Читать книгу Bovine Reproduction - Группа авторов - Страница 171

While B‐mode ultrasonography is currently the most commonly employed modality for examination of reproductive tissue, other ultrasound‐based diagnostic methods exist. Color Doppler, contrast‐enhanced ultrasonography and tissue elastography are adjunct imaging modalities used to investigate lesions in human testes [25] as well as other tissues.

The direction, relative velocity, and volume of blood flow in arteries can be assessed by use of Doppler ultrasonography [4]. A color Doppler ultrasonogram of the testicular artery dorsal to the testis within the vascular cone is shown in Figure 10.20. In a recent report using Doppler ultrasound, the resistive index in both the marginal and intratesticular portions (Figure 10.21) of the testicular artery of the bull were correlated with the total sperm in the ejaculate, immature sperm, abnormal sperm, and presence of the Dag defect [26]. Because of the relative ease of marginal testicular artery imaging (located medial to the testis), the authors conclude that this could be an “easy‐to‐perform parameter to evaluate the spermatogenesis quality” in bulls. And while the correlations in this report were significant, there was no evidence that they could be used to establish cut‐off values to distinguish between satisfactory and unsatisfactory breeding bulls.

Figure 10.20 Sagittal view of the vascular cone using color Doppler mode. The direction of blood flow in the supratesticular portion of the testicular artery is indicated by color and the velocity by shade within color.

Figure 10.21 Sagittal color Doppler image of the testis illustrating blood flow (colored areas) in the intratesticular portion of the testicular artery.

Tissue elastography measures the stiffness of tissue in response to an applied force. This force can be applied either mechanically or by the ultrasound waves themselves. A soft consistency of the testis is present in cases of testicular degeneration [27], but manual assessment of testis consistency is limited by both its subjective nature and the presence of intervening scrotal wall with varied skin texture and fat deposits. Mechanical systems that compress the scrotal surface have been proposed [28], but they still have limitations as they must be applied to the scrotal surface and do not directly measure the consistency of the testis. Tissue elastography offers the advantage of both more objective assessment of tissue stiffness and the ability to focus on the tissue of interest within the testis. Most focal lesions of the testes will differ in consistency in comparison to the surrounding normal parenchyma.

It is important to note that most inexpensive portable bovine ultrasound systems lack a color Doppler function and even much more expensive systems do not routinely offer elastography. Given the cost and limited clinical application in bulls, these modalities will be of more interest to researchers than to clinicians for the foreseeable future.