Effect of Phase Errors on Field Patterns Generated by an Ultrasound Phased-Array Hyperthermia Applicator

Phase quantization errors are inherent when digital electronic phase shifters are used to specify the driving signals for synthesis of power deposition patterns with ultrasound phased array hyperthermia applicators. The phase errors induced by quantization decrease as the number of bits used to specify phase increases. Phase errors can also be induced through inhomogeneous media or imperfect array fabrication. A quantitative study of the effect of phase digitization errors and Gaussian-distributed random phase errors on field patterns can partially reflect the sensitivity of hyperthermia phased array systems to phase distortions, since both phase digitization errors and Gaussian-distributed random phase errors behave somewhat like the random phase aberrations due to tissue inhomogeneities in the treatment volume. The intensity patterns and temperature profiles simulated in this paper were relatively insensitive to increases in either of the above types of phase error. Thus, specifying phase with only a single bit, which results in phase errors with a standard deviation of about 52°, or introducing Gaussian-distributed random phase errors with a standard deviation of about 52°, produces patterns that have considerable resemblance to the ideal cases.