Diaphragmatic ultrasonography (US) allows for quantification of diaphragm thickness, strain (rate) and excursion, and with this also the respiratory rate and duration of each contraction. Diaphragm thickness (expressed as thickening fraction) and strain reflect contractile activity and correlate well with diaphragmatic electrical activity and diaphragmatic pressure. Consequently, thickness and strain may be used as a surrogate for respiratory effort. Applications of diaphragmatic ultrasound include assessment of diaphragm function, atrophy detection, weaning prediction, and mechanical ventilation (MV) setting management. Other applications could be asynchrony detection and proportional ventilation (non-invasive neurally adjusted ventilatory assist (NAVA)). The use of diaphragmatic ultrasound in mechanical ventilation is gaining attention and therefore, technical problems and use cases are currently being investigated.
A diaphragm thickening fraction (TFdi or TFDI) as measured by ultrasound (US) are carried out by an operator who looks at the patient and takes an ultrasound image at end inhalation and end exhalation. The diaphragm thickness fraction is determined by subtracting the end inhalation thickness from the end exhalation thickness and dividing the difference by the exhale thickness according to Equation 1:
with Tei as the end-inspiratory thickness. The thickness of the diaphragm as varying over the breathing cycle (i.e. the thickening during inspiration) is a surrogate for the patient's respiratory effort (see, e.g., Tuinman P R, Jonkman A H, Dres M, Shi Z H, Goligher E C, Goffi A, de Korte C, Demoule A, Heunks L. Respiratory muscle ultrasonography: methodology, basic and advanced principles and clinical applications in ICU and ED patients—a narrative review. Intensive Care Med. 2020 April; 46(4):594-605. doi: 10.1007/s00134-019-05892-8. Epub 2020 Jan. 14. PMID: 31938825; PMCID: PMC7103016).
Diaphragm thickness measurements can be obtained with ultrasound (US) imaging. However, such measurements can suffer from artificial thickening if the US beam does not pass the diaphragm perpendicularly. If the US beam has an inclination with respect to the surface normal of α, then the diaphragm thickness appears to be d/cos α, i.e., it appears to be thicker by a factor of 1/cos α than it actually is. This can lead to inaccurate diaphragm thickness measurements.
The following discloses certain improvements to overcome these problems and others.
In one aspect, a diaphragm imaging device includes at least one electronic processor programmed to perform a diaphragm imaging method including receiving ultrasound imaging data of a diaphragm of a patient, the ultrasound imaging data being acquired by an associated ultrasound imaging probe with the probe at a plurality of different observable probe angles (βobs); for each observable probe angle, determining a corresponding apparent thickness (dI) of the diaphragm of the patient from the received ultrasound data acquired at that observable probe angle; and estimating a thickness (dD) of the diaphragm of the patient based at least on the apparent thicknesses (dI).
In another aspect, a diaphragm imaging method includes, with at least one electronic controller, receiving ultrasound imaging data of a diaphragm of a patient, the ultrasound imaging data being acquired by an associated ultrasound imaging probe with the probe at a plurality of different observable probe angles (βobs); for each observable probe angle, determining a corresponding apparent thickness (dI) of the diaphragm of the patient from the received ultrasound data acquired at that observable probe angle; and estimating a thickness (dD) of the diaphragm of the patient based at least on the apparent thicknesses (dI).
One advantage resides in acquiring accurate diaphragm thickness measurements.
Another advantage resides in correcting an angle of an ultrasound probe that is imaging a diaphragm to obtain an accurate diaphragm thickness measurement.
Another advantage resides in providing feedback to a user to correct an inclination angle of an ultrasound probe while imaging a diaphragm.
Another advantage resides in correcting an artificial thickening factor in a diaphragm thickness measurement.
A given embodiment may provide none, one, two, more, or all of the foregoing advantages, and/or may provide other advantages as will become apparent to one of ordinary skill in the art upon reading and understanding the present disclosure.
The disclosure may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the disclosure.
