Bone-specific kinetic model to quantify periosteal and endosteal blood flow using indocyanine green in fluorescence guided orthopedic surgery

Abstract

This letter describes a hybrid plug/compartment (HyPC) kinetic model to fit dynamic indocyanine green fluorescence data acquired in a porcine model of long bone traumatic fracture. Parametric images of periosteal blood flow, endosteal blood flow, total bone blood flow and fraction of endosteal-to-periosteal flow were obtained by applying the HyPC model on a pixel-by-pixel basis. Intraoperative discrimination between healthy and damaged bone could facilitate debridement reducing post-operative complications from non-union and infection. The ability to quantify periosteal and endosteal blood flow could inform nail vs. plate-and-screw decisions to avoid further compromising cortical blood supply.

Keywords: bone blood flow; bone debridement; indocyanine green; orthopedic trauma; tracer kinetics.

Figure 1

(A) A diagram showing the compartments of the HyPC model, overlaid onto the bone anatomy and how these compartments relate kinetically (Q_P, periosteal compartment; Q_E,c, endosteal capillary compartment; Q_E,m, endosteal medullary compartment) (B) The flow-scaled aggregate impulse residue function used in the HyPC model, showing the parameters recovered: PBF, EBF, T_P, T_E, M_P, k₂.

Figure 2.

Top Row. ICG intensity (black dots) measured during baseline, after endosteal flow is disrupted and after both endosteal and periosteal flow is disrupted. Curve fitting is performed in two steps: first, a plug flow model is fit to the initial slope (red line) then the entire curve is fit using the hybrid plug and compartment (HyPC) model (blue line). Bottom Row. The recovered flow-scaled impulse response functions, FR(t), corresponding to the curves in the top row are shown (black lines). For comparison, FR(t) estimated using Tikhonov deconvolution also shown (green lines).

Figure 3.

For each leg condition (baseline, osteotomy and osteotomy with full periosteum stripping), four images are shown: a white-light image acquired during surgery with the operating microscope, a fluorescence image acquired at a single time-point 30 s after ICG injection, parametric map of total bone blood flow (TBF) and the percent fraction of endosteal flow (EBF / TBF). Parametric maps are recovered by fitting the HyPC model on a pixel-by-pixel basis.