Design and validation of a clinical instrument for spectral diagnosis of cutaneous malignancy

Abstract

We report a probe-based portable and clinically compatible instrument for the spectral diagnosis of melanoma and nonmelanoma skin cancers. The instrument combines two modalities--diffuse reflectance and intrinsic fluorescence spectroscopy--to provide complementary information regarding tissue morphology, function, and biochemical composition. The instrument provides a good signal-to-noise ratio for the collected reflectance and laser-induced fluorescence spectra. Validation experiments on tissue phantoms over a physiologically relevant range of albedos (0.35-0.99) demonstrate an accuracy of close to 10% in determining scattering, absorption and fluorescence characteristics. We also demonstrate the ability of our instrument to collect in vivo diffuse reflectance and fluorescence measurements from clinically normal skin, dysplastic nevus, and malignant nonmelanoma skin cancer.

Fig. 1

(Color online) Schematic representation of spectral diagnosis system.

Fig. 2

(Color online) (a), (b) Clinical instrument. (c) Fiber optic probe used with the clinical instrument.

Fig. 3

(a) White light spectrum from the xenon flash lamp reflecting off a 20% reflectance standard. (b) Excitation pulses from the nitrogen laser at 337 nm and the dye laser at 445 nm. (c) Diffuse reflectance spectrum of a 1% intralipid solution. (d) Laser-induced fluorescence spectrum of a Rhodamine B solution (0.01 g/l).

Fig. 4

(a) Diffuse reflectance spectrum (solid curve) and the corresponding LUT fit (circles) from a tissue phantom [μ_s′ (λ₀) = 2.46 mm⁻¹ and [Hb] = 2 mg/ml]. Scatter plot of the extracted versus expected values of (b) μ_a(λ) and (c) μ_s′ (λ) for all tissue phantoms. The solid line indicates perfect agreement.

Fig. 5

(a) Data recorded from tissue phantoms with Stilbene 3 as fluorophore under test. The tissue phantoms contained a fixed scatterer concentration [μ_s′ (λ ₀) = 1 mm⁻¹] and varying concentrations of hemoglobin [0–2 mg/ml]. (b) Corresponding diffuse reflectance spectrum for each phantom. No measurement was possible for the intrinsic fluorescence phantom. (c) Intrinsic fluorescence spectra measured from a phantom (bold solid curve) and extracted by using the IFS model (dotted curve) compared with the laser-induced fluorescence spectrum (lighter solid curve).

Fig. 6

In vivo measurements from normal skin (bold solid curve), dysplastic nevus (lighter solid curve) and malignant BCC (dashed curve) from three different patients. (a) Diffuse reflectance. The circles indicate the LUT model fit. (b) Intrinsic fluorescence spectra from 337 nm excitation. The circles indicate the fit to the linear combination model. (c) Intrinsic fluorescence spectra from 445 nm excitation.