i2 = Image3DSlices[im];
k2 = Image[MorphologicalComponents[ColorNegate[i2[[6]]], 0.9]];
DynamicModule[{pts2 = {{-1, 1}/2}}, {LocatorPane[Dynamic[pts2],
Image[k2, ImageSize -> 300], LocatorAutoCreate -> True,
Appearance -> Graphics[{Red, Disk[]}, ImageSize -> 10]],
Dynamic@SelectComponents[k2, "Label",
MemberQ[PixelValue[k2, #] & /@ Round@pts2, 1. #] &]}]

k3 = Image3D[MorphologicalComponents[ColorNegate[im], 0.9]]
i1 = Image3DSlices[k3];
k1 = Image[i1[[6]]];
DynamicModule[{pts1 = {{-1, 1}/2}}, {LocatorPane[Dynamic[pts1],
Image[k1, ImageSize -> 300], LocatorAutoCreate -> True,
Appearance -> Graphics[{Red, Disk[]}, ImageSize -> 10]],
Dynamic@SelectComponents[k1, "Label",
MemberQ[PixelValue[k1, #] & /@ Round@pts1, 1. #] &]}]