As used herein, the singular form of “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. As used herein, statements that two or more parts or components are “coupled,” “connected,” or “engaged” shall mean that the parts are joined, operate, or co-act together either directly or indirectly, i.e., through one or more intermediate parts or components, so long as a link occurs. Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, upper, lower, front, back, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the scope of the claimed invention unless expressly recited therein. The word “comprising” or “including” does not exclude the presence of elements or steps other than those described herein and/or listed in a claim. In a device comprised of several means, several of these means may be embodied by one and the same item of hardware.
With reference to
In a more particular example, the medical imaging device 18 includes an ultrasound probe 20 that is configured to image the diaphragm of the patient P. The US probe 20 is positioned to acquire US imaging data (i.e., US images) 24 of the diaphragm of the patient P. For example, the US probe 20 is configured to acquire imaging data of a diaphragm of the patient P, and more particularly US imaging data related to a dimension (e.g., a position, a thickness, and so forth) of the diaphragm of a patient P during inspiration and expiration while the patient P undergoes mechanical ventilation therapy with the mechanical ventilator 2. In one example, the medical imaging device 18 includes an electronic processor 21 configured to control the ultrasound imaging device 18 to acquire the US images 24, and also includes a non-transitory computer readable medium 23 storing instructions executable by the electronic processor 21. The medical imaging device 18 can also include a display device 25. In another example, the electronic processor 13 of the mechanical ventilator 2 controls the ultrasound imaging device 18 to receive the ultrasound imaging data 24 of the diaphragm of the patient P from the US probe 20. The ultrasound probe 20 allows for continuous and automatic acquisition of the diaphragm thickness data (Tdi) from the acquired ultrasound imaging data 24.
Note that in the limiting case where the US fan beam 26 is oriented at 90° to the plane of the diaphragm D, then β=90° and sin(β)=1 and the imaged diaphragm thickness dI is equal to the physical diaphragm thickness dD, that is, dI=dD. However, obtaining this ideal perpendicular orientation is generally difficult or impossible using the external ultrasound probe 20 in an intercostal or subcostal position. Rather, the angle β will generally be less than (or greater than) 90° and hence dI>dD due to the tilt of the US beam fan 26 away from the perpendicular with the diaphragm D.
The US probe 20 can be moved by an operator relative to a skin surface of the patient P to acquire the US imaging data 24. If the fan of US beams 26 remains in a single plane, then the angle β does not change since the image plane does not change. Thus, the appearance of the thickness dI of the image 28 of the diaphragm D does not change. On the other hand, if the US probe 20 is tilted so that the image plane changes, then the angle β changes. This is shown in
In some examples, one or more external sensors (e.g., a camera—not shown) can be used to determine and angle between the image plan of the fan of US beams 26 and a skin surface S, as shown in
is measured for several angles of the ultrasound probe 20 respective to the skin (and hence equivalently for several different values of the angle β) and the smallest value of the apparent (i.e. imaged) diaphragm thickness dI is taken as being equal to the physical diaphragm thickness dD. This estimated value of dD may not be exact if the fan beam 26 cannot be positioned to be exactly perpendicular to the plane of the diaphragm D; however, since the derivative
becomes small as β approaches 90° the estimated value of dD may have sufficient accuracy. Note that this estimation of dD is done for different points in the respiratory cycle, typically at least including end-inspiration (where dD is thickest) and end-expiration (where dD is thinnest).
If greater accuracy is desired, then the set of datapoints can be extrapolated based on the expectation that the dI versus US probe angle curve should follow the expected
shape. For example, denoting the observable angle of the ultrasound probe 20 to the skin as an angle βskin, several ultrasound images can be acquired at different values of βobs to produce a dataset of (dI, βobs) data pairs. The angle β is given as β=βobs−βref where βref is an (unknown) angle offset between the unobservable angle β between the fan beam 26 and the plane of the diaphragm D and the observable angle βobs between the fan beam 26 and the skin (or other observable US probe angle reference). Then the set of (dI, βobs) data points are fitted to the equation
with the substitution β=βobs−βref yielding
with the two unknown fitted parameters being dD and angle βref. To accommodate noise in the (dI, βobs) data points, they can be fitted to a sinusoidal curve which is then matched to
Again, this estimation of dD is done for different points in the respiratory cycle, typically at least including end-inspiration (where dD is thickest) and end-expiration (where dD is thinnest). If images are acquired at 10 Hz or faster (i.e., at least 10 images per second) versus a respiratory cycle with a breath rate of typically no faster than about 60 breaths per minute (1 Hz) even for a newborn patient, sufficient data can be collected by sweeping the ultrasound probe 20 over a range of observable angles βobs two or three times, e.g. using manual tilting of the US probe 20 with the observable angle Gobs monitored by an external sensor as described herein.
