Uniform-MT CEST to isolate gagCEST contrast from asymmetric MT effects: First in vivo study on human knees at 7 T

Purpose: The extracelluar matrix of articular cartilage is mostly composed of type II collagen and proteoglycan (PG) aggregates with glycosaminoglycan (GAG) chains. Osteoarthritis (OA) is characterized by the loss of PGs in cartilage, and therefore in-vivo quantification of GAG concentration is important for the early diagnosis of OA. One promising method for measuring GAG content in articular cartilage is CEST. Measurement of this so-called gagCEST may be affected by the MT effects resulting from the background extracelluar matrix. Recently, we have proposed a new strategy to disentangle CEST effects from asymmetric MT effects by using a simultaneous two-frequency RF irradiation technique to make the MT effects uniform. In this work, we compare for the first time the uniform-MT (uMT) CEST method to the conventional CEST method through an in vivo human knee MRI study at 7 T.