  Meniscal tear in the knee joint is a highly common injury that can require an
ablation. However, the success rate of meniscectomy is highly impacted by
difficulties in estimating the thin vascularization of the meniscus, which
determines the healing capacities of the patient. Indeed, the vascularization
is estimated using arthroscopic cameras that lack of a high sensitivity to
blood flow. Here, we propose an ultrasound method for estimating the density of
vascularization in the meniscus during surgery. This approach uses an
arthroscopic probe driven by ultrafast sequences. To enhance the sensitivity of
the method, we propose to use a chirp-coded excitation combined to a mismatched
compression filter robust to the attenuation. This chirp approach was compared
to a standard ultrafast emission and a Hadamard-coded emission using a flow
phantom. The mismatched filter was also compared to a matched filter. Results
show that, for a velocity of a few mm/s, the mismatched filter gives a 4.4 to
10.4 dB increase of the signal-to-noise ratio compared to the Hadamard emission
and a 3.1 to 6.6 dB increase compared to the matched filter. Such increases are
obtained for a loss of axial resolution of 13% when comparing the point spread
functions of the mismatched and matched filters. Hence, the mismatched filter
allows increasing significantly the probe capacity to detect slow flows at the
cost of a small loss in axial resolution. This preliminary study is the first
step toward an ultrasensitive ultrasound arthroscopic probe able to assist the
surgeon during meniscectomy.
