Koroku Namekawa

Koroku Namekawa is an Aloka coauthor of the 1985 Color Doppler imaging paper with Chihiro Kasai, Akira Koyano and Ryozo Omoto. Their instrument combined pulse-echo acquisition with complex correlation processing; the paper reports experiments with moving targets and flowing water.^[ref] The shared authorship establishes his participation; it does not assign each circuit or experiment to one coauthor.

A useful engineering constraint is the acquisition-time budget. If an image has $N$ beam directions, each uses $n$ pulses separated by $T$, and overhead is ignored, its acquisition time is approximatelyFor an original example, $N=50$, $n=8$ and $T=0.20\mathrm{ms}$ give $t_{\mathrm{frame}}=0.080\mathrm{s}$ and $F=12.5$ frames per second. Doubling the ensemble to 16 pulses halves that ideal rate. These stipulated values illustrate the timing constraint, rather than a performance specification of Namekawa's instrument.

Longer averaging can improve a noisy autocorrelation estimate while reducing temporal coverage or image rate. It cannot create time that was not available between transmitted pulses. Thus a blood flow image is the outcome of both an estimator and a scanning schedule, not a simultaneous velocity observation at every displayed pixel.