the optimum transducer “ scanning ” speed for delivering a predetermined dose of ultrasound to a desired treatment area determined by a scanning plan is a function of both the cavitation related mechanical index ( mi ) and tissue temperature thermal index ( ti ) settings . while cavitation is a threshold mechanism there is both an amplitude factor beyond the threshold level and an exposure time factor involved in emulsifying a certain fraction of the treated fat , whereby low settings require a slow scanning speed and high settings require faster scanning speeds . the relationships can be estimated from the numerical values of mi and ti and further refined empirically using data from animal and clinical studies . furthermore , since the transducer is not 100 % energy efficient , its face ( skin contact area ) will create heat and if not properly controlled may present a hazard for potential skin burns . moving the transducer across the skin surface will also significantly reduce localized peak skin temperature . in the case where there is a sensor monitoring the transducer face temperature , control of the skin heating can be included in the speed indicator . if there is no transducer face temperature sensor the suggested transducer movement speed component due to tissue heating can be based on empirical data from animal and clinical studies . there are at least three approaches for addressing control of the ultrasound dose delivery , as summarized in fig1 a and 1 b , fig2 a and 2 b , and fig3 . one method requires the user to be part of the feedback loop , whereby the system , the transducer , or a separate device acts as a visual guide for the user to apply the desired scanning speed . the first embodiment is an example of this approach . another method consists of a subsystem that detects the transducer scanning velocity and in real time transfers this information to the system , which in turn adjusts parameters such as mi and ti ( i . e ., ultrasound dose ) to achieve the desired effect based on the actual speed of transducer movement . this relieves the user from precisely matching the desired scanning speed , but still requires the user to keep track of the transducer position and the ultrasound beam focal depth . the second embodiment is an example of this . a third method monitors the transducer position , which is transferred to the system in real time . with this information and the presence of a clock , the transducer velocity may also be easily calculated . now the system can automatically adjust the needed parameters such as mi , ti and focal length to accomplish the planned treatment , giving the user the freedom to move the transducer almost “ at will ”. the third embodiment is an example of this . it should be noted that there is much more value in using a 3d coordinate system , where the ( contoured ) skin defines two of the dimensions and the depth below the skin surface is the third , rather than a cartesian coordinate system fixed to the operating room or even fixed to localized patient movements . the connecting lines in the functional block diagrams in fig1 a to 3 have the following meaning . the occasional user control of the system / console is shown as 7 . item 8 indicates that the user reads the scanning speed indicator . item 9 indicates that the user views the actual scanning speed of the transducer . item 10 indicates that the user actually holds and moves the transducer . item 11 shows the transmit signals from the system to the transducer . item 12 shows the low level power supply and control signals from the system to the scanning speed pad 5 or optical sensor . item 13 indicates the path of sensor signals from the optical sensor to the built in decoder , which translates the information into position and speed . one embodiment ( fig1 a and 4 ) is to have a visual transducer scanning speed indicator on the transmitter ( main unit , console or system ) that moves with the same speed that is optimal for the transducer motion on the skin . the speed indicator can take the form of a moving cursor 2 on a screen 1 of the transmitter . the moving cursor can take many forms , the one shown in fig1 a , 1 b , 2 a , 2 b and 4 through 6 consists of four moving dots ( light sources such as leds ). these may be sequentially switched on and off at a controlled rate , or the first switched on , the second switched on , etc . with all being switched off and the cycle repeated after the last light source has been switched on , either of which is to be considered sequential switching on , or scanning . the user can then practice matching that speed while holding the transducer near the screen . when sufficiently proficient he / she can match the speed when scanning on the skin . as verification , the user can mark the skin for a certain distance and calculate the time needed to traverse that distance based on the numerical value of the desired velocity . another version ( fig1 b and 5 ) of the first embodiment is to have a visual transducer scanning speed indicator on the transducer itself 3 , for example in the form of an array of visual indicators ( light sources ) such as light emitting diodes ( leds ) 4 , which light up in a sequence corresponding to the desired speed of the transducer . it will then be up to the user to provide the “ feedback loop ” by moving the transducer at the indicated speed . here the user can perform the same verification as described above . a second embodiment is a separate flexible scanning speed guidance pad 5 ( fig2 a , 2 b and 6 ), which can be placed