Patent ID: 12186016

Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

Laser fractional injury covers a wide variety of tissue injury. For example, if the tissue being fractionally injured by a pulsing of a laser is heated to 100° C. or greater, the resulting fractional injury is typically denoted as being ablative. If the tissue being fractionally injured by the pulsing of the laser is not heated to 100° C. or greater, the resulting fractional injury is commonly denoted as being non-ablative. There are various forms of non-ablative fractional injury. For example, if the tissue being fractionally injured is heated to greater than 70° C. but less than 100° C., the fractional injury is commonly denoted as a fractional coagulation or tissue necrosis. Should the pulsing of the laser instead heat the tissue being fractionally injured to less than 70° C. but above 40° C., the fractional injury is often denoted as non-immediately destructive tissue heating.

Regardless of whether a fractional injury is ablative or not, there is a tension between achieving sufficient fractional injury and keeping the scan density at acceptable levels. To resolve this tension, a three-dimensional (3D) laser scan pattern for fractional injury is provided. The following discussion will address a fractional injury scan of the skin, but it will be appreciated that the 3D laser scan pattern disclosed herein is also applicable to both ablative and non-ablative fractional injury of other types of tissues than just skin. In a 3D scan, the heat delivered per pulse defines a plurality of pulse classes. Each pulse in a given class delivers the same amount of heat. It is a design choice as to how many classes of pulses a given 3D scan will include. In the following discussion it will be assumed that three classes are used without loss of generality. For example, a first class of pulses delivers more heat per pulse than the heat per pulse delivered by a second class of pulses. In turn, the second class of pulses provide a greater heat per pulse than a third class of pulses, and so on.

The heat delivered by each pulse may be defined by the energy (e.g., a total number of joules) delivered to the portion of skin being energized by the pulse. Alternatively, the energy delivered per area of skin being illuminated by the laser pulse (e.g., joules per cm2) may characterize the heat delivered by each pulse. With respect to delivering a given amount of energy (and thus heat), the pulse duration may be the same whereas the laser intensity or power is varied from one class of pulses to another. Alternatively, the laser power may be constant for each pulse, but the pulse duration varied from one class of pulses to another to control the amount of heat being delivered.

The spacing between pulses in each class is proportional to the heat delivered per pulse for the class. For example, with respect to the three classes of pulses discussed above, the first class has the greatest heat per pulse whereas the second class has more heat per pulse than the third class of pulses. If there are just three classes of pulses, the third class thus delivers the least amount of heat per pulse. Given these relative amounts of heat per pulse, the first class of pulses has a first pitch or spacing between adjacent pulses. The second class of pulses is similarly positioned to have a second pitch or spacing between adjacent pulses that is less than the first pitch. Finally, each pulse in the third class of pulses is positioned according to a third pitch that is less than the second pitch (and hence less than the first pitch).

The varied pitch for the classes of pulses leads to a “two-dimensional” nature to the scan since the skin may be deemed to form a plane defined by two dimensions. But there is a third dimension to the scan because of the varied depths of fractional injury provided by the pulse classes. For example, the first class of pulses are most energetic. In the case of an ablative dermal scan, the first class of pulses will thus ablate most deeply into the skin. The second classes of pulses have less energy and thus produce a fractional injury that does not extend as deeply into the tissue being treated. For example, in the case of an ablative dermal scan, the second class of pulses will not ablate as deeply into the skin as compared to the first class of pulses. The third class of pulses has even less energy than the second class of pulses. The third class of pulses will thus ablate more shallowly as compared to the other classes in an ablative 3D laser scan. If the skin surface is deemed to be defined by the X and Y axes in a Cartesian coordinate system, the varied fractional injury depth would be defined by the Z axis. The resulting three-dimensionality provides sufficient fractional injury without the risk of heat injury that would result from traditional laser scans. To provide a better appreciation of this advantageous feature, some traditional two-dimensional scan patterns will be discussed first, followed by a discussion of an example three-dimensional scan pattern.

A linear two-dimensional scan pattern100is shown inFIG.1. Each laser scan spot105is separated according to a regular pitch and arranged in linear rows and columns akin to a raster scan in a display. Because the linear nature of such a scan leads to facial injury having unnatural straight lines, a random two-dimensional scan pattern200was developed as shown inFIG.2. The spacing between each laser scan spot205is irregular and thus leads to a more natural appearing injury edge as the spots205are not aligned according to linear rows and columns. However, both scan100and scan200suffer from the tension discussed earlier between achieving sufficient ablation and the risks of excessive heat delivery. For example, suppose that a relatively large amount of heat is delivered for each laser scan spot105of scan100. As the pitch is reduced, tissue that was heated due to one laser scan spot105may be re-heated by an adjacent laser scan spot105. The pitch must thus be maintained to be relatively large, which reduces the scan density. Similarly, the energy delivered by each laser scan spot205must take into account the minimum pitch in the irregular spacing of scan200. Should the energy be too large, adjacent scan spots205will merge, which then destroys the desired surrounding of each ablated column of skin tissue with healthy tissue.

