Patent Description:
The clinical management of infants and the understanding of neuro-developmental disorders is limited by the absence of an effective and efficient imaging modality to evaluate early brain function. Functional magnetic resonance imaging (fMRI) is one the best techniques available for adult brain imaging but it is very complex to implement for neonates as its use at the bedside for brain imaging of vulnerable infants is especially challenging. In clinics, near-infrared spectroscopy (NIRS) or electroencephalography (EEG) are mainly used, two techniques with low spatial resolution and an activity measurement limited to the surface of the brain. Therefore, there is a need for a clinical neonatal cerebral functional imaging modality, efficient and easy to use, and for the development of portable innovative approaches that would allow for the real-time monitoring of brain function in infants.

Recently (See <NPL>)), ultrafast ultrasound imaging was introduced to achieve more than <NUM>,<NUM> ultrasound frames per second (compared to the typical <NUM> frames per second used in conventional ultrasound scanners). In the ultrafast Doppler (UfD) imaging mode (See for example <NPL>)), up to a <NUM>-fold increase in sensitivity for blood flow measurements in the human brain is obtained. Unlike conventional Doppler techniques, which are limited to the imaging of large vessels, UfD imaging enables the mapping of subtle hemodynamic changes in small brain vessels, i.e. with diameters smaller than <NUM>.

Functional ultrasound imaging (fUSI) leverages these blood flow maps to image brain activity according to neurovascular coupling that correlates local neural activity and relative changes in cerebral blood volume (CBV). By providing real-time images of deep brain activity with high spatiotemporal resolution, fUSI enables for example imaging of brain activity during epileptic events recorded by electroencephalography (EEG). fUSI also enables the mapping of functional brain "connectivity", i.e. the measurement of the brain activity when the brain is at rest.

As fUSI studies fluctuations in cerebral blood volume (CBV), its feasibility depends on the ability to observe the same imaging region during the whole time of acquisition, i.e. for durations of the order of the minute or even ten minutes. This is particularly important in the case of the mapping of functional brain connectivity where the patient is examined at rest, in the absence of external stimulation. As a matter of fact, the results are based on the correlations between the CBV signals from different areas of the brain. It is thus essential that the imaging region remains static.

For the first preclinical experiments in small animals, this was made possible by fixing the probe in a 3D printed mold, mounted on a motorized system, allowing it to be positioned in a plane of interest and to keep it in place throughout the acquisition. The rat or mouse was immobilized by a stereotaxic frame. In more recent experiments, metal, plexiglass or dental cement supports surgically implanted directly on the skull of the animal were developed, the probe then attaching to this frame with magnets or screws. For the intraoperative proof of concept in humans, the patient's head was locked in a stereotaxic frame, and the probe held by an articulated mechanical arm. In all these configurations, the skull was open or surgically thinned.

All these methods thus have in common that they are invasive and involve surgery. They are obviously inapplicable to infants.

In addition, although some functional imaging techniques such as fMRI have no other choice than to immobilize infants with straps, it is still desirable to constrain them as little as possible. Techniques aimed at preventing head movements should therefore be avoided as much as possible. This is especially true in the case of premature babies who need to be placed in an incubator to complete their development. Devices for monitoring heart rate, respiration and blood oxygen saturation are also added, as well as possibly syringe pumps to administer food and appropriate treatments.

These strong constraints both on the patient's fragility and on his immediate environment make it necessary to design an ultrasound probe holding device configured to attach to the head of the infant that may be usable in an incubator with the existing equipment, that doesn't hinder the movements of the infant, and that ensure the ultrasound probe stability during acquisition, typically for a duration of ten minutes.

The published utility model <CIT> describes a device, or head mount, for receiving a sonographic probe for setting and fixing it on the skull of an infant with a holding device which can be attached to the latter and on which the measuring probe rests adjustably in a probe bearing.

In a recent publication (See <NPL>)), it was reported a customized flexible and non-invasive head mount for real time functional ultrasound imaging of a newborn brain. More specifically, it was demonstrated that fUSI is feasible by ultrafast Doppler (UfD) imaging of the brain microvasculature, further combined with simultaneous continuous video-electroencephalography (EEG) recording and. To avoid motion artifacts usually encountered while manually handling the probe, a new ultrasound probe holding device was designed. The ultrasound probe was inserted into a semirigid biocompatible silicon head mount enabling a single-plan pivot, which was filled with ultrasound gel. This device was held together with EEG electrodes using soft non adhesive strips. This simple system has shown a very good robustness and first results of fUSI on newborns were obtained.

