Current understanding and future potential applications of cerebral microvascular imaging in infants

Abstract

Microvascular imaging is an advanced Doppler ultrasound technique that detects slow flow in microvessels by suppressing clutter signal and motion-related artifacts. The technique has been applied in several conditions to assess organ perfusion and lesion characteristics. In this pictorial review, we aim to describe current knowledge of the technique, particularly its diagnostic utility in the infant brain, and expand on the unexplored but promising clinical applications of microvascular imaging in the brain with case illustrations.

Figure 1.

Microvascular architecture of the brain. Microvascular imaging (MVI) anatomic features: (A) Superficial cortical vessels and pial branches (arrows). (B) Microvessels going through the deeper cortical layers. (C, D) Striatal vessels in the coronal and sagittal plane. (E) Superficial (arrows) and deep (dotted arrows) medullary vessels. Figure 2. General overview of microvascular anatomy by MVI. (F) A coronal image obtained at the level of the frontal horns of the brain shows the fan-like anatomic configuration of the microvessels. (G) A magnified view of the left hemisphere shows the details of the vessel distribution along with the cortex, superficial, deep, and periventricular white matter (arrows).

Figure 2.

General overview of microvascular anatomy by MVI. (A) A coronal image obtained at the level of the frontal horns of the brain shows the fan-like anatomic configuration of the microvessels. (B) A magnified view of the left hemisphere shows the details of the vessel distribution along with the cortex, superficial, deep, and periventricular white matter (arrows).

Figure 3.

Striatal vessels. (A-C) Coronal images obtained at the level of the deep gray matter from the more anterior component of the striatum at the level of the third ventricle passing through the caudate and putamen at the level of the M1 segments of the middle cerebral artery (origin of the Sylvian fissure), and extending posteriorly at the level of the thalamus and posterior sections of the lateral ventricle bodies. The striatal vascular distribution, including medial striatal vessels (A), lateral striatal vessels (B), and thalamoperforating vessels (C), can be observed.

Figure 4.

Preterm infant. A preterm male, born at 24 weeks, presents with severe systemic venolymphatic dysfunction. (A, B) Coronal grayscale ultrasound and MVI show an extensive number of tortuous small vessels, possibly representing venolymphatic structures, adjacent to the cortex accompanied by dilated superficial cerebral veins draining to the dural sinus.

Figure 5.

Hypoxic Ischemic Injury. A 2-week-old male with a clinical history of profound hypoxic ischemic encephalopathy. (A) Coronal MVI at the level of the M1 segments of the middle cerebral arteries and lateral striatal vessels, including the third ventricle and body of the lateral ventricles, shows enlargement of deep medullary vessels (dotted arrows) and reduction of the flow in the striatal vessels. (B) A normal MVI example at the same level is shown for comparison. (C, D) A coronal T2-weighted and FLAIR follow-up MRI after one week shows diffuse hyperintensity and a “swollen” appearance of the white matter (C) with signal saturation on FLAIR (D) as a consequence of cystic encephalomalacia.

Figure 6.

Stroke. A 1-week-old male, born at 39 weeks, was diagnosed with bilateral middle cerebral artery infarcts. (A, B) Coronal grayscale ultrasound and MVI at the level of the striatum demonstrate no significant differences between basal ganglia echogenicity (dotted circles), but evident asymmetric distribution of the striatal vessels in this region, reduced on the left side (dotted arrow). (C) Magnetic resonance imaging diffusion-weighted imaging shows extensive areas of restricted diffusion affecting the brain, confirmed in apparent diffusion coefficient map (not shown), involving the territory of the bilateral middle cerebral arteries but more prominently the left basal ganglia (arrow).

Figure 7.

Vascular malformation. A 2-day-old male newborn with a large vascular malformation in the posterior fossa. (A-D) MVI shows tortuosity of the supraclinoid segments of the internal carotid arteries with an apparent communication to the vertebrobasilar system by multiple large and small vessels (B, dotted arrow). Note the interesting reduction in the bilateral striatal microvascular flow potentially due to vascular steal phenomenon or cerebral edema. (E, F) Magnetic resonance angiogram (MRA) showing the 3D reconstruction of the vascular malformation communicating the arterial and venous systems by multiple and dilatated vessels. (G, H) Magnetic resonance imaging (MRI), axial arterial spin-label (ASL), and coronal T ₂-weighted show the presence of hyper-flow in the vascular malformation (arrow) and correlation with the MVI findings, as seen in image D.

Figure 8.

Brain tumor. A 4-day-old male with a diagnosis of tuberous sclerosis and subependymal giant cell astrocytoma. (A, B) Sagittal grayscale ultrasound and microvascular imaging (MVI) demonstrate a nodular lesion located in the foramen of Monro with the absence of significative microvascular flow (arrows). (C) Sagittal post-contrast T ₁-weighted imaging shows the nodular lesion presenting with homogeneous enhancement, consistent with subependymal giant cell astrocytoma (dotted arrow).

Figure 9.

Infection. A 2-month-old male with a history of prematurity and bacterial meningoencephalitis due to Escherichia coli. (A, B) MVI in parasagittal planes shows diffuse irregularity and tortuosity of the striatal vessels, the full extent to which better delineated using MVI than conventional color Doppler ultrasound. (C, D) Marked differences in cerebral microvascular flow can be observed using near-field coronal plane MVI when comparing to the corresponding color Doppler image (scale of ± 17.5 cm/s).

Figure 10.

Hydrocephalus. A 7-week-old female newborn with a clinical history of Prader-Willi syndrome underwent brain MVI. (A, B) Coronal MVI shows an increase of the flow in the ependymal vessels (arrow) and in the cortical vessels with relative reduction of the flow in the striatal vessels noted (dotted arrow). (C) Near-field sagittal MVI shows more avid superficial cortical microvascular flow (dotted arrow) than that appreciated using (D) color Doppler (scale of ±4 cm/s), obtained in the same plane.

Figure 11.

Extracorporeal membrane oxygenation (ECMO). (A) 4-day-old female newborn with persistent pulmonary hypertension and acute hypoxemic respiratory failure on ECMO underwent MVI, which shows decreased flow in the mildly tortuous striatal vessels (arrow). (B) MVI in a healthy neonate demonstrates normal flow in the striatal vessels.