WO2025109313A1

WO2025109313A1 - Breast density measurement device

Info

Publication number: WO2025109313A1
Application number: PCT/GB2024/052926
Authority: WO
Inventors: David Gibbins; Leigh CORNOCK; Stephen Chambers; Andrew Adams; Arthur MAGILL; Rhodri BEVAN; Christian Graff; Brandon Corbett
Original assignee: Micrima Ltd
Current assignee: Micrima Ltd
Priority date: 2023-11-24
Filing date: 2024-11-19
Publication date: 2025-05-30
Anticipated expiration: 2026-05-24

Abstract

A probe for an apparatus for measuring the density of breast tissue. The probe comprises two moveably coupled rigid arms, each having an engagement end, where the arms can be moved relative to each other to modify a distance between the engagement ends within a pre-determined range. The probe also comprises radiofrequency antennas disposed at the engagement end of each arm.

Description

Breast Density Measurement Device

FIELD OF INVENTION

The invention relates to a probe and system used for breast health measurements. In particular, the invention relates to a probe and system for measuring breast tissue density.

BACKGROUND

Breast Density is a measure of the extent of radio dense fibro-glandular tissue vs fat tissue in the breast. A ‘dense’ breast will contain more fibro-glandular tissue than a less dense breast, which will contain a higher volume of fat tissue. A meta-analysis of breast cancer risk factors indicates that the risk of breast cancer from high breast density is twice higher than other risk factors, except family history of the disease in women aged 40-49 years.

High breast density reduces mammographic sensitivity and limits earlier detection of breast cancer in 2D Full Field Digital Mammography (FFDM) through ‘masking’ effects.

Thus, there is a need for an improved system and probe for measuring breast density.

SUMMARY OF INVENTION

The invention is defined by the claims.

In particular, the invention provides a probe for an apparatus for measuring the density of breast tissue, the device comprising: two moveably coupled rigid arms, each having an engagement end, wherein the arms can be moved relative to each other to modify a distance between the engagement ends within a pre-determined range; and radiofrequency, RF, antennas disposed at the engagement end of each arm.

Having the two arms be rigid, but moveable, means that the engagement ends can be comfortably engaged with the surface of the breast whilst ensuring the distance between the engagement ends (and thus the RF antennas) does not change due to the forces exerted on the engagement ends by the surface of the breast. It has been realized that the distance between the engagement ends (and thus the antennas) is an important factor in measuring breast tissue density. This is because the distance between the engagement ends should be kept constant during the measurements. Keeping the arms rigid and moveable significantly reduces the likelihood that the distance changes during the measurements.

The device may also comprise a distance sensor configured to determine the distance between the engagement ends. Of course, it will be appreciated that such a sensor may differ based on the particular form of the device used. For example, if pivoting arms are used, a sensor measuring the angular separation of the arms can be used to determine the distance. Similarly, if the arms move linearly relative to each other, a linear movement sensor can be used to determine the distance.

The arms being moveably coupled to each other means that they can be rotated and/or translated relative to each other within. Such rotations/translations result in the distance between the engagement ends being modified (i.e., increased/decreased) within a pre-determined range of distances, where the pre-determined range is based on the limited range of motion of the moveably coupled arm(s).

It will be appreciated that the arms do not have to be directly coupled to each other and can, instead, be indirectly coupled to each other via another structure. For example, the arms could be both directly, and moveably, coupled to a rigid body. Thus, the arms can move relative to each other by moving relative to the rigid body.

The device may be a handheld device.

The predetermined range may be based on known breast diameters. For example, the predetermined range may be less than or equal to 300mm, 275mm, 250mm or 225mm.

The engagement ends of the two arms are arranged such that, when the distance between the engagement ends is within a pre-determined range, RF signals transmitted from one of the antennas can be received by the other antenna.

The probe may make direct contact with the surface of the breast. However, in some cases, the probe may not need to make direct contact with the breast for the measurements.

Each arm may comprise a portion adjacent to a corresponding distal end of the arm, opposite the engagement end. The distance between the portions of the arms may be larger than the distance between the engagement ends for any distance between the engagement ends which is within the pre-determined range. In other words, the arms may be structured such that a gap formed between the arms is wider than the distance between the engagement ends.

Having the distance between the portions be larger than the distance between the engagement ends means that a gap is provided between the arms. The gap (i.e., area/space) provided by the probe enables the antennas to be more easily placed on the breast as the operator can hold the arms during use without interfering with the breast. Additionally, this gap can accommodate the breast more comfortably when the probe is engaged with the breast with a minimized risk of trapping and/or pinching.

The two arms may be rotatable, or translatable, relative to each other such that, in a position in which the engagement ends of the arms are spaced apart from each other by a predetermined position suitable for contacting a human breast, each arm describes a path that defines a point of widest separation from a corresponding part of the respective other arm, wherein the point of widest separation is closer to a distal end of the arms, opposite the engagement ends, than to the engagement ends of the arms.