However, head mounts of the prior art have shown some drawbacks that limit their use. In particular, such head mounts can slide on the head skin, and the acoustic gel can leak out of the head mount. This has the effect of degrading the quality of the image, and rendering unusable any EEG electrodes used simultaneously. In addition, the installation of the device is tedious and can hardly be done alone.

The present disclosure relates to an ultrasound probe holding device configured to attach to the head of an infant, that ensures a very good stability of the ultrasound probe during acquisition, while enabling an easy installation and limiting the pressure exerted on the head of the infant.

In what follows, the term "comprise" is synonym of (means the same as) "include" and "contains", is inclusive and open, and does not exclude other non-recited elements. Moreover, in the present disclosure, when referring to a numerical value, the terms "about" and "substantially" are synonyms of (mean the same as) a range comprised between <NUM>% and <NUM>%, preferably between <NUM>% and <NUM>%, of the numerical value.

According to a first aspect, the present disclosure relates to an ultrasound probe holding device configured to attach to the head of an infant for transfontanellar imaging, comprising:.

An infant in the present description is a young child typically below <NUM> months of age, before the fontanel closes and therefore for which transfontanellar imaging is possible. It includes premature and full-term neonates.

The applicant has shown that such original arrangement of the ultrasound probe holding device according to the present description enables to finely adjust the pressure applied to the head of the infant, thanks to the repellent force exerted between the pad squeezer and the head pad when the device holder exerts the downward force on the pad squeezer.

The ultrasound probe holding device may be configured to attach to the head of an infant for transfontanellar imaging through any fontanel of the head of the infant, i.e. the anterior fontanel, the posterior fontanel, the sphenoid fontanels or the mastoid fontanels.

According to one or further embodiments, the repellent force has an amplitude which increases non-linearly with a distance between the head pad and the pad squeezer defined along said guidance axis. This enables to further limit the pressure exerted on the head of the infant. In some embodiments, the repellent force results in a configuration where, in operation, there is no or almost no contact in the direction of the guidance axis between the pad squeezer and the head pad.

According to one or further embodiments, the amplitude of the repellent force is such that the resulting pressure exerted on the head of the infant by the head pad ranges from around <NUM> kPa to around <NUM> kPa (<NUM> kPa = <NUM> N/m<NUM>), more advantageously from around <NUM> kPa to around <NUM> kPa. The pressure exerted on the head of the infant should be large enough to produce a sufficient stiction but not too large to keep the infant comfortable.

According to one or further embodiments, the axial guidance of the head pad along said guidance axis has a lateral mechanical backlash, enabling a relative movement between the pad squeezer and the head pad in a plane substantially perpendicular to the guidance axis. Such lateral backlash enables the possibility for the infant to slightly move his head while a stiction (i.e. a static friction) is preserved between the head pas and the head, thanks to the force exerted by the device holder.

According to one or further embodiments, such lateral mechanical backlash is smaller than around <NUM>.

According to one or further embodiments, such lateral mechanical backlash is greater than around <NUM>.

According to one or further embodiments, the repellent means comprise repellent magnets arranged respectively on the head pad and on the pad squeezer. The applicant has shown that repellent magnets are compatible with a lateral mechanical backlash of the axial guidance. Further, magnets enable exerting a repellent force whose amplitude increases nonlinearly with a distance between the head pad and the pad squeezer, along the guidance axis.

However, other repellent means are possible, e.g. repellent springs, cushioning material such as foam, cushion with elastic walls and liquid filling, cushion with gas filling.

According to one or further embodiments, a surface of the head pad configured to be in contact with the infant head is curved to adapt to the shape of the head. This enables an easy installation on the infant head, a distribution of the pad pressure over a large area of skin, and important stiction. For example, said curved surface has curvatures different in two perpendicular planes, typically coronal/sagittal planes. Such curvature may be chosen according to the age of the infant and its particular anatomy, so that using the device at different age only implies to choose the adapted head pad among a predefined panel, the other components remaining unchanged.

According to one or further embodiments, the surface of the head pad configured to be in contact with the infant head has a square section or a round section. The square section may prevent the rotation around the guidance axis of the head pad/or probe, for imaging preferentially in coronal/parasagittal sections, while the round section may enable imaging any section.