The non-transitory computer readable medium 15 of the mechanical ventilator 2 and/or the non-transitory computer readable medium 23 of the US imaging device 18 stores instructions executable by the electronic controller 13 (and/or the electronic processor 21) to perform a diaphragm imaging method or process 100. Although primarily described in terms of the electronic controller 13/non-transitory computer readable medium 15 of the mechanical ventilator 2, the method 100 can similarly be performed by the electronic processor 21/non-transitory computer readable medium 23 of the US imaging device 18.
With reference to
At an operation 103, an inclination angle β of the ultrasound probe 20 is calculated from the US imaging data 24. To do so, a position of a surface of the diaphragm of the patient P is determined from US imaging data 24. For example, a clinician can acquire the US imaging data 24 at a plurality of different orientations (i.e., different angles) relative to the skin of the patient P. The position of the surface of the diaphragm can be determined from the US imaging data 24 acquired at the plurality of different orientations. From the determined position of the surface of the diaphragm, the inclination angle β of the probe 20 can be calculated.
Once the inclination angle β of the probe 20 is calculated, a corrective action can be performed. In some embodiments, at an operation 104, a representation 30 of the calculated inclination angle α can be displayed on the display device 14 of the mechanical ventilator 2 (or on the display device 25 of the medical imaging device 18). The operator of the probe 20 can then adjust the orientation of the probe 20 relative to the skin of the patient P until a desired inclination angle β of the probe 20 is achieved. In some examples, a representation 30 of the standard inclination angle β can be displayed on the display device 14, and a representation of the current inclination angle β of the probe 20 can also be displayed. The operator can then move the probe 20 until the current inclination angle β matches the standard inclination angle β.
In other embodiments, at an operation 105, tactile feedback can be provided for an operator of the probe 20. The tactile feedback can be provided by the actuator 22 of the probe 20 (e.g., the thrust-producing device or gyroscope can vibrate to indicate that the operator should change the orientation of the probe 20, automatically move the probe 20, and so forth). In a particular example, a difference between the calculated inclination angle β and a standard inclination angle β′ (i.e., the angle between the normal {right arrow over (n)}i of the image plane and the normal of the skin surface S) can be determined, and the tactile feedback can be provided until the calculated inclination angle β matches the angle β′.
At an operation 106, a diaphragm thickness metric (i.e., a thickness of the diaphragm or a diaphragm thickening fraction) can be calculated based on the US Imaging data 24 and/or the calculated inclination angle β. The displayed representation 30 can include a representation of the calculated diaphragm thickness metric. In one example, the diaphragm thickness metric includes a diaphragm thickening ratio indicative of a diaphragm thickness during inspiration relative to a diaphragm thickness during expiration. In another example, the diaphragm thickness metric includes a mean diaphragm thickness over multiple respiratory cycles.
At an operation 107, one or more parameters of the mechanical ventilation therapy delivered to the patient P by the mechanical ventilator 2 can be adjusted, for example, based on the calculated diaphragm thickness metric, the inclination angle β of the probe 20, and so forth.
In some embodiments, the actual inclination angle β can be estimated, and the operator can either wait for the correct inclination angle β of the US beam (i.e., during a manual sweep/attitude variation), or to correct for the artificial thickening (i.e., for a given attitude) caused by the inclination angle β of the probe 20. Since the US imaging data 24 is formed by a divergent set of US beams, the same geometric distortion of the diaphragm thickness appears also for the individual beams. However, the US imaging data 24 is commonly resampled to a Cartesian grid. Thus, the divergence of the beams is compensated, and the diaphragm appears in the image as two straight lines of distance d/sin|β|.