The two arms may be rotatable, or translatable, relative to each other such that, in a position in which the engagement ends of the arms are spaced apart from each other by a predetermined position suitable for contacting a human breast, a widest point, measured in a direction orthogonal to a direction from the distal end to a mid-point between the engagement ends, of an area enclosed by the arms is wider closer to the distal ends than closer to the engagement ends.

The arms may be rotatably coupled to each other via a pivot.

One, or both, of the arms may be connected to the pivot such that they can rotate relative to the pivot’s axis. This rotation enables the distance between the engagement ends of the arm (i.e., the separation of the engagement ends) to be modified. As such, in use, the device can be “opened” by rotating the arm(s) outwards, moved towards the breast and then “closed”, by rotating the arm(s) inwards, to engage with the breast.

Of course, it will be appreciated that two pivots can be used, each one corresponding to one of the arms.

The probe may further comprise an angular sensor configured to determine the relative angular position of the arms.

When using a pivot (or other rotational coupling), the angular separation of the arms can be translated into a distance between the engagement ends (e.g., calculated from the known shape of the arms or using a pre-determined look-up table). As the arms are rigid, the distance at a particular angular separation will not change due to, for example, flexing of the arms when engaging the breast. The probe may further comprise a button configured to provide an actuation signal based on the button being actuated.

The probe may further comprise a brake for enabling and disabling relative movement between the arms.

As previously discussed, when measuring breast density using RF antennas, it is important to keep the distance between the antennas constant. As such, use of the brake during a measurement will prevent the arms from being moved, thus preventing the distance between the engagement ends from being modified. As such, use of the brake can improve measurements performed with the measurement device.

The probe may be arranged such that, when the brake disables the relative motion between the arms, the arms can be moved away from each other when a force is applied to the arms that is higher than a predetermined force.

Thus, the arms can be pulled away from each other even when the brake is actuated. For example, this may be advantageous if the probe causes discomfort on a subject (e.g., pinching/trapping of the breast).

For example, the brake may be configured to overcome up to the predetermined force (e.g., via friction). As such, when a force is applied to the arms which exceeds the predetermined force, the arms can be moved.

In another example, a safety feature may be included which disengages the brake from the arm(s) when a force exceeding the predetermined force is applied. When the arms are disengaged from the brake, relative movement is re-established.

When the brake is actuated (thereby disabling the movement), the arms may only be able to move away from each other when the force is higher than the predetermined force (i.e., not closer to each other).

The probe may further comprise a contact sensor configured to detect contact between the engagement ends and a breast.

The contact sensor may comprise one or more of a pressure sensor disposed at the engagement end of each of the arms and a light sensor disposed at the engagement end of each of the arms.

The contact sensors provide information which enables the operator to ensure full contact of the engagement ends, and thus the antennas, with the breast.

The antennas may have a bandwidth including the 3 - 8 GHz band.

The antennas may have a radiation pattern that varies in power by less than 3dB over a pre-determined angular beam width, relative to the antenna boresight, and within the pre-determined range in the 3 - 8 GHz band. Thus, in essence, a wide-beam antenna is provided. This means that the magnitude of the angle between the boresight of both antennas can be more than 0 (e.g., up to 30 degrees) without significantly affecting the measurements. This enables the arms to be rotated relative to each other (e.g., using the pivot) without having to rotate the antennas separately to ensure direct line of sight between both antennas. Additionally, this allows the antenna’s faces to be positioned at an angle which more naturally aligns with the shape of a breast compared to parallel antennas.

Depending on the form of the probe (e.g., max angular separation of the antennas), the antennas may have a radiation pattern that varies by less than 3dB over a pre-determined beam width of ±30, ±25, ±20 or ±15 degrees from the antenna boresight in the 3 - 8 GHz band within the pre-determined range. The pre-determined range may have a maximum distance of, for example, 100mm, 125mm, 150mm, 175mm, 200mm, 225mm, 250mm, 275mm or 300mm. The pre-determined range may have a minimum distance of, for example, 0mm, 10mm, 20mm, 30mm, 40mm or 50mm.

The probe may further comprise an electrically insulating and bio-compatible radome covering each antenna, wherein each radome is made of material having a relative permittivity of at most 30 in the 3 - 8 GHz band.

A radome is a structure made of material which is relatively transparent to radio waves. In other words, the radome allows radio waves to pass through. In this case, the radomes are not only used to protect the antennas from the environment, but are also used to protect the breast from the antennas. In particular, the radomes protect the breast from metallic components of the antennas, and thus potentially harmful electrical contacts.

It will be appreciated that, depending on the particular use case for the probe, each radome may be made of material having a relative permittivity of at most 10, 15, 20 or 25 in the 3 - 8 GHz band. In an example, the relative permittivity of the material used in the radome is 9.5.

Each radome may comprise an engagement surface for engaging with the breast and an inner surface facing towards the respective antenna, wherein the thickness between the inner surface and the engagement surface is at least 1 mm.