According to one or further embodiments, the device holder comprises a flexible material harness attached to the pad squeezer. Such flexible material may be fabric or plastic. In some embodiments, said harness may be removably attached to the pad squeezer, for example attached to hinged tabs of the pad squeezer. In other embodiments, said harness and the pad squeezer may be made in one piece.

According to one or further embodiments, the device holder is configured to attach electrodes for electroencephalography. This enables electroencephalography imaging in addition to ultrasound imaging.

According to one or further embodiments, the ultrasound probe holding device further comprises a probe holder configured to receive an ultrasound probe, wherein said probe holder is fastened to the head pad.

According to one or further embodiments, the probe holder is removably fastened to the head pad. For example, the probe holder is removably fastened to the head pad using magnets. When fastened to the head pas, the probe holder should be strongly fixed to avoid any possible move.

According to one or further embodiments, the probe holder and the head pad may also be made in one piece.

According to one or further embodiments, when the probe holder is removably fastened to the head pad, the probe holder can be fastened to the head pad in at least two positions, said at least two positions resulting from a rotation around an axis parallel to the guidance axis. For example, the probe holder can be fastened to the head pad in two positions resulting from a <NUM>° rotation. It enables, in operation, imaging different planes in the brain, for example coronal and sagittal sections.

According to one or further embodiments, the probe holder can be mounted rotatable in the head pad, around an axis parallel to the guidance axis.

According to a second aspect, the present disclosure relates to an ultrasound device for transfontanellar imaging of an infant, comprising:.

According to one or further embodiments, the ultrasound probe can be rotated around a rotation axis substantially perpendicular to said guidance axis.

According to one or further embodiments, the ultrasound probe can be rotated around a rotation axis substantially parallel to said guidance axis.

According to one or further embodiments, the ultrasound probe holding device comprises a probe holder and the ultrasound probe is configured to be removably fastened to said probe holder.

According to one or further embodiments, the ultrasound probe comprises a matrix of transducers and said matrix of transducers is rotatable around an axis substantially perpendicular to said guidance axis and/or is rotatable around an axis substantially parallel to said guidance axis.

According to a third aspect, the present disclosure relates to an ultrasound imaging system for transfontanellar imaging of an infant comprising:.

According to a fourth aspect, the present disclosure relates to a method for ultrasound brain imaging of an infant using the ultrasound imaging system of the third aspect, comprising:.

In the method according to the present description, the downward force applied on the pad squeezer along the guidance axis using the holding device enables a stiction (i.e. static friction) between the head of the infant and the head pad, thus limiting any move of the head pad, while keeping a controlled pressure on the head of the infant thanks to the repellent means of the ultrasound probe holding device.

According to one or further embodiments, the method further comprises adjusting the position of the head pad to adjust the field of view of the ultrasound probe. Such step may be made by acquisition of ultrasound images prior to applying the downward force on the pad squeezer using the holding device.

According to one or further embodiments, the method further comprises rotating the ultrasound probe around an axis substantially perpendicular to said guidance axis to image different tilted planes of the brain.

According to one or further embodiments, the method further comprises rotating the ultrasound probe around an axis substantially parallel to said guidance axis from at least one first position to a second position in order to image tilted coronal and sagittal sections of the brain.

According to one or further embodiments, the method further comprises electroencephalographic measurements using electroencephalographic electrodes arranged on said holding device.

Other advantages and features of the invention will become apparent on reading the description, illustrated by the following figures which represent:.

<FIG> illustrate respectively third quarter right and third quarter left exploded views of an ultrasound device <NUM> according to an embodiment of the present description.

The ultrasound device <NUM> in the example of <FIG> comprises an ultrasound probe <NUM> configured to emit ultrasound waves towards the brain of the infant and receive backscattered ultrasound waves and an ultrasound probe holding device <NUM> comprising a head pad <NUM> and a pad squeezer <NUM>. The head pad <NUM> is configured to be in contact with the head of the infant and comprises a central opening <NUM>. The pad squeezer <NUM> comprises a central opening <NUM> and is configured to cooperate with the head pad <NUM> to allow an axial guidance of the head pad along a guidance axis Δ. In operation, the guidance axis Δ is substantially perpendicular to a surface tangent to the head of the infant. As it is described in greater details below, the ultrasound probe holding device further comprises a device holder (not shown in <FIG>) configured to be attached to the head of the infant and to exert a downward force on the pad squeezer, along the guidance axis Δ. In the example of <FIG>, the ultrasound probe holding device <NUM> further comprises a probe holder <NUM> configured to receive the ultrasound probe <NUM>, wherein said probe holder is configured to be fastened to the head pad <NUM>.

