Resistivity Index Mapping in Kidney Based on Ultrasensitive Pulsed-Wave Doppler and Automatic Spectrogram Envelope Detection

Abstract

However, their suitability for any other type of signals is 472 something that needs to be studied further, for example, those 473 of liver or umbilical, where RI measurements are also of 474 interest in the clinic. 475 Another remark concerns the estimates of peak systolic and 476 end-diastolic velocities. One can see from Fig. 4 that both 477 algorithms tend to underestimate these velocities inasmuch 478 the aliasing effects become important. The MSNSI algorithm 479 presents a more important underestimation of the peak velocity 480 than the end-diastolic velocity; on the other hand, the MTM 481 underestimates both velocities to approximately the same 482 extent. This may explain why the MTM performs better than 483 the MSNSI in limited conditions when the aliasing effects are 484 important, even if the peak systolic and end-diastolic velocities 485 are underestimated. 486 This also put in evidence that the proposed method is not 487 useful to estimate these velocities in most of the cases. Based 488 on the simulation results, one could infer that the estimated 489 velocities could be quite accurate when the peak velocity is 490 lower than 3/4 of the velocity related to the sampling frequency 491 and the SNR is higher than 10 dB. 492 Another limitation is that no spectral broadening effect has 493 been considered in the proposed method, in the same way 494 as for the calculation of the spectrogram from which the RI 495 is measured by the conventional method, where, to the best 496 of our knowledge, no correction is made. However, several 497 works have shown the effects of spectral broadening on the 498 estimation of the maximum velocity; most of the studies on 499 this subject have been conducted under the assumption of 500 using focused US beams but few in the case of unfocused US 501 beams. The evaluation of the effects of spectral broadening 502 on the estimation of the maximum velocity is not simple and 503 requires extensive work since it depends on many parameters 504 such as the flow velocity, the angle between the US beam and 505 the flow direction, the characteristics of the US beam and the 506 transducer, and the use of focused or unfocused US beams,