Apparatus for determining a proper insertion depth of a biopsy needle to be inserted at a selected point on the body of a patient so that a sampling end of the needle just reaches to a designated target area within the body, comprises at least one straight calibrated pointing device, having a pivot point at one end thereof, and aligned to point through the selected point in a straight line passing through the designated target region, an image of the pointing device being formed on each of first and second image planes by utilizing radiation from respective first and second radiation source positions, along with images corresponding to the selected point and the target area. Needles are provided for casting an image on one at least one of the image planes, the needles being pivotably mounted at a further pivot point different from the pivot point of the pointing device and being constrained for movement in plane defined by the pivot point, the further pivot point and by the pointing device.