A New Inductive Proximity Sensor Based Guiding Tool to Locate Metal Shrapnel During Surgery

Abstract

Shrapnel injury is a major cause of death in victims of bomb blast, land mines, and gun fire. Currently, doctors rely on imaging systems to locate the shrapnel before surgery. But, since these images do not provide any real-time information of the location of the shrapnel, effectiveness of surgery solely depends on the doctors' skill to trace them. Therefore, in some cases, the shrapnel, in spite of being visible in the images, may become untraceable during surgery. Hence, an online tool that can help the surgeon in finding the location of the shrapnel during the surgery will be very effective. A prototype of such a tool has been realized using an inductive proximity sensor (IPS). The new IPS is small enough for inserting into the victim's body. Since the detection depth (DD) of an IPS decreases with its diameter, this IPS uses a differential sensing scheme for detection. Hence, the new sensor achieves DDs longer than its diameter. The design of the sensor takes care of the effects of parasitic parameters that become predominant as the size gets smaller and ensures repeatable results. The tool also features a special excitation scheme that has multiple advantages when compared with existing schemes. The details of the sensor, its excitation and performance against different targets under various conditions are presented in this paper.

Packaging and evaluation of an online tool for locating metal shrapnel during surgery

“…Before the surgery, doctors locate the shrapnel using CT / X-ray images. Since these imaging modalities cannot be used during the surgery [1], [2], the lack of real-time information forces the doctors to rely only on their skills to locate the shrapnel during the surgery. There were cases in which the shrapnel, in spite of being clearly visible in the images, became untraceable as it had penetrated deep into the tissues.…”

“…As a result, there was a clinical requirement for a shrapnel detection tool that can be used during the surgery (online tool), that can reduce the number of cuts to reach the shrapnel saving precious time, that requires minimum imaging facility (at the most an X-ray) and cheap enough for the remotest village hospitals in India. Hence a new shrapnel detection tool was envisaged based on a miniaturized Inductive Proximity Sensor (IPS) in [2]. The IPS was powered by a novel excitation scheme and the two were laid on a single PCB (printed circuit board) in the form of a probe.…”

“…This probe was then automated using NI LabVIEW software such that, when the probes sensed a metal target (shrapnel), its output would vary the frequency of an audio signal and the user could judge the depth of the impending target based on the shift in frequency heard. Since the kind of targets that the probe had to sense had varying features such as different shape, size, material, and orientation, a calibration of the probe was difficult and therefore the shift in audio frequency was a good solution to indicate the proximity of the target [2]. This probe however had to be packaged suitably for the surgical application.…”

“…Being small in size, the effect of parasitic elements like the inductance of various leads, mutual induction between the leads of exciting winding and detector winding etc. could affect its output [2]. Hence the exciting winding was designed such that its field would not only influence targets which are far away but also reduce the effect of parasitic elements.…”

“…The detector winding consisting of the sensing coil and dummy coil were wound such that there was minimum geometrical mismatch between them. This was to ensure that the offset voltage V OS produced in the absence of a target, due to the geometrical mismatch was as small as possible [2]. This would also ensure that the response due to target V m in the signal V d produced in its presence was high.…”