Apparent diffusion coefficient and T2* mapping on 3T MRI in normal and degenerative lumbar intervertebral discs

Purpose:
To assess the utility of diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps and T2* mapping in quantitative analysis of nucleus pulposus (NP) and annulus fibrosus (AF) of lumbar intervertebral discs with its correlation with modified Pfirrmann grading (MPG) for lumbar degenerative disc disease (LDDD).

Material and methods:
One hundred subjects (20-74 years of age) underwent T2-weighted, DWI with ADC and T2* magnetic resonance imaging. MPG was applied to L3-L4, L4-L5, and L5-S1 discs, and ADC and T2* values of NP and AF were calculated in the mid-sagittal plane by segmenting each disc into 5 regions of interest (ROI) (NP-3, AF-2). Mean ADC and T2* values, their correlation, and cut-offs among different grades were calculated at different ROIs across different levels.

Results:
Out of total 300 discs analysed; 68 were normal (grade I) discs and 232 were degenerated (grade II to VIII) discs, based on MPG. T2* and ADC values in NP, AF, and the entire disc were significantly lower in degenerated discs than in normal discs. There was significant (p < 0.001) negative correlation between ADC and T2* values with MPG. ADC and T2* cut-off values were statistically significant across grades, with area under the curve (AUC) values in moderate to high accuracy range (0.8 to > 0.9) for assessing the degree of LDDD.

Conclusions:
T2* and ADC value-based grade scales are highly accurate in evaluating the degree of disc degeneration with a high degree of objectivity in comparison to visual assessment-based MPG. Reduced ADC and T2* values of NP could serve as markers of early LDDD.