Having radomes with a thickness of at least 1 mm between the antennas and the breast provides some separation between the breast and the reactive near field of the antenna. This makes the performance of the antenna more predictable and less affected by the material in contact with it. Of course, it will be appreciated that other thicknesses may also be appropriate. For example, the thickness may be 2mm, 3mm, 4mm or 5mm.

The invention also provides a system for measuring the density of breast tissue, the system comprising: the probe; and a control unit configured to actuate one of the RF antennas of the probe when an actuation signal is received.

The control unit may be configured to actuate the brake of the probe based on the actuation signal being received.

The control unit may be further configured to determine a percentage of S11 response in the data signal from the antennas that is below -10dB in the 3 - 8 GHz band and determine that physical contact occurs between the engagement ends and the breast based on the percentage of S11 response being below a threshold percentage.

S11 response is commonly known as the reflection coefficient of an antenna and indicates how much power is reflected by the antenna, and thus not radiated (or absorbed as losses). S11 is commonly measured in decibels (dB) relative to frequency.

It has been realized that a physical contact between the engagement ends and a breast can be determined when the percentage of S11 response below -10dB (in the 3 - 8 GHz band) is less than a threshold percentage.

It is proposed to use 20% as the threshold percentage. Of course, it will be appreciated that other threshold percentages could be used (e.g., between 10% and 30%, between 15% and 25%, etc.).

Full physical contact of the engagement ends with the surface of the breast is important during the measurement to ensure that the amount of energy transferred into the breast is maximised, giving the largest signal to noise ratio and thus providing accurate measurements.

S21 transmission refers to the power transferred between two antennas. It is desired that the contact between the probe and breast tissue is such that energy transfer from the transmitting antenna into breast tissue is maximised. In one embodiment the quality of the contact between the probe and breast tissue is assessed using an S21 measurement. In one embodiment S21 measurement values, which may be mean or median S21 measurement values over a range of frequencies, at one frequency or frequency range are compared with S21 measurement values at another frequency or frequency range. Either or both S21 measurement values may be mean or median S21 measurement values over a range of frequencies. Alternatively, a measured S21 response is compared to a known/ template S21 response of the probe. This template response may be a response of the probe measured when the probe is not in contact with tissue. If a deviation of the frequency response by a predetermined magnitude from the template is detected, the embodiment is configured to conclude that energy transmission into tissue is satisfactory and that, consequently a good fit of the probe to breast tissue is being achieved. The required magnitude of the deviation and/or the frequency or frequency range used for assessing the deviation, may be determined experimentally and pre-set within control apparatus of the probe.

Of course, it will be appreciated that the other contact threshold values smaller than 10dB may be used in the equation above depending on the particular accuracy needed. For example, the contact threshold may be 5dB, 6dB, 7dB, 8dB or 9dB.

The invention also provides a probe for obtaining clinical measurements of a subject when in contact with the subject, the probe comprising a radiofrequency, RF, antenna covered by a radome, the radome having an engagement surface for engaging with the subject and an inner surface closest to the antenna, wherein the thickness of the radome between the engagement surface and the inner surface is at least 1mm.

The clinical measurements may be, for example, measurement used to determine breast tissue density. The radome protects the subject from the electronic components of the antenna. Additionally, the radome minimizes the effects of the reactive near field radiation thus improving the reliability of the measurements.

Preferably the antenna has a bandwidth in the microwave range. Even more preferably, the antenna has a bandwidth in the 3 - 8 GHz range.

BRIEF DESCRIPTION OF FIGURES

Exemplary embodiments of the invention are described below with reference to the accompanying figures, in which:

Figure 1 illustrates a probe for measuring breast tissue density;

Figure 2 illustrates the probe of Figure 1 at a maximum and a minimum separation;

Figure 3 illustrates the radiation pattern of an antenna;

Figure 4 illustrates an area of sensitivity within breast tissue;

Figure 5 illustrates a cross section of the engagement end of an arm;

Figure 6 shows a cross-section of an exemplary braking mechanism; and Figure 7 illustrates a system for measuring breast tissue density.

DETAILED DESCRIPTION

A probe for an apparatus for measuring the density of breast tissue is disclosed herein. The probe comprises two moveably coupled rigid arms, each having an engagement end for engaging with tissue on a side of the human breast, where the arms can be moved relative to each other to modify a distance between the engagement ends within a pre-determined operating range. The probe also comprises radiofrequency antennas disposed at the engagement end of each arm.

Figure 1 illustrates a probe 100 for measuring breast tissue density. The probe 100 has two arms 102 rotatably coupled about a pivot 112. Each arm 102 has an antenna 106 at an engagement end 104 of the arm 102 covered by a radome 108. The arms 102 also have a capture buttons 110. A braking mechanism 114 (i.e., a brake) is also provided where the arms 102 are rotatably coupled (i.e., around the pivot 112) to stop the arms 102 from rotating relative to each other.

An umbilical cord 116 is also provided to connect the probe to a control unit (not shown in Figure 1). The umbilical cord 116 may carry data and power lines from the antennas 106 and as well as an actuation line from the capture buttons 110.

