Real-Time Estimation of 3-D Needle Shape and Deflection for MRI-Guided Interventions

Abstract

We describe a MRI-compatible biopsy needle instrumented with optical fiber Bragg gratings for measuring bending deflections of the needle as it is inserted into tissues. During procedures, such as diagnostic biopsies and localized treatments, it is useful to track any tool deviation from the planned trajectory to minimize positioning errors and procedural complications. The goal is to display tool deflections in real time, with greater bandwidth and accuracy than when viewing the tool in MR images. A standard 18 ga × 15 cm inner needle is prepared using a fixture, and 350-μm-deep grooves are created along its length. Optical fibers are embedded in the grooves. Two sets of sensors, located at different points along the needle, provide an estimate of the bent profile, as well as temperature compensation. Tests of the needle in a water bath showed that it produced no adverse imaging artifacts when used with the MR scanner.

Keywords: Biomedical transducers; Bragg gratings; biopsy; magnetic resonance imaging (MRI); optical fiber sensors; strain measurement.

Fig. 1

Example of deflection estimation process based on beam theory. A needle is fixed at the base (y = 0 mm), and two point loads of −0.6 N and 0.2 N are applied at the midpoint (y = 75 mm) and at the tip (y = 150 mm) of the needle, respectively. The shaded dots in the curvature plot are sensor locations, which lead to an estimate for g(y).

Fig. 2

Prototype design with modified inner stylet incorporated with three optical fibers. Three identical grooves at 120° intervals are made on the inner stylet to embed optical fibers with FBGs along the needle length. (a) Midpoint cross section. (b) Magnified view of an actual groove. (c) Tip of the stylet. (d) Fixture design for EDM parallel grooves in the biopsy needle stylet.

Fig. 3

(a) Force profile approximated with Fourier series with different numbers of terms. (b) Curvature profile—first integral of the force profile. (c) Deflection profile—second integral of curvature profile. The insets show the curvature and the deflection profiles are quite similar.

Fig. 4

(a) Randomized force profiles with concentrated radial and axial tip forces. (b) Average tip deflection error plot with all possible sensor locations in a Monte Carlo simulation. The brighter region gives the lower tip deflection errors. (y₁ and y₂ are the locations of first and second set of sensors, respectively.)

Fig. 5

Curvature and temperature change calibration results. (a) Experiment 1 (x-axis loading). (b) Experiment 2 (z-axis loading). (c) Experiment 3 (temperature change)

Fig. 6

Screen capture of the display of the real-time monitoring system.

Fig. 7

RTFSE images of the biopsy needle with and without optical fibers and FBGs show the same degree of needle artifact. (a) Unmodified needle, coronal and sagittal view. (b) Modified needle, coronal and sagittal view. Maximum intensity projections (MIP) through a 3-D volume of acquired images show the cumulative bright artifact caused by the needle. The amount of artifact between the two needles is comparable. (c) MIP of the unmodified needle. (d) MIP of the modified needle.

Fig. 8

(a) MRI-scanned images with different deflections. The deflection relative to MR images were found using a measurement tool in OsiriX [35] software for viewing medical DICOM images. (b) Estimated needle deflections using FBG sensors.