on the patient adjacent to the intended transducer path . the flexible material can be silicone rubber or other material with leds ( or other visual indicators ) 6 molded in . the leds are sequentially switched on and off so that they provide visual scanning speed guidance in proximity to the transducer . the speed guidance pad can be manufactured in different lengths and / or from different materials to fit the desired treatment area , and can also be either disposable ( single patient use ), semi - disposable , or reusable . the leds can be powered either by batteries , as in the embodiment of fig2 a , or by the transmitter , embodiment of fig2 b , in which case a power cord is detachably connected to the guidance pad . by being connected to the transmitter , the system may display the scanning speed , scanning location or position , and range of scan distance if the pad is physically longer than the desired scan needed to match the system settings , while the battery operated solution either would require wireless transmission of the information , or require the user to set the scanning speed according to the transmitter &# 39 ; s displayed parameters . a third embodiment is an optical 2d location sensor technology similar or identical to those used in an optical computer mouse , as in fig3 and 7 . the sensor primarily consists of a light source 13 , a translucent membrane or cavity 16 , a lens 14 to collimate the reflected light from the skin 18 , which also goes through the acoustic coupling gel 19 and continues through an optical guide to an optical sensor array 20 embedded in an integrated circuit 17 . as indicated in fig3 the optical sensor is attached to or built into a transducer , generally like that of fig5 . the sensor information is passed through the transducer cable and processed in the system to find the position and velocity of the transducer . any speckle , phase shift , frequency shift or other characteristics may be used to detect motion and velocity . as with a computer mouse , the optical 2d location sensor can lose track of the transducer position if lifted from the surface ( skin ). this can be overcome with a simple calibration process , whereby the user moves the transducer to a marked calibration spot on the skin , push a calibration button on the transducer or on the system , and moves the transducer on the skin to the desired location . in the case of a “ brush - beam ” ( non circular symmetric beam ) it becomes important to scan approximately perpendicular to the width ( long axis ) direction of the brush - beam . this third embodiment is very adaptable to a scanning plan in which the user graphically composes a 3d volume using software within the system or off line , showing the relative location and amount of treatment wanted , both with respect to cavitation ( fat emulsification ), heating ( skin tightening ), or other aesthetic / dermatologic / therapeutic treatments . off line use of the scanning plan software allows data transfer to the system . during the procedure , the system can keep track of the transducer &# 39 ; s location and in real time can adjust critical parameters such as mi , ti and focal depth ( if equipped with electronic focusing ), so the desired treatment “ dose ” eventually will be delivered . the real time difference between the desired and actual delivered “ dose ” can also be displayed on the system graphically in a 2d format , so the user can concentrate the transducer motion in the area where more treatment is needed . this allows the user to move the transducer freely within certain boundaries with respect to both position and speed . for the best outcome with respect to the treatment plan , the transducer needs to be oriented perpendicular to the skin and in the case of a brush - beam transducer , the scanning velocity vector needs to be perpendicular to the brush width direction . however , an angular error relative to the exact perpendicularity is a cosine function , meaning that it is a weak dependency , so that in reality , perpendicularity need not be monitored , but can be continuously estimated by the user . the suggested speed shown by the various embodiments of the speed indicator can be based on mi , ti and instantaneous transducer face temperatures and / or acquired data from animal and clinical studies . while the above methods are intended to be used in conjunction with a non - invasive ultrasound lipoplasty transducer , the inventions , the scanning light source of the first two embodiments can be used on handheld transducers for other modalities , including aesthetic , dermatologic , or other therapeutic applications . in the claims to follow , a reference to a handheld external ultrasound treatment transducer is a reference to a handheld external ultrasound transducer useable for lipoplasty , skin tightening , aesthetic , dermatologic /, and other therapeutic purposes . thus , while certain preferred embodiments of the present invention have been disclosed and described herein for purposes of illustration and not for purposes of limitation , it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention .
methods for controlling and monitoring speed and position of a handheld medical transducer . three methods are presented of various means , two of which include the user in the feedback loop and the third is fully automatic . in the third , an optical position sensor similar to an optical computer mouse provides enough information that the system can respond to and correct for a freehand scanning motion by the user .