An important aspect of the probe 100 is the distance d_e between the engagement ends 104, further defining the distance between the antennas 106.

The arms 102 have a curved profile which gives the probe 100 it’s general look and enables an operator to comfortably grip each arm 102 during use. The arms 100 are offset from the pivot 112 creating a wide space between the arms 102 even when the antennas 106 are at their minimum separation. Although in Figure 1 the two arms are shown at a distance d_e in which the parts of the arms that carry the actuation buttons 110 are approximately parallel to each other, it will be appreciated that, for a smaller distance d_e or indeed for the smallest distance d_e for which the probe 100 is intended to be used, the widest portion of the probe 100 is between the lower left-hand and the lower right-hand corner of the arms. The arms therefore sweep away from the pivot point 112 to a position where the probe has its maximum width. From his position the space laterally occupied by the probe gradually narrows. This allows the operator to comfortably and securely hold the probe 100 during examinations whilst the probe 100 does not occupy a comparable amount of space close to the engagement ends 104. Put in other words, the probe 100 is wider closer to the pivot point 112 than closer to the engagement ends 104.

For this embodiment, the arms 102 may be referred to as calliper arms.

The calliper arms 102 can be hollow to house the braking mechanism 114, an angular separation measurement mechanism and a Printed Circuit Board Assembly (PCBA). The hollow arms 102 can further be used to allow them to secure and guide internal cabling. The cables (in the embodiment including one data and two RF) inside the calliper arms 102 can be arranged to terminate inside the probe 100 in such a manner which minimizes external forces on the respective connectors (e.g., to the PCBA).

In the embodiment, the probe 100 is shown with a body to which the two calliper arms 102 are connected. It will be appreciated that, in alternative embodiments the calliper arms 102 may be connected directly to each other without the need for an extra body.

In use, the operator holds the probe 100 by the calliper arms 102 and actuates the capture buttons 110 to initiate the breast measurement process.

The calliper arms 102 are rigid and support the antennas 106 during the measurement process. The space/gap formed between the components of the probe 100 allows the antennas 106 to be easily placed on the breast. Thus, breast tissue between the arms 102 is easily and comfortably accommodated without risk of trapping or pinching.

In this case, a gap is formed between the arms 102 by the curvature of the arms 102. However, it will be appreciated that the probe may comprise other components to provide the gap. For example, the probe may have a u-shaped body with arms movably coupled to the extremities of the body. The arms could then move (e.g., rotate and/or translate) relative to the body, where the gap is formed by the shape of the body.

In general, the probe uses two rigid arms to provide control over the two antennas such that they can travel/move to and from each other, linearly or angularly. For example, the probe could include a sliding clamp mechanism or a scissor type mechanism to control the movement of the arms.

Linearly, the antennas could be moveably coupled to two clamping surfaces and allowed to move in a linear motion to alter the distance d_e. The two arms could be moveably coupled to the clamping surfaces using a lead screw mechanism or a linear ratchet system.

The example probe 100 shown in Figure 1 requires the operator to rotate the arms 102 relative to each other by applying a torque to the arms 102 from the same side as the antennas 106 (relative to the point of rotation). An alternative design could operate more like scissor, where the distal ends of the arms (opposite the engagement ends 104) are on the opposite side of the pivot 112 to the engagement ends 104. The design could also be implemented with straight rather than curved arms, although this could restrict the gap between the arms.

Breast density can be determined from data signals received from the antennas as. For example, the breast density can be determined from permittivity measurements of the tissue. These properties can be obtained as described in John D. Garrett and Elise C. Fear “Average Dielectric Property Analysis of Complex Breast Tissue with Microwave Transmission Measurements”, Sensors 2015, 15, 1199-1216, the entirety of which is incorporated herein by reference.

Figure 2 illustrates the probe 100 of Figure 1 at a maximum and a minimum separation. Figure 2 a) shows the probe 100 at a minimum separation between the engagement ends 104. Figure 2 b) shows the probe 100 at a maximum separation between the engagement ends 104.

Here, a portion 202 of the arms 102 is defined adjacent to distal ends of the arms 102 opposite the engagement ends 104. As can be seen, the distance d_e between the engagement ends 104 is smaller than the distance d_p between the portions 202 of the arms 102 at both the minimum and maximum separation between the engagement ends 104. This ensures that the operator can hold the arms 102 of the probe during use.

The distance d_p between the portions 202 may refer to distance between two points on the portions 202 forming a path parallel to the path between the engagement ends 104 and/or the antennas. Multiple such paths could be formed between the portions. As such, the path may refer to the path with the minimum distance between the portions, the path with the maximum distance between the portions or the path with an average distance between the portions.

The proportion of the arms 102 attributed to the portion 202 will depend on the particular use case and form of the arms. Generally, the portion 202 should be defined such that each arm can accommodate an operator’s hand during use without interfering with the breast. For example, the portion may be 20mm, 30mm, 40mm or 50mm long from the distal ends in a direction orthogonal to the direction of the distance d_e between the engagement ends 104.