The operator continuously changes the inclination angle β of the probe 20 in a back-and-forth motion, which can be done at approximately 2 Hz (i.e., as shown in
The operator continuously changes the inclination angle β of the probe 20 back-and-forth, and the diaphragm thickness is continuously measured. Additionally, an inclination angle γ of the US probe 20 with respect to the lab coordinate system is measured. This can be done, for instance, using accelerometers or magnetometers (which can measure the angle γ between the US probe 20 and the earth's magnetic field) integrated into the US probe 20 or by tracking the probe with external sensors (e. g. optically (i.e., using a camera) or via radiofrequency (RF) tags). The measurement provides pairs of data points (e.g., angle, thickness, etc.). A model of the apparent diaphragm thickness as a function of the actual thickness and the angle is fitted (where the model contains just the artificial thickening by 1/sin|β and the unknown angle between the diaphragm normal and the 0° angle in the lab coordinate system). The model parameter for the actual thickness is provided to the user. The benefit of this approach is that it takes all images from an ultrasound sweep with the probe 20, resulting in a robust estimate of the inclination angle β of the probe 20.
In an initialization phase of the method 100, a sweep of the US probe 20 across a broad range of inclination angles β can be performed, including tracking of 3D position and orientation of probe 20 (e. g. optically, via RF tags, and so forth) to generate US images. From these images, a position of a local diaphragm surface can be determined. During inhalation and exhalation by the patient P, the US images 24 of the diaphragm can be acquired with the probe 20. The inclination angle β of the probe 20 can be estimated with a surface model and the determined local diaphragm surface, and the orientation of the probe 20 can be corrected based on the estimated inclination angle β.
The tactile feedback operation 105 can be performed in a variety of manners. For example, the US probe 20 is brought into a correct orientation. Then, a gyroscope constituting the actuator 22 is activated, which naturally acts to maintain the probe 20 in its orientation. The gyroscope 22 may be integrated in the US probe 20 or mounted to the US probe 20 as an add-on. For example, to counteract an attitude variation of 5 rad/s with a torque of 0.1 Nm would require a gyroscope 22 with a 5 cm diameter flywheel of 150 g, spinning at 25 k RPM. Another approach is to stabilize the US probe 20 by the torque generated from a thrust produced by an axial or centrifugal fan provided as an additional component of the actuator 22. Again, such a thrust generating device 22 could be integrated in the US probe 20 or mounted to the US probe 20 as an add-on. For example, a thrust of about 1 N (i. e. a torque of about 0.1 Nm when applied at 10 cm from a rotation point) could be generated by a 7.5×7.5 cm 2 centrifugal fan (e. g. ebm-papst RL 48-19/14) discharging through a 5 mm diameter tube. The active feedback can also be used to ensure the optimal contact area between the US probe 20 and the patient P.
In another embodiment, a 3D US probe 20 is employed, or a US probe 20 with two orthogonal fans. The US imaging data 24 is converted into a 3D point cloud, into which two 3D planes are fitted in a robust fashion (using e.g., a RANSAC approach). Finally, the orthogonal plane distance is provided to the operator.
It is beneficial to synchronize the US imaging data 24 with the mechanical ventilator 2 (i. e., thickness measurements are taken automatically in time windows around maximum inspiration and maximum expiration). This synchronization can be done using a common clock. The synchronization between the US probe 20 and the mechanical ventilator 2 allows comparing a measurement from different breaths. If consecutive breaths have similar respiratory muscle activity, points in the respiratory cycle can be selected from multiple breaths in a way that the chosen measurement gives the thickening fraction with the minimum diaphragmatic thickness for every point, this could ensure that the correct inclination angle β of the US probe 20 was used. This process can be applied to a subcostal and an intercostal data acquisition scenario.
The disclosure has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
This patent application claims the priority benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63/407,769, filed on Sep. 19, 2022, the contents of which are herein incorporated by reference. The following relates generally to the respiratory therapy arts, mechanical ventilation arts, ventilator induced lung injury (VILI) arts, ultrasound probe arts, and related arts.
Number | Date | Country | |
---|---|---|---|
63407769 | Sep 2022 | US |