Complex sentence: Although endogenous contrasts agents are noninvasive and simpler to use, they are limited by their inherent behavior and concentration, making it difficult to monitor certain processes if optical absorption is weak.
Split into simpler sentences: Although endogenous contrasts agents are noninvasive and simpler to use, they are limited by their inherent properties. Endogenous agents have an inherent behavior and concentration, making it difficult to monitor certain processes if optical absorption is weak.