It will be appreciated that the concept of providing a gap within the probe to accommodate the hands during use (i.e., during a measurement) can be applied to other types of probes described herein (e.g., probes using linearly moving arms). The distance d_e between the engagement ends 104 is kept within a predetermined range. This pre-determined range comprises an operational range of distances suitable for measuring breast tissue density.

It is proposed to use an ultra-wide band antenna with an operational frequency band of 3-8 GHz for the probe. For example, the antenna may be a cavity backed slot antenna as described in Gibbins, D. R et al. “A comparison of a wide-slot and a stacked patch antenna for the purpose of breast cancer detection”, IEEE Transactions on Antennas and Propagation, 58(3), 665 - 674.

This antenna has a H-plane radiation pattern that varies by less than 3dB over a beam width of +/- 30 degrees from boresight at all frequencies. The antenna is also relatively compact in nature, 13 x 20 x 25 mm, enabling it to be easily integrated into the engagement ends of the arms. Said antenna is also tuned to radiate effectively into high dielectric media like the human body to enable the maximum amount of energy to enter the body while minimising reflection.

Figure 3 illustrates the radiation pattern 304 of an antenna 106. The antenna 106 provides the means by which Radio Frequency (RF) signals are transmitted into and received from the breast tissue.

It will be appreciated from this figure that, the radiation emitted by the antenna decreases with increasing angular deviation from the boresight direction. If this reduction in power is relatively large, as is the case for antennas with a narrow beam width, there will be a significant difference between the measured magnitudes at an angle 6 and at boresight 302. If the reduction in power is relatively small, as is the case with wide beam antennas, the difference is measured magnitudes (at angle 6 and at boresight 302) is small.

Thus, having a wide beam antenna means that the variation in angle 6 of the antennas relative to each other, as, for example, caused by a tilting of the arms of the probes relative to each other, does not affect the magnitude of the measured RF signal.

Preferably, embodiments use antennae with a wide beam. In particular, antennae that have a minimum beam intensity of -3dB of the boresight intensity at +/- 30 degrees angular deviation from the boresight direction are preferred. As an example, a relatively narrow beam radiation pattern 306 is shown in Figure 3ln the example probe 100 shown in Figures 1 and 2, when the calliper arms 102 are manipulated, the angle 6 of transmission between antennas 106 varies from 0 degrees (antenna boresight) at a minimum separation distance d_e of 20 mm to a maximum angle of 19.01 degrees from boresight at a separation distance d_e of 200 mm. The wide beam produced by the proposed antenna means that the signal transmitted across the breast is substantially the same regardless of angle 6. This ensures that the magnitude of the measurement of the RF signals transmitted through the breast is largely agnostic of the angle 6 between the antennas 106.

Many other wide band antenna designs exist. For example, horn antennas and Vivaldi antennas give a directional pattern that tends to be narrower in width. This would produce greater variation in signal levels when mounted on a rotation-based probe but could be used on a linear probe where view angle does not change. Ultra wideband (UWB) dipole and monopole antennas could also be used, although they tend to have narrower bandwidth, and integration into a probe could be more complex due to the structure of these antennas. Yagi-Uda antennas also offer wide band performance but integration into the probe may be complicated by their relatively large size and configuration.

Wide beam widths can also be achieved using multi antenna arrays, either to cover different angles with different antenna or phased arrays in which the beam can be steered by means of phase control. These solutions are inherently larger in size and more complex than the antenna proposed above, particularly the RF infrastructure required for phase control.

Figure 4 illustrates an area of sensitivity a_s within breast tissue 402. Each RF measurement obtained from the antennas 106 has area of sensitivity a_s within breast tissue 402 that is somewhat cylindrical, where the linear axis of the cylinder is between the faces of the antennas 106 and the antennas 106 are positioned on the circular ends of the cylinder. A single measurement covers only a portion of the breast and could miss areas of dense tissue. This would affect the accuracy of the density assessment. Thus, it is proposed to take multiple measurements around the breast to ensure maximum coverage of the breast volume, ensuring that the assessment of density is representative of the breast.

The probe is used to measure the RF response between two antennas placed on the surface of the breast. In a complete breast scan, it is proposed to perform multiple measurements: four angles around the circumference of the breast, at three different positions along its length, giving a total number of 12 RF measurements per breast.

Complete coverage of the breast could be achieved using an antenna array where multiple antennas are placed against the breast at the same time and simultaneously measure the signal from one or multiple antennas. For example, multiple antennas with different boresight angles could be disposed on each arm, or more arms, with corresponding antennas, could be provided.

In an embodiment, antennas pairs could be used on each side of the breast. Each antenna pair could be mounted on a single arm, or separate arms could be provided for each antenna. The antennas within an antenna pair could be angled relative to one another such that they cover different parts of the breast. The antenna pairs could be mounted onto the arms in much the same way as the single antenna design discussed above. Of course, it will be appreciated that more than two antennas could be used for each side.

In order to achieve full contact with a larger numbers of antennas, two flat rigid planes comprising a plurality of antennas each could be used, where the flat planes are used to engage and compress the breast. The planes could be disposed at the end of each arm.

