Setting Standards for Reporting and Quantification in Fluorescence-Guided Surgery
Setting Standards for Reporting and Quantif ication in Fluorescence-Guided Surgery
Charlotte Hoogstins 1 2
Jan Jaap Burggraaf 2
Marjory Koller 0
Henricus Handgraaf 2
Leonora Boogerd 2
Gooitzen van Dam 0
Alexander Vahrmeijer 2
Jacobus Burggraaf
0 Department of Surgery , Nuclear Medicine and Molecular Imaging, and Intensive Care , University Medical Center, University of Groningen , Hanzeplein 1, 9713, GZGroningen , the Netherlands
1 Centre for Human Drug Research and Leiden Center for Academic Drug Research , Zernikedreef 8, 2333, CLLeiden , the Netherlands
2 Department of Surgery, Leiden University Medical Center , Albinusdreef 2, 2333, ZALeiden , the Netherlands
3 Leiden Academic Center for Drug Research , Rapenburg 70, 2311 EZ, Leiden , the Netherlands
Purpose: Intraoperative fluorescence imaging (FI) is a promising technique that could potentially guide oncologic surgeons toward more radical resections and thus improve clinical outcome. Despite the increase in the number of clinical trials, fluorescent agents and imaging systems for intraoperative FI, a standardized approach for imaging system performance assessment and post-acquisition image analysis is currently unavailable. Procedures: We conducted a systematic, controlled comparison between two commercially available imaging systems using a novel calibration device for FI systems and various fluorescent agents. In addition, we analyzed fluorescence images from previous studies to evaluate signal-to-background ratio (SBR) and determinants of SBR. Results: Using the calibration device, imaging system performance could be quantified and compared, exposing relevant differences in sensitivity. Image analysis demonstrated a profound influence of background noise and the selection of the background on SBR. Conclusions: In this article, we suggest clear approaches for the quantification of imaging system performance assessment and post-acquisition image analysis, attempting to set new standards in the field of FI.
Fluorescence; Optical imaging; Quantification; Image analysis; Signal-to-noise ratio; Phantom
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2,4
Introduction
Image-guided surgery (IGS) is a relatively new and emerging
platform, in which imaging techniques are applied
intraoperatively. The goal of IGS is to provide the surgeon with
realtime information on tissue in the surgical field, aiding in
Charlotte Hoogstins and Jan Jaap Burggraaf contributed equally to this
work.
surgical decision-making [1]. Fluorescence imaging (FI) is
ideal for intraoperative applications due to fast acquisition
times (milliseconds), flexibility in application, and portability
[2]. Various tumor-targeted near-infrared (NIR) fluorescence
agents have been successfully studied in clinical trials [3–6].
Moreover, there is great potential for a broad range of clinical
applications besides oncology, such as infectious and
inflammatory diseases [7]. Consequently, new study groups, industry
as well as hospitals are increasingly interested to explore and
implement this technology in clinical care.
As NIR light (wavelength 600–900 nm) is invisible to
the human eye, dedicated imaging systems are needed to
detect the fluorescence signal and to form a
twodimensional (2D) image demarking its tissue distribution.
The intraoperative detection of an imaging agent depends
on various biological and optical factors (Table 1). The
considerable increase in the number of clinical trials in
the FI field has led to the development of a variety of FI
systems [8]. However, as the imaging system represents
the last link in the chain, sensitivity (i.e., detection limit)
of the imaging system is crucial [9]. It is therefore
important to ascertain if an imaging system is sensitive
enough for the application of interest. Phantoms that
mimic relevant concentrations of a fluorescent agent in
scattering and absorption media can aid in the
quantification of the imaging system performance. However,
guidance or standard documents describing sensitivity
assessment for imaging systems, whether or not
including phantoms, is currently lacking [10, 11].
The interplay between biological and optical factors
ultimately results in a fluorescence image, in which the
fluorescence signal in both the target and background can be
semi-quantified. Using ImageJ (National Institute of Health,
Bethesda, USA, a public domain image processing and
analysis program) or proprietary software provided with the
imaging system software, area and pixel value statistics in
user-defined selections, known as a region of interest (ROI),
can be analyzed. Standardized methods for selection of ROIs
are not available, making this procedure prone to selection
bias. Using the measured fluorescence signal in the ROIs of
target and background, the signal-to-background ratio (SBR,
also reported as target or tumor-to-background ratio [TBR])
is calculated as:
mean signal tumor
SBR ¼ mean signal background
The SBR is the key determinant of sensitivity and
detectability in FI and is freq (...truncated)