during contraction of the heart muscle therefore it will be understood that distance f will be correlated with the amount of remaining myocardial tissue between the end of the tmr channel 269 and the epicardial surface 271 this information regarding remaining depth of tissue is vital to the cardiologist in performing tmr with regard to percutaneous tmr by controllably forming tmr channels initiating at an endocardial surface perforation of the epicardium can be avoided the ranging device of the present invention will be usefully operated at frequencies between about 500 hz and about 10 khz such frequencies will be fast enough to allow real time display of the thickening and thinning of the heart wall brought about as a result of the changes between the systole and diastole components of the beating heart cycle fig8 shows a comparison between the wall thickness or channel depth at 90 u00b0 or other angulation another feature of the present invention which will require additional calculations to be performed by the signal processing means software or logic is the ability to confirm perpendicular or other angle wall penetration by the laser delivery means or other interventional device it will be understood that if the distance h is greater than the distance i the distance i being the perpendicular distance from the tip 267 of the laser delivery means 120 to some other anatomical structure interface and the distance h being the distance in a non perpendicular direction of laser delivery means 120 39 to the same anatomical structure interface in other.