According to some embodiments, the axial guidance of the head pad along said guidance axis has a lateral mechanical backlash, enabling a relative movement between the pad squeezer and the head pad in a plane substantially perpendicular to the guidance axis. For example, the lateral mechanical backlash is smaller than around <NUM> and greater than around <NUM>. Such lateral backlash enables the possibility for the infant to slightly move his head while a stiction (i.e. a static friction) is preserved between the head pas and the head, thanks to the force exerted by the device holder.

<FIG> illustrate respectively exploded views, top view and side view of details of the head pad <NUM> and the pad squeezer <NUM> of the ultrasound probe holding device <NUM> illustrated in <FIG>.

<FIG> illustrates an exploded view of the probe holder <NUM> as shown in <FIG>.

<FIG> and <FIG> illustrate two different views of an ultrasound device <NUM> as shown in <FIG> arranged on the head <NUM> of an infant using a device holder <NUM> and <FIG> illustrates an ultrasound imaging system <NUM> for transfontanellar imaging using an ultrasound device according to the present description.

The ultrasound imaging system of <FIG> comprises an ultrasound device <NUM> according to the present description, with an ultrasound probe configured to emit ultrasound waves towards the brain of the infant <NUM> and receive backscattered ultrasound waves. It further comprises an electronic module <NUM> configured to receive electrical signals transmitted by the ultrasound probe <NUM> and generate converted signals, wherein said electrical signals result from the detection of the backscattered ultrasound waves, and a computer <NUM> configured to receive the converted signals from said electronic module and calculate imaging data from said converted signals.

As further described in details below, in the embodiments illustrated in <FIG>, <FIG> and <FIG>, the ultrasound probe <NUM> is removable from the probe holder <NUM> and the probe holder <NUM> is removably fastened to the head pad <NUM>. However, in some embodiments not shown in the figures, the probe holder <NUM> and the head pad <NUM> may form a single piece. In other words, the ultrasound probe <NUM> may be directly mounted on the head pad <NUM> configured as the probe holder. Further, the ultrasound probe <NUM> may be fixed to the probe holder, while still movable in rotation, as explained in details below.

As shown in <FIG>, the ultrasound probe holding device <NUM> further comprises repellent means configured to exert a repellent force between the pad squeezer <NUM> and the head pad <NUM> when the device holder <NUM> (not shown) exerts a downward force on the pad squeezer <NUM>. In the present description, a downward force is understood as a force exerted along the guidance axis, towards the head of the infant.

For example, the repellent means comprise repellent magnets <NUM>, <NUM> arranged respectively on the head pad <NUM> and on the pad squeezer <NUM>. More specifically, in the example of <FIG>, the head pad is provided with a plurality of repellent magnets, <NUM> in this example. Each magnet <NUM> is in this example arranged in a protrusion <NUM> to cooperate with the corresponding repellent magnet <NUM> fitted in a slot <NUM> of the pad squeezer <NUM>. For example, the poles of the magnets <NUM> of the pad squeezer <NUM> are oriented so as to repel out the magnets <NUM> of the head pad <NUM>, as illustrated in <FIG> with the double arrows. The magnets <NUM> and <NUM> therefore act as compressed springs and tend to move the pad squeezer <NUM> away from the head pad <NUM>. Thus, the more the pad squeezer <NUM> is pressed on the head pad <NUM>, the more the head pad <NUM> is pressed against the skull of the infant.

The use of magnets as repellent means enables exerting a repellent force having an amplitude which increases non-linearly with a distance between the head pad and the pad squeezer defined along said guidance axis. Such distance is for example defined between each of the magnets <NUM> and <NUM>. This enables to further limit the pressure exerted on the head of the infant. Practically speaking, the magnets may be configured to prevent any direct contact between the head pad and the pad squeezer, along the guidance axis. This consideration enables to perfectly control the pressure exerted on the head of the infant. This, combined with the backlash between the pad squeezer and the head pad, also enable substantial motion of the pad squeezer <NUM> in a plane perpendicular to the guidance axis while maintaining the pressure exerted by the head pad <NUM> on the head of the infant. This consideration enables to maintain the head pad <NUM> and the probe holder <NUM> in a fixed position on the head of the infant, regardless of motion of the pad squeezer <NUM> and/or the device holder <NUM>, for example due to the motion of the infant head.

