1. Brown, T. G., “Visualization of soft tissues in two and three dimension-limitations and developments,” Ultrasonics 5, p. 118 (1967)
2. Wells, P. N T “Physical Principles of Ultrasound Diagnosis,” Chapt. 4.7, Academic Press (1969).
3. Green. P. S., Schaefer, L. F., and Macovski, A., “Considerations for Diagnostic Ultrasonic Imaging,” Acoustical Holography, Vol. 4, p. 97 (1972).
4. McCready, V. P. and Hill, C. R., “Constant Depth Ultrasonic Scanner,” Brit. J. of Rad. 44, p. 747 (1971). (A method for spiral scan is described, but with the focal plane being a spherical surface.)
5. Jenkins, F.A. and White, H. E., “Fundamentals of Optics,” p. 23, McGraw-Hill (1957).