Figure 5 illustrates a cross section of the engagement end 104 of an arm 102. The antenna 106 is housed within the engagement end 104 of the arm 102 and covered by a radome 108. A 1 mm thick RAM (radar absorbent material) layer 502 is provided between the antenna 106, the arm 102 and the outer portions of the radome 108.

The RAM layer 502 is used to suppress electric fields on the metallic cavity at the back of the antenna 106. This reduces back radiation from antenna 106, thereby reducing the emissions of the antenna 106 into free space. Thus, the RAM layer 502 is used to reduce spurious radiation. Investigations have shown that a 1 mm thick RAM layer 502 can reduce spurious radiation by approximately 5dB. Of course, it will be appreciated that other thicknesses could be used depending on the use case and by how much spurious radiation should be reduced.

The radome 108 may be of a high dielectric, plastic component that sits at the front face of the antenna. The radome 108 can be seen mounted on the engagement end 104 of the arm 102 to cover the antenna 106. The proposed material for the radome 108 is PREPERM PPE 950 MED. This material has a relative permittivity of 9.5 and is practically lossless. In this case, the radome 108 is joined to the arm 102 via a stepped path of 6mm ensuring that the antenna 106 is electrically isolated from the breast and the operator.

The radome 108 is the only part of the probe which comes in contact with breast tissue. In other words, in order for the probe to operate, the radome 108 is applied to, and makes contact with, the skin of the breast. Thus, it is preferred for the radome 108 to be bio-compatible. The proposed plastic material for the radome 108 has been tested to EN ISO 10993-1 :2018 for bio compatibility. It is also easily cleaned between uses, thus preventing infection.

In conjunction with the material of the arms, the radome 108 electrically isolates the metallic components of the antenna from the breast and operator as is required by medical safety standards (BS EN 60601-1).

In the same way that ultrasound gel improves the transmission of soundwaves into a human body, the electrical properties of the radome 108 allow for a good match between antenna 106 and breast. Combined with the low loss of the radome material, this ensures that the amount RF energy entering the breast is maximised.

Preferably, the thickness of the radome, between the antenna 106 and an outer engagement surface is at least 1mm.

The radome 108 separates the extreme reactive near field of the antenna 106 from contact with the skin. This makes the performance of the antenna more predictable and less affected by the material in contact with it. In particular, the performance of the antenna 106 is affect by materials in close proximity to the antenna 106. In other words, the materials close the antenna 106 effectively tunes the antenna 106. The closer a material is to the antenna 106, the stronger this effect is. This effect occurs in the antenna near field. The radome 108 separates the antenna 106 face from variation in material properties in its direct vicinity, thereby limiting this effect. As such, the performance of the antenna 106 is more consistent.

It is noted that a coupling fluid/gel/paste layer could be introduced between the antenna 106 and the breast, thereby replacing the radome.

Operation without any breast contact (i.e. , with an air gap) could be implemented and thus the radome 108 could be removed.

It will be appreciated that the radome 108 described above can be used with other types of probes using RF antennas.

Figure 6 shows a cross-section of an exemplary braking mechanism 114. It is noted that the braking mechanism 114 may be referred to as a brake. The brake 114 comprises a spring-loaded brake ring 608 held to the pivot shaft 602 via a spring 610 and an annular electromagnet 606 coupled to a distal end 604 of one of the arms of the probe. The pivot shaft 604 is coupled to a distal end of the other arm of the probe to allow rotation between the arms.

When braking is not required, the braking ring 608 is held above the top surface of the electromagnet 606 by springs 610 which suspend it from the electromagnet 606. In this configuration, the arm connected to the electromagnet 606 can turn freely around the pivot shaft, allowing the arms of the probe to rotate relative to each other. When braking is required, the electromagnet 606 is energised and the braking ring 608 is pulled down on to the top surface of the electromagnet 606. Rotation is restricted by the friction between electromagnet 606 and the brake ring 608, thus preventing the rotation between the arms. Braking can be actuated when the operator presses the capture button to take a measurement.

The brake can be implemented by means of an off-the shelf electromagnetic device (ATO ATO-FBD-006) consisting of a spring-loaded braking ring and annular electromagnet as illustrated in Figure 6.

The purpose of the brake 114 is to prevent the angular movement of the arms while an RF measurement of the breast is carried out. The RF measurement takes approximately one sec to collect. By limiting the movement of the arms, the distance between the antennas is kept constant. Additionally, the angular position of the arms can be measured without risk of change when the brake is actuated.

Alternative braking mechanisms could include a ratchet mechanism, a compressive/fictional/clutch mechanism or any mechanism that makes use of a sprag clutch bearing.

For example, the electromagnetic brake discussed above can be replaced with a friction slip bearing, a bearing that requires a minimum amount of torque to move. This would allow the mechanism to be static until the user purposely exceeds the torque required to move the device.

A ratchet mechanism could also be used. In this case, the pivot shaft would support a ratchet and a pawl within the arms, thereby locking the mechanism at discrete angular intervals.

