Tissues that have higher echogenicity are called "hyperechoic" and are usually represented with lighter colors on images in medical ultrasonography.
In contrast, tissues with lower echogenicity are called "hypoechoic" and are usually represented with darker colors.
Areas that lack echogenicity are called "anechoic" and are usually displayed as completely dark.
[1] Echogenicity can be increased by intravenously administering gas-filled microbubble contrast agent to the systemic circulation, with the procedure being called contrast-enhanced ultrasound.
When gas bubbles are caught in an ultrasonic frequency field, they compress, oscillate, and reflect a characteristic echo- this generates the strong and unique sonogram in contrast-enhanced ultrasound.