ppm in all of the 14 lesions evaluated. An increase in normalized choline:creatine ratio was found in all the lesions in which the spectra were obtained with the voxel, including a variable portion of the lesion wall. Conclusion: DWI and MR spectroscopy help in determining the nature of cerebral tubercular lesions; however, since the findings are varied, they do not help in specific characterization.