Preferably, the braking mechanism used is able to release the locking mechanism when not required.

Even more preferably, the braking mechanism used is able to be forcibly disengaged to allow rotation of the arms away from each other (e.g., in case of discomfort during use).

An angular sensor can also be provided in the probe to determine the relative angular movement/separation between the arms when they rotate. From the angular separation of the arms, and the known size of the rigid arms, the distance d_e between the antennas can be determined.

For example, the rotational position of the calliper arms relative to one another can be measured via an opto-encoder. In this case, the opto-encoder consists of a patterned disk 612 mounted on the pivot shaft 602. The opto-encoder body 614, which can discern the angular position of the disk via the patterns on its surface, can be mounted on the same bracket as the electromagnet 606 as shown in Figure 6. When the arms of the probe move relative to one another, the pivot shaft 602 rotates along with opto-encoder disc 612. This movement is detected by the opto-encoder body 614 and the angular displacement is measured.

The opto-encoder may be a standard angular sensor (e.g., Avago AED8-9340- B13C),

The purpose of the angular sensor is to measure the angular separation of the antennas. The measurement can be carried out when the brake is applied so that the antennas are held static relative to one another. The purpose of measuring the angle is to convert that angular distance into the linear distance d_e between the antennas which is a vital piece of information when calculating breast density.

An alternative angular sensor may be a mechanical encoder in which circumferential copper tracks etched onto a PCB are used to encode the information and sensed via contact brushes. The same is also true for a magnetic encoder.

The opto-encoder described above makes use of an incremental encoder (i.e., measures relative angular position). However, an absolute encoder (i.e., measures absolute angular position from a known datum) could also be used.

Figure 7 illustrates a system for measuring breast tissue density. The system is a clinical measurement platform that utilizes non-ionizing radio-waves to scan human breast tissue to give an indication of equivalent mammographic breast density relating to the volume of high dielectric tissue within the breast. This can aid clinical decisions on patient treatment pathways.

The control unit may contain a power distribution network and a Radio Frequency (RF) transmitter/receiver unit. The control unit 702 is connected to the probe 100 via an umbilical cord 704 that carries RF and control cables. In this case, the probe 100 consists of two pivoted arms at the end of which are two antennas that are applied to the surface of the breast.

During an examination, the control unit 702 can be positioned on a desktop and the operator can sit opposite the subject and hold the probe 100 in two hands, one on each arm. The movement of the arms, as described above, enables the antennas on the end of the calliper arms to be gently pressed against the breast where a measurement is to be taken. The operator can then press either one of two capture buttons (as shown in Figure 1) to initiate the measurement. A measurement is taken, a process that lasts less than 1 second, and the arms of the probe are removed from the breast. This process can be repeated in 12 different locations around each breast as described above.

The control unit 702 may also be connectable to a display 706 to visually deliver the measurement. The control unit 702 can process the data to provide a clinical output relating to breast density.

The clinical output of the system may be a four-category variable that aligns with the internationally recognised Breast Imaging Reporting and Data System (BI-RADS). In X-ray mammography, the BI-RADS is a density estimation technique that typically involves a radiologist’s visual assessment of the mammogram. It is routinely reported for a large proportion of mammograms according to four categories: a (predominately fat), b (scattered densities), c (heterogeneously dense) and d (extremely dense).

The clinical output can be used to convey to the operator the density of the measured breast. By producing a density measure in BI-RADS, the system outputs a scale that is the current gold standard. Clinicians are used to using it, thus allowing the system to be more easily integrated into clinical practice. Many clinical studies have been carried out and protocols developed using the BI-RADS system. Producing a BI-RADS equivalent scale allows the system to leverage that existing clinical experience.

Alternatively, the system could output a percentage scale related to overall percentage of dense breast tissue to fatty tissue similar to the Boyd score. Of course, a different score could also be output (e.g. a density rating between 1 and 10). A binary output, where the breast is declared dense or not based on a predefined condition, could also be used.

The density measurement is based on the radio-frequency coupling between the two antennas located at the end of the arms. To achieve a measurement with minimal interference and noise, the antennas need to have optimal coupling to the breast surface. A fitting algorithm is proposed to automatically inform the operator, in real-time, of the status of the antenna’s connection to the breast and thus when is appropriate for a measurement to be taken. An additional benefit of the fitting algorithm is the prevention of over compressing the breast, in ensuring appropriate antenna contact is achieved, via the probe. The control unit 702 may be configured to perform the steps of the fitting algorithms.

The fitting algorithm output may be provided to the operator via the display 706. Alternatively, lights mounted on or in the probe’s arms could indicate the fitting algorithm’s output through different colours. The fitting algorithm proposed is split into resolving two separate metrics; a metric designed for assessing contact between the engagement ends of the probe and the breast, and another metric for assessing the air path between the engagement ends of the probe and the breast.

