Honestly what they're describing can be done on any MCU without PIO - set up clock division/PLL to provide ADC clock, use that same clock for timer source, set up a timer channel to trigger the pulse, set up a timer channel to trigger ADC DMA capture start, start the timer.
Congrats, now you have capture synchronized to pulse start "providing the sub-microsecond timing needed for ultrasound acquisition".
Congrats, now you have capture synchronized to pulse start "providing the sub-microsecond timing needed for ultrasound acquisition".