Figure 1

Transducer architecture and ultrafast plane-wave imaging workflow of HUS. (A) The HUS transducer integrates an acoustic lens, four impedance-matching layers, single-crystal piezoelectric elements and a backing material. The multilayer design improves acoustic coupling and receiving sensitivity, while the low operating frequency of approximately 1 MHz supports transcranial propagation over an imaging depth exceeding 20 cm. The colour map schematically represents the normalized acoustic field across the intracranial imaging range; (B) Broad plane-wave transmission insonifies a large field of view without sequential line-by-line scanning, enabling rapid acquisition of spatially coherent channel data; (C) The received radiofrequency signals are transferred to an adaptive beamforming pipeline. Channel-dependent delays and apodization are first calculated and applied, after which the signals are coherently combined, spatially weighted and subjected to image post-processing. In the illustrated acquisition sequence, plane waves are transmitted successively at five steering angles (α1–α5) with an inter-emission interval of 0.2 ms, corresponding to a raw acquisition rate of 5,000 frames s−1. Each group of five angular acquisitions is coherently compounded to improve image contrast and suppress angle-dependent artefacts while preserving high temporal resolution. Repeated compounding generates a continuous ultrafast image sequence that can support contrast-free two-dimensional structural imaging and visualization of major intracranial vessels."

Figure 2

Clinical examination of HUS transcranial ultrasound with a probe positioned at the patient's right temporal window, transmitting the ultrasound beam through the skull toward the midbrain/substantia nigra region. (A) Normal midbrain substantia nigra; (B) magnified view; (C) PD patients display substantia nigra hyperechogenicity with an area of 0.29 cm2."

Figure 3

Representative HUS images of a patient with intracerebral hemorrhage. Male, 67 yrs, History of hypertension. Numbness in the left hand and weakness of the left lower extremity for half a day. Stuporous state with sluggish pupillary light reflex. HUS cranial ultrasound scan through the left temporal window identifies hyperechoic hematomas in the right frontal lobe (A, 2.8 mL) and right temporal lobe (B, 17.8 mL); (C) The right lateral ventricle is hyperechoic and enlarged with midline shift, suggestive of intraventricular hemorrhage extension. Non-contrast CT shows hyperattenuation in the right frontal lobe (D), right temporal lobe and right ventricle (E), confirming right frontotemporal hemorrhage extending into the right lateral ventricle, with estimated hematoma volumes of 3.6 mL and 15.6 mL, comparable to transcranial ultrasound."

Figure 4

A 74-year-old male was admitted to the emergency department with 14 h of sudden limb weakness after a fall and urinary and fecal incontinence. (A) Baseline CT showed hyperattenuation of the right thalamus and lateral ventricle (hemorrhage), estimated hematoma volume 20.7 mL. Serial CT at day 4 (B), day 8 (C), day 11 (D) showed gradual shrinkage of the hyperattenuating lesion; (E) HUS ultrasound through the left temporal window detected hyperechoic hemorrhage in the right thalamus and lateral ventricle (23.9 mL). Follow-up ultrasound at day 4 (F) and day 8 (G) revealed progressive shrinkage and reduced echogenicity of the right intracerebral hematoma. (H) Day 11 ultrasound demonstrated substantial reduction of intraventricular hyperechoic signals, matching CT images."

Figure 5

Dual-mode HUS imaging of the middle cerebral artery (MCA) and its anatomical localization. Left: color Doppler flow imaging shows flow in the middle MCA. Right: grayscale imaging shows the MCA groove (red arrows), an anatomical landmark for MCA localization."

Table 1

Key hemodynamic parameters and their clinical significance in integrated cervico-cerebral ultrasound assessment"

Figure 6

HUS hemodynamic findings in a patient with CT angiography-confirmed severe stenosis of the M1 segment of the left middle cerebral artery. (A) Color Doppler shows incomplete focal filling of the left MCA, suggesting restricted local flow; (B) Repeated spectral Doppler measurements show focal left MCA velocities of 332-375 cm/s; (C) Post-stenotic flow velocity is 39 cm/s, markedly lower than at the stenotic segment; (D) Pre-stenotic flow velocity is 103 cm/s, providing a reference for hemodynamic changes across the stenosis; (E) Contralateral MCA velocity is 110 cm/s, serving as a side-to-side reference."