Phantom-based evaluation of near-infrared intracranial hematoma detector performance

Abstract

Near-infrared spectroscopy (NIRS) is emerging as a rapid, low-cost approach for point-of-care triage of hematomas resulting from traumatic brain injury. However, there remains a lack of standardized test methods for benchtop performance assessment of these devices and incomplete understanding of relevant light-tissue interactions. We propose a phantom-based test method for systems operating near the 800-nm oxy-/deoxy-hemoglobin isosbestic point and implement it to evaluate a clinical system. Semi-idealized phantom geometries are designed to represent epidural/subdural, subarachnoid, and intracerebral hemorrhages. Measurements of these phantoms are made with a commercial NIRS-based hematoma detector to quantify the effect of hematoma type, depth, and size, as well as measurement repeatability and detector positioning relative to the hematoma. Results indicated high sensitivity to epidural/subdural and subarachnoid hematomas. Intracerebral hematomas are detectable to a maximum depth of ∼2.5 cm, depending on thickness and diameter. The maximum lateral detection area for the single-emitter/single-collector device studied here appears elliptical and decreases strongly with inclusion depth. Overall, this study provides unique insights into hematoma detector function and indicates the utility of modular polymer tissue phantoms in performance tests for emerging NIRS-based cerebral diagnostic technology.

Keywords: hematoma detection; light–tissue interaction; near-infrared spectroscopy; standardization; tissue phantoms; traumatic brain injury.

Fig. 1

Schematic of phantoms representing (a) epi/subdural, (b) subarachnoid, and (c) intracerebral hematomas. Dark-shaded regions in (a) and (c) represent blood, light-shaded region in (b) represents blood–CSF mixture; hashed regions represent CSF layer. Layer thicknesses: 3 mm for scalp, 5 mm for skull, and 3 mm for CSF.

Fig. 2

Photographs of phantom layers incorporating (a) 5- and (b) 8.5-cm-diameter hematoma-simulating inclusions, as well as the (c) hematoma detector on its scaffold and (d) during a handheld measurement.

Fig. 3

Variations in hematoma inclusion position during lateral sensitivity measurements. Initially centered with the source and detector fibers, inclusions were repositioned either (a) along the S–D axis ($X$ direction) or (b) perpendicular to this axis ($Y$ direction). The hematoma inclusion was 5 cm in diameter, located 0 or 0.55 cm below the CSF layer; S–D separation distance was 4 cm.

Fig. 4

Effect of hemoglobin oxygenation level (${\mathrm{S}}_{\mathrm{t}}{\mathrm{O}}_{\mathrm{2}}$)—as measured by a CO-oximeter—on hematoma detector measurements.

Fig. 5

Repeatability of hematoma detector OD measurements ($n=5$) for four different acquisition protocols.

Fig. 6

Visualization of NIR light in the phantom during hematoma detector operation, as acquired from (a) above and to the side of the phantom; as well as directly below the hematoma layer for a 5-cm-diameter intracerebral hematoma [Fig. 1(c)] with thicknesses of (b) 0.5 and (c) 3 mm.

Fig. 7

Effect of CSF layer presence on system sensitivity to 5- and 8.5-cm-diameter intracerebral hematomas as a function of depth.

Fig. 8

NIRS system sensitivity to epi/subdural and subarachnoid hematomas over a range of hematoma thicknesses.

Fig. 9

Effect of volume/thickness and depth on detectability in intracerebral hematoma phantoms. Results are presented for hematoma diameters of (a) 5.0 and (b) 8.5 cm. Note that distance from phantom surface through CSF layer is 1.1 cm.

Fig. 10

Effect of device-hematoma lateral offset (a) along and (b) perpendicular to the S–D axis (as illustrated in Fig. 3). Results are presented for a 5-cm-diameter intracerebral hematoma located at depths of 0 and 0.55 cm below the CSF. The red dashed line indicates the detection threshold. Note that in (a), some part of the hematoma is directly below one of the fibers as long as the distance from the center is $<4.5\mathrm{cm}$, whereas in (b), some part of the hematoma is directly below the S–D axis as long as the distance from the center is $<2.5\mathrm{cm}$.