An apparatus (100,300), comprising: a transducer assembly (108, 308); a bending neck (106, 206, 306) connected to a proximal end of the transducer assembly (108, 308); and an insertion tube (103, 203, 303) disposed in tandem with the bending neck (106, 206, 306) and comprising a distal end (105, 205, 305) connected to a proximal end (111, 211, 321) of the bending neck (106,206, 306), and a proximal end (104, 204, 304) for manipulation of the transducer assembly (108, 308), the insertion tube (103, 203, 303) having a first durometer value at a first section, and a second durometer value at a second section, wherein the first durometer value is greater than the second durometer value, wherein the first section extends along a length of the insertion tube starting from the proximal end of the insertion tube, wherein the second section extends along a length of the insertion tube starting from the distal end of the insertion tube, wherein the first and second sections do not overlap, and wherein the insertion tube further comprises an interior channel; characterized in that the insertion tube comprises an inner jacket disposed circumferentially around the interior channel 220, wherein the inner jacket is a monocoil with helical shape, wherein a stiffness of the inner jacket is varied along the length of the insertion tube by selection of: a gauge, a thickness or a pitch of the monocoil; or by stacking and/or foregoing the monocoil at selected portions along the length of the monocoil that comprises the inner jacket. a transducer assembly (108, 308); a bending neck (106, 206, 306) connected to a proximal end of the transducer assembly (108, 308); and an insertion tube (103, 203, 303) disposed in tandem with the bending neck (106, 206, 306) and comprising a distal end (105, 205, 305) connected to a proximal end (111, 211, 321) of the bending neck (106,206, 306), and a proximal end (104, 204, 304) for manipulation of the transducer assembly (108, 308), the insertion tube (103, 203, 303) having a first durometer value at a first section, and a second durometer value at a second section, wherein the first durometer value is greater than the second durometer value, wherein the first section extends along a length of the insertion tube starting from the proximal end of the insertion tube, wherein the second section extends along a length of the insertion tube starting from the distal end of the insertion tube, wherein the first and second sections do not overlap, and wherein the insertion tube further comprises an interior channel; characterized in that the insertion tube comprises an inner jacket disposed circumferentially around the interior channel 220, wherein the inner jacket is a monocoil with helical shape, wherein a stiffness of the inner jacket is varied along the length of the insertion tube by selection of: a gauge, a thickness or a pitch of the monocoil; or by stacking and/or foregoing the monocoil at selected portions along the length of the monocoil that comprises the inner jacket. a gauge, a thickness or a pitch of the monocoil; or by stacking and/or foregoing the monocoil at selected portions along the length of the monocoil that comprises the inner jacket.