The contact assessment uses the S11 antenna reflection measurement data by converting the S11 complex data measured over the 3-8GHz bandwidth to magnitude in dB and calculating the percentage of S11 response that is below -10dB. The contact metric returns a pass if 20% or more of the S11 is below -10dB, otherwise the metric returns a fail.

From the perspective of preventing over compression of the breast, the probe could be provided with pressure sensors to assess the level of the compression on the breast by the engagement ends of the arms.

Light detection resistors could also, or alternatively, be provided on the corners of the engagement surfaces of the engagement ends (i.e., the surfaces of the probe arranged to engage the breast). When no light is detected (i.e. pre-determined threshold been met) on all sensors then contact has been met.

While certain arrangements have been described, the arrangements have been presented by way of example only, and are not intended to limit the scope of protection. The inventive concepts described herein may be implemented in a variety of other forms. In addition, various omissions, substitutions and changes to the specific implementations described herein may be made without departing from the scope of protection defined in the following claims.

Claims

CLAIMS:

1. A probe (100) for an apparatus for measuring the density of breast tissue, the device comprising: at least two moveably coupled rigid arms (102), each having an engagement end (104), wherein the arms (102) can be moved relative to each other to modify a distance between the engagement ends (104) within a pre-determined range; and radiofrequency, RF, antennas (106) disposed at the engagement end (104) of each arm (102).

2. The probe (100) of claim 1 , wherein each arm (102) comprises a portion (202) adjacent to a corresponding distal end, opposite the engagement end (104), and wherein a distance between the portions (202) of the arms (102) is larger than the distance (106) between the engagement ends (104) for any distance (106) between the engagement ends (104) which is within the pre-determined range.

3. The probe (100) of claims 1 or 2, wherein the arms (102) are rotatably coupled to each other via a pivot (112).

4. The probe (100) of claim 3, further comprising an angular sensor configured to determine the relative angular position of the arms (102).

5. The probe (100) of any of claims 1 to 4, further comprising a button (110) configured to provide an actuation signal based on the button (110) being actuated.

6. The probe (100) of any of claim 1 to 5, further comprising a brake (114) for enabling and disabling relative movement between the arms (102).

7. The probe (100) of claim 6, wherein the probe (100) is arranged such that, when the brake (114) disables the relative motion between the arms (102), the arms (102) can be moved away from each other when a force, higher than a predetermined force, is applied to the arms (102).

8. The probe (100) of any of claims 1 to 7, further comprising a contact sensor configured to detect contact between the engagement ends (104) and a breast. 9. The probe (100) of claim 8, where the contact sensor comprises one or more of: a pressure sensor disposed at the engagement end (104) of each of the arms

(102); and a light sensor disposed at the engagement end (104) of each of the arms (102).

10. The probe (100) of any of claims 1 to 9, wherein the antennas (106) have a bandwidth including the 3 - 8 GHz band.

11. The probe (100) of any of claims 1 to 10, wherein at least one of the antennas (106) has a radiation pattern (304) that varies in power by less than 3dB over a predetermined angular beam width, relative to the antenna boresight (302), and within the pre-determined range in the 3 - 8 GHz band.

12. The probe (100) of any of claims 1 to 11 , further comprising an electrically insulating and bio-compatible radome (108) covering each antenna (106), wherein each radome (108) is made of material having a relative permittivity of at most 30 in the 3 - 8 GHz band.

13. The device of claim 12, wherein each radome (108) comprises an engagement surface for engaging with the breast and an inner surface facing towards the respective antenna (106), wherein the thickness between the inner surface and the engagement surface is at least 1 mm.

14. A system for measuring the density of breast tissue, the system comprising: a probe (100) according to any of claims 1 to 13; and a control unit (702) configured to receive data signals from the antennas (106) and actuate one of the antennas (106) of the probe (100) when an actuation signal is received.

15. The system of claim 14, wherein the control unit (702) is further configured to: determine a percentage of S11 response in the data signals from the antennas

(106) that is below -10dB in the 3 - 8 GHz band; and determine that physical contact occurs between the engagement ends (104) and a breast based on the percentage of S11 response being below a threshold percentage. 16. The system of claims 14 or 15, wherein the control unit (702) is further configured to: determine a first median S21 transmission S₂i,i in the 3 - 4 GHz band from the data signals; determine a second median S21 transmission S_21;2 in the 7 - 8 GHz band from the data signals; and determine that there is no air path between the engagement ends (104) and a breast based on S_{21 1} < S_{21 2} + xdB, wherein x is a contact threshold smaller than 10dB.

17. The system of any of claims 15 to 16, wherein the control unit (702) is further configured to determine an indication of breast tissue density from the data signals and output said indication in the form of a breast imaging reporting & data systems, BI-RADS, classification.

18. A probe for obtaining clinical measurements of a subject when in contact with the subject, the probe comprising a radiofrequency, RF, antenna (106) covered by a radome (108), the radome (108) having an engagement surface for engaging with the subject and an inner surface closest to the antenna (106).

19. The probe of claim 18, wherein the thickness of the radome (108) between the engagement surface and the inner surface is at least 1 mm.