BACKGROUND:

Low back pain is a leading cause of disability worldwide with intervertebral disc degeneration (IVDD) being one of its major causes.

IVDD is progressive and irreversible structural failure of the disc's compartments that results in biomechanical dysfunction. The early changes in IVDD are primarily associated with the loss of proteoglycan content in the nucleus pulposus (NP) and reduction in the water binding capacity; eventually leading to loss of hydration and osmotic pressure.

Magnetic resonance imaging (MRI) is the most widely used method of assessing IVDD. Based on proton density, water content, and chemical environment, MR depicts disc hydration and morphology.

On T2- weighted MR images, normal intervertebral discs show a bright signal from the nucleus pulposus and inner fibres of the annulus. Signal from the outer fibres of the annulus fibrosus (AF) is very low. Disc degeneration is seen as a reduction in signal of the nucleus pulposus and inner fibres of the annulus. Severe disc degeneration causes decrease in the disc height. 

The Pfirrmann Grading system, one of the most frequently used MRI grading for IVDD, is derived from sagittal T2-WI and is based on MR signal intensity of Nucleus pulposus, disc structure, distinction between nucleus pulposus and annulus fibrosus, and disc height. It grades the intervertebral discs into 5 categories from Grade I to V. However, this is only a semi-quantitative grading, is evaluator dependent and can be influenced by variable imaging conditions.

Quantitative magnetic resonance imaging (qMRI) methods such as T2 mapping provide objective results, which have already shown excellent discriminability when it comes to disc degeneration.

METHODS:

This study was conducted over a period of 18 months in 100 patients of Indian population in the age group of 20 to 80 years with complaints of low back pain who underwent MRI lumbar spine.

The study has been done as per standard ethics and by maintaining confidentiality of reports. Written informed consent was taken from every patient.

EQUIPMENT: 

MR acquisition were performed in a single session on a 3.0T MR imaging scanner (MAGNETOM SKYRA; Siemens Medical Solutions, Erlangen, Germany) using a dedicated 32 channel phased array spine coil (3T Spine Matrix Coil, Siemens).

STUDY SAMPLE:

The study was approved by the institutional review board, and written, informed consent was obtained from all patients. Four hundred ninety four lumbar intervertebral discs from 100 patients (51 female, 49 male), with single or recurrent episodes of low back pain, were investigated. Inclusion criteria were the presence of low back pain, age between 20 and 70 years. Exclusion criteria were patient who did not give consent to the study, history of known spinal pathology or spinal anomaly, previous spine surgery, contraindications for MRI, or lumbar scoliosis of more than 15 degrees in the coronal MR images.

MR IMAGING:

Sagittal and axial T2-weighted fast spin echo (FSE) sequences were used for morphological Pfirrmann grading. For T2 relaxation time measurement, a multi echo-spin echo sequence in a sagittal plane was acquired. The detail MRI protocol is shown in figure 1.

Image analysis:

Morphological grading -

All intervertebral discs were classified by the proposed morphological Pfirrmann grading on the sagittal T2-weighted FSE image (figure 2 and 3).

T2 mapping - 

A mid sagittal section on T2 sagittal map (slice number 6 or 7 from the total of 13 slices) was selected. To evaluate regions of interest (ROIs) in a standardized and reproducible way, five equal sized circular non-overlapping ROIs were placed in the central 50% of the disc (figure 4). The mean and standard deviation values were measured. 

STATISTICAL ANALYSIS:

Computer software Statistical Package for Social Sciences (SPSS version 28.0, for Microsoft windows) and Microsoft Excel (Microsoft 365 office) were used for the data analysis in this study. For statistical convenience, NP anterior, NP central and NP posterior are collectively grouped under the broad term NP by taking out their mean. One-way ANOVA (Analysis Of Variance) with post test is used to compare the AF anterior, NP and AF posterior values at different lumbar intervertebral disc levels and different Pfirrmann grades. To test the statistical significance of the association of results between Pfirrmann grading and T2 mapping, p values were calculated.