What's the difference between CAS with 3D 4D Ultrasound and CAS with 4D Ultrasound?

Hello mamsh anong difference ng CAS with 3D and 4D Ultrasound sa CAS with 4d Ultrasound? Kasi ung sa accumed cost 4065 ung CAS with 4D ultrasound only wala daw pong 3D, while the Divine Birthing Home cost 5,500 CAS with 3D 4D ultrasound. Thanks po sa sasagot.