Of course, magnets could be replaced by other known repellent means such as springs or a cushioning material.

As explained before, in the example of <FIG>, the head pad <NUM> and the probe holder <NUM> form two separate parts. This configuration facilitates the installation and particularly the provision of the ultrasonic gel in operation. The head pad <NUM> is configured to be attached to the head of the infant and to receive, in operation, the ultrasonic gel in the cavity formed by the opening <NUM> and the skin of the head (not shown). As shown in <FIG>, the head pad <NUM> may comprise a 3D printed plastic support <NUM>, to which a silicone pad <NUM> is attached. The head pad <NUM> may be attached to the probe holder <NUM> with magnets (not shown).

As shown in <FIG>, the shape of the head pad <NUM> may be suitable for most infants. The surface of the head pad configured to be in contact with the infant head may be curved and the curvature of said surface may be different in the sagittal and coronal directions, the skull of the infant being not spherical but rather ovoid. The data of two radii of curvature therefore makes it possible to generate as many geometries as necessary to adapt to all anatomies. For a given curvature, a counter-mold may be 3D printed, taking in hollow the desired shape of the head pad.

In the embodiments shown in <FIG> and <FIG>, the different pieces of the holding device have a square section. Obviously, the description is not limited to a square shape and the head pad <NUM> and/or the pad squeezer <NUM> may have different shapes, for example round sections. All embodiments described in the present description may apply indifferently for different shapes of the head pad and/or the pad squeezer.

As detailed below, in order to secure the head pad <NUM> to the infant's head, a pad squeezer <NUM> is positioned over the head pad. As shown in the figures, the pad squeezer <NUM> may comprise a frame <NUM> with articulated tabs <NUM>, <NUM> configured to rest for example respectively on the forehead and occiput, as shown in <FIG>, <FIG>.

As shown in <FIG>, <FIG>, the pad squeezer <NUM> is attached to the head via a device holder <NUM>, for example a harness. The harness may comprise a flexible material, such as fabric or plastic. In the example shown in <FIG>, <FIG>, the harness <NUM> comprises straps that pass through the hinged tabs <NUM>, <NUM> of the pad squeezer <NUM> and attach to it, for example with fastener strips, such as Velcro ® strips. In some embodiments however, the harness and the pad squeezer may be made in one piece. As previously explained, the use of repellent magnets as described above can apply the necessary force to the head pad <NUM> to keep it in place, regardless of the tension of the harness straps.

<FIG> illustrates in more details a non-limitative example of a probe holder <NUM> configured to hold an ultrasound probe <NUM>. In this embodiment, the probe holder <NUM> is independent of the head pad <NUM>.

In the example shown in <FIG>, the ultrasound probe <NUM> comprises ultrasonic transducers arranged in a matrix <NUM>, for example a linear matrix, an electric probe cable <NUM> shown in part in <FIG>, a strapping <NUM>, said strapping being articulated along an axis Δ1, perpendicular to the guidance axis. The strapping <NUM> comprises in this example a mortise <NUM> configured to receive a tenon <NUM> of a rotation blocker module <NUM> of the probe holder. The probe holder <NUM> further comprises a body <NUM>. The rotation blocker module <NUM> may be fixed to the body <NUM> by sliding in two rails along the axes indicated in dashes in <FIG> and magnetized to the body of the probe holder. Plain arrows indicate the positions of the magnets. The probe holder <NUM> may further comprise a locking crank <NUM> fitted with a screw inserted into the tenon <NUM>, and sliding in an arcuate rail. The crank <NUM> makes it possible to tighten the screw, which then firmly places the tenon on the body of the module and thus prevent rotation of the probe.

In the embodiment shown in <FIG>, the rotation blocker module <NUM> has been designed to be easily replaced. The rail and magnet system enables module exchanges to be made directly in the patient's room.

A probe motorization system could also be designed and the manual rotation of the probe replaced with an electronically controlled rotation, using for example a servomotor. Such electronically controlled rotation could facilitate ultrasound tomography. As a matter of fact, by acquiring plane by plane B-Mode and Doppler images, it will become possible to reconstruct a 3D volume from these acquisitions.

Alternatively, an ultrasonic probe including a rotatable matrix of transducers may be used for acquisition of the plane by plane B-Mode and Doppler images.

