A system for supplementing ultrasound image needle guidance with magnetically detected needle position and tissue impedance measurements. The system comprises an ultrasound imaging system with the ultrasound probe being provided with a magnetometric detector for detecting the position of a magnetized needle, cannula, catheter or other tissue-penetrating tool. The tissue penetrating tool is provided with an electrode at or near its tip which is connected to a power source and impedance meter, the impedance measuring circuit being completed by use of a skin electrode or second electrode on the tool so that the electrical impedance of the patient's tissue can be measured. The measured impedance values and the magnetically detected position of the tool are superimposed on the ultrasound image so that the clinician can easily confirm the needle position in relation to the imaged anatomy. The impedance values may be color-coded or charted alongside or superimposed on the position or track of the needle as displayed on the ultrasound image.