  Flexible needle insertion procedures are common for minimally-invasive
surgeries for diagnosing and treating prostate cancer. Bevel-tip needles
provide physicians the capability to steer the needle during long insertions to
avoid vital anatomical structures in the patient and reduce post-operative
patient discomfort. To provide needle placement feedback to the physician,
sensors are embedded into needles for determining the real-time 3D shape of the
needle during operation without needing to visualize the needle
intra-operatively. Through expansive research in fiber optics, a plethora of
bio-compatible, MRI-compatible, optical shape-sensors have been developed to
provide real-time shape feedback, such as single-core and multicore fiber Bragg
gratings. In this paper, we directly compare single-core fiber-based and
multicore fiber-based needle shape-sensing through identically constructed,
four-active area sensorized bevel-tip needles inserted into phantom and \exvivo
tissue on the same experimental platform. In this work, we found that for
shape-sensing in phantom tissue, the two needles performed identically with a
$p$-value of $0.164 > 0.05$, but in \exvivo real tissue, the single-core fiber
sensorized needle significantly outperformed the multicore fiber configuration
with a $p$-value of $0.0005 < 0.05$. This paper also presents the experimental
platform and method for directly comparing these optical shape sensors for the
needle shape-sensing task, as well as provides direction, insight and required
considerations for future work in constructively optimizing sensorized needles.
