Testicular vascularity should be assessed both with color Doppler and power Doppler study.

Doppler settings should be optimized to detect slow flow (low PRF and maximized color gain without artifacts). In case of acute scrotum, the examination should start from the asymptomatic hemiscrotum to adjust Doppler settings and then to assess symmetrical vascularity by comparing flow findings with the pathological side [8]. Comparative evaluation acquires crucial importance in case of testicular torsion or acute inflammation.

Power Doppler has higher (5×) sensitivity than color Doppler to detect low-flow velocities because its direction is insensitive [6]; however, it is very susceptible to movement, and it is difficult to apply in case of acute scrotum of children (Fig. 38.2).

Testicular vascularity should also be assessed both with power Doppler and spectral Doppler: power Doppler confirms the presence of intratesticular flow, and spectral Doppler allows distinguishing an arterial waveform from a venous flow. Intratesticular arterial waveform typically shows a high diastolic flow with low resistance index (RI = 0.62; range 0.48–0.70), while the deferential or cremasteric artery shows a typical high resistive waveform without diastolic component and with high resistance index (RI > 0.70).

In case of acute scrotal, the important distinction between an inflammatory and ischemic cause is on spectral Doppler, by assessing a low or high resistive flow.

In case of acute orchitis, the inflammatory process causes vasodilatation with a reduction of RI mean value (Fig. 38.3) [3].

In case of testicular torsion, color Doppler and power Doppler demonstrate reduced or absent intratesticular flow compared with the unaffected side, respectively, depending on incomplete or complete torsion (Fig. 38.4). If the torsion is partial, the spectral Doppler can demonstrate a preserved arterial flow with increased RI. In case of complete torsion, no flow in the intratesticular vessels is demonstrated, and increased perfusion can be assessed in the extratesticular vessels near the scrotal wall with higher RI (Fig. 38.5) [9, 10].

Ultrasonography with Doppler imaging is very effective at visualizing and measuring blood flow only in large vessels with rapidly moving blood, but is unable to accurately detect flow in smaller vessels and capillaries. The development of endovascular contrast agents (as microbubbles) has subsequently allowed to obtain useful information about vascularity, perfusion rates, and potential tumor detection.

CEUS demonstrated an accuracy similar to contrast-enhanced multi-detector computed tomography (CE-MDCT) in detecting focal lesions, with the advantage of the real-time assessment of microvascular perfusion by using time-intensity curves, without the use of ionizing radiation.

Second-generation microbubble contrast agents consist of gas microbubbles (air or perfluorocarbon) stabilized by a biodegradable shell of protein, lipid, or polymer.

The small size of microbubbles (from 1 to 10 μm, as the size of a red blood cell) allows their passage unfiltered through the lungs, but the relative big size prevents entry into the interstitium allowing them to remain entirely intravascular (“pure blood pool” agents). Under US exposition, microbubbles oscillatory contract and expand themselves with the same resonance frequency of US waves, by amplifying the US signal. After circulating for several minutes, microbubbles dissolve: the gas is exhaled by the lungs, whereas the biodegradable shell is metabolized by the liver [11]. Microbubble contrast agents are not excreted by the kidney and do not affect renal function: they can be safely administrated to patients with renal insufficiency. Other advantages of CEUS include its safety, simplicity, patient tolerance, and lack of irradiation (conversely to CE-MDCT scans).