A procedure for installing an ultrasound probe using an ultrasound probe holding device according to the present description is greatly simplified.

First, a head pad <NUM> for example as shown in <FIG> may be placed on the fontanel of the infant. <FIG>, <FIG> illustrate transfontanellar imaging through the anterior fontanel; however, transfontanellar imaging may be performed through any fontanel of the infant. Then the pad squeezer <NUM> is positioned as well as the harness <NUM> (<FIG>, <FIG>), thus placing the head pad <NUM> on the head <NUM> of the infant. The skin of the head together with the head pad <NUM> forms a sealed cavity which can then be filled with ultrasound gel. The probe holder <NUM> as for example described in <FIG> may then be fixed to the head pad using for example magnets fitted in the inner part of the head pad <NUM>; the head pad <NUM> may thus be adjusted to accommodate the probe holder <NUM> with as little play as possible. The ultrasound probe <NUM> can then be tilted around the axis Δ1 (<FIG>) to image the desired plane. If necessary, by adjusting the pad squeezer <NUM> and the straps of the holder <NUM>, everything can be manually shifted slightly in order to properly center the probe on the fontanel.

In the example shown in <FIG>, the possibility of detaching the probe holder <NUM> from the head pad <NUM> allows to add gel if necessary, without changing the position of the head pad <NUM>. In addition, the double curvature of the head pad allows a good seal of the gel reservoir, which allows for example to simultaneously use an electroencephalogram and bring the electrodes as close as possible to the head pad without risk to create electrical bridges between the electrodes via the gel. Further, an attachment of the pad squeezer using a harness as shown in <FIG>, <FIG> is very quick to implement, such harnesses being available in different sizes to best adapt to the infant's morphology. The total weight of an ultrasound device <NUM> as shown in <FIG>, <FIG> may be less than around <NUM>.

The ultrasound probe holding device has been designed in a modular fashion making it possible to improve the fixation of the pad squeezer <NUM> without touching the head pad <NUM>. Further, the compactness of the ultrasound device is improved.

The ultrasound probe holding device according to the present description has made it possible to significantly increase the quality of the ultrasound images, and to achieve long recordings of up to <NUM> minutes.

Using an ultrasound imaging system as shown in <FIG> with an ultrasound device as described in the present description, first studies on the infant's sleep phases were carried out. Sequence formed by the repetition of a basic block were performed, wherein each block consists of an ultrafast Doppler acquisition composed of three plane waves tilted at [-<NUM> °, <NUM> °, <NUM> °], emitted with a pulse repetation frequency of <NUM>, and resulting on a framerate of <NUM>. These plane waves are emitted during <NUM>, allowing acquisition of 342images with a depth of <NUM>. A break of <NUM> is then made in order to leave time for the transfer of the data, their beamforming and their saving on a hard disk. This basic block therefore has a total duration of <NUM>. The effective transmission time of <NUM> was selected to enable registration of at least one cardiac cycle, infants having a heartbeat of <NUM> beats per minute. This basic block is repeated for <NUM>, which ultimately gives a film of <NUM> Power Doppler images with a rate of <NUM>.

After the installation of the ultrasound probe holding device, electroencephalography (EEG) electrodes may be installed on the scalp of the infant, at the locations remaining available on the skin. Those electrodes may also be part of the device holder, and installed in the same time than the ultrasound probe holding device is secured to the head of the infant. EEG electrodes may then be connected to an EEG recorder for joint EEG-fUSI recording combining ultrafast Doppler (UfD) imaging of the brain microvasculature and simultaneous continuous video-electroencephalography (EEG) recording.

Claim 1:
An ultrasound probe holding device (<NUM>) configured to attach to the head of an infant for transfontanellar imaging, comprising:
a head pad (<NUM>) configured to be in contact with the head of the infant and comprising a central opening (<NUM>), wherein the head pad is configured to receive an ultrasound probe;
a pad squeezer (<NUM>), comprising a central opening (<NUM>) and configured to cooperate with the head pad to allow an axial guidance of the head pad along a guidance axis (Δ) substantially perpendicular to a surface tangent to the head of the infant;
a device holder (<NUM>) configured to be attached to the head of the infant and exert a downward force on the pad squeezer, along said guidance axis; and
repellent means configured to exert a repellent force between the pad squeezer and the head pad when the device holder exerts the downward force on the pad squeezer.