Super-resolution ultrasound localization microscopy for the non-invasive imaging of human testicular microcirculation and its differential diagnosis role in male infertility

Testicular microcirculation is closely related to spermatogenic function and seminiferous tubular function. The diagnosis and monitoring of testicular diseases can be associated with testicular microcirculation; however, there are currently no effective non-invasive methods for super-resolution imaging of testicular microcirculation. In this study, we introduced state-of-the-art graph-based tracking with the Kalman motion model algorithm to non-invasively image human testicular microcirculation for the first time with a regular frame-rate clinical ultrasound imaging system (37 Hz). Two distinct testicular vessels with an 81 µm separation were resolved in the testicular vasculature, surpassing all other imaging modalities. In a retrospective study, we performed contrast-enhanced ultrasound examinations(CEUS) and ultrasound localization microscopy (ULM) processing on the included 76 infertile patients and 15 healthy controls from August 2021 to May 2023 and obtained super-resolution images of testicular microcirculation with sub-diffraction resolution. Through the results of one-way analysis of variance tests and receiver operating characteristic analyses, we found that the ULM-based parameters hold promise as clinical guidance for differentiating between non-obstructive and obstructive male infertility. The mean vessel diameter achieved an area under the curve (AUC) of 0.920 (95% confidence interval [CI]: 0.847–0.994, p < .001) with a cut-off value of 170.9 µm in oligoasthenospermia, and an AUC of 0.952 (95% CI: 0.875–1.000, p < .001) with a cut-off value of 169.9 µm in azoospermia patients, respectively, addressing a significant clinical challenge.