In sharp contrast, a three-dimensional laser scan pattern300such as shown inFIG.3achieves sufficient fractional injury without the risk of excessive heat. A three-dimensional scan uses at least two classes of laser pulses. In scan pattern300, three classes are used as discussed earlier. Pulses305and310are examples of a first class of pulses having a relatively large energy. The first class of pulses are also denoted herein as a series of first pulses. The large amount of energy per each first pulse provides a deep fractional injury column to stimulate regrowth of collagen in the dermis, but this significant fractional injury also delivers a relatively large amount of heat to the skin tissue. To limit excessive heating of tissues from adjacent pulses, adjacent first pulses such as pulses305and310are separated by a first pitch or separation325that is relatively large.

In contrast, a pair of adjacent pulses330and335in a second class of pulses are separated by a second pitch or separation340. The second class of pulses are also denoted herein as a series of second pulses. Because the energy per pulse is reduced for the second class of pulses as compared to the energy per pulse of the first class, each second pulse does not fractionally injure the tissue being treated as deeply and delivers less heat as compared to the first pulses. Due to this reduced amount of heat, second pitch340is smaller that first pitch325. In this fashion, the second class of pulses increase the scan density as compared to what would otherwise be possible if only the first class of pulses were used.

A pair of adjacent pulses320and315are examples of a third class of pulses having a reduced amount of energy per pulse as compared to the second class of pulses. The third class of pulses is also denoted herein as a series of third pulses. Each third pulse thus delivers the least amount of heat per pulse. The depth of the fractional injury from pulses320and315is thus smaller than that produced by pulses330and335. Due to this reduced amount of heat delivered per pulse, adjacent third pulses such as pulses320and315are separated by a third pitch345that is less than second pitch340(and thus less than first pitch325). Due to the reduced pitch, the third class of pulses increases the scan density as compared to what would be possible if only the first and second classes of pulses were used.

An example system400for a three-dimensional laser fractional injury of the skin of a patient is shown inFIG.4. A clinician positions a laser hand piece410to perform a laser scan of a skin portion415. A controller420controls a scanner (discussed further herein) that scans the laser beam to scan the appropriate laser pulses across skin portion415. At the same time, controller420controls the scan energy for each laser pulse to produce the desired number of laser pulses of each class within skin portion415. With skin portion415ablated, the user may then reposition laser hand piece410to begin a three-dimensional laser fractional injury of another skin portion. The laser scan and repositioning of the laser hand piece410is then repeated until all the skin portions to be treated are completed.

A distal portion505of an example laser hand piece is shown inFIG.5. A scanner515such as set of mirrors are controlled by controller405(FIG.4) to position the classes of laser pulses across a skin portion according to their respective pitches. The first class of pulses are represented by pulses520. Controller405includes a laser energy controller510that controls the amount of energy delivered by the pulses in each class. For example, laser energy controller510may control the pulse duration and/or the power of the laser beam for each pulse to control the amount of energy per pulse. A pair of pulses530are second class pulses whereas a triplet of pulses535are third class pulses.

The sequencing of the various classes of pulses may be based upon the heat energy being delivered per pulse. For example, suppose an area of tissue was to be fractionally injured with fifty first pulses, one-hundred second pulses, and two-hundred third pulses. It would be relatively slow to first pulse all the pulses in one class of pulses, then all the pulses in another class of pulses, and so on. To provide a faster scanning, a sequence such as 1-3-3-2-3-3-2 may sequentially repeated, wherein the 1 represents a pulse of the first class, a 2 represents a pulse of the second class, and a 3 represents a pulse of the third class. Given the energy of the initial first pulse in such a sequence, the subsequent pair of third class pulses need a certain spacing or pitch from the initial pulse. Similarly, the energy of the first second class pulse requires a certain spacing from the just ablated third class pulses, and so on. There is thus a temporal aspect to the spacing of the various pulses that takes into account the heat delivered by preceding pulses.

The pitch between adjacent first pulses may vary depending upon the energy per pulse in the first class of pulses. The following Table 1 for the first class of laser pulses gives some example depths in millimeters for the fractionally injured column of tissue that results from each pulse, the milli-Joules of energy being delivered by each pulse, the radius of each column (MTZ) in microns, the pitch in millimeters, and the resulting scan density:

TABLE 1DepthmJMTZPitchDensity0.75503000.7540%160315132%1.5903501.523%

The following Table 2 is analogous to Table 1, but is directed to the second class of laser pulses:

TABLE 2DepthmJMTZPitchDensity0.35101500.3543%0.45162000.4544%0.55262500.5545%

Similarly, the following Table 3 is also analogous to Table 1, but is directed to the third class of pulses:

TABLE 3DepthmJMTZPitchDensity0.1521500.15100%0.241500.275%0.2561500.2560%

An example method of laser fractional injury will now be discussed with respect to the flowchart ofFIG.6. The method includes an act600of pulsing a laser to provide a series of first pulses and a series of second pulses so that an energy delivered by each first pulse is greater than an energy delivered by an energy of each second pulse. Pulses520or pulses305and310are an example of the first series of pulses. In addition, the method includes an act605of scanning the series of first pulses and the second series of pulses across an area of tissue to be fractionally injured so that a first pitch separates adjacent ones of the first pulses and so that a second pitch separate adjacent ones of the second pulses, wherein the second pitch is less than the first pitch. Pulses330and335or pulses530is an example of the series of second pulses.

Those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.