High b-value diffusion (b = 3000 s/mm2) MR imaging in cerebral gliomas at 3T: visual and quantitative comparisons with b = 1000 s/mm2

BACKGROUND AND PURPOSE: High b-value diffusion-weighted imaging (DWI) provides different features not appreciated at lower b-value and have been recently studied in several clinical issues. The purpose of this study was to assess whether DWI at b = 3000 s/mm² is more useful in discriminating high-grade and low-grade gliomas than DWI at b = 1000 s/mm² at 3T.MATERIALS AND METHODS: DWIs at both b = 1000 and 3000 s/mm² were performed at 3T in 62 patients, 49 high-grade gliomas (20 World Health Organization WHO] grade III and 29 grade IV) and 13 low-grade gliomas (13 grade II). Visual assessments based on 5-point scaled evaluations, receiver operating characteristic (ROC) curve analysis, and quantitative assessment based on DWI signal intensity (SI) ratio (tumor SI/normal SI) and apparent diffusion coefficient (ADC) values were compared between DWIs at b = 1000 and 3000 s/mm².RESULTS: By visual assessment, DWI at b = 3000 s/mm² showed more conspicuous hyperintensity in high-grade gliomas and hypointensity in low-grade gliomas than DWI at b = 1000 s/mm². Sensitivity and specificity at b = 3000 s/mm² were higher than at b = 1000 s/mm² (83.7%, 84.6% vs 69.4%, 76.9%, respectively). Quantitative assessments showed that mean SI ratio of high-grade gliomas was significantly higher than that of low-grade gliomas at both b-values. The mean ADC value of high-grade gliomas was significantly lower than that of low-grade gliomas at both b-values. The difference between the SI ratios of high-grade and low-grade gliomas was significantly larger at b = 3000 s/mm² than at b = 1000 s/mm².CONCLUSION: DWI at b = 3000 s/mm² is more useful than DWI at b = 1000 s/mm² in terms of discriminating high-grade and low-grade gliomas at 3T.

Diffusion-weighted imaging (DWI) is a sensitive technique that reflects microscopic water diffusion with the use of a pair of strong diffusion gradients¹ and has been used routinely for the early detection of cerebral ischemia with diffusion restriction.² DWI and apparent diffusion coefficient (ADC) value have been studied in other clinical situations, including the differential diagnosis and grading of brain tumors.^3–15Although it is known that higher cellularity in high-grade glioma results in greater diffusion restriction and a reduction in ADC values, whereas lower cellularity in low-grade glioma increases ADC values,^8–14 DWI at a standard b-value (b = 1000 s/mm²) at 1.5T barely differentiates high-grade and low-grade gliomas in many cases because of overlapping signal intensities (SI) on DWI and ADC maps.Theoretically, a higher b-value DWI provides better contrast with its reflection of more tissue diffusivity and less T2 shinethrough effect.^{16, 17} However, at 1.5 or lower field strength, higher b-values are not usually used in clinical practice because of poor image quality secondary to an inferior signal-to-noise ratio (SNR).^18–21 Recently, stronger gradients and faster slew rates have permitted high b-value DWI, particularly in 3T units, because higher SNRs at 3T compensate for the inferior SNRs of high b-value DWI without increasing data acquisition time.The purpose of our investigation was to assess whether DWI at high b-value (b = 3000 s/mm²), is better than DWI at a standard b-value (b = 1000 s/mm²) for the differential diagnosis of high-grade and low-grade cerebral gliomas in clinical practice at 3T.