Quantitative chemical exchange saturation transfer MRI of intervertebral disc in a porcine model.

Purpose: Previous studies have associated low pH in intervertebral discs (IVDs) with discogenic back pain. The purpose of this study was to determine whether quantitative CEST (qCEST) MRI can be used to detect pH changes in IVDs in vivo.
Methods: The exchange rate k _sw between glycosaminoglycan (GAG) protons and water protons was determined from qCEST analysis. Its dependence on pH value was investigated in GAG phantoms with varying pH and concentrations. The relationship between k _sw and pH was studied further in vivo in a porcine model on a 3T MR scanner and validated using a pH meter. Sodium lactate was injected into the IVDs to induce various pH values within the discs ranging from 5 to 7.
Results: Phantom and animal results revealed that k _sw measured using qCEST MRI is highly correlated with pH level. In the animal studies, the relationship can be described as k _sw  =9.2 × 10 ⁶ × 10 ^-pH + 196.9, R ²  = 0.7883.
Conclusion: The exchange rate between GAG and water protons determined from qCEST MRI is closely correlated with pH value. This technique has the potential to noninvasively measure pH in the IVDs of patients with discogenic pain. Magn Reson Med 76:1677-1683, 2016. © 2016 International Society for Magnetic Resonance in Medicine.
(© 2016 International Society for Magnetic Resonance in Medicine.)